Major Receptors in the ANS

The major receptors in the Autonomic Nervous System include cholinergic and adrenergic receptors.

Cholinergic Receptors (Cholinoreceptors)

Cholinergic receptors respond to ACh, and its analogs, and are classified as muscarinic (respond to muscarine and ACh) or nicotinic (respond to muscarine and ACh).

M₁ Receptor

Location
Mechanism
Major Function

Nerve endings

G_q-Coupled

Increased phospholipase C→increased IP3, diacylglycerol, cytoplasmic calcium

M₂ Receptor

Location
Mechanism
Major Function

Heart, some nerve endings

G_i-coupled

Decreased adenylyl cyclase → decreased cAMP

M₃ Receptor

Location
Mechanism
Major Function

Effector cells: Smooth muscle, glands, endothelium

G_q-coupled

Increased phospholipase C→increased IP3, diacylglycerol, cytoplasmic calcium

N_N Receptor

Location
Mechanism
Major Function

ANS ganglia

Na⁺–K⁺ ion channel

Depolarizes, evokes action potential

N_M Receptor

Location
Mechanism
Major Function

Neuromuscular end plate

Na⁺–K⁺ ion channel

Depolarizes, evokes action potential

Adrenergic Receptors (Adrenoreceptors)

Adrenergic receptors are categorized as alpha or beta.

Alpha adrenergic receptors are located on vascular smooth muscle, presynaptic nerve terminals, blood platelets, fat cells, and neurons in the brain. The two subtypes, alpha-1 and alpha-2, use different G-coupling proteins.
Beta adrenergic receptors are located on most types of smooth muscle, cardiac muscle, some presynaptic nerve terminals, and lipocytes. Beta receptors have three major subtypes – beta-1, beta-2, and beta-3. All three subtypes use the same G-coupling protein.
An overview of the various adrenergic receptors can be found in this table adapted from Katzung.

Receptor	Location	G protein class	Effector/signaling pathway	Major function
Alpha₁ (α₁)	Effector tissues: smooth muscle, glands	G_q	Increased phospholipase C increased IP3, diacylglycerol, cytoplasmic calcium	Ca²⁺, causes contraction, secretion
Alpha₂ (α₂)	Nerve endings, some smooth muscle	G_i	Decreased adenylyl cyclase decreased cAMP	Transmitter release (nerves), causes contraction (muscle)
Beta₁ (β₁)	Cardiac muscle, juxtaglomerular apparatus	G_s	Increased adenylyl cyclase increased cAMP	Heart rate, force; renin release
Beta₂ (β₂)	Smooth muscle, liver, heart	G_s	Increased adenylyl cyclase increased cAMP	Relax smooth muscle; glycogenolysis; heart rate, force
Beta₃ (β₃)	Adipose cells	G_s	Increased adenylyl cyclase increased cAMP	Lipolysis

A summary table of autonomic receptors, including their structural family, functional family, physiologic ligands, effectors/transducers, and major functions is available here (link to Table Autonomic Receptors).

If you prefer videos, watch the following time stamps in this Osmosis video.

Alpha-1 adrenergic receptors are explained (Watch 6:16–8:01).

Alpha-2 adrenergic receptors are explained (Watch 9:11–9:44).

Beta adrenergic receptors are explained (Watch 6:17–9:10).

A review of adrenergic receptors is explained (Watch 9:45–10:27).

Table of Contents

Cholinergic Receptors (Cholinoreceptors)

M1 Receptor

M2 Receptor

M3 Receptor

NN Receptor

NM Receptor