Serotoninis 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. Other chemicals, such as drugs, can interfere with the
action of neurotransmitters. Agonistsmay mimic a neurotransmitter and bind to its recep-
tor site to produce the effect of the neurotransmitter. Antagonistsblock 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 gets incoming infor-
mation 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 electri-
cal in nature along the neuron. The neuron at rest is more negative inside the cell mem-
brane 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 concentra-
tions. 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 depo-
larizations jump from node to node. This is called saltatory conduction. Chemical neuro-72 STEP 4. Review the Knowledge You Need to Score High
Figure 7.4 Action potential.http://www.ebook3000.com