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14 Cards in this Set

  • Front
  • Back
multi unit
- each cell electrically independent
- line blood vessels, control iris
single unit
- cells electrically coupled by gap junctions and contract together
- line gastrointestinal tract, bladder and uterus
thick filaments of smooth muscle
- aligns with tails pointing toward middle of filament
- dumbell shape, bare zone in the middle
- thick and thin filaments interdigitate extensively
Smooth muscle contraction
- no troponin
- actin to myosin ratio 15:1
- dense bodies (like z-lines)
Differences from skeletal muscle
1) rate of cycling of cross bridges is 10-100 times slower than in skeletal muscle (prolonged period of attachement low maintenance heat)
2) slow onset of contraction and relaxation (stimulus leads to peak in .5s, and decays over 3s)
3) exerts greater force per area (able to shorten to 1/3 of rest length compared to 2/3 of skeletal
maintenance heat
- energy used by muscle when maintaining tension but not shortening
- doing no work, but cross-bridge cycling still occurs ATP is used
E-C Coupling
- initiated by Ca
- Extracellular Ca entering in via L-type or CaV1 channels (DHP)
- takes longer for Ca to enter
- calmodulin binds to 4 Ca, like troponin
- calmodulin --> myosin kinase --> P regulatory light chain in myosin head --> cycling
- myosin phosphatase de P
Innervation of Smooth muscle
- no synapses
- varicosities
- like a synaptic terminal
- transmitter containing vesicles but no corresponding post synaptic membrane
1) Ach
- E or I
- muscarinic
- Ach esterase in collagen in intracell matrix
- α or β
- diffuses away
resting potential of smooth muscle
-50 to -60

- multiunit cells don't carry AP
spike potentials
- length of 10 to 50 ms
plateau potentials
- 100 to 1000's of ms
- uterus, ureter, some blood vessels
Action Potentials
- approach Ca equilibrium potentials
- more affected by extracellular Ca than Na
slow wave potentials
- long periods of depolarization that aren't AP
- but at peak when depol is greatest can fire an AP or a short train of AP
- appear spontaneously
- regulated by:
1) stretching
2) hormones ↑ Ca influx