What is Neurotransmitters or acetylcholine ?

We know that transmission of signals from nerve to muscle is affected by acetylcholine or neurotransmitter substance. similarly neuron to neuron transmission is also achieved by acetylcholine. In addition to acetylcholine There are several other by chemical that function as neuro transmitter. A limited number have already been identify and news one are being identified.

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A chem­i­cal can be called a neu­ro­trans­mit­ters in a giv­en tis­sue only if its ful­fill cer­tain con­di­tions like:

• When applied to the post­sy­nap­tic mem­brane it should be able to pro­duce the same effect as does presy­nap­tic stimulation.
• It should also be released by the presy­nap­tic membrane
• Its action should be blocked by the same agent that block neur­al transmission.

The neu­ro­trans­mit­ter are either drived:

i) From amino acid tyro­sine, which includes dopamine ‚nor­ep­i­neph­rine (also called nora­dren­a­line), epi­neph­rine (also called adren­a­line )and serotonin.

ii) From neu­ropep­tides which include neu­ro­trans­mit­ter endor­phins and enkephalins , that reduce pain per­cep­tion. There­fore, these are also called nat­ur­al opi­ates (mor­phine like substance ).

The neu­rons that are involved in pain recep­tion have recep­tor mol­e­cules to which inter­nal opi­ates attach so that the pain recep­tor are inhib­it­ed from releas­ing their own trans­mit­ter sub­stance (sub­stance P )on two neu­rones in the pain per­cep­tion centres.Thus the relay of infor­ma­tion to the brain is blocked. the pain killing the effec­tive­ness of endor­phins is sim­i­lar to that of morphine.

Neurotransmitter have three mechanism of action ‚namely ionotropic, metabotropic and modulatory.

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• Ionotrop­ic mech­a­nism of action : Includes the open­ing of spe­cif­ic ion­ic Gates in the plas­ma mem­brane . Glu­ta­mate, GABA and acetyl­choline are all ionotrop­ic and so bind to their respec­tive and ionotrop­ic receptors.Glutamate is exci­ta­to­ry as it opens Na+ gates ‚lead­ing to de polar­iza­tion. GABA opens the Cl (chlo­ride ion) gates, there­by allow­ing the move­ment of Cl ion into neu­ron and lead­ing to hyper polar­iza­tion hence it is inhibito­ry. Acetyl­choline is ionotrop­ic and exci­ta­to­ry at nico­tinic synaps­es (acetyl­choline. Has two types of recep­tor one thats responds to nico­tine and called nictin recep­tor and anoth­er type known as mus­carinic recep­tor that responds to mus­carine , a drug obtained from cer­tain types of mush­rooms) , includ­ing the open­ing of Na⁺ gates . These ionotrop­ic effects are rapid (occur­ing typ­i­cal­ly with­in 10 mil­lisec­onds after neu­ro­trans­mit­ter release( and lasts for a short peri­od from 1 to 20 miliseconds.

• Metabotrop­ic Mech­a­nisms : of actin is more com­pli­cat­ed involv­ing a sequence of meta­bol­ic reac­tions. These effects typ­i­cal­ly involve a ” sec­ond mes­sen­ger ” , mol­e­cule taht May open or close an ion gate,After the pro­duc­tion of pro­teins or alter the struc­ture of the post­sy­nap­tic cell.The bio­genic amine epi­neph­rine is a metabotrop­ic trans­mit­ter that binds to the metabotrop­ic recep­tor of the plas­ma mem­brane. The effects are much low­er to occur ( 30 mil­lisec­ond after neu­ro­trans­mit­ter release )are longer last­ing ( up to sev­er­al sec­onds in duration).

• Neu­ro mod­u­la­tor mech­a­nism of action : Involves neu­ro mod­u­la­tor which are pep­tide mol­e­cules (shot pro­tein) whose func­tion lie some­where between that of a neu­ro­trans­mit­ter and a hormone.Neuro mod­u­la­tor may influ­ence and num­ber of neu­rons in the region of release includ­ing the neu­ron releas­ing them. Neu­ro­trans­mit­ter acts by pro­long­ing or lim­it­ing the effects of a neu­ro mod­u­la­tors. Most neu­rons syn­the­size and release both neu­ro­trans­mit­ter and neu­ro mod­u­la­tors . this com­bi­na­tion sup­ports a broad­er range of effects.

Neu­rons do not always func­tion in the way they should. things can go wrong in a dead­ly way if the synap­tic cleft is occu­pied by chem­i­cal that inter­fere with neurotransmission.