Neuroscience Week 3: Motor & Sensory Projections Flashcards
Major Motor & Sensory Projections
Motor
- Corticospinal tract
- Corticobulbar tract
Sensory
- Posterior column / medial lemniscus
- Trigeminothalamic pathway
- Anterolateral system (spinothalamic tract)
Lateral corticospinal tract
innervates distal musculature for fine motor movements
Anterior corticospinal tract
Proximal muscles gross motor movements
Corticobulbar (corticonuclear)
Face (CNs)
Identify
Internal capsule deep within the cerebrum
motor fibers consolidate here before entering the ipsilateral cerebral peduncle
Corticobulbar tract fiber path
Facial fibers emerge from the lateral convexity, descend medially and, generally, decussate to synapse on different cranial nerve nuclei throughout their descent.
Leg Corticospinal Tract path
Leg fibers emerge paracentrally, descend laterally through the brainstem into the ipsilateral medullary pyramid.
Arm Corticospinal Tract path
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.
Corticospinal tract
- 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
Posterior Column function
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.
Anterolateral system Function
(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.
Trigeminothalamic tract Function
which projects sensory information from the face (CN 5).
Ventroposterior thalamus
all three sensory pathways ascend the brainstem separately and then bundle within the thalamus before they project to the somatosensory cortex.
Spinothalamic tract Leg fibers
(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.
Spinothalamic Tract Arm fibers
Arm fibers synapse within the cervical spinal cord, and, also decussate and ascend the anterolateral cord and brainstem to the thalamus.
Posterior column/medial lemniscus tract Arm Fibers
Arm fibers synapse laterally
Posterior column/medial lemniscus tract Leg Fibers
Leg fibers synapse medially
Posterolateral Tract decussation
- 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.
Trigeminothalamic fibers decussate and path
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.
Which sensory pathway carries pain sensation?
Both the anteriolateral system and trigeminothalamic pathways
Which of the following carries facial motor fibers?
The corticobulbar (corticonuclear) tract
A stroke in the lateral convexity of the brain will affect, which of the following?
Facial motor and sensory fibers
Which of the following begins in the paracentral cerebral cortex?
Leg motor fibers
The lateral corticospinal tract decussates at what level?
medullo-cervical junction
The leg motor fibers lie lateral to the arm fibers at all of the following levels EXCEPT
The cerebral cortex
The arm motor fibers lie _______ to the leg fibers at all of the following levels EXCEPT in the cerebral cortex
Medial
Within the ventroposterior thalamus, which is the following lateral to medial orientation?
Leg arm face
