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