Development of skeltal muscle

DEVELOPMENT OF SKELTAL MUSCLE:

There are muscle forming cells in an embroy known as MYOBLASTS. These myoblasts fuse togeather to form eleongated cell which is nearly 30 to 40cm long known as MUSCLE FIBRE or MYOCYTE. As  myocyte is form by fusion of many myoblast so it is multinucleated. So we say that skeltal muscle fibre are multinucleated. after born there are very few myoblast present in a muscle there they are known as SATELLITE CELL. These satellite cells dont form new muscle they can only repair little damage of muscle. Myocyte is covered by ENDOMYSIUM. Bundle of myocyte is known as MUSCLE FASICULUS which is covered by PERIMYSIUM. Many muscle fasiculus group to form a muscle which is covered by EPIMYSIUM. Connective tissue connect skin with the muscle

ULTRASTRUCTURE:

Plasma membrane of muscle fibre is known as SARCOLEMMA

Cytoplasm of muscle fibre is known as SARCOPLASM

Mitochondria of muscle fibre is known as SARCOSOMES

Endoplasmic reticulum of muscle fibre is known as SARCOPLASMIC RETICULUM

As we know that Liver store large amount of glycogen. Muscle also stores large amount of glycogen which is present in sarcoplasm. Sarcoplasmic reticulum store calcium ion releasing calcium ion causes contraction of muscle. Sarcoplasm also contains a red colour protein called MYOGLOBIN(Oxygen storing protein)

Muscle fibre has many MYOFIBRILS. Myofibrils consist of MYOFILAMENT which are actin and myosin. Myosin diameeter is more therefore it also known as thick myofilament and actin known as thin filament. Skeltal muscle is striated which mean when we see it in simple microscope we see alternative light and dark bends which was form due to arrangment of myosin and actin. Actin or thin myofilament also consist of TROPONIN AND TROPOMYOSIN

PROTEIN IN MYOFIBRILS:

1-CONTRACTILE PROTEINS(MYOSIN AND ACTIN)

2-REGULATORY PROTEIN(TROPONIN AND TROPOMYOSIN)

3-STRUCTURAL PROTEINS(TITIN,DESMIN,NEBULIN etc)

About 300 molecule of myosin can make single thick filament. Myosin molecule consist of head,shaft and tail simply. In detail myosin molecule consist of 6 polypeptide chain 2 chain are heavy and 4 are light chains heavy chain twisted to form myosin head

Actually to make muscle contract myosin head need to be attached with thin filament but they dont attach to it because of troponin and tropomysin. So to attached then sarcoplasmic reticulum releases calcium ion which attach with troponin and due to this attachment troponin and tropomyosin conformation change in such a way that myosin head attach with thin filament and muscle contracts