There are four main types of receptors: channel-linked (ionotropic) receptors, G protein-linked (metabotropic) receptors, enzyme-linked receptors, and intracellular receptors. Channel-linked receptors have the fastest onset of action, in milliseconds, and include nicotinic cholinergic and NMDA receptors. G protein-linked receptors signal through second messenger systems and have an onset of seconds, such as adrenergic receptors. Enzyme-linked receptors signal through kinase pathways and have an onset of minutes, such as insulin receptors. Intracellular receptors include steroid receptors and regulate gene transcription with effects over days.

1. RECEPTOR TYPES
 CHANNEL LINKED (IONOTROPIC)
 G PROTEIN LINKED (METABOTROPIC)
 ENZYME LINKED
 INTRACELLULAR RECEPTOR
(RECEPTORS REGULATING GENE TRANSCRIPTION
/NUCLEAR RECEPTORS)

3. CHANNEL LINKED (IONOTROPIC) :
The cell surface has a selective ion channel like Na, K , Ca , or Cl .
 Onset of action through these types of receptors is fastest –
milliseconds.
 Nicotinic cholinergic receptors, GABA-A and NMDA receptors.
Cl-influx
Hyperpolarisation of neuronal
membrane(> -90mv)
-70 mv
Antianxiety, General
anaesthesia, Anticonvulsant
effects

4. G PROTEIN LINKED (METABOTROPIC) :
These are cell membrane receptors which are linked to effector
mechanisms through G-proteins.
 Effector mechanisms includes adenylyl cyclase, phospholipase C
 Onset of response in seconds.
 Eg : adrenergic receptors, histamine receptors

5. MECHANISMS: Through IP3-DAG
pathway
G-Protein receptors

6. Through C-AMP pathway

7. ENZYME LINKED(Kinase linked)
These cell membrane receptors are enzymatic in nature
 Insulin acts through this receptors.
 Onset of response in minutes.

8. INTRACELLULAR RECEPTOR
These includes
Steroids, Thyroxine and Vit–D
It takes days to produce its actions
(RECEPTORS REGULATING GENE
TRANSCRIPTION/NUCLEAR RECEPTORS)

9. Classification of ion channels
 Gating mechanism
 Leakage channels
 Voltage –gated channels
 Ligand –gated channels
 Ions transported
 Ca2+
ion channels
 Na+
ion channels
 Cl-
ion channels
 K+
ion channels

10.  Inhibitory function.
 Nicotinic cholinergic
 GABA-A
 Glycine
 Excitatory function
 NMDA
 kainate

11. G-PROTEIN COUPLED RECEPTORS:-
1. Adrenergic receptors
2. Cholinergic receptors
3. Seretonergic receptors
4. Dopaminergic receptors
5. Histaminergic receptors
6. GABA/BZ-receptors
7. Excitatory amino acid receptors
8. Opioid receptors
9. Purinergic receptors

12. 1)ADRENERGIC RECEPTORS
I α & β-ADRENERGIC RECEPTORS
 α -ADRENERGIC RECEPTORS
a) α -1RECEPTORS
b) α -2 RECEPTORS
2 β RECEPTORS
a) β -1RECEPTORS
b) β -2 RECEPTORS
c) β -3 RECEPTORS

13. 2)CHOLINERGIC RECEPTORS
 THERE ARE 2 TYPES OF RECEPTORS
 MUSCARINIC RECEPTORS
a)M-1
b)M-2
c)M-3
 NICOTINIC RECEPTORS
a)NM
b)NN
c)NN1
d)NN2

14. 3) SERETONERGIC (5-HT) RECEPTORS
1) 5-HT-1
2)5 HT-2
3)5 HT-3
4)5 HT-4

15. 4) DOPAMINERGIC RECEPTORS
 THERE ARE 2 CLASSES
1)D1-Receptors
2)D2-Receptors

16. 5) HISTAMINERGIC RECEPTORS
 There are 2 types
1)H1-Receptors
2)H2- Receptors

17. 6) GABA RECEPTORS
 Three different types of GABA-Receptors
are:-
1)GABAA
2)GABAB
3)GABAC

18. 7)EXCITATORY AMINO ACID
RECETORS :-
 These are of 4 types:-
1)NMDA
2)AMPA
3)Kainate
4)Metabotropic

19. 8) OPIOID RECEPTORS
 There are 3 types in this are:-
1)µ-Opioid Receptors
2)κ-Opioid Receptors
3)δ-Opioid Receptors

20. 9)PURINERGIC RECEPTORS
 There are 2 types in this are:-
1)p1(adenosin receptors)
2)p2(adenosin triphoshate/ATP receptors)