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Muscles - Anatomy & Physiology (view source)
Revision as of 11:58, 23 July 2008
, 11:58, 23 July 2008no edit summary
***Function - exercise, bursts of activity
***Function - exercise, bursts of activity
*Muscle activation is initiated by a nervous impulse crossing the Neuromuscular Junction
*Muscle activation is initiated by a nervous impulse crossing the Neuromuscular Junction
**The neurotransmitter, Acetylcholine (Ach), binds receptors in the muscle fiber to open Na+ channels
**The neurotransmitter, '''Acetylcholine (Ach)''', binds receptors in the muscle fiber to open Na+ channels
**This causes a wave of depolarization along the sarcoplasmic membrane, further opening voltage-gated Na+ channels, which propagates the signal along the sarcolemma
**This causes a wave of depolarization along the sarcoplasmic membrane, further opening voltage-gated Na+ channels, which propagates the signal along the sarcolemma
**Depolarization of the sarcoplasmic reticulum causes Calcium to be released, which activates muscle contraction
**Depolarization of the sarcoplasmic reticulum causes Calcium to be released, which activates muscle contraction
***Myosin heads bind Actin subunits, forming cross-bridges, hydrolyzing ATP and providing energy for contraction
***Myosin heads bind Actin subunits, forming cross-bridges, hydrolyzing ATP and providing energy for contraction
***Myosin heads undergo power stroke, displacing Actin and releasing ADP and Pi
***Myosin heads undergo power stroke, displacing Actin and releasing ADP and Pi
*Control of skeletal muscle activity is regulated by the '''thin filament'''
**In the off state, tropomyosin coiled-coils block the helical grooves of the actin filament
**Tropomyosin movement relieves the steric block, allowing access to myosin binding sites
***Calcium regulates muscle contraction by binding troponin-C, which is attached to the thin filament
***Calcium regulates muscle contraction by binding troponin-C, which is attached to the thin filament
***This causes inhibition of the steric block keeping Actin and Myosin from interacting
***This causes inhibition of the steric block keeping Actin and Myosin from interacting
*Increased Calcium causes a negative feedback inhibition of Ca release, and it is pumped back into the sarcoplasmic reticulum by the Ca/ATPase pump
==Smooth Muscle==
*Smooth muscle lacks troponin
*Control of smooth muscle contraction involves '''thin and thick filament regulation'''
* Thin filament regulation is carried out by the actin binding protein, '''Caldesmon''', which binds the thin filament and blocks myosin access
**'''Calmodulin''' (activated by binding Ca) binds caldesmon and causes its dissociation from actin, enabling contraction
*Thick filament regulation occurs by the '''phosphorylation''' of the '''regulatory light chain (RLC)'''
**Calmodulin-Ca binds and activates myosin light chain kinase (MLCK)
**MLCK then phosphorylates RLC, turning myosin on
**Myosin light chain phosphatase (MLCP) switches myosin off
==Tendon==
==Tendon==