Motor neuron

A nerve cell that carries signals from the central nervous system to muscles or glands, triggering contraction or secretion.

Neuromuscular junction: The synapse where a motor neuron communicates with a muscle fiber. Motor neurons release acetylcholine here to initiate muscle-fiber excitation.
Upper motor neuron: A neuron in the brain or brainstem that influences lower motor neurons. It carries descending commands that regulate many motor-neuron pools.
Stretch reflex: A reflex contraction triggered when a muscle is stretched. Sensory input can activate motor neurons through a fast spinal circuit.
Sensory neuron: A neuron that carries information from sensory receptors toward the central nervous system. Its usual signal direction is opposite to a motor neuron's.
Acetylcholine: A neurotransmitter used by motor neurons to signal skeletal muscle fibers. It carries the motor neuron's chemical message across the neuromuscular junction.
Lower motor neuron: A motor neuron whose axon directly innervates skeletal muscle. It forms the final neural link between central commands and muscle.
Spinal motor neuron: A motor neuron with its cell body in the spinal cord and an axon projecting outward. These cells drive most skeletal muscles below the head.
Pyramidal neuron: A glutamatergic projection neuron with a pyramid-shaped cell body, common in the cerebral cortex. Some pyramidal neurons send motor commands but do not directly innervate muscle.
Motor unit: A motor neuron and all the muscle fibers it controls. Its size determines how many fibers one motor neuron recruits together.
Alpha motor neuron: A lower motor neuron that innervates force-producing extrafusal muscle fibers. Its activation directly generates skeletal-muscle force.

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