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neuron — as precisely as a key fits a lock. For an instant, the neurotransmitter unlocks tiny
reuptake a neurotransmitter’s channels at the receiving site, and electrically charged atoms flow in, exciting or inhibiting
reabsorption by the sending the receiving neuron’s readiness to fire. The excess neurotransmitters finally drift away, to
neuron.
be either broken down by enzymes or reabsorbed by the sending neuron — a process called
reuptake Some antidepressant medications partially block the reuptake of mood-enhancing
.

neurotransmitters ( Figure 1.3-4 ).
Message is sent across synaptic gap. Message is received; excess serotonin Prozac partially blocks normal reuptake of the
molecules are reabsorbed by sending neuron. neurotransmitter serotonin; excess serotonin
in synapse enhances its mood-lifting effect.

Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
Sending
neuron
Action
potential
Reuptake
Synaptic gap

Receiving neuron

Serotonin Serotonin Prozac
molecule Receptor
(a) (b) (c)

Figure 1.3-4 Copyright © Bedford, Freeman & Worth Publishers.
Biology of antidepressants
Selective serotonin reuptake inhibitors (SSRIs) are popularly prescribed antidepressants. They relieve depression by partially blocking the reuptake
of the neurotransmitter serotonin. Shown here is the action of the SSRI fluoxetine, which is marketed under the brand name Prozac.

AP Science Practice Check Your Understanding
®

Examine the Concept Apply the Concept
▶ Explain reuptake . What two other things can happen to ▶ How would you explain neural communication to a friend?
excess neurotransmitters after a neuron reacts? Why was the discovery of neurons’ communication mechanism
▶ Explain what happens in the synaptic gap . so important?

Answers to the Examine the Concept questions can be found in Appendix C at the end of the book.

How Neurotransmitters Influence Us

1.3-3 How do neurotransmitters influence behavior, and how do drugs and other
1.3-3 How do neur otransmitters influence behavior , and how do drugs and other
chemicals affect neurotransmission?
chemicals affect neurotransmission?
In their quest to understand neural communication, researchers have discovered several
dozen neurotransmitters and almost as many new questions: Are certain neurotransmitters
found only in specific places? How do neurotransmitters affect our moods, memories, and
mental abilities? Can we boost or diminish these effects through drugs or diet?

32 Unit 1 Biological Bases of Behavior

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