Decussation :/

Extrapyramidal tract

*do NOT descend through the pyramids indirect with many synapses responsible for gross motor movements

Bilateral Innervation

All cranial nerves receive information from both sides of cortex; redundancy, maintenance Except CN #7 and CN #12, only

Extrapyramidal tract damage

Commonly seen in degenerative diseases and tumors Result in movement disorders, dyskinesias, disorders of involuntary movement *Parkinson's Disease

Corticobulbar tract

Cortex to brainstem *does not completely decussate but sends fibers to the cranial nerve on the other side for *bilateral innervation*

Corticospinal tract

Cortex to spinal nerves 90% decussate and synapse with spinal cord -> lateral 10% do NOT decussate -> anterior

Somatic Twist Hypothesis

Neural crossings (decussations) are the byproduct of a larger evolutionary change - switch from having ventral nerve cord to dorsal nerve cord

Decussation

When fibers cross from one side of a structure to the other; happens in medulla

Anterior Medulla

Where *motor fibers* decussate at the caudal end

Posterior Medulla

Where *sensory fibers* decussate at the caudal end

Medulla

Where decussation occurs; caudal part

Upper Motor Neuron Lesions

Will cause symptoms on the opposite (contralateral) side of body *damage to corticobulbar tract results in mild muscle weakness due to bilateral innervation

Pyramidal Tract

direct tracts, no synapses, discrete voluntary movements *descends through the pyramids *originate in the cortex and carry motor messages to brainstem and spinal cord corticobulbar + corticospinal