Motor Pathways I: Spinal Systems

Question 1

Describe the anatomy and function of the corticopontine system

Question 2

Describe in detail the anatomy and function of the major descending motor control systems that terminate in the spinal cord

Answer 2

corticospinal
reticulospinal
vestibulospinal
tectospinal
rubrospinal

Question 3

Review the anatomy and somatotopic organization of the tectospinal system in detail, noting the rostrocaudal and transverse placement of descending fiber bundles

Question 4

Compare decorticate and decerebrate rigidity and explain how these abnormal postures arise from brainstem injuries

Question 5

Compare and contrast the consequences of dysfunction involving upper motor neuron vs. lower motor neuron pathways

Question 6

Differentiate between spasticity and rigidity as features of upper motor neuron disease

Answer 6

Spasticity indicates pyramidal damage
- the unusual tightness, stiffness or “pull” of muscles
- combination of paresis, hyperreflexia, and especially hypertonia
- More resistance in one direction
- not velocity dependent
- indicates damage to the basal ganglia or vestibulospinal
tracts
- same resistance to all directions of movement (flexion and extension)
- not velocity dependent
- cogwheel in Parkinson’s

Rigidity is extrapyramidal
- A kind of hypertonia
-

Question 7

Describe the mechanisms explaining why “hyperreflexia” is a characteristic feature of upper motor neuron disease

Answer 7

increase in stretch reflexes

Loss of excitatory corticospinal fiber innervation to inhibitory interneurons that act on lower motor neurons