The Spinal Cord and Peripheries - UNFINISHED, DO REFLEXES

Question 1

Describe the anatomy of the spinal cord

Answer 1

• Grey matter surrounded by white matter
• Central canal in the centre
• Grey matter has ventral and dorsal horns

Question 2

How is the white matter of the spinal cord arranged?

Answer 2

• 3 columns: posterior, lateral and anterior

- Ascending pathways are sensory, descending are motor

Question 3

What are the four important nerve tracts associated with the cortex?

Answer 3

• Corticospinal (pyramidal)
• Posterior/dorsal column
• Lateral spinothalamic tract
• Corticobulbar tract

Question 4

What impulses does the corticospinal tract carry?

Answer 4

Motor impulses from motor cortex to skeletal muscles

Question 5

What impulses does the lateral spinothalamic tract carry?

Answer 5

Pain and temperature

Question 6

What impulses does the posterior/dorsal column tract carry?

Answer 6

Touch
Tactile localization
Vibration sense
Proprioception

Question 7

Describe the corticospinal pathway from brain to muscle

Answer 7

• Starts at motor cortex (area 4)
• Upper motor neuron (UMN) carries impulse down to medulla, crosses over at pyramid decussation
• Moves down spinal cord, synapses at ventral horn
• LMN carries impulse to skeletal muscle

Question 8

What are the corticobulbar fibres? Where do they cross over?

Answer 8

• Nerve fibres innervating the head and neck

- Most fibres provide bi-lateral innervation to the cranial nerve nuclei with the exception of CN 7 (in part) and CN XII

Question 9

Main structural difference between ascending and descending nerve tracts?

Answer 9

Ascending comprised of 3 neurons

Descending only has 2

Question 10

Describe the pathway of the posterior/dorsal column tract from receptor to brain

Answer 10

• 1st order neuron goes up the spinal cord, synapses in the lower medulla
• 2nd order neuron crosses over (decussates) in the medulla, called the medial lemniscus
• Medial lemniscus synapses at the thalamus
• 3rd order neuron goes from thalamus, through IC to post-central gyrus (3, 1, 2)

Question 11

Describe the pathway of the lateral spinothalamic tract from receptor to brain

Answer 11

• 1st order neuron synapses at dorsal horn
• 2nd order neuron crosses over at level of entry in SC
• 2nd order neuron travels up and synapses at thalamus
• 3rd order neuron up through IC to post-central gyrus

Question 12

What is a reflex?

Answer 12

Involuntary stereotyped pattern of response brought about by a sensory stimulus

Question 13

What white matter structure carries nerve impulses within the cranium for the 4 aforementioned tracts?

Answer 13

The Internal capsule

Question 14

Which cranial nerves are not bilaterally innervated by the UMN’s of the cortex via the corticobulbar tract?

Answer 14

• Facial (in part)

- Hypoglossal

Question 15

Describe the effect of an UMN lesion on one side in the corticobulbar tract with regards to the facial nerve

Answer 15

• The facial nerve has two motor nuclei (upper and lower), the lower is not bilaterally innervated but the upper is
• Therefore an UMN lesion causes drooping of the face on the contralateral side of the injury, only below the upper border of the cheek

Question 16

Describe the effect of an UMN lesion on one side in the corticobulbar tract with regards to the hypoglossal nerve

Answer 16

An UMN lesion of the hypoglossal nerve causes tongue deviation to the contralateral side

Question 17

How can you distinguish between Bell’s Palsy and an UMN lesion of the facial nerve?

Answer 17

• Bell’s is LMN: drooping of entire face on the contralateral side
• UMN lesion: drooping of the face below the upper border of the cheek on the contralateral side, due to bi-lateral innervation of the upper motor nuclei of CN 7

Question 18

What is the nerve that crosses at the medulla called in the dorsal column tract?

Answer 18

Medial Leminiscus

Question 19

How are UMN’s and LMN’s distributed in the spinal cord?

Answer 19

• UMN’s: white matter, myelinated axons coming from neuronal cell bodies of the cortex / brainstem
• LMN’s: grey matter, cell bodies of the lower motor neurones that synapse with the UMN’s