Changes

'''Eccentric''': muscle is active while lengthening.

'''Eccentric''': muscle is active while lengthening.

==Smooth Muscle==

==2. Smooth Muscle==

[[Image:Smooth Muscle 1.jpg|thumb|right|150px|Smooth muscle - Copyright RVC 2008]]

[[Image:Smooth Muscle 1.jpg|thumb|right|250px|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 properties

Smooth muscles has slower contraction and relaxation. An undeveloped sarcoplasmic reticulum means that smooth muscle depends on the plasmalemma release of Ca. Smooth muscle lacks troponin. The 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.

*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

*'''Multi-unit''': neurogenic contraction; no gap junctions; eg. iris

==Cardiac Muscle==

==Cardiac Muscle==