The Autonomic Nervous System
Dr. Hiwa K. Saaed
College of Pharmacy/University of Sulaimani
Drugs that produce their primary
therapeutic effect by Mimicking or
altering the functions of the ANS.
AUTOMATIC NERVOUS SYSTEM (ANS)
is the major involuntary portion of the NS
is responsible for automatic, unconscious
bodily function, such as control of
HR and BP and both GIT and GUT functions.
Two main divisions
• Brain & spinal cord
1. Afferent (sensory)
2. Efferent (motor)
• Somatic & ANS
CENTRAL NERVOUS SYSTEM (CNS)
Brain and spinal cord:
receives and processes incoming
sensory information and responds by
sending out signals that initiate or
modify a process
Peripheral Nervous System or PNS
• Includes all the neurons and ganglia
found outside the CNS
1. Afferent: sensory input to CNS
Afferent neurons carry sensory input from the periphery to the
CNS and modify motor output through the reflex arc.
2. Efferent: motor output from CNS
Efferent neurons carry motor signals from the CNS to the
peripheral areas of the body.
The efferent portion of the PNS is further divided
into two major functional subdivisions,
1. somatic (SNS): one motor neuron innervates
the skeletal muscles and control voluntary
(consciously) functions; movement, respiration
2. automatic nervous system (ANS).
The ANS is divided into 2 main divisions:
I. Parasympathetic autonomic nervous system (PANS)
dominates in sleep,
II. Sympathetic autonomic nervous system (SANS)
Dominates during activity; fight & flight.
III. Enteric NS located in the GIT,
send sensory input to both PANS & SANS
and receive motor output from them
-Myenteric plexus (plexus of aurbach)
-Submucous plexus (plexus of Meissner)
Location of Ganglia
Both the PANS and SANS have
relay station, or ganglia,
between the CNS and the end
organ, but the somatic system
The ANS, carries nerve
1. a preganglionic fiber that
leaves the CNS,
2. a postganglionic fiber that
innervates the effector.
Central roots of origin
Parasympathetic Division– also
called the craniosacral division
• The preganglionic fibers arise
from the cranial nerve nuclei III,
VII, IX, and X and sacral region
(usually S2-S4) of the spinal
cord, and synapse in ganglia
close to the effector organ.
• Thus, in contrast to the
sympathetic system, the
preganglionic fibers are long,
and the postganglionic ones
Sympathetic Division – also called
the thoracolumbar division
• The preganglionic fibers
arise from the thoracic
(T1-T12) and lumbar (L1-
L5) regions of the spinal
cord, and they synapse in
close and parallel to the
Postganglionic axons lead
to an effector organ.
the adrenal medulla,
• like the sympathetic ganglia, receives
preganglionic fibers from the sympathetic
• Lacking the axons,
• in response to stimulation by Ach, influences
other organs by secreting the epinephrine and
lesser amounts of NEP into the blood.
SYMPATHETIC AND PARASYMPATHETIC NS & EFFECTOR ORGANS
Functions of the Sympathetic Nervous System
• Is normally active, even at rest; however, it assumes a
dominant role when the body becomes stressed (trauma, fear,
hypoglycemia cold or exercise).
• Fight or Flight – Protective mechanisms designed to help
person cope with the stress or get away from it.
• For example, if you sense danger: Your heart rate increase,
BP rises, eyes dilates, blood sugar rises, bronchioles expand,
and blood flow shift from skin to skeletal muscles.
Functions of the Parasympathetic Nervous System
1. Rest and digest: maintains essential body functions; digestive
process and elimination of wastes.
2. Save energy.
3. Dilation of blood vessels in skin.
4. Decrease heart rate (bradycardia).
5. Increase secretion of digestive enzymes.
6. Constriction of smooth muscle of bronchi.
7. Increase in sweat glands.
8. Contraction of smooth muscles of urinary bladder.
The sympathetic NS
• The sympathetic NS function as a unit
and it often discharge as a complete
• These reactions are triggered both by
1. direct sympathetic activation of the
2. stimulation of the adrenal medulla to
is not a functional entity as such,
and never discharges as a complete
system. If it did it would produce
massive, undesirable and
Instead, discrete parasympathetic
fibers are activated separately, and
the system functions to affect
specific organs, such as stomach or
The Parasympathetic NS
Similarities between ANS & endocrine system:
The ANS, along with the endocrine system, coordinates
the regulation and integration of body function.
Nervous system has several properties in common with the
1. High level integration in the brain
2. The ability to influence processes in distant regions of
3. Extensive use of negative feedback
4. Both systems use chemical for the transmission of
Difference between ANS/ endocrine system:
ANS characteristics Endocrine system
Rapid response Slower response
Brief duration Long duration
Transmission of electrical
over nerve fibers
Sends signals to target
tissue by varying the level
of blood borne hormone
Drugs affecting the ANS
• are divided into two groups according to
the type of neuron.
• The cholinergic drugs act on receptors
activated by acetyl choline.
• The adrenergic drugs act on receptors
stimulated by norepinephrine or
The cholinergic neuron
• All preganglionic fibers of both sympathetic and
• All parasympathetic postganglionic.
• Few sympathetic postganglionic fibers (sweat gland).
• All Somatic (non autonomic) fibers to skeletal muscle
The adrenergic neuron
• Most sympathetic postganglionic fibers release
norepinephrine; are noradrenergic or simply
• Some peripheral sympathetic fibers release dopamine
• The adrenal medulla, a modified sympathetic
ganglion, receives sympathetic preganglionic fibers
and releases epinephrine (~85%) and to a lesser
amount norepinephrine (15%) into the blood.
• Parasympathetic – cholinergic receptors:
– muscarinic (M1 to M5)
– and nicotinic receptors
• Sympathetic – adrenergic receptors:
– alpha (α1, α 2),
– beta (β1 to β 3),
– and dopamine (D1 to D5) receptors.
Locations of muscarinic receptors:
these receptors have been found on:
• ganglia of the PNS
• the autonomic effector organs: heart, smooth
muscle, brain and exocrine glands.
1. M1 :gastric parietal cells,
2. M2 : cardiac cells and smooth muscle,
3. M3 : bladder, exocrine gland, and smooth muscle.
• Neurons: all five subtypes (M1-M5) have been found
Mechanisms of Ach signal transduction:
• M1, M3 & M5:
interacts with a G protein, designated Gq, which in turn
activates phospholipase C this leads to the hydrolysis of
PIP2 to yield IP3, DAG, which cause an increase in
intracellular Ca+2 this cation can then interact to:
stimulate or inhibit enzymes, or cause hyperpolarization,
secretion, or contraction.
• M2 :
stimulates a Gi that inhibits adenylyl cyclase and increase
Nicotinic receptors: (NN, NM)
Locations of nicotinic receptors: nicotinic
receptors are located in the:
– adrenal medulla,
– autonomic ganglia,
– neuromuscular junction.
Mechanisms of action:
• Ligand-gated ion channel.
• Binding of two Ach molecules elicits a
conformational change that allows the entry of
Na+ ions, resulting in the depolarization of the
• Nicotine initially stimulates and then blocks the