1. a motor neuron that regulates the primary extrafusal fibers of a muscle. Commonly referred to as alpha fiber. 2. alpha motion- a type of obvious motion in such a way that a target looks like it is widening or shrinking whenever considerably bigger or tinier varieties of it are provided in accelerated sequence. Commonly referred to as alpha motion.

ALPHA MOTOR NEURON: "When Cheryl's alpha motor neurons began to malfunction, she experienced periods of paralysis and muscle spasms."