Changes

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 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.

==Cardiac Muscle==

==3. Cardiac Muscle==

*Structural: striated but uninucleate, highly vascularized

 

*Gap junctions concentrated at intercalated discs

Cardiac muscle is striated but uninucleate and highly vascularized. There are gap junctions concentrated at intercalated discs.

**'''Myogenic Contraction''' spreads cell to cell and does not depend on nervous imput to individual cells

'''Myogenic Contraction''' spreads cell to cell and does not depend on nervous imput to individual cells. Areas of low electrical resistance allow rapid spread of action potentials. Contraction is regulated by autonomic neurons and circulating hormones. The contractile mechanism is similar to skeletal muscle, an increase in cytosolic Ca. There is a Ca influx across the plasma membrane AND the sarcoplasmic reticulum. The action potential has a prolonged plateau phase.

**Areas of low electrical resistance allow rapid spread of action potentials

**Contraction is regulated by autonomic neurons and circulating hormones

*Contractile mechanism similar to skeletal muscle: increase cytosolic Ca

**Ca influx across plasma membrane AND sarcoplasmic reticulum

*Action potential has a prolonged plateau phase

==Tendon==

==Tendon==