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sports sciencee > Motor unit > Flashcards

Motor unit Flashcards

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1
Q

what is a motor unit composed of

A

Motor unit (MU) is
composed of alpha motor
neuron (alpha MN), axon
and muscle fibres

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2
Q

how many muscle fibres does alpha MN innervate

A

<3000 muscle fibres

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3
Q

where is the alpha MN located

A

spinal cord

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4
Q

what is a motor neuron pool

A

group of alpha MNs that
innervates a muscle

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5
Q

what nerves does the axon of a alpha MN reach

A

peripheral nerves

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6
Q

what is the conduction velcity of APs

A

<120 m/s

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7
Q

where do alpha MN receive APs ?

A

from dendrites

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8
Q

what does EMG stand for

A

Electromyography

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9
Q

how does the differential EMG measure the difference in electrical potential

A

Difference in electrical
potential is measured
between:
* 1) Muscle electrode 1
and reference electrode
(m1+n)
* 2) Muscle electrode 2
and reference electrode
(m2+n)

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10
Q

what increases with the EMG signal

A

contraction force

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11
Q

how to increase contraction force

A

increasing number of motor units

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12
Q

what does the EMG consist of

A

1) muscle activity (m)
2) electric noise (n)

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13
Q

what is the needle EMG used for

A

to record action
potentials of separate
motor units (MUs)

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14
Q

describe when the shape of Motor units APs is abnormal

A

abnormalwhen muscles are denervated (nerve injury )

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15
Q

describe the low recruitment threshold in motor units

A

Low threshold MUs need low effort (weak neural drive) to be activated

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16
Q

describe the high recruitment threshold in motor units

A

An increase in effort leads to higher frequency of action potential in recruited
MUs, followed by recruitment of higher threshold MUs

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17
Q

MU recruitment: Heneman’s size principle?

A

MUs are recruited according to their sizes in the following order
neural drive increases
low: S type
medium: S, FR types
high: S, FFR, FF types

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18
Q

what are the 3 classifications of Motor units

A

S type
FR type
FF type

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19
Q

what is a key characteristics of the S type

A

(slow, fatigue, resistant, small)
Easily activated even by weak neural inputs

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20
Q

what is a key characteristics of the FR type

A

fatigue resistant, fast, medium size
Require stronger neural inputs for activation than S type

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21
Q

what is a key characteristics of the FF type

A
  • fast, fatigable, large size
  • Recruited only by very strong neural inputs
22
Q

what MU does waking and jumping require

A

Waking: type S (slow) MUs
Jumping: type II (fast)
motor units

23
Q

which muscle fibres is needed during light exercise

A

TYPE i

24
Q

which muscle fibres is needed during medium exercise

A

Type I + type IIA (FR)

25
Q

which muscle fibres is needed during high exercise

A

Type I + Type IIA + Type
IIX (FF)

26
Q

which type of fibre is always used in exercise

A

Type I fibres are always
recruited during exercise

27
Q

describe the mechanisms behind increasing force with MU recruitment

A

A number of activated
MUs increases with
effort, which then increases force

28
Q

describe the central fatigue when there is a slope of decline in max voluntary effort

A

s steeper than that of the
evoked contraction; hence, other mechanisms, in addition to the peripheral/muscle fatigue, contribute to the decline

29
Q

how is the isometric knee extension force induced

A

induced by stimulation
and max voluntary effort (MVC)

30
Q

what evidence is there of central fatigue

A

Alpha-MN firing rate
declines during sustained MVC contributing to decline in contraction force indicating central fatigue

31
Q

what is the function of Electromyography

A

to study the function of motor units

32
Q

the reflex arc; describe the 3 components and what is within them

A

receptors : e.g. proprioceptors , chemoceptors
integration centre: sensory nerves, interneurons (not shown here), α Motor neurons
effectors: skeletal muscle (or other organs, depending on the type of reflex)

33
Q

Muscle sensory receptors: proprioceptors components

A

muscle spindles, Golgi organs

34
Q

Proprioceptors: Muscle spindles key muscle fibres

A

extrafusal and intrafusal muscle fibres

35
Q

muscle spindles at work: describe and name the 2 types of sensory endings

A

Primary endings – respond to the rate of stretch (dynamic response) and the length of muscle (static response)
- Secondary endings – static
response only

36
Q

muscle spindles at work: function of γ motor neurons

A

γ motor neurons prevent
“unloading” of muscle spindles and regulate their sensitivity of spindles to stretch

37
Q

Proprioceptors: Golgi tendon organ function
and how are they activated

A

Activity of Golgi tendon organs signals
muscle tension. They can be activated by
muscle stretch or muscle contraction.

38
Q

how many synapses does this involve monosynaptic stretch reflex

A

Monosynaptic means ONE synapse is involved

39
Q

Monosynaptic stretch reflex: Sequence of events:

A
  1. Tendon is stretched when hit
    by the hammer
    * 2. Muscle is stretched
    * 3. Action potential (AP) is
    generated in a muscle spindle (stretch receptor)
    * 4. AP travels by an afferent
    fibre of the sensory neuron
  2. AP reaches the alpha motor neuron
    through the dorsal roots
    * 6. alpha motor neuron is depolarized
    and AP is generated
    * 7. AP travels by efferent fibre
    * 8. AP arrives at the
    neuromuscular junction and
    causes muscle contraction
40
Q

reciprocal inhibition: what inhibits knee flexors (hamstrings)

A

Stretch of the knee extensors (quadriceps muscle)

41
Q

reciprocal inhibition: what inhibits (hyperpolarisation) alpha motor neurons innervating hamstrings

A

a (fast conducting) afferents activate interneurons

42
Q

describe the autogenic inhibition reflex

A

neurons form Golgi tendon fires
motor neuron in inhibited
muscle relaxes and load is dropped

42
Q

reciprocal inhibition: what is the functional significance

A

coordination of antagonists - hamstring relaxed when quadriceps contract

42
Q

Employing Stretch Reflex:
Countermovement jump, when is greater positive work generated

A

Muscles can do a greater positive work when they are stretched before the contraction

43
Q

Countermovement jump: name the 2 beneficial mechanisms

A

storage of elastic energy
* Stretch reflex

43
Q

why do athletes stretch beforehand

A

athletes use ore stretching to increase power in movement

44
Q

Countermovement jump
Beneficial mechanisms: what does the stretch reflex facilitate

A

Stretch reflex facilitates voluntary muscle activation

45
Q

Countermovement jump
Beneficial mechanisms: what does the storage of elastic energy facilitate

A

Some energy is stored in elastic structures, for extension tendons, during the stretch phase and then released during the contraction phase

46
Q

what is plyometric exercise used for

A

improve power in sports

47
Q

what is a plymoetric exercise

A

explosive jumping training

48
Q

Plyometric exercise: what does stretch reflex assist

A

Stretch reflex assists recruitment of motor neurons by exciting or “facilitating” them

49
Q

what is the possible danger of plyometric exercise

A

muscle damage in stage 3

sports sciencee (8 decks)

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