Lower motor neurons

Lower Motor Neurons (LMNs) are the final common pathway for transmitting the command for voluntary movement from the brain to skeletal muscles. They are located in the anterior horn of the spinal cord and the cranial nerve nuclei of the brainstem.

Anatomy

Lower motor neurons originate in the brainstem and the spinal cord. They receive input from upper motor neurons that originates in the motor cortex. The axons of lower motor neurons exit the central nervous system through nerves that extend to muscles throughout the body.

Function

Lower motor neurons translate the neurotransmitter signals from the upper motor neurons into action by releasing neurotransmitters at the neuromuscular junction. This causes the muscle to contract. The type of contraction can be fine and precise, as in finger movements, or powerful, as in leg or arm movements.

Clinical significance

Damage to the lower motor neurons can result in flaccid paralysis (weakness), muscle atrophy (wasting), fasciculations (muscle twitching), and muscle hypotonia (reduced muscle tone). This is in contrast to damage to the upper motor neurons, which results in spastic paralysis (increased muscle tone), hyperreflexia (overactive reflexes), and a positive Babinski sign.

See also

• Upper motor neuron
• Motor neuron disease
• Motor cortex
• Neuromuscular junction
• Babinski sign

References

Lower motor neurons Resources
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