These are chemical messengers between two neurons or a neuron and an effector organ (viz. muscle, gland)
1. Concept of neurotransmission was given by Otto Loewi for which he won a noble prize in medicine and physiology in 1938
2. Classified into two categories based on size : small molecular or large molecular
3. Each neurotransmitter can have several subtypes of receptors. It is the receptor that determines the effect of neurotransmitter.
4. Receprors can either be ligand gated channels or G protein coupled receptor. Former have a quicker response time while latter having delayed and longer lasting effects
5. Receptors can also be present on presynaptic membrane: autoreceptor (present on same neuron from which neurotransmitter was secreted) or heteroreceptor ( present on presynaptic membrane of other neurons)