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Smooth muscle (Differences between skeletal and smooth (Less myosin (but…
Smooth muscle
Differences between skeletal and smooth
No sarcomeres in smooth
Less myosin (but similar actin)
10 to 15 actin filaments wrapped around each myosin
Spindle shaped cells
No NMJ
No t-tubules
No troponin
Less well developed SR
No sarcomeres
Subgroups
Vascular
Gastrointestinal
Respiratory
Urinary
Ocular
Reproductive
Clinical manipulations
Vasoconstriction/vasodilation
Change blood pressure
CHange reistance to flow
Changes perfusion
Explains the symptoms of milk fever (hypocalcaemia)
Explains treatment and side effects of asthma medication
Exccitation-contraction couping
Ca activates myosin ATPase, no troponin in smooth muscle
Ca mostly from extracellular space, not the SR
Ca drives myosin phosphorylation
Excitation
Ca2+ binds to calmodulin
Leads to activation of myosin light chain kinase (MLCK)
Phosphorylation of myosin enhances myosin ATPase --> contraction
Relaxation
Myosin light chain phosphatase (MLCP) dephosphorylates myosin ATPase
Decreases myosin ATPase activity
Electrical and chemical signals inducing rise in cystolic calcium
Electrical signal
Voltage-gates Ca channels open when sarcolemma depolarised
Spread of AP through gap junctions
Chemical signal
Ligand-gated or receptor operated Ca channels
Contraction without change in membrane potential
Can be excitatory or inhibitory