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Neurology > Spinal Reflexes > Flashcards

Spinal Reflexes Flashcards

1
Q

What are the subdivisions of intrafusal fibres?

A

Nuclear bag fibres = bag 1 (dynamic), bag 2 (static)

Chain fibres

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2
Q

What are the features of bag 1 fibres?

A

Very sensitive to rate of change of muscle length

Innervated by dynamic gamma motor neurons

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3
Q

What are the features of bag 2 fibres?

A

More sensitive to absolute length of muscle

Innervated by static gamma motor neurons

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4
Q

What are some features of chain fibres?

A

Sensitive to absolute length of muscle

Innervated by static gamma motor neurons

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5
Q

What are the two types of afferent fibre that innervate the intrafusal fibres?

A

Ia (Aalpha) fibres and II (Abeta) fibres

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6
Q

How are Ia afferent fibres organised?

A

Form primary annulospinal nerve ending winding around the centre of all intrafusal fibres

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7
Q

How are II afferent fibres organised?

A

Form flowerspray endings on all intrafusal fibres except bag 1 type = more slowly conducting

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8
Q

Do both types of afferent fibres that innervate intrafusal fibres respond to stretch the same way?

A

No = Ia fibres are more sensitive to rate of change of stretch, whereas II fibres are more sensitive to absolute length of intrafusal fibres

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9
Q

What does the Ia afferent fibre respond to?

A

Rate of change of muscle length and absolute length of the muscle

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10
Q

What does stimulation of the static gamma motor neuron cause?

A

Increase of steady state

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11
Q

What does stimulation of the dynamic gamma motor neuron cause?

A

Enhances the dynamic response of the Ia afferent fibre to stretch

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12
Q

What are the only kind of activities that cause static gamma motor neurons to be active?

A

Activities in which muscle length changes slowly and predictably

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13
Q

What behaviours cause dynamic gamma motor neurons to be active?

A

Behaviours in which muscle length changes rapidly and unpredictably

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14
Q

What do dynamic and static gamma motor neurons form?

A

A fusimotor system

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15
Q

Where are golgi tendon organs located?

A

At the junction of muscle and tendon = in series with extrafusal fibres

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16
Q

What is the function of golgi tendon organs?

A

Monitor changes in muscle tension = act to regulate muscle tension to protect from overload and keep within optimal range

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17
Q

What are golgi tendon organs innervated by?

A

Groub Ib sensory afferents = myelinated, slightly slower conducting than Ia fibres

18
Q

Where do group Ib afferents synpase once they enter the spinal cord?

A

Upon inhibitory interneurons which in turn synapse upon alpha motor neuorns of the homonymous muscle = forms basis of reverse myotatic reflex

19
Q

What does the reverse myotatic reflex involve?

A

Polysynaptic pathway = inhibitory neuron is interposed between the Ib afferent and alpha motor neuron

20
Q

What is the reverse myotatic reflex important in?

A

Execution of fine motor acts

21
Q

Where are proprioceptive axons located?

A

In the connective tissue of joints

22
Q

What do proprioceptive axons respond to?

A

Changes in angle, direction and velocity of movement of a joint = also prevent excessive flexion or extension

23
Q

What are proprioceptive axons a mix of?

A

Fast adapting and slowly adapting units that have either high threshold or low threshold for activation

24
Q

What are examples of endings of proprioceptive axons?

A

Free nerve endings, golgi type endings, Paciniform endings, Ruffini endings

25
Q

What are some features of free nerve endings of proprioceptive axons?

A

Found in capsule and connective tissue
Most numerous
High threshold and slowly adapting
Nocicepetive function

26
Q

What are some features of golgi type endings of proprioceptive axons?

A

Found only in ligaments
High threshold and slowly adapting
Protective role

27
Q

What are some features of Paciniform endings on proprioceptive axons?

A

Found in periosteum near articular attachments and fibrous part of joint capsule
Low threshold and slowly adapting
Acceleration detectors

28
Q

What are some features of Ruffini endings on proprioceptive axons?

A

Found mainly in joint capsule
Low threshold and slowly adapting
Static position and speed of movements

29
Q

Where does proprioceptive info arise from?

A

Muscle spindles, golgi tendon organs and joint receptors

30
Q

Where do spinal interneurons receive input from?

A

Primary sensory axons, descending axons from the brain, collaterals of LMN and other interneurons

31
Q

What types of input can spinal interneurons receive?

A

Excitatory or inhibitory

32
Q

What is the function of spinal interneurons?

A

Integrate incoming info to generate an output

33
Q

What is the function of inhibitory interneurons?

A

Mediate inverse myotatic response and reciprocal inhibition between extensor and flexor muscles

34
Q

What is the myotatic reflex an example of?

A

Reciprocal inhibition

35
Q

What occurs in the myotatic reflex?

A

Causes homonymous extensor muscle to contract but also causes simultaneous relaxation of antagonist flexor muscle

36
Q

What is the innervation of the myotatic reflex?

A

Ia afferent from muscle spindle extensor makes excitatory monosynaptic contact with alpha motor neuron innervating the homonymous muscle

37
Q

How does the Ia afferent fibre inhibit the alpha motor neuron that supplies the flexor muscle in the myotatic reflex?

A

Via polysynaptic pathways involving interneurons

38
Q

What is reciprocal inhibition important in?

A

Initiation of movement by the motor cortex

39
Q

What do excitatory interneurons mediate?

A

The flexor reflex and crossed extensor reflex

40
Q

What is the flexor reflex?

A

Noxious stimulus causes limb to flex by contraction of flexor muscles via exicitatory interneurons, and relaxation of extensor muscles via excitatory and inhibitory interneurons

41
Q

What is the crossed extensor reflex?

A

Noxious stimulus causes limb to extend by contraction of extensor muscles via excitatory interneurons, and relaxation of flexor muscles via excitatory and inhibitory interneurons

42
Q

What does the crossed extensor reflex enhance?

A

Postural support during withdrawl of a body part from painful stimulus

Neurology (48 decks)

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