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BIOE340 > smooth muscle excitation and contraction (midterm 1) > Flashcards

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
Q

what is smooth muscle activated by

A

nervous system, hormones, mechanical stimulation

26
Q

what do autonomic nerve fibers do

A

contract smooth muscles independently and branch diffusely on top of a sheet of muscle fibers

27
Q

what do vesicles of the autonomic nerve fiber endings contain

A

acetylcholine in some fibers, norepinephrine in others

28
Q

what determines if a smooth muscle is inhibited or excited

A

the type of receptor or circulating hormones - if acetylcholine is excitatory norepinephine is inhibitory and vice versa

29
Q

what is the resting membrane potential of smooth muscles

A

~ - 60 mV (~ 0 with action potential)

30
Q

what has the same action potential as skeletal muscle and what is it

A

unitary smooth muscle
- spike AP = typical
- slow wave potentials = self-excitatory
- plateauAP = prolonged contraction

31
Q

how many voltage-gated Na+ channels does smooth muscle have

A

fewer than skeletal, but more v-gated Ca+ channels (open slow and remain open longer)

32
Q

when does relaxation occur for smooth muscles

A

with low O2, high CO2, high H+, which can cause AP

BIOE340 (18 decks)

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