AUTONOMIC NERVOUS
SYSTEM
Dr. Ayisha Qureshi
Assistant Professor,
MBBS, MPhil
DIVISIONS OF THE PERIPHERAL NERVOUS SYSTEM
DIFFERENTIATING BETWEEN THE
SOMATIC & AUTONOMIC NERVOUS
SYSTEM
SOMATIC NERVOUS
SYSTEM
AUTONOMIC NERVOUS
SYSTEM
Somatic senses & special senses
Mostly interoceptors; some somatic
senses & special senses
CONTROL OF
cortex, basal ganglia,
MOTOR OUTPUT cerebellum, spinal cord.
Voluntary control; cerebral
Involuntary control; hypothalamus,
limbic system, brainstem. Limited
control from cerebral cortex.
MOTOR NEURON One-neuron pathway,
PATHWAY
Two-neuron pathway.
SENSORY INPUT
NEUROTRANSMI All Somatic neurons secrete Ach. All preganglionic fibers release Ach.
Postganglionic fibers release
TTERS &
different NT in case of Sym. & Paras.
HORMONES
EFFECTORS
Skeletal muscles.
Smooth muscles, cardiac muscles,
and glands.
RESPONSES
Contraction of skeletal muscle.
Contraction or relaxation of smooth
muscle; Increased or decreased
strength of contraction of cardiac
muscle; increased or decreased
secretion of the glands.
Type of nerve
fibers
α-motor neuron is large
diameter, & rapidly conducting
Preganglionic fibers: B fibers
Postganglionic fibers: C fibers
Somatic & Autonomic nervous system
The autonomic nervous system is the part of the peripheral
nervous system that is responsible for regulating involuntary body
functions, such as heartbeat, blood flow, breathing and digestion.
AUTONOMIC NERVOUS SYSTEM
Divisions of ANS
SYMPATHETIC NERVOUS
SYSTEM/ Thoracolumbar Division
• Fight, flight or Fright.
• Activated during exercise,
excitement and
emergencies.
PARASYMPATHETIC NERVOUS
SYSTEM/ Craniosacral Division
• Rest and Digest.
• Concerned with conserving
energy.
ANS
Sympathetic
Nervous System
Preganglionic
Fibers
Postganglionic
Fibers
Parasympathetic
Nervous System
Preganglionic
Fibers
Postganglionic
Fibers
Characteristics of ANS
• Nerve fibers: Both divisions have pre- & postganglionic fibers.
- Preganglionic neuron is myelinated.
- Postganglionic neuron is unmyelinated.
(In contrast to the large diameter and rapidly conducting α -motor
neurons, preganglionic axons are small-diameter, myelinated, relatively
slowly conducting B fibers.)
(The axons of the postganglionic neurons are mostly unmyelinated C
fibers and terminate on the visceral effectors.)
• Neurotransmitters:
Autonomic nerves release NT that may be excitatory or
inhibitory.
• Divergence:
Preganglionic fibers branch to synapse with an average of 8-9
postganglionic neurons.
• Convergence:
Postganglionic neuron receives synaptic input from a large
number of preganglionic fibers.
Divisions of the ANS
• Fight or Flight Response
• Thoracolumbar Division
• Shows mass activation
THE SYMPATHETIC SYSTEM
The Sympathetic System Outflow
Sympathetic Chain Ganglion
Paravertebral Ganglia
Prevertebral Ganglia
• Most of the sympathetic ganglia lie close
to the spinal cord and form the two
chains of ganglia, linked by short nerves
—one on each side of the cord—known
as the Sympathetic Trunks.
• Because the ganglia lie close to the
spinal cord, thus, the preganglionic
neurons are short while the
postganglionic neurons reaching the
target organs are very long.
• Joined to ventral rami by white and gray
rami communicans.
• In contrast, the parasympathetic ganglia
lie within or very close to the organs
innervated and ,thus, have very short
preganglionic and long postganglionic
neurons.
• Also called the Collateral
ganglia.
• Unpaired, not segmentally
arranged.
• Occur only in abdomen and
pelvis, closer to the innervated
organ.
• Lie anterior to the vertebral
column.
• Main ganglia:
See Next slide for figure
– Celiac, superior mesenteric,
inferior mesenteric, inferior
hypogastric ganglia.
See Next slide for figure
The Sympathetic System
Outflow
Myelinated preganglionic
fibers exit spinal cord in
ventral roots from T1 to L2
levels.
They exit from the Lateral
horn of the spinal cord.
Most sympathetic nerve
fibers separate from
somatic motor fibers and
synapse with
postganglionic neurons
within paravertebral
ganglia.
Ganglia within each row
are interconnected,
forming a chain of ganglia
that parallels spinal cord to
synapse with
postganglionic neurons.
Sympathetic System Outflow
Termination of Sympathetic
Preganglionic Fibers
Termination of Sympathetic
Postganglionic fibers
1.
• Axons leave the chain
ganglia and re-enter the
spinal nerves via gray rami
communicans to reach the:
1. Visceral targets
2. Smooth muscles
3. Sweat glands
2.
3.
4.
Postganglionic fibers in the
paravertebral ganglion of the
same segment.
Postganglionic fibers of the
paravertebral ganglion of an
upper or lower segment.
Pass thru the paravertebral
ganglion chain & end on
postganglionic neurons in
prevertebral ganglion close to
the viscera (celiac, superior and
inferior mesenteric ganglion).
Adrenal Medulla.
Sympathetic System Outflow
To the Periphery
To the Head
Sympathetic System Outflow
To the Thoracic regions
To the Abdominal Organs
The Adrenal
Gland
• The Adrenal gland is the major
organ of the sympathetic nervous
system.
• When stimulated, the adrenal
medulla secretes large quantities of
epinephrine and a little
norepinephrine directly into the
blood stream.
Sympathoadrenal system:
• Stimulated by mass activation
of the sympathetic nervous
system.
• Innervated by preganglionic
sympathetic fibers.
• Rest or Digest
• Craniosacral Division
• Shows stimulation of separate parasympathetic nerves
THE PARASYMPATHETIC SYSTEM
The Parasympathetic
Division
• Preganglionic fibers are located
in several cranial nerve nuclei
(III, VII, IX and X) and in the IML
column of the sacral spinal cord
(2-4 sacral segments).
• Preganglionic fibers synapse in
terminal ganglia located next to
or within organs innervated.
• Thus, the parasympathetic
preganglionic fibers are longer
while the parasympathetic
postganglionic fibers are short.
• Most parasympathetic fibers do
not travel with the spinal
nerves.
• Do not innervate blood vessels,
sweat glands, and arrector pili
muscles.
PARASYMPATHETIC DIVISION
(Cranial Outflow)
1.
Cranial Nerve III-
Occulomotor
Nerve
2.
Cranial Nerve VII
Facial Nerve
3.
4.
Cranial Nerve IX
Cranial Nerve X
GlossoPharyngeal
Nerve
Vagus Neve
Parasympathetic Division
(continued)
• 4 of the 12 pairs of cranial nerves (III, VII, X, XI) contain
preganglionic parasympathetic fibers.
• III, VII, XI synapse in ganglia located in the head.
• X synapses in terminal ganglia located in widespread
regions of the body.
• Vagus (X):
– Innervates heart, lungs, esophagus, stomach, pancreas,
liver, small intestine and upper half of the large
intestine.
• Preganglionic fibers from the sacral level innervate the
lower half of large intestine, the rectum, urinary and
reproductive systems.
There are 3 main types of neurotransmitters used extensively in ANS:
1. Acetylcholine
2. Norepinephrine
3. Epinephrine
CHEMICAL TRANSMISSION AT
AUTONOMIC JUNCTIONS
NEUROEFFECTOR
JUNCTION
• The synapse between an
autonomic postganglionic
neuron and its target cell is
called a Neuroeffector
Junction.
• The postganglionic axons
end in nerve terminals that
show swellings called
“varicosities” that consist
of vesicles containing the
Neurotransmitters.
• The diffuse release of NT
means that a single
postganglionic neuron can
affect a large area of target
tissue.
• Acetylcholine is the
neurotransmitter released by all
neurons whose axons exit the
CNS, including cranial motor
neurons, α-motor neurons, γmotor neurons, preganglionic
sympathetic neurons and
preganglionic parasympathetic
neurons.
• Postganglionic parasympathetic
neurons also release Ach,
whereas postganglionic
sympathetic neurons release
either Norepinephrine or Ach.
• Ach is degraded by
Acetylcholinesterase.
• Norepinephrine is degraded by
monoamine oxidase.
Neurotransmitters in ANS
CHOLINERGIC RECEPTORS
ADRENERGIC RECEPTORS
The principal transmitter is
ACETYLCHOLINE and include:
1. All preganglionic neurons.
2. All parasympathetic
postganglionic neurons.
3. Sympathetic postganglionic
neurons that innervate sweat
glands.
4. Sympathetic postganglionic
neurons that end on blood vessels
in skeletal muscles.
The Cholinergic receptors are further
subdivided into:
• Nicotinic Cholinergic receptors.
• Muscarinic Cholinergic receptors.
The principal transmitter is
EPINEPHRINE & NOREPINEPHRINE
and include:
1. All remaining sympathetic
postganglionic neurons.
2. The adrenal medulla is
essentially a sympathetic
ganglion & secretes NE and
Epinephrine directly into the
blood stream.
The Adrenergic receptors are further
subdivided into:
• Alpha receptors (α1 and α2)
• Beta receptors (β1, β2 and β3)
Responses to Cholinergic Stimulation
(continued)
Other Autonomic Neurotransmitters
• Certain noradrenergic, norcholinergic
postganglionic autonomic axons produce their
effects through other NTs. These include:
– Adenosine triphosphate (ATP).
– Vasoactive Intestinal peptide (VIP).
– Nitric Oxide (NO).
– Neuropeptide Y (NPY)
COMPARISON OF SYMPATHETIC &
PARASYMPATHETIC NERVOUS SYSTEM
RESPONSES OF EFFECTOR ORGANS
TO AUTONOMIC NERVE IMPULSES
Organs With Dual Innervation
• Most visceral organs receive dual innervation (innervation by
both sympathetic and parasympathetic fibers).
• Antagonistic effects:
– Sympathetic and parasympathetic fibers innervate the same cells.
• Actions counteract each other.
– Heart rate.
• Complementary:
– Sympathetic and parasympathetic stimulation produces similar effects.
• Salivary gland secretion.
• Cooperative:
– Sympathetic and parasympathetic stimulation produce different effects
that work together to produce desired effect.
• Micturition.
Organs Without Dual Innervation
• Regulation achieved by increasing or decreasing
firing rate.
• Adrenal medulla, arrector pili muscle, sweat
glands, and most blood vessels receive only
sympathetic innervation.
– Nonshivering thermogenesis.
Control of the ANS by Higher Brain Centers
• Sensory input transmitted to brain centers that integrate
information.
• Can modify activity of preganglionic autonomic neurons.
• Medulla:
– Most directly controls activity of autonomic system.
– Location of centers for control of cardiovascular, pulmonary, urinary,
reproductive and digestive systems.
• Hypothalamus:
– Regulates medulla.
• Cerebral cortex and limbic system:
– Responsible for visceral responses that are characteristic of
emotional states.
DISORDERS OF ANS
HORNER’S SYNDROME
Horner syndrome is a rare disorder
resulting from interruption of
preganglionic or postganglionic
sympathetic innervation to the face.
CAUSE:
• Injury to the nerves.
• Injury to the carotid artery.
• A stroke
• Lesion in the brain
SYMPTOMS:
The hallmark of Horner’s syndrome is
the TRIAD of:
1. Anhidrosis (reduced sweating)
2. Ptosis (drooping eyelids)
3. Miosis (constricted pupil)
Symptoms may also include
Enophthalmos (sunken eyes) and
vasodilation.
Raynaud’s Phenomenon
Raynaud’s Phenomenon refers to an
episodic reduction in blood flow primarily
to the fingers, often during exposure to
cold or during a stressful condition.
CAUSE:
It is a vasospastic disorder. There can be
many causes:
• Exaggeration of response to cold,
temperature or stress.
• Secondary to another disorder as
Rheumatoid arthritis, Sjogren’s
syndrome, carpal tunnel syndrome,
anorexia.
SYMPTOMS:
1. Triphasic color change in the fingers
from white to cyanotic blue to deep
red.
2. When there is vasospasm, the fingers
are pale and cold; then due to
reduced blood flow, the color turns
blue and there is intense pain; and
finally, once blood flow recovers,
there is tingling and swelling.