What is the difference between a nerve synapse and a neuromuscular junction?

The presynaptic part of both junctions are both almost identical, although different neurotransmitters can be used depending on location and function. Acetylcholine is usually found in neuromuscular junctions.
The functions of the two junctions are different. Although both carry a chemical 'message' across a gap, a nerve-nerve synapse continues this message in an electrical form whereas a neuromuscular junction results in muscle contraction.
In a nerve-nerve synapse, the neurotransmitter binds to receptors in the postsynaptic membrane, causing sodium to enter and depolarisation to occur. This depolarisation continues down the neurone, allowing the impulse to travel.
In a neuromuscular junction, the neurotransmitter binds to receptors on the sarcolemma (muscle membrane) causing sodium ion channels to open and depolarisation to occur. This depolarisation continues along the sarcolemma, down transverse tubules to the sarcoplasmic reticulum, where calcium is released, allowing the process of muscle contraction to begin.