Beta motor neurons (ß motor neurons), also called beta motoneurons, are a kind of lower motor neuron, along with alpha motor neurons and gamma motor neurons. Beta motor neurons innervate intrafusal fibers of muscle spindles with collaterals to extrafusal fibers (type of slow twitch fibers). Axons of beta motor neurons (as alpha and gamma motor neurons) are myelinated. Alpha, gamma and beta motor neurons are all efferent neurons that originate from the anterior grey column of the spinal cord and travel to skeletal muscles. Alpha motor fibers have a larger diameter and higher conduction velocity than beta and gamma motor fibers.