Cholinergic receptor

TYPES OF CHOLINERGIC RECEPTORS:
  • Nicotinic cholinergic receptor:
  1. Nicotine = agonist
  2. Directly opens a Na+ Ca + K+ channels
  3. Curare = antagonist
  4. NM : Skeletal muscle endplate
  5. NN : Ganglionic cells, adrenal medulla, CNS
  6. Nicotinic Receptor signal transduction pathway:
  • Ionotropic : ligand gated ion channel
  • Composed of 5 subunits
  • ACh binds to extracellular domains of α subunits
  • Receptor opens a central transmembrane ion channel
  • Changes in membrane potential or ionic concentration within cell
  1. Ionotropic Receptors:
  2. Work very fast; important role in fast neurotransmission
  3. Each is made of several subunits (together form the complete receptor)
  4. At center of receptors is channel or pore to allow flow of neurotransmitter
  5. At rest - receptor channels is closed
  6. When neurotransmitter bind -- channel immediately opens
  7. When ligand leaves binding site -- channel quickly closes
  8. Acetylcholine acting on nicotinic receptors produces Contraction of skeletal muscle
  9. D-tubocurarine is a skeletal muscle relaxant that acts by competitive inhibition of NM receptors at neuron-muscular junction.
  10. Bupropion is Nicotinic receptor antagonist
  11. Clinical :
  • In Myasthenia gravis, antibodies are present against Nicotinic Receptor
  • Dry mouth during antidepressant therapy is caused by blockade of Muscarinic acetylcholine receptors


  • Muscarinic receptors
  1. Selectively stimulated by muscarine and blocked by atropine.
  2. Located primarily on autonomic effector cells of heart, smooth muscles, respiratory tract etc and CNS.
  3. Subtypes are M1 ,M2, M3, M4 & M5
  4. Muscarinic antogonists Decrease gastric secretions, Decrease respiratory secretions & Fascilitates AV conduction
  5. Oxybutynin acts by Muscarinic receptor inhibition
  6. Clinical:Drug used for muscarinic symptoms seen in cobra envenomation is Neostigmine
  7. There are no Renshaw cells at the neuromuscular junction. 


  • Renshaw cells inhibit motor neurons in the anterior gray horn of the spinal cord.
  • Action potentials on the alpha motor neuron release acetylcholine (ACh) from the axon terminal.
  • The ACh diffuses across the synaptic cleft and stimulates nicotinic receptors on the muscle endplate, generating an action potential that causes contraction of the muscle fiber.
  • Cholinergic receptors on the muscle endplate are cation channels.
  • ACh and its receptors
DrugNmNnM1M2M3
ACh, Carbachol(maximum nicotinic effect), Methacholine, AChEi
(Physostigmine, Galantamine, Neostigmine, Pyridostigmine)
+++++
Nicotine, Varenicline++
Succinylcholine+/-
Atracurium, Vecuronium, Tubocurarine, Pancuronium-
Epibatidine, DMPP+
Trimethaphan, Mecamylamine, Bupropion, Dextromethophan, Hexamethonium-
Muscarine, Oxotremorine, Bethanechol, Pilocarpine+++
Atropine, Tolterodine, Oxybutynin---
Vedaclidine, Talsaclidine, Xanomeline, Ipatropium+
Pirenzepine, Telenzepine-
Methoctramin-
Darifenacin, 4-DAMP, Darifenacin, Solifenacin-
Exam Question
  • Action potentials on the alpha motor neuron release acetylcholine (Ach) from the axon terminal
  • Cholinergic receptors on the muscle endplate are cation channels
  • Alpha motor neurons excite, and Renshaw cells inhibit, the muscle endplate
  • In Myasthenia gravis, antibodies are present against Nicotinic Receptor
  • Nicotine receptor sites include Adrenal medulla, Skeletal muscle & Sympathetic ganglia
  • Carbachol has maximum nicotinic effect
  • Muscarinic antogonists Decrease gastric secretions, Decrease respiratory secretions & Fascilitates AV conduction
  • Oxybutynin acts by Muscarinic receptor inhibition
  • D-tubocurarine is a skeletal muscle relaxant that acts by competitive inhibition of NM receptors at neuron-muscular junction.
  • Dry mouth during antidepressant therapy is caused by blockade of Muscarinic acetylcholine receptors
  • Bupropion is Nicotinic receptor antagonist
  • Drug used for muscarinic symptoms seen in cobra envenomation is Neostigmine
  • Acetylcholine acting on nicotinic receptors produces Contraction of skeletal muscle
  • Nicotinic cholinergic receptors are ionic channel
  • Varenicline acts by Partial nicotine receptor agonist
  • Muscarinic cholinergic receptors are seen at Stomach, CNS , Glands
Don't Forget to Solve all the previous Year Question asked on Cholinergic receptor