Spinal Tracts

Question 1

Dorsal Column Tract

Answer 1

1st order sensory neuron in DRG
Enter spinal cord via dorsal root Fasciculus gracilis (medial) - lower half of body; fasciculus cuneatus (lateral) - upper half of body
Synapse at lower medulla on gracile & cuneate nuclei (2nd order sensory neuron)
Crossover via lemniscal decussation
Synapse at ventral posteriolateral thalamic nuclei (3rd order neuron)
Somatosensory cerebral cortex

Question 2

Somatosensory Pathway - Dorsal colum

Answer 2

1st order sensory neuron in DRG
Enter spinal cord via dorsal root & ascend to form fasciculus gracilis (medial for lower half of body) & fasciculus cuneatus
2nd order neuron at lower medulla in gracile & cuneate nuclei.
Axons cross via lemniscal decussation & ascend to thalamus
3rd order neuron in ventral posteriolateral thalamic nuclei, axons project to cerebral sensory cortex
For fine touch, vibration, 2 point discrimination, & proprioception

Question 3

Somatosensory pathways - spinothalamic (ventral)

Answer 3

1st order sensory neuron in DRG
Enter spinal cord via dorsal root & forms Lissauer’s track. Ascend ipsilateral 2 segments
2nd order neuron at dorsal horn 2 spinal segments above (same side). Axons cross to opposite side to form anterior spinothalamic tract (light touch) & lateral spinothalamic tract (pain & temp)
3rd order neuron thalamus, axons project to somatosensory cerebral cortex.
Dorsal column tracks (left) for fine touch, vibration, 2 point discrimination, & proprioception
Spinothalamic tracts (right) for light touch, pain, & temp

Question 4

Brown-Sequard Syndrome

Answer 4

Hemisection of spinal cord resulting in paralysis and loss of proprioception on same side as injury or lesion
Loss of pain and temperature sensation on opposite side

Question 5

White Matter-Corticospinal Tract

Answer 5

Cerebral cortex – upper motor neurons → Medulla → pyramidal tract → Lower medulla – pyramidal decussation (cross to contralateral side) → Spinal cord → lateral corticospinal tract (Contains more than 1 million myelinated axons) → Synapse with LMNs in ventral horn → Control voluntary, high skill, & fractionated movement.

Question 6

Corticospinal/Corticobulbar Track

Answer 6

Cerebral cortex → Internal capsule → Brain stem → Corticobulbar tract ends → Corticospinal tract pass through medulla & most form pyramidal decussation → Decussated fibers descend in lateral column of spinal cord → Small % (~3%) fibers never decussate but still descend in lateral column → 10% fibers descend in anterior column on same side & decussate in spinal cord before synapse with lower motor neurons → All upper motor neurons synapse with lower motor neurons in ventral horn.

Question 7

Pyramidal System - LMN lesions

Answer 7

Caused by trauma, toxins, infection, degenerative diseases or tumor

Question 8

LMN Lesions can cause

Answer 8

Flaccid paralysis
Muscle atrophy
Diminished/absent deep tendon reflexes
No pathological reflexes
Muscle fasciculations/fibrillation

Question 9

Pyramidal System - UMN Lesions

Answer 9

Caused by strokes, infections, tumors, trauma to spinal cord corticospinal tracts

Question 10

UMN Lesions can cause

Answer 10

Spastic paralysis
Little to no muscle atrophy
Hyperactive deep tendon reflexes
Pathological reflex
No fasciculations

Question 11

Basal Ganglia Lesions

Answer 11

Akinesia
Bradykinesia
Dyskinesia
Tremor
Athetosis
Chorea
Huntington's
Hemiballismus
Parkinson's

Question 12

Cerebellum Motor Lesions

Answer 12

Nystagmus - loss of equilibrium
Truncal ataxia - drunk gait
Ataxia - loss of coordination, jerking movements
Dysmetria - loss of distance estimation
Dysdiachokinesia - unable to rapidly alternated movement