A nerve cell has several adaptations that allow it to carry out needed functions, such as its myelin sheath, projections and divisions, and its extremely long length. Nerve cells are also known as neurons. There are billions of nerve cells inside the human body.
There are three types of neurons: sensory, motor and relay. Projections from the cell membranes are called dendrons, which have even smaller protruding extensions known as dendrites. Dendrites between nerve cells overlap, transmitting signals and communication from neuron to neuron at locations known as synapses.
Some neurons have a dendrite known as an axon. This dendrite is the longest projection of the cell and occasionally has a myelin sheath. This sheath surrounds the axon with cells that contain a fatty chemical known as myelin to protect it and speed up impulses traveling through the nerves. The myelin sheath is comparable to the plastic covering of an electric wire.
Receptors are specially adapted nerve cells that respond to certain stimuli. Nerve receptors within the eye, for example, respond to light stimuli. Nerve receptors within the ear are adapted to respond to audio stimuli, whereas nerve receptors in the skin respond to touch stimuli. Reflexes are automatic responses to stimulus that do not require the nervous system to communicate with the brain before they are carried out. Reflexes protect the body from harm.