VPB 121: Veterinary Physiology - II (2+1)

ACETYLCHOLINE RECEPTORS 

• The released acetylcholine diffuses across the synaptic cleft, reaches the postsynaptic membrane (sarcolemma), and binds with acetylcholine-specific receptors. This causes opening of ligand-gated ion channels in the sarcolemma. And diffusion of sodium ions into the muscle cell generating local potential change called end plate potential.

• Depolarization in the end plate potential opens voltage-gated Na⁺ channels at the postsynaptic membrane and leads to the generation of an action potential on the muscle cell membrane. Presence of the neurotransmitter in the presynaptic nerve terminal permits the transmission of action potential unidirectionally from the motor nerve to the skeletal muscle fibre.

• The binding activity of acetylcholine with its receptor remains for a very brief period. The acetylcholine is rapidly removed from the receptors by
  • Enzymatic hydrolysis of cholinesterase, located on the postsynaptic membrane hydrolyses acetylcholine into acetyl and choline molecules.
  • Diffusion of acetylcholine out of the synaptic cleft and is no longer available to act on the muscle.
• Myasthenia gravis is a neuromuscular disorder in which autoantibodies are produced against acetylcholine receptors. Hence, neuromuscular transmission is impaired and leads to paralysis.