Beta motor neuron
Beta motor neurons (β 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.
There are two kinds of beta motor neuron (as gamma motor neuron) that include:
- Static beta motor neurons. These motor neurons innervate nuclear chain fibers of muscle spindles, with collaterals to extrafusal muscle fibers.
- Dynamic beta motor neurons. The dynamic type innervates nuclear bag fibers of muscle spindles, with collaterals to extrafusal muscle fibers.
Gamma motor neurons innervate only intrafusal fibers of muscle spindles, but extrafusal fibers (i.e. slow and fast fibers) are innervated by alpha motoneurons.
- Williams & Warwick. Gray's Anatomy. Thirty-seventh edition.Churchill Livingstone. ISBN 0-443-04177-6