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top speed is 3 million times slower than that of electricity flowing through a wire. We
measure brain activity in milliseconds (thousandths of a second) and computer activity in
ENGAGE 1.3-1 nanoseconds (billionths of a second). Unlike a computer’s nearly instantaneous reaction,
your response to a sudden event, such as a book slipping off your desk during class, may
(20 minutes) The action potential is take a quarter-second or more. Your brain is vastly more complex than a computer but
one of the more complicated pro- slower at executing simple responses.
Like batteries, neurons generate electricity from chemical events. In the neuron’s
®
cesses discussed in AP psychology. chemistry-to-electricity process, ions (electrically charged atoms) are exchanged. The fluid
As such, it is useful to have several outside an axon’s membrane has mostly positively charged ions; a resting axon’s fluid
ways to explain this concept to your interior has a mostly negative charge. This positive-outside/negative-inside state is called
students. To provide an alternative the resting potential. When a neuron fires, the first section of the axon opens its gates,
rather like a storm sewer cover flipping open, and positively charged ions (attracted to the
explanation of action potential, use negative interior) flood in through the now-open channels. The loss of the inside/outside
Student Activity: Neural Transmission charge difference, called depolarization, causes the next section of axon channels to open,
with Hershey’s Kisses. This activity and then the next, like a line of falling dominos. This temporary inflow of positive ions is
the neural impulse — the action potential.
also illustrates neurotransmitters, Each neuron is itself a miniature decision-making device performing complex calcula-
myelin, excitation, and inhibition. tions as it receives signals from hundreds, even thousands, of other neurons. The mind bog-
gles when imagining this electrochemical process repeating up to 100 or even 1000 times a
M1.3a: Neural Transmission second. But this is just the first of many astonishments.
“What one neuron tells another neuron,” noted Nobel laureate Francis Crick (1994),
with Hershey’s Kisses “is simply how much it is excited.” Indeed, most neural signals are excitatory, somewhat
like pushing a neuron’s accelerator. Others are inhibitory, more like pushing its brake. If
excitatory signals exceed the inhibitory signals by a minimum intensity, or threshold, the
ENGAGE 1.3-1 combined signals trigger an action potential. (Think of it as a class vote: If the excitatory
Copyright © Bedford, Freeman & Worth Publishers.
people with their hands up outvote the inhibitory people with their hands down, then
the vote passes.) The action potential then travels down the axon, which branches into
(15 minutes) To illustrate variations threshold the level of junctions with hundreds or thousands of other neurons or with the body’s muscles and
in the speed of neural transmission, stimulation required to trigger a glands.
neural impulse.
use Student Activity: Reaction-Time refractory period in neural Neurons need short breaks (a tiny fraction of an eyeblink). During a resting pause called
Measure of Neural Transmission and processing, a brief resting pause the refractory period, subsequent action potentials cannot occur until the axon recharges
and returns to its resting state. Then the neuron can fire again.
that occurs after a neuron
Mental Processes. This activity makes has fired; subsequent action Increasing the level of stimulation above the threshold will not increase the neural
potentials cannot occur until the
the point that neural information trav- axon returns to its resting state. impulse’s intensity. Instead, the neuron’s reaction is an all-or-none response (also known
els through pathways. all-or-none response a as the all-or-nothing principle): Like mechanical mousetraps, neurons either fire or they don’t.
neuron’s reaction of either firing How, then, do we detect the intensity of a stimulus? How do we distinguish a gentle touch
M1.3a: Reaction-Time (with a full-strength response) or from a big hug? A strong stimulus can trigger more neurons to fire, and to fire more often.
But it does not affect the action potential’s strength or speed. Triggering a mousetrap with a
not firing.
Measure of Neural Transmission firmer push won’t make it snap harder or faster.
and Mental Processes Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
ENGAGE 1.3-1 AP Science Practice Check Your Understanding
®
(10 minutes) For another demonstra- Examine the Concept Apply the Concept
tion of the speed of neural transmis- ▶ ▶Explain the functions of the dendrites, the axon, and the cell ▶ ▶Explain how our nervous system allows us to experience the
sion, use Teacher Demonstration: body. difference between a slap and a tap on the back.
Neural Transmission of Dollars and ▶ ▶Explain the refractory period. ▶ ▶Explain how the all-or-none response is like a mousetrap.
Answers to the Examine the Concept questions can be found in Appendix C at the end of the book.
Senses. This activity makes the point
that neural information travels through
pathways. 30 Unit 1 Biological Bases of Behavior

M1.3a: Neural Transmission
of Dollars and Senses
• Threshold: A softer push of the lever will 15/12/23 9:21 AM
03_myersAPpsychology4e_28116_ch01_002_163.indd 30
not create a flush because it does not
ENGAGE 1.3-1 reach threshold.

(10 minutes) You can also demon- • Refractory period: To flush, the tank must
strate to your students how the action be full. Two flushes in a row cannot occur
potential works by comparing the if the tank has not had time to fill.
process to a flushing toilet. Here are Alternatively, you can turn this demon-
some concepts you may want to stration into an active learning activity by
highlight: giving students the three bulleted concepts
• All-or-none response: This and asking them, in pairs or small groups, to
response is similar to the strength figure out how each could be illustrated using
of each flush. When you depress a flushing toilet.
the lever, the flush is the same
each time.

30 Unit 1 Biological Bases of Behavior

03_HammerTE4e_47547_ch01_2a_163_4pp.indd 30 07/02/24 5:18 PM