The main difference between muscle and nerve cells is their structure and function. Muscle cells form muscle tissues which contract and relax muscles both voluntarily and involuntarily. Nerve cells form nervous tissues which rapidly receive and analyze information from a person's environment to produce an appropriate response.
A muscle cell's unique ability to contract provides important functions for the body, such as mobility, keeping a steady heartbeat and aiding the digestion of food. The type of muscle cell, of which there are three categories, determines its appearance and whether it has voluntary movement. The visual similarities between muscle cells are their long and narrow shape and the connective tissue components.
Nerve cells, of which there are billions, communicate with each other via electrical and chemical impulses, sending messages over long distances within the body. Nerve cells can signal messages that a person may be conscious of, such as if something is too hot, and are also responsible for internal functions, such as the processes in the liver that happen automatically. All nerves have the same basic parts: dendrites, a cell body and an axon.
Both muscle and nerve cells are equally important in the proper functioning of the human body.