Neurotransmitters and Their Types

  • A chemical substance present in neuron.
  • Transmits nerve impulse from one to another neuron.
  • Thus also called a mediator for impulse transmission.
  • Transmission occurs through synapse.
  • Discovered first by Otto Loewi in 1921.
  • Was an Austrian scientist who practically came out with this discovery.

Criteria for Neurotransmitters

  • Various substances are categorized as neurotransmitters.
  • Following criteria should be met for being a substance neurotransmitter.
  1. Must be present in a neuron.
  2. Produced by a neuron.
  3. Released by a neuron.
  4. Must act on target site after release.
  5. Must produce biological affect.
  6. Must be inactivated after showing affect.


  • Classified into different types on the different basis.
  • Some of the types are as follows.

A) Based on chemical nature

  • Substances with different chemical nature are identified as neurotransmitters.
  • Depending on it, they are kept in three groups. They are:

a) Amino acids

  • Involved in fast synaptic transmission that falls in this group.
  • Inhibitory and excitatory in function.
  • GABA, glycine, glutamate, aspartate falls in this group.

b) Amines

  • Modified amino acids.
  • Shows slow synaptic transmission.
  • Also inhibitory and excitatory in action.
  • Noradrenaline, adrenaline, dopamine, serotonin and histamine falls into this group.

c) Others

  • Acetylcholine like neurotransmitters does not belong to above group.
  • Formed from choline and acetyl co-enzyme A.
  • Presence of choline acetyltransferase is required.
  • Nitric oxide, a soluble gas also acts as neurotransmitters.

B) Based on function

  • Some neurotransmitters are related to excitation only.
  • Some cause inhibition of post synaptic neuron.
  • Depending on it, they are kept in two groups.

a) Excitatory neurotransmitters

  • Conducts impulse from presynaptic to post synaptic neuron.
  • Release does not cause development of action potential in post synaptic neuron.
  • Though it is released by pre synaptic neuron terminal.
  • But, it causes change only in resting membrane potential i.e., slight depolarization.
  • This change occurs by opening of sodium channels in the post synaptic membrane.
  • This results in influx of sodium ions from ECF.
  • This is called excitatory post synaptic potential (EPSP).
  • Thus, results in development of action potential in initial portion of post synaptic neuron.
  • Acetylcholine and noradrenaline falls into this group.

b) Inhibitory neurotransmitters

  • Inhibits the impulse conduction from pre to post synaptic neuron.
  • Potassium channels opens in the post synaptic membrane in result of its release in pre synaptic axon.
  • This happens as the action potential arrives on the axon.
  • This finally leads to potassium ions efflux.
  • Thus, hyperpolarization occurs which is called inhibitory post synaptic potential (IPSP).
  • Action potential won’t generate in the post synaptic neuron in IPSP development.
  • Gamma-amino butyric acid (GABA) and dopamine falls in this group.

Transportation and Release

  • Cell body of the neuron produces it.
  • Carried through axon and stored in axon terminal.
  • Stored in small packets called vesicles.
  • Stimulus influences these vesicles to open.
  • Thus, in synaptic cleft neurotransmitters are released.
  • Receptors on the surface of post synaptic cell are specific.
  • Thus, binding occurs after they are released.
  • G proteins, protein kinase or ligand-gated receptors are some examples.


  • After neurotransmitters function completely, they are inactivated.
  • Four mechanisms deactivate them.
  1. Diffuses out to the area where it cannot show its function.
  2. Specific enzymes present may destroy them.
  3. Astrocytes (macrophages) engulf them and thus removed.
  4. Reuptake into the axon terminal removes them also.





Neurotransmitters and Their Types