Nerve growth factor- a cytokine that promotes the growth and repair of sensory nerves and maintenance of sympathetic nerves.

Neural crest cells - cells derived4 from the ectoderm layer in the embryo. This layer folds to form a neural tube which will later become the spinal cord of the animal. Cells from the crest of this fold, leave the ectoderm and migrate into the mesoderm layer. These neural crest cells are thus of ectomesenchymal origin. They migrate to form the dental mesenchyme, supportive cells of the nervous system, the adrenal cortex and melanocytes of the skin.

Neuromuscular junction the synapse between the axon terminal of a motoneurone and a skeletal muscle fibre. The release at this synapse of the neurotransmitter substance, acetyl choline causes the muscle to contract.

Neuropeptides - compounds which have extremely potent affect to excite or depress nerve cells, in very low concentration. In this regard they are distinctly different from neurotransmitters. They include substances such as prostaglandins, substance P, endorphins and enkephalins. Neuropeptides also have receptors on lymphocytes and thus influence the immune response.

Neurotransmitters - chemicals which are secreted into a synapse in order to transmit an electrical nerve impulse from a nerve axon of one cell to the cell body of another nerve cell. They bind to receptors on nerve cells and are produced rapidly in high concentrations at nerve synapses. In these respects they differ from neuropeptides. There are many different neurotransmitter substances. They include acetyl choline, epinephrine, histamine, serotonin GABA and glutamate.