Spinal Tracts & Brain Stem RevisionDavid Eagle

Ascending Tracts: Fasciculus Gracilis

@ 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

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

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

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?

Ascending Tracts: Fasciculus Cuneatus

Ascending Tracts: Spinothalamic

@ 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

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.

Ascending Tracts: Spinocerebellar

@ 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

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

Function: • “Unconscious” proprioception

@ 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

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.

Descending Tracts: Lateral Corticospinal

@ 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

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.

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Descending Tracts: Ventral Corticospinal

@ 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

Function: • Mediates excitation of extensor muscles, maintaining extensor tone + posture.

Cord tracts @ risk in:• Vascular injury: anterior spinal a.

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Descending Tracts: Vestibulospinal

@ 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

Function: • Mediates excitation of flexor muscles.

Cord tracts @ risk in:• Vascular injury: anterior spinal a.

Descending Tracts: Rubrospinal

• 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 - Summary

• 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

Spinal Tracts - Injury

Brain Stem – Upper & Lower Midbrain

CN IV Nucleus

CN III Nucleus

Medial Lemniscus

Substantia Niagra

Corticospinal tracts

Red Nucleus

Edinger-Westphal NucleusNuceli: • EPW – Pupil response• CN III – Occulomotor• CN IV – Trochlear • • Red Nucleus CN V – Sensory (Mesencephalic nucleus proprioception) – flexor coordination

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

Corticobulbar tracts

CN V Sensory (proprioception)

Spinal Lemniscus

Brain Stem – Pons

Medial Lemniscus

CN VIII Nucleus

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 VII Nucleus

CN VI Nucleus

CN V Sensory (light touch)CN V Motor

Corticospinal tracts

Spinal Lemniscus

Brain Stem – Medulla

Medial Lemniscus

CN VIII Nucleus

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)

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

Nucleus Ambiguus

CN X Dorsal Nucl

CN V Sensory (Pain + temp)

Corticospinal tracts

Spinal Lemniscus

CN XII Nucleus

Nucleus Solitarius

Questions?