muscle tissue. introduction myocyte cell membrane cytoplasm smooth er muscle fibre sarcolemma...
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Muscle Tissue
Introduction
Myocyte
Cell membrane
Cytoplasm
Smooth ER
Muscle fibre
Sarcolemma
Sarcoplasm
Sarcoplasmic Reticulum
Muscle Tissue
Skeletal muscle
Cardiac muscle
Smooth muscle
striatedmuscle
Voluntary muscle
Involuntarymuscle
1. classification of muscle tissue
2. skeletal muscle
2.1 structure under LM LM: profile: cylindrical ; with cross striations.
sarcoplasm: numerous myofibrils with cross
striations along its length,which
leads to the periodic cross striations
of the muscle fibre.
nuclei: numerous, elliptical ,lie along the
periphery of the muscle fibre.
skeletal muscle
myofibril : looks like riband.
alternate dark band and light band.
cross striation: corresponding dark and light bands in
each myofibril lie at the same level of the muscle fibre.
Light band: I band Dark band: A band.H band; M line; Z line.
sarcomere : The part of a myofibril between two
consecutive Z-bands. (1/2I+A+1/2I ) It is the structural and functional unit of the myofibril, it is the basic structure of the contraction.
sarcomere
2.2.1 Myofibril: made up of thick filament (myosin filament)
and thin filament (actin filament ).
thick filament: made up of myosin molecules myosin: bean sprout in shape, having 2 heads and 1 tail.
The head has an ATP-binding site and an actin-
binding site.It is an inactive ATPase.
2.2 Ultrastructure of Muscle fibre ( EM )
thick filament
thin filament: made up of actin, tropomyosin
and troponin.
actin: its monomer appears spheral , each
monomer has a myosin binding site.
Monomers polymerise each other to form
a long double helix chain. tropomyosin: two helical polypeptide- chains.
localized in the grooves of the actin.
troponin : attached to the surface of tropomyosin.
able to combine with Ca2+
muscle fiber and myofibril
thick filament and thin filament
actin tropomyosin troponin
thin filament
distribution of the thick and
thin filaments in sarcomere
2.2.2 transverse tubule
Position: at the level of each A-I junction.
Formation: a finger-like inpushing from the surface
membrane of the muscle fibre, coming into very close contact with elements of the sarcoplasmic reticulum.
Function: conducting electrical action potentials from the
surface of the muscle fibre deep into the interior of the fibre.
2.2.3 sarcoplasmic reticulum
Position: between transverse tubules.
Structure:SER .Their middle parts surround the
myofibrils,while their terminal ends become expanding, forming terminal cisternae.
Function: regulating the concertration of calcium ion in
the sarcoplasm ; initiating muscle contraction by releasing calcium ions
triad
A triad consists of two terminal cisterns with a
T-tubule in the middle.
Function: Spread the nerve impulse deep into
the muscle fiber quickly.
transverse tubule and triad
2.3 mechanism of muscle contraction
sliding filament mechanism
1. Action potential causes Ca++ release from S.E.R. 2. Ca++ binds Troponin 3. Troponin moves Tropomyosin 4. Tropomyosin uncovers myosin binding site on actin 5. Myosin binds actin 6. ATPase is activated ,which leads to the release of energe.7. Myosin pulls actin chain along in one direction 8. Sarcomere shortens (Z lines move closer together) 9. Whole fiber shortens, ....... Contraction! 10.Ca++ pumps restore Ca++ to S.E.R. ...... Relaxation!
Relaxation is the reverse of these steps.
Muscle Contraction
the difference of myofibril in the states of expansion and contraction
3 cardiac muscle
3.1 structure under LM
LM: short and cylindrical, branched, with cross
striations connected end-to-end by junctions.
Junctions between neighboring cells are called
intercalated disc.
Nucleus: usually one central nucleus
cardiac muscle
Longitudinal and cross sections of cardiac muscle fibres
EM: 1) myofibrils are not obvious.
2) transverse tubules are wider , occurring
at the Z-line.
3) undeveloped sarcoplasmic reticulum,
usually forming diad.
4) intercalated disc consists of gap junction,
intermediate junction, desmosome, localized
at the level of Z- line
3.2 ultrastucture of cardiac muscle fibre
intercalated disc ( EM )
4 smooth muscle
4.1 structure of smooth muscle fibre
LM: spindle, no cross striation;
nucleus: a central ellipse nucleus.
smooth muscle fiber
longitudinal and cross sections of smooth muscle
EM: no myofibril but have thin and thick filaments, no obvious sarcomere. contractile unit: gathering of thick and thin filaments.
dense patch and dense body:
4.2 the ultrastructure of smooth muscle fibre
Cross section of muscle fibers
longitudinal section of muscle fibers
5 Key Points
1. sarcomere
2. Myofibril
3. transverse tubule and triad
4. Sarcoplasmic Reticulum
4. the ultrastructure of skeletal muscle and cardiac muscle
5. the structures of three muscle tissues under LM