Neurotransmitters can be categorized as either small molecular weight transmitters that act rapidly through ion channels or large molecular weight neuropeptides that act more slowly through second messenger systems. Small molecular transmitters are synthesized in presynaptic terminals, stored in vesicles, released in large quantities upon stimulation, and removed by reuptake or enzymatic degradation. In contrast, neuropeptides are synthesized by neurons in the central nervous system, released in smaller quantities, and more potent. Examples of excitatory and inhibitory chemical transmitters are provided. Hormones produced by the hypothalamus, pituitary, and gastrointestinal tract are also listed.

1. By: Olla BaEissa
Neurotransmitters (Synaptic transmitters):
1-The small molecular weight
rapidly acting transmitter
2- The large molecular weight
slow & prolonged acting transmitter
1-They are rapidly acting.
2-They act by activation of ion channels.
3- Responsible for transmission of sensory
impulses to the brain and motor signals to
the muscles.
4-They are synthesized in the pre-synaptic
terminals and stored in transmitter vesicles.
5-They are released in large quantities .
6- They are removed by active reuptake or
by enzymatic destruction.
1-Usually slow and prolonged action .
2- Act by second messenger system.
3-Include several families of peptides that
are present in other organs and systems
,beside the nervous system ,as endocrine
and gastrointestinal system.
4-Synthesized by neurons in the C.N.S and
so called neuropeptides .
5- Released in small quantities.
6-More potent.
A-Excitatory chemical transmitters as:
Glutamine , Enkephalin
Acetyl choline , Noradrenaline
Histamine , Nitric oxide
Serotonin , Aspartate
B-inhibitory chemical transmitters as:
Dopamine , Glycine
Gamma amino butyric acid (GABA).
A- Hypothalamic –releasing hormones
as: T.R.H & L.H.R.H .
B- Pituitary peptides
as: ACTH ,β-endorphin , prolactin, L.H ,
Thyrotropin, G.H, ADH & Oxytocin
C- GIT hormones
as: substance P , Gastrin , CCK , VIP