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BMS 752 (Medical Physiology) > Muscle > Flashcards

Muscle Flashcards

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USMLE® Step 1 flashcards
1
Q

what causes skeletal muscle excitation

A

neuromuscular somatic synaptic transmission

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2
Q

T/F cardiac muscle doesn’t require an outside stimulus

A

true, pacemaker cells will depolarize on their own, gap junctions allow for the AP to travel, and the ANS modulates the response

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3
Q

what causes smooth muscle excitation

A

either electric coupling or autonomic stimulation

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4
Q

what position is the myosin cross bridge in relation to actin at rest

A

at a 90 degree angle and not touching

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5
Q

what happens to actin and myosin during activation

A

myosin binds to actin

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6
Q

what happens when myosin binds to actin

A

ADP and P are released, allowing the myosin head to move from a 90 to 45 deg angle to actin

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7
Q

how does the myosin head uncouple from actin? how does it return to its resting state

A

ATP binds with myosin to release the actin filament, then ATP is hydrolyzed to return myosin to resting state

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8
Q

describe the entire process of cross bridge cycling

A
  1. myosin is at rest at right angles to actin, bound to ADP and P
  2. myosin binds to actin at binding sites, releasing ADP and P
  3. unbound myosin heads change confirmation and shift to a 45 in relation to actin
  4. ATP binds with myosin to uncouple it from actin
  5. ATP is hydrolyzed into ADP and P to return the head to a 90 deg rest position
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9
Q

what is the normal concentraion of calcium in the cytoplasm?

where is the majority of calcium stored

A

0

in the sacroplasmic reticulum

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10
Q

what is the function of Ca in excitation-contraction coupling

A

it links excitation with coupling by binding to troponin to move tropomyosin off myosin binding sites, allowing for activation

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11
Q

what is a T tubule? what is the function?

A

extensions of the cell membrane from one muscle cell to another

they allow for rapid activation of L type calcium channels and propogate depolarization to surrounding cells

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12
Q

what is the “triad” of cell structures that participate in propogation of action potentials between muscle cells

A

the sarcoplasmic reticulum of two cells sandwiching a T tuble

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13
Q

what is the difference in excitation-contraction coupling between skeletal and cardiac muscle cells

A

muscle cells use mechanical coupling between calcium release channels an on the SR and L type calcium channels on the T tubule

in cardiac cells L type calcium channels on the T tubule secrete calcium, which activates calcium release channels

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14
Q

describe the process of calcium release through mechanical coupling in skeletal muscle

A
  1. skeletal muscle is stimulated by AcH release from a neuron
  2. skeletal muscle depolarizes, opening L type calcium gated channels on the T tubule
  3. L type channels physically bind to calcium release channels on the SR
  4. calcium release channels release calcium into the T tubule to bind with troponin allow myosin cross bridges to form
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15
Q

how is the process of calcium release into t tubules different for cardiac muscle?

what is the alternative?

A

there is no mechanical binding

calcium for L type calcium channels binds to the calcium release channels, stimulating ion current

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16
Q

how is calcium removed from the cytoplasm?

A

Na-Ca pump and Ca pump remove calcium from the cell

Ca sequestering pump pumps Ca into the SR where it bound to calreticulin and calsequestrin

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17
Q

what happens to muscle cell when calcium is removed from the cytoplasm

A

with no calcium to bind troponin, tropomyosin will cover the cross bridge sides and block myosin attachments

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18
Q

isometric contraction

A

a contraction with myosin-actin cross bridge cycling, sarcomere shortening, but no movement

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19
Q

isotonic contraction

A

a muscle contraction where there is myosin actin cross bridging and sacromere shortening that results in shortening of the muscle fibers

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20
Q

what are the three phases of an isometric twitch

A

latent, contraction, relaxation

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21
Q

what is happening during the latent phase of an isometric twitch

A

there has been a stimulus received by the muscle but no calcium release until the end of the latent phase

22
Q

what is happening during the contraction phase of an isometric twtich

A

calcium that has been release by the SR binds to tropomyosin, allowing for cross bridge cycling

23
Q

what is happening during the relaxation phase of an isometric twitch

A

calcium is being pumped out of the cytoplasm to slow down cross bridge cycling

24
Q

summation

A

when successive depolarization events converge on a muscle cell, causing the release of more calcium and a stronger contraction

25
Q

unfused tetanus

A

when summation produces an average constant tension between contractions

26
Q

fused tetanus

A

when summation by repeated stimuli causes a max tension curve with no individual contractions

27
Q

elasticity

A

the force a subtance produces that resists change in shape

28
Q

compliance

A

the abilty for an object to change shape

29
Q

relate elasticity and compliance to a real world object

A

a rubber band is compliant because it will stretch, and elastic because it will produce force to counteract stretching force and return it to its original shape

30
Q

contractile component of muscle

A

cellular components that generate force (sarcomeres)

31
Q

series elastic component

A

the non-contractile parts of a cell and the tendons which produce force against stretch

32
Q

what regulates the maximum amount of force a sarcomere can generate

A

the amount of contact between actin and myosin

33
Q

described the amount of force produced by these situations

  1. actin myosin overlapping
  2. actin myosin in contact with no H band
  3. actin myosin in contact with an H band
  4. actin myosin with some heads exposed
  5. no contact of the myosin heads
A
  1. less force because some of the cross bridge sites are covered by the adjecent actin filament
  2. maximum number of cross bridges = max force
  3. max force because there are no exposed myosin heads
  4. less force because of fewer binding sites are accessible
  5. no force because there are no binding sites accessible
34
Q

what happens to active force as length increases? passive force?

A

active force decreases, passive force increases

35
Q

what three factors influence force generated by individual muscle fibers

A
  1. frequency of stimulation
  2. fiber diameter
  3. changes in fiber length
36
Q

how does stimulation frequency effect contraction strength

A

more frequent stimulus can result in summation of contractions

37
Q

how does fiber diameter effect force generation?

A

a larger fiber has a larger length constant and will conduct an AP further, allowing for the recruitment of other parallel fibers

38
Q

how does changing fiber length effect contraction strength

A

increasing the fiber lengh will stretch the sarcomeres, which can allow for more or less contract between the sarcomeres depending on the start position

39
Q

motor unit

A

a neuron and all the muscle fiber it innervates

40
Q

recruitment

A

the stimulation of multiple muscle fibers through a stronger stimulus

41
Q

threshold

A

the lowest stimulus that will produce a contraction

42
Q

maximal stimulus

A

the lowest stimulus that will produce maximal force production

43
Q

if motor unit 1 requires a 5 V stimulus, unit 2 a 10, and unit 3 a 15 V stimulus, how much will it take to stimulate all the motor units

A

15V

44
Q

T/F graded stimulus can activate individual fibers of a motor unit

A

false, motor units are all or none

45
Q

what are the three periods of an isotonic twitch

A

latent, plateau, and relaxiation

46
Q

what is happening in the latent phase of an isotonic contraction

A

muscle is developing tension without moving

47
Q

what is happening in the plateau phase of an isotonic contraction

A

there is no more tension being produced because the load is moving by shortening muscle fibers

48
Q

what is happening in the relaxation phase of an isotonic contraction

A

tension declines to zero

49
Q

what would happen if there were no plateau in an isometric contraction

A

there would be no shortening of sarcomeres greater than the elasticity of the tendons, so no movement would take place (isometric)

50
Q

describe the load-velocity curve

A

higher loads produce more force but less velocity, therefore less power

loads that are too low produce high speed but don’t generate much force, there for less power

51
Q

around what percent of maximum is power the highest

A

35%

BMS 752 (Medical Physiology) (13 decks)

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