Sympathetic vs parasympathetic System Differences

The nervous system is a huge and complex body system with many functions.

It is the one that regulates the whole of human anatomy and physiology.

In this article, we will discuss only the divisions in the autonomic nervous system with brief functions. 

But we will see few details leading to sympathetic vs parasympathetic System

The nervous system can be broadly divided as the

  1. The Central Nervous System {has the brain and spinal cord}
  2. The Peripheral Nervous System {has nerves from the brain and spinal cord)

This peripheral nervous system is again categorized as the

  • The visceral nervous system (somatic and sensory nervous system)
  • The autonomic nervous system 

This autonomic nervous system is divided as 

  • Sympathetic nervous system
  • Parasympathetic nervous system.

The Autonomic Nervous System is so-called because it is not under our ‘voluntary control.’

It is always active in regulating the body’s physiology. It controls the action of the organs at the subconscious level.

Autonomic Nervous System shares a relationship with the somatic nervous system and has functional links with it.

It also has a great relationship with the Endocrine System.

The examples are.
a) Cortisol is a catecholamine hormone secreted from Adrenal Cortex, and from sympathetic nerve endings.
b) The adrenal Medulla is itself a modified sympathetic ganglion. Hormones secreted from Adrenal Medulla are actually secreted from sympathetic nerve endings.
c) Thyroxine or the T4 hormone, secreted from the Thyroid gland increases the number of beta-adrenergic receptors in the heart.

Sympathetic Vs Parasympathetic

Sympathetic Vs Parasympathetic Nervous System

FeatureSympathetic Nervous SystemParasympathetic Nervous System
Also called asThoraco-lumbar outflow as its nerves emerges from the thoracic and lumbar regions of the vertebral column.Cranio-sacral outflow as its nerves emerges from the cranium and sacral vertebrae.
The nerves originNerves emerge from a level of T1 to 3rd or 4th lumber, i.e., L3 or L4.The parasympathetic parts of the cranial nerve include the 3rd nerve, i.e., Occulomotor 7th nerve, i.e., Facial, the 9th nerve, i.e., Glossopharyngeal, and the 10th nerve (Vagus nerve). The sacral counterpart of
the parasympathetic nervous system has the root value of S2 to S4.
Preganglionic nerve fiberThe preganglionic nerve
efferents come out through the efferent root of the spinal segment.

It then passes through the white rami, and it
communicates the white rami, which connects the ventral root to the paravertebral sympathetic chain. In this point or region, most of the
neural ends of preganglionic fiber send and relay with
postganglionic neurons.
The preganglionic nerve
efferents come out through the lateral horn of the spinal cord, the
preganglionic nerve fiber arises, traveling long up to the target organ where there is a ganglion, there they terminate.
NeurotransmittersTwo or more types of
neurotransmitters are seen in the Sympathetic Nervous System.
Acetylcholine: The
preganglionic nerve fibers that originate from the spinal cord and end up in the sympathetic ganglion secrete acetylcholine
inside the ganglion.
This acetylcholine acts on nicotinic receptors.

Noradrenaline: The
postganglionic nerve fibers originate from the sympathetic ganglion and end up in viscera secrets noradrenaline inside the viscera.

This secreted noradrenaline acts on adrenergic receptors,
The neurotransmitter of the parasympathetic nervous system is
only acetylcholine.
Receptor typesReceptors in the Sympathetic
nervous system include
adrenergic receptors, which are 5 in numbers- α1, α2, β1, β2, and β3.
Muscarinic receptors or
simply M receptors are of 5 types as
M1 – present in the brain
M2 – present in the heart
M3 – present in the
M4 – present in the
M5 – located in smooth
Postganglionic nerve fiberPostganglionic fiber is the
supplier of the sympathetic system.
It is the fiber which
connects the sympathetic
ganglion with different
visceral organs.
There are two other possibilities –
either they may return to the spinal cord through gray rami communicantes, or they may spread
along spinal nerves to supply to
autonomic effectors like sweat
glands or vascular smooth muscles.
The preganglionic nerve fibers
originate from inside the brain and
the spinal cord, and here, they are longer
unlike that of sympathetic nervous
a system where the postganglionic
nerve fiber was longer. The
postganglionic nerve fibers are very
short; originate from the
Parasympathetic ganglia situated
very close to the target organ.
Effect on the EyesThrough α receptors, they
constrict the soft tissue dilator- pupillae, which results in dilation of
of the eye.
They tend to constrict the pupil, stimulating the tissue constrictor-
Effect on salivary glandsSaliva secretion is minimizedSaliva secretion is profuse and enhanced
Effect on the gut of digestive systemThrough α receptors, they
decrease peristaltic movements by
decreasing motility and tone of stomach and intestine.
They increase the peristalsis of the gut as well as increase gastric emptying.
Effect on skinThrough α receptors, facilitates adrenergic sweating, by contraction
of pilomotor muscles, which causes sweating in the hands and palms.
No effect
On heartΒ1 receptors are exclusively present in the heart and kidneys. So stimulating them to increase heart rate. Through β1 receptors, It exerts positive chronotropic, dromotropic,
ionotropic and bathmotropic effects on the heart.
Effects on the heart include all opposite to that of the sympathetic
nervous system. It has negative ionotropic, chronotropic, and bathmotropic effects. All these effects are carried by the vagus nerve.
Effect on fats and lipids in the bodyThrough β3 receptors, being exclusively present in adipose tissue, initiate the lipolysis.Parasympathetic nervous
the system has no such effects.
On sex organsMale: Ejaculation
and vasoconstriction
Male: Erection
Effects on muscles and glandsIt causes vasodilation of skeletal muscles and liver. It causes dilation of bronchial smooth muscles. This property is used in inhalers, giving β2 agonists.They increase gland secretion, e.g., of gastric, pancreatic, etc.
Protection responseThe sympathetic nervous system is the actual seat of the triple F response. The 3 Fs stand for Fright Fight Flight. It prepares the body to tackle dangerous situations.The parasympathetic nervous system has no such effects.

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