Lct 33 - smooth muscle

Where is smooth muscle found?

Blood vessels, GI tract, bladder, uterus, airways, iris, reproductive tract

What is the difference between single-unit and multi-unit smooth muscle?

Single-unit: electrically coupled, contracts as sheet; Multi-unit: independently controlled

What triggers contraction in smooth muscle?

Rise in intracellular Ca²⁺ (mainly from ECF, also from SR via IP₃)

What protein does Ca²⁺ bind in smooth muscle?

Calmodulin (not troponin)

How is contraction initiated in smooth muscle?

Ca²⁺-calmodulin → activates MLCK → phosphorylates myosin → binds actin

How is smooth muscle relaxation achieved?

MLCP dephosphorylates myosin; Ca²⁺ pumped out or back into SR

How does noradrenaline affect smooth muscle?

↑ IP₃ → ↑ Ca²⁺ → contraction

How does nitric oxide affect smooth muscle?

↑ MLCP → relaxation

What are the structural features of smooth muscle cells?

Spindle-shaped, no striations, dense bodies, minimal SR, caveolae (instead of T-tubules)

How is smooth muscle contraction modulated?

By neurotransmitters, hormones, chemical stimuli, stretch, and enzyme activity (MLCK/MLCP)