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Muscles - Anatomy & Physiology (view source)
Revision as of 10:23, 24 July 2008
, 10:23, 24 July 2008no edit summary
*Smooth (aka Visceral)
*Smooth (aka Visceral)
*Cardiac
*Cardiac
==Skeletal Muscle==
==Skeletal Muscle==
[[Image:Striated Muscle 1.jpg|thumb|right|150px|Striated muscle - Copyright RVC 2008]]
[[Image:Striated Muscle 1.jpg|thumb|right|150px|Striated muscle - Copyright RVC 2008]]
*Each muscle is composed of multiple '''fascicles''', each of which consists of a bundle of muscle fibers
*Each muscle '''belly''' is composed of multiple '''fascicles''', each of which consists of a bundle of muscle '''fibers'''
*Muscle "fiber" means a single cell, which are multi-nucleate, and known as '''syncitia'''
*Muscle "fiber" means a single cell, which are multi-nucleate, and known as '''syncitia'''
**'''Parallel''' fibers: running from origin to insertion)
***Long fibers allow for a faster contraction and a greater range of motion
**'''Pennate''' fibers: at an angle to line of pull off an internal tendon or aponeurosis
***Short fibers allow for a greater force capacity
*Within each fiber are groups of parallel, longitudinal myofibrils
*Within each fiber are groups of parallel, longitudinal myofibrils
**Myofibrils are arranged as '''sarcomeres''', bound by Z-discs, which are the functional unit of muscle contraction
**Myofibrils are arranged as '''sarcomeres''', bound by Z-discs, which are the functional unit of muscle contraction
***High '''glycolytic''' activity
***High '''glycolytic''' activity
***Function - exercise, bursts of activity
***Function - exercise, bursts of activity
*'''Neurogenic Contraction''': Muscle activation is initiated by a nervous impulse crossing the Neuromuscular Junction to individual muscle fibers
*'''Neurogenic Contraction''': Muscle activation is initiated by a nervous impulse crossing the Neuromuscular Junction
**Each muscle fiber is controlled by a single motor neuron
**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
***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
*Increased Calcium causes a negative feedback inhibition of Ca release, and it is pumped back into the sarcoplasmic reticulum by the Ca/ATPase pump
*Types of Muscle Contraction:
**'''Concentric''': muscle shortens and bones are brought closer together
**'''Isometric''': muscle is active but does not change in length (force without motion)
**'''Eccentric''': muscle is active while lengthening
==Smooth Muscle==
==Smooth Muscle==
[[Image:Smooth Muscle 1.jpg|thumb|right|150px|Smooth muscle - Copyright RVC 2008]]
[[Image:Smooth Muscle 1.jpg|thumb|right|150px|Smooth muscle - Copyright RVC 2008]]
*Slower contraction and relaxation
**Undeveloped sarcoplasmic reticulum means that smooth muscle depends on the plasmalemma release of Ca: affects contractile prpperties
*Smooth muscle lacks troponin
*Smooth muscle lacks troponin
*Control of smooth muscle contraction involves '''thin and thick filament regulation'''
*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
*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
**'''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)'''
*Thick filament regulation occurs by the '''phosphorylation''' of the '''regulatory light chain (RLC)'''
**MLCK then phosphorylates RLC, turning myosin on
**MLCK then phosphorylates RLC, turning myosin on
**Myosin light chain phosphatase (MLCP) switches myosin off
**Myosin light chain phosphatase (MLCP) switches myosin off
*'''Single Unit''': myogenic contraction; depolarized by gap junctions; eg. intestinal smooth muscle
*'''Multi-unit''': neurogenic contraction; no gap junctions; eg. iris