A beta motor neuron is a kind of lower motor neuron

Lower motor neuron

Lower motor neurons are the motor neurons connecting the brainstem and spinal cord to muscle fibers, bringing the nerve impulses from the upper motor neurons out to the muscles...

, along with alpha motor neuron

Alpha motor neuron

Alpha motor neurons are large lower motor neurons of the brainstem and spinal cord. They innervate extrafusal muscle fibers of skeletal muscle and are directly responsible for initiating their contraction...

 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

Spinal cord

The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...

 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
  Nuclear chain fiber
  A nuclear chain fiber is a specialized sensory organ contained within a muscle. Nuclear chain fibers are intrafusal fibers which, along with nuclear bag fibers, make up the muscle spindle responsible for the detection of changes in muscle length....
  
   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
  Alpha motor neuron
  Alpha motor neurons are large lower motor neurons of the brainstem and spinal cord. They innervate extrafusal muscle fibers of skeletal muscle and are directly responsible for initiating their contraction...
  
  
• Muscle spindle
  Muscle spindle
  Muscle spindles are sensory receptors within the belly of a muscle, which primarily detect changes in the length of this muscle. They convey length information to the central nervous system via sensory neurons. This information can be processed by the brain to determine the position of body parts...
  
  
• Type Ia sensory fiber
  Type Ia sensory fiber
  Type Ia Sensory Fiber also called Primary Afferent Fiber is a type of sensory fiber. It is a component of a muscle fiber's muscle spindle which keeps track of how fast a muscle stretch changes .-Function of muscle spindles:...
  
  
• Type II sensory fiber
  Type II sensory fiber
  Type II sensory fiber is a type of sensory fiber, the second of the two main groups of stretch receptors. They are non-adapting, meaning that they keep responding even when the muscle has stopped changing its length. They are the second most highly myelinated fibers in the body.Their firing rate...
  
  
• Motor neuron
  Motor neuron
  In vertebrates, the term motor neuron classically applies to neurons located in the central nervous system that project their axons outside the CNS and directly or indirectly control muscles...
  
  
• Nerve fiber
  Nerve fiber
  A nerve fiber is a threadlike extension of a nerve cell and consists of an axon and myelin sheath in the nervous system. There are nerve fibers in the central nervous system and peripheral nervous system. A nerve fiber may be myelinated and/or unmyelinated. In the central nervous system , myelin...