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PT 631 Neuroanatomy > Lower Motor Neurons and Spinal Reflexes > Flashcards

Lower Motor Neurons and Spinal Reflexes Flashcards

1
Q

where does voluntary movement begin

A

anterior part of frontal lobe (primary motor cortex)

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2
Q

where does primary motor cortex receive sensory information from to create voluntary movement

A

posterior parietal cortex and sensory association areas

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3
Q

what are the motor planning areas

A

premotor and supplemental motor cortices

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4
Q

control circuits from _____ and _____ compare and provide additional information to regulate the motor plan via input to extrapyramidal tracts

A

cerebellum and basal ganglia

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5
Q

the primary motor cortex initiates the motor plan carried by the corticospinal/corticobulbar tracts to where

A
  • motor cranial nerve nuclei in brainstem
  • LMN in ventral horn of spinal cord
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6
Q

simultaneously while primary motor cortex is sending motor plan down the corticospinal/bulbar tracts, _______ carry information to the LMN to modify the motor plan

A

extrapyramidal tracts

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7
Q

_______ (spinal efferents) carry the motor plan to the skeletal muscles

A

ventral rami

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8
Q

where does the synapse occur allowing the result in motor unit response (contraction, relaxation, resting tone)

A

neuromuscular junction

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9
Q

where are cell bodies of UMN found

A

cerebral cortex, basal ganglia, cerebellum

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10
Q

axons descend from cerebral cortex or brainstem to the spinal cord

A

UMN

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11
Q

what do UMN affect

A
  • LMN (alpha motor neurons)
  • interneurons indirectly through extrapyramidal tracts
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12
Q

where do extrapyramidal tracts synapse

A

lamina 8 (interneurons)

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13
Q

where are cell bodies of LMN found

A

ventral rami of spinal cord

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14
Q

axons are nerves that extend to the periphery

A

LMN

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15
Q

excite or inhibit striated skeletal muscles

A

LMN

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16
Q

_____ receives afferent (sensory) input from skin, joints and muscles of trunk and limbs and transmits to brainstem, cerebellum, and thalamus (lamina 1-5)

A

dorsal horn

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17
Q

what is white mater made of

A
  • ascending tracts (sensory tracts)
  • descending tracts (pyramidal and extrapyramidal)
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18
Q

what contains LMN with axons that exit the spinal cord to skeletal muscles

A

ventral horn (lamina 8 and 9)

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19
Q

what communicates with ventral horn neurons to mediate reflex responses and pass on information from extrapyramidal tracts to influence voluntary motor responses

A

interneurons (lamina 10)

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20
Q

what do lateral descending tracts influence

A

flexor tone

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21
Q

what do anterior descending tracts influence

A

extensor tone

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22
Q

cell bodies in ventral horns are clustered into

A

motor neuron pools

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23
Q

cell bodies in ventral horn that innervate axial and proximal muscles

A

medial motor pool

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24
Q

cell bodies in ventral horn that innervate distal muscles

A

lateral motor pool

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25
Q

cell bodies in ventral horn that innervate extensors

A

anterior motor pool

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26
Q

cell bodies in ventral horn that innervate flexors

A

posterior motor pool

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27
Q

groups of muscles innervated by single spinal nerve

A

myotomes

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28
Q

C5

A

elbow flexion

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29
Q

C6

A

wrist extension

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30
Q

C7

A

wrist flexion, finger extension

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31
Q

C8

A

finger extension

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32
Q

T1

A

finger abduction

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33
Q

L1, 2

A

hip abduction

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34
Q

L3, 4

A

knee extension

35
Q

L5, S1

A

knee flexion

36
Q

L5

A

great toe extension

37
Q

S1

A

great toe flexion

38
Q

large cell bodies found in lamina VIII and IX

A

alpha motor neurons

39
Q

have large myelinated axons and project to extrafusal skeletal muscle fibers

A

alpha motor neurons

40
Q

what is released to activate skeletal muscles

A

achetycholine

41
Q

small cell bodies in ventral horn

A

gamma motor neurons

42
Q

medium-sized myelinated axons that project to intrafusal fibers in muscles spindle to maintain stretch sensitivity

A

gamma motor neurons

43
Q

help to regulate muscle tone and active in reflex arc

A

gamma motor neurons

44
Q

an alpha motor neurons and all the muscle fibers it innervates

A

motor units

45
Q

what make up motor neurons

A

alpha motor neuron, axon, and neuromuscular junction

46
Q

smaller diameter, slower axons; postural and slowly contracting muscles; high resistance to fatigue (aerobic)

A

slow twitch motor units

47
Q

large diameter, faster axons; speed and power muscles; easily fatigued (anaerobic)

A

fast twitch motor units

48
Q

order of requirement from smaller to larger alpha motor neurons

A

henneman’s size principle

49
Q

the point where motor axons from alpha motor neurons synapse with muscle fibers

A

neuromuscular junction

50
Q

depolarization of motor axon results in release of what

A

acetycholine

51
Q

T/F acetycholine is always excitatory in skeletal muscles

A

T

52
Q

what are the spinal cord mechanisms that organize and synchronize muscle contractions to allow SC to deliver the effective motor plan that was communicated by UMN

A

reciprocal inhibition, muscle synergies, stepping pattern generators, spinal reflexes

53
Q

the inhibition of antagonist muscles during agonist contractions

A

reciprocal inhibition

54
Q

what is reciprocal inhibitions achieved

A

interneurons in the spinal cord that link LMNs into functional groups

55
Q

during reciprocal inhibition, a muscle contracts and the muscle spindles within the muscle send signals to the spinal cord that activate ______ that inhibit the motor neurons of the antagonist; also prevent activation of antagonist muscle when an agonist is reflexively relaxed

A

interneurons

56
Q

describes activity of muscles that are often activated by a normal nervous system; multiple spinal segments activated at the same time to produce a synchronous movement

A

muscle synergies

57
Q

muscle syngeries occur due to coordination by ______ that receive afferent information from II afferents and then project to muscles acting at other joints

A

interneurons

58
Q

what do muscle synergies result in

A

fractionated movement

59
Q

pathological synergies occur with what

A

UMN lesions

60
Q

adaptable networks of spinal interneurons that activate LMN to produce repetitive, rhythmic alternating output

A

stepping pattern generators

61
Q

activated by descending signals from UMN to interneurons in the anterior commissure (Renshall cells)

A

stepping pattern generators

62
Q

involuntary responses to an external stimulus

A

reflexes

63
Q

sensory receptor stimulated, sends signal to primary afferent, synapse occurs between dorsal horn cells and ventral horn cells, efferent response to effector

A

spinal reflexes

64
Q

do you need input from brain/cortex for spinal reflexes

A

no

65
Q

muscle contraction in response to a quick stretch (aka DTR); quick stretch activates signals from muscle spindles to alpha motor neurons of the same muscel

A

muscle spindles (monosynaptic/phasic reflexes)

66
Q

stimulated by cutaneous stimulus by receptors in the skin; spinal segment receiving the afferent input relays information to interneurons; interneurons coordinate a response to multiple spinal segments to produce the reflexive response

A

polysynpatic reflexes (Cutaneous)

67
Q

withdrawal or crossed-extension reflex

A

polysynpatic reflexes (Cutaneous)

68
Q

types of involuntary muscle contractions

A
  • muscle cramps
  • fasciculations
  • myoclonus
  • fibrillations
69
Q

severe, painful muscle contractions

A

muscle cramps

70
Q

eye twitch; get a twitch in muscle that is fatiguing

A

fasciculations

71
Q

brief, involuntary contractions; hiccups, head jerk as you fall asleep

A

myoclonus

72
Q

always a sign of LMN; cannot see them

A

fibrillations

73
Q

random; spontaneous, brief contractions of a single muscle fiber not visible on the surface of skin; always pathological; occurs when a muscle membrane is unstable owing to denervation, trauma, or electrolyte imbalance; detected by EMG

A

fibrillations

74
Q

occurs when LMN cell bodies, axons and/or neuromuscular junctions are destroyed

A

LMN lesions

75
Q

signs of LMN lesion

A
  • decrease or loss of reflexes (hypo)
  • muscle weakness and/or atrophy
  • decrease or loss of muscle tone (hypotonia or flaccidity)
  • fibrillations
76
Q

lack of muscle use

A

disuse atrophy

77
Q

damage to nervous system leading to muscle weakness

A

neurogenic atrophy

78
Q

differentiates the site of injury; motor neuron, nerve, neuromuscular junction, muscle; records electric potential when nerve is electrically stimulated; measures velocity it takes for electrical signal to travel from site of proximal electrical stimulation to distal point

A

nerve conductive velocity test (NVC)

79
Q

needle inserted into muscle to measure electrical activity at needle insertion, rest, minimal muscle contraction, maximal muscle contraction; distinguishes between denervation vs myopathy

A

electromyography (EMG)

80
Q

common LMN disorders

A
  • polio/post polio syndrome
  • myasthenia gravis
  • trigeminal neuralgia
  • guillain barre’ syndrome
  • peripheral nerve injury
  • peripheral neuropathy
81
Q

disruption of CNS cell bodies and pathways from cortex, brainstem and descending tracts in spinal cord

A

UMN lesion

82
Q

signs/sx of UMN lesion

A
  • hypertonia (spasticity, rigidity, clonus)
  • hyperreflexive
  • paralysis/paresis
  • neurogenic atrophy
  • pathological synergies
  • abnormal postural control
83
Q

injury or disease to ventral horn cells, spinal nerve, neuromuscular junction, muscle

A

LMN lesion

PT 631 Neuroanatomy (17 decks)

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