Spinal Cord

Question 1

Fasiculus Gracilis

• Where is is located in the spinal cord?
• What information does it carry?
• What type of fibers is it carrying (diameter, myelin)?
• Describe the pathway of fibers from origin to termination, including:
  
  • Location of synapses
  • Point at which it crosses midline
• Somatotopic distribution in cord?

Answer 1

• Located in the dorsal funiculus (more medial)
• Carries discriminative touch information from T7 and below
• Alpha-beta fibers (large, myelinated)
• First synapse is in ipsilateral nucleus gracilis (medulla)
  
  • Fibers immediately cross (internal arcuate fibers)
  • Ascend contralaterally in medial lemniscus
  • Synapse in VPL thalamus
  • Projects to primary somatosensory cortex (3,1,2)
• Caudal receptors represented most medially

Question 2

Spinothalamic tract

• Ascending or descending?
• Location of cell bodies?
• Found in what spinal levels?
• Location in spinal cord section?
• Where does it cross?
• Location of synapse?
• Function?
• Other notes?

Answer 2

• Ascending (second order neurons) - contralateral
• Cell bodies in dorsal horn
• All spinal levels
• anterior/lateral funiculus border
• Within 2 levels (up/down) of cord entry (primary fibers ascend/descend in Lissauer’s tract, second order fibers cross in anterior white commissure)
• first synapse: dorsal horn (ipsilateral)
• second synapse: VPL thalamus
• third synapse: post-central gyrus
• Function: pain/temperature (lateral), light touch (anterior)

Question 3

Anterior Spinocerebellar

1. Ascending or descending?
2. Location of cell bodies?
3. Found in what spinal levels?
4. Location in spinal cord section?
5. Where does it cross?
6. Location of synapses?
7. Function?

Answer 3

1. Ascending (second order neuron) - contralateral
2. Cell bodies in gray matter of dorsal horn
3. Spinal levels: lumbosacral gray matter
4. Peripheral lateral funiculus
5. Crosses immediately after primary order fibers synapse
6. Synapses in the ipsilateral (to cell body - crosses a second time in cerebellum) cerebellum via the superior cerebellar peduncle
7. Function: Gross unconscious proprioception of the lower body

Question 4

Posterior Spinocerebellar

1. Ascending or descending?
2. Location of cell bodies?
3. Found in what spinal levels?
4. Location in spinal cord section?
5. Where does it cross?
6. Location of synapses?
7. Function?
8. Other notes?

Answer 4

1. Ascending (second order neurons) - ipsilateral
2. Cell bodies in Clarke’s nucleus (C8-L3)
3. All spinal levels L3 and above
4. Periphery of lateral funiculus
5. Does not cross
6. Synapses in the cerebellum via the inferior cerebellar peduncle
7. Fine motor proprioception of the distal lower limbs
8. Below L3, first order fibers run in gracilis, synapse in Clarke’s nucleus at L3

Question 5

Cuneocerebellar Tract

1. Ascending or descending?
2. Location of cell bodies?
3. Found in what spinal levels?
4. Location in spinal cord section?
5. Where does it cross?
6. Location of synapse?
7. Function?

Answer 5

1. Ascending (second order neurons) - ipsilateral
2. Cell bodies located in the accessory cuneate nucleus (medulla)
3. Not found in cord
4. Not found in cord
5. Does not cross
6. Ipsilateral cerebellum via the inferior cerebellar peduncle
7. Function: fine motor unconscious proprioception for distal upper limbs

Question 6

Anterior Corticospinal Tract

1. Ascending or descending?
2. Location of cell bodies?
3. Found in what spinal levels?
4. Location in spinal cord section?
5. Where does it cross?
6. Location of synapse?
7. Function?

Answer 6

1. Descending pathway
2. Motor cortex
3. Ends by T6
4. Anterior funiculus (ventral)
5. Pyramidal decussation (medulla/cord interface)
6. …
7. Function unclear

Question 7

Lateral Corticospinal Tract

1. Ascending or descending?
2. Location of cell bodies?
3. Found in what spinal levels?
4. Location in spinal cord section?
5. Where does it cross?
6. Location of synapse?
7. Function?

Answer 7

1. Descending - contralateral
2. Motor cortex (Level 5 pyramidal cells)
3. Found at all levels
4. Lateral funiculus
5. Pyramidal descussation (medulla/cord interface)
6. Ventral horn of gray matter
7. Initiate motor movements (body)

Question 8

Fasiculus Cuneatus

• Where is is located in the spinal cord?
• What information does it carry?
• What type of fibers is it carrying (diameter, myelin)?
• Describe the pathway of fibers from origin to termination, including:
• Location of synapses
• Point at which it crosses midline
• Somatotopic distribution in cord?

Answer 8

• Dorsal funiculus (more lateral)
• Discriminative touch for body T6 and above
• Alpha-beta fibers (large, heavily myelinated)
• Origin: somatosensory receptors in periphery
• Fibers ascend ipsilaterally, synapse in nucleus cuneatus (medulla)
• Cross immediately (internal arcuate fibers)
• Ascend to VPL thalamus as medial lemniscus
• Project to primary somatosensory cortex (3,1,2)
• Most caudal receptors represented most medially