The Nervous System
The nervous system is the control center of the body. It is made of three main components; the brain, the spinal cord, and the nerves. There are also two types of nervous systems; the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS is made of the brain and the spinal cord. The brain processes messages sent to it and responds to them. These messages and responses are called impulses. These impulses travel up and down the spinal cord and to and from the brain. However, these impulses originated from the PNS. The PNS is all of the nervous system excluding the brain and the spinal cord. In other word, all of the nerve cells AKA neurons. Neurons are made of five main parts, the cell nucleus, cell body, dendrites, axon, and axon terminal. The dendrites detect impulses to transfer through the neuron. The impulse then travels through the cell and the axon to the axon terminal. The axon speeds up the impulse to quickly travel to the next neuron over the synapse. The eye and ear are part of the PNS and utilize these neurons. When light enters the eye, it goes through the cornea, iris, pupil, and the lens to get to the optical nerve. The photoreceptive cells that make the optical nerve then send an electrical impulse to the brain for processing. As you can imagine, the ear is a different situation. The outer ear funnels sound waves into the middle ear to vibrate the ear drum. When it vibrates, it strikes the hammer which strikes the anvil which strikes the stirrup. Then the stirrup vibrates a nerve in the ear which sends an electrical impulse to the brain to process and hear sound. The nervous system relates to all of the other systems because the brain controls them and the spinal cord and nerves deliver the message and commands. For example, the brain send messages through the spinal cord and the nerves to pump blood throughout the body.
The picture to the left depicts a diagram of the human nervous system network.
That is a picture of a human brain.