Dr. Kusai M. Alsalhanie
OBJECTIVES
1. The student should be able to define the organization
and function of the autonomic nervous system (ANS).
2. The student should be able to define the effects of the
ANS.
3. The student should be able to list the receptors and
neurotransmitters of the ANS.
4. The student should be able to list the sympathetic
stress response.
OVERVIEW
Internal Environment
 Plasma membrane (metabolic needs)
 Skin (temperature, pH, and electrolyte levels)
 Maintaining a stable internal environment is the
responsibility of the autonomic nervous system
(ANS).
 Internal sensory receptors (baroreceptor,
chemoreceptor, thermoreceptor).
 Autonomic control centers, contain neural circuits,
compare incoming data with internal preset values.
 In case of deviation, they adjust the function of one
or more organs to maintain HOMEOSTASIS.
Organs of
homeostasis
How does the ANS work?
 SNS vs. PSNS
 The actions of the SNS and PSNS often appear
antagonistic, but, in practice, they work in close
cooperation with each other.
HOMEOSTASIS
 State of physiologic equilibrium or the processes that
sustain such an equilibrium.
 Vital parameters
I. Mechanisms
 Both the cellular and organismal Level
 3 basic components:
 Sensory component (Receptor Protein)
 Integrator (Neural Circuit)
 Effector component (Excretory Organ)
 Typically form a negative feedback control system
Mechanism
II. Redundancy
 Multiple control pathways that are layered
 Number of layers reflecting the relative importance of
the parameter under control
 Example?
 Why Redundancy?
III. Functional reserve
 Normal quiet breathing uses only 10% of total lung
capacity
 Cardiac output at rest is 20% of maximal attainable
values
 Why??
Organization of The Nervous System
Central Nervous System
Peripheral Nervous System
Autonomic Nervous System
Sympathetic
Parasympathetic
ORGANIZATION
 ANS operates subconsciously and largely






independently of voluntary
Control
sleep or our conscious minds are focused on a task at
hand
Exceptions?
afferent nerves
nerve efferents
Difference from CNS
Afferent pathways
 Baroreceptors (BP)
 Thermoreceptors (skin temp)
 Chemoreceptors (glucose levels, pH, PO2, and PCO2)
 Mechanoreceptor (lungs, bladder, GI destintion)
 Nociceptive (visceral pain sensation)
Efferent pathways
I. Autonomic ganglia
Ganglia comprise clusters of nerve cell bodies and their
dendritic trees.
Preganglionic vs. postganglionic neurons
 Sympathetic ganglia:
Location
Paravertebral and Prevertebral
 Parasympathetic ganglia:
Location
Efferent Pathway
Efferent Pathway
II. Sympathetic Efferent
(T1–L3)
Preganglionic neurons leave the spinal cord via a ventral
root, enter a nearby paravertebral ganglion, and then
terminate in one of several possible locations:
 within the paravertebral ganglion;
 within a more distant sympathetic chain ganglion; or
 within a prevertebral ganglion or the adrenal medulla.
Efferent Pathway
III. Parasympathetic Efferent
Brainstem nuclei & S2-S4
Cranial nerves
Pelvic splanchnic nerves
Terminate within remote ganglia located close to or
within the walls of their target organs.
NEUROTRANSMISSON
Parasympathetic Ganglionic Synapse
Acetylcholinesterase
ACH
Action Potential
Na+
Preganglionic neuron
a ba
Na+
Nicotinic
Receptor
Postganglionic neuron
I. Preganglionic transmitters




Skeletal muscles: Nm
ANS preganglionic cell bodies & chromaffin cells: Nn
Pancuronium: Nm/ N1
Trimethaphan: Nn/ N2
 N receptors (ligand -gated)
 ACh binds to 2 nicotinic receptor binding sites.
 Causes ion channel to open within the receptor protein.
 Opens a
Na+ channel.
 Always excitatory
Parasympathetic Organ Synapse
Acetylcholinesterase
Effector
Organ
K+
Na+
G
Action Potential
ACH
Muscarinic
Receptor
Postganglionic neuron
II. Postganglionic transmitters
 1. Parasympathetic:
All PSNS postganglionic neurons release Ach.
Muscarinic AChRs:
 M1 (salivary glands, stomach) (Gq)
 M2- (cardiac nodal cells)
(Gi)
 M3-type (smooth muscle, many glands) (Gq)
Paradoxical activity of M3 (lung vs. blood vessels)
M vs. N Ach Receptors
Sympathetic Organ Synapse
Effector
Organ
Na+
NE
Action Potential
Adrenergic
Receptor
Postganglionic neuron
II. Postganglionic transmitters
 2. Sympathetic:
Most SNS postganglionic neurons release
norepinephrine from their terminals.
Adrenergic receptors:
 Alpha 1- (smooth muscle) (Gq)
 Beta 1- (cardiac muscle) (Gs)
 Beta 2- (smooth muscle) (Gs)
 less commonly, Alpha 2- (synaptic terminals) (Gi)
Exceptions
 Sweat glands:
» Postganglionic neurons involved with stress-related excretion release
»
»
norepinephrine (“sweaty palms”)
Postganglionic neurons involved with thermoregulation release
acetylcholine
M3
 Adrenal gland:
» Preganglionic neurons do not synapse in the paraverterbral sympathetic
»
»
ganglion
Preganglionic neurons synapse directly on the adrenal gland, release
acetylcholine, and activate nicotinic receptors (Nn) on the adrenal gland
Adrenal glands release epinephrine into systemic circulation
 Fight & Flight
 Rest & Digest
Organs With Dual Innervations
 Dual innervations
 Innervations by both
Sympathetic fibers
Parasympathetic fibers
 Most visceral organs receive dual innervations
 Effects of dual innervations
 Antagonistic
 Complementary
 Cooperative
Organs With Dual Innervations
 Antagonistic :
 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.
 Organ receive only sympathetic innervations Adrenal medulla
 Arrector pili muscle
 Sweat glands
 Most blood vessels, Why?
Clinical Application
Horner’s syndrome
 Characterized by Constriction of the pupil
 Enophthalmos
 Drooping of eye lid
 Anhydrosis on affected side of face
 Occurs due to Damage of stellate ganglia
 Paralysis of Cervical Sympathetic nerve trunk
Horner’s syndrome
Horner’s syndrome
Questions?
Thank
You