Smooth Muscle: excitation and contraction Flashcards
What are features of smooth muscle?
Spindle shaped cells
Lack striations
single nucleus
sliding filament mechanism
What is phasic smooth muscle?
Muscle that spends most of the time in a relaxed state, contracting periodically
eg. the bladder
What is tonic smooth muscle?
Remains contracted for most of the time
eg. LOS
What is multi-unit smooth muscle?
each cell contracts and relaxes on its own
eg. vascular smooth muscle
What is single unit smooth muscle?
all smooth muscle cells in the organ behave as one unit
eg. GI tract
What does an increase in cytosolic calcium lead to?
Binding of calcium by calmodulin - activates myosin light chain kinase (contraction)
How is smooth muscle different to skeletal muscle?
Increase in cytosolic calcium resulting from most stimuli does not activate all cross-bridges
What is the rising phase of smooth muscle AP due to?
Influx of calcium ions
What controls vascular tone and how?
Endothelium by EDH and various vasoactive substances
What causes calcium sparks?
EDHF
What does EET activate?
Transient receptor channel in sarcolemma of smooth muscle which causes influx of Ca2+ which opens RyR channels - calcium sparks
What do Ca2+ sparks activate?
Large conductance K+ channel - hyperpolarization
What does hyperpolarization cause?
Decreases basal Ca2+ influx
Decreasing intracellular Ca2+
Relaxing muscle
