2011. 1. 27. 16:50

Beta motor neuron




Beta motor neuron

From Wikipedia, the free encyclopedia


A beta motor neuron (or beta motoneuron) as alpha motor neuron and gamma motor neuron is a kind of lower motor neuron. These motor neurons (β-MNs) innervateintrafusal 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.







Stained motor neuron from human spinal cord; Courtesy Wikimedia Commons.