The Nervous System: Learn It 4—Neurotransmitters

There are several different types of neurotransmitters released by different neurons, and we can speak in broad terms about the kinds of functions associated with different neurotransmitters (Table 1). Much of what psychologists know about the functions of neurotransmitters come from research on the effects of medications on treating psychological disorders.

Recall that psychologists who emphasize a biological perspective focus on the physiological causes of behavior—they would assert that psychological disorders like depression and schizophrenia are associated with imbalances in one or more neurotransmitter systems. According to this perspective, psychotropic medications can help improve the symptoms associated with these disorders. Psychotropic medications are drugs that treat psychiatric symptoms by restoring neurotransmitter balance.

Psychoactive drugs can act as agonists or antagonists for a given neurotransmitter system.

agonists and antagonists

Agonists are chemicals that mimic a neurotransmitter at the receptor site and, thus, strengthen its effects. An antagonist, on the other hand, blocks or impedes the normal activity of a neurotransmitter at the receptor. Agonists and antagonists represent drugs that are prescribed to correct the specific neurotransmitter imbalances underlying a person’s condition. For example, Parkinson’s disease, a progressive nervous system disorder, is associated with low levels of dopamine. Therefore, a common treatment strategy for Parkinson’s disease involves using dopamine agonists, which mimic the effects of dopamine by binding to dopamine receptors. The drug LSD is structurally very similar to serotonin, and it affects the same neurons and receptors as serotonin.

neurotransmitter activity

Table 1. Major Neurotransmitters and How They Affect Behavior
Neurotransmitter Involved in Potential Effect on Behavior
Acetylcholine Muscle action, memory Increased arousal, enhanced cognition
Beta-endorphin Pain, pleasure Decreased anxiety, decreased tension
Dopamine Mood, sleep, learning Increased pleasure, suppressed appetite
Gamma-aminobutyric acid (GABA) Brain function, sleep Decreased anxiety, decreased tension
Glutamate Memory, learning Increased learning, enhanced memory
Norepinephrine Heart, intestines, alertness Increased arousal, suppressed appetite
Serotonin Mood, sleep Modulated mood, suppressed appetite

Certain symptoms of schizophrenia are associated with overactive dopamine neurotransmission. The antipsychotics used to treat these symptoms are antagonists for dopamine—they block dopamine’s effects by binding its receptors without activating them. Thus, they prevent dopamine released by one neuron from signaling information to adjacent neurons.

Psychotropic drugs are not instant solutions for people suffering from psychological disorders. Often, an individual must take a drug for several weeks before seeing improvement, and many psychoactive drugs have significant negative side effects. Furthermore, individuals vary dramatically in how they respond to a drug. To improve chances for success, it is not uncommon for people receiving pharmacotherapy to undergo psychological and/or behavioral therapies as well. Some research suggests that combining drug therapy with other forms of therapy tends to be more effective than any one treatment alone (March et al., 2007).