Beta motor neuron

A beta motor neuron (or beta motoneuron) is a kind of lower motor neuron, along with alpha motor neuron and gamma motor neuron. These motor neurons (β-MNs) 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 motoneuron) are myelinated. Alpha, gamma and beta motor neurons originate from the anterior horn of spinal cord and travel to skeletal muscles (efferent neurons). Alpha motor fibers have a larger diameter and higher conduction velocity than beta and gamma motor fibers.

Types of beta motoneuron

There are two kinds of beta motoneuron (as gamma motoneuron) 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 motoneurons innervate only intrafusal fibers of muscle spindles, but extrafusal fibers (i.e. slow and fast fibers) are innervated by alpha motoneurons.

See also

• Gamma motor neuron
• Alpha motor neuron
• Muscle spindle
• Type Ia sensory fiber
• Type II sensory fiber
• Motor neuron
• Nerve fiber

References

• Williams & Warwick. Gray's Anatomy. Thirty-seventh edition.Churchill Livingstone. ISBN 0-443-04177-6
• http://musom.marshall.edu/anatomy/grosshom/Musclesensory.html