Nicotinic receptors

Location

Nicotinic acetylcholine receptors are present mainly at four locations

• CNS
• Adrenal medulla
• Autonomic ganglia
• Neuromuscular junction

At adrenal medulla sympathetic fibers release acetylcholine which acts on nicotinic acetylcholine receptors.

Types

Based on their function, they can be classified into three types

• Neuronal
• Ganglionic
• Muscular

Neuronal

Neuronal receptors are present within the CNS and adrenal medulla and responsible for CNS stimulation and release of catecholamines respectively. Within the CNS they play important role as excitatory receptors responsible for CNS stimulation, decreased fatigue and increased alertness.

Ganglionic

Ganglionic type nicotinic receptors are present at autonomic ganglia and responsible for ganglionic transmission. One of the interesting point here is that they are present at both sympathetic and parasympathetic ganglia. So their role is to conduct ganglionic transmission to fill the gap between preganglionic and postganglionic fibers.

That's why ganglionic stimulants will stimulate both sympathetic and parasympathetic systems producing mixed effects.

Muscular

These are one of the important nicotinic acetylcholine receptors widely involved in our physiological functions. These muscular type receptors are present on all skeletal muscles and produce contraction.

Nicotinic receptors are ionotropic receptors coupled with sodium channels. When these receptors are activated the sodium channels are opened leading to depolarisation of the membrane. This depolarisation may lead to contraction by excitation-contraction coupling.

A class of drugs called neuromuscular blockers act on these receptors and inhibit their action to produce muscle relaxations.