Muscle Physiology

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terms

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MUSCLE FIBER = THE MUSCLE CELL
SARCOLEMMA = CELL MEMBRANE OF MUSCLE
SARCOPLASM = THE CYTOPLASM OF MUSCLE
SARCOPLASMIC RETICUUM = ER OF MUSCLE CELL
MYOFIBRILS = CONTRATILE FILAMENTS – GROUPS OF MYOFILAMENTS
MYOFILAMENTS = CONTRACTILE FILAMENTS THAT MAKE UP MYOFIBRILS
SARCOMERE = A FUNCTIONAL UNIT OF A SKELETAL MUSCLE

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know

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muscle belly-> epimysium (deep fascia) inbtwn perimysium

fasciulus-> endomysium (inbtwn)

sarcomella, sarcomere, Sarcoplasm around myofibril which are made of myofilament-cylindrerical organelles

they have thin (actin)
and thick (myosin )

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contractile proteins and regulatory proteins

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contractile: myosin/actn
regulartorY: trypomysin and troponin

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myosin has 2 heads (one for ATP and the other for actin to attach)

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myosin head has two sites.
One site is for binding for ATP, once ATP attaches to this it will be hydrolysed into ATP and ip. The other site is for actin to attach.

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actin

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has only one site for myosin head to bind

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tropomyosin-one that covers myosin head binding site ON ACTIN

troponin- stabilizes tropomyosin in a way that it covers actin, but when calcium binding site ttachs, there will be natural affinity for attachment

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TROPOMYOSIN – This blocks the myosin head binding site present on the actin with the help of assistance from troponin during resting state of muscle.
TROPONIN – 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.

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sarcomere

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functional unit of skeletal muscle
sarcomere is the portion of the myofilaments between two successive z lines. Sarcomere is Greek word, sarco-Muscle and mere –small.

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zlines
mline'
A band
I band

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z line stabilizes actions
stabilizes myosoin
(overlapping of thick and thin filament (light no pass)
actin filament (light passes)

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SR

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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.

has Sarcotublars (t-tubules) Ca pump, cA back in to lateral sac

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Sarcollema

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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+).

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sarcomere at rest : 2.5 u

sarcomere contracted 3.5 u

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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

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sliding filament theory

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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 ca+ from lateral sac to sarcoplasm. Elevation of Ca+ 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

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continues

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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 .

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only stops when

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ATP attaches to myosin to deattach myosin head from actin
and CA go back to lateral cisterns in Sarcoplasm

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rigor mortis

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no more ATP produciton 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 in state of contraction which results in stiffening of the body called as RIGOR MORTIS.