The Nervous system

-by Karthik Gurumurthy

The command center for an animal’s body is its nervous system. This system directs an animal’s activities and guides how an animal reacts to its environment. One of the most important functions of the nervous system is to control homeostasis. It is in charge of both physiological actions (heart rate, breathing, shivering) and the behavioral actions (eating, drinking, moving) of the body.

Nervous systems are made up of cells called neurons, which carry messages to and from different parts of the body to tell it what to do. Neurons send bits of electricity, called impulses, from one neuron to the next. In most animals, group of neurons join together in long bundles called nerves. Nerves are like information “highways” for the messages being sent and received through impulses.

More active animals tend to have more complex nervous systems. A sponge anchored to the seafloor is one of the least active animals. It has no nervous system at all, though it can react to its environment in simple ways. A jellyfish floating in the ocean has a loose web of neurons called nerve net that extends through its body. When one neuron is stimulated, it sends impulses through the whole nerve net, making the entire body react. For example, if a jellyfish senses something nearby, the nerve net responds by directing the body to make swimming motions towards potential food or away from danger.

In the bodies of flying insects and slithering worms, group of neurons gather together in simple brainlike organs called ganglia. From these organs, thick nerves called nerve cords extend through the center of the body. Smaller and smaller nerves branch off from the nerve cords to reach all areas of the body.