Sympathetic vs parasympathetic System Difference

Nervous System in human is broadly classified into
three board categories
a) The Central Nervous System comprising of the brain and spinal
b) The Autonomic Nervous System
c) The Peripheral Nervous System
Here, we discuss the Autonomic Nervous System
Autonomic Nervous System controls the action of the organs at the
subconscious level. It is the part of system not under voluntary control.
This is why it is named as ‘autonomic.‘
Autonomic Nervous System shares a relationship with the Somatic
Nervous System and has functional links with it. Although the
Autonomic fibers share either sympathetic or parasympathetic nerves up
to CNS, it has a common pathway with somatic nerves inside CNS. So,
there may be some interconnections.

Autonomic Nervous System has a great relationship with Endocrine
System. Like examples are given.
a) Cortisol is a catecholamine hormone secreted from Adrenal
Cortex, and from sympathetic nerve endings.
b) Adrenal Medulla is itself a modified sympathetic ganglion.
Hormones secreted from Adrenal Medulla is 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.

Classifications: Autonomic Nervous System is composed of two
types of Nervous System:
1. Sympathetic Nervous System
2. Parasympathetic Nervous System

Sympathetic Vs Parasympathetic

Sympathetic Vs Parasympathetic Nervous System

Sympathetic Nervous SystemParasympathetic Nervous System
Sympathetic Nervous System
efferents or in short the
sympathetic efferents arise from
the spinal cord as thoracolumbar
outflow. It extends from a level of
T1 to 3 rd or 4 th lumber, i.e. L3 or
The parasympathetic nervous
system has a craniosacral
outflow, i.e. it originates from
only brain and sacral part of
spinal cord. The
Parasympathetic parts of
cranial nerve include the 3 rd
nerve, i.e. Occulomotor7 th
nerve, i.e. Facial, 9 th nerve, i.e.
Glossopharyngeal and 10 th
nerve, i.e. Vagus nerve. The
sacral counterpart of
Parasympathetic nerve system
has root value of S2 to S4.
The preganglionic nerve
efferents come out through
efferent root of the spinal
segment. It then passes
through the white rami, and it
communicates the white rami
which connect 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.
Two or more types of
neurotransmitters are seen in
the Sympathetic Nervous
preganglionic nerve fibers that
originate from the spinal cord
and ends up in the sympathetic
ganglion secrete acetylcholine
inside the ganglion. This
acetylcholine acts on nicotinic
b) Noradrenaline: The
postganglionic nerve fibers
that originate from the
sympathetic ganglion and ends
up in viscera secrets
noradrenaline inside the
viscera. This secreted
noradrenaline acts on
adrenergic receptors, which are
5 in numbers- α1, α2, β1, β2,
and β3.
The neurotransmitter of the
Parasympathetic Nervous System is
only acetylcholine.
Receptors 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
a) M1 – present in the brain
b) M2 – present in the heart
c) M3 – present in the
d) M4 – present in the
e) M5 – located in smooth
Postganglionic 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
spinal cord, and here, they are longer
unlike that of sympathetic nervous
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.
Through α receptors, they
constrict the soft tissue dilator-
pupillae, which results in dilation of
pupils of the eye.
They tend to constrict the pupil,
stimulating the tissue constrictor-
Through α receptors, they
decrease peristaltic movements by
decreasing motility and tone of
stomach and intestine .
They increase peristalsis as well
as increases gastric emptying.
Through α receptors, Facilitates
adrenergic sweating, by contraction
of pilomotor muscles, which causes
sweating in hands and palms.
They increase salivation and
Β1 receptors are exclusively
present in heart and kidneys. So
stimulating them to increase heart
rate. Through β1 receptors, It exerts
positive chronotropic, dromotropic,
ionotropic, and bathmotropic effects
on heart.
Effects on the heart include all
opposite to that of sympathetic
nervous system. It has negative
ionotropic, chronotropic,
bathmotropic effects. All these
effects are carried by vagus nerve.
Through β3 receptors, Being
exclusively present in adipose tissue,
it initiates the lipolysis.
Parasympathetic Nervous
System has no such effects.
It 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.
The sympathetic nervous system
is the actual seat of triple F
response. The 3 Fs stand for Fright
Fight Flight. It prepares the body to
tackle dangerous situations.
Parasympathetic Nervous
System has no such effects.

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