Neuroanatomy - Descending (motor) Pathways

Question 1

Name and describe the 2 types of upper motor neurones

Answer 1

Direct:
- originate from primary motor cortex (parietal)
- descend via brain stem
- occur at conscious level

Indirect:
- originate from brainstem
- descend to spinal cord
- occur at unconscious level

All descend to lower motor neurones

Question 2

Describe the path of the corticospinal tract

Answer 2

• direct/pyramidal

Lateral:
- 85% fibres
- decussates in medulla
- synapses with LMN in anterior horn at each level of spinal cord

Anterior:
- 15% fibres
- stays ipsilateral until relevant spinal level, then decussates

Question 3

Describe the function the corticospinal tract

Answer 3

Lateral: precise voluntary movement of distal limbs (hands and feet)
- inc. fractionation

Anterolateral: action of proximal and axial muscles
- maintenance of upright posture
- integrated movt of trunk & limbs

Question 4

What is fractionation?

Answer 4

When a single digit receives an excitatory stimulus (to move), while interneurons inhibit movement of the other digits

Question 5

Describe the path of the corticobulbar tracts

Answer 5

• direct/pyramidal
• synapse with LMN cell bodies within cranial nerve nuclei

Question 6

Describe the function of the corticobulbar tracts

Answer 6

• muscle activity of face, head, neck
• often affected in MND (leads to changes in tone of muscles)

Question 7

Describe the path of the rubrospinal pathway

Answer 7

• indirect/parapyramidal
• originates in midbrain (red nucleus)

Question 8

Describe the function of the rubrospinal pathway

Answer 8

• precise UL distal movt (hands)
• active before movt begins
• well-learned, automatic movt

Question 9

Describe the path of the reticulospinal pathway

Answer 9

• indirect/parapyramidal
• originates in pons (reticular formation - collection of nuclei)

Question 10

Describe the function of the reticulospinal pathway

Answer 10

• regulation of tone in trunk & limbs
• wakefulness

Question 11

Describe the path of the tectospinal pathway

Answer 11

• indirect/parapyramidal
• originates in midbrain nuclei

Question 12

Describe the function of the tectospinal pathway

Answer 12

• movt of head & eyes in response to visual stimuli

Question 13

Describe the path of the vestibulospinal pathway

Answer 13

• indirect/parapyramidal
• originates in medulla (vestibular nuclei)
• ipsilateral
• receives info via vestibulo-cochlear nerve from vestibular system

Question 14

Describe the function of the vestibulospinal pathway

Answer 14

• ## regulates posture and balance (mainly extension in LL)