Descending Pathways

Question 1

Describe the roles of the 2 systems of descending tracts

Answer 1

Lateral (corticospinal tracts): voluntary movement, control of distal muscles, controlled by the cerebral cortex

Ventromedial (uncrossed tracts): posture and locomotion, control of axial and proximal muscles, controlled by the brainstem

Question 2

What are the defining features of voluntary movement?

Answer 2

• goal/purpose intended
• triggered by willful decision
• demonstrates multiple levels of control of movement
• learned

Question 3

Describe the steps involved in voluntary movement

Answer 3

• sensory integration: target identified, location of target understood
• planning: movements required decided
• execution: command from cortical and brainstem centres ordered and initiated

Question 4

Describe the function of the premotor cortex

Answer 4

• prepares for voluntary movement
• required a stronger and longer stimulus than the primary cortex
• required initial stimulation of the primary cortex

Question 5

Describe the effect of premotor damage

Answer 5

Apraxia: unable to perform tasks involving complex sequences of movement

Question 6

What are the important input sources required for the corticospinal tract?

Answer 6

• sensory receptors (somatic sensory/premotor area/posterior parietal cortex)
• cerebellum (planning movement and corrective feedback from proprioception)
• basal ganglia (initiates complex movement and motor correction)

Question 7

What are the functional divisions of the pyramidal tracts?

Answer 7

• corticospinal tract: supplies musculature of the body

* corticobulbar tract: supplies musculature of the head and neck

Question 8

Describe the corticospinal tract

Answer 8

• begins in cerebral cortex
• neurons converge and descend through internal capsule
• here they pass through the crus cerebri of the midbrain then pass pons and medulla forming the medullary pyramids
• at inferior end of medulla divides into 2 tracts (lateral and anterior)

Lateral: fibres decussate and descend into spinal cord and terminate in ventral horn. LMN leave and supply muscles of the body.

Anterior: fibres maintain ipsilateral as they descend into the spinal cord. They then decussate and terminate in the ventral horn of cervical and upper thoracic segmental levels.

Question 9

Describe the signs of a corticospinal tract lesion

Answer 9

UMN Syndrome

• positive Babinski sign
• increase in muscle tone
• increase stretch reflexes
• hemiparesis (arm flexors stronger than extensors, opposite in the leg)
• clonus (involuntary rhythmic contractions)

Question 10

What components make up the ventromedial pathways?

Answer 10

• postural set (predictive instability)

* reflexive (unexpected instability)

Question 11

What are the cranial nuclei outputs and relays occuring in the brainstem?

Answer 11

• vestibulospinal: balance
• reticulospinal: muscle tone, orientation, breathing
• rubrospinal: cerebellar influenced upper limb movement
• tectospinal: head movements to follow sight