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Spinal Tracts & Brain Stem Revision
David Eagle
Ascending Tracts:
Fasciculus Gracilis
Function:
• Fine touch
• “Conscious” proprioception
• Below T6
Brain stem tracts @ risk in:
• Medial Medullary
Syndrome (from occlusion
of Vertebral a./lower Basilar
a.)
Cord tracts @ risk in:
• Tabes Dorsalis (from
Neurosyphilis)
• Direct injury: stabbing,
iatrogenic.
• Vascular injury?: 2 x
posterior spinal arteries
supply posterior 1/3 of cord.
@ Thalamus:
• Synapse in Ventral Posterior
Lateral Nucleus + ascends to
contralateral cortex
@ Midbrain:
• Ascends in Medial Lemniscus
@ Pons:
• Ascends in Medial Lemniscus
@ Medulla:
• Synapses in Nucleus Gracilis
• Decussates to ascend
contralateral to stimulus
@ Spinal Level (below T6)
• Via dorsal root ganglia
• Enters + ascends ipsilateral to
stimulus in Fasciculus Gracilis
in Dorsal Columns
Ascending Tracts:
Fasciculus Cuneatus
Function:
• Fine touch
• “Conscious” proprioception
• T6 + above
Brain stem tracts @ risk in:
• Medial Medullary
Syndrome
Cord @ Risk in:
• MS
• Tabes Dorsalis
• Iatrogenic injury
• Vascular injury?
@ Thalamus:
• Synapse in Ventral Posterior
Lateral Nucleus + ascends to
contralateral cortex
@ Midbrain:
• Ascends in Medial Lemniscus
@ Pons:
• Ascends in Medial Lemniscus
@ Medulla:
• Synapses in Nucleus
Cuneatus
• Decussates to ascend
contralateral to stimulus
@ Spinal Level (T6 + above)
• Via dorsal root ganglia
• Enters + ascends ipsilateral to
stimulus in Fasciculus
Cuneatus in Dorsal Columns
Ascending Tracts:
Spinothalamic
Function:
• Pain
• Temperature
• “Deep” touch/pressure
Brain stem tracts @ risk in:
• Lateral Medullary
Syndrome (from occlusion
of Vertebral a./PICA)
Cord @ Risk in:
• Syringomyelia: from
enlargement of central canal
• Vascular injury: 1 x
anterior spinal artery
supplies anterior 2/3 of
cord.
@ Thalamus:
• Synapse in Ventral Posterior
Lateral Nucleus + ascends to
contralateral cortex
@ Midbrain:
• Ascends in Spinal Lemniscus
@ Pons:
• Ascends in Spinal Lemniscus
@ Medulla:
• Ascends in Spinal Lemniscus
@ Spinal Level
• Via dorsal root ganglia
• Synapses
• Decussates (within 2-3 levels)
via Ventral White Commisure
to ascend contralateral to
stimulus
Ascending Tracts:
Spinocerebellar
Function:
• “Unconscious”
proprioception
Brain stem tracts @ risk in:
• Lateral Medullary
Syndrome
• Dorsal Medullary
Syndrome (from PICA
occlusion)
Cord @ Risk in:
• Vascular injury: anterior
spinal a.
• Friedreich’s ataxia
@ Superior Cerebellar Peduncle:
• Ventral decussate again
• And enter cerebellum
ipsilateral to stimulus
@ Inferior Cerebellar Peduncle:
• Dorsal enter cerebellum,
ipsilateral to stimulus
@ Spinal Level
• Via dorsal root ganglia
• Synapses
• Dorsal ascend ipsilateral in
Dorsal Spinocerebellar Tract
• Ventral decussate and ascend
contralateral in Ventral
Spinocerebellar Tract
Descending Tracts:
Lateral Corticospinal
Function:
• 75 - 90% of voluntary,
skilled motor
Brain stem tracts @ risk in:
• Medial Medullary
Syndrome
• Locked-in Syndrome
(from Basilar a.
occlusion/trauma)
Cord tracts @ risk in:
• Vascular injury: anterior
spinal a.
@ Cortex:
• UMN descends from
contralateral cortex via
Internal Capsule
@ Midbrain:
• Descends in Cerebral
Peduncle
@ Pons:
• Descends in fascicles
@ Medulla:
• Decussates in Caudal
Medulla
• To descend in Pyramids, then
Lateral Corticospinal Tract,
ipsilateral to effector
@ Spinal Level
• Synapse with LMN in Ventral
Horn
Descending Tracts:
Ventral Corticospinal
Function:
• 10 - 25% of voluntary,
skilled motor
Brain stem tracts @ risk in:
• Medial Medullary
Syndrome
• Locked-in Syndrome
Cord tracts @ risk in:
• Vascular injury: anterior
spinal a.
.
@ Cortex:
• UMN descends from
contralateral cortex via
Internal Capsule
@ Midbrain:
• Descends in Cerebral
Peduncle
@ Pons:
• Descends in fascicles
@ Medulla:
• Descends in Pyramids, then
Ventral Corticospinal Tract,
contralateral to effector
@ Spinal Level
• Decussate
• Synapse with LMN in Ventral
Horn
Descending Tracts:
Vestibulospinal
Function:
• Mediates excitation of
extensor muscles,
maintaining extensor tone +
posture.
Cord tracts @ risk in:
• Vascular injury: anterior
spinal a.
.
@ Pons:
• Arises in Lateral Vestibular
Nuclei
• Receives input from labyrinth
(via cn VIII) + cerebellum (via
inf. Cerebellar peduncle)
@ Medulla:
• Descends just dorsal to the
Pyramids, then Lateral
Vestibulaospinal Tract,
ipsilateral to effector
@ Spinal Level
• Synapse with LMN in Ventral
Horn
Descending Tracts:
Rubrospinal
Function:
• Mediates excitation of
flexor muscles.
Cord tracts @ risk in:
• Vascular injury: anterior
spinal a.
@ Midbrain:
• Arises from Red Nucleus
• Receives input from
cerebellum (via sup.
cerebellar peduncle)
• Decussates to descend in
Rubrospinal Tract, ipsilateral
to effector
@ Pons:
• Descends in Rubrospinal
Tract
@ Medulla:
• Descends in Rubrospinal
Tract
@ Spinal Level
• Synapse with LMN in Ventral
Horn
Spinal Tracts - Summary
• Ascending tracts:
– all rise ipsilateral to the stimulus, except for
spinothalamic + ventral part of spinocerebellar
• Descending tracts:
– All descend ipsilateral to the effector muscle,
except for ventral corticospinal
Spinal Tracts - Injury
• Hemi-section of cord:
– Loss of dorsal columns  loss of ipsilat. fine touch + proprioception
– Loss of dorsal spinocerebellar  some ipsilat. intention tremor/ataxia
– Loss of ventral spinocerebellar  some contralat. intention tremor/ataxia
– Loss of spinothalamic  loss of contralat. pain, temperature + pressure
– Loss of lateral corticospinal  loss of ipsilat. 75-90% fine motor
– Loss of vestibulospinal  loss of ipsilat. extensor tone
– Loss of rubrospinal  loss of ipsilat. flexor tone
– Loss of ventral corticospinal  minor loss of contralat. fine motor
Spinal Tracts - Injury
• Anterior Spinal Artery Occlusion (anterior 2/3 of cord):
– Dorsal columns maintained  fine touch intact
– Loss of most spinocerebellar  bilat. intention tremor/ataxia
– Loss of spinothalamic  loss of bilat. pain, temperature + pressure
– Loss of some? lateral corticospinal and all ventral corticospinal  loss of
most? bilat. fine motor
– Loss of vestibulospinal  loss of bilat. extensor tone
– Loss of rubrospinal  loss of bilat. flexor tone
Brain Stem – Upper & Lower Midbrain
Nuceli:
• EPW – Pupil response
• CN III – Occulomotor
• CN IV – Trochlear
•
• Red Nucleus CN V – Sensory
(Mesencephalic nucleus
proprioception) – flexor coordination
Edinger-Westphal Nucleus
CN III Nucleus
Medial Lemniscus
Spinal Lemniscus
Substantia Niagra
Benedikt’s syndrome:
• Occlusion of posterior cerebral a.
• Loss of CNIII  Ipsilat. CNIII Palsy
• Loss of Red Nucl.  ataxia
• Loss of corticospinal/bulbar 
contralat. hemiparesis
Weber’s syndrome:
• Tumour in the inter-peduncular
fossa
• Loss of CNIII  Ipsilat. CNIII Palsy
• Loss of corticobulbar tracts 
contralat. bulbar palsy
Red Nucleus
CN V Sensory
(proprioception)
Corticospinal tracts
Corticobulbar tracts
CN IV Nucleus
Brain Stem – Pons
Nuclei:
• CN V – Sensory part (Chief
nucleus - light touch)
• CN V – Motor part
• CN VI – Abducens
• CN VII - Facial
• CN VIII – Vestibular part
Occlusion of pontine arteries:
• Loss of CNV  loss of ipsilat.
mastication + facial sensation
• Loss of CNVI loss of lateral
gaze in ipsilat. eye
• Loss of CNVII  ipsilat. facial
palsy
• Loss of CNVIII  N+V,
nystagmus, vertigo
•Loss of medial lemniscus  loss
of contralat. fine touch
• Loss of spinal lemniscus  loss
of contralat. pain + temp
• Loss of corticospinal tracts 
loss of all contralat. fine motor
CN VIII Nucleus
CN VI Nucleus
CN V Sensory
(light touch)
CN V Motor
Spinal Lemniscus
CN VII Nucleus
Medial Lemniscus
Corticospinal tracts
Brain Stem – Medulla
Nuclei:
• CN V – Sensory part (pain + temp)
• CN VIII – Cochlear part
• CN X Dorsal Nucleus – Parasymp on CN X
• CN XII – Accessory
• Nucleus Solitarius – Taste + carotid +
arotic body input (CN VII, IX, X)
• Nucleus Ambiguus – Motor for speech +
swallowing (CN IX, X)
CN XII Nucleus
Nucleus Solitarius
CN VIII Nucleus
Occlusion of vertebral as./PICA:
• Loss of CNV  loss of ipsilat. pain + temp
• Loss of CNX DN  loss of vagal input?
• Loss of CNXII  tongue protrudes
towards side of lesion
• Loss of CNVIII  N+V, nystagmus, vertigo
• Loss of NS  Loss of taste +
homeostasis?
• Loss of NA  Loss of speech, swallow +
gag
• Loss of medial lemniscus, spinal
lemniscus & corticospinal tracts
CN X Dorsal Nucl
CN V Sensory
(Pain + temp)
Spinal Lemniscus
Nucleus Ambiguus
Medial Lemniscus
Corticospinal tracts
Questions?