**Nervous system**- It is composed of the brain, spinal cord, and nerves. This system functions to control and regulate the body’s responses to internal and external stimuli. It also plays a role in the coordination of other organ systems. It is divided into two major divisions: the central nervous system and the peripheral nervous system.

An **impulse(movement of ions)** begins at the cell body and is transmitted down the shaft of the axon towards the axon terminals

The three types of neurons are sensory neurons, motor neurons, and interneurons.

Sensory neurons – they are activated when the senses receive stimuli from the environment

Motor neurons – transmit impulses from the brain and spinal cord to the muscles, glands, and organs in the body

Interneurons – transmits impulses between sensory and motors neurons

The **myelin sheath** is the insulating membrane that covers the axon at nodal phases along the shaft of the axon and helps to accelerate the movement of ions along the axon

There should be a sufficient strength to produce an impulse, particularly pain. However, the level of pain is going to vary depending on two factors. The first factor is the number of sensory neurons activated by the stimulus. The second factor is the stimulation’s frequency, wherein the stimulation must be stronger than the impulse.