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MINISTRY OF HEALTH CARE OF THE REPUBLIC OF
UZBEKISTAN
TASHKENT MEDICAL ACADEMY
DEPARTMENT OF “HISTOLOGY AND MEDICAL BIOLOGY”
Subject: Histology
THEME: " Muscular tissue "
The text of the lecture
Tashkent - 2012
LECTURE: Muscle tissue - 2:00 hours
The purpose of the lecture: to give a total picture of the origin, structure, muscle
tissue, providing the features of the movement (contraction).
Plan lectures:
1. Classification of muscle tissue.
2. Total morphofunctional characteristics of muscle tissue.
3. Striated muscle tissue
a) Skeletal
b) heart
4. Smooth muscle tissue.
5. Muscle tissue neurodermal origin (myoneural tissue)
6. Myoid cells.
Classification:
I. Morphofunctional.
II. Histogenetic.
I. Morphofunctional - in its structure based on the principle organelle
reduction.
I.1. Striated (textus muscularis striatus)
I.1.a. Skeletal I.1.b. Heart
I.2. Smooth (neischerchennye) (textus muscularis nostiatus)
II. Histogenetic or depending on the source of the development.
II.1. Mesenchymal
II.2. Epidermal (skin from the endoderm and prechordal
plate)
II.3. Neural (from the neural tube)
II.4. Coelomic (myoepicardial plate)
II.5. Somatic (myotom)
II.1.-II.3. - Smooth muscle tissue.
II.4.-II.5. - Striated muscle tissue.
Histogenetic classification adopted as the basis, in accordance with the concept
of stem cells and differonah.
Basic concepts:
1. Transverse striations of muscle:
Contractile elements - myosin filaments
a) continuously polymerized
b) form of actin filaments continuously existing myofibrilles
a) myosin and actin filaments form a space-oriented bundles.
2. Smooth muscle:
1. Myosin filaments depolymerize beyond reductions do not interact with actin
filaments.
2. Ca + +-ions cause polymerization and interaction of myosin with actin.
3. Contractile framework is reticular structure, the transverse striations are not
formed.
Skeletal striated muscle tissue.
Development: myoblasts - in the mesenchyme differentiated into two distinct lines:
a) The muscular tube - myosymplasts
b) myosatelite.
Myoblasts during differentiation in myosymplasts fuse to form muscle tubes
(miotuby) - they are initially located in the center of the nucleus, well developed
SHARE, on the periphery of the myofibrils under cytolemma. Subsequently, the
core is displaced by cytolemma, myofibrils fill most of the fibers.
SHARE significantly reduced.
This definitive structure of the muscle fiber is called myosymplasts.
Miosatellity located on the surface myosymplasts.
Construction:
Structural basis of skeletal striated muscle is the muscle fiber, consisting of
1) myosymplasts and 2) miosatellitotsita covered by a common basement
membrane.
Cytolemma myosymplasts and thin (20-40 nm), connective tissue sheath
(basement membrane) - called the sarcolemma.
Under the sarcolemma located up to several tens of thousands of elongated oval
nuclei. Their poles are general-purpose organelles - Golgi complex (CG),
fragments of rough endoplasmic reticulum (SHARE).
Myofibrils - fill in the rest of the cytoplasm, arranged in parallel, lengthwise.
Sarcomere - the structural unit of a myofibril.
Each myofibril is, respectively, the transverse light and dark areas, interspersed at
regular distances. Each myofibril is surrounded by anastomosing loops smooth
endoplasmic reticulum (SER) and mitochondria.
Each sarcomere is separated from the adjacent Z-line. Z-Line - is a network
of protein (mainly alpha-actin) fibrillar molecules associated with the ends of actin
filaments. The actin filaments are associated with the Z-line actinin molecules (one
way) and the molecules of myosin filaments (the other end), inextensible
molecules nebulin. The middle part of the myofibrils between two Z-lines of dark
(A-disk or strip), formed only myosin filaments. In the middle of a disk is located
transversely M-line, formed by molecules myomezyne. For the M-lines attach the
ends of the myosin filaments. Ratio of actin filaments and myosin 6: 1 (hexagonal
arrangement). Therefore, actin filaments are attached to one end of the Z-lines and
myosin in the M-line.
The other ends of the two filaments are connected to each other, coming into the
spaces between the filaments, myosin filaments but do not reach the Z-line, and
actin to the M-line in the relaxed state of muscle fibers. The ends of the myosin
filaments are fixed to the Z-line protein molecules of titin.
Actin and myosin filaments interact with the participation of proteins
tropomyosin and troponin.
Cytolemma muscle fiber forms a border between the light (I) and dark (A)
drives the long invaginations, in the form of tubes (T - tubules). They are involved
in the transport of Ca + + in the fiber and back. When a signal on the reduction of
muscle fiber, the action potential travels along plasmolemma and distributed on the
membrane of T-tubules. As a consequence, through the T-tubules come Ca + +.
They are released from the membranes of GER (here it's called sarcoplasmic
reticulum). Increasing the concentration of Ca + + activates the interaction of the
contacting parts of the actin and myosin filaments. As a result, actin filaments are
deeply between myosin, reaching the M-line. The distance between adjacent Zlines is halved. Light I-drive disappears. When an action potential disappears, Ca +
+ are removed from the cytoplasm to the ERT and via T-tubules. The actin
filaments "slide out" from between myosin filaments. Again, different light (I) and
dark (A) discs of myofibrils. Muscle fiber relaxes.
Metabolic processes that contraction and relaxation, require energy that is
released in the conversion of ATP to ADP, oxygen accumulated in myoglobin. The
energy released in the conversion of glycogen to carbon dioxide and water.
Myosatellitocytus, Involved in physiological and reparative regeneration of
skeletal muscle. They are oval-elongated, adjacent to cytolemma muscle fibers.
The kernel is the same oval-elongate, larger. The cytoplasm is narrow rim around
the nucleus. Organelles is not enough. When activated, these cells and subsequent
differentiation of the core is clarified, the cytoplasm increases dramatically
increased organelles and myofibrils appear. The gradual transformation of the
ultrastructure
myosatellitocytus occurs in close unity with the maturation of myosymplasts.
The physiological and reparative regeneration
The dynamics of age, when the muscle is growing at a mitotic division and
differentiating cells formed embedded in the ends of myosymplasts.
Muscle damage after a certain distance the ends of fibers break down and are
absorbed by macrophages. Restoring the integrity of the fiber by two mechanisms:
1. Compensatory hypertrophy of the remaining fibers.
2. Proliferation and subsequent differentiation miosatellitotsitov implies they are
embedded in the fibers or form new fibers.
Skeletal muscle as the organ.
Anatomically, each muscle is isolated from the outside of the next, performing
another function (adduction, abduction, etc.), connective tissue sheath (fascia),
which is called epimizy. (Dense fibrous connective tissue). Each muscle consists of
several large groups of muscle fibers, surrounded by thick layers of loose
connective tissue (perimizy). Between the individual fibers are small thin layer of
loose connective tissue (endomysium).
Cardiac muscle tissue
Forms of heart muscle membrane - the myocardium. It consists of narrow fibers
which ramify and anastomose with each other. These fibers are separated
endomysium, and bundles of fibers - perimiziem. Fibers, in contrast to skeletal
muscle tissue formed by cells - cardiomyocytes, with each other through
intercalated disk. Cardiac muscle tissue develops from myoepicardial plate. There
are 3 types of cardiac myocytes:
I. The contractile
II 1. sinus (pacemaker)
II 2. transient
atypical
II 3. conductive
III. secretory
During embryogenesis, initially differentiated contractile, then secretory
cardiomyocytes. Later - cardiomyocytes conduction system - atypical.
Differentiation of all types of cardiac myocytes is accompanied by (proceeds)
integrating them into the fabric fullnes system. Morpho-logical equivalent of 3.2
should be regarded education processes at the ends of cardiomyocytes anastomosis
with 2-3 adjacent cardiomyocytes, formation of a contact area of the intercalated
disk. Highly intercellular contacts such as Nexus (slit), desmosomes and fascia
adhaerentes combine all types of cardiomyocytes in a single fabric system,
providing synchronous contraction and relaxation of the atria and ventricles.
Contractile cardiomyocytes: highly cell length of 100-150 microns in diameter 10-20 mm. Form close to cylindrical. Sarcolemma consists of plasmolemma and
basement membrane thickness of 10-40 nm. In the structure contains a basement
membrane along with the basic substance of elastic and collagen fibers, capable of
binding Ca + +.
In the central part of the contractile cardiomyocytes is 1, less than 2 (10-13%),
oval-shaped nucleus. At the core of the poles are mitochondria, small pieces of CG
single profiles SHARE.
Myofibrils occupy most of the cytoplasm. They are typical of striated muscle
structure. Between the myofibrils in a significant number of mitochondria are welldeveloped cristae. In the ventricles of the contractile cardiomyocyte mitochondria
occupy 35-38% of the volume of the cytoplasm.
At the level of Z-line is the T-system, in contact with the profiles of GER, forming
a dyad or triad.
Atypical conducting impulses, cardiomyocytes are cardiac conducting system,
ensure its rhythmic contractions, synchronous change of contraction and
relaxation. There are 3 types:
1. Pacemaker (pulse-generating, P) cardiomyocytes.
2. Transient.
3. Purkinje myocytes (bridging).
1. Pacemaker, the P-cells - a group of cells under the epicardium in the left ear of
the heart with a few cell contacts, generating spontaneous impulses with a
frequency - 70-80 in 1 min.
Shape: round or polygonal, diameter ≈ 10 mm.
Sarcolemma forms a broad and deep invaginations with a diameter of 1-2 microns.
T-system is absent.
Myofibrils are few, randomly arranged.
Z-bands poorly defined.
Mitochondria are numerous, small, with few cristae. Profiles of the ERT and CG
are rare, but the content of Ca + + is high.
2. Transient conductive cardiomyocytes.
The shape of cells - spindle.
Sizes larger than that of P-cells (about 12 microns).
T-System - short tubules in some cells.
Myofibrils lot, located at an angle to each other, up to a perpendicular direction.
Mitochondria, KG, GER - moderately developed. Contacts between cells are
numerous.
3. Conducting Purkinje cells.
Terminal cells of the vascular system. Large, greater than 15 microns in diameter.
Arranged in 1-2 layers between the endocardium and myocardium, are rare - in the
thickness of the myocardium, form a chain.
Core - the center of round or oval.
Myofibrils is less than in contractile cardiomyocytes, they are in different
directions. The central part of the cell is filled, usually with granules of glycogen.
Mitochondria - in moderation with a moderate number of cristae, detected at the
poles of the nucleus near the sarcomeres. SHARE underdeveloped T - system is
missing. Intercalated disk less tortuous than in contractile cardiomyocytes.
Conclusion. Cardiac striated muscle tissue, unlike skeletal:
1. Has a cellular structure.
2. Several types of cells.
3. Contacts between cells are complex and integrate their activities into a single
fabric system.
4. Regeneration is accomplished by compensatory hypertrophy of surviving
cardiomyocytes.
5. High sensitivity to hypoxia, contractile and less-abnormal cardiomyocytes.
Smooth muscle tissue.
Phylogenetically the youngest type of muscle tissue compared with striated cardiac
or somatic.
Has a common histogenetic origin of fibroblasts:
stem cell → premioblast → myoblasts → smooth myocyte.
Smooth muscle tissue is a part of the gastrointestinal tract, urinary genital system,
airways, blood vessels.
Structure.
Smooth myocyte - spindle cell.
Length - 20 (vessels) to 500 microns (womb).
Width - 5-8 pm.
Kernel - one large, elongated, spindle-shaped. The content of the DNA-diploid.
Characterized by the presence of many bubbles plasmolemma, which function as
the T-system of striated muscle ": Controls the flow of Ca + + into the cell.
Contractile apparatus of smooth myocytes.
Thin actin filaments associated with tropomyosin (troponin is absent), form
three-dimensional network, elongated obliquely and longitudinally, attached to
tsitolemme, and along the poles to the attachment plates (dense bodies).
Attachment plates occupy 30-50% of the circuit cells and consist of a
actinin, actin, seen as the functional equivalent of Z-lines of the striated muscles.
Thanks to them, actin filaments are fixed to the cell surface and the side of the
poles.
Myosin filaments monomers are close to the actin filaments, but depolymerize able
to reduce.
Therefore, to reduce the actin filaments form a lattice structure, mounted on the
perimeter of the cell. Next to them are able to depolymerize myosin proteins.
With the transfer of excitation is opening of potential-dependent channels and
entry into the cytoplasm from the extracellular space of Ca + + ions.
Simultaneously, activation in the cytoplasm of phospholipase release of Ca + +
from its stores. As a result, increasing the concentration of Ca + + polymerization
of myosin filaments. As a result, formation of cross-linking of myosin along actin
filaments. Smooth myocyte reduced by acquiring the folded form.
Removal of Ca + + from the cell via vesicles, and cytoplasmic plasmolemma depot
contributes to the depolymerization of myosin and myosin-akto complexes
decompose. Smooth myocyte relaxes.
Myoneural tissue.
Muscle tissue of iris and ciliary body is formed by smooth mononuclear myocytes,
or miopigmentotsitami.
Morphologically similar to smooth myocytes.
Myopigmentocyte a pigmented body contains a large number of mitochondria and
pigment granules. Myofilaments thin (7 nm) and thick (15 nm) similar to actin and
myosin filaments of smooth myocytes. Myopigmentocyte around a basement
membrane and Remak's fiber.
Myoid cells.
Genetically different cells, united community structure: the cytoplasm contains
contractile filaments smooth or striated muscle tissue.
Sources of Myoid cells: entomezenhima, ectoderm, neuroectoderm, prechordal
plate.
1) myofibroblasts - entomezenchime derivatives.
Found in the granulation tissue healing wounds. Like the smooth myocytes in the
cytoplasm of many contractile filaments (1 / 3 - 2 / 3 of cytoplasm). In the
cytoplasm of well-developed CG and SHARE (for collagen).
2) Myoid cells in the walls of the convoluted seminiferous tubules.
3) Myoendocrene cells - cells in the juxtaglomerular apparatus SOUTH.
4) Myoepiteliocytes (ectodermal) - in the end secretory parts of the salivary, sweat
and mammary glands.
5) Myoid medulla of the thymus cells (from the prechordal plate).
Conclusion.Myoid cells - 1. Are part of 2. Are derived from stem cells to the
tissue.
3. Contain actin and myosin filaments or smooth or striated muscle.