Spinal Tracts Brain Stem Revision David Eagle Ascending

Spinal Tracts & Brain Stem Revision David Eagle

Ascending Tracts: Fasciculus Gracilis Function: • Fine touch • “Conscious” proprioception • Below T 6 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 T 6) • Via dorsal root ganglia • Enters + ascends ipsilateral to stimulus in Fasciculus Gracilis in Dorsal Columns

Ascending Tracts: Fasciculus Cuneatus Function: • Fine touch • “Conscious” proprioception • T 6 + 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 (T 6 + 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 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) 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 XII Nucleus Solitarius CN VIII Nucleus CN X Dorsal Nucl CN V Sensory (Pain + temp) Spinal Lemniscus Nucleus Ambiguus Medial Lemniscus Corticospinal tracts

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