Muscular tissue

Question 1

Layers of skeletal muscle

Answer 1

1. Epimysium: cover the whole muscle (several fascicles)
2. Perimysium: cover the fascicle (several muscle fibers)
3. Endomysium: cover the single muscle cell or fiber (several myofibrils)

Question 2

Sarcomere

Answer 2

is contractile unit of striated muscle containing alternate arrangement of I band (light band - contains actin microfilament) and A band (dark band - contains myosin thick filaments) which extends between two adjacent Z disks.

Question 3

Skeletal muscle cells and unit

Answer 3

Mesenchymal cells –> myoblasts –> myotubes–> myofilaments–>myofibrils–>single muscle fiber–>fascicles–>muscle

Question 4

Triad formation

Answer 4

arrangement of two lateral sarcoplasmic reticulum in connection with central T tubule produces Triad.
T tubule is finger like projection of sarcolemma (plasma membrane) into the sarcoplasm

Question 5

Sarcosome

Answer 5

Striated myofibril with alternate I and A band is surrounded by mitochondria which is called sarcosome

Question 6

Different bands and disks of sarcomere

Answer 6

1. Z disks - forms scaffolding of sarcomere
2. I band - light band, contains actin myofilaments attached to Z disks by alfa-actinin and extends into A band
3. A band - dark band, contains myosin thick filaments
4. H band - light pale band that bisect A band and contains creatine kinase to form ATP to use during muscle contraction
5. M line - Run in the middle of the H band - represents lateral arrangement of myosin

Question 7

Actin and myosin composition and essential proteins

Answer 7

Actin: F actin is double stranded and striated myofilament contains monomer G actin
Composition:
a. Tropomyosin,
b. Troponin I binds to actin, C binds to calcium and T binds to tropomyocin
At resting stage of muscle Ca occupies high affinity region of troponin - not available for interaction between F actin and myosin
During contraction Ca occupies low affinity region of troponin - then I binds to actin and T binds to tropomyosin leads to interaction of actin and myosin - muscle contraction

Myosin II: contains two heavy and two light chains
1. one end of two heavy chain contains globular head has 3 points of attachment for actin, for ATPase and for light chain
2. light chains - 1 x essential and 1 x regulator

Titin: protein anchors myosin microfilament to Z disk and extends to M line - provides elasticity, act as a template, limit the displacement range

Nebulin: protein run along the length of actin microfilament to stabilize it

Desmin is an intermediate filament protein that holds microfibrils together and anchored to sarcolemma - the point of anchoring is known as costamere. Function: stability, attachment and determines distribution and function of mitochondria

Question 8

Skeletal, cardiac and smooth muscle major difference

Answer 8

Skeletal muscle: (striated)
1. Triad formation
2. extensive SR
3. T tubule found at junction of A-I
4. multinucleated peripheral nucleus

Cardiac muscle: (striated)
1. Diad formation by T tubule and one SR
2. T tubule found at level of Z disk
3. abundant mitochondria
4. contains intercalated disks
5. central nucleus

Smooth muscle: (nonstriated)
1. Contains caveolae instead of T tubule
2. Actin-myosin not organised in sarcomere
3. Gets Ca extracellularly not from SR
4. contains tropomyosin but not troponin, sarcomere
5. Central nucleus
6. myosin light chain kinase responsible for Ca sensitivity and contraction