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KINE2011: Human Physiology > Module 4: Lecture 5 > Flashcards

Module 4: Lecture 5 Flashcards

1
Q

the number of motor units that are recruited to contract is dependent on/

A

the amount of tension required within that muscle

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2
Q

every one of the muscle fibers that are innervated by the motor neuron, are all going to be the same?

A

fiber type
- slow twitch vs fast twitch

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3
Q

why is there a mosaic patten of motor units? (the fibers of the motor unit are interspersed across a larger area)

A

because it allows more of a smooth transfer of force across the muscle
- if they were compact and localized, you would have uneven distribution of muscle

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4
Q

true or false: different muscles can have different numbers and sizes of motor units to vary the power and dexterity of movement

A

true

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5
Q

what are we talking about when we are talking about the sizes of motor units?

A

the number of muscle fibers that are innervated by that motor neuron

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6
Q

less fibers per motor unit = ?

A

greater control of fine movements

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7
Q

more fibers per motor unit = ?

A

less control of fine movement

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8
Q

what is the notion of asynchronous recruitment of motor units?

A

motor units are activated asynchronously
- depending on the amount of force that needs to be generated, you will first recruit some motor units, and as you need to generate more and more forces, you will begin to recruit additional motor units to generate more and more force

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9
Q

what are type one muscle fibres?

A

-more slow twitch and oxidative metabolism
- much more fatigue resistant

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10
Q

what are type two muscle fibres?

A
  • larger, more powerful
  • fatigue quickly
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11
Q

which muscle fibres tend to be recruited first?

A

type 1

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12
Q

what is Henneman’s size principle?

A

describes the relationship between the size of a motor unit and its sequence of recruitment (ie, when it first begins to discharge action potentials)
- motor units are recruited according to the magnitude of their force output, from smallest to largest

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13
Q

what are the benefits of orderly recruitment of motor units?

A
  • minimizes fatigue by first activating fatigue-resistant (T1) muscle fibres (larger, more powerful units are recruited when more force is needed)
  • allows the finer control of muscle forces (weaker units allow smaller gradation of force during low-level contractions)
  • simplified the control of force (CNS is not burden by determining which motor units to activated (occurs automatically according to size of motor neuron))
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14
Q

what is whole muscle tension determined by?

A

the whole number of fibres contracting

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15
Q

what is frequency of motor unit activation?

A

tension developed by each contracting fibre
- changing the frequency of action potentials

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16
Q

by changing action potential in the muscle, what are we changing in the muscle?

A

the amount of calcium in the muscle which is going to adjust how much force the muscle fibres are generating

17
Q

what does frequency of stimulation influence?

A

the extent to which tension can be developed

18
Q

are muscles characteristics critical for the actual force generated?

A

yes

19
Q

one action potential leads to?

A

one twitch
- 1:1 ratio relationship between our motor unit turning on and out muscle fiber turning on

20
Q

what would happen if you were to regenerate a second action potential within the muscles already at full rest? why?

A

you are going to generate the same amount of force
- because the frequency was too slow to summit any of the calcium

21
Q

what results in a twitch summation in the muscles?

A

if a muscle fibre is restimulated before it has completely relaxed, the second twitch is added on to the first twitch, resulting in summation
- the cytosolic calcium will increase to greater than before

  • by giving repeated action potentials in close succession, BEFORE your SERCA pump can sequester all of the calcium within the muscle, you will be allowing, through the SERCA pump, the calcium to build upon one another
  • SERCA pump cannot remove calcium fast enough so it just builds on itself
22
Q

is the amount of calcium released from a single twitch sufficient to fully activate all of your thin filaments?

A

no
- only a few of your cross bridges will form

  • however, if you give the muscle more action potentials and more calcium, it will expose more binding sites, allowing more cross bridges to form
23
Q

what is the SERCA pumps role in twitch summation?

A

the SERCA pump is what removes calcium from the cytosol. SERCA cannot remove calcium as fast as an action potential can be generated so the calcium from the previous action potential is just being built on faster than it is being removed

24
Q

in what process is specifically twitch summation going to happen?

A

when you get the initial force being generated with a little bit of relaxation prior to the second twitch being generated

25
Q

what is the name for when we achieve action potentials so frequently that there is no time for the muscle to relax? (a type of twitch summation)

A

Tetanus

26
Q

are all your thin filaments fully activated (fully exposed) when your muscles have undergone tetanus?

A

yes
- all of your cross bridges are being formed, and that motor unit is generating the maximum amount of force it can generate

27
Q

how can you dictate the number of cross bridges that can form in the muscle?

A

by altering the amount of calcium in the muscle

28
Q

what is the difference between twitch summation and temporal summation of EPSP at the postsynaptic neuron?

A

the twitch summation is building tension

29
Q

why is twitch summation possible?

A

because the duration of the action potential (1-2msec) is shorter than the twitch duration/duration of the mechanical activity (100msec)

29
Q

where does the name of the twitch summation tetanus come from?

A

the bacterial infection that occurs in which it is a neurological condition that results in full contracture
- you get this idea of lockjaw - clenching of the jaw

30
Q

is it possible to have multiple action potentials fired within a given twitch duration?

A

yes

31
Q

what is the upper limit to the number of action potentials your motor neurons can generate?

A
  • because of the refractory period in the motor neuron
  • fibre type dependent (not important)
32
Q

what are the two key mechanisms what the CNS can control muscle force?

A
  1. Motor unit recruitment (Hennemans size principle)
  2. Motor unit activation (frequency of action potentials) rate (fusion of muscle twitches)

KINE2011: Human Physiology (29 decks)

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