Muscle tissue- discussion, viva

Muscle tissue:

1. What are the types of muscle tissue based on histology?
• Skeletal muscle, cardiac muscle, smooth muscle
2. What is sarcolemma, sarcoplasm?
• The cell membrane or the plasma membrane of the muscle fiber is called as sarcolemma and the cytoplasm of the muscle fiber is called as sarcoplasm
3. What are myofibrils?
• Myofibrils are composed of myofilaments (contractile proteins) actin and myosin and are present in the sarcoplasm of the muscle fiber
4. Myofilamentsàmyofibrilsà muscle fibersàmuscle fascicles/ bundlesàmuscle

Skeletal muscle:

1. What are the identifying features of skeletal muscle?
• Voluntary, Long, cylindrical, unbranched muscle fiber
• Multinuclei present deep to sarcolemma at the periphery of the muscle fiber
• Distinct cross-striations are seen
2. Why is it called as striated muscle?
• It is called as striated muscle because of the cross-striations which are seen as light I-band and dark A-band under light microscope
3. What are cross-striations?
• Cross-striations are formed due to the regular arrangement of the actin and myosin. under light microscope they are seen as light I-bands and dark A-bands
4. What is sarcomere?
• Sarcomere is the smallest contractile unit present between two adjacent Z-lines. They are repeated throughout the entire length of each myofibril
5. What are the coverings of skeletal muscle? or Give the connective tissue arrangements in C.S of skeletal muscle
• Epimysium: outer dense irregular connective tissue covering of the muscle
• Perimysium: less dense irregular connective tissue covering the bundles of muscle fibers
• Endomysium: thin layer of reticular connective tissue covering each muscle fiber
6. What is syncytium?
• Syncytium is a multinucleated cell that results from multiple cell fusions of uninuclear cells
7. What are the structures present along with connective tissue sheaths?
• Blood vessels, nerves and lymphatics
8. What are the features of the muscle fiber in cross-section?
• All the fibers are all most same in size
• One or two nuclei seen in each muscle fiber deep to sarcolemma
• Cross-sections of myofibrils observed
• Surrounding each fiber is the connective tissue sheath endomysium, blood vessels, nerves and lymphatics
9. What are the features of skeletal muscle in longitudinal section?
• Section of each long, cylindrical unbranched muscle fibers
• Multinuclei present deep to sarcolemma
• Cross-striations seen as light I-band and dark A-band
10. What are cross-striations?
• Cross-striations are the light (I band) and dark (A) bands observed under light microscope due to regular arrangement of protein filaments actin and myosin
11. What are motor end plates?
• Motor end plates or neuromuscular junctions are the sites where impulse from axon is transmitted to the skeletal muscle fiber
12. What is present between the individual muscle fibers?
• Connective tissue sheath endomysium with blood vessels, nerves and lymphatics
13. Give examples for skeletal muscle?
• All muscles attached to bones. Flexor pollicis longus, deltoid etc.
14. What are the differences between skeletal muscle and cardiac muscle?
• Refer the table below
15. What are the differences between skeletal muscle and smooth muscle?
• Refer the table below

Cardiac muscle:

1. What are the characteristic features of cardiac muscle?
• Cardiac muscle is involuntary, short, cylindrical, branched fibers
• One or two nuclei present in the center of the fiber
• Cross-striations and intercalated discs seen
2. What are cross-striations?
• Cross-striations are the light I-band and dark A-band observed under light microscope due to regular arrangement of protein filaments actin and myosin
3. What are intercalated discs?
• Intercalated discs are characteristic features of cardiac muscle
• They are the junctional complexes present between the adjacent muscle fibers
• The gap junction in the intercalated disc enable ionic communication and continuity between adjacent cardiac muscle fibers
4. Give examples of cardiac muscle
• Walls and septa of heart, walls of large vessels (aorta, pulmonary trunk) attached to heart
5. What are the differences between cardiac muscle and skeletal muscle?
• Refer the table below
6. What are the differences between cardiac muscle and smooth muscle?
• Refer the table below

Smooth muscle:

1. What are the characteristic features of smooth muscle?
• Involuntary, non-striated, spindle shaped fibers
• Single nucleus present in the center of the muscle fiber
2. Do the smooth muscle fibers contain actin and myosin?
• Yes, the fibers contain actin and myosin
3. Why is it called as non-striated or smooth muscle fibers?
• The myofilaments actin and myosin are not arranged regularly as in skeletal and cardiac muscle. So they appear smooth
4. What are the features observed in cross-section?
• They are present in small fascicles
• The size and shape of each fiber varies depending on the plane of section passing through the fiber
• If the plane passes through the center of the fiber, the section is larger with large central nucleus
• If the plane passes at the tapered end of the fiber, the section is very small without nucleus
• If the plane passes between the two, the fiber appears small with smaller nucleus
5. Give examples for smooth muscle fibers
• Walls of visceral hollow organs like respiratory, GIT, urinary tract, reproductive tracts and blood vessels
6. What are the differences between smooth muscle and skeletal muscle?
• Refer the table below
7. What are the differences between smooth muscle and cardiac muscle?
• Refer the table below

	Skeletal muscle	Cardiac muscle	Smooth muscle
Muscle cells (fibers)	Long cylindrical un-branched muscle fibers.	Tubular fibers branch and anastomoses.	Spindle shaped.
Striations	Cross striations of alternating light (Isotropic or I bands) and dark bands (Anisotropic or A bands). Light band bisected by a dark transverse line, the Z line. Dark band shows the lighter zone in center, the H band.	Faint cross-striated banding patterns.	Lack visible cross striations.
Nuclei	Multinucleated, flat or oval, peripherally arranged.	Uni-nucleate, central in position.	Uni-nucleate, central in position.
Distinguishing feature	Sarcomere, the smallest repetitive subunit of the contractile apparatus lies between two Z lines. Sarcomere consists of thick and thin filaments. Thick filament mainly composed of myosin and thin filament actin  tropomyosin and troponin.	Intercalated disk, faintly seen, under the light microscope, represent the junctional complexes.	-
Functions	Movements.	Autonomic, rhythmic, involuntary movements.	Involuntary movement - i.e. churning of food, movement of urine from the kidney to the bladder, parturition of the fetus.
E.g.	Muscles attached to the bone.	Heart.	Walls of hollow organs (stomach, intestine, uterus, ureter).