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First Semester: Physiology 1 > Lecture 11: Muscle 3, 4, 5 > Flashcards

Lecture 11: Muscle 3, 4, 5 Flashcards

1
Q

Muscle twitch

A

a single action potential in a muscle fiber causes a brief, weak contraction called a twitch

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2
Q

Why does a twitch normally not take place in the body

A

It is too short and too weak to be useful

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3
Q

Whole muscles

A

Muscle fibers are arranged into these where they can function cooperatively to produce contractions of variable grades of strength, stronger than a twitch

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4
Q

Two primary factors can be adjusted to accomplish gradation of whole-muscle tension

A
  1. The number of muscle fibers contracting within a muscle

2. The tension developed by each contracting fiber

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5
Q

The greater the number of fibers contracting,

A

the greater the total muscle tension

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6
Q

Larger muscles consisting of more muscle fibers are capable of

A

generating more tension than the smaller muscles with fewer fibers

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7
Q

Each whole muscle is innervated by

A

a number of different motor neurons

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8
Q

When a motor neuron enters a muscle,

A

it branches with each axon terminal supplying a single muscle fiber

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9
Q

One motor neuron innervates a number of muscle fibers, but

A

each muscle fiber is supplied by only one motor neuron

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10
Q

When a motor neuron is activated, all of the muscle fibers it supplies are

A

stimulated to contract

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11
Q

Motor unit

A

One motor neuron plus all of the muscle fibers it innervates

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12
Q

Each muscle consists of a number of intermingled

A

motor units

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13
Q

Activation of only one or a few motor units lead to

A

A weak contraction of muscle

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14
Q

Motor unit recruitment

A

more and more motor units are recruited (stimulated) to contract

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15
Q

How much stronger the contraction will be with recruitment depends on

A

the size of the motor unit (the number of muscle fibers controlled by a single motor neuron)

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16
Q

The number of muscle fibers per motor unit and number of motor units per muscle depends on

A

the specific function of the muscle

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17
Q

For muscles that produce precise, delicate movements (ex. the eye), a single motor unit may contain

A

as few as 12 muscle fibers

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18
Q

Small motor units allow

A

a fine degree of control over muscle tension

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19
Q

For muscles that are designed for powerful, coarsely controlled movement, a single motor unit may contain

A

1000 or more muscle fibers

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20
Q

More powerful contractions occur at the expense of

A

precisely controlled movements

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21
Q

Asynchronous recruitment of motor units

A

Delays or prevents fatigue during sustained contraction involving only a portion of the motor units of the muscles

Important for supporting weight of body against force of gravity

22
Q

Asynchronous recruitment of motor units is possible for ________ contractions but not for _______ contraction

A

submaximal

maximal

23
Q

The type of muscle fiber recruited varies with

A

the type of tension required of the whole muscle

24
Q

Muscles consist of a mixture of fiber types that differ ______, with some

A

metabolically

being more resistant to fatigue than others

25
Q

During endurance activities

A
  • Motor units most resistant to fatigue are recruited first

- The last fibers to be recruited when there is further demand for increases in tension are those that fatigue rapidly

26
Q

Three factors that influence the extent to which tension can be developed

A
  • Frequency of stimulation
  • Extent of fatigue
  • Length of the fiber at the onset of contraction
27
Q

A single stimulation produces

A

a single twitch

28
Q

All normal activities involve

A

sustained muscle contractions

29
Q

Although an action potential triggers contraction of a muscle fiber, the action potential and its refractory period

A

are completed long before the contraction and relaxation phases are completed

30
Q

Contractile mechanism in a muscle fiber exhibits no

A

refractory period

31
Q

_____ of a muscle is not required before a second action potential can stimulate a second contraction

A

relaxation

32
Q

Frequency of action potentials in a skeletal muscle increases

A

frequency of contraction

33
Q

If a muscle fiber is restimulated after it has completely relaxed, the second twitch is

A

the same magnitude as the first twitch

34
Q

If a muscle fiber is completely stimulated before it has completely relaxed, the second twitch

A

is added to the first which results in Wave (Twitch) Summation

35
Q

There is continued stimulation of a muscle, never allowing it to relax completely and tension

A

rises to a peak

36
Q

Incomplete tension

A

the state of a muscle producing peak tension during rapid cycles of contraction and relaxation

37
Q

Tetanus

A

Muscle fiber is stimulated so rapidly that it does not have a chance to relax at all between stimuli.

A smooth sustained contraction of maximal strength

38
Q

Mechanism of Tetanus

A
  1. First action potential leads to Ca release from SR which leads to a contraction
  2. Relaxation begin as Ca is pumped back into SR
  3. If next action potential occurs before relaxation is complete then:
    - Not enough time for all Ca to re-eter SR. Ca levels around the myofibrils remains elevated
    - The magnitude of cross-bridge cycling and tension development increase correspondingly
39
Q

Tetanus
As frequency of action potentials increases, the duration of elevated _______ ____ concentration increases, as well as ____ ______ until

A

cystolic Ca
contractile activity
a maximum contraction is reached

40
Q

Virtually all normal muscular contractions involve complete

A

tetanus of the participating muscle fibers

41
Q

Tetanus disease

A
  • caused by Clostridium tetani
  • bacteria release Tetanus toxin which prevents release of GABA from inhibitory presynaptic vesicles from the terminals of the neurons that supply skeletal muscles that result in uncontrolled spasm
42
Q

Length-tension relationship

A

In a muscle fiber, the amount of tension generated during a contraction depends on the number of cross-bridge interactions that occur in all of the sarcomeres along the myofibrils

43
Q

The number of cross bridge interactions is determined by

A

the degree of overlap between thick and thin filaments

44
Q

When the muscle is stimulated to contract, what myosin heads can bind to active sites and produce tension

A

Those within the zone of overlap

45
Q

Tension produced by the intact muscle fiber can be related to the structure of the

A

individual sarcomere

46
Q

Length A

A
  • Optimal range of sarcomere length
  • Maximum number of cross bridges formed
  • Tension produced is highest
  • Muscles of the body are positioned that their relaxed length is approx. their optimal length, thus are capable of achieving near maximal tetanic contraction when stimulated
47
Q

Length B

A
  • Increase in sarcomere length
  • Reduced overlap of potential cross-bridge overlap
  • Reduced tension developed
48
Q

Length C

A
  • Zone of overlap disappears
  • Thick and thin filaments cannot interact
  • As a result, muscle fiber cannot actively produce any tension and a contraction cannot occur
49
Q

Length D

A
  • Sarcomeres are as short as they can be
  • Thick and thin filaments are jammed against the Z-lines
  • Cross-bridge can occur, but the myosin heads cannot pivot
  • Less tension is produced
50
Q

For every muscle there is an optimum length at which

A

maximal force can be achieved

51
Q

Muscle fibers can contract forcefully when stimulated over

A

a relatively narrow range of resting length

First Semester: Physiology 1 (34 decks)

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