smooth muscle excitation and contraction (midterm 1) Flashcards

1
Q

what is the difference between smooth and skeletal muscle (control-wise)

A

smooth is involuntarily controlled (i.e. intestines) and skeletal is voluntarily controlled (i.e. bicep)

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2
Q

what are smooth muscles composed of

A

small fibers (1-5 um in diameter and 20-500 um in length)

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3
Q

how much bigger are skeletal muscle fibers then smooth muscle fibers

A

30x greater in diameter and several 100x as longer

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4
Q

what causes contraction in both smooth and skeletal muscle

A

the same attractive forces between myosin and actin filaments

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5
Q

what are the outer surfaces of multi-unit smooth muscle covered by

A

thin layer of collagen and glycoprotein to help insulate separate fibers from one another

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6
Q

what are the types of smooth muscle

A

multi-unit smooth muscle and unitary smooth muscle

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7
Q

what is the main difference between unitary and multi-unit smooth muscles

A

multi-unit contract independently and unitary contract together as a single unit

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8
Q

what’s an example of multi-unit smooth muscle

A

iris muscle of the eye

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9
Q

what’s an example of unitary smooth muscle

A

uterus and blood vessels

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10
Q

how are smooth and skeletal muscles similar

A
  • contains both actin and myosin filaments that bind to create force
  • contraction process is activated by Ca++
  • ATP provides the energy for contraction
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11
Q

what are the major differences between smooth and skeletal muscle (mechanisms)

A
  • smooth muscle doesn’t contain the normal troponin complex found in skeletal muscle contraction
  • smooth muscle is irregular compared to skeletal
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12
Q

what does polar myosin filaments (such as in cross-bridges) allow for

A

contraction in opposite direction

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13
Q

what are dense bodies

A

attached to cell membrane (particularly actin) and dispersed inside the cell - they serve the same role as Z discs in skeletal muscle

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14
Q

what does binding dense bodies of adjacent cells together by intercellular protein bridges cause

A

transmit force from cell to cell

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15
Q

how much myosin is interspersed among actin

A

15x less myosin than actin

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16
Q

what do cross-bridges allow myosin to do

A

pull an actin filament in one direction while pulling another actin in the opposite direction on the other side, leading to smooth muscle cells contraction 80% their length (<30 % for skeletal)

17
Q

how long does smooth muscle contraction last for

A

hour or days maintaining force

18
Q

what is the latch mechanism

A

actin-myosin binding cycle is slow (1/10-1/300 as skeletal energy consumption), so the actin-myosin binding time is long

19
Q

how does maintaining force of smooth muscle occur

A

initially, A-M binding frequency increases => force
then decreases and time increases

20
Q

why is the max force of contraction of smooth muscle greater than skeletal

A

due to the prolonged period of attachment of myosin cross-bridges to actin filaments

21
Q

what is stress-relaxation

A

the original force of contraction may be returned within seconds after it has been elongated or shortened

22
Q

what is an example of stress-relaxation

A

bladder
bladder volume increases, tension increases
bladder stretch increases, decreased A-M overlap and tension
- can increase bladder volume with no change in tension

23
Q

what is calmodulin

A

initiates contraction by activating myosin cross-bridges

24
Q

what is skeletal muscle activated by

A

nervous system

25
what is smooth muscle activated by
nervous system, hormones, mechanical stimulation
26
what do autonomic nerve fibers do
contract smooth muscles independently and branch diffusely on top of a sheet of muscle fibers
27
what do vesicles of the autonomic nerve fiber endings contain
acetylcholine in some fibers, norepinephrine in others
28
what determines if a smooth muscle is inhibited or excited
the type of receptor or circulating hormones - if acetylcholine is excitatory norepinephine is inhibitory and vice versa
29
what is the resting membrane potential of smooth muscles
~ - 60 mV (~ 0 with action potential)
30
what has the same action potential as skeletal muscle and what is it
unitary smooth muscle - spike AP = typical - slow wave potentials = self-excitatory - plateauAP = prolonged contraction
31
how many voltage-gated Na+ channels does smooth muscle have
fewer than skeletal, but more v-gated Ca+ channels (open slow and remain open longer)
32
when does relaxation occur for smooth muscles
with low O2, high CO2, high H+, which can cause AP