Psychology: A Self-Teaching Guide

The Biology of Behavior: Is the Brain the Organ of Mental Life? 33

that induces delusions. Some of the principal antipsychotic drugs block receptor

sites for dopamine. (See the section on drug therapy in chapter 15.)

(a) Identify a neurotransmitter associated with depression.

(b) Identify a neurotransmitter associated with schizophrenia.

Answers: (a) Serotonin; (b) Dopamine.

Three basic kinds of neurons are (1) sensory, (2) association, and (3) motor.

Sensory neuronsmake it possible for us to be in contact with the outside world.

They are sensitive to light, sound, chemicals that induce taste sensations, and so

forth. The rods and cones in the retina of your eye are sensory neurons.

Association neuronscommunicate with each other. Most of the neurons in

your brain are association neurons. They allow you to think, remember, and per-

ceive. It is the rich complexity of association neurons that makes self-

consciousness possible.

Motor neuronscommunicate with muscle fibers, and these too are cells of

the body. Complex contractions and relaxations of muscle fibers make it possible

for us to talk, walk, and otherwise act.

(a) Sensory neurons make it possible for us to be in contact with.

(b) Association neurons communicate with.

(c) Motor neurons communicate with.

Answers: (a) the outside world; (b) each other; (c) muscle fibers.

The brain contains about 3 billion neurons. The rest of the nervous system

contains approximately the same amount. The population of the planet Earth

is rapidly approaching 6 billion people. It is impressive to think that the quantity

of neurons you possess is roughly equivalent to the human population of our

world.

When a neuron releases neurotransmitters it is like a gun; when it “fires,” it

sends forth a spray of neurotransmitters. The formal term for “fire” is depolar-

ize.When a neuron depolarizes, it alternates from (1) a resting negative electrical

potential to (2) a positive electrical potential, and (3) returns to a negative electri-

cal potential again. This completes a cycle. In some cases a neuron can complete

2,000 to 3,000 cycles in a single second.

A nerveis a bundle of axons. Think of the axons as thin rope fibers and the

nerve as the thick rope itself. Nerves are identified as afferent or efferent. Affer-

ent nervesmove toward an objective. Efferent nervesmove away from a source.

The optic nerve is an afferent nerve; it carries visual messages toward the brain.