Neurotransmitters

The brain chemicals that make it all happen!

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.

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.

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.

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 8 of them (and you’ve already met a few, like dopamine, norepinephrine, and oxytocin!).

There are two basic types of neurotransmitters:

Excitatory (these make actions happen)

and

Inhibitory (these inhibit actions, or stop actions from happening)

8 Major Neurotransmitters

• Acetylcholine• Dopamine• GABA• Glutamate• Glycine• Norepinephrine• Seratonin• Oxytocin

AcetylcholineType: 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.

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.

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.

Glutamate

Type: Excitatory

Actions: Glutamate may be the most powerful neurotransmitter. It plays an important role in learning and memory. Clinical significance: Glutamate is also known as an “excitotoxin” because some people are very sensitive to glutamate and too much of it may trigger neurological diseases, such as Huntington’s Disease.

Glycine

Type: Inhibitory

Actions: Glycine controls many motor and sensory pathways. Clinical significance: Glycine is exitatory when an embryo is developing. After birth, it is a major inhibitor, working mostly on neurons in the spinal cord.

NorepinephrineType: 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.

SerotoninType: Inhibitory

Actions: Contributes to 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

OxytocinType: 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.