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Module 1.3a

How Neurons Communicate AP Exam Tip
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1.3-2 How do nerve cells communicate with other nerve cells?
1.3-2 How do nerve cells communicate with other nerve cells?
Note the important shift here. So
far, you have been learning about
Neurons are interweaved so intricately that even with a microscope, you would struggle to see how just one neuron operates. The
where one neuron ends and another begins. Scientists once believed that the axon of one cell action potential is the mechanism
fused with the dendrites of another in an uninterrupted fabric. Then British physiologist Sir for communication within a single
Charles Sherrington (1857–1952) noticed that neural impulses were taking an unexpectedly neuron. Now you are moving on
to a discussion of two neurons
long time to travel a neural pathway. Inferring that there must be a brief interruption in the and how communication occurs
transmission, Sherrington called the meeting point between neurons a synapse . between them — very different, but
We now know that the axon terminal of one neuron is, in fact, separated from the equally important. Both ideas are
®
important for the AP exam.
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
receiving neuron by a tiny synaptic gap (or synaptic cleft ). Spanish anatomist Santiago Ramón
y Cajal (1852 –1934) marveled at these near-unions of neurons, calling them “protoplasmic

kisses.” “Like elegant ladies air-kissing so as not to muss their makeup, dendrites and axons synapse [SIN-aps] the junction
,
don’t quite touch,” noted poet Diane Ackerman (2004 p. 37 ). How do the neurons execute between the axon tip of the
Copyright © Bedford, Freeman & Worth Publishers.
this protoplasmic kiss, sending information across the synaptic gap? The answer is one of sending neuron and the dendrite
the important scientific discoveries of our age. or cell body of the receiving
neuron. The tiny gap at this
Neuroscientist Solomon Snyder (1984) captured your brain’s information processing in junction is called the synaptic gap
simple words: It’s “neurons ‘talking to’ each other at synapses.” When an action potential or synaptic cleft.
reaches the button-like terminals at an axon’s end, it triggers the release of chemical mes- neurotransmitters chemical

sengers, called neurotransmitters ( Figure 1.3-3 ). Within 1/10,000th of a second, the neu- messengers that cross the synaptic
rotransmitter molecules cross the synaptic gap and bind to receptor sites on the receiving gap between neurons. When
released by the sending neuron,
neurotransmitters travel across the
Figure 1.3-3 synapse and bind to receptor sites
How neurons communicate on the receiving neuron, thereby
influencing whether that neuron
1. Electrical impulses (action potentials) travel
down a neuron’s axon until reaching a tiny junction will generate a neural impulse.
known as a synapse.
Sending neuron

Receiving neuron
Action potential

Synapse

Sending
neuron
Action
potential
Reuptake

2. When an action potential 3. Excess neurotransmitters are reabsorbed
reaches an axon’s end (a process called reuptake), drift away, or
(terminal), it stimulates the are broken down by enzymes.
release of neurotransmitter
Synaptic gap Axon terminal molecules. These molecules
cross the synaptic gap and
bind to receptor sites on the
receiving neuron. This
allows electrically charged
atoms to enter the receiving
neuron and excite or inhibit
a new action potential.

Receptor sites on Neurotransmitter
receiving neuron

The Neuron and Neural Firing: Neural Communication and the Endocrine System Module 1.3a 31

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