(A) A schematic representation of the neuromuscular system. The sensory neurons (shown in blue) convey information (in the form of electrical pulses) from different parts of the body to the brain. Motor neurons (red) in the brain and the spinal cord send electrical pulses along the axons (which form the motor nerve) to the muscle fibers to make them contract. In diseases such as amyotrophic lateral sclerosis, there is evidence that degeneration begins at the neuromuscular junction between the terminals of the axons and the muscle and progresses along the axon towards the cell body. (B) Fluorescence microscopy of the neuromuscular junction (NMJ). The panels on the left show a fully innervated neuromuscular junction, with the axon labeled in green (top left) and the muscle labeled in red (middle left). The merged panel (bottom left) shows the complete overlap of the nerve terminal with the muscle (yellow). The panels on the right show a denervated neuromuscular junction in which the axon no longer overlaps with the muscle.