motor function

Question 1

descending motor pathways diagram

Answer 1

Question 2

corticobulbar pathways

Answer 2

Question 3

voluntary muscle pathway: lateral corticospinal tract (largest pathway)

Answer 3

primary motor cortex -> Betz cell (5th layer) fibres with long axon pass down through internal capsule (through basal ganglia) down same side to midbrain (cerebral peduncle) where can see externally -> passes down through pons where can’t see externally due to transverse fibres (link 2 halves of cerebellum) -> pyramids reemerge at medulla -> decussation at base of medulla -> descend in spinal cord down lateral corticospinal tract -> project to ventral horn (grey matter with large alpha motor neurones - synapse) and ventral root at appropriate level -> go out to musculature (contralateral control)

Question 4

voluntary muscle pathway: anterior corticospinal tract

Answer 4

very similar, but descend at anterior corticospinal tract with decussation at level of spinal cord -> innervate thorax, intercostal and axial musculature - not many muscles so not huge motor neurone component at this level (ipsilateral)

Question 5

corticobulbar tract (refers to motor neurones in brainstem - cranial nerve nuclei) e.g. hypoglossal

Answer 5

primary motor cortex -> fibres through internal capsule -> synapse in brainstem -> hypoglossal (XII) nucleus near midline in medulla -> nerve fibres pass out to supply motor activity to tongue