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2017 physiology > Exam 3 (chapter 12 part 2) > Flashcards

Exam 3 (chapter 12 part 2) Flashcards

1
Q

sequence of events whereby an action potential in the sarcolemma causes contraction

  • dependent of neural input from the motor neuron
  • requires Ca++ release from the sarcoplasmic reticulum
A

excitation contraction coupling (skeletal muscle)

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2
Q

what is excitation contraction coupling in skeletal muscle dependent on and what does it require?

A

neural input (from motor neuron) Ca++ release (from SR)

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3
Q

SR =

A

sarcoplasmic reticulum

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4
Q

point of contact between a motor neuron and a skeletal muscle cell

A

neuromuscular junction

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5
Q
  • each motor neuron innervates ___________ muscle cells

- each muscle fiber receives input from ___________ motor neuron

A

several, one

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6
Q

what neurotransmitter is released at the neuromuscular junction?

A

acetylcholine

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7
Q

The region of a sarcolemma adjacent to the axon terminals at a neuromuscular junction is called the _________ ________ __________.

  • high density of acetylcholine receptors
  • highly folded
A

motor end plate

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8
Q

does the motor end plate have high or low surface area? why?

A

high (folded), more acetylcholine receptors

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9
Q

Synaptic potential at Neuromuscular junction

A

end plate potential

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10
Q

T/F: motor neuron action potentials always create muscle cell action potentials

A

True

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11
Q

what happens if there is no Ca++?

A

troponin holds tropomyosin over myosin binding sites on actin (no cross bridges form, muscle relaxed)

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12
Q

what are the 6 steps of excitation-contraction coupling in skeletal muscle?

A

action potential in sarcolemma, action potential down T tubules, Ca++ channels open on SR, Ca++ increases in cytosol, Ca++ binds to troponin shifting tropomyosin, crossbridge cycling occurs

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13
Q

action potential in sarcolemma, action potential down T tubules, Ca++ channels open on SR, Ca++ increases in cytosol, Ca++ binds to troponin shifting tropomyosin, crossbridge cycling occurs

A

the 6 steps of excitation-contraction coupling in skeletal muscle

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14
Q

SR Ca++ channels are _________ gated and coupled to _____ ____________

A

voltage, T tubules

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15
Q

how is a contraction terminated in skeletal muscle (3 steps)?

A

Ca++ leaves troponin, tropomyosin covers myosin binding sites on actin, Ca++ removed from cytoplasm

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16
Q

how is Ca++ removed from the cytoplasm?

A

Ca++ ATPase actively transports to the SR

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17
Q

contraction produced in a muscle fiber in response to a single action potential

  • all or nothing event for a muscle fiber at rest
  • can be defined for a muscle fiber, motor unit, or whole muscle
A

Twitch

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18
Q

what are the 3 phases of the twitch?

A

latent period, contraction phase, relaxation phase

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19
Q

time from action potential in muscle cell to onset of contraction

  • only a few milliseconds
  • excitation-contraction coupling
A

latent period

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20
Q

time that tension is increasing

  • 10-100 msec
  • crossbridge cycling
A

contraction phase

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21
Q

what occurs during the latent period of a twitch?

A

excitation contraction coupling

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22
Q

what occurs during the contraction phase of a twitch?

A

crossbridge cycle

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23
Q

time that tension is decreasing back to zero

  • longer than contraction phase
  • Ca++ reuptake
A

relaxation phase

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24
Q

what occurs during the relaxation phase of a twitch?

A

Ca++ reuptake

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25
Q

contractile elements

- repeating units of myosin and actin (myofibrils)

A

sarcomeres

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26
Q

series of elastic elements

A

connective tissue, tendons

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27
Q

force exerted by contracting muscle

A

tension

28
Q

force opposing contraction

Ex: weight to be moved

A

load

29
Q

length of muscle is constant

  • contractile elements contract, generating tension
  • LOAD > TENSION
  • stretches series of elastic elements
  • does NOT shorten (load not lifted)
A

isometric twitch contraction

30
Q

LOAD > TENSION

A

isometric twitch contraction

31
Q

tension of muscle is constant

  • TENSION > LOAD
  • load is lifted as muscle shortens
A

isotonic twitch contraction

32
Q

TENSION > LOAD

A

isotonic twitch contraction

33
Q

what is an example of isometric twitch contraction?

A

Trying to lift a building, pushing a wall

34
Q

what is an example of isotonic twitch contraction?

A

lifting a 10 pound weight

35
Q

purely isotonic contractions are __________

A

rare

36
Q

why are purely isotonic contractions rare?

A

load changes as limb position changes (isometric continues until tension exceeds load)

37
Q

what 2 factors do graded muscle contractions depend on?

A

tension produced by each fiber (number of cross bridges that bind to actin), number of fibers contracting

38
Q

more cross bridges that bind = _____________ force

A

more

39
Q

T/F: tension remains constant as muscle shortened (isotonic)

A

True

40
Q

increases in _____ of action potentials increase tension in two ways

  • treppe
  • summation
A

frequency

41
Q

stepwise increase in force when the frequency of stimulation is increased

  • one motor unit
  • tension goes back to 0 before increasing again
A

treppe

42
Q

contractions overlapping and summing due to repeated action potentials

  • one muscle fiber
  • not all Ca++ removed, so tension does not go back to 0
A

contraction summation (recruitment)

43
Q

A smooth sustained muscle contraction, such as occurs in skeletal muscle when stimulation frequency is high enough

A

tetanus

44
Q

Latent period is _____ the twitch and has __ slope

A

before, no slope

45
Q

The contraction phase is at the _____ of the twitch, and has a ____ slope

A

beginning

positive

46
Q

The relaxation phase is ____ of the twitch and has a _____ slope

A

the second half

negative

47
Q

one nerve stimulus arrives at a muscle fiber so soon that the fiber has only partially relaxed from the previous twitch

A

incomplete tetanus

48
Q

When a muscle is stimulated repeatedly at a high rate, the amount of tension gradually increases to a sustained maximum tension.

A

complete tetanus

49
Q

____ _____ ______: inherent ability of a muscle to generate force
- depends on the number of cross bridges in each sarcomere and the geometric arrangement of sarcomere

A

force generating capacity

50
Q

more crossbridges/sarcomere = __________ force

A

more

51
Q

more sarcomeres in parallel (not in series) = ___________ force

A

more

52
Q

number of thick and thin filaments per area is ___________ even though fiber diameter varies

A

constant

53
Q

larger diameter leads to more filaments which leads to ___________ force

A

more

54
Q

lower diameter leads to less filaments which leads to _____ force

A

less

55
Q

length of a fiber at the onset of a contraction affects ___________ generated

A

force

56
Q

resting length of muscle at which the fiber can develop the greatest amount of tension
- due to maximum overlap of thick filament cross bridges and thin filaments

A

optimal length (for force generation)

57
Q

when are most muscles at optimal length?

A

normal body positions

58
Q

what is optimal fiber length due to?

A

maximum overlap of thick filament cross bridges and thin filaments

59
Q

does muscle growth increase the number of cells? if not, what happens?

A

no, they grow larger (increase diameter (hypertrophy)

60
Q

______: Increase in muscle size

A

Hypertrophy

61
Q

what is the work of a muscle cell?

A

generate force

62
Q

length that decreases cross bridge overlap

A

longer than normal body position (longer than optimal length)

63
Q

thin filaments overlap each other

A

less than optimal length

64
Q

amount of tension developed depends on the amount of _______ bound to troponin

A

Ca2+

65
Q

at high frequencies, release exceeds _____________

- Ca++ increase in cytosol

A

reuptake

66
Q
  • all troponin has Ca++ bound to it
  • Crossbridge cycling maxed out
  • Maximum tetanic contraction
A

saturation

2017 physiology (20 decks)

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