The Central Nervous System

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Every behavior begins with biology. Our behaviors, as well as our thoughts and feelings, are produced by the actions of our brains, nerves, muscles, and glands. In this chapter we will begin our journey into the world of psychology by considering the biological makeup of the human being, including the most remarkable of human organs—the brain. We’ll consider the structure of the brain and also the methods that psychologists use to study the brain and to understand how it works.

We will see that the body is controlled by an information highway known as the nervous system. A collection of hundreds of billions of specialized cells that transmit information between different parts of the body, a collection of hundreds of billions of specialized and interconnected cells through which messages are sent between the brain and the rest of the body. The nervous system consists of the central nervous system (CNS) which is made up of the brain and the spinal cord, and the peripheral nervous system (PNS) which is the nerves that link the CNS to the skin, muscles, and glands., the neurons that link the CNS to our skin, muscles, and glands. And we will see that our behavior is also influenced in large part by the endocrine system. The chemical regulator of the body, composed of the glands that secrete hormones., the chemical regulator of the body that consists of glands that secrete hormones.

Although this chapter begins at a very low level of explanation, and although the topic of study may seem at first to be far from the everyday behaviors that we all engage in, a full understanding of the biology underlying psychological processes is an important cornerstone of your new understanding of psychology. We will consider throughout the chapter how our biology influences important human behaviors, including our mental and physical health, our reactions to drugs, as well as our aggressive responses and our perceptions of other people. This chapter is particularly important for contemporary psychology because the ability to measure biological aspects of behavior, including the structure and function of the human brain, is progressing rapidly, and understanding the biological foundations of behavior is an increasingly important line of psychological study.

The Neuron Is the Building Block of the Nervous System

Learning Objectives

Describe the structure and functions of the neuron.

Draw a diagram of the pathways of communication within and between neurons.

List three of the major neurotransmitters and describe their functions.

The nervous system is composed of more than 100 billion cells known as neurons. A neuronneuronOne of the more than 100 billion cells in the nervous system. is a cell in the nervous system whose function it is to receive and transmit information. As you can see in Figure 3.2, “Components of the Neuron”, neurons are made up of three major parts: a cell body, or somasomaThe part of the neuron that contains the nucleus of the cell and that keeps the cell alive., which contains the nucleus of the cell and keeps the cell alive; a branching treelike fiber known as the dendritedendriteThe part of the neuron that collects information from other cells and sends the information to the soma., which collects information from other cells and sends the information to the soma; and a long, segmented fiber known as the axonaxonThe part of the neuron that transmits information away from the cell body toward other neurons., which transmits information away from the cell body toward other neurons or to the muscles and glands.

Figure 3.2. Components of the Neuron

Figure 3.3.

The nervous system, including the brain, is made up of billions of interlinked neurons. This vast interconnected web is responsible for all human thinking, feeling, and behavior.

Some neurons have hundreds or even thousands of dendrites, and these dendrites may themselves be branched to...
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