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Module 1.2 Overview of the Nervous

System

LEARNING TARGET
1.2-1 Explain the different functions of the nervous system’s main divisions, and
describe the three main types of neurons.
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.

The Nervous System

1.2-1 What are the functions of the nervous system’s main divisions, and what
1.2-1 What ar e the functions of the nervous system’s main divisions, and what
are the three main types of neurons?
are the three main types of neurons?
My [DM’s] nervous system recently gave me an emotional roller-coaster ride. Before send-
nervous system the body’s ing me into a magnetic resonance imaging (MRI) machine for a shoulder scan, the tech-
speedy, electrochemical nician asked if I had issues with claustrophobia (fear of enclosed spaces). “No, I’m fine,”
communication network,
consisting of all the nerve cells I assured her, with perhaps a hint of macho swagger. Moments later, as I found myself on
of the peripheral and central my back, stuck deep inside a coffin-sized box and unable to move, my nervous system had a
nervous systems. different idea. Claustrophobia overtook me. My heart began pounding, and I felt a desperate
central nervous system urge to escape. Just as I was about to cry out for release, I suddenly felt my nervous system
(CNS) the brain and spinal cord. having a reverse calming influence. My heart rate slowed and my body relaxed, though my
peripheral nervous system Copyright © Bedford, Freeman & Worth Publishers.
arousal surged again before the 20-minute confinement ended. “You did well!” the techni-
(PNS) the sensory and motor cian said, unaware of my emotional roller-coaster ride. What happens inside our brain and
neurons that connect the central body to produce such surging and subsiding emotions? Is the nervous system that stirs us
nervous system (CNS) to the rest
of the body. the same nervous system that soothes us?
Our body’s nervous system is made up of neurons, or nerve cells, that communicate
nerves bundled axons that

form neural cables connecting via chemical messengers called neurotransmitters (see Module 1.3 ). This communication
the central nervous system with network takes in information from the world and the body’s tissues, makes decisions, and

muscles, glands, and sensory sends back information and orders to the body’s tissues ( Figure 1.2-1 ).
organs. A quick overview: The brain and spinal cord form the central nervous system (CNS) ,

sensory (afferent) neurons the body’s decision maker. The peripheral nervous system (PNS) is responsible for

neurons that carry incoming gathering information and for transmitting CNS decisions to other body parts. Nerves are

information from the body’s electrical cables formed from bundles of axons (the neuron extension that passes messages
tissues and sensory receptors to
the brain and spinal cord. to other neurons or to muscles or glands; see Module 1.3 ). Nerves link the CNS with the
body’s sensory receptors, muscles, and glands. The optic nerve, for example, bundles a mil-
motor (efferent) neurons
neurons that carry outgoing lion axons into a single cable carrying the messages from the eye to the brain ( Mason &
information from the brain and Kandel, 1991 ).
spinal cord to the muscles and Information travels in the nervous system through three types of neurons. Sensory
glands. neurons carry messages from the body’s tissues and sensory receptors inward (which
interneurons neurons within biologists term afferent ) to the brain and spinal cord for processing. Motor neurons
the brain and spinal cord; they (which are efferent ) carry instructions from the CNS outward to the body’s muscles
communicate internally and and glands. Between the sensory input and motor output, information is processed via
process information between
.

the sensory inputs and motor interneurons Our complexity resides mostly in these interneurons. Our nervous system
outputs. has a few million sensory neurons, a few million motor neurons, and billions and billions
of interneurons.

22 Unit 1 Biological Bases of Behavior

03_myersAPpsychology4e_28116_ch01_002_163.indd 22 15/12/23 9:21 AM