Corticospinal

Question 1

corticospinal tract function

Answer 1

voluntary motor pathway for the body

Question 2

corticobulbar (corticonuclear) tract function

Answer 2

carries out movements for the cranial nerve motor nuclei that innervate the face

Question 3

corticospinal and corticobulbar tracts

• arise…
• descend through…
• end in…

Answer 3

arise in cerebral cortex
descend through internal capsule
end in
-brainstem motor nuclei or
-ventral horn of spinal cord

Question 4

where do most of the fibers descending to the spinal cord from the corticospinal and corticobulbar tracts cross
-what about the other fibers

Answer 4

in the lower medulla at the pyramidal decussation

descend ipsilaterally to individual segments and then cross

Question 5

corticospinal tract

-location of primary cells of origin

Answer 5

precentral gyrus (primary motor cortex; area 4)
area 6 (premotor region; lateral premotor and supplementary motor)
area 8 (frontal eye fields)
primary somatosensory cortex (areas 3, 1, 2)

Question 6

the fibers that make up the corticospinal tract exit the _____ of the cortex and travel through the _____

Answer 6

gray matter

medullary white matter (fiber bundles underlying the cortex)

Question 7

medullary white matter

• what is it?
• specific names, in sequence

Answer 7

fiber bundles underlying the cortex
names
-corona radiata
-posterior limb of the internal capsule
-cerebral peduncles
-corticospinal fibers in the ventral pons
-pyramids

Question 8

corticospinal tract

-at lower end of medulla, 85% of fibers cross at _____ and continue descent as _____

Answer 8

cross at pyramidal decussation

continue as lateral corticospinal tract

Question 9

lateral corticospinal tract

• located in
• function

Answer 9

lateral funiculus

innervate extremities

Question 10

corticospinal tract

• fibers that do not cross at the pyramidal decussation descend as the _____
• where do these cross
• function

Answer 10

anterior corticospinal tract
cross at the segmental level
innervate lower motor neuronal pool

Question 11

anterior corticospinal tract

-located in

Answer 11

anterior funiculus

Question 12

termination location of corticospinal tract fibers

Answer 12

interneurons (97%)

Question 13

where do corticospinal fibers terminate?

Answer 13

cervical region (55%)
thoracic region (20%)
lumbar region (25%)

Question 14

what excites or inhibits the lower motor neurons to influence the activity of a given motor unit

Answer 14

interneurons

Question 15

lower motor neurons innervate muscles _____ to the cell body location in the spinal cord

Answer 15

ipsilateral

Question 16

corticoreticulospinal pathways

• runs parallel to…
• cells giving rise to these fibers are located in the…

Answer 16

parallel to corticospinal tract
located in
-supplementary motor area
-lateral premotor area

Question 17

corticoreticulospinal pathway

• axons descend to the level of the _____
• what happens at this level

Answer 17

descend to level of pontine and medullary reticular formation
synapse bilaterally

Question 18

reticulospinal fibers

• descend into….
• what happens there?

Answer 18

descend into the spinal cord
synapse in the ventral horn on the lower motor neuron pool
-primarily on interneurons

Question 19

corticoreticulospinal pathway

-purposes

Answer 19

premotor and secondary motor areas provide information to primary motor cortex for voluntary movement
premotor areas activate the reticular formation and subsequently the reticulospinal fibers
-information is transferred to the spinal cord for initiation of complementary activation of axial and proximal limb musculature

Question 20

corticoreticulospinal

• information from primary motor cortex descends for _____
• this is termed….

Answer 20

fine motor control distally on the extremities, i.e. the fingers
this precise individual movement is termed fractionated movement

Question 21

corticoreticulospinal
-purpose of complementary activation of axial and proximal limb musculature by the reticular formation and reticulospinal fibers

Answer 21

sets the platform for movement in anticipation of the fractioned movement

Question 22

other descending pathways that are classified as upper motor neurons

Answer 22

pontine (medial) reticulospinal pathway
medullary (lateral) reticulospinal pathway
lateral vestibulospinal pathway
medial vesticulospinal pathway
tectospinal pathway
rubrospinal pathway

Question 23

pontine (medial) reticulospinal pathway

• ipsi or contra
• function
• works with the…

Answer 23

primarily ipsilateral
facilitory to axial and limb musculature
-especially the extensors
works with medial vestibulospinal tract

Question 24

medullary (lateral) reticulospinal pathway

• ipsi or contra
• function

Answer 24

bilateral (greater ipsilateral)
facilitory to flexor musculature
inhibitory to axial and limb extensor musculature

Question 25

lateral vestibulospinal pathway - ipsi or contra - function

Answer 25

ipsilateral | excitatory on extensors of lower extremity musculature (inhibits flexor musculature)

Question 26

medial vestibulospinal pathway - ipsi or contra - descends to... - function

Answer 26

projects bilaterally descends only to cervical and upper thoracic levels control of neck and upper thoracic musculature

Question 27

tectospinal pathway - descends to... - function

Answer 27

descends only to cervical levels | coordinates neck movement toward a stimulus

Question 28

rubrospinal pathway - ipsi or contra - descends how far? - main functional level - -why?

Answer 28

contralateral descends the entire length of cord functions mostly at cervical level -in species with bipedal locomotion this tract has diminished in importance and functions mostly at the cervical level

Question 29

rubrospinal pathway | -function

Answer 29

involved in flexor activation of the UE -primarily distal musculature plays a role in fractionated movements of the wrist and fingers

Question 30

medial vs. lateral activation systems - differentaiton defined primarily by... - medial are involved in... - lateral are involved in...

Answer 30

location of the axons of the upper motor neurons medial -involved in more postural movements and activities -named for both their position in the cord and their function lateral -involved with distal limb musculature, i.e. fractionated movement

Question 31

medial activation system - location - consists of what pathways

Answer 31

``` located in anterior funiculus consists of -anterior corticospinal -medial (pontine) reticulospinal -medial vestibulospinal -lateral vestibulospinal -tectospinal ```

Question 32

lateral activation system - location - consists of what pathways

Answer 32

``` located in lateral funiculus consists of -lateral corticospinal -rubrospinal -lateral (medullary) reticulospinal ```

Question 33

other descending components

Answer 33

``` primary somatosensory cortex raphespinal cerulospinal spinomesencephalic spinoreticular ```

Question 34

primary somatosensory cortex - sends axons caudally through _____ - axons terminate _____ - function

Answer 34

sends axons caudally through lateral corticospinal pathway axons terminate in dorsal horn though to function as a feedback mechanism that integrates cortical understanding of sensation with incoming sensory information

Question 35

raphespinal and cerulospinal pathways - where do they originate - function

Answer 35

originate in reticular formation nuclei - Raphe nuclei and Locus Ceruleus involved in modification of afferent sensory information at the dorsal horn level

Question 36

spinomesencephalic and spinoreticular pathways | -function

Answer 36

activate a number of reticular system components | these descending components play a role in the modulation of incoming pain stimuli