A specialized contact zone between a motor neuron and a muscle fiber.
When the nerve influx reaches the tip of the neuron, vesicles release acetylcholine into the synaptic cleft. This molecule binds to nicotinic receptors in the muscle membrane, creating a potential motor plaque. If this signal reaches the threshold, it triggers a potential for muscle action that spreads along the fibre and causes contraction. Acetylcholinesterase then degrades acetylcholine to allow the system to "reset" quickly.
Precise micro-architecture
On the nerve side, the synaptic end concentrates the calcium channels that orchestrate vesicle exocytosis. On the muscle side, the motor plate exhibits membrane folds aligning receptors and voltage-dependent sodium channels to amplify the signal. This spatial adjustment guarantees reliable, fast and energy-efficient transmission, even in sustained efforts.
Health, Diseases and Therapeutic Targets
The neuromuscular junction is a key point in many diseases. In autoimmune myasthenia, antibodies target nicotinic receptors, inducing fatigability and muscle weakness; treatments aim to increase acetylcholine availability or modulate immunity. Conversely, botulinum toxin blocks the release of neurotransmitters, which explains both its medical use (spasticity, dystonia) and its toxicity. Research is also exploring the plasticity of this junction — its ability to adapt to training, aging or injury — to promote motor recovery.
Other Words That May Be of Interest to You
- Neuron :
- Basic cell of the nervous tissue, capable of receiving, analysing, reproducing and transmitting information in the form of an electrical or chemical signal.
- Motor neuron :
- Motor neurons involved in the transmission of motor information from the brain to the spinal cord and peripheral organs.