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Neuro Quiz 2 > Descending Tracts - Sheet1 > Flashcards

Descending Tracts - Sheet1 Flashcards

1
Q

Why does the descending tracts exist (what purpose do they serve)?

A

way for the higher centers of the brain to control spinal motor neurons

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2
Q

What are the roles of the descending tracts on the spinal cord? (4)

A

produce movement, modify tone, control autonomic function, modulate sensory transmission

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3
Q

Where do most descending tracts synapse onto? (3)

A

1) interneurons 2) directly onto alpha-motor neurons, or 3) gamma neurons (gamma loop)

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4
Q

What is the purpose of descending tracts synapsing onto interneurons?

A

indireclty affect alpha motor neurons (ie reflex excitability)

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5
Q

What is the purpose of descending tracts synapsing onto alpha-motor neurons?

A

generate movements - obviously

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6
Q

What is the purpose of descending tracts synapsing onto gamma neurons?

A

produce reflex contraction of muscles to a new length “set point” where it stabilizes the limb

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7
Q

Descending tracts in the ventral funiculus control:

A

axial function

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8
Q

Descending tracts in the lateral funiculus control:

A

limb function

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9
Q

What are the two tracts that the cerebral cortex uses to control the body?

A

corticospinal and corticobulbar tracts

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10
Q

How are the motor neurons of the ventral horn organized?

A

MEDIAL: axial muscles. LATERAL: limbs

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11
Q

Motor neurons to flexor muscles are situated _____ to extensors in the ventral horn of the spnial cord

A

dorsal

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12
Q

Motor tracts that run in the lateral funiculus tend to interact more with motor neurons of:

A

distal/limb functions

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13
Q

Motor tracts that run in the anterior funiculus tend to interact more with motor neurons of:

A

axial functions

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14
Q

What is the gamma loop?

A

activation of gamma motor neurons that can contract intrafusal fibers (muscle spindles)&raquo_space; activate the spindle afferent&raquo_space; reflex pattern where the muscle shortens and the antagonist muscle lengthens

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15
Q

The descending tracts run in these two funiculus:

A

ventral + lateral funiculus

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16
Q

The medial motor systems control:

A

axial muscle tone and trunk/neck movement

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17
Q

The medial motor system can be found running in this tract:

A

ventral (anterior) funiculus of spinal cord

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18
Q

What makes up the medial longitudinal fasciculus (MLF)? (3)

A

Pontine reticulospinal tract, tectospinal tract, medial vestibulospinal tract

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19
Q

Where does the medial longitudinal fasciculus end?

A

upper thoracic region

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20
Q

Where does the medial longitudinal fasciculus distribute?

A

bilaterally

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21
Q

What is the origin of the tectospinal tract?

A

superior colliculus (deep layers; receives input from cortex, visual, auditory, somatic sensory systems; “multi-sensory”. Runs in the Anterior funiculus of spinal cord

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22
Q

What does the tectospinal tract decusssate?

A

Midbrain (dorsal tegmental decussation)

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23
Q

Where does the tectospinal tract run?

A

Medial Funiculus @ the Medial Longitudinal Fasiciculus (MLF)

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24
Q

Where does the tectospinal tract terminate?

A

Medial part of the intermediate gray matter of the upper thoracic levels

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25
Q

T/F the tectospinal tract distributes bilaterally

A

True.

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26
Q

What is the function of the tectospinal tract?

A

Reflex head and arm movement to stimuli (esp visual and auditory)

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27
Q

What is the origin of the Medial Vestibulospinal Tract?

A

Medial Vestibular nuclei (midbrain) and runs in the Anterior funiculus of spinal cord

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28
Q

Where does the Medial Vestibulospinal Tract run?

A

Medial Funiculus @ the Medial Longitudinal Fasiciculus (MLF)

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29
Q

Where does the Medial Vestibulospinal Tract terminate?

A

cervical and upper thoracic levels

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30
Q

T/F the Medial Vestibulospinal Tract distributes bilaterally

A

True.

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31
Q

What is the function of the Medial Vestibulospinal Tract?

A

Reflex muscle function in response to vestibular stimuli

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32
Q

What is the origin of the pontine reticulospinal tract?

A

Pontine lateral Gaze center (Paramedian pontine reticular formation, PPRF) in pons

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33
Q

Where does the pontine reticulospinal tract run?

A

Medial funiculus @ the Medial Longitudinal Fasiciculus (MLF

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34
Q

Where does the pontine reticulospinal tract terminate?

A

cervical and upper thoracic levels

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35
Q

T/F the pontine reticulospinal tract distributes bilaterally

A

True.

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36
Q

What is the function of the pontine reticulospinal tract?

A

Allow coordination of head and eye movements

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37
Q

What is the origin of the lateral vestibulospinal tract?

A

Lateral vestibular nucleus

38
Q

Where does the lateral vestibulospinal tract run?

A

Ventral part of lateral funiculus, near the cap of the ventral horn

39
Q

Where does the lateral vestibulospinal tract terminate?

A

Extends the length of the spinal cord

40
Q

T/F the lateral vestibulospinal tract distributes bilaterally

A

False. It’s an ipsilateral tract

41
Q

What is the function of the lateral vestibulospinal tract?

A

Vestibular righting reflexes – strong activator of extensor motor neurons

42
Q

What is the origin of the medullary reticulospinal tract?

A

medulla

43
Q

Where does the medullary reticulospinal tract run?

A

Ventral part of lateral funiculus, near the cap of the ventral horn

44
Q

Where does the medullary reticulospinal tract terminate?

A

Extends the length of the spinal cord

45
Q

T/F the medullary reticulospinal tract distributes bilaterally

A

False. It’s an ipsilateral tract

46
Q

What is the function of the medullary reticulospinal tract?

A

Activates inhibitory interneurons of the spinal cord to modulate: 1) gross movements and muscle tone via gamma motor neurons 2) sensory transmission 3) descending autonomic and respiratory control fibers

47
Q

What is the origin of the rubrospinal tract?

A

Red nucleus (receives input from the cortex and cerebellum)

48
Q

What does the rubrospinal tract decusssate?

A

Midbrain at the ventral tegmental decussation

49
Q

Where does the rubrospinal tract run?

A

Brainstem and lateral funiculus

50
Q

Where does the rubrospinal tract terminate?

A

Intermediate gray matter of the spinal cord and in the dorsal horn; extends the length of the spinal cord

51
Q

What is the function of the rubrospinal tract?

A

Control movements of more proximal limb flexor muscles

52
Q

What is the corticospinal tract?

A

Projections from the cerebral cortex to the spinal cord

53
Q

What is the corticobulbar tract?

A

Projections from the cerebral cortex to the brainstem

54
Q

What is the corticofugal tract?

A

Projects from the frontal cortex to the pons

55
Q

What is the origin of the corticospinal tract?

A

Motor cortex (precentral gyrus (Betz cells); traverse the internal capsule, enters the cerebral peduncles to pass through the pons; comprises the pyramid of the medulla

56
Q

What does the corticospinal tract decusssate?

A

Pyramidal decussation at the lowest part of the medulla

57
Q

Where does the corticospinal tract run? (remember that axons that decussate run in separate tracts than those that do not decussate!)

A

AXONS THAT DECUSSATE: Corticospinal tract (lateral funiculus). AXONS THAT DO NOT DECUSSATE: anterior funiculus

58
Q

Where does the corticospinal tract terminate?

A

All levels of the spinal cord at interneurons (which control alpha-motor neurons), but also in the dorsal horn where the tracts may influence sensory transmission and reflexes

59
Q

What is the function of the corticospinal tract?

A

1) Voluntary/highly skilled limb movements, 2) Sensory transmission through dorsal horn

60
Q

The axons of the corticospinal tract will either decussate or not. What is the functional differences of the two?

A

DECUSSATE: important in fine-control of limbs and digits. NON-DECUSSATION: crude movement of axial muscles

61
Q

What is the functional significance of the corticospinal tract?

A

inhibitory to reflexes within the spinal cord

62
Q

T/F motor cortex controls single muscles.

A

False. Individual neurons encode particular directions of movement (ie these neurons control groups of motor neurons involved in a particular movement)

63
Q

What precedes movement?

A

cortical neuron activity in the SUPPLEMENTARY MOTOR AREAS, followed by activity in the PRIMARY MOTOR CORTEX

64
Q

What is the purpose of the supplementary motor areas?

A

initiation of movements and decides on the type of motor program to initiate

65
Q

What is the origin of the corticobulbar tract?

A

cortex (various parts

66
Q

Where does the corticobulbar tract terminate? (6)

A

BRAINSTEM: 1) facial nerve nuclei (relay from the face part of somatosensory and anterior cingulate), 2) pontine nuclei (relay to cerebellum), 3) sensory nuclei (modulate sensory transmission), 4) reticular formation (visceral centers that modify muscle tone, autonomic responses, and overall alertness), 4) brainstem areas that give rise to descending motor tracts (red nucleus, reticular formation, superior colliculus) 6) eye movement control

67
Q

What is unique about the corticobulbar tract that goes to the facial nucleus?

A

Facial nucleus Fibers to the LOWER face are strictly CROSSED at the pons (lesions to a tract result in contralateral lower face weakness). Fibers to the UPPER face, tongue, and jaw are BILATERALLY innervated (lesions do not produce clinical weakness

68
Q

Damage to a corticobulbar tract of the UPPER face results in________ because of______

A

no clinical weakness because corticobulbar fibers to the upper face are BILATERAL.

69
Q

Damage to a corticobulbar tract of the LOWER face results in________ because of______

A

lower face weakness on the CONTRALATERAL side because corticobulbar fibers to the lower face are strictly crossed!

70
Q

What is the facial nerve nuclei?

A

where the corticobulbar tract terminates in the brainstem. Relays info from the face part of the somatosensory and anterior cingulate nucleus

71
Q

What is the pontine nucleus?

A

where the corticobulbar tract terminates in the brainstem; relays to the cerebellum

72
Q

What is the sensory nucleus?

A

where the corticobulbar tract terminates in the brainstem; modulates sensory transmission

73
Q

What is the reticular formation?

A

where the corticobulbar tract terminates in the brainstem - visceral centers that modify muscle tone, autonomic responses, and overall alertness

74
Q

What happens if you disrupt the reticular formation in the brainstem?

A

dramatic increase in spinal cord reflexes, suggesting that the net effect of this pathway is inhibitory

75
Q

What is responsible in supporting and stabilizing muscles?

A

indirect corticospinal projections

76
Q

What happens if you have lesions in the corticospinal tract?

A

1) weakness/deficits in CONTRALATERAL fine-motor control (when the lesion is above the pyramidal decussation); most severe distally with preservation of the axial muscles. 2) hyperactive myotactic and withdrawal reflexes, 3) spasticity (due to lack of inhibition of indirect corticospinal tracts)

77
Q

What is associated with spasticity?

A

hyperactive reflexes due to lack of inhibition of spinal cord reflex pathways and other motor tracts

78
Q

What normally happens when the sole of the foot is scratched?

A

normal plantar response (toes go down)

79
Q

What happens when the sole of the foot is scratched if there is a disruption of the descending motor tracts (upper motor neuron lesion)?

A

great toe goes up while other toes fan up and out

80
Q

What comprises the upper motor neurons? Lower motor neurons?

A

UPPER: descending tracts. LOWER: anterior horn cells

81
Q

What happens if you damage the upper motor neurons? Lower motor neurons?

A

UPPER: little atrophy, spasticity, increased reflexes, + babinski sign. LOWER: significant atrophy, flaccid paralysis, decreased or no reflexes

82
Q

What do descending autonomic fibers participate in?

A

Control autonomic outflow

83
Q

Where do descending autonomic fibers originate?

A

Brainstem, hypothalamus, amygdala, cerebral cortex

84
Q

Where do descending autonomic fibers run?

A

lateral funiculus

85
Q

Where do descending autonomic fibers terminate

A

Neurons of lateral horn, sacral parasympathetics, and interneurons that connect to them

86
Q

T/F the descending autonomic fibers distributes bilaterally

A

False. It’s an ipsilateral tract

87
Q

What is the purpose of the Fasciculus Proprius (Propriospinal Tract)?

A

Intersegmental spinal cord reflexes

88
Q

Where does the Fasciculus Proprius (Propriospinal Tract) run?

A

Ascending/descending axons that interconnect spinal cord levels

89
Q

What is the decorticate posturing? What causes it?

A

POSTURE: arms are drawn up toward the chest while the legs are extended. CAUSE: lesions above the red nucleus (in brainstem, rostral to the midbrain)

90
Q

What is the dececerebrate posturing? What causes it?

A

POSTURE: extension and internal rotation of the arms while the legs are extended. CAUSE: overactivity of the vestibulospinal pathway, which facilitates etensors (implies damage to the pons)

Neuro Quiz 2 (17 decks)

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