Study GuideBiology–Nervous Coordination1. Animal Nerve CellsLiving organisms need to react quickly to what is happening around them and inside their bodies. Inanimals, this fast response is made possible bynervous coordination, which is the job of thenervous system.Nervous coordination usually begins when astimulus(such as light, sound, heat, or pain) is detectedbyreceptorsin the sense organs, often found at the body surface. The response to this stimulususually involves amuscle or a gland. To make this happen, signals travel along a pathway made ofspecial cells callednerve cells.1.1 What Are Neurons?Animal nerve cells are calledneurons. They are highly specialized cells designed to carry messagesquickly. In humans, there are about12 billion neurons, most of which are located in thebrain andspinal cord.Each neuron has three main parts:•Cell body–the main part of the cell that contains the nucleus•Dendrites–short, branched extensions that receive incoming signals•Axon–a long extension that carries signals away from the cell bodyThe axon is usually covered by a fatty layer called themyelin sheath, which helps the signal travelfaster. A group of axons bundled together forms anerve.1.2 Types of NeuronsNeurons work together in teams, and they can be grouped into three types based on their function:•Sensory neuronsThese neurons detect stimuli from the environment (such as touch, temperature, or light) andcarry signals toward the brain or spinal cord.Preview Mode
This document has 22 pages. Sign in to access the full document!