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Neuroscience > L46 Spinal Reflexes > Flashcards

L46 Spinal Reflexes Flashcards

1
Q

Define reflexes

A

predictable stereotyped response to a specific stimulus (specific muscular rnxs to stretch)

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2
Q

Define monosynaptic reflex

A

afferent and efferent limbs are directly connected (deep tendon reflex)

one single synapse

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3
Q

Define polysynaptic reflex

A

afferent and efferent limb are interconnected with one or more interneurons (pupillary light reflex, cutaneous reflex)

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4
Q

what are the components of the reflex arc?

A 
sensory receptor (muscle spindle, golgi tendon organ)
afferent neuron
synapse on efferent neuron (LMN)
NMJ
muscle
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5
Q

what are examples of reflexes

A
  • deep tendon (myotactic) reflex
  • golgi tendon (inverse myotactic) reflex
  • flexion crossed extension reflex
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6
Q

what is the afferent limbs?

A

muscle spindle and Ia fibers
golgi tendon organ and Ib fibers
free nerve endings and Adelta fibers

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7
Q

what make up efferent limbs?

A

alpha motor neuron
homonymous muscle
synergist muscle
antagonist muscle

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8
Q

what is the nature and purpose of the deep tendon reflex?

A

when a muscle is passively stretched, it reflexively contracts
the reflex dictates muscle tone under regulation by UMN

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9
Q

what segments are involved in inspiration using the diaphragm

A

C3,4,5

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10
Q

what segments are involved in shoulder abduction using the deltoid?

A

C5

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11
Q

what segments are involved in elbow flexion involving the biceps brachi and brachialis

A

C5,6

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12
Q

what segments are involved in wrist extension using ECRL and ECRB

A

C6,7

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13
Q

what segments are involved in elbow extension using triceps?

A

C7,8

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14
Q

what segments are involved in finger flexion using FDS and FDP

A

C8

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15
Q

what segments are involved in finger abduction and adduction using interossei

A

C8, T1

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16
Q

what segments are involved in thigh adduction using AL and AB

A

L2,3,4

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17
Q

what segments are involved in knee extension using quads

A

L3,4

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18
Q

what segments are involved in great toe extension using EHL

A

L5, S1

19
Q

what segments are involved in ankle plantar flexion using gastroc and soleus

A

S1,2

20
Q

what segments are involved in anal contraction using sphincter ani externus

A

S2,3,4

21
Q

what is the landmark for the ankle jerk reflex

A

S1

22
Q

what is the landmark for the knee jerk reflex

A

L2,3,4

23
Q

what is the landmark for the biceps and brachioradialis reflex

A

C5,6

24
Q

what is the landmark for the triceps reflex

A

C7

25
Q

describe the scale for reflex testing

A 
pretty subjective...
0 no response
1+ low normal
2+ average normal
3+ high normal
4+ hyperactive with clonus
  • normal responses vary widely within a range
  • differences between sides = DISEASE!
26
Q

define clonus

A

a series of involuntary, rhythmic, muscular contractions and relaxations. They are not like fasciculations because they are not small twitches, they are large motions usually initiated by a reflex

27
Q

the stretch (myotactic) reflex works as a _____ to maintain muscle length at a desires value

A

negative feedback loop

28
Q

what is the function of the gamma motor neurons in the myotactic reflex?

A

Are responsible for contracting the ends of the muscle spindle to keep its length identical to the muscle fibers in an effort to maintain monitoring of the muscle length at all times

29
Q

why are inverse myotactic reflexes slower than myotactic reflexes?

A

because Ib fibers are small diameter and because the inverse myotactic reflex is polysynaptic and myotactic reflex is monosynaptic

30
Q

what is the function of the inverse myotactic reflex?

A

protect muscle and tendon when stimulated constantly

maintain posture

31
Q

Describe the flexion reflex or the “withdrawal reflex”

A

In response to painful (nociceptive) stimuli, causing ipsilateral rapid flexion

a protective mechanism

ipsilateal extensor responses are suppressed

Pain afferents (A-delta and C-fibers) will stimulate
excitatory interneurons (present at each spinal segment) that synapse on alpha motor neurons to flex the necessary muscle
32
Q

describe the flexor crossed extensor reflex

A

The Flexion Reflex is often associated with this Flexion Crossed Extension Reflex in the contralateral limb

This will support the contralateral leg to maintain balance if the flexion reflex causes the ipsilateral leg to lift when you step on a pin

c. SUMMARY
i. Ipsilateral flexor stimulation and extensor inhibition
ii. Contralateral flexor inhibition and extensor stimulation

33
Q

Summary of the flexor crossed extensor reflex

  • ipsilateral flexor _____ and extensor ____
  • contralateral flexor _____and extensor ___
A

stimulation, inhibition

inhibition, stimulation

34
Q

what type of reflex is the plantar reflex?

A

polysynaptic

35
Q

what does a normal adult plantar reflex look like?

A

toes all flex

36
Q

what does an abnormal plantar reflex look like?

A

toes fan out and big toe extends

37
Q

why do newborns to 1 yo have +babinski sign or abormal plantar reflex (toes are fanning)? (non-pathological positive plantar reflex)

A

because their pyramidal (corticospinal) tract is immature and not completely myelinated yet

38
Q

what does a positive babinski sign in adults indicate?

A

cortical, axonal disruptions, demyelination etc.

39
Q

what are causes of hyporeflexia (diminished or absent reflexes)?

A
  • lesion of spinal cord segment
  • leison of the efferent limb (LMN lesion)
  • disease of the NMJ
  • lesion of the muscle
  • peripheral n. lesion
  • lesion of afferent limb (sensory loss)
40
Q

what does hyperreflexia suggest?

A

UMN lesion

clonus confirms it

41
Q

where can UMN damage be located?

A

in motor center (precentral gyrus etc.) or somewhere along motor tracts

42
Q

what does hyperreflexia usually follow

A

spinal shock in spinal cord transections!

43
Q

describe spinal shock

A

acute transection of the spinal cord leads to this

during this period (right after accident), spinal reflexes below the lesion are suppressed and it may take several weeks until spinal reflexes truetn

poorly understood

Neuroscience (54 decks)

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