Neurotransmitters

Neurotransmitters

So far, researchers have discovered about 15–20 different neurotransmitters, and new ones are still being identified. The nervous system communicates accurately because there are so many neurotransmitters and because neurotransmitters work only at matching receptor sites. Different neurotransmitters do different things.

Neurotransmitter	Major functions	Excess is associated with	Deficiency is associated with
Acetylcholine	Muscle movement, attention, arousal, memory, emotion		Alzheimer’s disease
Dopamine	Voluntary movement, learning, memory, emotion	Schizophrenia	Parkinsonism
Serotonin	Sleep, wakefulness, appetite, mood, aggression, impulsivity, sensory perception, temperature regulation, pain suppression		Depression
Endorphins	Pain relief, pleasure
Norepinephrine	Learning, memory, dreaming, awakening, emotion, stress-related increase in heart rate, stress-related slowing of digestive processes		Depression
GABA	Main inhibitory neurotransmitter in the brain
Glutamate	Main excitatory neurotransmitter in the brain	Multiple sclerosis

Agonists and Antagonists

Agonists are chemicals that mimic the action of a particular neurotransmitter. They bind to receptors and generate postsynaptic potentials.

Nicotine and Receptors

Nicotine is an acetylcholine agonist, which means that it mimics acetylcholine closely enough to compete for acetylcholine receptors. When both nicotine and acetylcholine attach to a receptor site, the nerve fibers become highly stimulated, producing a feeling of alertness and elation.

Antagonists are chemicals that block the action of a particular neurotransmitter. They bind to receptors but can’t produce postsynaptic potentials. Because they occupy the receptor site, they prevent neurotransmitters from acting.

Paralysis and Poison Arrows

Curare is a drug that causes paralysis. As an acetylcholine antagonist, it binds to acetylcholine receptors at nerve-muscle junctions, preventing communication between nerves and muscles. Doctors sometimes use curare to immobilize patients during extremely delicate surgery. South American tribes have long used curare as an arrow poison.