descending tracts

Question 1

What are the descending tracts?

Answer 1

Carry motor signals sent from brain to lower motor neurones

Divided into 2 groups:
- Pyramidal tracts
- Extrapyramidal tracts

Question 2

Where do pyramidal tracts originate and where do they go?

Answer 2

Originate in cerebral cortex

Carry motor fibres to the spinal cord and brainstem

Question 3

What are the pyramidal tracts responsible for?

Answer 3

Voluntary control of musculature of body and face

Question 4

Where do the extrapyramidal tracts originate and where do they go?

Answer 4

Originate in the brainstem

Carry motor fibres to the spinal cord

Question 5

What are the extrapyramidal tracts responsible for?

Answer 5

Involuntary and automatic control of all musculature such as muscle tone, balance and posture

Question 6

What 2 tracts can the pyramidal tracts be divided into?

Answer 6

Corticospinal tracts

Corticobulbar tracts

Question 7

Why are the pyramidal tracts called the pyramidal tracts?

Answer 7

Pass through the medullary pyramids

Question 8

What do the corticospinal tracts supply?

Answer 8

Musculature of the body

Question 9

What do the corticobulbar tracts supply?

Answer 9

Musculature of the head and neck

Question 10

Describe the decussation of the corticospinal tract

Answer 10

• Divides in two at the inferior bit of the medula
• Fibres in the lateral corticospinal tract decussate, then descend into the spinal cord, terminating in the ventral horn at all segmental levels
• Anterior corticospinal tract remains ipsilateral, descending into the spinal cord. They then decussate and terminate in the ventral horn of the cervical and upper thoracic segmental levels

Question 11

Describe where the corticobulbar tracts go and where they synapse

Answer 11

• Arise from the lateral aspect of the primary motor cortex
• Neurones terminate on the motor nuclei of the cranial nerves. Here they synapse with LMNs, which carry motor signals to the muscles of the face and neck

Question 12

What are the 4 extrapyramidal tracts?

Answer 12

• Vestibulospinal
• Reticulospinal
• Rubrospinal
• Tectospinal

Question 13

Describe the vestibulospinal tracts

Answer 13

• 2 pathways - medial and lateral
• Arise from vestibular nuclei, which receive input from the organs of balance. The tracts convey this balance info to the spinal cord, where it remains ipsilateral
• FIbres in this pathway control balance and posture by innervating ‘anti-gravity’ muscles (flexors of the arm and extensors of the leg)

Question 14

What are the 2 reticulospinal tracts?

Answer 14

Medial reticulospinal

Lateral reticulospinal

Question 15

Describe the medial reticulospinal tract

Answer 15

Arises from the pons. Facilitates voluntary movements, and increases muscle tone

Question 16

Describe the lateral reticulospinal tract

Answer 16

Arises from the medulla. Inhibits voluntary movement, reduces muscle tone

Question 17

Describe the rubrospinal tracts

Answer 17

• Originate in the red nucleus, a midbrain structure
• Fibres emerge, decussate, and descend into the spinal cord
• Have contralateral innervation
• Exact function unclear - maybe to do with fine control of hand movements

Question 18

Describe the tectospinal tracts

Answer 18

• Pathway begins at superior colliculus of midbrain
• Superior colliculus receives input from optic nerves
• Neurones then quickly decussate, and enter the spinal cord. Terminate at cervical levels of the spinal cord
• Coordinates movements of the head in relation to vision stimuli

Question 19

Signs of an UMN lesion

Answer 19

Hypertonia: increased muscle tone
Hyperreflexia: increased muscle reflexes
Clonus: involuntary rjythmic muscle contractions
Babinski sign: extension of the hallux in response to blunt stimulation of the sole of the foot
Muscle weakness