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SKELETAL MUSCLE PHYSIOLOGY
Terms in this set (21)
Muscle is made up of muscle fibres, which are enclosed together
by a connective tissue
Each muscle fibre is a
The cell membrane of the muscle is called
cytoplasm is called
Inside the muscle fibre cytoplasm many myofibrils are present which are
cylindrical organelles made up of myofilaments.
The myofilaments are two types
1. Thick filament - myosin
2. Thin filaments -actin ,tropomyosin ,troponin
Myosin and actin are
troponin and tropomyosin are
consists of myosin heads or cross bridges projecting from all around the myosin filament, the myosin head has two sites.
One site is for binding for ATP, once ATP attaches to this it will be hydrolysed into ADP and ip. The other site is for actin to attach.
it has myosin head binding site.
This blocks the myosin head binding site present on the actin with the help of assistance from troponin during resting state of muscle.
is attached to tropomyosin to stabilize it in such a way that it blocks the myosin head binding site on the actin in resting state and troponin has calcium binding site.
Normally there will be natural affinity for attachment between the myosin head and active site for it present on the actin but during resting stages, this is prevented by tropomyosin.
It is the functional unit of skeletal muscle; sarcomere is the portion of the myofibril between two successive z lines. Sarcomere is Greek word, sarco-Muscle and mere -small. It consists of actin filaments attached to z lines at one end and other end overlaps the myosin filament which is at the centre of the sarcomere. Actin is stabilized by z lines where as myosin filaments are by M line (protein) in the centre.
The portion of the Sarcomere where thick filaments are present and the portion where the thick filament overlapped by actin filaments are called as
AN-ISOTROPIC band(Aband) and where only actin filaments present are called isotropic band(Iband).AN -ISOTROPIC means light cannot pass through where as isotropic means light can pass through.
It is modified endoplasmic reticulum which is horizontally placed and it is divided in to many segments and lateral end of each segment is enlarged to form lateral sac or lateral cisterns which are the store house of ca+. The sarcoplasmic reticulum has Ca+ ATP ase pump.
It is the outer covering of muscle fiber which actually conducts the action potential after neuromuscular transmission .one thing we have to remind here that is sarcolemma invaginates in to the sarcoplasm transversely (cytoplasm of muscle )at the junction of A and I Band to form T tubule .
On either side of the T tubule is lateral sac .one T tubule and two lateral sac together is called triad, between the T tubule and lateral sac there is small gap which is bridged by some channel proteins (voltage gated Ca+).
MECHANISM OF MUSCLE CONTRACTION: This whole process is also called as sliding filament theory
After neuromuscular transmission nerve action potential is converted into muscle action potential which is transmitted along the sarcolemma and then it enters the T tubule which is called as T tubule potential. This T tubule potential opens the bridging CHANNEL protein between the T tubule and lateral sac, resulting in release of Ca2+ from lateral sac to sarcoplasm. Elevation of Ca2+ concentration in sarcoplasm results in binding of Ca+ to the troponin and this causes conformational change in troponin resulting in movement of troponin ,as the troponin is attached tropomyosin this also start to move away from the blocking position .
There will be formation of actin—myosin complex, that is myosin head bind with its active binding site present on the actin due to natural affinity as i mentioned earlier .
Once after binding the energy stored in the myosin head due to partial hydrolysis of ATP during resting state as well as ip phosphate is released,
Due this the myosin head under goes conformational change that pull the actin filament towards the center of Sarcomere,
This results in sliding of actin filament over the myosin filament ,at a given instant many cross bridges (myosin head) binds ,detaches consequently and once again reattaches ,and this process continues which is called as cross bridge cycle .
The attachment formed between the myosin head and actin is released only when a new molecule of ATP binds to myosin head and Ca+ has to pumped back to lateral cistern.
Sarcomere at rest
It length is around 2.5 microns
Z lines are farther away
I band is larger
Sarcomere at contracted state
Length is 1.5 microns
I band disappears
A band remains same
Z line moves closer
During stretching of a muscle the sarcomere length reach up to 3.5 microns
After death there will be no more production ATP which required for pumping of Ca+ from sarcoplasm to lateral cistern and also new molecule of ATP is required for detachment of myosin head from the actin, so the muscles will remain is state of contraction which results in stiffening of the body called
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