This document provides an introduction and outline for a review of the autonomic nervous system presented by Marc Imhotep Cray, M.D. It includes topics such as homeostasis, neuroanatomy and neurophysiology of the ANS, neurotransmitters, receptors, and autonomic pharmacology. The goals are to describe the sympathetic and parasympathetic divisions, their interactions in maintaining homeostasis, and the effects of their stimulation. Key concepts like the "fight or flight" response and negative feedback systems are discussed. An overview of the organization of the nervous system and efferent autonomic pathways is also provided.
Incoming and Outgoing Shipments in 3 STEPS Using Odoo 17
ANS Physiology and Pharmacology Review
1. ANS Physiology and Pharmacology
Introduction | Review of the
Autonomic Nervous System
Prepared and presented by:
Marc Imhotep Cray, M.D.
Basic Medical Sciences Teacher
http://www.imhotepvirtualmedsch.com/
From Henry Gray (1821–1865)
Anatomy of the Human Body 1918
2. Marc Imhotep Cray, M.D.
2
*Suggested Review Books & Resources
*e-Books & learning tools available to enrolled learners at thePOINT
If you are using a different review book, the chapters may
be organized differently, but the material covered is
approximately the same. Simply find the corresponding
material in your book for each lecture.
Companion Notes:
ANS Summary Notes
Formative Assessment
Clinical Correlate:
e-Medicine Article
Epilepsy and the Autonomic
Nervous System
Review Test for
Autonomic Nervous
System answers and
explanations
Review Test for
Autonomic Nervous
System
3. Marc Imhotep Cray, M.D.
Overall Goal of Reviews
“ Deconstruction, Reconstruction,
Integration and Relationships”
3
The nineteenth-century physiologist
Claude Bernard put it this way:
“After carrying out an analysis of
phenomena, we must . . . always
reconstruct our physiological
synthesis, so as to see the joint
action of all the parts we have
isolated. . . .”
http://en.wikipedia.org/wiki/Claude_Bernard
4. Marc Imhotep Cray, M.D.
Topics Outline
4
Homeostasis
Basic Neuroanatomy and Neurophysiology of ANS
Neurotransmitters
Receptors
Receptor-Ligand Interactions & Signal Transduction
Autonomic and Somatic Pharmacology Terminology
5. Marc Imhotep Cray, M.D.
Review Objectives
5
After presentation you should be able to:
Describe the two divisions of the ANS and the main functions and
effects of each division.
Explain how sympathetic and parasympathetic nerves interact
with each other to regulate organ function (maintain homeostasis)
Describe the fight or flight reaction and explain how sympathetic
activation affects the activities of the different organs
List the main organ effects caused by parasympathetic stimulation
Describe the different autonomic receptors that are stimulated by
acetylcholine, norepinephrine, and epinephrine
Describe signaling mechanisms and pharmacology of ANS
receptor subtypes
6. Marc Imhotep Cray, M.D.
Autonomic Nervous System (ANS)
6
The autonomic nervous system (ANS) is the
part of the nervous system that is responsible
for homeostasis
Except for skeletal muscle, which gets its
innervation from the somatomotor nervous
system, innervation to all other organs is
supplied by the ANS
7. Marc Imhotep Cray, M.D.
Autonomic Nervous System
vs. Endocrine System in Homeostasis
7
Autonomic nervous system (ANS) is the moment-to-
moment regulator of the internal environment, regulating
specific functions that occur without conscious control:
respiration,
circulation,
digestion,
body temperature,
metabolism,
sweating, secretions of certain endocrine glands
Endocrine system, in contrast, provides slower, more
generalized regulation by secreting hormones into the
systemic circulation to act at distant, widespread sites over
periods of minutes to hours to days
8. Marc Imhotep Cray, M.D.
ANS and Endocrine System
[common properties]
8
high-level integration in the brain
ability to influence processes in distant
regions of body
extensive use of negative feedback
maintain homeostasis
both systems use chemicals for
transmission of information
9. Marc Imhotep Cray, M.D.
9
Referring to animal systems,
pioneering 20th century
physiologist Walter Cannon
coined the word homeostasis
in 1926
“Coordinated physiological reactions
which maintain most of the steady
states in the body are so complex,
and are so peculiar to the living
organism, that it was suggested
(Cannon, 1929) that a specific
designation for these states be
employed – homeostasis”
Courtesy National Library of Medicine (NLM)
Walter Cannon coined the word homeostasis
Cannon, WB, Organization for Physiological
Homeostasis/PDF
Physiological Rev July 1, 1929 9:399-431
http://en.citizendium.org/wiki/File:William_cannon.jpg
#Licensing
Also see:
Cray MI. Walter Cannon, Homeostasis
and the Physiological Response to
Stress, A Web Interactive PowerPoint
Presentation
10. Marc Imhotep Cray, M.D.
10
Homeostasis (1)
The physiologic process of maintaining
an internal environment (ECF
environment) compatible with normal
health
Autonomic reflexes maintain set points
and modulate organ system functions
via negative feedback in pursuit of
homeostasis
11. Marc Imhotep Cray, M.D.
Homeostasis (2)
11
A dynamic steady state of the constituents in the
internal environment (ECF) that surrounds and
exchanges materials with the cells
Factors homeostatically maintained:
(Controlled Variables)
Concentration of nutrient molecules
Concentration of O2 and CO2
Concentration of waste products
pH
Concentration of water, salts, and other electrolytes
Temperature
Volume and pressure
12. Marc Imhotep Cray, M.D. 12
Nervous Endocrine
WirelessWired
Hormones
Short Distance Long Distance
Closeness Receptor Specificity
Rapid Onset Delayed Onset
Short Duration Prolonged Duration
Rapid Response Regulation
versus
Neurotransmitters Hormones
Short Distance Long Distance
Homeostasis (3)
13. Marc Imhotep Cray, M.D.
13
ERROR
SIGNAL
COMPARATOR
SET
POINT
+
-
CONTROLLED
VARIABLE
(SEE NEXT SLIDE)
SENSOR
EFFECTOR
-NEGATIVE
FEEDBACK
Components of a negative
feedback control system
Negative feedback:
Initiation of responses
that counter deviations of
controlled variables
from their normal range
Measures control variable
Recognizes deviation of
normal set point value
Redrawn after: Kibble JD, Halsey CR, Homeostasis: In Medical
Physiology -The Big Picture; McGraw-Hill ,2009:2
Attempt to restore
set point value
Important variable maintained
within a normal range Effector opposes stimulus
stretch receptors, chemo-,
baro-, osmo-, and thermo-
receptors etc.
14. Marc Imhotep Cray, M.D.
14
Controlled Variable Typical Set Point Value
(Arterial Blood Sample)
Arterial O2 partial pressure
Arterial CO2 partial pressure
Arterial blood pH
Glucose
Core body temperature
Serum Na+
Serum K+
Serum Ca2+
Mean arterial blood pressure
Glomerular filtration rate
100 mm Hg
40 mm Hg
pH 7.4
90 mg/dL (5 mM)
98.4°F (37°C)
140 mEq/L
4.0 mEq/L
4.5 mEq/L
90 mm Hg
120 mL /min
Examples of Physiologic
Controlled Variables
Adopted from: Kibble JD, Halsey CR, Homeostasis: In Medical Physiology -
The Big Picture; McGraw-Hill ,2009:3
15. Marc Imhotep Cray, M.D.
Some Important Negative Feedback
Control Systems
15
From Carroll RG. Elsevier’s Integrated Physiology. Mosby, Inc. 2007; TABLE 1-3, Pg. 5
16. Marc Imhotep Cray, M.D.
16
ERROR
SIGNAL
COMPARATOR
SET
POINT
+
Mean Arterial Blood
Pressure (MAP)
SENSOR
EFFECTOR
-NEGATIVE
FEEDBACK
Example: Baroreceptor Reflex
control of blood pressure
stretch receptors in
Aortic arch and
Carotid sinus
N 95
mm Hg
CNS|
Medulla Oblongata
cardiac
contractility,
vascular tone,
urinary fluid
excretion
Receptors:
• Aortic arch transmits via vagus nerve to solitary nucleus of medulla (responds
only to BP)
• Carotid sinus transmits via glossopharyngeal nerve to solitary nucleus of
medulla (responds to and in BP)
17. Marc Imhotep Cray, M.D.
Baroreceptors(2)
17
Hypotension - arterial pressure stretch afferent baroreceptor firing
efferent sympathetic firing and efferent parasympathetic stimulation
vasoconstriction, HR, contractility, B P
Important in the response to severe hemorrhage
• Carotid massage - pressure on carotid artery stretch afferent
baroreceptor firing H R
Can by tried for Tachycardia (SVT)
• Contributes to Cushing reaction (triad of hypertension, bradycardia,
and respiratory depression) intracranial pressure constricts arterioles
cerebral ischemia and reflex sympathetic increase in perfusion pressure
( hypertension) stretch reflex baroreceptor induced-bradycardia
Also see next 2 Slides
18. Marc Imhotep Cray, M.D.
18
From http://www.zuniv.net/physiology/book/chapter6.html
19. Marc Imhotep Cray, M.D.
19
Mean Arterial Pressure Control and
Autonomic & Hormonal Feedback Loops
Katzung & Trevor. Pharmacology Examination & Board Review
10th Ed. M-H 2014
20. Marc Imhotep Cray, M.D.
Organization of the Nervous System
BRAIN & SPINAL CORD CENTRAL
NERVOUS
SYSTEM (CNS)
PERIPHERAL
NERVOUS
SYSTEM (PNS)
AFFERENT
(Sensory)
NERVES
EFFERENT
(Motor)
NERVES
EXTEROCEPTORS INTEROCEPTORS SOMATIC AUTONOMIC
EFFECTOR
ORGANS
SKELETAL
MUSCLES
SMOOTH MUSCLE,
CARDIAC MUSCLES
AND GLANDS
VOLUNTARY
Monosynaptic
INVOLUNTARY
Pre & Post Ganglionic Fiber
21. Marc Imhotep Cray, M.D.
21
Peripheral Nervous System (PNS)
Peripheral nerves contain both motor and sensory
neurons
Motor neurons:
somatic innervate skeletal muscles
autonomic innervate smooth muscle, cardiac muscle,
and glands (autonomic motor neurons)
Sensory neurons are not subdivided into somatic and
autonomic b/c there is overlap in function (input can be
from either somatic or ANS)
e.g., pain receptors can stimulate both somatic
(withdrawal reflex) and autonomic reflexes (increased
heart rate)
22. Marc Imhotep Cray, M.D.
22
Generic Neuron Anatomy
From: http://en.wikipedia.org/wiki/Neuron
Basic structural unit of nervous system >>> neuron
23. Marc Imhotep Cray, M.D.
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Autonomic (Visceral) Reflex
“Functional unit of the ANS”
Afferent fibers from periphery to CNS
CNS integration
Cortex
Thalamus
Hypothalamus
Medulla
Spinal cord
Efferent fibers from CNS to periphery
See Baroreflex pdf
24. Marc Imhotep Cray, M.D.
Sympathetic Nervous System Wiring
24
Gray ramus
Sympathetic trunk
White ramus
Intermediolateral cell column
(IML)
Dorsal root
ganglion
See: ANS Summary Notes
25. Marc Imhotep Cray, M.D.
25
organ receptors ( in the viscus ) >>>> sensory (afferent ) neuron >>>>CNS
lateral horn cell of spinal cord >>>> motor (efferent) neuron ( two neurons: pre
& post ganglionic ) >>>> effector organ ( smooth, cardiac muscle or gland )
From: http://www.alexmed.edu.eg/forums/showthread.php?2116-Today-s-lecture-gt-gt-gt-BY-M..S
Functional Unit of ANS >>> Reflex Arc
Illustration
Afferent fibers from
periphery to CNS
CNS integration
Spinal cord
Medulla
Hypothalamus
Thalamus
Cortex
Efferent fibers from
CNS to periphery
Effector response
26. Marc Imhotep Cray, M.D.
26
Neurotransmitters
Chemicals synthesized and stored in
neurons
Liberated from axon terminus in response
to action potentials
Interact with specialized receptors
Evoke responses in the innervated tissues
See: IVMS Neurotransmitters Notes
27. Marc Imhotep Cray, M.D.
ANS Neurotransmitters
27
Class
Small molecule
Transmitters
Catecholamines
Chemical
Acetylcholine
Dopamine
Norepinephrine
Synthesis
Choline + acetyl
CoA, via the
enzyme choline
Acetyltransferase
From the amino
acid tyrosine via
the enzyme
Tyrosine
hydroxylase
in the
catecholamine
pathway
From dopamine
in the
catecholamine
pathway
Postsynaptic
Receptors
Nicotinic
(cation channel)
Muscarinic
(G-protein–
coupled)
D1 (stimulatory
G- protein–
coupled)
D2 (inhibitory
G-protein–
coupled)
α & β Adrenergic
receptors
Signal
Termination
Extracellular
hydrolysis by
Acetylcholinestrase
Reuptake
Reuptake or
breakdown via the
enzymes
monoamine oxidase
and catechol–O-
methyltransferase
Functions
ANS
Movement
control
Cognition
ANS
Movement
control
General
affect
ANS
Alertness
General
affect
N.B Epinephrine is a catecholamine released upon stimulation of SANS, produced in
the adrenal medulla. It is a neurohormone, not an ANS neurotransmitter
28. Marc Imhotep Cray, M.D.
28
Efferent Autonomic Nerves
general arrangement
Innervation of smooth muscle, cardiac
muscle, and glands
Preganglionic neuron
Peripheral ganglion - axodendritic synapse
Postganglionic neuron(s)
Effector organ(s)
Pre
Ganglion
Post
Effector
organ
29. Marc Imhotep Cray, M.D.
29
Anatomic Divisions of the ANS
Parasympathetic (PANS) (CN3,7,9,10) & (S2-S4)
Preganglionic axons originate in brain, and sacral spinal cord
Peripheral ganglia are near, often within* the effector organs
Ratio of postganglionic-to-preganglionic axons is small,
resulting in discrete responses
Sympathetic (SANS) T1-L2/L3
Preganglionic axons originate in the thoracic and lumbar cord
Peripheral ganglia are distant from the effector organs
Ratio of post-to-preganglionic axons is large, resulting in
widely distributed responses
Enteric Nervous System (ENS) (Discussed in GI)
Has been described as a "second brain" for several reasons:
operate autonomous of SANS & PANS
Vertebrate studies show when the vagus nerve is severed,
ENS continues to function
* Exceptions are the four paired parasympathetic ganglia of the head and neck
30. Marc Imhotep Cray, M.D.
30
Schematized Anatomic Comparison of
PANS & SANS (1) (click to expand)
31. Marc Imhotep Cray, M.D.
31
Schematized Anatomic Comparison of
PANS & SANS (2)
Pre
Ganglion Effector
organ
PostThoracic or lumbar
cord
Pre
Ganglion Effector
organ
Post
Cranial or sacral cord
Parasympathetic
Sympathetic
Effectors: cardiac muscle, smooth mm, vascular endothelium,
exocrine glands, and presynaptic nerve terminals
ANS functions:
circulation
digestion
respiration
temperature
sweating
metabolism
some endocrine
gland secretions
33. Marc Imhotep Cray, M.D.
33
Somatic Nervous System
(included for comparison)
Efferent innervation of skeletal muscle
No peripheral ganglia
Rapid transmission, discrete control of
motor units
Voluntary
Any spinal
segment
Motor neuron
Striated muscle
Myelinated with a high
conduction velocity
In contrast
Postganglionic neurons of
ANS are unmyelinated with a low
conduction velocity
34. Marc Imhotep Cray, M.D.
34
Neurochemical Transmission in
Peripheral Nervous System (PNS)
Cholinergic nerves
Acetylcholine is the neurotransmitter
Locations
Preganglionic neurons to all ganglia
Postganglionic, parasympathetic neurons
“Preganglionic” fibers to adrenal medulla
Postganglionic, sympathetic neurons to sweat
glands in most species
Somatic motor neurons
35. Marc Imhotep Cray, M.D.
35
Cholinergic
Neurotransmission
Pre
Ganglion
Effector
organs
PostThoracic or lumbar
cord
Pre
Ganglion Effector
organ
Post
Cranial or sacral cord
Parasympathetic
Sympathetic Denotes ACh
Denotes ACh
36. Marc Imhotep Cray, M.D.
36
Adrenergic
Neurotransmission
Adrenergic nerves
Norepinephrine is the neurotransmitter
Locations
Postganglionic, sympathetic axons
Pre
Ganglion
Effector
organs
PostThoracic or lumbar
cord
Sympathetic Denotes Norepinephrine
Denotes ACh
37. Marc Imhotep Cray, M.D.
37
Adrenal Medulla
Presynaptic nerves are cholinergic
Medullary cells (*Chromaffin cells) synthesize
and release two, related catecholamines into
the systemic circulation
Epinephrine (adrenaline)
Norepinephrine
Epi and NE stimulate adrenergic sites
*They release catecholamines: ~80% Epinephrine and ~20%
Norepinephrine into systemic circulation for systemic effects on multiple
organs (similarly to secretory neurons of the hypothalamus), can also send
paracrine signals, hence they are called neuroendocrine cells
38. Marc Imhotep Cray, M.D.
38
Adrenal Medulla(2)
Cholinergic neuron
Adrenal medulla
Epi and NE released
into systemic circulation
Denotes ACh
Chromaffin cells are neuroendocrine cells found in the
medulla of the adrenal glands
They are in close proximity to pre-synaptic
sympathetic ganglia of the sympathetic nervous
system, with which they communicate
structurally they are similar to post-synaptic
sympathetic neurons
39. Marc Imhotep Cray, M.D.
39
Summary of Actions of SANS and PANS (1)
SYMATHETIC
Fright-Fight-or-Flight
widely distributed responses
PARASYMPATHETIC
Rest-Relax-Restoration
discrete responses
increase in heart rate decrease in heart rate
decrease in gastric motility increase in gastric motility
decrease secretion of salivary
and digestive glands
increase in secretion of salivary
and digestive glands
dilation of pupils constriction of pupils
ejaculation penile erection
vasoconstriction
contraction of smooth muscle in
walls of bladder
dilation of bronchioles
increased secretion of sweat
glands
Of note: Cannon’s emergency reaction:
An immediate sympathetic response to life-
threatening situations with both SANS and
PANS overactivity. The PANS phenomenon
includes vagal cardiac arrest with involuntary
defecation and urination
40. Marc Imhotep Cray, M.D.
40
Summary of Actions of SANS and PANS (2)
Illustration from: Toy E, Rosenfeld G, Loose D, Briscoe D. CASE 1, Autonomic
Sympathetic Nervous System, In Case Files: Pharmacology;
McGraw-Hill 2 ed. 2008:16
(click to expand)
Sympathetic
Responses
heart rate increases
blood pressure
increases
blood is shunted
from skin & viscera
to skeletal muscles
blood glucose
increase
bronchioles dilate
pupils dilate
Parasympathetic
Responses
slows heart rate
protects retina from
excessive light (near
lowers blood pressure
empties the bowel
and bladder
increases
gastrointestinal
motility
promotes absorption
of nutrients
41. Marc Imhotep Cray, M.D.
41
ACh Synthesis, Release, and Fate (1)
Synthesized from choline and acetyl-CoA
Released in response to neuronal depolarization
(action potential)
Calcium enters the nerve cell
Transmitter vesicles fuse with cell membrane
ACh released by exocytosis
Inactivated by acetylcholinesterase (AChE)
43. Marc Imhotep Cray, M.D.
Cholinergic Neuron Pharmacology
43
From Le T., Bhushan V.
First Aid 2015. M-H 2015; Pg. 249
44. Marc Imhotep Cray, M.D.
44
NE Synthesis, Release, and Fate (1)
Catecholamine - synthesized in a multistep
pathway starting with tyrosine as the rate limiting
step
Released by exocytosis in response to axonal
depolarization
Duration of activity primarily limited by neuronal
reuptake
Minor metabolism by synaptic monoamine oxidase
(MAO) and catechol-O-methyl transferase (COMT)
45. Marc Imhotep Cray, M.D.
NE Synthesis, Release, and Fate (2)
45
VMAT-Vesicular Monoamine
transporter
46. Marc Imhotep Cray, M.D.
Adrenergic Neuron Pharmacology
46
From Le T., Bhushan V.
First Aid 2015. M-H 2015; Pg. 249
47. Marc Imhotep Cray, M.D.
47
Receptors*
Specialized proteins that are binding sites for
neurotransmitters and hormones
Postsynaptic cell membranes
(neurotransmitters)
Cell nucleus (steroid hormones)
Linked to one of many signal transduction
mechanisms
“Receptor” (According to Rang & Dale Pharmacology):
A target or binding protein for a small molecule (ligand),
which acts as an agonist or antagonist.
Rang HP, Maureen M. Dale MM, Ritter JM , Flower J Henderson G . Rang & Dale's
Pharmacology, Churchill Livingstone; 7th edition 2011
*“not to be confuse with other drug targets such as enzymes etc.”
48. Marc Imhotep Cray, M.D.
48
Ligand-Receptor Interactions
Complementary conformations in 3 dimensions
Similar to enzyme-substrate interactions
Physiologic interactions are weak attractions
H-bonding, van der Waal’s forces
Drug mechanisms
Agonists - bind and activate receptors
Antagonists - bind but DO NOT activate receptors
"Receptor" according to IUPHAR:
(International Union of Basic and Clinical Pharmacology)
A cellular macromolecule, or an assembly of macromolecules, that is
concerned directly and specifically in chemical signaling between and within
cells. Combination of a hormone, neurotransmitter, drug, or intracellular
messenger with its receptor(s) initiates a change in cell function.
See: Basic Receptor Pharmacology/ PDF
49. Marc Imhotep Cray, M.D.
Steps in Signal Transduction Process
See: G-protein Signal Transduction (video animations)
49
There are three general classes of signal transducing receptors:
G-proteins are one and are referred to as serpentine receptors
Also see:
http://themedicalbiochemistrypage.org/s
ignal-transduction.html
Binding of the neurotransmitter,
hormone or drug to receptor>
signaling of G-protein> enzyme
activation> production of a
second-messenger> protein
kinase activation >
phosphorylation of specific
proteins (effect)> termination
50. Marc Imhotep Cray, M.D.
50
The neurohormone epinephrine and its receptor (pink) is used in tis example:
The activated receptor releases the Gs alpha protein (tan) from the beta and gamma
subunits (blue and green) in the heterotrimeric G-protein complex. The activated Gs alpha
protein in turn activates adenylyl cyclase (purple) that converts ATP into the second
messenger cAMP From: http://en.wikipedia.org/wiki/Signal_transduction
Mechanism of cAMP dependent signaling
GPCR structure & function (simplified)
G-Protein Coupled Receptor
Binding of the
neurotransmitter, hormone
or drug to receptor>
signaling of G-protein>
enzyme activation>
production of a second-
messenger> protein kinase
activation
>phosphorylation of
specific proteins
(effect)>termination
51. Marc Imhotep Cray, M.D.
51
3 major G-Protein class subtypes: Compose the largest class of *receptors:
1) Gq Messenger Pathway: (used by H1, Alpha 1, V1, M1, M3 Receptors)
(HAVM1&3)
Receptor → Gq → Phospholipase C that turns Lipid into PIP2 that is split into IP3
(Increases IC Calcium) and DAG (Activates Protein Kinase C - PKC)
2) Gαs Messenger Pathway: (used by Beta 1, Beta 2, D1, H2, V2 Receptors)
(1D2BHV)
Receptor → Gαs → Adenylyl Cyclase (AC) that turns ATP into cAMP that activates
Protein Kinase A - PKA
3) Gαi Messenger Pathway: (used by M2, Alpha 2, and D2 Receptors)
(2MAD)
Receptor → Gαi that inhibits Adenylyl Cyclase that in turn decreases cAMP , thus
making less active Protein Kinase A
G Protein Messenger Pathways
* Remember there are four major classes of ligand–receptor interactions
(more on this in Pharm.)
52. Marc Imhotep Cray, M.D.
52
Sympathetic (Adrenergic-Noradrenergic-R)
Alpha 1 Receptor - q - Vasoconstriction and Pupillary Dilator Muscle
contraction (Mydriasis), and increased Intestinal Sphincters and
Bladder Sphincter contraction
Via PLC-IP3-DAG
Alpha 2 Receptor - i - Decreased Sympathetic Outflow, and
decreased Insulin release
Via Inhib. AC-cAMP
Beta 1 Receptor - s - Increase Heart Rate, Increase Contractility,
Increase Renin release, and increase Lipolysis
Via Stim. AC-cAMP
Beta 2 Receptor - s - Vasodilation, Bronchodilation, Increase Heart
Rate, Increase Contractility, Increase Lipolysis, Increase Insulin
release, Decrease Uterine Muscle tone
Receptor G-Protein Class Major Function
G-protein-linked
2nd messenger mechanisms (1)
53. Marc Imhotep Cray, M.D.
53
G-protein-linked
2nd messenger mechanisms (2)
Parasympathetic (Ach-Cholinergic-R)
M1 Receptor - q - found in CNS and Enteric Nervous System
M2 Receptor - i - Decrease Heart Rate and Contractility of Atria
M3 Receptor - q - Increase Exocrine Gland secretions (Sweat
Gland, Parietal Cells), Increase Gut Peristalsis, Increase Bladder
Contraction, Bronchoconstriction, Increase Pupillary Sphincter
Muscle Contraction (Miosis), Ciliary Muscle Contraction
(Accommodation)
Receptor G-Protein Class Major Function
N.B. Nicotinic ACh receptors are ligand-gated Na+/K+ channels
54. Marc Imhotep Cray, M.D.
54
G-protein-linked
2nd messenger mechanisms (3)
Dopamine:
D1 Receptor - s - Relax Renal Vascular Smooth Muscle
D2 Receptor - i - Modulate Neurotransmitter release (especially in
Brain)
(For sake of completeness)
Histamine:
H1 Receptor - q - Increase Mucus production in Nose and Bronchi,
Bronchiole Constriction, Pruritis, Pain
H2 Receptor - s - Increase Gastric Acid secretion (Parietal Cells)
Vasopressin:
V1 Receptor - q - Increase Vasoconstriction
V2 Receptor - s - Increase Water Permeability and Water
Reabsorption in Collecting Tubule (V2 in 2 Kidneys)
Receptor G-Protein Class Major Function
55. Marc Imhotep Cray, M.D.
55
Cholinergic Receptors
Activated by ACh and cholinergic drugs
Anatomic distribution
Postganglionic, parasympathetic neuroeffector
junctions
All autonomic ganglia, whether
parasympathetic or sympathetic
Somatic neuromuscular junctions
56. Marc Imhotep Cray, M.D.
56
Schematic of Cholinergic Receptor Locations
Pre
Ganglion
Effector
organs
PostThoracic or lumbar
cord
Pre
Ganglion Effector
organ
Post
Cranial or sacral cord
Parasympathetic
Sympathetic Denotes ACh receptors
Denotes ACh receptors
57. Marc Imhotep Cray, M.D.
57
Cholinergic Receptor Subtypes
Muscarinic
Postganglionic, parasympathetic, neuroeffector
junctions (M1-M5)
Nicotinic
Distinction of two different subtypes
Ganglia - type II or type NG
Neuromuscular junctions - type I or type NM
N.B.-Nicotinic ACh receptors are ligand-gated
Na+/K+ channels
58. Marc Imhotep Cray, M.D.
58
Schematic representation of
Cholinergic Receptor Subtype Locations
Pre
Ganglion Effector
organ
PostThoracic or lumbar
cord
Pre
Ganglion Effector
organ
Post
Cranial or sacral cord
Parasympathetic
Sympathetic
N1
M
N1
59. Marc Imhotep Cray, M.D.
59
Adrenergic Receptors
Activated by NE, Epi, and adrenergic drugs
Anatomic distribution
Postganglionic, sympathetic, neuroeffector
junctions
Subtypes
Alpha-1, 2; Beta-1, 2, 3
60. Marc Imhotep Cray, M.D.
60
Schematic representation of
Adrenergic Receptor Locations
Sympathetic
Pre
Ganglion
paravertebral ,
prevertebral or lateral
Effector
organs
PostThoracic or lumbar
cord
Alpha or Beta
adrenergic receptors
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61
Organ system integration
Parasympathetic
Discrete innervation
Energy conservation
Sympathetic
Highly distributed innervation, global responses
Energy expenditure
Fight or flight responses
Functional Significance of the
Autonomic Nervous System (1)
“Organ system integration & Dual innervation”
62. Marc Imhotep Cray, M.D.
62
Functional Significance of the
Autonomic Nervous System (2)
Dual innervation
Organ responses moderated by both
parasympathetic and sympathetic influences
Parasympathetic dominant at rest
Predominate tone
Balance of opposing neurologic influences
determines physiologic responses
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67
Muscarinic Cholinergic Receptor
(mAChR)
Myocardium
Agonists decrease HR, contractility and AV conduction
velocity
Antagonists used clinically to increase HR & facilitate AV
conduction such as in heart block
Iris sphincter muscle
Agonists evoke pupillary constriction (miosis)
Antagonists evoke mydriasis
Gastrointestinal tract
Agonists increase peristalsis and relax sphincter
Urinary bladder
Agonists evoke urination
Detrusor muscle (bladder) contraction
Trigone (sphincter) relaxation
68. Marc Imhotep Cray, M.D.
68
Receptor Function Distribution
α1 Constriction of smooth
muscles
Blood vessels and
piloerectors in skin
(vasoconstriction and goose
bumps)
Sphincters (bladder,
gastrointestinal [GI])
Uterus and prostate
(contraction)
Eye (contraction of the radial
muscle = pupillary
dilation/mydriasis)
α2 Inhibition of sympathetic
autonomic ganglia
(decreases SANS)
Presynaptic ganglionic
neurons
GI tract (less important
pharmacologically)
Effect of ANS on Organ Systems (1)
Sympathetic (NE)
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69
Effect of ANS on Organ Systems (2)
Sympathetic (NE)
Receptor Function Distribution|Organ
β1 Increase cardiac
performance and liberation
of energy
Heart-most important
(increased chronotropy,
inotropy, dromotropy)
Fat cells (release fat for
energy via lipolysis)
Kidney (release renin to
conserve water)
β2 Relaxation of smooth
muscles and liberation of
energy
Lungs (bronchodilation)
Blood vessels in muscles
(vasodilation)
Uterus (uterine relaxation)
GI (intestinal relaxation)
Bladder (bladder relaxation)
Liver (to liberate glucose via
glycogenolysis)
70. Marc Imhotep Cray, M.D.
Effect of ANS on Organ Systems (3)
Parasympathetic (Ach)
Receptor Function Distribution|Organ
N (Nicotinic) "Nerve to nerve" & "nerve to
muscle" communication
SANS & PANS ganglia
Neuromuscular junction (NMJ)
M (Muscarinic) To oppose most sympathetic
actions at the level of the organs
Lung (bronchoconstriction)
Heart (slower rate, decreased
conduction, decreased
contractility)
Sphincters of GI and bladder
(relax)
Bladder (constriction)
GI (intestinal contraction)
Eye (contraction of the
circular muscle = pupillary
constriction or miosis)
Eye (contraction of the ciliary
muscle = focus for near vision)
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71
Exception
Sympathetic innervation of adrenal medulla is direct from
spinal cord and uses ACh as neurotransmitter
Adrenal gland functions as a special form of ganglion that secretes
Epi & NE in a 4 to 1 ratio directly into the bloodstream
Sympathetic postganglionic neurons that innervate renal
vascular smooth muscle release dopamine rather than
norepinephrine
N.B. Note
There is no parasympathetic fiber innervation of blood vessels, but
bld vessels do have muscarinic receptors
For example, in the coronary arteries stimulation M3 receptors
cause the release of NO which result in vasodilation
Sweat glands are innervated by sympathetic nerves, but paradoxically
use mAChR
Sexual arousal is parasympathetic, but orgasm is sympathetic
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72
Autonomic and Somatic NS
Pharmacology Terminology
Many drugs evoke effects by interacting with receptors
Affinity
Efficacy or (synonym) Intrinsic activity
Agonists
Mimic physiologic activation
Have both high affinity and efficacy
Antagonists
Block actions of neurotransmitters or agonists
Have high affinity, but no efficacy
Often used as pharmacologic reversal agents
74. Marc Imhotep Cray, M.D.
74
Cholinergic-
Receptor
Type
Physiologic
Agonist
Signaling
Mechanism
Pharmacologic
Agonist
Pharmacologic
Antagonist
N1=NM Acetylcholine Ionotropic
receptor
Nicotine D-Tubocurarine
N2=NG Acetylcholine Ionotropic
receptor
Nicotine Hexamethonium,
mecamylamine
M1–5 Acetylcholine Various Bethanechol,
methacholine,
pilocarpine
Atropine,
benztropine,
ipratropium
Signaling Mechanisms and Pharmacology of
ANS Receptor Subtypes- PANS
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75
Summary: Take Home Points (1)
ANS functions involve a variety of effector tissues,
including: cardiac muscle, smooth mm, vascular
endothelium, exocrine glands, and presynaptic
nerve terminals
To understand ANS function , and by extension how to
pharmacologically manipulate the ANS, you will need
understand how the two divisions of the ANS coexist and
function, how each subdivision exerts its effects, and
finally what physiologic and pharmacologic mechanisms
exist to increase or decrease each subdivision’s activity
76. Marc Imhotep Cray, M.D.
76
By using drugs that mimic or block the actions of chemical
transmitters and / or their receptor mechanisms, we can
selectively modify autonomic functions
Autonomic drugs are useful in many clinical conditions, however
a large number of drugs used for other clinical purposes have
unwanted effects on autonomic function; and because of the
ubiquitous nature of the ANS, autonomic drugs are frequently
non-selective and thus can be associated with side effects
Bottom line| memorization of receptors, their distribution,
signal transduction mechanisms and their effects is mandatory
and will enable you to accurately predict effects, side effects,
potential toxicities and interactions of ANS drugs
Summary: Take Home Points (2)
77. Marc Imhotep Cray, M.D.
77
Articles
Laurie Kelly McCorry. Physiology of the Autonomic Nervous System
Am J Pharm Educ. 2007 August 15; 71(4): 78.
Goldstein DS, Robertson D, Straus SE, et al. Dysautonomias: clinical disorders of the
autonomic nervous system. Ann Intern Med 2002;137(9):753–63.
Cannon, WB, Organization for Physiological Homeostasis. PDF Physiological Rev July 1,
1929 9:399-431
PowerPoint Presentation:
Cray MI. (2014) Walter Cannon, Homeostasis and the Physiological Response to Stress,
A Web Interactive PowerPoint Presentation
Review Books
Kibble JD, Halsey CR, Homeostasis: In Medical Physiology -The Big Picture; McGraw-Hill
,2009
Costanzo L., Neurophysiology: In BRS Physiology , LLW 5thEd , 2011
Toy E, Rosenfeld G, Loose D, Briscoe D. CASE 1, In Case Files: Pharmacology; McGraw-
Hill 2 ed. 2008
Rosenfeld GC, Loose DS. BRS Pharmacology (Board Review Series); LLW 6thEd, 2013
References and further study:
THE END, THANK YOU FOR YOUR ATTENTION