Introduction: Controlled by the brain, the nervous system is the body system that collects all kinds of information from both inside and outside of an organism's body and then processes it in order to create an appropriate response. For example, a field mouse, while searching for food, hears something approaching it. While the drive for food is very strong, so is the need for survival. The sense receptors of the mouse will collect as much information about the situation as possible (the direction of the sound, the volume of sound, if there are any smells, etc.) and send it to the brain. Here, the brain will sort through all the information and then send signals across special cells called neurons to the various organs of the mouse to elicit an appropriate response. This may include signals to the leg muscles to run away or to the throat to create a warning call. Most multicellular animals have a nervous system.

The primary component of the nervous system is called the neuron (or nerve cell). This diagram shows what nerve cells look like. The signal enters the nerve cell through projections called dendrites (A). The dendrites then carry the signal to the main cell body (B) where it is interpreted. The signal then gets passed to the axons (F), which then carry it away from this cell to the next. Axons are protected an nourished by special cells called Schwann cells that make up a covering called myelin. It is believed that axons with myelin can transmit signals faster than those without it.

The nervous system can be divided into two parts - the central nervous system and the peripheral nervous system. The organs of the central nervous system include the brain and spinal cord. The brain is the control center for the entire body and the spinal cord is the relay center, acting as a broadcast center for the signals from the brain to the rest of the body.

The peripheral nervous system is made from all the nerves that go all over the body, reaching into the appendages (arms and legs).

The five senses are also part of the nervous system. The eyes, ears, nose, tongue, and touch receptors are the way an organism is able to investigate its environment and take the necessary actions for survival.

Directions for this Lesson: Answer the practice questions and then watch the videos to learn more about how the nervous system operates.