Exam 2- smooth muscle Flashcards

1
Q

describe smooth muscle

A

non-striated: no z-line, so no sarcomeres (actin and myosin form loosely associated bundles with each other, instead of sarcomeres)

  • smooth muscle cells are much smaller- thinner and shorter than skeletal muscle
  • smooth muscle is circular- forms rings around hollow organs (blood vessels, airways, GI tract)
  • when smooth muscle contracts and relaxes, regulates the area of the tube it surrounds (contraction reduces diameter of the tube)
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2
Q

smooth muscle that surrounds arteries

A

thick layer of smooth muscle surrounding arteries- contracts and relaxes- changes blood flow and blood pressure

  • regulates airways that leads to lungs
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3
Q

describe smooth muscle in GI tract

A

in GI tract, have both circular and longitudinal strands of smooth muscle

  • circular contracts and squeezes/mixes the contents
  • longitudinal contracts in wave-like form and propels the contents through
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4
Q

describe the variety of contractions by smooth muscle

A
  • depends on organ its associated with and that organs function
  • smooth muscle generally maintains a more tonic contraction (a base line level of contraction that maintains muscle tone- more tonic than twitch in skeletal
  • some smooth muscle is phasically active- results in a slow, rhythmic contraction (push food through intestines)
  • more common is tonic function- maintains constant level of muscle contraction (the muscle that surrounds blood vessels and airways maintain tonic tone, controls diameter of vessels)
  • smooth muscle that surrounds sphincters is also tonic
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5
Q

tonic function of smooth muscle occurs here…

A

blood vessels, airways, sphincters

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6
Q

smooth muscle of esophagus and urinary bladder

A

mostly relaxed and only contract intermittently/sporatically (eliminate urine)

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7
Q

brief structure of smooth muscle

A

no sarcomere
- actin and myosin arranged in stair-step arrangement
- actin attaches directly to inside of cell membrane itself at a dense body, anchored by alpha actinin (dense bodies are parts of smooth muscle membrane itself)

  • when smooth muscle contracts, does not shorten linearly like skeletal muscle does –> smooth shortens by twisting and bulging (twists in spiral like fashion)
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8
Q

describe actin structure in smooth muscle

A

actin still double stranded string of beads, binding sites all along globular actins that make up actin fulaments

  • tropomyosin wraps around actin (but no troponin –> so have to activate/initiate actin and contraction in a different way)
  • small globular proteins called calponin attached to tropomyosin (unsure function)
  • caldesmon wraps around actin, caldesmon masks the actin binding sites in smooth muscles at rest
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9
Q

myosin of smooth muscle

A

stays the same

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10
Q

intermediate filaments of smooth muscle

A

non-contractile protein filaments that connect the dense bodies all throughout the membrane

  • network of ropes that rope through the membrane, when muscle contracts, the ropes tighten up and help to contract the muscle cell
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11
Q

what are the small indentations/invaginations of membrane in smooth muscle called

A

caveolae (function like T-tubule)
- underneath caveolae is SR (SR much less developed in smooth muscle)

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12
Q

do smooth muscle cells contain gap junctions?

A

may or may not, some do to communicate directly with one another

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13
Q

smooth muscle is very diff at ___ and ___ level than skeletal muscle in most cases

A

cellular
molecular

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14
Q

smooth muscle is ___, meaning that the AP that initiates contraction in smooth muscle originates at the membrane of the smooth muscle itself (generates its own AP, instead of from motor neuron)

A

myogenic

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15
Q

describe how smooth muscle generates its own Ap

A

funny sodium channel (not voltage or ligand-gated), stays open and leaky all the time- this allows sodium current to slowly diffuse through membrane and slowly and spontaneously depolarize membrane to threshold- doesn’t need any external stimulus

  • as it gets near threshold, depolarization recruits calcium channel called T-type (transient type) calcium channel
  • funny sodium channel and calcium channel depolarize membrane to threshold –> at threshold, activation of voltage-gated L-type (long lasting) calcium channel, stays open

–> as a result of L-type channel opening, inward directed calcium current –> wave of depolarization of the AP

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16
Q

what ion causes an AP in smooth muscle

A

calcium (instead of sodium)

17
Q

describe the transmembrane potential, the overshoot, and wave of repolarization

A
  • maximum transmembrane potential is -60 mV
  • wave of depolarization is a little slower and less powerful b/c influx of calcium is a little slower
  • AP depolarizes membrane to +10
  • once hit overshoot, L-type channel closes and voltage-gated potassium channels repolarize the membrane
  • wave of repolarization gets no where near -90 mV b/c funny sodium channels are still open and begin to depolarize the membrane again
    • gets to -60, potassium channels begin to close, all the other channels begin to open rhythmically and spontaneously cause another AP
18
Q

caleolae’s function in contraction

A

(short, small T-tubule like invaginations of membrane)

  • L-type calcium channels most heavily located in caveolae
  • initial inward movement of calcium called calcium spark- calcium itself activates ryanodine receptor, results in outward diffusion of calcium which floods the smooth muscle (called calcium-induced-calcium-release) –> build up of all the calcium which initiates contraction of smooth muscle
19
Q

2 types of smooth muscle: ___ and ___ unit…

A

single and multi unit

single unit- muscle cells that have gap junctions that connect each other- depolarization in one cell, influx of calcium- calcium signal directly sent to adjacent cell, so immediate contraction, keeps goin on down the line (only need to depolarize one cell, then get contraction in entire muscle)
- smooth muscle still can receive neural signals to speed/slow down (regulate muscle, instead of initiate- only one cell needs the neural signal to act on the whole muscle

multi unit- cells have to each be regulated by the nervous system to speed up/slow down

20
Q

how is myosin activated to be ready for contraction in smooth muscle?

A

calcium floods smooth muscle through calcium spark and calcium-induced-calcium-release –> Ca binds to calcium-binding protein called calmodulin –> activates enzyme called myosin light chain kinase (MLCK) –> MLCK phosphorylates the myosin head, this takes myosin from folded up configuration to normal straightened, ready to work configuration to interact with actin

21
Q

how is actin activated to be ready for contraction?

A

at rest, actin-tropomodulin-caldesmon complex (caldesmon masks actin binding sites, need to get caldesmon off)

  • can do this through calcium-calmodulin complex, which binds directly to caldesmon and pulls it off –> activates actin, actin can interact with myosin –> allows powerstroke
  • other way to pull caldesmon off is to activate a MAP kinase, that phosphorylates caldesmon –> pulls it off actin
22
Q

describe muscle relaxation in smooth muscle

A

similar to skeletal-

calcium pump ATPase pumps calcium back into SR, also calcium ATPase in muscle itself which pumps it back to interstitial fluid

  • also sodium pump: (3 Na out and 2 K in), the 3 sodium work in a sodium-calcium exchange, sodium comes in and pushes calcium back out
23
Q

the main mechanism for getting calcium out of SR to start depolarization and contraction is calcium-induced-calcium-release through ryanodine receptor), what is the 2nd mechanism?

A

ligand-gated channel which activates a G protein –> activates enzyme called phospholipase C- converts membrane phospholipids to IP3 –> IP3 interacts with IP3 receptor on membrane of SR, opens another calcium channel, which facilitates release of calcium from SR

24
Q

contraction of smooth muscle is regulated by nerves…

A

the nerves do not form classical NMJ with smooth muscle membranes, instead, the terminals just spread out and form webbed-like structure with little swellings all along the terminus (swellings contain the neurotransmitter, which is released and regulates smooth muscle contraction- speeds or slows)