A neuromuscular junction is a specialized synapse between a somatic motor neuron and a skeletal muscle fiber. The cell body of a somatic motor neuron lies in the spinal cord, with its axon extending towards multiple muscle fibers. The branching axon penetrates the perimysium forming multiple axon terminals, which develop enlarged tips called synaptic end bulbs. These bulbs are separated by a narrow synaptic cleft from the muscle fibers. The sarcolemma of the muscle fiber across the synapse forms a motor end plate. This region has specialized invaginations embedded with multiple channel proteins, which also act as receptors for neurotransmitters, such as acetylcholine. Once an electrical impulse arrives at the synaptic end bulb of the pre-synaptic neuron, it causes an influx of extracellular calcium ions. These ions stimulate the exocytosis of the stored synaptic vesicles filled with the neurotransmitter acetylcholine. The acetylcholine released in the synaptic cleft then diffuses to bind to specific receptors on the motor end plate.