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Neurophysiology > Muscle receptors and spinal reflexes > Flashcards

Muscle receptors and spinal reflexes Flashcards

1
Q

What is proprioception

A

The sense of body position in space based on specialised receptors in the muscles and tendons

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2
Q

What are the 2 types of proprioception

A

Static (joint-position) and dynamic (kinaesthesia, limb movement)

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3
Q

What 3 ways is info from muscle receptors integrated by the nervous system

A

Input for spinal reflexes, subconscious control of movement via the cerebellum, conscious proprioception via the dorsal column system and cerebeal cortex

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4
Q

What are the 2 components of the stretch reflex

A

Short latency component M1

Long latency component M2

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5
Q

What is the knee jerk stretch reflex called

A

The quadriceps patellar tendon reflex

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6
Q

What are the 4 types of mechanoreceptors involved in mechanoreceptors

A

Muscle spindles and Golgi tendon organs, joint mechanoreceptors, skin mechanoreceptors

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7
Q

What are the 2 main types of muscle receptor

A

Muscle spindles and Golgi tendon organs

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8
Q

What do the muscle receptors tell the CNS

A

The relative positions of body parts

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9
Q

What do muscle spindles signal

A

Stretch

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10
Q

What do Golgi tendon organs signal

A

Tension produced by muscle contraction

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11
Q

What are 2 types of joint mechanoreceptors

A

Larger fibres signal joint position

Smaller Aδ fibres are most active at the extremes of movement and are protective

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12
Q

What do skin mechanoreceptors signal (proprioception)

A

Postural information, speech/facial expression

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13
Q

What does muscle contain along with muscle spindles and GTOs

A

Nociceptors involved in pain perception

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14
Q

Where are muscle spindles located

A

In the fleshy part of muscles, in parallel with extrafusal fibres and attached to muscle connective tissue

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15
Q

Where are Golgi tendon organs located

A

In tendons at the ends of a muscle, in series of extrafusal fibres

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16
Q

What is the shape/size of muscle spindles

A

Small(2-4mm long), encapsulated, spindle-shaped

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17
Q

What are the 3 main components of a muscle spindle

A

Intrafusal muscle fibres
Sensory nerve fibres
Gamma motor nerve fibres (axons)

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18
Q

What sections of intrafusal muscle fibres are non-contractile vs contractile

A

Central part- non-contractile, contains the nuclei

Ends- contractile

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19
Q

Describe the sensory nerve fibres in the muscle spindle

A

Large diameter, myelinated, wrap around the non-contractile centre of intrafusal fibres, terminals sensitive to stretch of the intrafusal fibre

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20
Q

Describe the gamma motor nerve fibres in the muscle spindle

A

Small diamater, innervate the contractile ends of intrafusal fibres

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21
Q

What are the 2 types of intrafusal fibres in muscle spindles

A

Nuclear chain fibres

Nuclear bag fibres

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22
Q

How many nuclear chain fibres vs nuclear bag fibres are in each spindle

A

NC- variable no per spindle

NB- 2-3 per spindle

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23
Q

What are nuclear chain fibres

A

Nuclei aligned in a single row in the centre of the fibre

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24
Q

What are nuclear bag fibres

A

Nuclei are collected in a bundle in the middle of the fibre

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25
Q

What are the two FUNCTIONAL types of intrafusal fibres in muscle spindles

A

Static aka non-adapting

Dynamic aka rapidly-adapting

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26
Q

What type of intrafusal fibres are static

A

ALL NUCLEAR CHAIN FIBRES ARE STATIC

Nuclear bag fibres CAN be static

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27
Q

What type of intrafusal fibres are dynamic

A

ONLY NUCLEAR BAG FIBRES- their contractile ends are more viscous, so stretching occurs in the central nuclear part

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28
Q

What do static intrafusal fibres measure

A

LENGTH of the spindle at any instant

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29
Q

What do dynamic intrafusal fibres meaure

A

RATE OF CHANGE of length of spindle

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30
Q

What are the 2 types of sensory afferent nerves at the muscle spindles

A

Aa afferent, group II afferent

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31
Q

What do the Aa afferent nerves do at muscle spindles

A

Record from the centre of ALL fibres, so report dyamic and static info
Fastest fibres!

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32
Q

What do the group II afferent nerves do at muscle spindles

A

Record from static bag and chain fibres only, so report primarily static info ab spindle/muscle length

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33
Q

Gamma motor nerves- dynamic or static?

A

Separate gamma motor nerves supply dynamic and static intrafusal fibres to modulate their activity

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34
Q

What did Sherrington (1906) demonstrates about the stretch reflex by cuttin the dorsal and ventral roots

A

The stretch reflex is not an intrinsic property of the muscle, but requires sensory input and a motor path to the muscle

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35
Q

What are spinal reflexes

A

Reflexes with neural circuitry fully contained in the spinal cord, that receive direct sensory info from the muscles/joints/skin

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36
Q

What does the stretch reflex act to do

A

Counter stretching and change in muscle length

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37
Q

How do afferent sensory fibres sense stretch in the intrafusal fibres

A

Stretch channels in their terminals open, altering their ionic current
Cell is depolarised and generates APs, signalling stretch

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38
Q

Which type of sensory afferent fibre is involved in the stretch reflex

A

Group Ia myelinated afferent fibres

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39
Q

What are the 3 types of alpha motor neurons involved in the stretch reflex

A

Those supplying the homonymous muscle, those supplying synergist muscles, those supplying antagonist muscles

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40
Q

What joins Ia afferents to alpha motor neurons supplying antagonist muscles in the stretch reflex

A

An inhbitory interneuron

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41
Q

Stretch reflex- what happens to the quadriceps muscle when you tap the knee tendon

A

Deforms the tendon, causing limb extension that stretches the quadriceps muscle

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42
Q

Stretch reflex- what happens when the quadriceps muscle stretches

A

Intrafusal fibres within muscle spindles detect stretch

Ia afferent terminals detect this stretch so Ia afferents increase firing

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43
Q

Stretch reflex- what do Ia afferents branch to form excitatory synapses with in the spinal cord

A

ALL the motor neurons innervating homonymous muscle
60% of the motor neurons innervating synergist muscles
Inhibitory interneurons for antagonist motor neuron

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44
Q

Stretch reflex- what is the effect of the excited homonymous and synergist alpha motor neurons

A

Cause contraction of the quadricepts muscle and synergist muscles -> lower leg swings forward

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45
Q

Stretch reflex- what is the effect of inhibited antagonist alpha motor neurons

A

The antagonist hamstring muscle relaxes, so it doesn’t oppose the action of the quadriceps muscle, allowing leg extension

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46
Q

Stretch reflex- what is reciprocal inhibition

A

The simultaneous excitation of the stretched muscle (and its synergists) and inhibition of antagonist muscles

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47
Q

What type of loop is the stretch reflex

A

A negative feedback loop

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48
Q

What is stretch reflex component M1

A

Strong and fast, predominantly controlled by monosynaptic connection in spinal cord, involved with axial and proximal muscle control

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49
Q

What is stretch reflex component M2

A

Slower but longer lasting (shorter than reaction time), involves the cerebral cortex, involved with fine voluntary distal limb movements,

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50
Q

What descending tracts modulate the stretch reflex

A

Corticospinal tract, vestibulospinal tract, reticulospinal tract

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51
Q

How does the corticospinal tract modulate the stretch reflex

A

Inhibits stretch reflexes to allow voluntary movement

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52
Q

How does the vestibulospinal tract modulate the stretch reflex

A

Primarily engages extensor antigravity muscles

53
Q

How does the reticulospinal tract modulate the stretch reflex

A

Modulates intensity of reflex activity via gamma motor neurons

54
Q

What cells are engaged by recurrent processes

A

Renshaw inhibitory interneurons- inhibit a muscle that is firing repeatedly, preventing fatigue

55
Q

What are functions of the stretch reflex resisting stretch

A

Posture, holding a heavy object, muscle tone

56
Q

What maintains muscle spindle sensitivity during voluntary movement (primarily contraction)

A

Alpha-gamma motor neuron coactivation

This is the simultaneous activation of alpha and gamma motor neurons

57
Q

How does dynamic vs static gamma motor neuron activity differ across movement type

A

Gamma static activity- slow predictable movements

Gamma dynamic activity- rapid unpredictable movements

58
Q

What happens to the stretch reflex in Klipper-Feil syndrome

A

The M2 component also occurs on the contralateral side of the body

59
Q

What is muscle tone

A

Resistance of the muscle to stretch

60
Q

What is the result of lack of descending control of reflex pathways

A

Hyperactive stretch reflex, meaning hypertonic (spastic) muscle

61
Q

Sherrington- what is the result of removing cortical but not brainstem locomotor influences in decerebrate cats

A

Limbs showed increased reflexes and spastic paralysis- hypertonus

62
Q

How are Golgi tendon organs innervated by a sensory afferent

A

A single Ib afferent fibre interweaves with the collagen fibres inside the GTOs at the muscle-tendon junction

63
Q

What is the effect of muscle contraction on Ib afferent fibres in golgi tendon organs

A

Muscle contraction causing tendon tension, straightening of the collagen bundles compresses and stimulates the Ib afferent nerve

64
Q

Functinos of GTOs

A

Clasp-knife reflex, prevents overstretching
Graded response to small changes in tension means involvement in fine movement
Modulate reflex pathways

65
Q

How do Golgi tendon organs afferent signals contribute to reflex pathways

A

GTO Ib afferents provide feedback inhibition onto homonymous motor neurons via a spinal interneuron

66
Q

How is GTO function protective in providing feedback inhibition of reflex pathways

A

If excessive load is placed on a muscle, Golgi-tendon senses tension caused by muscle contraction- clasp-knife reflex causes relaxation, protecting muscle

67
Q

What is state-dependent reflex reversal

A

Ib afferents inhibit extensor motor neurons during rest, but during locomotion they recruit an alternative EXCITATORY interneuron path to excite them

68
Q

What do leg extensors vs flexors do during locomotion

A

Extensors- recruited during stance phase, ‘anti-gravity’ function
Flexors- recruited during swing phase, voluntary movement

69
Q

What is the flexor withdrawal reflex

A

Protective reflex pathway that pulls a damaged limb away from a painful stimulus

70
Q

How does the flexor withdrawal reflex work

A

If we stand on a painful thing, sensory neuron collaterals in the spinal cord activate ascending pathways for pain and postural adjustment, and cause contraction of flexors / inhibition of extensors that move the foot away from the stimulus

71
Q

What reflex occurs at the same time as the flexor withdrawal reflex

A

A contralateral ‘crossed-extensor’ supporting reflex- contralateral extensors contract and flexors are inhibited as weight shifts to contralateral leg, supporting the body

72
Q

What is the Babinski response

A

Flexor withdrawal reflex, elicited by stroking the sole of the foot forward along its lateral aspect and across the ball, causing flexion of the toes to push away the stimulus

73
Q

What is an abnormal response to the Babinski response

A

Extension of the big toe and fanning out of the other toes, a sign of an upper motor neuron lesion

74
Q

What is an exception to the Babinski response being a sign of upper motor neuron lesion

A

Newborns- extension is the norm due to immaturity of descending tracts

75
Q

What is the effect of lower motor neuron lesion

A

Weakness (paresis) or actual paralysis, loss of reflexes, reduced muscle tone and muscle wasting

76
Q

What is a lower motor neuron lesion

A

Anything that damages the sensory afferent or lower motor neuron or motor neuron in the spinal cord

77
Q

What is an upper motor neuron lesion

A

Anything that damages the corticospinal tract

78
Q

What is the result of an upper motor neuron lesion

A

Paralysis, increased stretch reflexes and muscle tone are increased (spastic), less wasting

79
Q

What is the most characteristic lesion producing paralysis, hyperreflexia and spasticity

A

Stroke- only occurs in its full form when the cereberal cortex or internal capsule is damaged

80
Q

What are reflex responses

A

Rapid, stereotyped motor behaviours (can be modulated )

81
Q

What are motor neuron pools

A

A cluster of motor nuclei of all the motor neurons that innervate a muscle

82
Q

What is the proximal-distal rule

A

motor neurons innervating the most proximal (axial) muscles are located most medially in the spinal cord VS motor neurons innervating the most distal muscles are located more laterally

83
Q

What is the flexor-extensor rule

A

The motor neurons that innervate extensor muscles lie ventral to those innervating flexor muscles

84
Q

What is a motor unit

A

The smallest functional unit in the nervous system- a single motor neuron and the several muscle fibres it innervates

85
Q

What are the 3 types of motor units

A

Fast fatigable, slow fatigue resistant, fast fatigue ressitant

86
Q

What are fast fatigable motor units

A

Fibres contract and relax repeatedly, but fatigue rapidly when stimulated repeatedly
Generate the greatest force during contraction

87
Q

What are slow fatigue resistant motor units

A

FIbres have a much longer contraction time, highly fatigue resistant, generate 1-10% of the force of fast fatigable fibres

88
Q

What are fast fatigue resistant motor units

A

Intermediate properties, contract slower than fast fatigable fibres but almost as fatigue resistant as slow fatigue-resistant fibres

89
Q

What is the effect on afferent sensory fibres during muscle contraction

A

Extrafusal fibres slacken and shorten, so intrafusal fibres are no longer stretched, firing rate in afferent endings decreases

90
Q

Why do GTOs respond best to muscle contraction

A

Durnig contraction, muscle fibres pull directly on collagen fibres, mean small stretches of the tendon can deform the nerve endings

91
Q

What 2 phases make up the change of length o a muscle

A

Dynamic (length changes) and steady-state (new muscle length is stabilised)

92
Q

What is the firing rate of Ia and II afferent sensory nerves during the dynamic phase of stretch

A

Ia endings fire at a much higher rate than during the steady state phase
Group II endings increase their firing gradually, but it is not much higher than in steady-state phase

93
Q

What is the firing rate of Ia and II afferent sensory nerves durnig the steady state phase of stretch

A

When a muscle lengthens, both Ia and II endings increase their firing to a higher steady state rate

94
Q

What type of stimuli do Ia endings respond best to

A

Sensitive to small changes in muscle length and transient stimuli eg taps or vibration

95
Q

How do Ia fibres show velocity sensitivity as a muscle shortens also

A

Ia endings stop firing, then resume at a lower rate when shortening stops

96
Q

How do Ia fibres respond as muscle length increases

A

As muscle length increases, firing rate increases- increased firing rate reflects the rate of change aka VELOCITY SENSITIVITY

97
Q

What is the effect of short transient stimuli on group II sensory afferent endings

A

No effect- changes in muscle length occur too quickly to alter their steady state discharge

98
Q

What is the importance of alpha-gamma coactivation

A

If the spindles stopped firing when muscles contracted, they would not convey any info about length changes when it was critical- gamma motor neurons ensure this info is transmitted

99
Q

What do gamma motor neurons do in alpha-gamma coactivation

A

Gamma motor neurons innervate intrafusal muscle fibres while alpha motor neurons innervate extrafusal fibres
Both neurons are stimulated during muscle contraction, meaning the activity of the spindle afferents continues

100
Q

How does gamma motor neurons stimulating the ends of intrafusal fibres have an effect

A

The polar contractile regions shorten, which stretches the central region from both ends, stretching the spindle afferent terminals so they can continue firing

101
Q

How is alpha-gamma coactivatino useful during slow voluntary, precise movements

A

eg trajectory of finger movement during flexion reflects variation in the rate of contraction, meaning firing of Ia afferents mirrors any irregularities in this trajectory
This info can be used by CNS to compensate for irregularities and smooth movement, fine-tuning the info it receives

102
Q

Why are stretch reflexes weaker and less stereotyped in intact animals that decerebrate animals

A

Descending pathways from higher brain areas are continuously modulating the strength of stretch reflexes to meet the requirements of ongoing action

103
Q

What are synergist musclesq

A

Muscles that control the same joint and inhibit antagonist motor neurons

104
Q

What are the components of muscle tone

A

Intrinsic muscle stiffness, neural, stretch reflex

105
Q

Functions of muscle tone

A

Maintenance of posture, allows muscles to store energy like springs for later release eg in walking, smoothing movement

106
Q

How does muscle tone smooth movement

A

Muscle elasticity smooths out any jerks in movement starts and stops, allowing the muscles to achieve equilibrium length more gradually

107
Q

How are most reflexes able to be modified

A

Most reflex pathways are polysynaptic, with interneurons between the sensory and motor neurons that receive input from multiple sources

108
Q

What is a myotatic unit

A

The group of muscles around a joint linked together by a system of reflex pathways

109
Q

How is reciprocal inhibtion also invovled in voluntary movement

A

It prevents prime mover muscles having to act against the contraction of opposing muscles

110
Q

How does the brain inhibit antagonist muscles during volutnary movement

A

Descending axons from the motor cortex make direct excitatory connectinos to spinal motor neurons AND collaterals to Ia inhibitory interneurons that inhibit antagonist motor neurons

111
Q

What type of interneuron inhibits antagonist muscles during voluntary movement

A

Ia inhibitory interneurons in the spinal cord

112
Q

What type of interneuron inhibits the homonymous msucle during voluntary movement (negative feedback)

A

Ib inhibitory interneurons

113
Q

What do Ia inhibitory neurons in the spinal cord receive input from for modulating joint stiffness

A

Excitatory and inhibitory input from all major descending pathways, allowing the brain to change the balance to control the amount of joint stiffness needed

114
Q

How do Ia inhibitory interneurons coordinate muscle action

A

Control co-contraction aka simltaneous contraction of the prime mover and antagonist muscle, stiffens and stabilises the joint

115
Q

What different sources do Ib inhibitory interneurons receive input from

A

GTOs, Ia afferents from muscle spindles, cutaneous afferents, excitatory/inhibitory descending input

116
Q

What sort of mechanism do the Ib inhibitory interneurons provide by receiving input from GTOs

A

Negative feedback mechanism for regulating muscle tension, parallel to the negative feedback from muscle spindles for regulating muscle length

117
Q

Explain the negative feedback mechanism controlled by Ib inhibitory interneurons in the spinal cord

A

Increased muscle tension-> increased GTO activity-> Ib inhibitory interneurons excited->homonymous motor neurons inhibited-> decreased muscle tension

118
Q

How do converging inputs on Ib inhibitory interneurons allow fine control of exploratory movements

A

eg when the hand contacts an object, muscle force is inhibited by combined activatino of tendon organs and cutaneous afferents, softening contact
Descending pathways can modulate eg enhancing inhibition for a fragile object

119
Q

What is local sign

A

Fixed spatial relationship between the locus of a stimulus and the particular muscles that contract

120
Q

Example of how stimulus quality affects the reflex effect of cutaneous eg foot

A

eg light pressure ->generalised extensor response in whole leg
eg painful stimulus- flexor withdrawal

121
Q

Example of a rhythmic reflex

A

Scratch reflex in furry animals- leg is brought to stimulus for rhythmic scratching, crossed extension reflex maintains the animal’s standing posture

122
Q

How is the scratch reflex unique

A

Fully manifested in animals where the spinal cord had been severed at the cervical level, and still kinda effective when dorsal roots were cut, showing sustained rhythmic alteration of movement doesn’t depend on supraspinal or peripheral input

123
Q

What is the half-centre model

A

Describes how a central neural circuit is organised- interneurons controlling flexor and motor neurons have reciprocal inhibitory connections

124
Q

What are central pattern generators in walking

A

Local spinal circuits that coordinate the contractino of the muscle groups needed to geenrate stepping, allowing automatic locomotion

125
Q

Where are central pattern generators located

A

Innate to spinal circuitry- a cat can still walk on a treadmill if their spinal cord is severed at 1-2 weeks or at the lower thoracic level, suggesting descending input is not needed

126
Q

What is the swing phase in walking

A

When foot is off the ground and flexing forwards

Contraction of flexor muscles

127
Q

What is the stance phase in walking

A

When the foot is planted and the leg is extending relative to the body
Contraction of extensor muscles

128
Q

What is the result of holding a cat’s hind leg on walking

A

The other continues stepping normally in a rhythmic cycle, showing each limb has its own independent pattern generator

129
Q

What is the relationship between central pattern generators in different limbs

A

Pattern generators are coupled during normal locomotion- the movements of L and R hind legs in walking cat are exactly out of phase

Neurophysiology (23 decks)

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