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Neuroanatomy and Physiology > Lecture 11- Descending Tracts > Flashcards

Lecture 11- Descending Tracts Flashcards

1
Q

OVERVIEW

A

OVERVIEW

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2
Q

Motor system comprises the _________ portion of a neural loop

A

efferent

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3
Q

Somatomotor signals originate in the ________ cortex of the frontal lobe.

A

somatomotor (precentral gyrus)

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4
Q

What 5 CNS structures modify motor signals?

A
  • Basal nucleus/thalamus
  • Cerebellum
  • Reticular formation
  • Limbic system
  • Red nucleus/substantia nigra
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5
Q

Motor signals move in _______ tracts.

A

descending

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6
Q

Where are the somatomotor neurons located?

A
  • spinal cord ventral horn gray matter

- brainstem CN nuclei: CN 3, 4, 6; 5, 7; 9, 10; 11, 12

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7
Q

The motor pathway is a __ neuron pathway

A

2

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8
Q

The ______ motor neurons connect the precentral gyrus to somatomotor neurons and form descending tracts

A

upper

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9
Q

The _______ motor neurons are in CN nuclei of brainstem or spinal cord/ventral horn and are carried in peripheral nerves.

A

lower

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10
Q

What are the 2 lower motor neuron types?

A
  • alpha motor neurons

- gamma motor neurons

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11
Q

Alpha motor neurons are ________ diameter myelinated ____ neurons that synapse with _________ muscle fibers to contract whole muscle.

A
  • large
  • fast speed
  • extrafusal
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12
Q

Gamma motor neurons are ________ diameter myelinated _______ neurons that synapse with __________ (muscle spindle) muscle fibers that keep the muscle spindle sensitive during whole muscle contraction.

A
  • medium
  • medium speed
  • intrafusal
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13
Q

Lower motor neurons release NT __________ which binds ________ receptors on muscle cell membrane to always depolarize the muscle

A
  • acetylcholine

- nicotinic

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14
Q

Small diameter (slow conducting) ______ motor neurons innervate _____ twitch (red) muscle fibers

A
  • alpha

- slow

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15
Q

Larger diameter (fast conducting) _______ motor neurons innervate ______ twitch (white) muscle fibers

A
  • alpha

- fast

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16
Q

What does Henneman’s size principle state?

A

Typically slow twitch muscle fibers (small diameter) are activated before fast twitch muscle fibers (large diameter) allowing the 2 types of muscle fibers to contract together

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17
Q

Muscle contractions can be initiated in what 2 ways?

A
  • somatomotor cortex and control centers in brain = VOLUNTARY
  • spinal cord/brain stem = REFLEX
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18
Q

Descending tracts have specific somatotopic tracts (homonculus) on the precentral gyrus for what 3 things?

A
  • postural gross movement tracts
  • fine movement
  • limb flexion
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19
Q

Collateral connections between tracts (motor to motor or motor to sensory) help coordinate movement = _________.

A

context

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20
Q

What are the 4 functions of collateral connections?

A
  • reciprocal inhibition
  • muscle synergism
  • proprioception
  • stepping pattern generators
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21
Q

What is reciprocal inhibition?

A

antagonist inhibition during agonist contraction

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22
Q

What is muscle synergism?

A

coordinated muscle action

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23
Q

What is proprioception?

A

information of body position in time and space is used to coordinate muscle contraction

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24
Q

What is stepping pattern generators?

A

alternate flexion/extension of the lower limbs

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25
Q

SKELETAL MUSCLE CONTRACTION REVIEW

A

SKELETAL MUSCLE CONTRACTION REVIEW

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26
Q

What is a motor unit?

A

a SINGLE somatomotor neuron (axon) and all the muscle fibers it activates

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27
Q

What is a motor neuron pool?

A

group of motor neuron cell bodies (motor units) in ventral horn that innervate a single muscle.

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28
Q

How are motor neuron pools arranged somatotopically in the ventral horn?

A
  • flexors dorsal
  • extensors ventral
  • axial muscles medially
  • appendicular muscles laterally
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29
Q

REFLEXES

A

REFLEXES

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30
Q

What is a reflex? Can it occur without brain input?

A
  • predictable response to a given stimulus

- yes, occurs without brain input

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31
Q

Reflexes are _______ dependent, meaning the state of the NS will affect the properties of the reflex ie. signals from the brain influence spinal reflexes.

A

context

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32
Q

If you are relaxed the reflex response may be ____ intense than if you are anxious.

A

less

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33
Q

What is the reflex pathway?

A
  • sensor/receptor
  • sensory neuron
  • INTERNEURON connection in brainstem or spinal cord
  • motor neuron
  • skeletal muscle
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34
Q

Most skeletal muscle movement is NOT reflex movement, it is _________.

A

voluntary

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35
Q

Difference between tonic and phasic stretch reflexes?

A
  • phasic- brief response to stimulus

- tonic- responds to stimulus for the duration of stimulus

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36
Q

What is the phasic pathway?

A
  • quick stretch stimulus
  • muscle spindle
  • Ia sensory neuron (annulospiral bag and chain)
  • DRG
  • spinal cord dorsal horn (also dorsal column to postcentral gyrus)
  • synapses w/ alpha somatomotor neuron
  • skeletal muscle
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37
Q

What is a monosynaptic reflex?

A

Where the sensory neuron synapses directly with motor neuron (no interneuron)

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38
Q

Phasic pathways are _______ and involve a _______ spinal cord level.

A
  • uncrossed

- single

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39
Q

Constant tonic reflexes result from lesion of the brain or spinal cord = ___________ lesion

A

UMN

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40
Q

tonic sensory neurons type II sensory neuron (_________/_______) signal when the muscle spindle is stretched but these signals are normally prevented from activating somatomotor neurons by upper motor neuron inhibition; UMN lesion removes the inhibition and allows the constant afferent signal to produce a constant efferent signal = ________________

A
  • flowerspray/chain

- tonic reflex contraction

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41
Q

Cutaneous reflexes are more complex and involve _________ (minimum __ neuron pathway)

A
  • interneurons

- 3

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42
Q

What is the golgi tendon reflex pathway?

A
  • increased tendon stretch
  • golgi tendon organ
  • Type Ib afferent
  • spinal cord INHIBITORY interneuron
  • inhibit alpha motor neuron to homolgous muscle
  • muscle w/ stretched tendon relaxes
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43
Q

Cutaneous reflexes involve _________ spinal cord segments affecting multiple effectors (more than 1 muscle) on the same side.

A

-multiple

44
Q

What is the flexor withdrawal reflex pathway?

A
  • pain stimulus
  • sensory neuron (Type III or IV)
  • ascends/descends for several segments via Lissauer’s tract
  • activates multiple levels of ventral horn alpha motor neurons
  • multiple flexor muscles
  • withdrawal from pain stimulus
45
Q

Cutaneous reflexes crossover in the _________ = _______________.

A
  • spinal cord

- crossed flexor withdrawal reflex

46
Q

DESCENDING TRACT

A

DESCENDING TRACT

47
Q

Descending tracts are __ neuron pathways

A

2

48
Q

The Medial Motor Tracts are locates in the medial spinal cord _______ matter and function in ______ muscle posture; girdle muscles/stabilizers

A
  • white

- axial

49
Q

What are the 5 medial motor tracts?

A
  • Tectospinal Tract
  • Medial Reticulospinal Tract
  • Medial Vestibulospinal Tract
  • Lateral Vestibulospinal Tract
  • Medial (Anterior) Corticospinal Tract
50
Q

The tectospinal tract has sensory input from ______, auditory, or ___________ (pain, touch)

A
  • visual

- somatosensory

51
Q

The tectospinal tract starts and has its soma located in the _______________ = tectum of midbrain (superior and inferior colliculi) in the mesencephalon.

A

-corpora quadrigeminae

52
Q

The tectospinal tract crosses at the ________ and travels in the _______ column of the spinal cord white matter

A
  • midbrain (mesencephalon)

- anterior

53
Q

The tectospinal tract ventral horn connection is _____ motor neurons of the ventral horn in the ______ region to control ______ muscles.

A
  • medial
  • cervical
  • axial
54
Q

What is the effect of the tectospinal tract?

A

head turning

55
Q

The medial reticulospinal tract has sensory input from the ________ system which monitors and filters sensory input through the brain stem.

A

-reticular

56
Q

The medial reticulospinal tract starts and has its soma in the _______________ of the metencephalon.

A

pontine reticular formation

57
Q

The medial reticulospinal tract travels in the _________ column.

A

-anterior

58
Q

Where does the medial reticulospinal tract cross?

A

It doesn’t

59
Q

The medial reticulospinal tract has medial somatomotor neurons along the entire ___________.

A

spinal cord

60
Q

What is the effect of the medial reticulospinal tract?

A

prepare postural (axial) and girdle muscles for limb activity; reaching

61
Q

The medial vestibulospinal tract has sensory input from the vestibular apparatus for ______ and _______ equilibrium.

A

static and dynamic (linear and angular)

62
Q

The medial vestibulospinal tract starts and has its soma in the _____________ nuclei which is a elongated nucleus in the ______ and ____________.

A
  • medial vestibular

- pons and myelencephalon

63
Q

Where does the medial vestibulospinal tract cross?

A

myelencephalon (medulla) (bilateral)

64
Q

The medial vestibulospinal has medial somatomotor neurons along the _____ and _______ spinal cord

A

cervical and thoarcic

65
Q

What is the effect of the medial vestibulospinal tract?

A

-BALANCE in response to head movement (coordinates with tectospinal tract)

66
Q

The lateral vestibulospinal tract has sensory input from the vestibular apparatus for _________.

A

center of gravity

67
Q

The lateral vestibulospinal tract starts and has its soma in the ___________ nuclei located in the ___________.

A
  • lateral vestibular

- pons

68
Q

The lateral vestibulospinal tract travels in the ________ column.

A

anterior

69
Q

Where does the lateral vestibulospinal tract cross?

A

It doesn’t

70
Q

The lateral vestibulospinal tract has medial somatomotor neurons along the entire ___________.

A

spinal cord

71
Q

What are the effects of the lateral vestibulospinal tract?

A
  • upright posture/balance

- stimulates axial extensors, and inhibits axial flexors when a person is standing upright

72
Q

The medial (anterior) corticospinal tract has diverse associative input from the ______ and __________ cortex.

A

premotor and parietal

73
Q

The medial (anterior) corticospinal tract starts and has its soma in the _________ cortex

A

somatomotor cortex

74
Q

How does the medial corticospinal tract descend from the somatomotor cortex (order)?

A
  • internal capsule
  • crus cerebri
  • pons
  • pyramids
  • medial corticospinal tract in anterior column
75
Q

Where does the medial (anterior) corticospinal tract cross?

A

It doesn’t

76
Q

The medial (anterior) corticospinal tract has medial somatomotor neurons in the _______ and ________ spinal cord.

A

cervical and thoracic

77
Q

What are the effects of the medial (anterior) corticospinal tract?

A

balance to prepare postural muscles for voluntary movements

78
Q

The Lateral Motor Tracts are located in the lateral spinal cord _______ matter and function in fine movements of _____ and __________

A
  • white

- face and extremities

79
Q

What are the 3 Lateral Motor Tracts?

A
  • lateral corticospinal tract
  • rubrospinal tract
  • lateral (medullary) reticulospinal tract
80
Q

The lateral corticospinal tract has input from the ______ and _______ cortex

A

prefrontal and motor associative cortex

81
Q

The lateral corticospinal tract starts and has its soma in the _________ cortex = UMN

A

somatomotor

82
Q

How does the lateral corticospinal tract descend from the somatomotor cortex (order)?

A
  • internal capsule
  • crus cerebri
  • pons
  • pyramids
83
Q

Where does the lateral corticospinal tract cross?

A

decussation of pyramids

84
Q

The lateral corticospinal tract is located in the _______ ventral horn and has somatomotor neuron in ventral horn = LMN in ________ and __________ plexus regions of spinal cord

A
  • lateral

- brachial and lumbosacral

85
Q

What are the effects of the lateral corticospinal tract?

A
  • fine movements of extremities

- fractionation of movement

86
Q

What is fractionation of movement?

A

activate individual muscles independent of other hand muscles innervated by lateral somatomotor neurons at the same level.

87
Q

The rubrospinal tract has input from the ______ cortex

A

motor

88
Q

The rubrospinal tract starts and has its soma in the ____________ of the mesencephalon.

A

red nucleus

89
Q

Where does the rubrospinal tract cross?

A

mesencephalon

90
Q

The rubrospinal tract descends from the pons to the medulla to the spinal cord ________ column.

A

lateral

91
Q

The rubrospinal tract has lateral somatomotor neurons in _________ plexus region of spinal cord

A

brachial

92
Q

What are the effects of the rubrospinal tract?

A

activate wrist and hand extensor muscles

93
Q

The lateral (medullary) reticulospinal tract recives input from the _____ cortex.

A

motor

94
Q

The lateral (medullary) reticulospinal tract starts and has its soma in the ______________ of the medulla.

A

reticular nuclei

95
Q

The lateral (medullary) reticulospinal tract descends the spinal cord in the _________ column.

A

medial (?)

96
Q

Where does the lateral (medullary) reticulospinal tract cross?

A

It doesn’t

97
Q

The lateral (medullary) reticulospinal tract has lateral somatomotor neurons in ______ and __________ plexus of spinal cord.

A

brachial and lumbosacral

98
Q

What are the effects of the lateral (medullary) reticulospinal tract?

A

prepare postural (axial) and girdle muscles for limb activity; reaching

99
Q

Corticobulbar tracts receive input from the ________ cortex

A

premotor

100
Q

Corticobulbar tracts descend to ___________ nuclei in pons, medulla, and cervical spinal cord

A

cranial nerve

101
Q

Muscles of the upper face are controlled __________ by CN7

A

bilaterally

102
Q

Muscles of the lower face are controlled by the ___________ hemisphere

A

contralateral

103
Q

Corticobulbar tracts involve what cranial nerves and function?

A 
CN5= muscles of mastication
CN7= muscles of facial expression
CN9,10= pharynx and larynx
CN11= neck muscles
CN12= tongue muscles
104
Q

What are the 2 nonspecific upper motor tracts that are activated by the limbic system and provide context to affect other descending tracts?

A
  • ceruleospinal tract

- raphespinal tract

105
Q

The ceruleospinal tract mediates its effects by releasing ________ from the ___________.

A
  • NEpi

- locus ceruleus

106
Q

The raphespinal tract mediates its effects by release of ________ from __________

A
  • serotonin

- raphe nuc.

Neuroanatomy and Physiology (19 decks)

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