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Neurophysiology Loyola > Reflexes & Gait > Flashcards

Reflexes & Gait Flashcards

1
Q

What are the 2 main sensors involved in muscle sensation?

A

Muscle spindle (senses length), which will activate the alpha motor neuron; Golgi tendon organ (senses force or contraction), which inhibits the alpha motor neuron

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2
Q

What are the components of the reflex circuit?

A
  1. Receptor
  2. Afferent (sensory) nerve fiber
  3. Interneuron
  4. Efferent (motor) nerve fiber
  5. Effector organ
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3
Q

What are the components of the myotatic reflex?

A

Primary sensory endings Ia afferent fibers innervate the sensors called muscle spindles and detect rate + amount of stretch; secondary sensory endings type II fiber detects the amount of stretch

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4
Q

What is the function of the myotatic reflex?

A

To correct for unexpected loads

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5
Q

What is the effect of the myotatic reflex on homonymous muscles?

A

Muscle contraction that opposes the original stretch

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6
Q

What is the effect of the myotatic reflex on synergistic muscles

A

Activation of synergistic muscle to aid in the muscle contraction that opposes stretch

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7
Q

What is the effect of the myotatic reflex on antagonist muscles

A

Inhibition of antagonist muscles via glycinergic interneuron Ia ii inhibition of alpha motor neuron that goes to the antagonist muscle

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8
Q

Define reciprocal inhibition

A

Type 1a fiber activation of an alpha-MN resulting in the contraction of homonymous and synergistic muscles + inhibition of antagonistic muscle via interneurons (1a inhibitory neurons OR Ia ii)

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9
Q

Define recurrent inhibition

A

RC inhibition returns to the motor neuron that opposes the action of the muscle that resulted in the excitation of the RC;

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10
Q

What is the function of Renshaw cells (RC)

A

Renshaw cells are small MNs in the ventral horn that are excited by ACh release by axon collaterals of alpha-MNs; upon activation, RC axons release inhibitory glycine

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11
Q

How do gamma-MNs function

A

Will slack when alpha-MNs are activated, making it so that no further signaling can occur; normal movement requires the co-activation of both alpha and gamma -MNs

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12
Q

What is the gamma loop

A
  1. Gamma-MN activation conrtacts the polar region of intrafusal muscle
  2. Contraction stretches equatorial region by pulling ends
  3. Stretch of intrafusal fiber activates 1a afferents, exciting alpha-MNs innervating homonymous muscle
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13
Q

Give examples of multisegmental reflexes

A

Moro reflex, which is stimulated by sudden movement of the head backwards and results in a reflexive wide abduction of the arms and rapid breath intake + flexion of the legs (normal in infants <6 months of age)

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14
Q

What elicits the M wave on an EMG recording

A

High stimulation intensity and moderate stimulation intensity; does not occur under low stimulation intensity

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15
Q

What elicits the H reflex on an EMG recording?

A

Results from low stimulus intensity as well as moderate stimulus intensity; does not occur when there is high stimulation intensity

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16
Q

What do central pattern generators do?

A

Produces semi-automatic movements like walking, running, chewing

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17
Q

Where does central pattern generation occur

A

Spinal cord and brain stem

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18
Q

How is central pattern generation initiated (from which region)?

A

External trigger initiates it to arise from the mesencephalic locomotor region; increase output to increase speed of a slow walk to a sprint

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19
Q

What part of the muscle sensor system do gamma motor neurons modulate?

A

Muscle spindle

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20
Q

Where are muscle sensors located?

A

Between the ligament/tendon and the muscle

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21
Q

Why do spindles sense stretch?

A

They’re trapped in parallel

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22
Q

What is the simplest reflex?

A

Myotatic reflex

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23
Q

What is the only monosynaptic reflex in humans?

A

Myotatic reflex

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24
Q

What does the myotatic reflex look like on a physical exam?

A

Knee-jerk/patellar reflex

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25
Q

What are the steps of the myotatic reflex, starting with stimulation of the patellar tendon and ending with the leg kick (8 steps)

A
  1. Stimulate patellar tendon
  2. Quadriceps muscle stretches
  3. 1a & II afferent fibers of femoral nerve activated via muscle spindle
  4. Signal travels to spinal cord (L4)
  5. Cross the mono-synapse
  6. Stimulate the alpha motor neuron to the quadriceps muscle
  7. Contraction of the quadriceps (simultaneous inhibition of the flexor muscle)
  8. Leg kick
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26
Q

How fast is the myotatic reflex?

A

50 ms

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27
Q

Describe the central region of the intrafusal fibers

A

Lacks contractile proteins (doesn’t contract) and is innervated by the 1a fibers; type II fibers innervate the ends

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28
Q

Where are the contractile proteins of the intrafusal fibers contained?

A

The ends, which are innervated by the gamma (efferent) fibers as well as the type II fibers

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29
Q

What is the muscle spindle

A

A capsule containing intrafusal fibers

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30
Q

When does the muscle spindle stretch passively?

A

When the whole muscle (extrafusal) is contracted

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31
Q

Do intrafusal fibers contribute to the force of contraction?

A

NO

32
Q

How are muscle spindles oriented relative to the extrafusal fibers?

A

Parallel

33
Q

Are there more extrafusal fibers or more muscle spindles?

A

More muscle spindles

34
Q

Which fibers detect stretch?

A

Ia sensory fibers

35
Q

Which part of the fiber do gamma motor neurons innervate

A

polar regions

36
Q

What is the function of gamma motor neurons

A

To contract the fiber (stretching it as a result)

37
Q

Normal function of a muscle needs coactivation of which motor neurons?

A

Alpha and gamma

38
Q

What does Golgi tendon organ activation do?

A

Inhibit contraction

39
Q

How many synapses does the GTO reflex have?

A

2 (disynaptic)

40
Q

How is the GTO activated?

A

Via muscle contraction or tension (force), located in a capsule by the tendon

41
Q

Which fibers are involved with the GTO reflex?

A

It depends on Ib afferent fibers that activate an inhibitory (glycinergic) interneuron, which will inhibit homonymous and synergistic muscles via their alpha-MNs

42
Q

What is the inverse of the myotatic reflex?

A

The GTO reflex opposes and terminates the myotatic reflex’s function

43
Q

What is the impact of RC inhibition of Ia ii inhibitory interneurons?

A

disinhibition of MNs to the antagonistic muscles (rapidly inhibits contraction, terminates alpha-MNs, and produces a brief contraction)

44
Q

What condition may result from recurrent inhibition?

A

Tetanus

45
Q

What is the effect of forebrain damage on gamma-MNs?

A

Brainsteam gamma-MNs postural activation of extensor muscles takes over, producing spasticity

46
Q

How does activation of gamma-MNs alone cause muscle contraction?

A

Via indirect excitation of alpha-MNs

47
Q

Define multi-segmental reflexes

A

Reflexes that involve more than one segment of the spinal cord, coordinates muscles at different spinal cord levels; postural

48
Q

What coordinates the Moro reflex?

A

Fasciculus proprius

49
Q

Bilateral Moro dysfunction is indicative of what?

A

brain damage, spinal cord damage

50
Q

unilateral Moro reflex dysfunction is indicative of what?

A

Clavicle damage, birth trauma (brachial plexus damage AKA Erb Duchenne Palsy, hemiplegia)

51
Q

Describe the tonic neck reflex

A

Rotation of the head to one side elicits extension of the ipsilateral arm and flexion of the contralateral arm

52
Q

persistence of the tonic neck reflex (TNR) past 4 months is predictive of what?

A

Poor motor development

53
Q

What is the effect of a lower motor neuron injury on a reflex?

A

Decreases its strength

54
Q

What is the effect of an upper motor neuron injury on a reflex?

A

Increases its strength

55
Q 
What do the following grades in describing reflexes mean?
0
1+
2+
3+
4+
A 
0 - absent
1+ - hypoactive
2+ - normal
3+ - hyperactive without clonus 
4+ - hyperactive with clonus
56
Q

What is the oscillatory motor response to muscle stretch in Hz?

A

3-7 Hz

57
Q

What causes clonus?

A

A lack of normal cortical inhibition of a deep tendon reflex, resulting in rapid, strong, oscillating muscular contractions

58
Q

When does clonus occur?

A

Whern there is sustained tension placed on one of the muscles controlling a joint, like the wrist or ankle

59
Q

What is the normal Babinski reflex?

A

Toe flexion

60
Q

What is a positive Babinski’s sign?

A

Toes extend and separate, this is abnormal and indicates an upper motor neuron lesion affecting the lower extremity in question

61
Q

What often accompanies a positive babinski’s sign

A

Spastic hypertonia

62
Q

The clasp-knife reflex is an example of _____________

A

interneuron release of spasticity

63
Q

What is the clasp-knife reflex?

A

Gradual muscle stretch leads to reflex resistance, followed by muscle extension at a critical length. There is brief excitation followed by a powerful, long-lasting inhibition of homonymous and synergistic muscles

64
Q

Which mechanoreceptors are overactive in the clasp-knife reflex

A

group II and group IV mechanoreceptors; central effects pronounced because of reduced descending inhibition of segmental interneurons

65
Q

How is hyporeflexia related to the myotatic reflex?

A

Hyporeflexia is an abnormal decrease in myotatic reflex

66
Q

What may be the cause of hyporeflexia?

A

Lesion of sensory input from muscle spindles; a motoneuron lesion to the anterior horn of the spinal cord

67
Q

What are the clinical outcomes of hyporeflexia

A

Peripheral neuropathy, Guillain-Barre, muscular dystrophy, myasthenia gravis

68
Q

What happens in an EMG recording when there is low stimulus intensity?

A

AP travels orthodromically, excites an alpha-MN, which travels to the muscle, causing contraction resulting in the H reflex

69
Q

What happens in an EMG recording when there is high stimulation intensity?

A

All fibers are activated, all antidromic signals collide with orthodromic signals and cancel out; only the M response will be observed

70
Q

Do central pattern generators depend on sensory feedback from the periphery?

A

NO

71
Q

What is the crossed extensor reflex/nociceptive withdrawal

A

A polysynaptic reflex that involves contralateral activation/inhibition of muscle groups opposite to those innervated on the ipsilateral side of the spinal cord: muscle groups excited on one side are inhibited on the opposite side

72
Q

What is the function of the crossed extensor reflex/nociceptive withdrawal

A

Allow for body weight support on the opposite leg of a withdrawal reflex; supports alternating leg muscle activation on the opposite side of the body during walkng/running

73
Q

Do central pattern generators require supraspinal input or peripheral feedback?

A

NO, neither are required

74
Q

Gait arises from ___________

A

spinal circuits

75
Q

Central pattern generator of the spinal cord generates _____________

A

rudimentary pattern = fundamental leg stride pattern

Neurophysiology Loyola (7 decks)

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