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EPHE 380 > Motor Units > Flashcards

Motor Units Flashcards

1
Q

alpha motor neurons innervate what types of fibres

A

extrafusal

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2
Q

gamma motor nuerons innervate what type of fibres

A

intrafusal

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3
Q

Dynamic gamma MN innervate

A

dynamic bag or Bag 1 fibres

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4
Q

static gamma MN innervate

A

static bag or bag 2 and chain muscle fibres

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5
Q

how many fibres per MU in small

A

<10

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6
Q

how many fibres per MU in large

A

> 1000

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7
Q

effects of age on motor units

A

decrease in number of motor neurons
re-innervation takes places
increase in size of MU’s
increase in innervation ratio

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8
Q

muscle fibers types are classified by what three factors

A

myosin heavy chain gene, fatigue resistance and contraction speed

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9
Q

what factors can affect fibre type distribution

A

training, spaceflight, cross-innervation, immobilization

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10
Q

motor neuron qualities Type II alpha

A

large cell body
large diameter axon
high AP conduction velocity (90-120m/s)
innervate many large muscle fibres

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11
Q

Type 1 alpha motor nuerons qualities

A

smaller cell body
smaller axon diameter
innervate fewer fibers
slower conduction velocities (60-80m/s)

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12
Q

muscle force varied by

A

recruitment (number of active MUs)
Rate coding (changing drift rate of different MUs)
Synchronicitiy

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13
Q

how is fatigue avoided in MU firing

A

asynchronous firing

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14
Q

which fibre produces more force at all firing rates

A

Type II

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15
Q

which fibre type produced greater percent of max at all firing rates

A

Type I

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16
Q

Hennemans Size Principle

A

Regardless of neuron size, same absolute change in V is required to reach threshold

  • resistance of smaller neurons is greater than larger neurons
  • according to Ohm’s law, to get threshold delta V when same amount of current is given to all nuerons, resistance is higher in smaller neurons, so voltage is higher in smaller nuerons, so they will fire at a lower current than larger neurons will!
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17
Q

assuming constant synaptic drive to MU pool, MU will be recruited from (size to size)

A

smallest to largest

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18
Q

What is Rheobase

A

minimum current required to recruit and maintain during of a MU

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19
Q

in human experiments, MU thresholds are usually determined by

A

force recruitment threshold

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20
Q

what three MU differences are there between the two hands

A

recruitment threshold, firing rate and force fluctuations

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21
Q

does D or ND hand have higher firing rate

A

ND

22
Q

does D or ND hand have higher force

A

ND

23
Q

does D or ND hand have higher recruitment threshold

A

ND

24
Q

does untrained D or ND have have higher synchrony

A

ND

25
Q

violations to the size principle

A

electrical stimulation
- extracellular stimulation reverse recruitment order because the whole nerve trunk is stimulated and it is easier to the the outside current to pass through a bigger axon
Cat paw shake
-high threshold unit preferentially recruited for maximal velocity repetitive cyclic movements
Eccentric contractions
- fast, high force eccentric contraction recruit large MU’s due to short amount of time needed to withstand the load, prevention of injury

26
Q

4 alterations in control of MU firing rate

A

MU synchronization
MU firing frequency
MU doublet firing
Fatigue and Muscle wisdom

27
Q

what are the two benefits or asynchronous firing

A

smooth contraction

less fatigue

28
Q

pros and cons to MU synchronization

A

PRO: high force and faster contraction
CON: fatigue, loss of fine motor control

29
Q

how can you measure the synchrony (2 ways)

A

single MU records and cross correlograms

30
Q

what do you look for in MU records to find synchrony

A

look at temporal firing rates (referenced vs correlated)

31
Q

what do you look for in cross-correlation histogram to find synchrony and what do the two types of peaks you find mean

A

peak at time zero = synchrony
narrow peak = less time at synchrony (less force, more control)
broad peak = more time at synchrony = more force, less control

32
Q

what is the mechanisms behind short term synchrony

A

common presynaptic input directly to the motor neuron

33
Q

what is the mechanisms behind broad peak synchrony

A

common pre-synaptic input to the interneurons before the MN innervating the muscle that will be in synchrony

34
Q

what kind of training increases synchrony

A

weight training

35
Q

musicians have higher for lower synchrony

A

lower in both hands

36
Q

untrained people have higher or lower synchrony and what hand is lower between D and ND

A

lower, and lowest in D hand, bc fine movement is required

37
Q

what is doublet firing

A

two very close timed firing of neurons

38
Q

what is the increase in doublet discharges after training

A

5.2% to 32.& %

39
Q

what is different about MU activation in doublet firing

A

it is earlier

40
Q

what does doublet firing allow MU’s to do

A

enhance maximal firing rate

41
Q

what does synchrony do to the steadiness of force output

A

decreases it, higher standard deviation

42
Q

what is dystonia

A

increase muscle co activation that impairs coordination
“smearing” in somatosensory cortex
increased synchronous discharge of MU

43
Q

what is fatigue

A

acute impairment of performance due to physical activity

44
Q

what is fatigue quantified as

A

decrease in maximal force that a muscle can exert

45
Q

what happens to MU discharge rate throughout a fatiguing contraction

A

reduced

46
Q

fatigue increases what two factors in MU firing

A

variability and patter

47
Q

want happens to M wave during fatigue and how soon before returning to normal

A

amplitude decreases, return to normal after 10min

48
Q

four main mechanical changes during muscular fatigue

A

decline in force, slower force development, slower relaxation, decreases power production

49
Q

four main electrical changes during fatigue

A

early hyper-polarization with decline in force, late hyperpolarization with slower force development, slowed conduction with flows relaxation, and reduced EMG

50
Q

what is muscle wisdom defined as

A

teh ability of the muscle to reduce discharge rate of its motor neurons to match the change in reduction of relaxation rate

51
Q

what does muscle wisdom create

A

increased summation and more economical contractions, essentially a shift in the force frequency relationship, so the same amount of force cane generation with a reduced frequency of contraction

52
Q

three Main factors in muscle wisdom

A

intrinsic membrane properties (adaptation)
- same synaptic input results in fewer APs
Increased feedback
-from group III and groupIV afferent and disfacillitation of Ia afferent
-reduction in central output
-descending command to MN is reduced in fatigue

EPHE 380 (4 decks)

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