Slide #19

Motor Unit

• The neuron, the axon (nerve fiber) and the muscle fibers that the nerve activates.
• A motor unit is all of one fiber type (Slow or Fast)
• If a muscle fiber loses its innervation and recruits a new nerve for stimulation then it might change its fiber type.

Pathology

Spinal Muscular Dystrophy

• Axons slowly die causing muscle fibers to lack innervation until they recruit axons from new nerves.
• Motor Units become ENORMOUS resulting in large fasciculations.
• "Type Grouping" occurs in which many muscle fibers of the same twitch type cluster.

What is the difference between fasciculations and fibrillations?