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Structure and Function

The nervous system plays a key role in maintaining homeostasis, the state of dynamic equilibrium in the internal environment of the body. More complex than the most advanced computer, the nervous system is capable of storing vast amounts of data as well as receiving and sending thousands of messages throughout the body instantly and simultaneously.

While the nervous system functions as a total system, you may find it more easily understood if we divide it into its two major parts: the central nervous system (CNS) and the peripheral nervous system (PNS). However, we first begin by looking at the most essential element: the neuron.


Your brain is something like a very complex computer with infinite data-storage capabilities.

A nerve cell, known as a neuron, is illustrated in Figure 5-1. Neurons vary in size and shape, but they all have the following key parts: cell body, axon, and dendrites. The cell body houses all of the microscopic structures that keep the cell energized and functioning. The dendrites, which resemble the branches of a tree, are responsible for receiving information from the internal and external environment and bringing this information to the cell body. The axon sends electrical impulses and transmits signals to other cells. The axon may be short or quite long and is sometimes covered in a special protective layer called the myelin sheath.

image Learning Style Tip

Use the illustrations by tracing them with your fingertip, naming the various parts aloud, and describing their functions as you do so. This is useful for visual, auditory, verbal, and kinesthetic learners.

The central nervous system (CNS) comprises the brain and spinal cord (Fig. 5-2). This is where data storage and information processing occurs. The brain is made up of three major divisions: the cerebrum, which makes up the largest portion; the cerebellum; and the brainstem. The cerebrum is divided into two hemispheres sometimes called the left and right brains. They are connected by a structure called the corpus callosum.

The surface of the cerebrum, called the cortex, is characterized by deep folds and shallow grooves, which increase its surface area and maximize function. The cortex is full of neurons as well as specialized support cells that carry nutrients to the neurons called glia. It is divided into four areas known as the frontal, temporal, parietal, and occipital lobes. Each of these areas is responsible for specific functions such as sensory perception, movement, emotions, memory, and behavior. The cerebellum is sometimes called the “little brain.” It is located inferior and ...

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