there are three kinds of nerve cells: sensory, motor and inter-neurons. Nerve’s function is to transmit signals throughout the body.

Sensory neurons are neurons that can receive internal or external stimuli and transmit excitability to the central nervous system, called sensory neurons. Sensory cells such as the retina and inner ear, ganglion cells of the brain and spinal cord are sensory neurons.

Relay Neuron：Accept the nerve impulses from other neurons, and then transfer the impulse to another neuron, and play a contact role, also known as joint neurons. Inter neurons are distributed in the central nervous system.

motor neuron：A part of the nerve cell formation pathway that is pulsed from the brain or spinal cord to the muscle or gland.

Action potential is a process that occurs in the neuron. First, the cells are stimulated by an external stimulus greater than the threshold intensity. Part of the cell membrane is depolarized, causing a small amount of sodium ions to flow into the membrane. When depolarization reaches the threshold potential level, sodium ions and depolarization form positive feedback, causing sodium ions. A large amount of inflow until the equilibrium potential of sodium ions (inside positive and negative), then the action potential is formed. When the depolarization on the membrane reaches a certain level, the inflow of sodium ions stops, the potassium ions flow out, and the action potential gradually disappears.