Smooth Muscle Physiology

Front 1

multi unit

Back 1

- each cell electrically independent
- line blood vessels, control iris

Front 2

single unit

Back 2

- cells electrically coupled by gap junctions and contract together
- line gastrointestinal tract, bladder and uterus

Front 3

thick filaments of smooth muscle

Back 3

- aligns with tails pointing toward middle of filament
- dumbell shape, bare zone in the middle
- thick and thin filaments interdigitate extensively

Front 4

Smooth muscle contraction

Back 4

- no troponin
- actin to myosin ratio 15:1
- dense bodies (like z-lines)

Front 5

Differences from skeletal muscle

Back 5

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

Front 6

maintenance heat

Back 6

- energy used by muscle when maintaining tension but not shortening
- doing no work, but cross-bridge cycling still occurs ATP is used

Front 7

E-C Coupling

Back 7

- 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

Front 8

Innervation of Smooth muscle

Back 8

- no synapses
- varicosities
- like a synaptic terminal
- transmitter containing vesicles but no corresponding post synaptic membrane

Front 9

Neurotransmitter

Back 9

1) Ach
- E or I
- muscarinic
- Ach esterase in collagen in intracell matrix
2)NE
- α or β
- diffuses away

Front 10

resting potential of smooth muscle

Back 10

-50 to -60

- multiunit cells don't carry AP

Front 11

spike potentials

Back 11

- length of 10 to 50 ms

Front 12

plateau potentials

Back 12

- 100 to 1000's of ms
- uterus, ureter, some blood vessels

Front 13

Action Potentials

Back 13

- approach Ca equilibrium potentials
- more affected by extracellular Ca than Na

Front 14

slow wave potentials

Back 14

- 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