Spinal Tracts & Brain Stem Revision David Eagle

Ascending Tracts: Fasciculus Gracilis @ Thalamus: Synapse in Ventral Posterior Lateral Nucleus + ascends to contralateral cortex @ Midbrain: Ascends in Medial Lemniscus @ Pons: @ 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. Tables Dorsalis: gives degen of myelin in dorsal columns, rare in the UK. Iatrogenic: possible damage in spinal surgery, high spinal block, misplaced epidural

Ascending Tracts: Fasciculus Cuneatus @ Thalamus: Synapse in Ventral Posterior Lateral Nucleus + ascends to contralateral cortex @ Midbrain: Ascends in Medial Lemniscus @ Pons: @ 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? MS: often affects myelination of fasciculus cuneatus in cervical spine, leading to loss of proprioception in hands, therefore loss of dexterity. Rather than giving complete loss of fine touch, usual gives altered sensation/parasthesia/formication

Ascending Tracts: Spinothalamic @ Thalamus: Synapse in Ventral Posterior Lateral Nucleus + ascends to contralateral cortex @ Midbrain: Ascends in Spinal Lemniscus @ Pons: @ Medulla: @ 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. Can cut spinothalamic tracts as neurosurgical relief of intractable pain. Pain + temp decussate within 1 level of entry, deep touch/pressure decussate higher, therefore deep touch/pressure may be maintained for a few dermatomes below the loss of pain + temp.

Ascending Tracts: Spinocerebellar Function: “Unconscious” proprioception @ 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 Friedreich’s ataxia: inherited disorder especially affecting spinocerebellar tracts, giving gross in-coordination and wide, reeling gait.

Descending Tracts: Lateral Corticospinal @ 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: Ventral 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. . Maintains limited skilled motor function in loss of lateral corticospinal tract.

Descending Tracts: Vestibulospinal Function: Mediates excitation of extensor muscles, maintaining extensor tone + posture. @ 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 Cord tracts @ risk in: Vascular injury: anterior spinal a. . Also there is a medial vestibulospinal that contributes to the Medial Longitudinal Fasciculus

Descending Tracts: Rubrospinal @ 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: @ Spinal Level Synapse with LMN in Ventral Horn Function: Mediates excitation of flexor muscles. Cord tracts @ risk in: Vascular injury: anterior spinal a.

Ascending tracts: Descending tracts: 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

Loss of dorsal columns  loss of ipsilat. fine touch + proprioception 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 Loss of corticospinal: gives LMN symptoms (fasciculations, flaccid) at level of insult, UMN symptoms (spastic, hypertonic) below level of insult. Loss of spinothalamic: as pain + temp decussate above level, ipsilat. loss of pain + temp at level of insult, contralat. loss of pain + temp below level; contralat. loss of deep pressure at and below level of insult.

Anterior Spinal Artery Occlusion (anterior 2/3 of cord): 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 Loss of corticospinal: gives LMN symptoms at level of insult, UMN symptoms below level of insult

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 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 corticobulbar tracts  contralat. bulbar palsy Edinger-Westphal Nucleus CN III Nucleus Medial Lemniscus Spinal Lemniscus Substantia Niagra Red Nucleus CN V Sensory (proprioception) Corticospinal tracts Corticobulbar tracts CN IV Nucleus

CN V – Sensory part (Chief nucleus - light touch) CN V – Motor part 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 CN V, VI, VII often lost together as all their nerves leave the Pons caudally, along with loss of Spinal Lemniscus (=caudal tegmental pontine syndrome) CN VIII often lost with tracts in the cerebellar peduncle giving N+V, vertigo, nystagmus + ataxia (=dorsal medullary syndrome) Corticospinal tracts

CN V – Sensory part (pain + temp) CN VIII – Cochlear part 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 Nucleus Solitarius CN VIII Nucleus CN X Dorsal Nucl CN V Sensory (Pain + temp) Spinal Lemniscus Nucleus Ambiguus Lateral medullary syndrome (eg occlusion of PICA) = loss of inf cerebellar peducle (loss of co-ord), loss of nucleus ambiguus (loss of speech, swallow + gag), loss of CN V spinal part (loss of ipsilat pain +temp on face), loss of soinal lemniscus (loss of contralat pain + temp on body) Medial medullary syndrome (eg occlusion of vertebral a.) = loss of corticospinal before decussation (loss of 100% contralat. Skilled motor), loss of medial lemniscus (loss of contralat fine touch), loss of CN XII (tongue devaites to side of lesion) Medial Lemniscus Corticospinal tracts

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