Lecture 6: Spinal Cord Periphery/Spinal Tracts

Question 1

Describe the passage of motor neuron fibres (Upper & Lower)

Answer 1

Upper Motor Neurons originate in the cerebral cortex & brainstem

Then then synapse in the spinal cord or cranial nerve nuclei

From there Lower Motor Neuron’s travel to the muscles they innervate

Question 2

Whats are corticobulbar vs corticospinal tracts?

Answer 2

Tracts of white matter, spefically UMNs.

Corticobulbar fibres terminate in the brainstem, in cranial nerve nuclei.

Corticospinal fibres terminate in the spinal cord

Question 3

Most motor fibres descend by the corticospinal tract, describe its passage:

Answer 3

• > UMN starts in Primary Motor Cortex
• > Passes through the posterior limb of the internal capsule

-> Passes through cerebral peduncle to the brainstem
(Here corticobulbar fibres split off and synapse in contralateral cranial nerve nuclei)

-> Most corticospinal fibres decussate in the pyramids and enter the lateral corticospinal tract
(Some stay on the same side travelling as the anterior corticospinal tract)

-> When they get to the level they supply the fibres synapse in the grey matter of the spinal cord and exit through the ventral horn as spinal nerves

Question 4

What do fibres of the corticospinal tract do?

Answer 4

They are involved in voluntary (So skeletal) skilled movements

Question 5

How do Upper & Lower motor neurons affect reflexes?

Answer 5

Reflexes occur through LMNs and are dampened by UMN.

Hence an UMN lesion would lead to hyperreflexia and increased tone

Question 6

Whats different about the set up of ascending spinal tracts (i.e. sensory) vs descending?

Answer 6

Sensory tracts have 3 neurons rather than 2, called:

• 1st order neurons
• 2nd order neurons
• 3rd order neurons

Question 7

There are two main sensory tracts, what are they and what do they do?

Answer 7

• Posterior/dorsal Column
  Rsponsible for fine touch, tactile localisation, vibration and proprioception
• Lateral Spinothalamic Tract
  Responsible for pain & Temp

Question 8

Whats the structural difference between the posterior/dorsal column and the lateral spinothalamic tract?

Answer 8

• Both have 3 neurons
• Both 3rd order neurons connect a nucleus in the thalamus to the Post Central Gyrus of the parietal lobe.
• In both the 2nd order neuron does the crossing over

However, in the dorsal column the 1st order neuron travels up the dorsal column and synapses in the medulla
Whereas, in the lateral spinothalamic tract they synapse in the grey matter at the level they enter.

Question 9

Define a reflex?

Answer 9

An involuntary stereotyped pattern of response brought about by a sensory stimulus

Question 10

List & locate the important spinal tracts (Sensory & motor)

Answer 10

Pyramidal Tracts
- Corticospinal (lateral & anterior) - Found in Lateral White Matter

Extrapyramidal Tracts: (mainly anteromedial white matter)

• Rubrospinal (Starts in red nucleus of midbrain, involved in posture, only extrapyramidal tract in the lateral white matter)
• RecticuloSpinal (Split into pontine & medullary origins, handle reflexive control of posture & balance using trunk & anti-gravity limb muscles)
• Vestibulospinal (Handles posture & balance)

Sensory:

• Dorsal Column (Carries most sensory info) - In posterolateral white matter
• Spinothalamic (Anterior & Lateral) Carries nociception & temp from contralateral body - In anteromedial white matter

Also remember tectospinal which Maintains eye stability as the body moves, Originating in the Superior Coliculus