Production of acetyl choline:
The synthesis is done in the nerve fiber itself from choline and acetyl coenzyme A. The choline comes either from the diet or endogenous biosynthesis from serine. Acetyl coenzyme A is a co-enzyme formed in the mitochondria of the nerve cell from the metabolism of carbohydrates.
The synthesis of acetylcholine requires energy but is facilitated by an enzyme: choline-acetyl-transferase. This is synthesized in the cell body and then migrates to the nerve end.
The travel of acetylcholine
After synthesis, acetylcholine is stored in the vesicles of the presynaptic membrane. The number of vesicles in a presynaptic terminus, each containing 1,000 to 50,000 acetylcholine molecules, is estimated at 300,000.
The arrival of an action potential at an axonal termination induces the opening of Ca ++ channels depending on the potential. The ensuing Ca ++ ion entry causes fusion of the vesicles to the plasma membrane and release of the Ach in the synaptic cleft. The ACh then diffuses on the other side of the synapse and by attaching itself on postsynaptic receptors, it causes a modification of the membrane ionic permeability (via ionotropic and / or metabotropic receptors).
