The point at which the axon of one neuron makes contact with the dendrites of another neuron is called a synapse. The contact made at the synapse is chemical. When a nervous impulse reaches the end of an axon, a chemical messenger, called the Neurotransmitter, is destroyed by an enzyme released by the same axon, as shown by the above photo.
Neurotransmitters are chemicals that are used to relay, amplify and modulate electrical signals between a presynaptic and a postsynaptic neuron. A chemical is classified as a neurotransmitter if it respects the following conditions:
- It is synthesized endogenously
- It is available in sufficient quantity in the presynaptic neuron to exert an effect on the postsynaptic neuron
- Externally administered, it must mimic the endogenously released substance
- A biochemical mechanism for inactivation must be present
There are over 100 substances actually known or can possibly be neurotransmitter...:
- It is particularly important in the stimulation of muscle tissue and memory. Alzheimer's Disease is associated directly with the deterioration of the neurons which produce acetylcholine.
- Dopamine is critical to the way the brain controls our movements and is a crucial part of the basal ganglia motor loop. Shortage of dopamine, causes Parkinson's disease, in which a person loses the ability to execute smooth, controlled movements.
- Plays an important role in learning, memory, apetite, and emotions.
- Serotonin is believed to play an important part of the biochemistry of depression, bipolar disorder and anxiety. It is also believed to be influential on sexuality.
- Endorphins regulate feelings of pain and hunger.