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YEAR 3 NEURO > PHYSIOLOGY - Motor units and muscle spindles > Flashcards

PHYSIOLOGY - Motor units and muscle spindles Flashcards

1
Q

what is the somatic motor system

A

skeletal muscles and the elements of the nervous system that control them

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2
Q

LMNs receive input from ___ ___ and ___

A

UMNs
proprioceptors
interneurons

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3
Q

what 2 neurones comprise LMNs

A

alpha and gamma

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4
Q

what is an alpha motor neurone

A

innervates the bulk of the muscle fibres within a muscle that generates force

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5
Q

what is a gamma motor neurone

A

innervates a sensory organ within the muscle known as a muscle spindle

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6
Q

biceps brachii and ____ work as synergists

A

brachialis

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7
Q

triceps brachii and ____ work as synergists

A

anconeus

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8
Q

biceps brachii and brachialis oppose (antagonists) what muscles

A

triceps brachii and anconeus

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9
Q

what muscles control movement of the trunk and maintain posture

A

axial muscles

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10
Q

what muscles mediate locomotion and where are they found

A

proximal (girdle) muscles - found in shoulders, elbow, pelvis, knee

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11
Q

axons of LMNs exit the spinal cord in the ____ roots or via _____

A

vental roots

or via cranial nerves

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12
Q

each ventral root joins with ____ to form ____

A

each ventral root joins with a dorsal root to form a mixed spinal nerve containing motor and sensory fibres

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13
Q

are the motor neurones distributed equally in the spinal cord

A

no

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14
Q

where are greater numbers of motor neurones found in the spinal cord

A

the cervical enlargement and lumbar enlargement

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15
Q

what nerve levels is the cervical enlargement and what does it supply

A

C3 - T1

arm

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16
Q

what nerve levels is the spinal enlargement and what does it supply

A

L1 - S3

leg

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17
Q

motor neurones supplying the axial musculature occur at what levels

A

all

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18
Q

what is the smallest functional component of the motor system

A

motor unit

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19
Q

what is a motor unit

A

an alpha-MN and all of the skeletal muscle fibres that it innervates

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20
Q

what is a motor neurone pool

A

the collection of a-MNs that innervates a single muscle

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21
Q

what 2 mechanisms control force of contraction

A

frequency of AP discharge of the a-MN

the recruitment of additional synergistic motor units

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22
Q

each AP causes a muscle ____

A

twitch - rapid sequence of contraction followed by relaxation

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23
Q

in the ventral horn, LMN cell bodies innervating axial muscles are _____ to those innervating distal muscles

A

medial

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24
Q

in the ventral horn, LMN cell bodies innervating flexors are ____ to those innervating extensors

A

dorsal

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25
Q

what are the 3 sources of input into an a-MN that regulate its activity

A

central terminals of DRG cells whose axons innervate the muscle spindles
UMNs in motor cortex and brain stem
spinal interneurons

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26
Q

what 2 things does muscle strength depend on

A

activation of muscle fibres

force production by innervated muscle fibres

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27
Q

what 3 things influence the activation of muscle fibres

A

firing rate of the LMNs involved
number of LMNs that are simultaneously active
the coordination of the movement

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28
Q

what 2 things influence force production by innervated muscle fibres

A 
fibre size 
fibre phenotype (fast or slow contracting muscle)
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29
Q

a single AP in an a-MN causes muscle fibre to ____.

_____ __ ______ causes a sustained contraction

A

twitch

summation of twitches

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30
Q

where would you see small motor units with a few fibres

A

fine movements e.g. extraocular eye muscles

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31
Q

where would you see large motor units with thousands of fibres

A

large antigravity postural muscles e.g. leg muscles

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32
Q

small motor units are innervated by ___ a-MNs

A

small (soma diameter)

- same true for converse

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33
Q

true/false

motor units contain muscle fibres of only one type of either fast or slow fibres

A

true

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34
Q

a-MNs innervating fast type tend to be smaller/larger

A

larger

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35
Q

the motor end plate is usually where on a muscle fibre

A

centre - some muscle fibres may have multiple endplates

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36
Q

true/false

motor unit types are dispersed within a muscle

A

true

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37
Q

what are the 2 major types of skeletal muscle fibre

A

fast twitch and slow twitch

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38
Q

in what 2 ways do fast and slow twitch muscle fibres differ

A

differ in how myosin ATPase splits ATP to provide energy for cross bridge cycling
express different myosin heavy chains

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39
Q

what is another name for type I fibres

A

slow oxidative / slow

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40
Q

where is ATP derived from in type I fibres

A

oxidative phosphorylation

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41
Q

type I fibres have ___ contraction and relaxation

A

slow

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42
Q

type I fibres fatigue quickly/slowly

A

fatigue resistant

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43
Q

what colour are type I fibres and why

A

red fibres

high myoglobin content

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44
Q

what are the 2 types of type II fibres

A

type IIa and IIb

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45
Q

where is ATP derived from in type IIa fibres

A

largely from oxidative phosphorylation

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46
Q

where is ATP derived from in type IIb fibres

A

mainly from glycolysis

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47
Q

are type IIa fibres or type IIb fibres fatigue resistant

A

IIa fatigue resistant

IIb fast fatiguing

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48
Q

type IIa fibres are ____ in colour and reasonably well _____

A

red

vascularised

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49
Q

type IIb fibres are ____ in colour and _____ vascularised

A

pale

poorly

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50
Q

what is another name for type IIa fibres

A

fast oxidative / fatigue resistant

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51
Q

what is another name for type IIb fibres

A

fast glycolytic / fast fatiguing

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52
Q

compare the mitochondria in types I IIa and IIb

A

I - high
IIa - high
IIb - low

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53
Q

compare the glycogen content in types I IIa and IIb

A

I - low
IIa - intermediate
IIb - high

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54
Q

compare the myosin ATPase activity in types I IIa and IIb

A

I - low
IIa - high
IIb - high

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55
Q

what is the Henneman size principle

A

the susceptibility of an a-MN to discharge APs is a function of its size
- smaller MNs have a lower threshold than larger ones

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56
Q

fast fatiguing (IIb) motor units are ___ a-MNs and have a ___ threshold

A

large

high

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57
Q

fatigue resistant (IIa) motor units are _____ a-MNs and have a ___ threshold

A

intermediate size and threshold

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58
Q

slow motor units are ___ a-MNs and have a ___ threshold

A

small

low

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59
Q

______ motor units are more easily activated and trained by any training

A

slow

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60
Q

muscles with small motor units have a ____ gradation of force

A

fine

61
Q

muscles with large motor units have a ____ gradation of force

A

coarse

62
Q

motor units are recruited by what order

A

order of their size - smaller more easily activated

63
Q

what does recruitment of motor units by size allow

A

fine control of muscle force across a wide range of tensions developed

64
Q

motor units are recruited in an order appropriate to the physical task that is being performed. what is the order? and what does this allow

A

type I before type IIa then IIb

increasing increments towards the maximal force that the muscle exerts

65
Q

type I units are used for

A

standing

66
Q

type IIa units are used for

A

running / walking

67
Q

type IIb units are used for

A

jump / sprint

68
Q

what is the myotatic reflex

A

monosynaptic reflex arc - when a skeletal muscle is pulled it pulls back

69
Q

how is change of length and rate of change sensed by a muscle

A

sensory organ - muscle spindle

70
Q

what do spindles consist of (4)

A
  • fibrous capsule
  • intrafusal muscle fibres
  • sensory afferents that innervate the intrafusal fibres
  • gamma motor neurone efferents that innervate the intrafusal fibres
71
Q

what do extrafusal muscle fibres do

A

generate muscle force

72
Q

what sensory afferents innervate the intrafusal muscle fibres

A

Ia - myelinated and very fast conducting

73
Q

what do you strike to cause a knee jerk reflex

A

patellar tendon

74
Q

biceps reflex

A

C5 C6

75
Q

supinator reflex

A

C5 C6

76
Q

nerve of biceps reflex

A

musculocutaneous

77
Q

nerve and muscle of supinator reflex

A

radial nerve

brachioradialis

78
Q

triceps reflex

A

C7

79
Q

knee reflex

A

L3 L4

80
Q

muscle of knee reflex

A

quads

81
Q

ankle reflex

A

S1 S2

82
Q

muscle of ankle reflex

A

gastrocnemius

83
Q

describe the myotatic reflex

A

1) stretch of muscle spindle
2) activation of Ia afferent
3) excitatory synaptic transmission in spinal cord mediated by glutamate
4) activation of a-MN
5) contraction of muscle

84
Q

monosynaptic reflex most prominent in flexor/extensor muscles

A

extensor

85
Q

how can the myotatic reflex be reinforced

A

jendrassik manoeuvre - as patient to interlock fingers and try to pull them apart when instructed and illicit jerk immediatley

86
Q

intrafusal fibres of muscle spindles are innervated by ___-MNs and ___ sensory afferents

A

gamma

1a

87
Q

which parts of the intrafusal fibre do the gamma-MNs innervate and which do the Ia sensory afferents innervate

A

non-contractile equatorial region - 1a sensory afferent

contractile polar ends - gamma-MNs

88
Q

gamma-MNs cell bodies are where

A

in the ventral horn of the spinal cord

89
Q

gamman-MNs are driven by ___

A

higher centres not 1a afferents

90
Q

stimulation of gamma-MNs causes

A

spindle to contract

91
Q

in the reflex arc, a-MNs firing causes the muscle to contract which makes the spindle go taut/slack, increasing/decreasing 1a afferent firing

A

slack

decreasing

92
Q

how is the sensitivity of the spindle maintained during voluntary movement

A

intrafusal fibres contract in parallel with extrafusal fibres - a and y MNs are co-activated by higher centres

93
Q

in a reflex arc, when the spindle goes slack, if the muscle were stretched again what would happen
what happens to reset the tension

A

no 1a firing and no a-MN activation

Y-mn contraction of both ends to reset sensitivity

94
Q

if both a-MNs and y-MNs are stimulated what happens

A

spindle under tension, 1a response is maintained during contraction

95
Q

what forms the efferent portion of a reflex arc

A

a-MN

96
Q

Y-mns have a key function in what (2)

A

maintaining muscle tone

non-conscious proprioception

97
Q

LMNs arise in what laminae of the spinal cord

A

VIII and IX

98
Q

what is the difference in control of a and y MNs

A

a-MN: under control of UMNs and 1a sensory afferents

y-MN: just under control of UMNs

99
Q

why is it important for the y-MNs to keep the spindle taut

A

maintain tension to preserve sensitivity to muscle stretch by the spindle

100
Q

Sensitivity to the stretching of muscle spindles allows for information on muscle length and velocity to be relayed to the ____ via ____ tracts

A

cerebellum

spinocerebellar tracts

101
Q

how is tone increased in a muscle

A

increased y-MN firing as muscle spindle becomes hypersensitive to stretch –> greater activation and recruitment of a-MNs via reflex arc
stiff muscle on passive movement

102
Q

what are the 2 types of intrafusal fibres

A

nuclear bag fibres

chain fibres

103
Q

what are the 2 types of nuclear bag fibres

A

bag 1 - dynamic

bag 2 - static

104
Q

describe the difference between the sensitivity of bag 1 and bag 2 fibres

A

bag 1 (dynamic) - very sensitive to rate of change of muscle length

bag 2 (static) - more sensitive to the absolute muscle length

105
Q

describe the difference between the innervation of bag 1 and bag 2 fibres

A

bag 1 - innervated by dynamic Y-mns

bag 2 - innervated by static Y-mns

106
Q

what are nuclear chain fibres sensitive to

A

absolute length of the muscle

107
Q

nuclear chain fibres are innervated by

A

static y-MNs

108
Q

the 3 types of intrafusal fibre are

A

dynamic nuclear bag fibre
static nuclear bag fibre
nuclear chain fibre

109
Q

what are the 2 different afferent fibres that innervate the intrafusal fibres

A 
1a fibres (Aa)
II fibres (Ab)
110
Q

___ fibres form a primary annulospiral nerve ending winding around the centre of all intrafusal fibres

A

1a fibres (Aa)

111
Q

type II fibres which are more slow/fast conducting, form flowerspray endings on all intrafusal fibres except ___

A

slowly

bag 1 dynamic type (think: dynamic too fast for it)

112
Q

both afferents respond to ___

A

stretch

113
Q

which fibres are more sensitive to rate of change of stretch and which fibres are more sensitive to absolute length of intrafusal fibres

A

1a - rate of change of stretch

II - absolute length of intrafusal fibres

114
Q

what do 1a fibres respond to

A

both rate of change (dynamic response) and absolute length (static response)

115
Q

in activities in which muscle length changes slowly and predictably only ____ y-MNs are activated

A

static

116
Q

when are dynamic y-MNs activated

A

behaviour in which muscle length is changing rapidly and unpredictably

117
Q

where are golgi tendon organs located

A

junction of muscle and tendon

118
Q

what do the golgi tendon organs monitor what by how

A

force generated by a muscle by measuring tension in its tendon

119
Q

golgi tendon organs are in (parallel/series) with extrafusal fibres

A

in series

120
Q

golgi tendon organs are innervated by group __ sensory afferents

A

1b

121
Q

group 1b sensory afferents are slower/quicker, more/less myelinated than group 1a

A

slower

less

122
Q

golgi tendon organs regulate muscle tension to (2)

A

protect muscle from overload (weight lifting)

regulate muscle tension to an optimal range

123
Q

group 1b sensory afferents enter the spinal cord and synapse upon ____

A

inhibitory interneurones

124
Q

group 1b sensory afferents enter the spinal cord and synapse upon inhibitory interneurones which synapse upon ___ to do what

A

a-MNs of homonymous muscle to form the reverse myotatic reflex - inhibition of a-MN supplying homoymous muscle to cause relaxation

125
Q

the reverse myotatic reflex is mono/poly synaptic

A

poly

126
Q

proprioceptive feedback of the reverse myotatic reflex is important for what

A

proper execution of fine motor acts - fragile objects require a steady but not too powerful grip

127
Q

proprioceptive axons are found in ____
and respond to ____
and prevent

A

connective tissue of joints
changes in angle, direction and velocity of movement of a joint
excessive flexion or extension

128
Q

what kind of proprioceptive axons are most numerous

A

free nerve endings

129
Q

where are free nerve endings found

A

in capsule and connective tissue

130
Q

free nerve endings are
HT/LT
SA/FA
function

A

HT
SA
nociceptive

131
Q

golgi type endings are found

A

only in ligaments

132
Q

golgi type endings are
HT/LT
SA/FA
function

A

HT
SA
protective role

133
Q

paciniform endings are found

A

periosteum near articular attachments and fibrous part of joint capsule

134
Q

paciniform endings are
HT/LT
SA/FA
function

A

LT
SA
acceleration detectors

135
Q

ruffini endings are found

A

mainly in joint capsule

136
Q

ruffini endings are
HT/LT
SA/FA
function

A

LT
SA
static position and speed of movements

137
Q

proprioceptive information arises from what 3 things

A

muscle spindles
golgi tendon organs
joint receptors

138
Q

what is the role of spinal interneurones

A

coordinated control of flexors and extensors for limb movements

139
Q

what 4 things do spinal interneurones receive input from

A

primary sensory axons (1a and 1b fibres)
descending axons from brain
collateral branches of LMNs
other interneurones

140
Q

what kind of interneurone mediates the inverse myotatic reflex

A

inhibitory

141
Q

what else do inhibitory interneurones mediate

A

reciprocal inhibition between extensor and flexor muscles

142
Q

outline an example of reciprocal inhibition

A

knee jerk reflex - quads extends - for this to happen hamstrings needs to relax
1a afferent from muscle spindle of extensor makes an excitatory monosynaptic contact with a-MN of homonymous muscle VIA a polysynaptic pathway involving inhibitory interneurone - the 1a fibre also inhibits the a-MN supplying the flexor muscle

143
Q

how does the motor cortex use reciprocal inhibition in initiation of movement

A

when an extensor voluntarily contracts it stretches the opposing flexor which would stimulate the myotatic reflex however descending controls cause inhibitory interneurones to inhibit the a-MN of the opposing muscle allowing unopposed extension

144
Q

what 2 things do excitatory interneurones mediate

A

flexor reflex

crossed extensor reflex

145
Q

what is the flexor reflex

A

noxious stimuli causes limb to flex by contraction of flexor muscles via excitatory interneurones and relaxation of extensor muscles via excitatory and inhibitory interneurones

146
Q

what is the crossed extensor reflex

A

noxious stimuli causes limb to extend by contraction of extensor muscles via excitatory interneurones and relaxation of flexor muscles via excitatory and inhibitory interneurones

147
Q

which reflex enhances postural support during withdrawal of foot from a painful stimulus

A

crossed extensor reflex

148
Q

what is the only monosynaptic reflex in humans

A

myotatic reflex

149
Q

dynamic and static y-MNs form a ____ motor system that allows control of motor tasks of varying complexity

A

fusiform

YEAR 3 NEURO (12 decks)

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