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Neuroscience > Descending Tracts > Flashcards

Descending Tracts Flashcards

1
Q

Where do somatomotor signals originate?

A

somatomotor cortex (precentral gyrus)

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2
Q

what CNS structures modify somatomotor signals?

A
  1. basal nucleus/thalamus
  2. cerebellum
  3. reticular formation
  4. limbic system
  5. red nucleus/substantia nigra
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3
Q

where are somatomotor neurons located?

A
  1. spinal cord ventral horn gray matter
  2. brainstem CN nuclei
    • 3, 4, 5, 6, 7, 9, 10, 11, 12
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4
Q

where are LMN located?

A

somatomotor neurons in CN nuclei of brainstem

OR

spinal cord/ventral horn

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5
Q

where are the efferent axons of LMN?

A

they are carried in peripheral nerves

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6
Q

efferent neurons from LMN release what NT?

A

acetylcholine

always depolarizing (excitatory) the muscle never hyperpolarize

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7
Q

what types of neuron innervates slow twitch (red) muscle fibers?

A

small diameter (slow conducting) alpha motor neurons

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8
Q

what types of neurons innervate fast twitch (white) muscle fibers?

A

large diameter (fast conducting) alpha motor neurons

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9
Q

What is the Henneman’s Size principle?

A

slow twich muscle fibers are recruited and activated before fast twitch fibers

this allows 2 fiber types to contract together

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10
Q

what are the 2 ways muscle contractions can be initiated?

A
  1. order comes from somatomotor cortex (voluntary)
  2. order comes from the spinal cord (reflex)
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11
Q

T/F: a reflex does not require an UMN for integration

A

TRUE

the LMN acts as the integrator

However, an UMN can be invovled in modulating the respones to the reflex

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12
Q

T/F: all cardiac and smooth muscle activity are reflexive?

A

TRUE

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13
Q

what is the role of collateral connections between tracts?

A

helps to coordinate movement and provide context

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14
Q

Collateral connections can include what type of coordinating activity?

A
  1. reciprocal inhibition
  2. muscle synergism
  3. proprioception
  4. stepping pattern generators
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15
Q

What are the 2 types of descending tracts?

A
  1. specific somatotopic tracts
  2. nonspecific upper motor neuron tracts
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16
Q

Specific somatotopic tracts can include what types of tracts?

A
  1. postural gross movement tracts
  2. tracts that carry info for fine movement
  3. tracts for limb flexion
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17
Q

T/F: motor unit and motor neuron pools are the same thing

A

FALSE

motor unit = single somatomotor neuron and all muscle fibers it activates

motor neuron pool = group of motor neuron cell bodies in a ventral horn that innervate a single muscle

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18
Q

how are motor neuron pools organized within the ventral horn?

A
  1. flexors are dorsal
  2. extensors are ventral
  3. axial muscles are medial
  4. appendicular muscles are lateral
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19
Q

Define reflex

A

a predictable response to a given stimulus

occur w/o brain input (similar to a neural loop)

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20
Q

reflexes are _______ dependent

A

content

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21
Q

what does the phrase “reflexes are content dependent” mean?

A

the state of the nervous system will affect the properties of the reflex

(if you are relaxed the response may be less intense than if you were anxious)

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22
Q

what are the 2 broad categories for reflexes?

A
  1. Stretch reflexes
  2. Cutaneous reflexes
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23
Q

A stretch reflex that is a result of an UMN lesion will be ______

A

tonic

it will respond to the stimulus for the duration of the stimulus

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24
Q

What is a phasic stretch reflex?

A

a reflex that responses briefly to the stimulus

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25
Q

what is a monosynaptic reflex?

A

a reflex when the sensory neuron synapses directly with the motor neuron

*there is no interneuron

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26
Q

Briefly describe the pathway of a stretch reflex

A

quick stretch stimulus → muscle spindle → Ia sensory neuron (annulospiral/bag and chain) → DRG → spinal cord dorsal horn → synapses w/alpha somatomotor neuron → skeletal muscle

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27
Q

what is an uncrossed reflex?

A

a reflex that involves a single spinal cord level

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28
Q

what normally prevents tonic stretch reflexes?

A

UMN inhibition

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29
Q

what is a tonic reflex contraction?

A

UMN lesion removal of the inhibition of a tonic reflex

it will allow the constant afferent signals to produce a constant efferent signal

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30
Q

what are 3 characteristics of a cutaneous reflex?

A
  1. involves interneurons (minimum 3 neuron pathway)
  2. involved multiple spinal cord segments
  3. crossover in the spinal cord = crossed flexor withdrawl reflex
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31
Q

a golgi tendon reflex is what type of reflex?

A

cutaneous reflex

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32
Q

Descending tracts can be divided into what 4 categories?

A
  1. Medial Motor Tracts
  2. Lateral Motor Tracts
  3. Corticobulbar Tracts
  4. Nonspecific Upper Motor Tracts
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33
Q

What tracts are included in the Medial Motor Tracts?

A
  1. Tectospinal tract
  2. Medial Reticulospinal Tract
  3. Medial Vestibulospinal Tract
  4. Lateral Vestibulospinal Tract
  5. Medial (Anterior) Corticospinal tract
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34
Q

What is the sensory input to the tectospinal tract?

A

visual, auditory, or somatosensory (pain and touch)

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35
Q

where does the Tectospinal tract start?

A

Soma = corpa quadrigemina

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36
Q

where does the Tectospinal tract crossover?

A

at the level of the mesencephalon

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37
Q

after crossing over, where does the tectospinal tract descend/travel?

A

tectospinal tract in anterior column of spinal cord white matter

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38
Q

Where does the tectospinal tract terminate/end/connect?

A

medial motor neurons of the ventral horn in the cervical region

these control axial muscles

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39
Q

what supplies sensory input to the Medial Reticulospinal Tract?

A

reticular system

40
Q

where does the Medial Reticulospinal tract begin?

A

soma = pontine reticular formation of metencephalon

41
Q

where is the medial reticulospinal tract located?

A

anterior column of spinal cord descending from metencephalon

42
Q

where does the medial reticulospinal tract cross?

A

it doesn’t

it remains uncrossed

43
Q

what is the destination/end point of the medial reticulospinal tract?

A

medial somatomotor neurons along the entire spinal cord

44
Q

what is the role of the medial reticulospinal tract?

A

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

45
Q

what supplies sensory input to the medial vestibulospinal tract?

A

vestibular apparatus/static and dynamic equilibrium

46
Q

where does the medial vestibulospinal tract begin?

A

soma = medial vestibular nuclei

(elongate nucleus in pons and medulla)

47
Q

where does the medial vestibulospinal tract travel?

A

anterior column of spinal cord

48
Q

where does the medial vestibulospinal tract cross?

A

at the medulla

49
Q

what is the destination/end point of the medial vestibulospinal tract?

A

medial somatomotor neurons along the cervical and thoracic spinal cord (brachial plexus)

50
Q

what is the role of the medial vestibulospinal tract?

A

effect = balance in response to head movement (coordinate with tectospinal tract to maintain balance with head turning)

51
Q

what provides sensory input to the lateral vestibulospinal tract?

A

vestibular apparatus/center of gravity

52
Q

where does the lateral vestibulospinal tract begin?

A

soma located in lateral vestibular nuclei located in pons

53
Q

where does the lateral vestibulospinal tract travel?

A

anterior column of spinal cord

54
Q

where does the lateral vestibulospinal tract cross?

A

it doesn’t

it remains uncrossed

55
Q

what is the destination/end point of the lateral vestibulospinal tract?

A

medial somatomotor neurons along entire spinal cord

56
Q

what is the role of the lateral vestibulospinal tract?

A

effect = upright posture/balance: stimulates axial extensors, and inhibits axial flexors when a person is standing upright

57
Q

what provides input to the medial (anterior) corticospinal tract?

A

diverse associative input from pre-motor and parietal cortex of frontal lobe

58
Q

where does the medial (anterior) corticospinal tract begin?

A

soma = somatomotor cortex (pre-central gyrus of frontal lobe)

59
Q

describe the pathway of the medial (anterior) corticospinal tract

A

leaves the precentral gyrus and descends to the medulla through the internal capsule then the crus cerebrii and then the pons until it reaches the pyramids

60
Q

where does the medial (anterior) corticospinal tract cross?

A

it doesn’t

it is the 10% that remains uncrossed at the pyramids

61
Q

what is the destination/end point of the medial (anterior) corticospinal tract?

A

medial somatomotor neurons in the cervical and thoracic spinal cord

62
Q

what is the role/effect of the medial (anterior) corticospinal tract?

A

balance to prepare postural muscles for voluntary movements

63
Q

where are all medial motor tracts located in the spine?

A

medial spinal cord white matter

64
Q

what is the general function of all medial motor tracts?

A

function in axial muscle/posture

girdle muscles/stabilizers

contextual info

65
Q

which medial motor tracts do not cross?

A

medial reticulospinal tract

lateral vestibulospinal tract

medial (anterior) corticospinal tract

66
Q

which medial motor tracts cross (2)?

A

tectospinal tract

medial vestibulospinal tract

67
Q

What tracts are included in the Lateral Motor Tracts?

A
  1. lateral corticospinal tract
  2. Rubrospinal tract
  3. Lateral (medullary) reticulospinal tract
68
Q

where are all the lateral motor tracts located in the spinal cord?

A

lateral spinal cord white matter

69
Q

what is the general function of all the lateral motor tracts?

A

function in fine movements of face, and extremities

70
Q

what supplies input to the lateral corticospinal tract?

A

pre-frontal cortex and motor associative cortex

71
Q

where does the lateral corticospinal tract begin?

A

soma located in somatomotor cortex (pre-central gyrus) of the frontal lobe = UMN

72
Q

how does the lateral corticospinal tract descend from the frontal lobe?

A

descends to medulla → corticospinal tracts through internal capsule → crus cerebri → pons → pyramids

73
Q

where does the lateral corticospinal tract cross?

A

decussation of the pyramids in caudal closed medulla

74
Q

what is the lateral corticospinal tract’s destination/end point and how does it get there?

A

lateral somatomotor neurons in ventral horn (LMN) in brachial plexus and lumbosacral plexus regions of spinal cord

gets there via the lateral spinal column (lateral corticospinal tract)

75
Q

what is the effect of the lateral corticospinal tract?

A

fine movements of extremities

fractionation of movement

76
Q

what does fractionation of movement mean?

A

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

77
Q

what supplies input to the rubrospinal tract?

A

motor cortex

78
Q

where does the rubrospinal tract begin?

A

soma = red nucleus of mesencephalon

79
Q

where does the rubrospinal tract cross and descend?

A

crosses at mesencephalon

descends in pons → medulla → spinal cord lateral column

80
Q

what is the destination of the rubrospinal tract?

A

lateral somatomotor neurons in brachial plexus region of spinal cord

81
Q

what is the effect of the rubrospinal tract?

A

activates wrist hand extensor muscles

82
Q

what supplies input to the lateral (medullary) reticulospinal tracts?

A

motor cortex

83
Q

where does the lateral (medullary) reticulospinal tract begin?

A

reticular nuclei of the medulla

84
Q

where does the lateral (medullary) reticulospinal tract cross and how does it descend?

A

it doesn’t cross

descends in the lateral spinal column

85
Q

what is the destination of the lateral (medullary) reticulospinal tract?

A

lateral somatomotor neurons in the brachial and lumbosacral plexus of spinal cord

86
Q

what is the effect of the lateral (medullary) reticulospinal tract?

A

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

87
Q

the corticobulbar tracts is also known as what?

A

Corticobrainstem Tract

88
Q

what supplies input to the corticobrainstem tract?

A

associative cortex = premotor cortex

89
Q

where does the corticobrainstem tract begin?

A

pre-central gyrus of frontal lobe (somatomotor cortex)

90
Q

Describe how the corticobrainstem descends and where it heads

A

descends to cranial nerve nuclei in pons, medulla, and cervical spinal cord via internal capsule and cerebral peduncles

91
Q

where are the LMN for the corticobrainstem tract?

A

somatomotor neurons in cranial nerve nuclei

92
Q

where does the corticobrainstem tract cross?

A

in brainstem pons and medulla

(muscles of upper face = controlled by bilateral cerebral hemispheres CN 7)

(muscles of lower face = controlled by contralateral hemisphere of CN 7)

93
Q

what are the effects of the corticobrainstem tract?

A
  1. CN 5 controls muscles of mastication
  2. CN 7 controls muscles of facial expression
  3. CN 9, 10 control pharynx and larynx muscles
  4. CN 11 controls traps and SCM
  5. CN 12 controls tongue muscles
94
Q

what tracts make up the nonspecific upper motor tracts?

A
  1. cerulospinal tract
  2. raphespinal tract
95
Q

what activates the nonspecific upper motor tracts and what is their role?

A

both are activated by the limbic system (emotions) and provide context to affect other descending tracts

96
Q

how does the cerulospinal tract work?

A

mediates it effects by release of NE from locus ceruleus

97
Q

how does the raphespinal tract work?

A

mediates its effects by release of serotonin form raphe nucleus

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