Neurotransmitters are chemical messengers that help communicate between neurons or neurons and muscles. They are classified based on their composition into small molecule transmitters like acetylcholine, amines such as dopamine and serotonin, amino acids like glutamate and GABA, and peptide or gas transmitters. Receptors are also classified as ionotropic, which allow ion flow when activated by a neurotransmitter, or metabotropic, which initiate intracellular responses. Common excitatory neurotransmitters include glutamate and acetylcholine, while inhibitory ones include GABA and glycine. Together, neurotransmitters and receptors facilitate both excitation and inhibition in the nervous system to regulate functions like movement, mood, and learning.

1. Neurotransmitters

2. • Overview
What are neurotransmitters?
Classification of neurotransmitters based on their composition
 Small molecule transmitter
 Peptide transmitter’
 Transmitter gases
Types of receptors
 Ionotropic receptors
 Metabotropic receptors

3. What are Neurotransmitters?
• Neurotransmitters are chemical messengers which help to communicate
information between neurons or from neurons to muscles.
• A neurotransmitter influences a neuron in one of three ways: excitatory, inhibitory
or modulatory.
• They are molecules and therefore they are divided on the basis of their molecular
structure.

4. Classification of Neurotransmitters
Neurotransmitters
Small-Molecule
Transmitters
Peptide transmitters
Soluble
Gases/Transmitter
Gases

5. Small Molecule Transmitters
• They are small molecules which are produced in axon terminals and are also
released from here .
• They replaced in presypnatic membrane.
• We derive these neurotransmitters through our food,
• The types of food we eat can influence the level activity of these
neurotransmitters.
• They are released quickly and their effects are not as long lasting as peptides
effects.

6. Small Molecule Transmitters
Acetylcholine Amine Amino Acid

7. Acetylcholine
Where is it most produced mostly?
• In CNS- efferent axons
• In PNS- Ganglions of ANS and target organs of parasympathetic system.
Distribution of acetycholinergic neurons
• Dorsolateral pons- elicit most characteristics of REM sleep.
• Basal Forebrain- involved in activating the cerebral cortex, and facilitating learning,
especially perceptual learning.
• Medial septum- control the electrical rhythms of hippocampus and modulate its
functions of developing new memories.
Effects of Ach released in the brain are generally facilitatatory and All muscular
movement is accomplished by the release of acetylcholine

10. Amines/biogenic amines/ Monoamine
• Amines are molecules which contain amino group.
• Amines are divided into Catecholamine and Indolamine
• Catecholamines are a group of neurotransmitters that arise in sequence from the amino acid
Tyrosine.
• Indolamines are biologically synthesized from the essential amino acid Tryptophan is
synthesized into serotonin.

12. Amines
Catecholamine
Dopamine Epinephrine Norepinephrine
Indolamine
Serotonin

14. Dopamine
Dopamine is a neurotransmitter which is associated with reward mechanism.
• Other Functions: include movement, attention and learning and reinforcing
effect of drugs which people tent to abuse.
• The brain contains several systems of dopaminergic neurons. The three most
important originate in brainstem and they are –
 Nigriostriatal System
 Mesolimbic System
 Mesocortical System

18. Norepinephrine And Epinephrine
Norepinephrine/noradrenaline is found in the neurons in ANS .
• It is secereted through axonal varicosities in adrenal medulla.
• Function: Sympathetic Nervous System, is responsible for tonic and reflexive
changes in cardiovascular tone.
• Epinephrine/adrenaline is a hormone produced by the adrenal medulla.
• Function: responses to metabolic or global challenges to homeostasis, eg.
manifestations of emotional distress.

20. Serotonin
It is also called 5-hydroxytrptamin.
What serotonin does?
• It plays an important role in regulation of mood, in the control of eating,
sleep, arousal and also in regulation of pain.
• Serotonergic neurons are involved in the control of dreaming.
Where are they found?
• Location – 9 clusters of the ralphe nuclei of the midbrain, pons and
medulla.
There are atleast 9 types of serotonin receptors.

23. Amino Acid
Glutamate GABA Glycine
Amino acids containing an amine group (NH2)

24. Glutamate
It is believed that these neurotransmitters are the first to have evolved.
Where are they found and when they become a neurotransmitters?
• It is widely present in neurons, but only become neurotransmitters if packed in
the vesicles in axon terminal
What does Glutamate do?
• Glutamate is primary excitatory neurotransmitter in the brain and spinal cord.
It is produced in abundance by the cells metabolic process.
There are 4 types of receptors- 3 are ionotropic and 1 is metabotropic receptors.

25. GABA( gamma-aminobutyric acid)
It is produced from glutamic acid by the action of an enzyme (glutamic acid
decarboxylase. Or GAD) that removes a carboxyl group.
• It is an inhibitory neurotransmitter, and is widespread throughout brain and
spinal cord.
• There are two types of receptors- two, c is ionotropic and controls a chloride
channel metabotropic and controls a potassium channel.
• Neurons in the brain are highly interconnected. Without inhibitory synapses it
will make brain unstable.

27. Glycine
• It is an inhibitory neurotransmitter in the spinal cord and lower portions of
the brain.
• The glycine receptor is ionotropic, and it controls a chloride channel.
• Glycine is an important protein in DNA replication.

29. Petides/ Neuropeptides
• They are chains or polymers of amino acids.
• Peptide transmitters are made directly from instructions contained in the cell’s
DNA.
• They are produced in Axon terminals of the neurons.
• They act as a neurotransmitters and neuromodulators.
• Peptides-released-destroyed by enzymes. – no mechanism of reuptake and
recycling.

30. • One of the best know peptides are endogenous opioids.
• Endogenous opioids- are a class of peptides secreted by the brain which helps in
in reduction of the pain. Eg enkephalin.
• Other functions: in the nervous system, for example, they serve as hormones, are
active in responses to stress.
• Peptide transmitters activate receptors that indirectly influence cell structure and
function.
• They are produced through the digestive break down of food into amino acids.
(cannot be taken orally).

31. Soluble Gases/ Transmitter Gases
The soluble gases nitric oxide (NO) and carbon monoxide (CO) are the most unusual
neurotransmitter.
Where are they stored?
• They are neither stored in synaptic vesicles nor released from them.
• instead, they are synthesized as needed
Nitric Acid uses as neurotransmitters
• It controls the muscles in intestinal walls, and it dilates blood vessels in brain regions that
are in active use.
• It also dilates blood vessels in the genital organs and is therefore active in producing
penile erections in males.
• Sildenafil citrate (trade name Viagra) is a widely used treatment for male erectile
dysfunction and acts by enhancing the action of NO.

32. Types of Receptors for
Neurotransmitters
Ionotropic Receptors Metabotropic Receptors

33. Ionotropic Receptor
Ionotropic receptors allow the movement of ions across a membrane.
• An ionotropic receptor has two parts: a binding site for a neurotransmitter and
channel or pore.
• When the neurotransmitter binds to an ionotropic receptor, it twists the receptor
enough to open its central channel, which is shaped to let a particular type of
pass through.
• The channels controlled by a neurotransmitter are transmitter-gated or ligand-
gated channels. (A ligand is a chemical that binds to another chemical.) That is,
when the neurotransmitter attaches, it opens a channel.

35. Metabotropic Receptors
• It has a binding site but unlike ionotropic receptor it does not have a pore.
• It either produces the ion channels or bring change in cell’s metabolic activity.
• When a neurotransmitter attaches to a metabotropic receptor, it bends the
receptor protein that goes through the membrane of the cell.
• Bending the receptor protein detaches that G protein (guanyl nucleotide-binding
proteins)
• Bending the receptor protein detaches that G protein, which is then free to take its
energy elsewhere in the cell.
• The g- protein have 3 important sub-units.

36. • Subunit a either binds with Ion Channel or with an Enzyme.

39. • No one neurotransmitter is associated with a single kind of receptor or a
single kind of influence on the postsynaptic cell.
• At one location it may bind to an metabotropic and other to ionotropic
leading to inhibitory or excitatory effect.
• For example, acetylcholine has an excitatory effect on skeletal muscles,
where it activates an ionotropic receptor; but it has an inhibitory effect on the
heart, where it activates a metabotropic receptor.

40. References:
• 1.Whishaw I, Kolb B. Fundamentals of human neuropsychology. New York, NY:
Worth Custom Publishing; 2015 (types of receptors)
• 2. Carlson N. Foundations of physiological psychology. Boston: Allyn and
2002. (SMT- Amines)
• 3. Kalat J. Biological Psychology. 11th ed. Belmont,CA: Wadsworth, Cengage
Learning; 2013.
• 4.Els.net. (2018). Adrenaline and Noradrenaline. [online] Available at:
http://www.els.net/WileyCDA/ElsArticle/refId-a0001401.html
• Queensland Brain Institute. (2018). What are neurotransmitters?. [online]
Available at: https://qbi.uq.edu.au/brain/brain-physiology/what-are-
neurotransmitters .

41. Thank You