Neurotransmitters are chemicals that neurons release to communicate with each other at synapses. There are over 100 types of neurotransmitters but about 10 are responsible for most brain activity. The major neurotransmitters are dopamine, acetylcholine, GABA, norepinephrine, serotonin, and oxytocin. They can be either excitatory, making actions happen, or inhibitory, stopping actions from happening. Imbalances in neurotransmitters are associated with various mental and neurological disorders.

1. Neurotransmitters
The brain chemicals that
make it all happen!

2. Remember neurons?
They have branching
dendrites coming off
the soma (or cell body)
and, at the end of the
long axon, they have
branching axon
terminals, each one
ending in a little knob
called a terminal
button.

3. When neurons
communicate with each
other, which they do all
the time, they send
chemical messengers
from the terminal
button of one neuron
to the tip of a dendrite
on another. The
chemicals are released
into the tiny space
between the two
neurons, known as the
synapse.

4. This is how the signal is passed from one neuron to
another. This happens very quickly. The average human
brain has 100 BILLION neurons, all working at once.
The chemicals that are released in the synapse are called
neurotransmitters.
In the drawing on the next slide, neurotransmitters are
represented by the red dots being released from a terminal
button of one neuron and being received by the dendrite of
another neuron.

6. There may be as many as 100 different types of
neurotransmitters in our brains. However, 99% of the work
in the brain is done by about 10 different chemicals.
In this class, we’ll learn about 6 of them (and you’ve already
met a few!).

7. There are two basic types of neurotransmitters:
Excitatory
(these make actions happen)
and
Inhibitory
(these inhibit actions, or stop things from happening)

8. The Big Six
• Dopamine
• Acetylcholine
• GABA
• Norepinephrine
• Seratonin
• Oxytocin

9. Dopamine
Type: Excitatory AND inhibitory
Actions: involved in controlling movement and posture. It
also modulates mood. Play a role in addiction.
Clinical significance: The loss of dopamine in certain
parts of the brain causes extreme muscle rigidity similar to
Parkinson’s Disease.
Factoid: Meditation and music both stimulate the release
of dopamine and increase our sense of well-being.

10. Acetylcholine
Type: Excitatory
Actions: Triggers muscle contraction and stimulates the
release of certain hormones. It is involved in wakefulness,
attentiveness, anger, aggression, sexuality, and thirst,
among other things.
Clinical significance: Alzheimer’s disease is associated
with a lack of acetylcholine in certain regions of the brain.
Factoid: Many venoms and toxins in animals, plants, and
bacteria repress the action of acetylcholine, causing
paralysis and eventually death in victims.

11. GABA (gamma-aminobutyric acid)
Type: Inhibitory
Actions: GABA contributes to motor control, vision, and
many other cortical functions. It also regulates anxiety.
Clinical significance: Some drugs that increase the level
of GABA in the brain are used to treat epilepsy and to calm
the extreme trembling of people suffering from
Huntington’s disease.

12. Norepinephrine
Type: Excitatory
Actions: Important for attentiveness, emotions, sleeping,
dreaming, thinking, and learning. Norepinephrine is also
released as a hormone (epinephrine or adrenaline) into the
blood, where it causes blood vessels to contract and heart
rate and blood pressure to increase (fight or flight).
Clinical significance: Norepinephrine plays a role in
mood disorders such as bipolar disorder.
Factoid: Drugs that raise levels of norepinephrine are
used to treat Attention Deficit Disorder, such as Ritalin and
Adderall.

13. Serotonin
Type: Inhibitory
Actions: Contributes regulating body temperature, sleep,
mood, appetite, and pain.
Clinical significance: Depression, suicide, impulsive
behavior, and aggressiveness all appear to involve
imbalances in serotonin.
Factoid: Some anti-depressants, such as Prozac, work by
keeping released serotonin from being reabsorbed, keeping
serotonin levels in the brain higher. These drugs are called
SRIs or Serotonin Reuptake Inhibitors

14. Oxytocin
Type: Inhibitory
Actions: Involved in social recognition and bonding, and
may be involved in generosity and the formation of trust
between people
Clinical significance: Released in large amounts in
women during labor and birth. Appears to stimulate non-
learned maternal behavior in mammals.
Factoid: Is released by hugging and touching (non-sexual
and sexual), is also released at orgasm.