Motor and sensory tracts
Steven, a 56-year-old gentleman, was recently involved in a road traffic accident which resulted in profound weakness of his left leg. On examination he has loss of vibration and proprioception of his left leg, loss of pain sensation of his right leg and no plantar reflex of his right leg. What is the cause of the patients signs?
Motor tracts (descending tracts)
-
Pyramidal tracts: originate in cerebral cortex. Responsible for voluntary movement.
-
Extrapyramidal tracts: originate in brain stem. Responsible for involuntary movement (tone, balance, posture)
Pyramidal tracts
-
Corticospinal: supplies body
-
Corticobulbar: supplies head and neck
Corticospinal
The lateral corticospinal tract is responsible for most motor functions (the anterior spinal tract is responsible for fine movement, especially of hands).
Lateral corticospinal tract
-
Cell body located in motor cortex (pre-central gyrus of frontal lobe)
-
Passes through internal capsule to the medulla
-
Crosses over (decussates) in medulla
-
Synapses with lower motor neurone in anterior horn of spinal cord
A lesion above where the tract crosses (e.g. brain) will lead to opposite sided weakness [e.g. stroke]
A lesion below where the tract crosses (e.g. spinal cord) will lead to same sided weakness [e.g. Brown-Sequard – see below]
Sensory tracts (ascending tracts)
The two main conscious sensory pathways are the dorsal column and spinothalamic pathways.
Dorsal column: delicate touch, proprioception, vibration, pressure
Spinothalamic: pain, temperature, coarse touch
Dorsal column: delicate touch, proprioception, vibration, pressure
-
Peripheral nerve synapses in spinal cord
-
Travels up spinal cord
-
Crosses over (decussates) in the medulla
-
Travel through the thalamus
-
Ends in the sensory region (post-central gyrus) of parietal lobe
A lesion above the where the tract crosses (e.g. brain) will lead to opposite fine touch loss [e.g. stroke]
A lesion below where the tract crosses (e.g. spinal cord) will lead to same sided fine touch loss [e.g. Brown-Sequard – see below]
Spinothalamic: pain, temperature, coarse touch
-
Peripheral nerve synapses in spinal cord
-
Crosses over (decussates) in the spinal cord
-
Travel through the thalamus
-
Continues up the spinal cord
-
Ends in the sensory region (post-central gyrus) of parietal lobe
A lesion above where the tract crosses (e.g. brain) will lead to same sided loss of pain sensation [e.g. stroke]
A lesion below where the tract crosses (e.g. spinal cord) will lead to opposite sided loss of pain sensation [e.g. Brown-Sequard – see below]
Steven, a 56-year-old gentleman, was recently involved in a road traffic accident which resulted in profound weakness of his left leg. On examination he has loss of proprioception and vibration of his left leg, loss of pain sensation of his right leg and no plantar reflex of his right leg.
Steven is suffering from Brown-Sequard syndrome – this is caused by injury to half of the spinal cord (a complete injury would lead to complete paralysis and complete loss of sensation).
The hemi-section injury at the spinal cord level results in
-
Same sided weakness below the level of the injury (since corticospinal tract crosses over higher up in the in the medulla so an injury below will affect the same side)
-
Same sided loss of vibration and proprioception below the level of the injury (since the dorsal column crosses over higher up in the medulla so an injury below will affect the same side)
-
Opposite sided loss of pain and temperature below the level of the injury (since the spinothalamic tract crosses over in the spinal cord. For example an injury at T12 will affect the opposite side from below T12 (ie from L1).
Take home messages
-
A lesion in the brain (e.g. stroke) can lead to SAME sided loss of pain and OPPOSITE sided loss of fine touch and power
-
A lesion of one side of the spinal cord can lead to SAME sided loss of fine touch and power and OPPOSITE sided loss of pain
Lesions below L1 will likely present with lower motor neurone signs (click here for further information) since the spinal cord ends at L1
Dorsal column: delicate touch
Spinothalamic: sharp