PHYL3001 Lecture Notes - Lecture 7: Verapamil, Submucous Plexus, Action Potential

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LECTURE SEVEN: Physiology of Smooth Muscle
Summary of Second Year:
Smooth muscle control is by Ca2+ binding to calmodulin in the cytosol
Ca2+-calmodulin activates myosin light chain kinase (MLCK)
MLCK phosphorylates smooth muscle light chains and activates their
ATPase
Phosphorylation of myosin controls contraction of smooth muscle
Smooth Muscle:
Not striated
Often controlled by autonomic nerves
Found in
o Blood vessels
o Respiratory system
o Alimentary tract
o Bladder
o Uterus, vas deferens
Contractions are slow
Very resistant to fatigue
Contraction used little energy
Tone can be maintained indefinably state of partial contraction
Some smooth muscle are phasic show rhythmic/pulsatile contractions
Smooth Muscle Activation:
Myogenic originates in muscle e.g. response to stretch
Electrical depolarization by slow waves in gut or artificially e.g. K+
solutions
Autonomic nerves can excite or inhibit contraction ACh, NA, VIP,
ATP, NO
Local mediators e.g. histamine, endothelin, NO
Hormones e.g. angiotensin, adrenaline
Contractile agonists
o ACh muscarinic/M-cholingeric receptor
o Noradrenaline a-adrenergic receptor
o ATP P2X receptor ligand-gated ion channel
Inhibitory/relaxant agonists
o NO granulate cyclase receptors most common
o Noradrenaline b-adrenergic
Multi Unit Smooth Muscle:
Discrete motor units like skeletal muscle
Units must be activated separately
Always produce smooth tonic contractions when activated
Not rhythmic
Found in eye, large blood vessels, airways
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Document Summary

Summary of second year: smooth muscle control is by ca2+ binding to calmodulin in the cytosol, ca2+-calmodulin activates myosin light chain kinase (mlck, mlck phosphorylates smooth muscle light chains and activates their. Atpase: phosphorylation of myosin controls contraction of smooth muscle. Atp, no: local mediators e. g. histamine, endothelin, no, hormones e. g. angiotensin, adrenaline, contractile agonists, ach muscarinic/m-cholingeric receptor, noradrenaline a-adrenergic receptor, atp p2x receptor ligand-gated ion channel. Inhibitory/relaxant agonists: no granulate cyclase receptors most common, noradrenaline b-adrenergic. Multi unit smooth muscle: discrete motor units like skeletal muscle, units must be activated separately, always produce smooth tonic contractions when activated, not rhythmic, found in eye, large blood vessels, airways. Single unit smooth muscle: cells function as a single unit, gap junctions between cells connecting pacemaker cell to surrounding cells, tonic in bladder, small blood vessels, phasic in gut, uterus, often show slow waves or basal electrical rhythm.

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