A unit of striated muscle tissue. Cheat Sheet: Muscle tissue

1.The structural and functional unit of smooth muscle tissue is:

a) muscle fibers

b) myocyte (muscle cell)

c) myofibril

2.Striated muscle tissue is present:

a) in vessels, internal organs

b) in skeletal muscles

c) in the glands of external secretion

3.Uninuclear undifferentiated cells from which new myosymplasts can develop:

a) myosatellitocyte

b) myofibril

c) myocyte

4. Consists of cells interconnected in chains resembling muscle fibers:

a) smooth muscle tissue

c) cardiac muscle tissue

5. Consists of myosymplasts and myosatellitocytes:

a) smooth muscle tissue

b) skeletal striated muscle tissue

c) cardiac muscle tissue

6.Greater strength and speed of contractions is characteristic of:

a) smooth muscle tissue

b) striated muscle tissue

7. The structural and functional unit of striated muscle tissue is:

a) muscle fibers

b) myocyte (muscle cell)

c) myofibril

8.Smooth muscle tissue is found in:

a) myocardium (the muscular layer of the heart)

b) vessels, internal organs

9. Consists of spindle-shaped cells:

a) cardiac muscle tissue

b) skeletal striated muscle tissue

c) smooth muscle tissue

10. Structure with numerous nuclei located under the sarcolemma:

a) myosatellitocyte

b) myosymplast

c) myocyte

11. The section of myofibril between two telophragms:

a) sarcolemma

b) sarcoplasm

c) sarcomere

12. Involuntarily shortens:

a) smooth muscle tissue

b) striated muscle tissue

nervous tissue:

1.Nervous tissue is made up of:

a) nerve fibers and endings

b) nerve cells and neuroglia

c) neurofibrils and chromatophilic substance

2. Axon (neurite) conducts impulse:

a) from the body of the nerve cell

b) to the body of the nerve cell

3. Pseudo-unipolar neurons are a type of:

a) unipolar

b) bipolar

c) multipolar

4. Dendrites conduct impulse:

a) from the body of the nerve cell

b) to the body of the nerve cell

5. Bipolar nerve cells have:

a) 1 neurite and 1 dendrite

6.Multipolar nerve cells have:

a) 1 neurite and 1 dendrite

b) 1 neurite and several dendrites

c) 1 dendrite and several neurites

7. Special structures of nerve cells:

a) neurites and dendrites

b) ribosomes and mitochondria

c) neurofibrils and chromatophilic substance

8. Lines cavities in the brain and spinal cord:

a) oligodendrocytes

b) astrocytes

c) ependymocytes

9. Receptor nerve endings are formed:

a) terminal branches of neurites of sensory neurons

b) terminal branches of the dendrites of sensory neurons

c) terminal branches of the dendrites of motor neurons

10. Motor nerve endings in striated muscle tissue are called:

a) neuromuscular spindles

b) lamellar bodies

c) neuromuscular endings (motor plaques)

Skeletal muscle tissue.

It has a non-cellular structure. It is represented by a cellular derivative - myosymplast or muscle fiber. It is limited to the plasma membrane by a very long plasma cord containing a large number of nuclei. It is formed by the fusion of embryonic mononuclear cells after they have reached a certain degree of differentiation. These cells - *myoblasts* merge with each other, forming thin muscular tubes. From that moment on, their nuclei divide togut. The rapid synthesis of contractile fibers and their construction begins.

Many structural cells are given the prefix Sarco when naming. The meat is covered with a plasmalemma and on top is a basement membrane, which is built from fibrils and peat substance, the Sarcolemma consists of a plasmalemma and a basement membrane. Between the basement membrane and the plasma membrane, in some places, mononuclear cells are myosatellites. These are cambial cells, cat. Unlike nuclei, simplasts can divide, forming the only source of replenishment of nuclei in a simplast.

M.o. muscle fiber is a cellular-symplastic complex (symplast + satellite). They are the structural and functional unit of skeletal muscle tissue.

The length of the fiber can reach several tens of centimeters. The outer membrane contains fibers tightly fused with endomysium. These are loose layers of connective tissue that surround each fiber. Endomysium regulates nutrition, metabolism and fiber functioning. Allocate more perimysium - puts on a bundle of fibers. From above, the muscle is enclosed in the epimysium, which corresponds to the fascia of the muscle.

In the anterior part of the muscular tract, muscle tissue does not pass to the organ level (no epimysium).

In addition to the trophic function, fixation of muscle tissue to the tendon or cartilage is provided. The nuclei are pushed to the periphery, because the entire mass of cells is literally crammed with myofibrils, they are oriented longitudinally with longitudinal striation. Cross striation - alternation of dark and light stripes, which are visible only in a relaxed state, forms a transverse striation of muscle tissue.

NATURE OF TRANSVERSAL STRINGING

Each myofibril has many myofilaments. Thin filaments - actin filaments from the globular protein actin. They also have regulatory proteins tropamine and propamiazine between them. Thick myofilaments - myosin - fibrillar protein. It has a fibrillar tail, a rod, at one end it has a head that can change the angle of inclination. Protruding 6 heads are always located along this circle (located parallel to each other, the heads protrude). Actin and myosin filaments are located strictly one above the other. The threads are laced with a special protein that performs a structural function. Laced places are considered at the light-optical level.

Actin filaments are connected along the Z line or telophragm, myosin - along the M line of the mesophragm.

The section, which only includes actin filaments, constitutes a simple refraction, forming an I - disk (isotropic refraction). Between them is A - disks (anichotropic) - has a 2nd refraction. H-disk in the middle of M. The distance between the 2 Z-lines is called the sarcomere.

When a muscle fiber contracts, the boundary of each sarcomere decreases. The contraction is based on the mechanism of sliding threads relative to each other. The movement of myofibrils for each other occurs due to the movements of the paddle-shaped heads of myosin. If the drag is relaxed, there is no sliding, because regulatory protein does not allow touching actin filaments.

To reduce, you need to remove the block; 2 conditions:

1) high concentration of Ca ions in the surrounding hyaloplasm. Ca ions also stimulate ATP activity, providing energy for the heads.

2) The specific membrane apparatus of the fiber, which includes the T-system and the sarcoplasmic reticulum.

The T-system is a derivative of the outer membrane, i.e. plasma membranes. From the plasmolemma, at very constant intervals, tubular channels extend into the depth of the fiber, which are located parallel to the fiber penetrating it across. When such a tube stumbles upon a myofibril, it bifurcates, forming rings, etc. This ring falls on a certain space (the place of contact between actin and myosis filaments). The T-system provides instantaneous and simultaneous conduction of excitation from the plasmolema to each sarcomere. Initially, the excitation comes from the nerve cell. The axon branches on the surface of the muscle fiber membrane, forming a mediator, connected. with plasma membrane receptors.

The sarcoplasmic reticulum is a smooth ER. Calcium depot in muscle cells. Ca2+ is hidden, its release is needed.

Each myofibril is packed on the outside with a juice-plasmic reticulum.

In each triad, T-tubules come very close to the muscular sarcoplasmic reticulum. Nerve impulses change the state of the sarcoplasmic membrane. Further, membrane ring channels open in it, then Ca2 + comes out of the smooth ER.

When the nerve impulse stops, Ca2+ is pumped back into the terminal cisterns, as a result, the muscle relaxes.

By nature, the contraction of cardiac muscle tissue is tetanic (rapidly contracts and relaxes).

TROPHIC APPARATUS OF MUSCLE FIBER.

Numerous nuclei that provide constant synthesis of contractile proteins.

Free ribosomes, many mitochondria - in long rows between myofibrils (usually elongated). The presence of inclusions is characteristic: glycogen myoglobin. Myoglobin is a pigmented inclusion that is red in color.

SUPPLY OF MUSCLE WITH OXYGEN,

Glycogen is the material for ATP production via the glycolytic pathway.

At the moment of contraction, the supply of oxygen stops. The supply of oxygen is not enough for a long time. Thick fibers are white (the use of ATP synthesis under anaerobic conditions), but they are not capable of long-term work. Their opposite is red fibers (thin), many myoglobin. They work long and hard.

Muscle fibers consist of myofibrils, and myofibrils of sarcamers - transverse muscle tissue - a structural unit.

The structural unit of the heart muscle is cardiomyocytes, which are connected to each other by intercellular contacts, hence the rapid contraction.

The area of ​​​​connection of cardiomyocytes is intercalated discs.

CONDUCTION SYSTEM OF THE HEART.

The pacemakers themselves, without external impulses, contract with a certain frequency. The excitation of the membrane is transmitted throughout the conduction system.

PATCHES of the 1st ORDER - sinoatrial node - a derivative of sinus cardiomyocyte cells. These are small small cells - few myofibrils, the main difference is the unstable resting potential, i.e. they always have a slow flow of ions through the membrane, hence the excitation is somewhere around 70 bpm.

Conducting system - fast transmission of impulses. to working cardiomyocytes.

PATCHES of the 2nd ORDER - atrioventricular node speed is approximately 30-40 contractions. per minute (not enough for normal life) Submits to the 1st pacemaker.

PATCHES of the 3rd ORDER - a bundle of Giss - an even lower frequency of heart rhythm regulation.

Intermediate cardiomyocytes are very large (Purkinje fibers). The goal is to be as fast as possible. class convey excitement.

In addition to automation, heart contractions are nervous regulation (vagus nerve); sympathetic and parasympathetic fibers (accelerate and slow down the speed of contractions. There are a number of humoral factors.

So secretory cardiomyocytes in the region of the ears of the heart secrete biologically active substances (natriuretic factor), which are aimed at regulating water and sodium metabolism and therefore affecting blood pressure.

GENERAL PRINCIPLES OF ORGANIZATION OF NEURAL TISSUES AND THE NERVOUS SYSTEM.

The nervous tissue consists mainly of cells, there is little intercellular substance.

CLASSIFICATION OF NERVE CELLS.

1. Nerve cells, or neurons, which provide specific functions - the conduction and transmission of excitation.

2. Cells of neurology or gynal cells, auxiliary (trophic function).

With a few exceptions, they are formed from the neural tube. Cells of the neural tube - mdunoblasts - which, at the early stages of embryogenesis, differ. in 2 directions:

Neuroblasts hence neurons

Spongioblasts hence neurogy

Neurons - their main function is to conduct or transmit excitation.

Cell structure different sizes that have a body called the perikaryon, are centrally located, have a large nucleus, and larger or smaller processes.

The processes are divided into 2 types:

Axon (neuritis (- always 1. Excitation from the body to the end of the axon

Dentrites - excitation to the body of nerve cells, various

If all organelles general purpose, even the cell center and specific. structure - basophilic content - these are granules or small grains located in the cytoplasm around the nucleus. This is an accumulation of granular ER (for the production of an indicator of sl-but the speed of ER.) Specificity in different types of neurons is also called the main content or tigroid.

Special purpose organelles - neurofibrils - long threads of neurofilaments and microtubules.

They are built from fibrillar proteins and are located in the axons of n.cl. They provide a quick transfer of the mediator to the end of the long process of the axon (fast current of the axoplasm).

Neurons are characterized by a special type of intercellular contacts - a synapse - which also ensures the conduction of excitation in one direction.

Mass release of the contents of the granules by exocytosis to the outside, but the mediator in the synaptic cleft is connected to the receptors of the membrane, but the excitation of the dendrite membrane.

2 sipons: chemical, electrical

Mediators of different types:

Acetylchonin is the most common membrane permeability excitatory mediator.

Postein membrane connecting enzyme acetylchominesterase - breaks down excess acetylcholine into syn. cracks.

Lack of sl-but continuous impulse sl-but convulsions.

Brake - isobutyric acid - stabilizes the action (channels do not open).

One neuron has several different mediators and there are receptors for different mediators.

But sometimes the difference in mediators types of m.

Cholinergic sl-but acetylcholine

Adrenergic sl-but norepinephrine

Morphological classification. (mainly the number of processes

1) Unipolar

2) Bipolar

3) Multipolar

Functional classificationz (Depends on the structure of the m. endings of the class)

1) Receptor neurons

2) Efferent

3) Associative

1) Receptor (afferent or sensitive) to them. specialized dendrite ending. Their dendrite is specialized. for the perception of some stimuli (external or internal).

Depending on the perceived stimulus:

Extrareceptors (perceive excitation from the external environment)

Intrareceptors (send information about the state internal organs)(from internal environment)

Proprioceptors (from the musculoskeletal system)

Mechanoreceptors

Baroreceptors, pain receptors, thermoreceptors.

2) Efferent (motor), specialized axon. The end of the axon falls on any working organ that responds to excitation. In most cases, the target is muscle cells. Sometimes some of the accretory cells are also targeted.

1st naming motor endings. At the point of contact, muscle fibers do not contain a basement membrane - a neuromuscular synapse.

3) Associative. Their nerve endings are called terminal devices of class. Form interneural synapses.

Neurology. These are cells of the nervous tissue that perform supporting, protective, trophic, secretory and delimiting functions. Cells are very diverse.

Microglia is a macrophage of the nervous tissue. is of monocytic origin. Normally, f is the destruction of obsolete neurons.

Macrorgia - different cells:

Ependymocytes, cells lining the cavity of the spinal canal and ventricles of the brain. This is a border tissue that forms a single-layer epithelium.

Long processes go into the thickness of the brain, and the supporting function, secretory, is also delimited.

Originating from a neural germ. Ependyma participates in the formation of a thematic-neutral barrier between cr. and yaykvor) This barrier has a very strong tendency. selectivity.

Certain in-va pass only in one direction. With meningitis antibiotic sl-but in the cerebrospinal fluid.

Olipondrocytes, Schwann cells, form the chalk sheath of the lower fibers. 1) lemmocytes

2) sobelites 9 okrug. n.cell body - protective and trophic functions

Astrocytes - sprout cells, similar to neurons. Fill the space between neuronamite. The processes and the body tightly cover the capillary, but next to each vessel - a case. Dr. processes extend to neurons. By transcytosis, they transfer nutrients, thus participating in trophism. This is the tematoencephalic barrier (blood and n. tk).

One of the strictest barriers. Most neurons mature after birth, but mediators are perceived by immunocompetent cells as antigens. To protect neurons from an autoimmune response, neurons do not come into contact with blood anywhere. This barrier state includes:

1) endothemia

Basement membrane of capillaries

Astrocytes (astrocytes)

Sometimes there is also an Ivanovskaya cell

3) - transvascular limiting membrane

A nerve fiber is a process of a neuron connected to neuroglial cells. The processes of neurons themselves are called axial cylinders. Cells that are covered with apodedrocytes are also called lemmocytes. The lemocyte can contact the oval cylinder in two different ways, soft myelinated (soft) and non-myelinated (non-flecked) muscle fibers. The axial cylinders are immersed in the lemmocyte, the double membranes of the lemmocyte, on which the mesaxon axial cylinder is suspended.

Myelin formation in the event that a lemmcite (Schwann cell) wraps around the axial cylinder many times. Cytoplasm on the surface with it v organelles. Many layers of plasma membrane. When stained with silver or osmium, therefore, in black color - this is called myelin. Myelinated shafts are mainly in the somatic part of the nervous system; without myelin for the autonomic nervous system. One lymphocyte can simultaneously serve several axial cylinders of a cable-type windrow. There are two types of receptors, free and non-free.

NERVOUS SYSTEM.

It combines the mechanism into a single whole and provides communication with the external environment and performs a regulatory function.

Synthetic neural theory is based on:

1. The nervous system consists of individual cells of neurons, but the structural unit of the nervous system is the neuron.

2. Neutons are interconnected only by specialized contacts - synapses.

3. As a functional unit, the neuron is in a state of either excitation or rest.

4. There are two types of synapses: excitatory and inhibitory.

The basis of the activity of the morphological nervous system is the reflex arc. This is a chain of neurons through which the impulse comes from the receptor to the executive organ. reflex arcs have different features in different parts of the nervous system.

In catfish and vegetative departments, reflex arcs have their own characteristics. Spinal sensory neurons.

Dendrites on the periphery of nerve endings. Axons enter the CNS.

Having given the type of neurons, small dark ones and large light ones. The sensory neuron follows to the back of the brain followed by the transfer of excitation to the motor neuron (anterior horns of the nucleus) of the body of their CNS, and the axon follows to the muscle cell forming a motor plaque.

The autonomic neural arch is more complex. The sensitive department is the same. in the autonomic nuclei (lateral horns) of the spinal cord, a switch occurs to the preganglionic neuron, its axon stretches to the autonomic ganglion, where it switches to the postganglionic neuron, which ends on the working organ.

Sympathetic (work) and parosympathetic (rest) NS.

Preganglionic - non-long postganglionic long sympathetic NS. Intramural or intraorgan ganglia - in the wall or near the walls of the nervous organ.

They differ in that they include three different types of cells - Dogel cells:

1. Sensory neurons

2. motor

3. associative

Preganglionic long, postganglionic short - parasympathetic.

Metasympathetic nervous system conditional autonomy regardless of the central nervous system. The nodes differ in that various biologically active substances can play a mediator role.

Nerve ganglion nodes allow the reflex arcs to work.

STRUCTURAL AND FUNCTIONAL
CHARACTERISTICS OF THE SKELETAL
MUSCLES AND THE MECHANISM OF ITS
ABBREVIATIONS

Structural unit of skeletal muscle
is a muscle fiber - highly elongated
multinucleated cell.
The length of the muscle fiber depends on the size
muscles and ranges from a few millimeters
up to several centimeters. Fiber thickness
varies from (10-100 microns).
Muscle types
There are three types in the human body
muscles:
skeletal, cardiac (myocardium) and smooth.
On microscopic examination in
skeletal and cardiac muscles
striation is detected, therefore their
called striated muscles.

Skeletal muscles are mainly attached to
bones, which led to their name.
Skeletal muscle contraction is initiated
nervous
impulses
And
obeys
conscious
control
those.
carried out arbitrarily.
Smooth muscle contraction is initiated
impulses, some hormones and not
depends on the will of the person.

The muscle fiber is surrounded by a bilayer
lipoprotein electroexcitable membrane sarcolemma,
which
covered
network
collagen fibers that give it strength and
elasticity.
There are several types of skeletal muscle
muscle fibers: slow twitch
(MS) or red and fast twitching
(BS) or white.
Molecular mechanism of contraction.
Skeletal muscles contain contractile
proteins:
actin
And
myosin.
Mechanism
their
interactions during elementary act
muscular
cuts
explains
theory
sliding threads, developed by Hasley and
Hanson.

The structure of the muscle fiber

Sarcolemma - the plasma membrane that covers
muscle fiber (connects to the tendon, which
attaches muscle to bone tendon transmits force
produced by the muscle fibers of the bone and thus
way
carried out
movement).
Sarcolemma
has selective permeability for various
substances and has transport systems, by using
which maintain different concentrations of ions
Na +, K +, as well as Cl- inside the cell and in the intercellular
liquid, which leads to the appearance of
membrane potential surface - required
conditions for the occurrence of excitation of the muscle fiber.
sarcoplasm
–
gelatinous
liquid,
filling
gaps
between
myofibrils
(contains
dissolved
proteins,
trace elements,
glycogen, myoglobin, fats, organelles). About 80%
fiber volume is occupied by long contractile filaments
- myofibrils.

cross tube system. This is the T network.
tubules (transverse), is a continuation
sarcolemmas; they connect through
among myofibrils. Provide fast
transmission of nerve impulses
excitation) inside the cell to individual
myofibrils.
Sarcoplasmic reticulum (SR) - network
longitudinal tubules, arranged in parallel
myofibrils; this is the place of Ca2+ deposition,
which is necessary to ensure the process
muscle contraction.
The contractile proteins actin and myosin form
in myofibrils thin and
thick
myofilaments.
They
are located
parallel to each other inside the muscle cell
myofibrils
present
yourself
contractile elements of muscle fiber bundles of "threads" (filaments).

Myofibril structure:
1. Partitions - called Z - plates,
divide them into sarcomeres.
Sarcomere structure:
They show a regular sequence
alternating transverse light and dark
stripes,
which
conditioned
special
interposition
actin
And
myosin
filaments
(transverse
banding).
The middle of the sarcomere is occupied by "thick" filaments
myosin. (A - dark disk)
On
both ends of the sarcomere are
thin filaments of actin. (I-disk light)

Actin filaments attach to Z -
plates, Z itself - plates
limit the sarcomere.
In a resting muscle, the ends of thin and
fat
filaments
only
weakly
overlap at the boundary between A and I disks.
H - zone (lighter) in which there is no
overlapping
threads
(Here
only myosin filaments are located)
is in drive A.
M - the line is in the center of the sarcomere
- a place to hold thick threads
(constructed from supporting proteins.)

The theory of sliding threads.

Sarcomere shortening:
The muscle contracts as a result of the shortening of the set
sarcomeres connected in series
myofibrils.
During contraction, thin actin filaments
glide along thick myosin cells, moving between them
to the middle of their bundle and sarcomere.
The main position of the theory of sliding threads:
During muscle contraction, the actin and
myosin filaments do not shorten (the width of the A-disk
always remains constant, while I-disks and H-zones
shrink when contracted).
The length of the threads does not change when the muscle is stretched (thin
filaments are pulled out from the gaps between the thick
threads, so that the degree of overlap of their bundles
decreases).

10. Operation of cross bridges.

The movement of the heads creates a combined force,
like a "stroke" that promotes actin filaments to
middle of the sarcomere. Only through rhythmic
separation and reattachment of myosin
actin filament heads can be pulled up to
middle of the sarcomere.
When muscles relax, myosin heads
separated from actin filaments.
Since actin and myosin filaments can easily
slide relative to each other, resistance
relaxed muscle stretch is very low.
Muscle lengthening during relaxation wears
passive character.

11. Conversion of chemical energy into mechanical.

ATP is the direct source of energy for
abbreviations.
During muscle contraction, ATP is broken down into
ADP and phosphate.
Rhythmic activity of the transverse bridges, i.e.
e. cycles of their attachment to actin and detachment
from it, providing muscle contraction,
are possible only with the hydrolysis of ATP, and
respectively, and upon activation of ATPase, which
directly involved in the breakdown of ATP into
ADP and phosphate.

12. Molecular mechanism of muscle contraction.

The contraction is triggered by a nerve impulse. At the same time, in
synapse - the point of contact of the nerve ending with
The sarcolemma secretes the mediator (neurotransmitter) acetylcholine.
Acetylcholine (Ax) causes a change in permeability
membranes for some ions, which in turn
leads to the appearance of ionic currents and is accompanied by
membrane depolarization. As a result, on her
surface, an action potential occurs or
excited.
Potential
actions
(excitation)
propagates deep into the fiber through the T-systems.
Nerve impulse causes a change in permeability
membranes of the sarcoplasmic reticulum and leads to
release
ions
Ca2+
from
bubbles
sarcoplasmic reticulum.

13. Electromechanical interface

Sending a command to shorten from
excited cell membrane
myofibrils
V
depth
cells
(electromechanical
conjugation)
includes
V
myself
some
sequential processes, key
role in which Ca2+ ions play.

14.

1. Electromechanical pairing occurs
through capacity building
action on the membranes of the transverse system
inside the cell, then the excitation passes to
longitudinal system (EPR) and causes
release of deposits in muscle
Ca2+ cell into the intracellular space,
that surrounds the myofibrils. This is what leads to
reduction
2. Ca2+ is removed from the intracellular space
in the depot (ER channels) due to the work of calcium
pumps on EPR membranes.
3. Only through electrical transmission through
transverse system, fast
mobilization of calcium stores in the depth of the fiber, and
only this can explain the very short
latency period between stimulus and
reduction.

15.

Functional role of ATP:
- in a resting muscle - prevents connection
actin filaments with myosin;
- in the process of muscle contraction - supplies
necessary energy for the movement of thin threads
relatively thick, resulting in shortening
muscles or developing tension;
- in the process of relaxation - provides energy
active transport of Ca2+ into the reticulum.

16. Types of muscle contractions. Optimum and pessimum of muscle contraction

Depending on the change in the length of the muscle fiber
there are two types of its contraction - isometric and
isotonic.
Muscle contraction in which the length of the muscle
decreases with the force it develops, is called
auxotonic.
Maximum force at auxotonic experimental
conditions (with an tensile elastic connection between the muscle and
force sensor) is called the maximum auxotonic
abbreviations. It is much less than the strength that develops
muscle at constant length, i.e. with isometric
reduction.
Contraction of a muscle in which its fibers shorten
at a constant voltage, is called isotonic.
Muscle contraction, in which its tension increases
and the length of the muscle fibers remains unchanged,
called isometric

17.

Muscular work is equal to the product
distance (muscle shortening) by the weight of the load,
which the muscle lifts.
With isotonic tetanic activation
muscles from the load depends on the amount of shortening and
the rate of muscle shortening.
The lower the load, the more shortening in
unit of time. Unloaded muscle
shortened from maximum speed, which
depends on the type of muscle fibers.
The muscle power is equal to the product
of the force developed by it to the speed of shortening

18.

A relaxed muscle that maintains its “resting length” due to
fixing both its ends, does not develop a force that
would be transmitted to the sensor. But if you pull one of her
end, so that the fibers stretch, it arises
passive voltage. Thus, the muscle is able
rest is elastic. Resting muscle modulus with
stretching increases. This elasticity is mainly due to
extensible structures that are located
parallel
relatively
tensile
myofibril
("parallel
elasticity")
.
myofibrils
V
in a relaxed state, they practically do not have
tensile strength; actin and myosin filaments
related
transverse
bridges,
easily
glide
relative to each other. Preliminary degree
stretching determines the amount of passive stress
resting muscle and the amount of additional force,
which a muscle can develop if activated at a given
length.

19.

The peak force under such conditions is called
maximum isometric contraction.
With a strong stretch of the muscle, the force of contraction
decreases because actin filaments are pulled out of
myosin bundles and, accordingly, a smaller zone
overlapping of these threads and the possibility
formation of cross bridges.
With a very strong stretching of the muscle, when
actin and myosin filaments stop
overlap, myofibrils are not able to
develop strength. This proves that muscle strength
is the result of an interaction
actin and myosin filaments (i.e.
formation of transverse bridges between them).
In vivo muscle contraction
are mixed - the muscle is usually not only
shortens, but its tension also changes.

20.

Depending on the duration, allocate
solitary and tetanic muscle contractions.
Single muscle contraction in the experiment
cause a single electrical stimulation
current. In isotonic mode, single
contraction begins through a short latent
(latent) period, followed by the rise phase
(shortening phase), then a decline phase (phase
relaxation) (Fig. 1). Usually a muscle
shortened by 5-10% of the original length.
The duration of PD of muscle fibers is also
varies and is 5-10 ms, taking into account deceleration
phases of repolarization.
Muscle fiber obeys the law "all or
nothing”, i.e. responds to threshold and
suprathreshold irritation with the same
the size of a single contraction.

21.

The contraction of a whole muscle depends on:
1. from the strength of the stimulus with direct irritation
muscles
2. on the number of nerve impulses entering the muscle when
nerve irritation.
An increase in the strength of the stimulus leads to an increase in the number
contracting muscle fibers.
A similar effect is observed in natural conditions - with
an increase in the number of excited nerve fibers and frequency
impulses (more PD nerve impulses enter the muscle), the number of contracting muscle fibers increases.
With single contractions, the muscle gets tired
slightly.
Tetanic contraction is a continuous long
skeletal muscle contraction. It is based on the phenomenon
summation of single muscle contractions.
Single Curve
gastrocnemius contraction
frog muscles:
1-latent period,
2- phase shortening,

22.

When applied to a muscle fiber or
directly
on
muscle
two
fast
successive stimuli,
emerging
reduction
It has
big
amplitude and duration. At the same time, actin filaments and
myosin additionally slide relative to each other
friend. Previously not involved in the reduction may be
contracted muscle fibers, if the first
the stimulus caused subthreshold depolarization in them,
and the second increases it to a critical value.
Summation of contractions upon repeated stimulation
muscle or the supply of PD to it occurs only
when the refractory period is over
(after the disappearance of the PD of the muscle fiber).

23.

Upon receipt of impulses to the muscle during its
relaxation, dentate tetanus occurs, during
shortening time - smooth tetanus (Fig.).
The tetanus amplitude is greater than
maximum single muscle contraction.
Tension developed by muscle fibers
with smooth tetanus, usually 2-4 times more,
than with a single contraction, however, the muscle
gets tired faster. Muscle fibers are not
manage to restore energy resources,
used up during the cut.
The amplitude of the smooth tetanus increases with
an increase in the frequency of nerve stimulation. At
some (optimal) stimulation frequency
the amplitude of the smooth tetanus is the largest (optimum stimulation frequency)

24.

Rice. Abbreviations calf muscle frogs at
increased frequency of irritation of the sciatic nerve
(st / s - stimuli per second): a - single contraction;
bd - superimposing contraction waves on each other and
education different types tetanic contraction.
At a frequency of 120 st / s - a pessimal effect
(muscle relaxation during stimulation) – e

25.

With excessively frequent nerve stimulation (more than 100
imp/s) the muscle relaxes due to the block
conduction of excitation in the neuromuscular
synapses - Vvedensky's pessimum (pessimum
irritation frequency). Pessimum Vvedensky can be
get and with direct, but more frequent irritation
muscles (more than 200 imp/s). Pessimum Vvedensky not
is the result of muscle fatigue or neurotransmitter depletion in the synapse, as evidenced by the fact
resumption of muscle contraction immediately after
reduce the frequency of irritation. Braking
develops at the neuromuscular junction
nerve irritation.
Under natural conditions, muscle fibers
contract in serrated tetanus mode or
even single consecutive contractions.

26.

However, the form of muscle contraction in general
resembles a smooth tetanus.
Causes
this
asynchrony
discharges
motor neurons and contractile asynchrony
reactions of individual muscle fibers, involvement
in the reduction of their large number, due to
which the muscle contracts smoothly and smoothly
relaxes, can stay in
reduced state due to alternation
contractions of many muscle fibers. At
this muscle fiber of each motor
units are reduced synchronously.

27.

The functional unit of a muscle is
motor unit
Concepts. Innervation of skeletal muscle fibers
carried out by motor neurons of the spinal cord
brain stem. One motor neuron with its branches
axon innervates several muscle fibers.
The combination of a motor neuron and its innervated
muscle fibers are called motor
(neuromotor) unit. Number of muscle
fibers of the motor unit varies widely
within different muscles. motor units
small in muscles adapted for fast
movements, from several muscle fibers to
several dozen of them (muscles of the fingers, eyes,
language). On the contrary, in the muscles that carry out
slow movements (maintaining a posture with muscles
trunk), motor units are large and include
hundreds and thousands of muscle fibers

28.

At
reduction
muscles
V
natural
(natural) conditions can be registered
its electrical activity (EMG electromyogram) using needle or skin electrodes. In a completely relaxed muscle
almost no electrical activity. At
small
tension,
For example
at
maintaining
poses,
motor
units
are discharged at a low frequency (5-10 imp/s),
at high voltage pulse frequency
rises to an average of 20-30 imp/s. EMG allows you to judge the functional ability
neuromotor units. From a functional point
motor units are divided into
slow and fast.

29.

motor neurons and slow muscle fibers (red).
Slow motor neurons are usually low threshold, so
as usual, these are small motor neurons. sustainable level
impulses in slow motor neurons are already observed
with very weak static muscle contractions, with
maintaining posture. Slow motor neurons are capable of
maintain a long discharge without a noticeable decrease
impulse frequency for a long time.
Therefore, they are called low-fatigue or
tireless motor neurons. Surrounded by slow
rich in muscle fibers capillary network, allowing
receive large amounts of oxygen from the blood.
Increased myoglobin content facilitates transport
oxygen in muscle cells to mitochondria. myoglobin
causes the red color of these fibers. Besides,
fibers contain a large number of mitochondria and
substrates of oxidation - fats. All this causes the use of slow muscle fibers more
efficient aerobic oxidative pathway

30.

Fast motor units are made up of
fast motor neurons and fast muscle
fibers. Fast high threshold motor neurons
are included in the activity only to ensure
relatively large in strength static and
dynamic muscle contractions, as well as at the beginning
any cuts to increase speed
buildup of muscle tension or report
moving part of the body required acceleration. How
more speed and strength of movements, i.e. the more
the power of the contractile act, the greater the participation
fast motor units. Fast
motoneurons are fatigued - they are not
capable of long-term maintenance
high frequency discharge

31.

Fast muscle fibers (white muscle fibers)
fibers) are thicker, contain more
myofibrils are stronger than
slow fibers. These fibers surround less
capillaries, cells have fewer mitochondria,
myoglobin and fats. Activity of oxidative
enzymes in fast fibers are lower than in
slow, but the activity of glycolytic
enzymes, glycogen stores are higher. These fibers are not
have great endurance and more
adapted for powerful, but relatively
short term contractions. Activity fast
fiber is important to perform
short-term high-intensity work,
e.g. sprinting

32.

The rate of contraction of muscle fibers is
in direct proportion to the activity of myosin-ATP-ase
- enzyme that breaks down ATP
promotes the formation of cross bridges
and interaction between actin and myosin
myofilaments. The higher activity of this
enzyme in fast muscle fibers
provides more high speed their
contractions compared to slow fibers
Tone - weak general muscle tension
(develops at a very low frequency of stimulation).
The strength and speed of muscle contraction depends on
the number of motor movements involved in the contraction
units (the more motor units
activated, the stronger the contraction).
Reflex tone - (observed in some
groups of postural muscles) a state of involuntary
sustained muscle tension

33.

muscle efficiency
During muscle activation, an increase
intracellular concentration of Ca 2+ leads to
reduction and increased breakdown of ATP; at
this increases the metabolic rate of the muscle
100-1000 times. According to the first
thermodynamics (the law of conservation of energy),
chemical energy released in the muscle
must be equal to the sum of mechanical energy
(muscle work) and heat generation

34.

Efficiency.
Hydrolysis of one mole of ATP gives 48 kJ of energy,
40-50% - turns into mechanical work, and
50-60% dissipated as heat at startup
(initial heat) and during contraction
muscles, the temperature of which
rises. However, under natural conditions
the mechanical efficiency of the muscles is about 20-30%, since during
reduction time and after it processes
requiring energy costs, go beyond
myofibrils (work of ion pumps,
oxidative regeneration of ATP - heat
recovery)

35.

Energy
metabolism
.
In
time
lengthy
uniform
muscular
activity, aerobic ATP regeneration occurs for
check
oxidative
phosphorylation.
The energy needed for this is released into
from the oxidation of carbohydrates and fats. System
is in a state of dynamic equilibrium
the rates of formation and splitting of ATP are equal.
(intracellular
concentration
ATP
And
creatine phosphate are relatively constant)
lengthy sports loads speed
splitting of ATP in muscles increases in 100 or in
1000 times. Continuous loading is possible if
speed
recovery
ATP
increases
according to consumption. Oxygen consumption
muscle tissue increases by 50-100 times;
increased rate of glycogen breakdown
muscles.

36.

Anaerobic digestion - glycolysis: ATP is formed in 2-3
times faster, and the mechanical energy of the muscle is 2-3 times
higher than during long-term operation, provided
aerobic mechanisms. But resources for anaerobic
metabolism are quickly exhausted, metabolic products
(lactic acid) cause metabolic acidosis.,
which limits performance and causes
fatigue. Anaerobic processes are necessary for
providing energy for short-term extreme
efforts, as well as at the beginning of a long muscle
work, because the adaptation of the oxidation rate (and
glycolysis) to an increased load requires some time.
Oxygen debt approximately corresponds to
the amount of energy received anaerobically, not yet
compensated by aerobic ATP synthesis.
Oxygen debt is due to (anaerobic)
hydrolysis of creatine phosphate, can reach 4 liters and can
increase to 20 liters. Part of the lactate is oxidized in the myocardium
and part (mainly in the liver) is used for synthesis
glycogen.

37.

The ratio of fast and slow fibers. How
The more fast fibers a muscle contains, the more
its possible force of contraction.
Cross section of a muscle.
The terms "absolute" and "relative" muscle strength:
"total muscle strength" (defined by maximum
tension in kg, which it can develop) and "specific
muscle strength "- the ratio of this tension in kg to
physiological cross section of the muscle (kg/cm2).
The more physiological cross section muscle,
the more weight it can lift. For this reason
muscle strength with oblique fibers is greater
force developed by a muscle of the same thickness, but with
longitudinal arrangement of fibers. To compare strength
different muscles the maximum load that they are able to
raise, divide by the area of ​​their physiological transverse
section (specific muscle strength). Calculated in this way
strength (kg / cm2) for the triceps muscle of the human shoulder - 16.8,
biceps of the shoulder - 11.4, flexor of the shoulder - 8.1,
gastrocnemius muscle - 5.9, smooth muscles - 1 kg/cm2.

38.

In various muscles of the body, the ratio between
number of slow and fast muscle fibers
is not the same, therefore, the force of their contraction, and
the degree of shortening is variable.
With a decrease in physical activity - especially
high intensity, which requires
active participation of fast muscle fibers, the latter become thinner (hypotrophic) faster,
than slow fibers, they decrease faster
number
Factors affecting the force of muscle contraction.
The number of contracting fibers in a given muscle. WITH
an increase in contractile fibers increases
the strength of muscle contractions as a whole. In natural
conditions, the force of muscle contraction increases with
an increase in nerve impulses to
muscle,
in the experiment - with an increase in the strength of stimulation.

39.

Moderate stretching of the muscle also leads to
increase its contractile effect. However
when overstretched, contraction force
decreases. This is demonstrated in an experiment with
dosed stretching of the muscle: muscle
overstretched so that the actin and myosin filaments do not
overlap, then the total muscle strength is zero.
As you approach the natural length of rest,
at which all heads of myosin filaments are capable of
contact with actin filaments
muscle contraction grows to a maximum.
However, as the length decreases further
muscle fibers due to the overlap of actin filaments and
myosin muscle contraction force again
decreases due to a decrease in the possible
contact between actin and myosin filaments.

40.

The functional state of the muscle.
When a muscle is fatigued, the amount of its contraction
decreases.
The work of a muscle is measured by the product
lifted load by the amount of its shortening.
The dependence of muscle work on load
obeys the law of average loads. If the muscle
contracts without load, its external work is equal to
zero. As the load increases
increases, reaching a maximum at average
loads. Then it gradually decreases from
load increase. Work becomes equal
zero with a very large load, which the muscle at
its contraction is not able to raise the tension
100-200 mg.

41.

SMOOTH MUSCLE.
Smooth muscle has no transverse
striation. Cells in the form of spindles connected
special intercellular contacts (desmosomes).
The speed of myofibril gliding and ATP splitting
lower by 100-1000 times. Well adapted for
prolonged sustained contraction, which is not
leads to fatigue and significant energy consumption.
Capable of spontaneous tetanic contractions
which are of myogenic origin and not
neurogenic as in skeletal muscle.
myogenic arousal.
Myogenic excitation occurs in cells
pacemakers (pacemakers), which have
electrophysiological properties.
Pacemaker potentials depolarize their membrane
to a threshold level, triggering an action potential. Sa
2+ enters the cell - the membrane depolarizes, then

42.

The spontaneous activity of pacemakers can be modulated
autonomic nervous system and its mediators
(acetylcholine enhances activity leading to more frequent and
strong contractions, and norepinephrine has
opposite action).
Excitation propagates through "gap junctions"
(nexuses) between plasma membranes
adjacent muscle cells. The muscle behaves like
single functional unit, synchronously reproducing
the activity of your pacemaker. Smooth muscle May be
completely relaxed in both short and extended
condition. A strong stretch activates the contraction.
Electromechanical interface. Excitation
smooth muscle cells causes either an increase in the entry of Ca
through voltage-gated calcium channels, or
releases from calcium depots, which in any case
leads to an increase in intracellular concentration
calcium and causes the activation of contractile structures.
Relaxation is slow. ion uptake rate
Sa is very low.

Subject: " Muscle tissues"

Question 1 . General structural features of muscle tissues

It combines several different types, but the main property is common - contractility. Therefore, all muscle tissues have similar structural features:

1. Cells are elongated and are combined into cords, or even into symplasts (muscle fibers).

2. The cytoplasm is filled with myofilaments - filaments of contractile proteins (myosin and actin), the mutual sliding of which ensures contraction. The nature of the arrangement of myofilaments depends on the type of muscle tissue.

3. High energy demands require many mitochondria, inclusions of myoglobin, fat and glycogen.

4. Smooth ER is specialized for the accumulation of Ca 2+ , which initiates contraction.

5. The plasma membrane of muscle cells is excitable.

According to the morpho-functional classification, there are:

1. Striated muscle tissue. In their cytoplasm, the main component is myofibrils (organelles of general importance), which create the effect of striation. These fabrics are of two types:

Skeletal. Formed from myotomes of somites.

Cardiac. It is formed from the visceral leaf of the splanchnotome.

2. Smooth muscle tissue. Its cells do not contain myofibrils. Formed from mesenchyme.

This group also includes myoepithelial cells, which are of ectodermal origin, and the muscles of the iris, which are of neural origin.

Question 2 . Skeletal muscle tissue Organization of the muscle fiber

The structural and functional unit of this tissue is the muscle fiber. It is a long cytoplasmic cord with many nuclei that lie just below the plasmalemma. Muscle fiber in embryogenesis is formed by the fusion of cells - myoblasts, i.e., is a cellular derivative - symplast.

The muscle fiber keeps overall plan cellular organization. It has all the organelles of general importance, many inclusions, as well as organelles of special importance. All fiber components are adapted to perform the main function - reduction - and are divided into several devices.

The contractile apparatus consists of myofibrils. These are organelles that stretch along the entire fiber and occupy most of the entire volume of the cytoplasm. They are able to significantly change their length.

Apparatus protein synthesis It is represented mainly by free ribosomes and is specialized in the production of proteins for building myofibrils.

The excitation transmission apparatus is formed by the sarcotubular system. It includes smooth ER and T-tubules. Smooth ER (sarcoplasmic reticulum) has the form of flat tanks that braid all myofibrils. It serves to accumulate Ca 2+ . Its membranes are able to quickly release calcium to the outside, which is necessary for the shortening of myofibrils, and then actively pumps it inside. The outer membrane of the muscle fiber (sarcolemma) forms numerous tubular invaginations penetrating the entire fiber in transverse directions. Their totality is called the T-system. T-tubules are in close contact with the ER membranes, forming a single sarcotubular system. To each T-tube ... ..

The energy apparatus is composed of mitochondria and inclusions. Mitochondria are large, elongated and lie mostly in chains, filling all the space between myofibrils. The substrates for ATP production are glycogen and lipid droplets. Inclusions of myoglobin, a specific muscle pigment, provide fibers with oxygen in case of prolonged and intense muscle work.

The lysosomal apparatus is poorly developed. Serves mainly for the processes of intracellular regeneration.

Question 3 The mechanism of muscle contraction

To understand it, it is necessary to familiarize yourself with the molecular organization of myofibrils - organelles specialized in contraction. These are long strands that form longitudinal bundles of a thousand or more myofibrils, which almost completely fill the cytoplasm of the fiber.

Each myofibril is built from a huge number of actin and myosin filaments.

Thin actin filaments are built from globular actin protein molecules, which are combined into two spirally twisted chains. The thicker myosin filament is built from 300-400 myosin protein molecules. Each molecule includes a long tail, to which a movable head is attached at one end. Heads can change the angle of their inclination. The tails of many molecules are stacked in a dense bundle, forming a filament rod. The heads remain on the surface. On the two edges of the thread, the heads lie in different directions.

Thanks to additional proteins, myofilaments have a stable diameter and a stable length of about 1 µm. Filaments of the same type form neatly fitted bundles or stacks. Myofibrils are formed from repeatedly alternating bundles of actin and myosin filaments. High orderliness in the arrangement of myofilaments is achieved with the help of various proteins of the cytoskeleton. For example, the protein actinin forms a Z-line (telophragm), to which the edges of thin actin filaments are attached on both sides. This is how an actin stack is formed. Other proteins organize thick myosin filaments into a stack, lacing them in the middle. They form an M-line (mesophragm). When alternating stacks, the free ends of thin and thick threads go behind each other, ensuring mutual sliding relative to each other at the moment of contraction. As a result of this organization, light areas, called I-discs (isotropic), and dark areas, called A-disks (anisotropic), are repeated many times in the myofibril. This creates the effect of transverse striation. The isotropic regions correspond to the central part of the actin stack and contain only thin filaments. Anisotropic disks correspond to the whole myosin stack, and they include a purely myosin part (H-band) and those areas where the ends of thin and thick filaments overlap.

The area between the two Z-lines is called the sarcomere. The sarcomere is the structural unit of the myofibril. (20 thousand sarcomeres per myofibril). The strict organization of myofibrils is provided by a wide range of different cytoskeletal proteins.

During contraction, the length of the myofibril decreases due to the simultaneous shortening of all I-discs. The length of each sarcomere decreases by 1.5-2 times. The contraction process is explained by Huxley's theory of slip, according to which, at the moment of contraction, the free, overlapping ends of actin and myosin filaments enter into molecular interactions and move deeper relative to each other. Gliding begins with the fact that the protruding myosin heads form bridges with the active centers of actin filaments. Then the angle of inclination of the head decreases, the bridges make, as it were, rowing movements, displacing the actin filament as well. After that, the bridge opens, which is accompanied by the hydrolysis of 1 ATP molecule. The binding of myosin heads to the actin filament is regulated by special proteins. These are troponin and tropomyosin, which are embedded in the actin filament and prevent contact with the myosin heads. With an increase in the Ca 2+ concentration in the hyaloplasm, the conformational state of these regulatory proteins changes and their blocking effect is removed. The rowing movements are repeated hundreds of times in one muscle contraction. Relaxation occurs only after the concentration of Ca 2+ decreases.

Question 4. Excitation transfer apparatus

The contraction is triggered by a nerve impulse, which is transmitted through the motor plaque to the membrane of the muscle fiber, causing a wave of depolarization, which instantly covers the T-tubules. They stretch from the surface through the entire fiber, encircling the myofibrils in ringlets along the way. Smooth ER cavities filled with calcium envelop myofibrils with a sheath, in close contact with T-tubules. On both sides, extensive membrane cavities of the EPS (terminal cisterns) are adjacent to each T-tubule. Such a complex is called a triad. There are two triads for each sarcomere. Due to membrane contacts, depolarization of T-tubules changes the state of ER membrane proteins, which leads to the opening of calcium channels and the release of calcium into the hyaloplasm. There is a reduction. Triads match the processes of excitation and contraction. After ejection, special membrane pumps actively pump Ca 2+ back into the ER, where it binds to the Ca-binding protein.

Question 5. cardiac muscle tissue

forms the muscular wall of the heart - the myocardium. Its morpho-functional unit is a single cell - a cardiomyocyte. Cells are connected to each other by special structures - intercalated discs, and as a result, a three-dimensional network of cell strands (functional syncytium) is formed, which ensures synchronous contraction during systole.

Cardiomyocytes are elongated cells with several branches, covered over the plasmolemma with a basement membrane. Their nuclei (1 or 2) lie centrally.

The myocardium contains several populations of cardiomyocytes:

A) contractile or working

B) conductive

B) secretory

Question 6. Working cardiomyocytes

make up the bulk of the myocardium and provide contraction. Their organization is similar to muscle fibers, but has a number of differences.

contraction apparatus. Myofibrils as a whole have a longitudinal direction, but repeatedly anastomose with each other.

The sarcotubular network is less developed. T-tubules are wider, lie less frequently, and each is in contact with only one ER cisterna (dyad). Upon excitation, a part of Ca 2+ enters the hyaloplasm from the intercellular space through the plasmolemma and T-tubule membranes, and only after that does the Ca-induced release of Ca 2+ from the EPS occur.

Energy apparatus. There are many mitochondria, they are large with densely packed cristae, since the energy demands of the myocardium are very high. Between themselves, they are united by special compounds - intermitochondrial contacts and form a single functional system - the mitochondrion. This integration is extremely important for rapid and synchronous myocardial contraction. Substrates for ATP production are supplied by lipid droplets, inclusions of glycogen and myoglobin. The motochondria themselves are capable of accumulating calcium.

The ends of neighboring cells or their adjoining branches are connected by intercalary discs. The disk has a stepped shape. The transverse sections are formed by desmosomes and give the connection mechanical strength. The longitudinal sections contain many gap junctions - nexuses, which are especially numerous in the atria. Thanks to the ion channels of the nexus, excitation quickly spreads along the entire muscle.

The myocardium is richly supplied with blood. All spaces between cardiomyocytes are filled with loose connective tissue, in which capillaries branch. Here the branching of the nerve fibers of the autonomic nervous system ends. Unlike skeletal muscle tissue, not neuromuscular synapses (motor plaques) are formed here, but only varicose veins. The nervous system has only a regulatory effect on the contractile activity of cardiomyocytes. The autonomic system only increases (sympathetic department) or decreases (parasympathetic department) the frequency and strength of heart contractions.

The rhythmic generation of impulses that cause the heart to constantly contract is provided by special cells of the myocardium itself. The totality of these cells is called the conduction system of the heart, and the ability of the heart to contract regardless of nerve stimuli is called the automatism of the heart.

Question 7 . Conducting system

includes specialized cardiomyocytes, also called atypical. These include:

Pacemaker cells or pacemakers. Their main property is the unstable resting potential of the outer membrane. Thanks to the K/Na pump, there is always more sodium inside the cell and more potassium outside. This difference between the ions creates an electric potential on both sides of the plasmalemma. With a certain stimulation, sodium channels in the membrane open, sodium rushes out and the membrane depolarizes. In pacemaker cells, due to the constant small leakage of ions, the plasmalemma regularly depolarizes without any external signals. This causes an action potential to spread to neighboring cells, causing them to contract. The main pacemakers are the cardiomyocytes of the sinoatrial node. Every minute they generate 60-90 pulses. Second-order pacemakers form the atrioventricular node. They generate impulses at a frequency of 40 impulses per minute, and normally their activity is suppressed by the main pacemakers. Pacemaker cardiomyocytes are small light cells with a large nucleus. Their contractile apparatus is poorly developed.

Conducting cardiomyocytes provide rapid transmission of excitation from pacemakers to working cardiomyocytes. These cells are combined into long strands that form the bundle of His and Purkinje fibers. The bundle of His is composed of medium-sized cells with sparse long winding myofibrils and small mitochondria. Purkinje fibers contain the largest cardiomyocytes that can contact several working cells at once. Myofibrils here form a rare disordered network, the T-system is not developed. There are no intercalated disks, but the cells are united by many nexuses, which ensures a high speed of impulse conduction.

Question 8. Secretory cardiomyocytes

In the atria, there are outgrowth cells in which GREPs, the Golgi complex, and secretory granules are well developed. Myofibrils are very poorly developed, since the main function is the production of a hormone (natriuretic factor), which regulates electrolyte metabolism and blood pressure.

Question 9 . smooth muscle tissue

Made up of smooth myocytes. Contractile filaments in these cells do not have a rigid order and myofibrils are not formed in them. As a result, there is no transverse striation. Smooth myocytes are rather large spindle-shaped cells, covered on top with a basal membrane, which is connected to the intercellular substance. In the center is an elongated nucleus, at the poles of the rEPS, the Golgi complex and ribosomes. Cells secrete components of the intercellular substance for their outer shell, as well as some growth factors and cytokines. Lots of small mitochondria. The sarcoplasmic reticulum (smooth ER) is poorly developed; it acts as a calcium depot. There is no T-tubule system, and their function is performed by caveolae. Caveoli are small invaginations of the plasmalemma in the form of bubbles. They contain high concentrations of calcium, which is taken from the intercellular space. At the moment of excitation, Ca 2+ comes out of the caveolae, which initiates the release of Ca 2+ from the sarcoplasmic reticulum.

The organization and functioning of the contractile apparatus are peculiar. Actin and myosin filaments are very numerous, but do not form myofibrils. For their ordering in the myocyte, there is a system of dense bodies. These are rounded support formations from the protein a-actinin and desmin. In them, 10-20 thin actin filaments are fixed at one end. Some bodies form attachment plates in the sarcolemma, others lie in chains directly in the hyaloplasm. Thus, a stable network of actin filaments is formed in the myocyte. Thick myosin filaments have different length and very labile.

Each contraction is preceded by a release of calcium, which binds to a special protein, calmodulin. This activates an enzyme that allows the rapid assembly of myosin filaments. They are embedded between actin filaments, form bridges with them, and their heads begin to make rowing movements. With mutual sliding of the threads, the dense bodies approach each other, and the cell as a whole shortens. Thus, in smooth myocytes, calcium interacts with myosin filaments, and not with actin filaments, as in striated ones. The ATPase activity of myosin is much lower. Together with the constant assembly and disassembly of myosin filaments, this leads to the fact that smooth muscle cells contract more slowly, but can maintain this state for a long time (tonic contractions). Cells are connected to each other by rvst, which is woven into their basement membranes, as well as by various intercellular contacts, including nexuses. The contractile activity of myocytes is under the control of nervous and humoral factors. In the connective tissue layers there are varicose extensions of the axons of the autonomic nervous system. Their mediators depolarize the nearest myocytes, and the excitation is transmitted to the rest through slot-like contacts.

Due to a wide range of membrane receptors, smooth myocytes are sensitive to many biologically active substances (adrenaline, histamine, etc.) and react in different ways, depending on organ specificity.

Question 10. Histogenesis and regeneration

Skeletal muscle tissue. From the somite myotome, mononuclear actively dividing cells, myoblasts, differentiate. They merge into chains - muscle tubes, the numerous nuclei of which no longer divide. In the tubules, active synthesis of contractile proteins and the formation of myofibrils begin, which gradually fill the entire cytoplasm, pushing the nuclei to the periphery. A muscle fiber is formed, inside which myofibrils are constantly updated. Between the plasmalemma and the basement membrane covering it, in some places, mononuclear cells are preserved - myosatelites - cambial cells that can divide and include their nuclei in the composition of the fibers. The growth of muscle tissue in an adult occurs mainly due to hypertrophy of the fibers, and their number remains constant. After damage, myosattelites can merge, forming new fibers.

Cardiac muscle tissue is formed from the myoepicardial plate as part of the visceral leaf of the splanchnotome. The division of cardiomyocytes ends shortly after birth, but in the next 10 years, polyploid and binuclear cells can form. Since there are no cambial cells, only intracellular regeneration and hypertrophy of cardiomyocytes is possible. It occurs as a result of long physical activity, or in pathological conditions (hypertension, heart defects, etc.). After the death of myocytes (myocardial infarction), a connective tissue scar is formed. Recently, it has been established that individual atrial myocytes retain the ability to undergo mitosis.

Smooth muscle tissue regenerates through both hypertrophy and hyperplasia

Muscle tissues They are a group of tissues of different origin and structure, united on the basis of a common feature - a pronounced contractile ability, thanks to which they can perform their main function - to move the body or its parts in space.

The most important properties of muscle tissue. Structural elements of muscle tissues (cells, fibers) have an elongated shape and are capable of contraction due to the powerful development of the contractile apparatus. The latter is characterized by a highly ordered arrangement actin And myosin myofilaments, creating optimal conditions for their interaction. This is achieved by the connection of contractile structures with special elements of the cytoskeleton and the plasmolemma. (sarcolemma) performing a supporting function. In part of muscle tissue, myofilaments form organelles of special significance - myofibrils. Muscle contraction requires a significant amount of energy, therefore, in the structural elements of muscle tissues there are a large number of mitochondria and trophic inclusions (lipid drops, glycogen granules) containing substrates - energy sources. Since muscle contraction proceeds with the participation of calcium ions, the structures that carry out its accumulation and release are well developed in muscle cells and fibers - the agranular endoplasmic reticulum. (sarcoplasmic reticulum), caveolae.

Muscle tissue classification based on features of their (a) structure and function (morphofunctional classification) and (b) origin (histogenetic classification).

Morphofunctional classification of muscle tissues highlights striated (striated) muscle tissue And smooth muscle tissue. Striated muscle tissues are formed by structural elements (cells, fibers), which have a transverse striation due to a special ordered mutual arrangement of actin and myosin myofilaments in them. The striated muscle tissues are skeletal And cardiac muscle tissue. Smooth muscle tissue consists of cells that do not have transverse striations. The most common type of this tissue is smooth muscle tissue, which is part of the walls of various organs (bronchi, stomach, intestines, uterus, fallopian tube, ureter, bladder and blood vessels).

Histogenetic classification of muscle tissues identifies three main types of muscle tissue: somatic(skeletal muscle tissue) coelomic(heart muscle) and mesenchymal(smooth muscle tissue of internal organs), as well as two additional ones: myoepithelial cells(modified epithelial contractile cells in the terminal sections and small excretory ducts of some glands) and myoneural elements(contractile cells of neural origin in the iris).

Skeletal striated (striated) muscle tissue in its mass exceeds any other tissue of the body and is the most common muscle tissue of the human body. It ensures the movement of the body and its parts in space and the maintenance of posture (part of the locomotor apparatus), forms oculomotor muscles, muscles of the wall of the oral cavity, tongue, pharynx, larynx. A similar structure has non-skeletal visceral striated muscle tissue, which is found in the upper third of the esophagus, is part of the external anal and urethral sphincters.

Skeletal striated muscle tissue develops in the embryonic period from myotomes somites, giving rise to actively dividing myoblasts- cells that are arranged in chains and merge with each other at the ends to form muscle tubules (myotubules), turning into muscle fibres. Such structures, formed by a single giant cytoplasm and numerous nuclei, are traditionally referred to in Russian literature as symplasts(in this case - myosymplasts), however, this term does not exist in accepted international terminology. Some myoblasts do not fuse with others, being located on the surface of the fibers and giving rise to myosatellitocytes- small cells, which are the cambial elements of skeletal muscle tissue. Skeletal muscle tissue is made up of bundles striated muscle fibers(Fig. 87), which are its structural and functional units.

Muscle fibers skeletal muscle tissue are cylindrical formations of variable length (from millimeters to 10-30 cm). Their diameter also varies widely depending on the belonging to a particular muscle and type, functional state, degree of functional load, nutritional status

and other factors. In muscles, muscle fibers form bundles in which they lie parallel and, deforming each other, often acquire an irregular multifaceted shape, which is especially clearly seen in transverse sections (see Fig. 87). Between the muscle fibers are thin layers of loose fibrous connective tissue that carry blood vessels and nerves - endomysium. The transverse striation of skeletal muscle fibers is due to the alternation of dark anisotropic discs (bands A) and bright isotropic disks (bands I). Each isotropic disk is cut in two by a thin dark line Z - telophragm(Fig. 88). The nuclei of the muscle fiber are relatively light, with 1-2 nucleoli, diploid, oval, flattened - they lie on its periphery under the sarcolemma and are located along the fiber. Outside, the sarcolemma is covered with a thick basement membrane, into which reticular fibers are woven.

Myosatellitocytes (myosatellite cells) - small flattened cells located in shallow depressions of the muscle fiber sarcolemma and covered with a common basement membrane (see Fig. 88). The nucleus of the myosatellitocyte is dense, relatively large, the organelles are small and few. These cells are activated when muscle fibers are damaged and provide their reparative regeneration. Merging with the rest of the fiber under increased load, myosatellitocytes participate in its hypertrophy.

myofibrils form the contractile apparatus of the muscle fiber, are located in the sarcoplasm along its length, occupying the central part, and are clearly identified on the cross sections of the fibers in the form of small dots (see Fig. 87 and 88).

Myofibrils have their own transverse striation, and in the muscle fiber they are arranged in such an orderly manner that the isotropic and anisotropic disks of different myofibrils coincide with each other, causing the transverse striation of the entire fiber. Each myofibril is formed by thousands of repeating successively interconnected structures - sarcomeres.

Sarcomere (myomer) is a structural and functional unit of a myofibril and is its section located between two telophragms (Z lines). It includes an anisotropic disk and two halves of isotropic disks - one half on each side (Fig. 89). The sarcomere is formed by an ordered system thick (myosin) And thin (actin) myofilaments. Thick myofilaments are associated with mesophragma (line M) and are concentrated in an anisotropic disk,

and thin myofilaments are attached to telophragms (Z lines), form isotropic disks and partially penetrate the anisotropic disk between thick filaments up to light H stripes at the center of the anisotropic disk.

The mechanism of muscle contraction described the theory of sliding threads, according to which the shortening of each sarcomere (and, consequently, myofibrils and the entire muscle fiber) during contraction occurs due to the fact that as a result of the interaction of actin and myosin in the presence of calcium and ATP, thin filaments are pushed into the gaps between thick ones without changing their length. In this case, the width of the anisotropic disks does not change, while the width of the isotropic disks and H bands decreases. The strict spatial ordering of the interaction of many thick and thin myofilaments in the sarcomere is determined by the presence of a complexly organized supporting apparatus, which, in particular, includes the telophragm and mesophragm. Calcium is released from sarcoplasmic reticulum, elements of which braid each myofibril, after receiving a signal from the sarcolemma through T-tubules(the set of these elements is described as sarcotubular system).

Skeletal muscle as an organ consists of bundles of muscle fibers connected together by a system of connective tissue components (Fig. 90). Covers the outside of the muscle epimysium- a thin, strong and smooth sheath made of dense fibrous connective tissue, extending deeper into the organ thinner connective tissue septa - perimysium, which surrounds the bundles of muscle fibers. From the perimysium inside the bundles of muscle fibers depart the thinnest layers of loose fibrous connective tissue surrounding each muscle fiber - endomysium.

Types of muscle fibers in skeletal muscle - varieties of muscle fibers with certain structural, biochemical and functional differences. Typing of muscle fibers is carried out on preparations when setting up histochemical reactions for detecting enzymes - for example, ATPase, lactate dehydrogenase (LDH), succinate dehydrogenase (SDH) (Fig. 91), etc. In a generalized form, three main types of muscle fibers can be conditionally distinguished, between which there are transitional options.

Type I (red)- slow, tonic, resistant to fatigue, with a small force of contraction, oxidative. Characterized by small diameter, relatively thin myofibrils,

high activity of oxidative enzymes (for example, SDH), low activity of glycolytic enzymes and myosin ATPase, predominance of aerobic processes, high content of myoglobin pigment (which determines their red color), large mitochondria and lipid inclusions, rich blood supply. Numerically predominate in muscles performing long-term tonic loads.

Type IIB (white)- fast, tetanic, easily tiring, with great force of contraction, glycolytic. They are characterized by large diameter, large and strong myofibrils, high activity of glycolytic enzymes (for example, LDH) and ATPase, low activity of oxidative enzymes, predominance of anaerobic processes, relatively low content of small mitochondria, lipids and myoglobin (which determines their light color), a significant amount of glycogen, relatively poor blood supply. They predominate in muscles that perform fast movements, for example, the muscles of the limbs.

Type IIA (intermediate)- fast, resistant to fatigue, with great strength, oxidative-glycolytic. On preparations, they resemble type I fibers. They are equally capable of using the energy obtained by oxidative and glycolytic reactions. According to their morphological and functional characteristics, they occupy a position intermediate between type I and IIB fibers.

Human skeletal muscles are mixed, that is, they contain fibers of various types, which are distributed in them in a mosaic pattern (see Fig. 91).

Cardiac striated (striated) muscle tissue occurs in the muscular membrane of the heart (myocardium) and the mouths of the large vessels associated with it. The main functional property of cardiac muscle tissue is the ability to spontaneous rhythmic contractions, the activity of which is influenced by hormones and the nervous system. This tissue provides the contractions of the heart that keep the blood circulating in the body. The source of development of cardiac muscle tissue is myoepicardial plate of the visceral leaf of the splanchnotome(coelomic lining in the neck of the embryo). The cells of this plate (myoblasts) actively multiply and gradually turn into cardiac muscle cells - cardiomyocytes (cardiac myocytes). Lined up in chains, cardiomyocytes form complex intercellular connections - insert discs, linking them to cardiac muscle fibers.

Mature cardiac muscle tissue is formed by cells - cardiomyocytes, connected to each other in the region of the intercalated discs and forming a three-dimensional network of branching and anastomosing cardiac muscle fibers(Fig. 92).

Cardiomyocytes (cardiac myocytes) - cylindrical or branching cells, larger in the ventricles. In the atria, they usually have an irregular shape and are smaller. These cells contain one or two nuclei and a sarcoplasm, covered with a sarcolemma, which is surrounded by a basement membrane on the outside. Their nuclei - light, with a predominance of euchromatin, well-marked nucleoli - occupy a central position in the cell. In an adult, a significant part of cardiomyocytes - polyploid, more than half - dual-core. The sarcoplasm of cardiomyocytes contains numerous organelles and inclusions, in particular, a powerful contractile apparatus, which is highly developed in contractile (working) cardiomyocytes (especially in ventricular ones). The contractile apparatus is presented cardiac striated myofibrils, skeletal muscle tissue fibers similar in structure to myofibrils (see Fig. 94); together they cause transverse striation of cardiomyocytes.

Between the myofibrils at the poles of the nucleus and under the sarcolemma are very numerous and large mitochondria (see Fig. 93 and 94). Myofibrils are surrounded by elements of the sarcoplasmic reticulum associated with T-tubules (see Fig. 94). The cytoplasm of cardiomyocytes contains the oxygen-binding pigment myoglobin and accumulations of energy substrates in the form of lipid drops and glycogen granules (see Fig. 94).

Types of cardiomyocytes in cardiac muscle tissue differ in structural and functional features, biological role and topography. There are three main types of cardiomyocytes (see Fig. 93):

1)contractile (working) cardiomyocytes form the main part of the myocardium and are characterized by a powerfully developed contractile apparatus, which occupies most of their sarcoplasm;

2)conducting cardiomyocytes have the ability to generate and quickly carry out electrical impulses. They form knots, bundles and fibers conducting system of the heart and are divided into several subtypes. They are characterized by weak development of the contractile apparatus, light sarcoplasm and large nuclei. IN conductive heart fibers(Purkinje) these cells are large (see Fig. 93).

3)secretory (endocrine) cardiomyocytes located in the atria (especially right

vom) and are characterized by a process form and weak development of the contractile apparatus. In their sarcoplasm, near the poles of the nucleus, there are dense granules surrounded by a membrane containing atrial natriuretic peptide(a hormone that causes loss of sodium and water in the urine, vasodilation, lowering blood pressure).

Insert discs carry out communication of cardiomyocytes with each other. Under a light microscope, they look like transverse straight or zigzag stripes crossing the cardiac muscle fiber (see Fig. 92). Under an electron microscope, the complex organization of the intercalated disk is determined, which is a complex of intercellular connections of several types (see Fig. 94). In the area of ​​transverse (oriented perpendicular to the location of myofibrils) sections of the intercalated disk, neighboring cardiomyocytes form numerous interdigitations connected by contacts of the type desmosome And adhesive fascias. Actin filaments are attached to the transverse sections of the sarcolemma of the intercalated disc at the level Z lines. On the sarcolemma of the longitudinal sections of the intercalary disc there are numerous gap junctions (nexuses), providing ionic bonding of cardiomyocytes and transmission of the contraction impulse.

smooth muscle tissue part of the wall of hollow (tubular) internal organs - bronchi, stomach, intestines, uterus, fallopian tubes, ureters, bladder (visceral smooth muscle) as well as vessels (vascular smooth muscle). Smooth muscle tissue is also found in the skin, where it forms the muscles that raise the hair, in the capsules and trabeculae of some organs (spleen, testis). Due to the contractile activity of this tissue, the activity of the organs of the digestive tract, the regulation of respiration, blood and lymph flow, the excretion of urine, the transport of germ cells, etc. are ensured. The source of development of smooth muscle tissue in the embryo is mesenchyme. The properties of smooth myocytes are also possessed by some cells of a different origin - myoepithelial cells(modified contractile epithelial cells in some glands) and myoneural cells irises of the eye (develop from the neural bud). The structural and functional unit of smooth muscle tissue is smooth myocyte (smooth muscle cell).

Smooth myocytes (smooth muscle cells) - elongated cells predominantly faith-

tenoid shape, not having transverse striation and forming numerous connections with each other (Fig. 95-97). Sarcolemma each smooth myocyte is surrounded basement membrane, into which thin reticular, collagen and elastic fibers are woven. Smooth myocytes contain one elongated diploid nucleus with a predominance of euchromatin and 1-2 nucleoli located in the central thickened part of the cell. In the sarcoplasm of smooth myocytes, moderately developed organelles of general importance are located together with inclusions in cone-shaped areas at the poles of the nucleus. Its peripheral part is occupied by the contractile apparatus - actin And myosin myofilaments, which in smooth myocytes do not form myofibrils. Actin myofilaments are attached in the sarcoplasm to oval or fusiform dense bodies(see Fig. 97) - structures homologous to Z lines in striated tissues; similar formations associated with the inner surface of the sarcolemma are called dense plates.

The contraction of smooth myocytes is provided by the interaction of myofilaments and develops in accordance with the model of sliding filaments. As in striated muscle tissues, the contraction of smooth myocytes is induced by the influx of Ca 2+ into the sarcoplasm, which is released in these cells. sarcoplasmic reticulum And caveoli- Numerous flask-shaped protrusions of the surface of the sarcolemma. Due to their pronounced synthetic activity, smooth myocytes produce and secrete (like fibroblasts) collagens, elastin, and components of an amorphous substance. They are also able to synthesize and secrete a number of growth factors and cytokines.

Smooth muscle tissue in organs usually represented by layers, bundles and layers of smooth myocytes (see Fig. 95), within which the cells are connected by interdigitations, adhesive and gap junctions. The arrangement of smooth myocytes in layers is such that the narrow part of one cell is adjacent to the wide part of the other. This contributes to the most compact packing of myocytes, ensuring the maximum area of ​​their mutual contacts and high tissue strength. In connection with the described arrangement of smooth muscle cells in the layer, cross sections are adjacent sections of myocytes, cut in the wide part and in the region of the narrow edge (see Fig. 95).

MUSCLE TISSUE

Rice. 87. Skeletal striated muscle tissue

1 - muscle fiber: 1.1 - sarcolemma covered with a basement membrane, 1.2 - sarcoplasm, 1.2.1 - myofibrils, 1.2.2 - fields of myofibrils (Konheim); 1.3 - nuclei of the muscle fiber; 2 - endomysium; 3 - layers of loose fibrous connective tissue between bundles of muscle fibers: 3.1 - blood vessels, 3.2 - fat cells

Rice. 88. Skeletal muscle fiber (diagram):

1 - basement membrane; 2 - sarcolemma; 3 - myosatellitocyte; 4 - the core of the myosymplast; 5 - isotropic disk: 5.1 - telophragm; 6 - anisotropic disk; 7 - myofibrils

Rice. 89. Plot of myofibril fiber of skeletal muscle tissue (sarcomere)

Drawing with EMF

1 - isotropic disk: 1.1 - thin (actin) myofilaments, 1.2 - telophragm; 2 - anisotropic disk: 2.1 - thick (myosin) myofilaments, 2.2 - mesophragm, 2.3 - H band; 3 - sarcomere

Rice. 90. Skeletal muscle (cross section)

Stain: hematoxylin-eosin

1 - epimysium; 2 - perimysium: 2.1 - blood vessels; 3 - bundles of muscle fibers: 3.1 - muscle fibers, 3.2 - endomysium: 3.2.1 - blood vessels

Rice. 91. Types of muscle fibers (cross section of skeletal muscle)

Histochemical reaction for the detection of succinate dehydrogenase (SDH)

1 - fibers of type I (red fibers) - with high activity of SDH (slow, oxidative, resistant to fatigue); 2 - IIB type fibers (white fibers) - with low SDH activity (fast, glycolytic, fatigued); 3 - fibers of type IIA (intermediate fibers) - with moderate activity of SDH (fast, oxidative-glycolytic, resistant to fatigue)

Rice. 92. Cardiac striated muscle tissue

Stain: iron hematoxylin

A - longitudinal section; B - cross section:

1 - cardiomyocytes (form cardiac muscle fibers): 1.1 - sarcolemma, 1.2 - sarcoplasm, 1.2.1 - myofibrils, 1.3 - nucleus; 2 - insert disks; 3 - anastomoses between fibers; 4 - loose fibrous connective tissue: 4.1 - blood vessels

Rice. 93. Ultrastructural organization of cardiomyocytes of various types

Drawings with EMF

A - contractile (working) cardiomyocyte of the ventricle of the heart:

1 - basement membrane; 2 - sarcolemma; 3 - sarcoplasm: 3.1 - myofibrils, 3.2 - mitochondria, 3.3 - lipid drops; 4 - core; 5 - insert disk.

B - cardiomyocyte of the conduction system of the heart (from the subendocardial network of Purkinje fibers):

1 - basement membrane; 2 - sarcolemma; 3 - sarcoplasm: 3.1 - myofibrils, 3.2 - mitochondria; 3.3 - glycogen granules, 3.4 - intermediate filaments; 4 - cores; 5 - insert disk.

B - endocrine cardiomyocyte from the atrium:

1 - basement membrane; 2 - sarcolemma; 3 - sarcoplasm: 3.1 - myofibrils, 3.2 - mitochondria, 3.3 - secretory granules; 4 - core; 5 - insert disc

Rice. 94. Ultrastructural organization of the region of the intercalated disc between neighboring cardiomyocytes

Drawing with EMF

1 - basement membrane; 2 - sarcolemma; 3 - sarcoplasm: 3.1 - myofibrils, 3.1.1 - sarcomere, 3.1.2 - isotropic disk, 3.1.3 - anisotropic disk, 3.1.4 - bright H band, 3.1.5 - telophragm, 3.1.6 - mesophragm, 3.2 - mitochondria, 3.3 - T-tubules, 3.4 - elements of the sarcoplasmic reticulum, 3.5 - lipid drops, 3.6 - glycogen granules; 4 - intercalary disc: 4.1 - interdigitation, 4.2 - adhesive fascia, 4.3 - desmosome, 4.4 - gap junction (nexus)

Rice. 95. Smooth muscle tissue

Stain: hematoxylin-eosin

A - longitudinal section; B - cross section:

1 - smooth myocytes: 1.1 - sarcolemma, 1.2 - sarcoplasm, 1.3 - nucleus; 2 - layers of loose fibrous connective tissue between bundles of smooth myocytes: 2.1 - blood vessels

Rice. 96. Isolated smooth muscle cells

stain: hematoxylin

1 - core; 2 - sarcoplasm; 3 - sarcolemma

Rice. 97. Ultrastructural organization of a smooth myocyte (section of a cell)

Drawing with EMF

1 - sarcolemma; 2 - sarcoplasm: 2.1 - mitochondria, 2.2 - dense bodies; 3 - core; 4 - basement membrane