The Synapse

Neurotransmitter molecules, released by synaptic vesicles, cross the tiny synaptic space (or cleft) between the axon terminal (or synaptic knob) of the sending neuron and the dendrite of the receiving neuron, where they latch on to a receptor site, much the way a key fits into a lock. This is how they pass on their excitatory or inhibitory messages.


Synaptic transmission—communication between neurons.
When a neural impulse reaches the end of an axon, tiny oval sacs, called synaptic vesicles, at the end of most axons release varying amounts of chemical substances called neurotransmitters. These substances travel across the synaptic space and affect the next neuron.

Synaptic transmission
Synaptic transmission



SUMMARY TABLE  
MAJOR NEUROTRANSMITTERS AND THEIR EFFECTS
Acetylcholine (ACh) Generally excitatory Affects arousal, attention, memory, motivation, movement. Too much: spasms, tremors. Too little: paralysis, torpor.
Dopamine Inhibitory Inhibits wide range of behavior and emotions, including pleasure. Implicated in schizophrenia and Parkinson's disease.
Serotonin Inhibitory Inhibits virtually all activities. Important for sleep onset, mood, eating behavior.
Norepinephrine Generally excitatory Affects arousal, wakefulness, learning, memory, mood.
Endorphins Inhibitory Inhibit transmission of pain messages.