Descending Pathways (handout based)

Question 0

Originate in: Cerebral cortex, Cerebellum & Brainstem

Answer 0

Upper Motor Neurons

Question 1

Are entirely within the CNS; Form descending tracts

Answer 1

Upper Motor Neurons

Question 2

Begin in CNS; Made up of alpha motor neurons (A-α)

Answer 2

Lower Motor Neurons

Question 3

From anterior horns of spinal cord

Answer 3

Lower Motor Neurons

Question 4

From brainstem cranial nerve nuclei

Answer 4

Lower Motor Neurons

Question 5

Make up spinal and cranial nerves

Answer 5

Lower Motor Neurons

Question 6

Classified according to where they synapse in the ventral horn (UMN); Innervate postural and girdle muscles

Answer 6

Medial activation system

Question 7

Classified according to where they synapse in the ventral horn (UMN); Associated with distally located muscles used for fine movements

Answer 7

Lateral activation system

Question 8

Classified according to where they synapse in the ventral horn (UMN); Facilitate local reflex arcs

Answer 8

Nonspecific activating system

Question 9

the most important descending tract

Answer 9

Corticospinal tract

Question 10

descends through all levels of the neuraxis except the cerebellum

Answer 10

Corticospinal tract

Question 11

arises primarily from area 4, and 6, 3,1 and 2

Answer 11

Corticospinal tract

Question 12

passes through the internal capsule, the cerebral peduncle, the basis pontis, and the pyramids of the medulla oblongata

Answer 12

Corticospinal tract

Question 13

in the caudal medulla, about 75 to 90% of the fibers decussate to form the lateral CST in the lateral funiculus of the SC

Answer 13

Corticospinal tract

Question 14

about 8 % of fibers remain uncrossed and form the anterior CST (Türck’s bundle) in the anterior funiculus

Answer 14

Corticospinal tract

Question 15

Fibers in the anterior CST decussate at segmental spinal levels

Answer 15

Corticospinal tract

Question 16

roughly about 98 percent of fibers in the pyramidal tract are crossed; remaining 2 percent remain ipsilateral and form the tract of Barnes

Answer 16

Corticospinal tract

Question 17

fibers terminate on motor neurons in the lateral part of the ventral horn that supply the distal limb musculature

Answer 17

Lateral corticospinal tract

Question 18

fibers terminate on motor neurons in the medial part of the ventral horn that supply the neck, the trunk, and the proximal limb musculature

Answer 18

Anterior corticospinal tract

Question 19

constitutes the largest component of the cortically originating descending fiber system

Answer 19

Corticopontocerebellar tract

Question 20

has been estimated to contain approx 19M fibers, in contrast to the pyramidal tract, which contains approx 1 M

Answer 20

Corticopontocerebellar tract

Question 21

originates from wide areas of the cerebral cortex, but primarily from the primary sensory and motor cortices, and descends in the internal capsule, cerebral peduncle, and basis pontis, from which its fibers project on pontinenuclei

Answer 21

Corticopontocerebellar tract

Question 22

it plays a role in the rapid correction of movement

Answer 22

Corticopontocerebellar tract

Question 23

lesions result to ataxia that occurs contralateralto frontal or temporal lobe pathology

Answer 23

Corticopontocerebellar tract

Question 24

Innervates the head; Most fibers terminate in reticular formation near cranial nerve nuclei

Answer 24

Corticobulbar tract

Question 25

Corticobulbar tract

Answer 25

face areas of the cerebral cortex ➡️ genu of the internal capsule ➡️cerebral peduncle (occupy a dorsolateralcorner of the CST segment as well as a small area in the medial part of the base of the peduncle) ➡️ basis pontis(where they intermix with corticospinalfibers) and pyramid but do not reach the spinal cord

Question 26

The majority of cranial nerve nuclei receive bilateral cortical input

Answer 26

Corticobulbar tract

Question 27

Direct corticostriateprojections reach the neostriatumvia the internal and external capsules

Answer 27

Corticostriate fibers

Question 28

from the prefrontal cortex, cingulate gyrus, olfactory cortex, hippocampus, and septal area

Answer 28

Corticohypothalamic fibers

Question 29

reach the hypothalamus via the internal capsule

Answer 29

Corticohypothalamic fibers

Question 30

considered by some as an indirect CST -because of the similarity in the site of termination of both tracts, and because the red nucleus receives an input from the cortex

Answer 30

Rubrospinal tract

Question 31

function of this tract is not well understood; it is believed to play a role in the turning of the head in response to light stimulation

Answer 31

Tectospinal tract

Question 32

neurons of origin in the superior colliculuscross in the dorsal tegmentaldecussationand descend throughout the neuraxis to occupy a position in the anterior funiculusof the cervical spinal cord

Answer 32

Tectospinal tract

Question 33

Fibers of this tract terminate on neurons in laminaeVI, VII, and VIII

Answer 33

Tectospinal tract

Question 34

from the lateral vestibular nucleus, descends ipsilaterally in the pons, medulla, and spinal cord, where it occupies a position in the lateral funiculus

Answer 34

Lateral VestibulospinalTract

Question 35

terminates on interneurons in laminaeVII and VIII, with some direct terminations on alpha motor neuron dendrites in the same laminae

Answer 35

Lateral Vestibulospinal Tract

Question 36

facilitates extensor motor neurons and inhibits flexor motor neurons

Answer 36

Lateral vestibulospinal tract

Question 37

Origin in the medial vestibular nucleus

Answer 37

Medial vestibulospinal tract

Question 38

fibers join the ipsilateral and contralateral medial longitudinal fasciculus, descend in the anterior funiculus of the cervical cord segments, and terminate on neurons in laminaeVII and VIII

Answer 38

Medial vestibulospinal Tract

Question 39

plays a role in controlling head position

Answer 39

Medial vestibulospinal tract

Question 40

The neurons of origin of these tracts are located in the reticular formation of the pons and medulla oblongata

Answer 40

Reticulospinal tract

Question 41

they modify sensory activity through their interaction with spinothalamic neurons in the dorsal horn

Answer 41

Reticulospinal tract

Question 42

originate predominantly from the hypothalamus

Answer 42

Descending Autonomic Pathway

Question 43

are small-caliber fibers that follow a polysynaptic route and are scattered diffusely in the anterolateralfuniculusof the spinal cord

Answer 43

Descending autonomic pathway

Question 44

project on neurons in the intermediolateralcell column

Answer 44

Descending autonomic pathway

Question 45

Lesions of this system result in autonomic disturbances

Answer 45

Descending Autonomic Pathway

Question 46

Serotonergicfibers from the raphenucleus of the medulla oblongata

Answer 46

Descending Monoaminergic Pathways

Question 47

Noradrenergic fibers from the nucleus locus ceruleusin the rostralponsand caudal midbrain

Answer 47

Descending monoaminergic pathway

Question 48

Enkephalinergic fibers from the periaqueductal gray matter in midbrain

Answer 48

Descending Monoaminergic pathway

Question 49

descend in the lateral and anterior funiculi both ipsilateral and contralateral to their site of origin

Answer 49

Descending monoaminergic pathway

Question 50

descend in the lateral and anterior funiculiboth ipsilateraland contralateralto their site of origin

Answer 50

Descending Monoaminergic pathway

Question 51

The CST facilitates _______ motor neurons and inhibit _______ motor neurons

Answer 51

Flexor; extensor

Question 52

The CST descends through all levels of the neuraxis except the __________.

Answer 52

Cerebellum

Question 53

The CST passes through the ____________ of the internal capsule

Answer 53

posterior limb

Question 54

The anterior CST is also referred to as __________.

Answer 54

turck's bundle

Question 55

The remaining 2% of the CST that remains uncrossed throughout its course is referred to as the ___________.

Answer 55

tract of Barnes

Question 56

The __________________ constitutes by far the largest component of the cortically originating descending fiber system

Answer 56

corticopontocerebellar tract

Question 57

Considered as indirect CST

Answer 57

Rubrospinal tract

Question 58

is believed to play a role in the turning of the head in response to light stimulation

Answer 58

Tectospinal tract

Question 59

___________________ facilitates extensor motor neurons and inhibits flexor motor neurons

Answer 59

Lateral Vestibulospinal tract