Definition

1. Noun:
   • A nerve cell that transmits signals from the central nervous system to muscles or glands: A motor neuron is a specialized neuron that carries outgoing (efferent) impulses from the brain or spinal cord to effector organs, such as muscles, causing them to contract or glands, causing them to secrete.

Usage Examples

• Noun:
  • Damage to the motor neurons can result in muscle weakness.
  • The signal from the brain travels down the spinal cord through a motor neuron to the hand muscle.
  • Amyotrophic lateral sclerosis (ALS) is a disease that affects motor neurons.

Advanced Usage

• "Upper motor neuron": Refers to neurons whose cell bodies are in the brain's motor cortex and which synapse onto neurons in the spinal cord. Lesions here often cause spasticity.
  • The physician tested for signs of an upper motor neuron lesion.
• "Lower motor neuron": Refers to neurons whose cell bodies are in the spinal cord or brainstem and which directly innervate muscles. Lesions here cause flaccid paralysis and muscle wasting.
  • The loss of reflexes indicated a problem with the lower motor neurons.

Variants and Related Words

• Motoneuron (n): An alternative, less common spelling for motor neuron.
• Motor neuron disease (MND) (n phrase): A group of neurological disorders that selectively affect motor neurons.
• Efferent neuron (n phrase): A synonym describing the neuron's function of conducting impulses from the central nervous system.

Synonyms

• Efferent neuron: A neuron that carries nerve impulses away from the central nervous system.
• Motoneuron: A direct variant term.

Related Phrases and Concepts

• Motor unit: A single motor neuron and all the muscle fibers it innervates.
  • A precise movement involves the activation of specific motor units.
• Neuromuscular junction: The synapse or connection point between a motor neuron and a muscle fiber.
  • The neurotransmitter acetylcholine is released at the neuromuscular junction.

Noun

1. a neuron conducting impulses outwards from the brain or spinal cord