1. Spinal Tracts & Brain Stem Revision
David Eagle

2. 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 risk in:
Medial Medullary Syndrome (from occlusion of Vertebral a./lower Basilar a.)
Cord 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

3. 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 risk in:
Medial Medullary Syndrome
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

4. 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 risk in:
Lateral Medullary Syndrome (from occlusion of Vertebral a./PICA)
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.

5. 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 risk in:
Lateral Medullary Syndrome
Dorsal Medullary Syndrome (from PICA occlusion)
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.

6. 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:
% of voluntary, skilled motor
Brain stem risk in:
Medial Medullary Syndrome
Locked-in Syndrome (from Basilar a. occlusion/trauma)
Cord risk in:
Vascular injury: anterior spinal a.

7. 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:
% of voluntary, skilled motor
Brain stem risk in:
Medial Medullary Syndrome
Locked-in Syndrome
Cord risk in:
Vascular injury: anterior spinal a. .
Maintains limited skilled motor function in loss of lateral corticospinal tract.

8. 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 risk in:
Vascular injury: anterior spinal a. .
Also there is a medial vestibulospinal that contributes to the Medial Longitudinal Fasciculus

9. 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 risk in:
Vascular injury: anterior spinal a.

10. 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

11. 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 % 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.

12. 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

13. 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

14. 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

15. 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

16. Questions?