MUSCLE TISSUE. (=MT). It includes 5 types.
-
STRIATed SKELETAL MT (is developed from MYOTOME of SOMITE),
-
STRIATed CARDIAC MT (is developed from mesoderm portion, named MYOEPICARDIAL PLATE). It locates in MYOCARDIUM.,
-
SMOOTH MT of mesenchymal type, developing from MESENCHYME.
-
SMOOTH MT of ectodermal type, developing from SURFACE ECTODERM.
-
SMOOTH MT of neural type, developing from NEURAL TUBE.
STRIATED MT means - because organelles MYOFIBRILLS contain visible in microscope
alternating DARK bands (or
A-bands) and LIGHT bands (or
I-bands).
SMOOTH MT means - because microscopically dark and light bands in cells are absent.
-
STRIATed SKELETAL MT.
It is composed of
striated skeletal mucle FIBRes (=SSMF). One SSMF is composed of
2 components: A)
Multinucleated
MYOSYNCYTIUM, with funct.. of
contraction, B)
mononucleated
SATELLITE cells, as origin of
REGENERATION for syncytium after its rupture. Skeletal MT
well regenerates due to proliferation of SATELLITE cs. Structure of
MYOSYNCYTIUM (=MC): It has a)
10, 000 nuclei in SARCOplasm
periphery (below SARCOlemma), b) abundance of
MYOFIBRILLs occupy
center of SARCOplasm.(SARCOplasm – is CYTOplasm of MC; SARCOlemma – is plasma membrane of MC). MYOFIBRILLs contain CROSS STRIATION, locating in SARCOMEREs.
MYOFIBRILL is composed of structural units- SARCOMERs. SARCOMERE is composed of ½
I-band+1
A-band+1/2
I-band.
I-band contains ONLY
thin (or
ACTIN) myofilaments.
A-band contains
ACTIN (or
thin) myofilaments and
MYOSIN (or
thick) myofilaments.
-
STRIATed CARDIAC MT.
It is composed of
cardiac muscle fibres (=CMF). One
CMF – is
chain of MONOnucleated cardiac muscle CELLS, attached each to other by
intercalated disks. (
NO syncytium and
NO satellite cs in myocardium).
Types of
CARDIAC
MUSCLE
CELLS (=CMCs):
1) CONTRACTILE CMC. It is: a)
CYLINDRICAL-shaped, b) contains
1-2 nuclei in centre, c)abundance of MYOFIBRILLs in cytoplasm periphery, d) lives ALWAYS in
Go-phase(
NEVER divides by
mitosis), e) is placed in miocardium of VENTRICLes. Funct.: proyide heart CONTRACTION.
2) SECRETORY CMC. It is: a)
STAR-(STELLATE)-shaped, b) abundance of rER and
secretory GRANULES in cytoplasm, c) are placed in myocardium of ATRIA. Funct.: secretion of cardiac
hormone “NATRIURETIC PEPTIDE”. 3) Conducting CMC, including
P-cells (pace-maker) and Purkinje fibres. Funct.:
P-cell
generates 60-80 potentials of action per min.
Regeneration of CMCs: After necrosis
NEW CMCs are
NOT developed (because live in
Go-phase). But FIBROBLASTS, locating in ENDOMISIUM, form
collagen SCAR, replacing xone of necrosis.
-
SMOOTH MT of mesenchymal type:
It locates in wall of stomach, intestine, blood vessels, urinary bladder, myometrium. This tissue is composed of
bundles of
SMOOTH MUSCLE CELLS (=SMC).
One SMC is: a)
SPINDLE-shaped, b) in cytoplasm abundance of THICK and THIN myofilaments WITHOUT cross striation; c) myofilaments attach to plasma membrane by DENSE BODIES. Funct.: if SMCs are in intestine, it provide
peristalsis; If SMCs are in arterioles wall, it regulate level of
blood pressure.
-
SMOOTH MT of ectodermal type
It is composed of
MYOEPITHELAL cells (=MECs).
One MEC is a)
BASKET-shaped with long cytoplasmic PROCESSES, surrounding
secretory portions of exocrine glands, b) in cytoplasm abundance of THICK and THIN myofilaments.
Funct.: MEC contracts and
compresses secretory portion, providing
releasing of secretory products (saliva, milk) into ducts.
-
SMOOTH MT of neural type.
It locates in eye
IRIS and form muscles, DILATING and CONSTRICTING of PUPIL.
It is composed of smooth muscle cells with one long process.
Skeletal muscle and myocardium
BETWEEN muscle fibres contain layers of loose irregular connective tissue, named
ENDOMISIUM and PERIMISIUM. Main cell type in its – is differentiated FIBROBLAST. Funct.:
Fibroblasts form
collagen SCAR in:a) MYOCARDIUM after its
NECROSIS
(or
INFARCT) and in 2) MYOMETRIUM after operation CESARIAN section.
. Usually endomisium provide TROPHIC function and INNERVATES muscle fibres.
Составитель – доцент В.В. Бондаренко.
