Difference Between Adrenergic and Cholinergic (With Table)

Another key difference between them is that adrenergic pathway is associated with Sympathetic Nervous System while cholinergic pathway is associated with parasympathetic pathway.  

Furthermore, sympathetic nervous system related to the adrenergic pathway stimulates the heart by increasing its activity while parasympathetic nerves related to cholinergic pathway down regulates the heart’s activity.

There are basically two types of adrenergic nerve receptor, they are alpha and beta receptors while cholinergic nerve receptors are of two types, nicotinic and muscarinic. Adrenergic receptors are G-protein bound receptors while cholinergic receptors are inotropic and metabotropic.

Adrenergic pathway is responsible for the fight or flight response by releasing the catecholamines adrenalin from the adrenal gland whereas cholinergic pathway is in charge of the digest and rest response.

Adrenergic nerves are a part of the Sympathetic nervous system that houses the adrenergic receptors. These are G-protein coupled receptors that bind with a number of catecholamines that are released from the adrenal gland.

The two main neurotransmitters associated with adrenergic receptor binding are epinephrine or adrenaline and norepinephrine or noradrenaline. These are also responsible for the bodies fight or flight response.

When the sympathetic nervous endings in the heart bind with these neurotransmitters, they increase the heart’s activity by increasing heart rate and myocardial contractibility along with the conduction velocity.

Apart from their effect on heart, they also improve temporary performance of the body by directing blood from unimportant organs to skeletal muscles. Other effects include dilation of pupils, increasing blood pressure, expanding the lung cavity, etc. 

Adrenergic receptors are of two type’s alpha and beta, which are further divided based on their function and effect on the body. Adrenaline when binds to these receptors cause vasoconstriction with alpha and vasodilation with beta receptor.

Cholinergic pathway is related to the parasympathetic nervous system that involves the functions of cholinergic receptors. These receptors are regarded as intropic and metabotropic and are activated by the neurotransmitter Acetylcholine (ACh).

Acetylcholine neurotransmitters bind to the muscarinic and nicotinic receptors, the two main cholinergic receptors to carry out its functions. The cholinergic system drives the digest and rest response of the body.

The vagus or the parasympathetic nervous ending in the heart are responsible for the cholinergic effects on it. When Acetylcholine binds to these receptors in the heart, they are responsible for down regulating the heart’s functions.

This effect of lowering heart beat and blood pressure by acetylcholine binding is a balancing act of the body. Other effects of acetylcholine include dilating blood vessels, increasing bodily secretions and smooth muscle contraction.

These receptors are found all over the body but mainly in the target organs such as sensory glands, respiratory tracts, heart and eyes and gastro-intestinal tract. They are also found in the somatic efferent nerves in the skeletal muscles.

Cholinergic receptors are part of both Somatic and Autonomic nervous system and are further divided into Nicotinic and Muscarinic receptors. Nicotinic receptors bind to nicotine and muscarinic receptors binds to muscarine.  

Adrenergic and Cholinergic receptors are part of the Autonomous nervous system of our body. They are governed by the neurotransmitters binding to them for regulating their specific functions.

The main difference between adrenergic and cholinergic is that adrenergic receptors bind to the neurotransmitter adrenaline or epinephrine and noradrenalin or norepinephrine and that of cholinergic bind to acetylcholine.

The next key difference is that adrenergic receptors are associated with the sympathetic nervous systems while the cholinergic receptors are associated with the parasympathetic nervous system.

The adrenergic nerve endings in the heart and the specific receptors present are responsible for the increased heart activity when they bind to the adrenaline neurotransmitters while that of cholinergic receptors in the heart down regulate heart’s activity when stimulated.

Binding with adrenergic receptors also include effects such as dilation of pupils, increasing blood pressure, expanding the lung cavity, and redirecting blood flow into skeletal muscles to improve glucose availability.

Binding with cholinergic receptors are associated with dilating blood vessels, increasing bodily secretions and smooth muscle contraction apart from down regulating heart’s activity.

Adrenergic receptors are of two types alpha and beta which are further divided into Alpha₁ and alpha₂ and beta_1, beta₂and beta₃ depending upon their functions. Cholinergic receptors are also divided into nicotinic and muscarinic which binds to nicotine and muscarine respectively. Another difference is that the adrenergic receptors work by a G-protein coupling method whereas cholinergic receptors bind by ligand-gated intropic and metabotropic mechanisms.  

References

1. https://journals.physiology.org/doi/abs/10.1152/ajplegacy.1962.202.5.872
2. https://science.sciencemag.org/content/132/3422/301.abstract