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Motor Control > Nerves and Muscle > Flashcards

Nerves and Muscle Flashcards

1
Q

Extrafusal fibres

A

main fibres of muscles, respnsible for muslcular force porduction with skeletal muscles

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2
Q

intrafusal fibres

A

muscle fibres contained within sensory organs called muscle spindles (inside) but not force producing

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3
Q

three types of motor neurons that innervate different fibre types

A

Alpha motor neurons: innervate only extrafusal fibres
beta - extrafusal and intrafusal
gamma - only intrafusal

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4
Q

single motor neuron innervation rule

A

in a mature animal, any given skeletal muscle fibre is innnervated by one and only one motor neuron

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5
Q

motor unit - what is it?

2 characteristics

A

the whole alpha motor neuron together with all the extrafusal muscle fibres that it innervates

  • smallest functional unit of the neuromotor system
  • produces synchronized chontraction of innervated muscle fibres - to reduce computational load
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6
Q

neuromuscular junction

A

synaptic connection between motor neuron axon terminal and muslce fibre (AP down axon to terminal - synchonized contraction of all the muscles that this alpha connects to)

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7
Q

motor end plate

A

region of muslce fibre that receives neurotransmitter (ACh) from neuromuscular junction, produces EPSP at motor end plate that radiates along muscle fibre as motor unit action potential (MUAP)

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8
Q

twitch contraction (2)

A

propagation of single AP along muscle fibre

muscle fibre generates contractile force for short time and then relaxes

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9
Q

tetanic contraction (2)

A

propagation of train of APs along muscle fibr at relatively high frequency
force developed by muscle fibre is continuously above zero but may show variation due to individual twitches - no time to relax

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10
Q

innervation ratio - what is it?

2 example

A

average number of fibres in a motor unit for a given muscle
fine control: small ratio - 5-100 fibres (extraocular, hand)
gross muscles: high ratio - 1000 fibres (back, thighs)

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11
Q

Are all muscle fibres innervated are?

A

of the same fibre type

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12
Q

ratio of action potential to motor unit action potential

A

1:1 - alpha motor neuron to muscle cell (all fibres)

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13
Q

As age increases, what happens to your motor neurons?

A

innervate more muscle fibres which loses the accuracy

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14
Q

physical differences in motor units (2) both are related to

A

size of the cell body
diameter of axon
alpha MN

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15
Q

Muscle fibre types innervated are differentiated by (3)

A

physiological - vascularization, mitochondrial density etc.
contractile - capacity for force production
- fatigibility - low force/fatigue
mid force/fatigue (postural muscles)
high force/fatigue

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16
Q 
fast fatigue, fast twitch (3) - name 
- cell body 
- axon diameter 
- muscle fibres innervated (2) 
NCV
A 
FF [MU1] 
largest cell body 
thickest axon diameter 
muscle fibres innervated: 
- highest force capacity 
- quickest fatigue 
nerve conduction velocity - ~100ms
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17
Q 
fast resistant, fast twitch (3) - name 
- cell body 
- axon diameter 
- muscle fibres innervated (2) 
NCV
A 
FR[MU2]
mid-size cell body 
mid-size axon diameter 
muscle fibres innervated 
- mid-level force capacity 
- fatigue resistant 
nerve conduction velocity - less than FF [MU1], immediate properties
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18
Q 
fatigue-resistant, slow twitch (3) - name 
- cell body 
- axon diameter 
- muscle fibres innervated (2) 
NCV
A 
S [MU3] 
smallest cell body 
thinnest axon diameter 
muscle fibres innervated 
- lowest force capacity 
- high fatigue - resistant 
nerve conduction velocity = ~40m/s
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19
Q

Motor units and force production principle

A

muscle utilize neural input for purpose of creating muscle contraction which produces force

20
Q

How can forces be graded?

A

Magnitude of force generated depends on

  • number of active motor units
  • firing/discharge rates of active units
21
Q

same force output can be achieved by

A

more MUs firing at lower frequency OR fewer MUs firing at higher frequency

22
Q

how to maximize force output

A

More MUs and high frequency

23
Q

Henneman size principle

A

the order in which the motor units of a muslce are recruited into force production is determined by the size of associated motor neuron - smaller MU to larger MU
- [S]->[FR]->[FF]

24
Q

low grade contractions achieved by

A

fatigue resistant, slow twitch [s] - can last over an hour

25
Q

Larger MUs are recruited as

A

contraction force increases, but [s] does not decrease

26
Q

increases in muscle tension (force) achieved by

A

orderly recruitment of MU

27
Q

derecruitment

A

as force output declines - derecruitment follows inverse order FF, FR, S

28
Q

Reasons for force decline? (2)

A 
voluntary decline (muscle relaxation) 
Fatigue (sustained contraction) - MU drop out
29
Q

How to record MU activity in a muscle

A

electromyography

30
Q

EMG: what is it and ow does it work?

A

electromyography - algebraic sum of MUAP train - MUAP firing over time
graphical rep of the electrical acivity of a skeletal muscle
“electrode” records MUAPs as they pass beneath the site of recording

31
Q

How does MUAP get detected by the recording electrodes?

A

AP crosses neuromuscular junction to depolorize all muscle fibres within a MU - release of Ach then postsynaptic neurons receive the signals

32
Q

In what direction do MUAPs propagate?

A

both directions along the muscle fibre

33
Q

what are the 2 types of electrodes?

A

intramuscular (fine wire) EMG

Surface (inferential) EMG

34
Q

Intramuscular (fine-wire) EMG (3)

A

Records MUAP within targeted muscle only
small, muscle specific receptive zone
precise and accurate recording from receptive zone

35
Q

suface/inferential EMG (3)

A

extramuscular
records MUAP of all MU in proximity to electrodes - multiple MU within/across muscle
precision requires knowledgeable application

36
Q

2 principles of recording MUAP

A
  1. distance from recording site affects amplitude of recorded MUAP - alpha motor neuron synapses with muscle fibre(s) which get detected by the electrodes on the muscle fibre - as we get further away the amplitude gets smaller
  2. recorded sighal h(t) represents the sum of all MUAP occurring within the vicinity of recording electrodes at that point in time
37
Q

what do we do to raw EMG data?

A

we rectify it - half way rectified is to turn all the negative ones into positives, after rectifying both - full way - we can use it to infer force

38
Q

appearance of EMG signal depends on 3

A

anatomy, neurophysiology, instrumentation

39
Q

how does anatomy construct EMG signal? 1-3

A

MU

  • alpha MN and associated muslce fibres
  • # of muscle fibres innervated
  • contractile properties of innervated fibres
40
Q

how does neurophysiology construct EMG signals? 1-2

A

MUAPs

  • # MU recruited - depends of force
  • firing frequency of MUs - depends on force
41
Q

3 ways to use EMG

A

Clinical, sport, industrial

42
Q

clinical applications of EMG - 3

A

diagnosis - duration and amplitude
surgical intervention - effects intended
rehab - muscle activity - after a stroke

43
Q

purpose of ground electrode

factors affecting signal quality

A

take out background activity/system noise by taking out the common activity between it and the electrodes
cable sway, light, electrical appliances

44
Q

sport application of EMG

A

performance - pro vs amateur

45
Q

industrial application of EMG

A

fatigue - of different muscle groups - ergonomics/work injuries

46
Q

Semmler - EMG activity for elbow flexor groups before and after 4 weeks of casting - 2 -3

A

no change in force production, however, neural strategy is altered
- conpensatory recruitment of synergistic muslces at onset
- brachialis dropout (MU fatigue)
- intermittent firing in synergistic muscles following dropout
CNS strategy to compensate for fatigue

Motor Control (9 decks)

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