Abnormal Psychology

Understanding Psychological Disorders: The Neuropsychosocial Approach 41

Adrenaline (also called epinephrine) plays a role in attention and in the fi ght-or-

fl ight response (Nemeroff, 1998). Too little of this substance in the brain contributes

to depression, and too much can lead to over-arousal and feelings of apprehension

or dread.

Noradrenaline (also called norepinephrine) also plays a role in attention and

the fi ght-or-fl ight response. Too little contributes to distractibility, fatigue, and de-

pression (Meana et al., 1992); too much has been implicated in schizophrenia and

anxiety disorders (Nutt & Lawson, 1992).

Glutamate is a fast-acting excitatory neurotransmitter found throughout the

brain. It plays a role in registering pain and in the formation of new memories. Too

much glutamate is involved in various disorders, including substance abuse (Kalivas &

Volkow, 2005), and too little is associated with other disorders, notably schizophre-

nia (Muller & Schwarz, 2006).

Gamma-amino butyric acid (GABA) is a common inhibitory substance. Too

little of it is associated with anxiety and (possibly) panic disorder (Goddard et al.,

2001); too much appears to undermine motivation.

Endogenous cannabinoids are involved in emotion, attention, memory, appe-

tite, and the control of movements (Wilson & Nicoll, 2001). Too little of these

substances is associated with chronic pain; an excess is associated with eating

disorders, memory impairment, attention diffi culties, and possibly schizophrenia

(Giuffrida et al., 2004).

You may have noticed that these descriptions of what the chemical substances

do are fairly general. There’s a reason for that: The effects of these substances

depend only in part on their nature; the effects also depend on the nature of the

receiving neurons. Thus, we must next look more closely at what’s on the receiving

end of these chemical substances.

Chemical Receptors

A neuron receives chemical signals at its receptors, specialized sites that respond

only to specifi c molecules (see Figure 2.5). Located on the dendrites or on the cell

body, receptors work like locks into which only certain kinds of keys will fi t (Kelsey,

Newport, & Nemeroff, 2006; Lambert & Kinsley, 2005). However, instead of liter-

ally locking or unlocking the corresponding receptors, the neurotransmitter mol-

eculesbind to the receptors and affect them either by exciting them (making the

receiving neuron more likely to fi re) or by inhibiting them (making the receiving

neuron less likely to fi re). We noted earlier that a sending neuron can make a receiv-

ing neuron more or less likely to fi re, and now we see how these effects occur: The

sending neuron releases specifi c neurotransmitters.

Although each neuron produces only a small number of neurotransmit-

ters, those chemicals often bind to many different types of receptors (Kelsey,

Newport, & Nemeroff, 2006). When a neuron fires, the effect of this event

depends on how its neurotransmitters bind to receptors on the receiving neuron.

The same chemical can have different effects on a neuron depending on which

kind of receptor it binds to. For example, dopamine acts as a neurotransmitter

in the subcortical reward circuits of the nucleus accumbens. In fact, most abused

substances directly or indirectly affect dopamine activity, which in turn acti-

vates those reward circuits; this pleasurable experience leads many individuals

to want to use the abused substance again to reexperience that state (Tomkins &

Sellers, 2001). However, dopamine also acts as a neuromodulator in the frontal

lobes (Robbins, 2000), and disruption of its role in executive functions may be

critical in schizophrenia.

Abnormal Communications Among Neurons

How can communications among neurons at the synaptic cleft go awry, and

thereby lead to psychological disorders? Scientists point to at least three ways in

which such communications can be disrupted: First, neurons might have too many

or too few dendrites or receptors, making the neurons more or less sensitive, re-

spectively, to even normal amounts of neurotransmitter substances in the synaptic

Receptors

Specialized sites on dendrites and cell bodies

that respond only to specifi c molecules.