Lower motor neuron
1880695
224517751
2008-07-09T05:42:00Z
Alexiusnovius
6940758
'''Lower motor neurons''' ('''LMNs''') are the [[motor neuron]]s connecting the [[brainstem]] and [[spinal cord]] to [[muscle fibers]], bringing the [[action potential|nerve impulses]] from the [[upper motor neuron]]s out to the [[muscle]]s. A lower motor neuron's axon travels through a [[foramen]] and terminates on an effector (muscle).
==Classification==
The axons of lower motor neurons are a [[type of motor fibers]]. Lower motor neurons are classified based on the type of muscle fiber they innervate:
* [[Alpha motor neuron]]s (α-MNs) innervate [[extrafusal muscle fiber]]s, the most numerous type of muscle fiber and the one most involved in [[muscle contraction]].
* [[Gamma motor neuron]]s (γ-MNs) innervate [[intrafusal muscle fiber]]s, which are involved with [[muscle spindle]]s and the sense of [[proprioception|body position]].
==Physiology==
[[Glutamate]] released from the upper motor neurons triggers [[depolarization]] in the lower motor neurons in the ventral horn which in turn causes an action potential to propagate the length of the [[axon]] to the [[neuromuscular junction]] where [[acetylcholine]] is released to carry the signal across the [[synaptic cleft]] to the postsynaptic receptors of the [[muscle cell]] membrane, signaling the muscle to contract.
==Consequences of lesions==
Damage to lower motor neurons ([[lower motor neurone lesion]]s) is indicated by abnormal [[Electromyography|EMG]] potentials, [[fasciculation]]s, [[paralysis]], [[weakening of muscles]], and neurogenic [[atrophy]] of skeletal muscle.
{{neuroanatomy-stub}}
{{Nervous tissue}}
[[Category:Somatic motor system]]
[[Category:Efferent neurons]]
[[ja:下位運動ニューロン]]