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Yr 2 - Control > Spinal Reflexes > Flashcards

Spinal Reflexes Flashcards

1
Q

Upper and lower motor neurons diagram:

A
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2
Q

What is a reflex arc?

A

A fast, predictable automatic response to a change in the environment or a stimulus.

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3
Q

Reflex arcs have five functional components. What are these?

A
  1. Sensory receptor; fires action potential upon stimulus
  2. Sensory afferent neuron; carries AP to spinal cord (cell body in dorsal root ganglion)
  3. Integration centre; relays sensory to motor
  4. Motor neuron; lower motor neurons in ventral horn of spinal cord send their efferent axons to effector organ
  5. Effector organ (muscle/gland)
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4
Q

What is a monosynaptic reflex?

A

1 synpase involved (between sensory and motor); rapid

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5
Q

What is a polysynaptic reflex?

A

2 or more synapses (involves interneuron), slower but more complex

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6
Q

What is the myotatic stretch reflex?

A

Muscle contraction, in response to stretching (change of length) within the muscle

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7
Q

For the myotatic stretch reflex;

  • what is the receptor (that senses a change in length of muscle)?
  • what are the functions of this reflex?
A
  • receptor; muscle spindle
  • functions:
    • Antigravity
    • Posture
    • Movement
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8
Q

What do muscle spindle receptors detect?

A

Muscle spindles are skeletal muscle sensory receptors within the body of a muscle that primarily detect changes in the length of this muscle (stretch) –> providing axial and limb position information to the central nervous system

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9
Q

What type of reflex is the ‘patellar tap reflex’ an example of?

A

Myotatic stretch reflex

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10
Q

Describe the patellar tap reflex steps

A
  1. Patellar/quadriceps tendon is tapped; causing stretch of quadriceps muscle
  2. Muscle spindle receptors sense change in stretch (activation of muscle spindle) and increase firing of 1a afferent fibres to spinal cord (via dorsal horn)
  3. Afferent terminals synapse directly with and excite the alpha motor neuron (in ventral horn of spinal cord) –> this is a monosynaptic reflex
  4. Increased alpha motor neurone efferent axon activity
  5. Contraction of the agonist homonymous muscle (effector muscle) i.e. muscle from which afferent arose
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11
Q

What are 1a afferent fibres?

A

Sensory afferent fibre coming from muscle spindles

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12
Q

Is the patella tap reflex mono or polysynaptic?

A

Monosynaptic

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13
Q

Purpose of the patellar tap reflex test?

A
  • Assess the nervous tissue between and including the L2 and L4 segments of the spinal cor
  • Assess the integrity of the muscle spindle/1a afferent fibres/efferent fibres
  • Assess integrity of neurological function
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14
Q

is the patellar tap reflex ipsilateral or contralateral?

A

Ipsilateral; same leg that we tap that sends fibres to same side of spinal cord that will send fibres to same leg

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15
Q

What is reciprocal inhibtion?

A

Reciprocal inhibition describes the relaxation of muscles on one side of a joint to accommodate contraction on the other side.

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16
Q

Describe the antagonist response during the patellar tap reflex (i.e. reciprocal inhibition)

A
  1. Tapping the patellar tendon activates the 1a afferent and leads to:
    1. Direct excitation of the motor neurones innervating agonist (extensor) muscle groups –> causing jerk
    2. Indirect inhibition via the 1a inhibitory interneuron of motor neurones innervating antagonist (flexor) muscle groups –> In order to decrease the activity of the alpha motor neuron that is going towards hamstring muscle (i.e. decreased firing on flexor/antagonist muscle)
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17
Q

Purpose of the antagonist response in the patellar tap reflex?

A

In order to decrease the activity of the alpha motor neuron that is going towards hamstring muscle (i.e. decreased firing on flexor/antagonist muscle)

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18
Q

Difference in pathway between agonist and antagonist response of patellar tap reflex (i.e. monosynaptic or polysynaptic)?

A

Agonist –> monosynaptic (no interneuron)

Antagonist –> polysynaptic (interneuron present)

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19
Q

How is the myotatic stretch reflex used during the addition of a load? e.g. carrying an increasingly heavy tray

A
  • If an additional load is added, the muscle recognises the stretch immediately and can compensate with a stronger contraction.
  • This also protects the inhibited antagonist muscles from being injured from excessive stretching.
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20
Q

Describe the pathway during an addition of a load; arm muscle groups

N.B. mention antagonist AND agonist

A

Addition of load leads to:

  1. Stretch of the flexor biceps brachii and activation of the 1a afferent fibres
  2. Direct excitation of agonist (flexor) muscle groups (biceps)
  3. Indirect inhibition via the 1a inhibitory interneuron of antagonist (extensor) muscle groups (triceps brachii)
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21
Q

What type of stretch is involved in holding a tray of an increasing load?

A

Myotatic stretch reflex

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22
Q

What is the inverse myotatic (Golgi tendon) stretch reflex?

A

Controls the tension of an active muscle, in response to muscle contraction to avoid tendon damage

23
Q

For the inverse myotatic (Golgi tendon) stretch reflex;

  • What is the receptor?
  • Function?
A
  • Receptor; Golgi tendon organ
  • Functions:
    • Tension feedback
    • Overload protection
24
Q

What is a Golgi tendon organ?

A
  • a proprioceptive sensory receptor organ that senses changes in muscle tension
  • it lies at the origins and insertion of skeletal muscle fibres into the tendons of skeletal muscle.
25
Q

Describe the inverse myotatic (Golgi tendon) pathway

A
  1. Golgi tendon organ receptors detect increased tension –> excitation
  2. Increased firing of 1b afferent fibres
  3. Indirect inhibition via an inhibitory interneuron of the alpha motor neurons (as want decreased activation - inverse myotatic)
  4. Decreased alpha motor neuron activity to homonymous muscle (effector muscle)
  5. Result: relaxation/inhibition of homonymous muscle
26
Q

Example of inverse myotatic (Golgi tendon) reflex pathway; leg muscle groups

A

If tension on quadriceps is too much (e.g. in gym):

  • Golgi tendon organ receptor is activated and sends 1b afferent fibres to spinal cord
  • Via inhibitory interneurons, there is a decrease in the activity of the lower motor neurons going to the quadriceps
    • Indirect inhibition via an inhibitory inter-neurone of motor neurones, innervating the homonymous muscle and relaxation
  • BUT simultaneously; there is indirect excitation of motor neurons innervating antagonist muscle groups (hamstrings)
    • As quadriceps are relaxing, hamstrings need to contract

N.B. both of these pathways are indirect (require interneurons)

27
Q

When would the inverse myotatic (Golgi tendon) reflex kick in?

A

To protect a muscle that is under an increased amount of tension (protective reflex)

28
Q

What is the crossed extensor/flexor withdrawal reflex?

A

Flexor withdrawal: Mediates the flexion of the limb that comes into contact with the noxious stimuli

Crossed extensor: A reflex in which the contralateral limb compensates for loss of support when the ipsilateral limb withdraws from painful stimulus in a withdrawal reflex. E.g. when one foot steps on a nail, the crossed extensor reflex shifts the body’s weight onto the other foot, protecting and withdrawing the foot on the nail.

  • Noxious (harmful/unpleasant) cutaneous stimulation causes flexion withdrawal from the offending stimulus.
  • Simultaneous extension of contralateral limb (crossed extensor) may occur for weight bearing.
29
Q

Function of the crossed extensor/flexor withdrawal reflex?

A
  • Damage limitation of avoidance
  • Maintained balance on limb withdrawal
30
Q

Describe sequence of events on activation of the cutaneous nociceptor e.g. stepping on nail

A
  1. Cutaneous nociceptor (pain receptor) detects noxious stimulus –> activation
  2. Increases firing of A-delta and C afferents; enter dorsal horn of spinal cord
  3. Interneurons then synapse with lower motor neurons which do 2 things:
    1. activate the ipsilateral flexors –> can flex at knee and withdraw foot from stimulus
    2. inhibit the ipsilateral extensors –> antagonist
  4. Some interneurons then cross the midline to synapse with lower motor neurons which do 2 things:
    1. inhibit the contralateral flexors –> antagonist
    2. activate the contralateral extensors –> weight-bearing on other leg (maintain balance)

N.B. these receptors are polysynaptic

31
Q

What are 1b afferent fibres?

A

Golgi tendon organ receptor, responds to muscle tension changes

32
Q

Summary of main spinal reflexes; fill in the table

A
33
Q

What are ‘alpha’ motor fibres?

A

The alpha motor neuron (AMN) innervates the main fibers that cause muscle contraction.

34
Q

Which muscle is the agonist in the patellar tap reflex?

A

Quad –> extensor

35
Q

Which muscle is the antagonist in the patellar tap reflex?

A

Hamstring (flexor)

36
Q

What is the agonist muscle during addition of load when carrying a heavy tray?

A

Flexor biceps brachii

37
Q

What is the antagonist muscle during addition of load when carrying a heavy tray?

A

Triceps brachii

38
Q

Is the antagonist pathway in the patellar reflex mono or polysynaptic?

A

Polysynaptic

39
Q

What is the receptor in the patellar tap reflex?

A

Muscle spindle

40
Q

What is the receptor in the addition of load reflex?

A

Muscle spindle

41
Q

What is the receptor in the inverse myotatic stretch reflex?

A

Golgi tendon organ

42
Q

What is the receptor in the crossed extensor/flexor withdrawal reflex?

A

Nociceptors

43
Q

Which afferent fibres are involved in the Crossed Extensor/Flexor Withdrawal Reflex?

A

A-delta and C pain fibres

44
Q

Which afferent fibres are involved in the inverse myotatic stretch?

A

1b afferent fibres

45
Q

Which afferent fibres are involved in the patellar tap reflex?

A

1a afferent fibres

46
Q

What does the myotatic stretch reflex regulate?

A

muscle length

47
Q

What does the inverse myotatic stretch regulate?

A

muscle force

48
Q

What is the desired outcome of the Golgi tendon reflex?

A

Relaxation of homonymous muscle

49
Q

What spinal levels are being tested in the biceps reflex?

A

C5/C6

50
Q

What spinal levels are being tested in the bracioradialis reflex?

A

C6

51
Q

What spinal levels are being tested in the extensor digitorum reflex?

A

C6/C7

52
Q

What spinal levels are being tested in the triceps reflex

A

C6-C8

53
Q

What spinal levels are being tested in the patellar reflex?

A

L2-L4

54
Q

What spinal levels are being tested in the Achilles reflex?

A

S1/S2

Yr 2 - Control (71 decks)

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