Psychology2016

62 CHAPTER 2

might actually collapse (as a deer might do when being chased by another animal). This

collapse occurs because the parasympathetic division overresponds in its inhibition of

the sympathetic activity. The heart slows, blood vessels open up, blood pressure in the

brain drops, and fainting can be the result.

THE PARASYMPATHETIC DIVISION If the sympathetic division can be called the fight-or-

flight system, the parasympathetic division might be called the “eat-drink-and-rest” sys-

tem. The neurons of this division are located at the top and bottom of the spinal column, on

either side of the sympathetic division neurons (para means “beyond” or “next to” and in

this sense refers to the neurons located on either side of the sympathetic division neurons).

In looking at Figure 2. 8 , it might seem as if the parasympathetic division does

pretty much the opposite of the sympathetic division, but it’s a little more complex than

that. The parasympathetic division’s job is to return the body to normal functioning after

a stressful situation ends. It slows the heart and breathing, constricts the pupils, and reac-

tivates digestion and excretion. Signals to the adrenal glands stop because the parasym-

pathetic division isn’t connected to the adrenal glands. In a sense, the parasympathetic

division allows the body to restore all the energy it burned—which is why people are

often very hungry after the stress is all over.

The parasympathetic division does more than just react to the activity of the sym-

pathetic division. It is the parasympathetic division that is responsible for most of the

ordinary, day-to-day bodily functioning, such as regular heartbeat and normal breathing

and digestion. People spend the greater part of their 24-hour day eating, sleeping, digest-

ing, and excreting. So it is the parasympathetic division that is typically active. At any

given moment, then, one or the other of these divisions, sympathetic or parasympathetic,

will determine whether people are aroused or relaxed.

parasympathetic division
part of the ANS that restores the body
to normal functioning after arousal
and is responsible for the day-to-day
functioning of the organs and glands;
peat-drinM-and-rest system.q

Concept Map LO. 2.4, 2.5

Interactive

central nervous system

(comprised of the brain

and spinal cord) spinal cord

brain

true core of nervous system: takes information

from senses, processes it, makes decisions,

sends commands to rest of body; exhibits a

great deal of neuroplasticity; may also change

through neurogenesis

long bundle of neurons that

carries information to and

away from the brain; helps

control pain response

spinal cord reflexes involve

several different neurons

(sensory neurons,

interneurons, and motor

neurons)

spinal reflexes enable fast,

often lifesaving, actions

that do not require

conscious thought

peripheral nervous system

(comprised of the nerves and

neurons not contained in the

brain and spinal cord; allows

the brain and spinal cord to

communicate with the sensory

systems and to control the

muscles and glands of the

body; divided into somatic

and autonomic nervous

systems)

Nervous System

autonomic nervous system

controls automatic functions

of the body (organs, glands,

involuntary muscles)

somatic nervous system

controls the voluntary muscles

of the body

sympathetic division: ”fight-or-flight” functions—

reacts to stressful events and bodily arousal

parasympathetic division: “eat-drink-and-rest” functions—

restores body to normal functioning after arousal and is

responsible for day-to-day functioning of glands and organs

sensory pathway: sensory neurons

carrying information to spinal cord and/or brain

motor pathway: nerves that carry

information to voluntary skeletal muscles

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