5 Steps to a 5 AP Psychology 2019

Biological Bases of Behavior ❮ 85

Serotonin is associated with sexual activity, concentration and attention, moods, and emo-
tions. Lack of serotonin is associated with depression. Opioid peptides such as endorphins
are often considered the brain’s own pain killers. Gamma-aminobutyric acid (GABA)
inhibits firing of neurons. Benzodiazepine (Valium) and anticonvulsant drugs increase
activity of GABA. Huntington’s disease is associated with insufficient GABA-producing
neurons in parts of the brain involved in coordination of movement. Seizures are associated
with malfunctioning GABA systems. Norepinephrine, also known as noradrenaline, is
associated with attentiveness, sleeping, dreaming, and learning. It is also released as a hor-
mone into the blood where it contracts blood vessels and increases heart rate. Other chemi-
cals, such as drugs, can interfere with the action of neurotransmitters. Agonists may mimic a
neurotransmitter and bind to its receptor site to produce the effect of the neurotransmitter.
Antagonists block a receptor site inhibiting the effect of the neurotransmitter or agonist.

Neuron Functions

All your behavior begins with the actions of your neurons. A neuron receives incoming
information from its receptors spread around its dendrites. That information is sent to
its cell body, where it’s combined with other incoming information. Neural impulses are
electrical in nature along the neuron. The neuron at rest is more negative inside the cell
membrane relative to outside of the membrane. The neuron’s resting potential results
from the selective permeability of its membrane and the presence of electrically charged
particles called ions near the inside and outside surfaces of the membrane in different con-
centrations. When sufficiently stimulated (to threshold), a net flow of sodium ions into the
cell causes a rapid change in potential across the membrane, known as the action potential
(see Figure 7.4). If stimulation is not strong enough, your neuron doesn’t fire. The strength
of the action potential is constant whenever it occurs. This is the all-or-none principle.
The wave of depolarization and repolarization is passed along the axon to the terminal
buttons, which release neurotransmitters. Spaces between segments of myelin are called nodes
of Ranvier. When the axon is myelinated, conduction speed is increased since depolarizations
jump from node to node. This is called saltatory conduction. Chemical neurotransmitters are

+80

+60

+40

+20

0

–20

–40

–60

–80

1

Depolarization

Repolarization

Resting

potential Refractory

period

Resting

potential inside of axon

is –70mV to

outside of axon

for a typical neuron

23

Time (in milliseconds)

Voltage (in milliv

olts)

45

Figure 7.4  Action potential.