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Neuroanatomy Exam 1 > Spinal Reflexes > Flashcards

Spinal Reflexes Flashcards

1
Q

Lower motor neuron cell bodies reside in

A

ventral horn of spinal cord

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2
Q

Lower motor neuron axons run in

A

peripheral nerves that terminate in skeletal muscle

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3
Q

Relexes involve what kind of neurons

A

alpha motor and gamma motor neurons

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4
Q

Alpha motor neurons

A

Largest neurons residing in ventral horn of spinal cord
Innervate typical skeletal muscle fibers (extrafusal) which when stimulated cause contraction of the gross muscle to produce movement

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5
Q

Gamma motor neurons

A

Smaller neurons in the ventral horn of spinal cord

Inenrvate the contractile (polar) portions of intrafusal fibers enclosed within muscle spindles

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6
Q

Reflex Definition

A

a simple stereotyped response to a specific sensory stimulus

  • Involuntary
  • Protective
  • Confined to spinal cord (nonconcious)
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7
Q

Reflex consists of:

A
  1. Receptor
  2. Afferent limb
  3. Interneuron
  4. Efferent limb
  5. Effector
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8
Q

Receptor

A

in skin, skeletal muscle, tendon, or joint capsule

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9
Q

Afferent Limb

A

formed by sensory (pseudounipolar) neuron whose cell body is housed in DRG
Peripheral process is in skin, skeeltal muscle, tendon or joint capsule
Central process synapses in spinal cord gray metter

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10
Q

Interneurons

A

may or may not be a component of the reflex arc

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11
Q

Efferent limb

A

formed by motor neuron whose cell body is usually located in the ventral horn of spinal nerve
Axon synapses in skeletal muscle

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12
Q

Effector

A

skeletal muscle that responds to stimulus

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13
Q

Reflexes can be

A

Intrasegmental
Intersegmental
Suprasegmental

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14
Q

Intrasegmental

A

involve or affect only a single spinal cord level

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15
Q

Intersegmental

A

involve or affect numerous spinal cord levels

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16
Q

Suprasegmental

A

are influenced by neurons residing in cerebral hemisphere or brainstem and through their connections influence reflex activity occuring at the spinal cord level

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17
Q

Biceps reflex

A

C5 C6

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18
Q

Triceps reflex

A

C6 to C8

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19
Q

Quadriceps Reflex

A

L2 to L4

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20
Q

Gastrocnemius Reflex

A

S1 to S2

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21
Q

Muscle Stretch Reflex

A

consists of 2 neurons (one sensory and one motor)

May be elicited by tapping a large tendon

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22
Q

Ex of muscle stretch reflex

A

Quadriceps stretch reflex (patellar tendon)

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23
Q

Tapping of the patellar tendon does what

A

Displaces the patella slightly which then stratches the extrafusal fibers and also stretches the muscle spindles of the quadriceps muscle

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24
Q

Receptors in patellar tendon reflex =

A

muscle spindles that are mebedded in the muscle

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25
Q

Muscle stretch will trigger

A

the sensory endings on intrafusal fibers to fire

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26
Q

The central process (axon) will synapse with

A

alpha motor neuron and stimulates in
reflex is monosynaptic
Quad will contract slightly causing extension of the leg at the knee joint
Reflex induced contraction

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27
Q

What does the muscle stretch reflex compensate for

A

muscle stretch

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28
Q

What does the muscle stretch reflex protect

A

the muscle fibers from overstretching

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29
Q

Reciprocal Inhibition

A

An extension of and enhances the stretch reflex

30
Q

Receptor in reciprocal inhibition

A

muscle spindle at peripheral end of a fiber

31
Q

In reciprocal inhibiton central process of sensory neuron…

A

bifurcates
One branch forms excitatory synapse with an alpha mtoor neuron (stimulates quad to contract)
Other branch forms excitatory synapse with inhibitory interneuron which inhibits another alpha motor neuron that innervates the hamstring muscle

32
Q

So how does the reciprocal inhibition work?

A

As one muscle is stimulated to compensate for the stretch, another muscle is simultaneously inhibited

33
Q

Autogenic Inhibition

A

Enhances the stretch reflex to prevent overcontraction

34
Q

Receptor with autogenic inhibition

A

GTO
When quad contracts, it exerts tension on its tendon which in turn stretched and activates the GTOs
Muscle contraction triggers the sensory endings innervating tendons to fire

35
Q

When sensory neurons peripheral process innervating the tendon is activated,

A

the central process stimulated an inhibitory interneuron which will inhibit an alpha motor neuron that innervated the quad

36
Q

What does autogenic inhibtion limit

A

muscle overcontraction

37
Q

What does autogenic inhibition protect

A

tendon

38
Q

Stimulation of GTO plays a role in

A

muscle relaxation

39
Q

Flexor Reflex

A

Withdrawal, Nociceptive

40
Q

Receptors for flexor reflex

A

cuteneous

lightly myelinated Adelta fibers or unmyelinated C fibers of sensory neurons whose cell bodies are in DRG

41
Q

Peripheral process of flexor reflex is located in

A

skin or in subcutaneous connective tissue

42
Q

Stimulus with flexor reflex is

A

painful or causes tissue injury

43
Q

The flexor reflex occurs in the

A

affected limb

44
Q

Central process in flexor reflex enters

A

dorsolateral tract where it branches into short ascedning and short descending fibers and they form excitatory synapses with interneurons in gray matter of the spinal cord

45
Q

The ___ interneurons synapse with the alpha motor neurons that innervate ___ muscles of the lower lib, stimulating their ___ and withdrawal of the lower limb

A

Excitatory
Flexor
Contraction

46
Q

The ____ interneurons synapse with the alpha motorneurons that innervate the ___ of the same limb to inhibit them causing _____

A

Inhibitory
Extensors
Relaxation

47
Q

Flexor reflex involves how many spinal cord levels

A

many

48
Q

Crossed Extension Reflex Receptors

A

Cutaneous

Lightly myelinated A delta of unmyelinated C fibers

49
Q

When would the crossed extension reflex happen?

A

When standing or walking and one of the limbs contacts a noxious stimulus

50
Q

The crossed extension reflex occurs in which limb?

A

the unaffected limb so that the weight of the body can be shifted

51
Q

The crossed extension reflex involves

A

commissural interneurons whose axons cross the midline to synapse with excitatory and inhibitory interneurons located in the ventral horn of the spinal cord on the opposite side

52
Q

What does the excitatory interneuron do in crossed extension reflex

A

stimulates an alpha motor neuron that causes contraction of the limb extensors

53
Q

What does the inhibitory interneuron do in crossed extension reflex

A

inhibits an alpha motor neuron that innervates the limb flexors

54
Q

Muscle tone

A

tension created by variable contraction of skeletal muscle fibers

55
Q

Muscle tone results from

A

stimulation of gamma motor neurons and the stretch reflex

56
Q

Gamma motor neurons are a component of

A

gamma loop and are associated with maitenece of muscle tone

57
Q

Gamma motor neurons are under ___ control

A

supraspinal

NOT under control of the sensory fibers innervating the intrafusal fibers

58
Q

There are no signals relayed back from the muscle spindles to the gamma motor neurons

A

say it :)

59
Q

Gamma motor neurons stimulate

A

polar (contractile) portions of the intrafusal fibers –> they contract –> pull away from midline –> stretching the central (nonctractile region) of intrafusal fibers –> annulospiral endings of the Ia sensory fibers are stretched and fire

60
Q

The central processes of Ia fibers enter the spinal cord and synapse with

A

alpha motor neurons that innervate the skeletal muscle (extrafusal fibers)

61
Q

Stimulation of gamma motor neurons does what

A

increases muscle tone

62
Q

Inhibition of gamma motor neurons does what

A

decreases or inhibits muscle tone

63
Q

Antigravity muscles do what

A

neutralize the effect gravit has on the body so that we are able to stand upright

64
Q

The gamma loop includes what 5 components

A
  1. Gamma motor neurons
  2. Intrafusal fibers
  3. Ia fibers
  4. Alpha motor neurons
  5. Extrafusal fibers
65
Q

Alpha Gamma co-activation

A

during voluntary movement, the axons of descending motor tracts converge on both alpha and gamma motor neurons to simulate simultaneously

66
Q

Stimulation of the alpha motor neurons cause

A

the extrafusal fibers of the gross muscle to contract and simultaneously the stimulation of the gamma motor neurons cause the polar (contactile) ends of the intrafusal fibers to contract

67
Q

Alpha Gamma co activation is a way via which

A

as the length of the gross muscle changes during voluntary movement (stimulation of alpha) there is a corresponding adjustment of intrafusal fibers (via gamma) so that the muscle spindles sensitivity to stretch is maintained regardless of muscle length

68
Q

Muscle spindles are

A

stretch receptors that must detect changes in muscle length at all times

69
Q

As a gross muscle contracts, it becomes

A

shorter

but there is no corresponding shortening of muscle spindles

70
Q

During voluntary movement the ____ modulates the sensitivity of the intrafusal fibers

A

alpha gamma coactivation

71
Q

Alpha gamma coactivation 4 steps

A
  1. Gamma motor neurons stimulate the polar ends of the intrafusal fibers
  2. Polar ends contract, pulling away from the middle of the intrafusal fibers
  3. Stretched the central (non contractile) portion of intafusal fibers
  4. The stretching keeps the central part of the intrafusal fibers tight so even the slightest additional stress placed on it when the gross muscle stretches from the contracted side, will stimulate the sensory fibers
72
Q

Lesion involving alpha and gamma motor neurons would result in

A
  1. Flaccid paralysis (muscles limp and can’t contract)
  2. Atrophy
  3. Hypotonia (reduced tone)
  4. Hyporeflexia (dminished reflexes) or Areflexia (absence of reflexes)

Neuroanatomy Exam 1 (9 decks)

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