Ascending Spinal Tracts

Question 1

Dorsal Column / Medial Lemniscus

• Function?
• Crosses?
• Neuron order?

Answer 1

• Discriminative touch/touch localization, pressure, vibration, joint position sense from the body. (Gives rise to stereognosis, graphestesia)
• Crosses in the lower medulla in internal arcuate fibers.
• 3 neuron order
  1) Sensory receptor through DRG, up fasciculus gracilis (LE), or fasciculus cuneata (UE).
  2) Synapses in the medulla and crosses in the lower medulla (internal arcuate fibers). Now the neuron is called the medial lemniscus.
  3) Synapses in the thalamus at the ventral posterolateral nucleus and goes up the brainstem through the internal capsule to the primary somatosensory cortex.

Question 2

Trigeminal Lemniscus

• Function?
• Crosses?
• Neuron order?

Answer 2

• Discriminative touch/touch localization, pressure, vibration, and joint position (proprioception) from the face.
• Crosses at the Pons (trigeminal main sensory nn).
• 3 neuron order:
  1) peripheral receptors axon travel through trigeminal ganglion through main sensory nucleus in the pons.
  2) Synapses at the trigeminal sensory nucleus. Crosses in the pons (segregates to 3 bands). Travels through trigeminal lemniscus, through midbrain, to ventral posteromedial nucleus in thalamus.
  3) Synapses at the thalamus (VPM). Travels to lateral aspect of primary somatosensory cortex (homunculus).

Question 3

Spinothalamic (anterolateral) Pathway

• Function?
• Crosses?
• Neuron order?

Answer 3

• Discriminative; fast pain, crude touch, temp.
• Crosses in the SC in the anterior white commissure.
• may cross 1-2 SC levels up (runs in Lissauer’s tract).
• 3 neuron order:
  1) Peripheral receptor through DRG –> to DH of SC.
  2) Synapses at DH and crosses immediately at the entry SC level –> runs up anterolateral aspect of SC to VPL in the thalamus.
  3) Synapses in the thalamus and travels to the primary somatosensory cortex.

Question 4

Trigeminothalamic Tract

• Cell bodies?
• Type? Conscious or unconscious?
• Function?
• Crosses?
• Neuron order?

Answer 4

• Ascending Pathway (Cell bodies in DRG)
• Somatosensory, unconscious
• Discriminative/fast pain, crude touch, temperature from FACE
• Crosses at Spinal N Of Trigeminal N in Medullar
• 3 Neuron Order:
  1) peripheral receptor travels to trigeminal ganglion → pons & travels down to lower medulla & crosses.
  2) Synapses on the spinal nucleus of trigeminal N in medulla → crosses midline → ascends medially to VPM of thalamus
  3) Synapses in VPM of the thalamus → travels to the primary somatosensory cortex.

Question 5

Spinmesencephalic

• Function?
• Crosses?
• Neuron order?

Answer 5

• Medial pain system (slow pain) - turning eyes/head toward source of pain (noxious input)
• visual regard and attention to pain
• Crosses at the DH of SC
• 2 neuron order:
  1) Free nerve endings project to DH of SC and crosses over immediately –> synapses with interneurons in DH (lamina)
  2) Project to 2 areas of the midbrain - superior colliculus and peri aqueduct also gray.

Question 6

Spinoreticular

• Cell bodies?
• Type? Conscious or unconscious?
• Function?
• Crosses?
• Neuron order?

Answer 6

• ascending pathway - cell bodies in DRG
• Somatosensory, conscious and unconscious (divergent pathway)
• medial pain system (slow pain) - arousal, attention to pain, perception.
• sleep/wake cycle, as intense pain can affect sleep and demand attention
• Crosses at the DH of SC
• 2 neuron order:
  1) FNE project to DH of SC and crosses over immediately –> synapses with interneurons in DH (lamina)
  2) Synapses in brainstem reticular formation (midbrain, pons, medulla) –> projects to interlaminar nuclei of thalamus

Question 7

Spinolimbic/Spinoemotional Tract

• Cell bodies?
• Type? Conscious or unconscious?
• Function?
• Crosses?
• Neuron order?

Answer 7

• Ascending pathway - cell bodies in DRG
• Somatosensory, conscious and unconscious (divergent pathway)
• Medial pain system - emotion context and behavior reactions to pain
• only divergent pathway that keeps rising above brainstem
• only tract that is perceived as pain
• crosses at post synapses / DH
• 3 neuron order:
  1) FNE project to DH of SC and crosses over immediately
  2) synapses with interneurons in DH (lamina)
  3) Travels to medial and intralaminar nuclei in thalamus, synapses with 3rd order neurons going to limbic system, insular cortex, post central gyrus (parietal lobe).
• runs with spinothalamic tract

Question 8

Posterior (Dorsal) Spinocerebellar

• Cell bodies?
• Type? Conscious or unconscious?
• Function?
• Crosses?
• Neuron order?

Answer 8

• Ascending Pathway (cell bodies in DRG) * spinocerebellar tract *
• Somatosensory , unconscious
• Convey high fidelity info from lower body proprioceptors / finer coordination / postural adj.
• info from mm/tendons/jt receptors
• no cortical projections
• fast transmission to the cerebellum, allowing for finer coordination (postural adj.)
• DOES NOT CROSS (IPSILATERAL)
• 2 Neuron Order
  1) receptor info from mm/jt/ tendon travels in the cord from thoracic & lumbar levels.
  2) synapses in DH (Clarke’s nucleus/column) in lamina VII → projects to the cerebellar cortex via inferior cerebellum peduncle LE

Question 9

Cuneocerebellar

• Cell bodies?
• Type? Conscious or unconscious?
• Function?
• Crosses?
• Neuron order?

Answer 9

• Ascending Pathway (cell bodies in DRG) * spinocerebellar tract*
• Somatosensory , unconscious
• Convey high fidelity info from upper body proprioceptors / finer coordination / postural adj.
• info from mm/tendons/jt receptors
• no cortical projections
• fast transmission to the cerebellum, allowing for finer coordination/postural adj.
• DOES NOT CROSS (IPSILATERAL)
• 2 Neuron Order
  1) Receptor info from mm, joints, tendons travels in cord ipsilaterally
  2) Synapses in lateral cuneate nucleus (nucleus cuneatus) of medulla & enters the cerebellum through inferior cerebellar peduncle.

Question 10

Anterior (Ventral) Spinocerebellar

• Cell bodies?
• Type? Conscious or unconscious?
• Function?
• Crosses?
• Neuron order?

Answer 10

• Ascending Pathway (cell bodies in DRG) * Spinocerebellar tract *
• Somatosensory, unconscious
• Low fidelity, internal (slow) feedback to cerebellum about spinal reflex circuits (interneuron activities) & descending mm activity from LEs. Automatic postural adjustment & coordination.
• Occurs in thoracolumbar SC.
• Crosses in SC ant white comm (& in cerebellum *)
• ONLY SPINOCEREBELLAR TRACT THAT CROSSES!!!
• 2 Neuron Order:
  1) cell bodies of interneuron pools are located in lateral & ventral horns
  2) synapses in grey matter & crosses immediately in anterior white commissure → ascends in contralateral tract to midbrain → enters both sides of the cerebellum through superior peduncles.

Question 11

Rostrospinocerebellar

• Cell bodies?
• Type? Conscious or unconscious?
• Function?
• Crosses?
• Neuron order?

Answer 11

• Ascending Pathway (cell bodies in DRG)
• Somatosensory, unconscious * Spinocerebellar tract *
• Low fidelity, internal (slow) feedback to cerebellum about spinal reflex circuits (interneuron activities) & descending mm activity from UEs. Automatic postural adjustment & coordination.
• Occurs in thoracolumbar SC.
• DOES NOT CROSS (IPSILATERAL)
• 2 Neuron Order:
  1) Info from reflex circuits from mm enters the cervical spine.
  2) Synapses in INP in grey matter & ascends in contralateral tract to the midbrain & enters the cerebellum through inferior & superior peduncles.
• ipsilateral!