Neuroscience Week 3: Motor & Sensory Projections

Question 1

Major Motor & Sensory Projections

Answer 1

Motor

• Corticospinal tract
• Corticobulbar tract

Sensory

• Posterior column / medial lemniscus
• Trigeminothalamic pathway
• Anterolateral system (spinothalamic tract)

Question 2

Lateral corticospinal tract

Answer 2

innervates distal musculature for fine motor movements

Question 3

Anterior corticospinal tract

Answer 3

Proximal muscles gross motor movements

Question 4

Corticobulbar (corticonuclear)

Answer 4

Face (CNs)

Question 5

Identify

Answer 5

Question 6

Internal capsule deep within the cerebrum

Answer 6

motor fibers consolidate here before entering the ipsilateral cerebral peduncle

Question 7

Corticobulbar tract fiber path

Answer 7

Facial fibers emerge from the lateral convexity, descend medially and, generally, decussate to synapse on different cranial nerve nuclei throughout their descent.

Question 8

Leg Corticospinal Tract path

Answer 8

Leg fibers emerge paracentrally, descend laterally through the brainstem into the ipsilateral medullary pyramid.

Question 9

Arm Corticospinal Tract path

Answer 9

Arm fibers emerge from the upper convexity, descend in between the facial and leg fibers, medial to the leg fibers through the brainstem into the ipsilateral medullary pyramid.

Question 10

Corticospinal tract

Answer 10

• As the lateral corticospinal tracts decussate and descend through the medullo-cervical junction and shift posterolaterally to enter the lateral funiculus of the cervical spinal cord: the arms remain medial to the legs.
• Arm and leg fibers decussate at the cervicomedullary junction.
• Within the subcortical white matter/internal capsule –leg fibers switch medial/lateral position with the arm fibers.
• Another within the medullary pyramid –the leg fibers switch medial/lateral position with the arm fibers.
• At the internal capsule the leg and arm fibers switch
• At the medullary pyramid
• arms remain medial to the legs
• 95 % decussate within the cervicomedullary junction and enter the lateral CST
• The other 5% continue ipsilaterally and the arms decussate at the cervical spinal cord and the remaining leg cords cross at the lumbar spinal cord and enter the anterior CST

Question 11

Posterior Column function

Answer 11

Posterior column/ medial lemniscus carries input from the sensory fibers from the body, which transmits vibration and joint position sensory information along with select other large fiber modalities, including two-point discrimination.

Question 12

Anterolateral system Function

Answer 12

(which, notably comprises the spinothalamic tract), which carries input from the small sensory fibers from the body, which transmit pain, itch, and thermal sensory information.

Question 13

Trigeminothalamic tract Function

Answer 13

which projects sensory information from the face (CN 5).

Question 14

Ventroposterior thalamus

Answer 14

all three sensory pathways ascend the brainstem separately and then bundle within the thalamus before they project to the somatosensory cortex.

Question 15

Spinothalamic tract Leg fibers

Answer 15

(its position is largely unchanged throughout its spinal cord and brainstem ascent):

Leg fibers synapse within the lumbar spinal cord and then decussate and ascend the anterolateral cord and brainstem to the thalamus.

Arm fibers synapse within the cervical spinal cord, and, also decussate and ascend the anterolateral cord and brainstem to the thalamus.

Question 16

Spinothalamic Tract Arm fibers

Answer 16

Arm fibers synapse within the cervical spinal cord, and, also decussate and ascend the anterolateral cord and brainstem to the thalamus.

Question 17

Posterior column/medial lemniscus tract Arm Fibers

Answer 17

Arm fibers synapse laterally

Question 18

Posterior column/medial lemniscus tract Leg Fibers

Answer 18

Leg fibers synapse medially

Question 19

Posterolateral Tract decussation

Answer 19

• Leg fibers emerge grom gracile nucleus and arm fibers from cuneate nucleus
• The arm and leg fibers decussate and switch at the internal arcuate decussation
• Arm fibers ascend the brainstem medial to the leg fibers as the medial lemniscus to the thalamus.
• The arm fibers ascend medial to the leg fibers.

Question 20

Trigeminothalamic fibers decussate and path

Answer 20

Decussate within the pons and ascend the brainstem, medially, to the thalamus (note: we simplify the originations of the trigeminothalamic tracts for our purposes, here)

Within the thalamus, the facial fibers project to the ventroposterior medial nucleus (VPM) and the body fibers (arms and legs) project to the ventroposterior lateral nucleus (VPL).

Twisting thalamocortical sensory projections to the cerebral cortex. The sensory fibers again reverse their orientation:

Leg fibers project medially to terminate in the posterior paracentral gyrus.

Arm fibers project lateral to the legs and terminate in the upper convexity of the postcentral gyrus.

Facial fibers project lateral to both of them and terminate in the lower lateral postcentral gyrus.

Question 21

Which sensory pathway carries pain sensation?

Answer 21

Both the anteriolateral system and trigeminothalamic pathways

Question 22

Which of the following carries facial motor fibers?

Answer 22

The corticobulbar (corticonuclear) tract

Question 23

A stroke in the lateral convexity of the brain will affect, which of the following?

Answer 23

Facial motor and sensory fibers

Question 24

Which of the following begins in the paracentral cerebral cortex?

Answer 24

Leg motor fibers

Question 25

The lateral corticospinal tract decussates at what level?

Answer 25

medullo-cervical junction

Question 26

The leg motor fibers lie lateral to the arm fibers at all of the following levels EXCEPT

Answer 26

The cerebral cortex

Question 27

The arm motor fibers lie _______ to the leg fibers at all of the following levels EXCEPT in the cerebral cortex

Answer 27

Medial

Question 28

Within the ventroposterior thalamus, which is the following lateral to medial orientation?

Answer 28

Leg arm face