QS Study

Neurotransmitters are highly active chemical agents released at the nerve ending and transmit impulses from nerve to nerve or nerve to effector tissue. They are also found at the axon endings of motor neurons, where they stimulate the muscle fibers. Neurotransmitters are often referred to as the body’s chemical messengers.

Fig: Neurotransmitter


(A) According to a type of action –

  • Excitatory: Glutamic acid, nitric oxide.
  • Inhibitory: Dopamine, Serotonin, GABA.
  • Both excitatory and inhibitory: Acetylcholine, norepinephrine.

(B) Small-molecule, rapidly acting transmitters –

Class I: Acetylcholine

Class II: The amines –

  • Nor-epinephrine – is a neurotransmitter that plays an important role in alertness is involved in the body’s fight or flight response.
  • Serotonin – plays an important role in regulating and modulating mood, sleep, anxiety, sexuality, and appetite.
  • Epinephrine – is considered both a hormone and a neurotransmitter.
  • Histamine – acts as a neurotransmitter in the brain and spinal cord.
  • Dopamine – plays an important role in the coordination of body movements.

Class III: Amino Acids –

  • Gama-amino butyric acid (GABA)
  • Glycine, Glutamate, Aspartate.

Class IV: Nitric Oxide (NO)

Fig: Neurotransmitter classification

(C) Neuropeptide, slowly acting (large molecule) or growth factor

  • Hypothalamic releasing and inhibitory hormones.
  • Anterior and posterior pituitary hormones.
  • Peptides act on gut and brain, substance-p, gastrin, VIP.