DESCENDING TRACTS

What are the two types of motor neurons in a typical descending pathway?

• Upper motor neurons (UMNs)

• Lower motor neurons (LMNs)

• Motor

• Sensory

Where do upper motor neurons originate from?

• Cerebral cortex

• Cerebellum

• Brainstem

What is the characteristic of the pyramidal system regarding the decussation of upper motor neurons?

• 75 – 85% Decussate in pyramids

• Remainder decussate near synapse with lower motor neurons

What are the components of the pyramidal system?

• Corticospinal Tract

• Corticobulbar Tract

• Reticulospinal Tract

• Vestibulospinal Tract

What happens when lesion occurs in the rubrospinal tract?

• Impairment of distal arm and hand movement

• Involuntary tremors

• Impairment of proximal muscles

• Intention tremors (similar to cerebellar lesions)

Where does the vestibulospinal tract originate from?

What is the function of the reticulospinal tract?

What is the function of upper motor neurons (UMNs) in a descending pathway?

• To carry signals from the brain to the spinal cord

• To directly innervate muscles

What happens when there is damage to upper motor neurons (UMNs) in a descending pathway?

• It can lead to spasticity and hyperreflexia

• It can lead to flaccidity and hyporeflexia

What are the clinical manifestations of damage to lower motor neurons (LMNs) in a descending pathway?

• It can lead to muscle weakness and atrophy

• It can lead to spasticity and hyperreflexia