Smooth muscle Flashcards
What is smooth muscle?
Involuntary muscle found in visceral organs, and surrounding blood vessels, follows sliding mechanism principles and regulation by calcium
Size and division
Small, divided through lifetime, changes in size on response to to tyle of workload. Ex.uterus
Are there t tubules?
No.
What does calcium regulate here
Myosin, not actin, there is no troponin-tropomyosin complex
How is actin attached ?
In dense bodies, which are analogia to z-line
What is the mechanism?
Increase in calcium causes activation of myosin light chain kinase, adds phosphate group to target, power stroke, shortening
Myosin is
Slow
Types of contraction
Phasic single contraction followed by relaxation, tonic- amount of tension proportional to stimulus, can be suistaned over time, ex. Blood vessels
Regulation of contraction
-mechanically gated channels (stretching), because of increase in blood volume,
calcium enters and muscle contractsnti return to original tonic state
-ligand gated channels(receptors)- modulated by ANS. Different response to same neurotransmiter depending upon receptor type(norephinephrine)
-hormones- oxytocin - contraction of uterus
-paracrine agents- K+,H+
- voltage gated channels
Pacemakers
Unusual type muscle with unstable resting membrane potential, rhytmic pattern of AP and contraction, efflux of K+, found in Gi tract, stomach, walls od small intestine
Single unit smooth muscle
Few cells are innervated, rest connected through gap junctions. Entire sheet responds, synchronous contraction and relaxation, gi tract, uterus, arterioles
Multi unit smooth muscle
Each cell inervated no gap junctions, single cell response, muscle within hair on arms
