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PSIO 259 > Muscle Physiology > Flashcards

Muscle Physiology Flashcards

1
Q

What are the 4 mechanics of skeletal muscle contraction?

A
  • twitch
  • force
  • length
  • velocity
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2
Q

What is a twitch?

A

contraction produced in a muscle fibre in response to a single AP

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3
Q

What is the all-or-none principle?

A
  • the principle that the strength by which a nerve or muscle fiber responds to a stimulus is independent of the strength of the stimulus
  • If that stimulus exceeds the threshold potential, the nerve or muscle fiber will give a complete response; otherwise, there is no response
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4
Q

A twitch can happen for a ______, _______ or ______.

A
  • muscle fibre
  • motor unit
  • whole muscle level
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5
Q

What are the 3 phases of a twitch?

A
  • latent period
  • contraction phase
  • relaxation phase
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6
Q

What happens during the latent period?

A
  • AP in cell –> onset of contraction (2-3 ms)

- excitation-contraction coupling

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7
Q

What happens during the contraction phase?

A
  • 10-100 msec, tension development peaks

- crossbridge cycling

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8
Q

What happens during the relaxation phase?

A
  • peak - end of contraction (longest)

- Ca2+ reuptake, crossbridges decrease

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9
Q

What is the cause of summation and tetanus?

A
  • tension depends on Ca2+ bound to troponin
  • high frequencies = release exceeds reuptake
  • saturation
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10
Q

In summation, action potential lasts ___ msec.

A

2 msec.

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11
Q

In summation, how long does contraction last?

A

10-200 msec.

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12
Q

In summation, contractions can ____ and _____.

A

overlap and sum

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13
Q

In summation, high frequencies = ______ exceeds _____.

A

release exceeds reuptake

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14
Q

In summation, Ca2+ increases in cytosol –>

A

saturation

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15
Q

Describe saturation in summation.

A
  • all troponin has Ca2+ bound to it
  • cross bridge cycling maxed out
  • maximum tetanic contraction
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16
Q

What are the 2 types of twitches?

A
  • isometric

- isotonic

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17
Q

Contractile elements =

A

sacromeres

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18
Q

Series elastic elements =

A

connective tissue, tendons

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19
Q

Force exerted by contracting muscle =

A

tension

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20
Q

Force opposing contraction (ie. weight to be moved) =

A

load

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21
Q

In isometric twitch contraction, the length is _______.

A

constant

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22
Q

In isometric twitch contraction, _____ _____ contract, generating ______.

A
  • contractile elements

- tension

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23
Q

Isometric twitch contraction occurs when:

A

load > tension

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24
Q

What happens when load > tension in isometric twitch contraction?

A
  • stretches series of elastic elements

- muscle does not shorten, load not lifted

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25
Q

Isotonic twitch contraction is _____ tension.

A

constant

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26
Q

Isotonic twitch contraction occurs when:

A

tension > load

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27
Q

What happens when tension > load in isotonic twitch contraction?

A

load is lifted as muscle shortens

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28
Q

In normal muscle activity, some purely _______ contractions occur.

A
  • isometric

- postural

29
Q

In normal muscle activity, purely ______ contractions are rare.

A

isotonic

30
Q

In normal muscle activity, load generally _____ constant.

A

not

31
Q

In normal muscle activity, load changes as ____ ____ changes.

A

limb position

32
Q

Graded muscle contractions depend on 2 factors:

A
  • tension produced by each fibre

- number of fibres contracting

33
Q

What consists of tension produced by each fibre?

A
  • number of active cross bridges that bind to actin

- more crossbridges that bind –> more force

34
Q

Force generating capacity =

A

inherent ability of muscle to generate force

35
Q

Force generating capacity depends on:

A
  • the number of crossbridges in each sarcomere

- the genetic arrangement of sarcomeres

36
Q

More crossbridges/sarcomere =

A

more force

37
Q

More sarcomeres in parallel =

A

more force

38
Q

Number of thick and thin filaments/area =

A

constant

39
Q

Is fibre diameter constant?

A

no, it varies

40
Q

Large diameter =

A

more filaments = more force

41
Q

Length of fibre at the _____ of contraction affects:

A
  • onset

- force generated

42
Q

What is optimal length?

A
  • resting length of muscle at which the fibre can develop the greatest amount of tension
  • due to maximum overlap of thick filament crossbridges and thin filaments
43
Q

Most muscles are at _____ length.

A

optimal

44
Q

If a muscle is at greater than optimum length …

A

decrease crossbridge overlap

45
Q

If muscle is at less than optimum length…

A
  • thin filaments overlap each other

- Z lines contact thick filaments

46
Q

More fibres contracting =

A

greater tension

47
Q

Recruitment:

A

stimulating more muscle fibres to contract

48
Q

Recruitment occurs at level of…

A

motor unit (MU)

49
Q

Activation of the motor neuron activates:

A

all muscle fibres in the motor unit

50
Q

Increases in tension occur in steps proportional to…

A

the size of the motor unit

51
Q

What motor units are used in muscles for delicate movements?

A

small motor units

52
Q

What motor units are used in muscles for strength?

A

large motor units

53
Q

Number of motor units varies in _____ ______.

A

different muscles

54
Q

Small fibre diameter in motor units are used for what movements?

A

weaker

55
Q

Large fibre diameter in motor units are used for what movements?

A

stronger

56
Q

Small motor units =

A
  • small fibres
  • small motor neuron cell bodies
  • small axon diameters
57
Q

Large motor units =

A
  • large fibres
  • large motor neuron cell bodies
  • large axon diameters
58
Q

The size principle:

A

order of muscle unit recruitment related to the size of muscle units

59
Q

The size principle says ____ excited first, _____ last.

A
  • small

- large

60
Q

Why are large motor units excited last?

A
  • difficult to depolarize to threshold

- greater synaptic input

61
Q

When muscle contracts isotonically, _____ period of shortening _____ with increasing load.

A
  • latent

- increases

62
Q

When muscle contracts isotonically, duration of shortening with _______ load.

A
  • decreases

- increasing

63
Q

When muscle contracts isotonically, velocity of shortening ______ with _____ load.

A
  • decreases

- increasing

64
Q

When muscle contracts isotonically, the rate of change of the distance is _____.

A

shortened

65
Q

Velocity of shortening reaches 0 when…

A

load > or equal to max tension

66
Q

Velocity of shortening is greatest when…

A

no load on muscle

67
Q

As the angle of pennation increases, there is…

A

greater force development (not power)

68
Q

Greater mechanical advantage with a _____ angle of insertion (_____ to force arm) = _____ force development, but a _____ in the rate at which that force is developed (power)

A
  • greater
  • closer
  • greater
  • reduction
69
Q

Potassium is thought to contribute to fatigue due to…

A
  • increased efflux out of the cell into the tissue space (Na+/K+ pump activity)
  • impairs membrane excitability

PSIO 259 (22 decks)

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