Transcript Autonomic Nervous System RICHARD E. FREEMAN MD MPH 2013

Autonomic Nervous
System
RICHARD E. FREEMAN MD MPH
2013
Lock Haven University
NERVOUS SYSTEM - REVIEW
HOMEOSTASIS

The body’s ability to maintain a stable,
relatively constant condition through
multiple dynamic equilibrium adjustment
and regulation mechanisms.
Divisions of the Nervous System
Location
Direction
Control
Action
Structures
NEUROTRANSMITTER
Neurotransmitters endogenous
chemicals that transmit signals from a
neuron to a target cell (FREQUENTLY
another neuron or muscle) across a
synapse.
 Examples: Acetylcholine, epinephrine,
norepinephrine, serotonin, dopamine etc

THE SYNAPSE
COMING AND GOING

AFFERENT:

ARRIVING from the SENSORS to THE
CENTRAL NERVOUS SYSYTEM


INCOMING
EFFERENT:

EXITING from the THE CENTRAL
NERVOUS SYSTEM to the EFFEXORS

OUTGOING
 ALL
NERVES IN THE AUTONOMIC
NERVOUS SYSTEM ARE EFFEFENT
GANGLION VS PLEXUS
 Ganglia: mass of neuron cell bodies that
interconnect and relay info via synapses
 Dorsal
Root ganglia: afferent (sensory)
 Autonomic ganglia: efferent (motor)
 Basal ganglion: Brain-relay stations for
multiple
cerebral/cerebellar/thalamic/hypothalamic/brai
n stem functions


Examples: striatum, caudate nucleus, globus pallidum,
substantia nigra, etc
Plexus: intersecting and recombining
nerve fibers- (major highway intersections)
AGONIST VS. ANTAGONIST

An agonist is a chemical that binds to cell
(neuroreceptor) & triggers or stimulates a
response by that cell.
Epinephrine – Beta receptor
stimulate- speeds up the heart
 Example:

An antagonist blocks the action of an
agonist either by blocking the receptor or
causing the inverse (opposite) action of
the agonist.
Metoprolol – Beta Blocker- slows
the heart rate
 Example:
Somatic versus Autonomic Pathways
ANS = 2 neurons span the distance from CNS to effectors
• presynaptic neuron cell body in CNS -- brain or spinal cord
• postsynaptic neuron cell body in a peripheral ganglion (not dorsal root ganglion)
AUTONOMICGENERAL PROPERTIES
General Properties of the ANS

Motor (EFFERENT)system that controls
visceral organs
 glands,

cardiac and smooth muscle
Regulates unconscious processes that
maintain homeostasis
ANS carries out its actions without our
intent
 INVOLUNTARY

TWO Divisions of the ANS

SYMPATHETIC DIVISION:
 prepares


body for physical activity
(Flight or Fight)
PARASYMPATHETIC DIVISION:
 calming
affect on many body functions & assists in
bodily maintenance
 (Rest and Digest)
Central Control of Autonomic Function

ANS is regulated by several levels of the CNS
 Limbic system connected to hypothalamus
 Hypothalamus

(major visceral motor control center)
 Reticular
 Spinal
formation & brainstem nuclei
cord reflexes
 WILL BE MORE SPECIFIC LATER!!
Visceral Reflexes

Unconscious, automatic responses to stimulation
 1. Receptors detect internal stimuli -
 2. Afferent neurons (incoming) connect to interneurons
(connecting) in the CNS
 3. Interneurons synapse with efferent neurons (outgoing)
 4. Efferent neurons carry motor signals to the effectors
EFFECTORS—



GLANDS,
SMOOTH MUSCLE,
CARDIAC MUSCLE,
Visceral Reflex Arc
EXAMPLE:
Visceral Reflex to
BLOOD PRESSURE CHANGES
AUTONOMIC TONE

AUTONOMIC TONE:
 normal
rate of activity that represents the
BALANCE of the two systems:
 Goal: Maintain Homeostasis
ACCELERATOR AND BRAKE

Effects of each system depend upon
neurotransmitters released
Sympathetic and
Parasympathetic “Tone”


the BASAL AND BALANCED rate of activity of
each system
this background activity allows for an increase or
decrease in activity by a single system
 EXAMPLES:

sympathetic tone normally causes about
50 % vasoconstriction
 increasing or decreasing “tone” can change vessel
diameter


parasympathetic tone provides background G.I.
activity
Sympathetic Tone and Vasomotor Tone
Sympathetic division
prioritizes blood vessels to
skeletal muscles & heart in
times of emergency.
Blood vessels to skin
vasoconstrict to minimize
bleeding if injury occurs
during stress or exercise.
Dual Innervation

Most of viscera receive nerve fibers from both
parasympathetic & sympathetic divisions
 antagonistic
effects oppose each other
 cooperative effects seen when 2 divisions act on
different effectors to produce a unified effect

Example: Sexual response
Parasympathic: “Gets it up” – Erection
 Sympathetic: “Gets it out” - Ejaculation

 Normally,
equally
both divisions do not innervate an organ
Control WITHOUT Dual
Innervation
Adrenal medulla, arrector pili muscles,
some sweat glands & many blood vessels
receive only sympathetic fibers
 Sympathetic tone is a baseline firing
frequency
 Vasomotor tone can shift blood flow from
one organ to another according to
changing needs

SYMPATHETIC NERVOUS
SYSTEM
NEUROTRANSMITTERS OF
THE SYMPATHETIC SYSTEM

Preganglionic: (short fiber)
 Acetylcholine

(Nicotinic)
Postganglionic: (long fiber)
 Norepinephrine
 Acetylcholine
(rarely)
Pathways of Preganglionic Sympathetic Fibers
Efferent Pathways of Sympathetic NS
Collateral Ganglia & Abdominal Aortic Plexus
Adrenal Glands: Sympathetic ganglia


Paired glands sit on
superior pole of each
kidney
Cortex





Mineralcorticoids: aldosterone
Glucocorticoids: cortisol
Androgens: testosterone
Medulla: catecholamines
Sympathoadrenal system

the closely related
functioning adrenal medulla
and Symphathetic NS

EPINEPHRINE, NOREPIPHRINE
DOPAMINE

ALL ACT LIKE
HORMONES
Stress Response



mass sympathetic discharge
 increase in arterial pressure, heart rate and
contractility, blood flow to muscles, blood glucose,
metabolic rate, muscle strength, mental activity,
blood coagulation
prepares the body for vigorous activity need to
deal with a life-threatening situation
AKA - the fight or flight response
Summary of
Sympathetic
Innervation



BODY WALL:
 Effectors are innervated by sympathetic fibers found in spinal
nerves (mixed with afferent fibers)
 FREQUENTLY travel WITH SOMATIC NERVES
 Piloerector muscles, sweat glands, vessels
HEAD AND THORACIC CAVITY:
 Effectors are innervated by fibers in sympathetic nerves
 FREQUENTLY travel WITH CRANIAL NERVES
ABDOMINAL CAVITY:
 Effectors are innervated by sympathetic fibers in splanchnic
nerves.
Summary of the end organ (effector) response to
Sympathetic stimulation








Apocrine/eccrine glands
Eyes:

Pupillary

Lacrimal
Endocrine:

Adrenal cortex

Adrenal medulla
Digestive:

Gallbladder

Intestine

Internal anal sphincter

pancreatic glands

salivary gland
Lungs:

Bronchial muscles

Bronchial secretions
Cardiovascular:

Coronary arteries,

skeletal muscle vessels,

peripheral vascular bed,

myocardium
Urinary:

Bladder wall muscle

Internal urethral sphincter
Reproduction:

penis/clitoris
internal muscle system
Increased secretions
Dilation
Slight Increased secretion
Increased secretion
Increased secretion
Relaxation
Decreased peristalsis
Contraction (pucker up!!)
Decreased secretion
Decreased secretion
Dilation
Reduced production
Dilation (beta); Constriction (alpha)
Dilation (beta); Constriction (alpha)
Constriction
Increased rate
Relaxation
Contraction
No action
Male ejaculation/female orgasm
PARASYMPATHETIC SYSTEM
Parasympathetic Nervous System
Division of Autonomic NS
 Functions in harmony (opposition) to SNS
 Regulates visceral organs

 SLUDGE:
salivation, lacrimation, urination,
defecation, GI functions, emesis

Pre and postganglionic neurons synapse
close to the organ of innervation (unlike
the SN where the ganglion is typically
farther away from the target organ).
Efferent Pathways of Parasympathetic NS
Parasympathetic Functions of Cranial Nerves

Oculomotor nerve (III)


Facial nerve (VII)
Glossopharyngeal (IX)

Vagus nerve (X)
Vagus
Nerve
Summary of the end organ effect of the
Parasympathetic stimulation








Apocrine/eccrine glands
Eyes:

Pupillary

Lacrimal
Endocrine:

Adrenal cortex

Adrenal medulla
Digestive:

Gallbladder

Intestine

Internal anal sphincter

pancreatic glands

salivary gland
Lungs:

Bronchial muscles

Bronchial secretions
Cardiovascular:

Coronary arteries,

skeletal muscle vessels,

peripheral vascular bed,

myocardium
Urinary:

Bladder wall muscle

Internal urethral sphincter
Reproduction:

penis/clitoris

internal muscle system
No action
Constriction
Greatly increased secretion
No action
No action
Contraction
Increased peristalsis- defecation
Relaxation
Greatly increased secretion
Greatly increased secretion
Constriction
Greatly increased
No action
No action
No action
Decreased contraction rate
Contraction
Relaxation
Dilation of penile/clitoral vessel- erection
No action
AUTONOMIC NERVOUS
SYSTEMNEUROTRANSMITTERS
Neurotransmitters & Receptors



Types of neurotransmitters released and types of receptors
on target cells determines effects of ANS
Sympathetic NS has longer lasting effects
Many other substances also released as neurotransmitters

enkephalin, substance P, neuropeptide Y, neurotensin, nitric oxide
Cholinergic Receptors for ACh

Acetylcholine binds to 2 classes of
receptors
 nicotinic

receptors (cholinergic receptor)
Between pre and postganglionic neurons of BOTH
sympathetic and parasympathetic NS
 muscarinic
receptors (cholinergic receptor)
Between postganglionic neurons and target organ
in ALL parasympathetic neurons
 Between some postganglionic neurons and target
organs in sympathetic NS

ACETYLCHOLINE

CHOLINESTERASE
RASEHIBITORS
NICOTINIC RECEPTORS
FUNCTION

A key function of nicotinic receptors is to
trigger rapid neural and neuromuscular
transmission. OPENING Na+
ChannelsRAPID DEPOLARIZATION
AND REPOLARIZATION
NICOTINIC RECEPTORS
LOCATION

Nicotinic receptors are found in:
 The

somatic nervous system
(neuromuscular junctions in skeletal muscles).
 BOTH
sympathetic and parasympathetic
nervous system (autonomic ganglia)
 .POST GANGLIONIC NEURON
 The central nervous system
CLINICAL FINDINGS:
NICOTINIC RECEPTOR STIMULATION
SYMPATHETIC NERVOUS SYSTEM








(due to ganglionic stimulation of the adrenal gland).
Hyperglycemia, glycosuria, ketosis.
Hypertension.
Leukocytosis with a left shift.
Mydriasis (pupillary dilation) in up to 13% of the cases.
Sweating.
Tachycardia, tachydysrhythmias.
Urinary retention.
NICOTINIC RECEPTOR STIMULATION
(CHOLINESTERASE INHIBITOR)
Monday
 Tuesday
 Wednesday
 Thursday
 Friday

Mydriasis (pupillary dilation)
Tachycardia
Weakness
Hypertension
Fasciculations
MUSCARINIC RECEPTORS
MUSHROOM POISON


Muscarinic receptors are located in the:
PARASYMPATHETIC NERVOUS SYSTEM.
 Cardiac


conduction system.
 Exocrine glands.
 Smooth muscles.
Sympathetic nervous system.
 Sweat glands.
Central nervous system.
MUSCARINIC RECEPTORS
Slower BUT response is prolonged
 May be excitatory or inhibitory.
 Do not affect skeletal muscles
 Do influence the activity of smooth
muscle, exocrine glands, and the cardiac
conduction system.


MODULATE ONLY- DO NOT INITIATE (due
to intrinsic electrical/mechanical rhythmic
activity)
MUSCARINIC RECEPTORS

No channels; Receptor activates guanine
nucleotide binding protein (G-protein)
activates many intracellular activities
MUSCARINIC ACTIONS

CARDIAC EFFECTS.

AV blocks, with escape rhythms.
 Bradycardia.
 Ventricular dysrhythmias.

EXOCRINE GLAND ACTIVITY.






Bronchorrhea.
Hyperamylasemia.
Lacrimation.
Rhinorrhea.
Salivation.
SMOOTH MUSCLE ACTIVITY.

Bladder stimulation, sphincter relaxation.
 Bronchospasm.
 Miosis (pupillary constriction), eye pain due to ciliary spasm.
 Nausea, vomiting, cramps, diarrhea
Parasympathetic* (muscurinic)
TOXIDROME
SLUDGE
Salivation
 Lacrimation
 Urination


Defecation
GI pain
 Emesis

DUMBELS
Defecation/Diaphoresis
Urination
Miosis (pupillary
constriction)
Bronchospasm and
Bronchorrhea
Emesis
Lacrimation
NEUROTRANSMITTERS OF THE
SYMPATHETIC NERVOUS SYSTEMADRENERGICS (catecholamines)




NOREPINEPHRINE
HORMONE &
NEUROTRANSMITTER
Post ganglionic
sympathetic neurons
Adrenal medulla

EPINEPHRINE
HORMONE &
NEUROTRANSMITTER

Adrenal medulla

Adrenergic Receptors for NE

Norepinephrine binds to 2 classes of
receptors
 Alpha
(adrenergic)
 Beta (adrenergic)
Beta 1
 Beta 2

Adrenergic Receptors and Function

Alpha

Beta
 Vasoconstriction
 Vasodilation
 Iris
 Cardioacceleration
Dilation
 Intestinal relaxation
 Pilomotor contraction
 Bladder Sphincter
Contraction
 Increased
myocardial
strength
 Uterus relaxation
 Bronchodilation
 Glycogenolysis
 Bladder wall relaxation
END ORGAN EFFECTS OF
AUTONOMIC STIMULATION
OR INHIBITION
EYE
 SYMPATHETIC
 Meds:
--pupillary dilation (mydriasis)
phenylephrine, cocaine, epinephrine
 PARASYMPATHETIC--pupillary
constriction
and accommodation (focusing) of the lens
 Meds:

pilocarpine – muscarinic receptor
GLAUCOMA
Dual Innervation of the Iris
GLANDS OF THE BODY
SYMPATHETIC
 stimulates the sweat glands
PARASYMPATHETIC
stimulate the nasal, lacrimal, salivary, and
G.I. gland
GI TRACT
 SYMPATHETIC
 has
very little effect
 PARASYMPATHETIC
 stimulates
muscle
overall activity including G.I. smooth
Enteric Nervous System
Nervous system of the digestive tract
 Composed of 100 million neurons found in
the walls of the digestive tract (no
components found in CNS)
 Has its own reflex arcs
 Regulates motility of viscera and secretion
of digestive enzymes and acid in concert
with the ANS –peristalsis - sequential

Enteric Nervous System
HEART
 SYMPATHETIC
increases the rate and contractility
 systemic (adrenal medulla) –
epinephrine/norepinephrine and some direct
 SA Node

 PARASYMPATHETIC
decreases heart rate
 Vagus Nerve-cholinergic
 AV node

BLOOD VESSELS
 SYMPATHETIC
Vasoconstriction-arterioles
 Raises blood pressure

 PARASYMPATHETIC

some vasodilation
SECTION
PHARMOCOLOGY &
THE AUTONOMIC NERVOUS SYSTEM
ADRENERGIC OR SYMPATHOMIMETIC
AGONISTS



act like norepinephrine and epinephrine
these drugs have an effect which is much more
prolonged than that of either norepi or epi
 Phenylephrine/oxymetolazine stimulates alpha receptors
 Isoproterenol, stimulates both beta1 and beta2 receptors
 albuterol stimulates only beta2 receptors
some drugs act indirectly by increasing the release of
norepi from its storage terminals
 ephedrine, tyramine, and amphetamine
ADRENOGENIC ANTAGONIST &
SYMPATHOLYTIC


synthesis and storage




phentolamine and phenoxybenzamine
Prazosin (Minipress) Blood pressure
Terasosin (Hytrin) - alpha-1 blocker- BPH
beta blockers


guanethidine
alpha blockers


reserpine
release from the nerve terminal


drugs that block (antagonist) the effect of norepi and epi:
antagonist
beta1 and 2 - propranolol, beta1 - metoprolol
ganglionic blockers
ANS pharmacology

PARASYMPATHOMIMETIC DRUGS



CHOLINESTERASE INHIBITORS



nicotine
 activates nicotinic receptors
pilocarpine and methacholine
 activates muscarinic receptors, cause profuse sweating
Donepezil (Aricept) Rivastigmine (Exelon)– Alzheimer’s
neostigmine, pyridostigmine,and ambenonium
 potentiates the effect of acetylcholine
ANTIMUSCARINIC DRUGS

atropine and scopolamine
 blocks the effect of acetylcholine on effector cells

. Nicotinic and muscarinic receptors
(Choose ALL correct answers)
A. Are both acetylcholine receptors.
B. Have the same structure.
C. Have different physiology.
D. Have different functions.
E. None of the above.

When compared with the action of nicotinic receptors,
muscarinic receptors: (Choose ALL correct answers)
A. Are faster.
B. Initiate rather than modulate smooth muscle activity.
C. Have primarily parasympathetic effects on the
peripheral nervous system.
D. Stimulate sweating via the sympathetic nervous
system.
E. None of the above.

Muscarinic receptors are found in:
(Choose ALL correct answers)
A. Skeletal muscle.
B. Smooth muscle.
C. Exocrine glands.
D. Sweat glands.
E. None of the above.

. Cholinesterase inhibitor toxicity leads to the
following clinical findings mediated by
muscarinic receptors: (Choose ALL correct
answers)
A. Miosis (pupillary constriction).
B. Bronchorrhea.
C. Nausea.
D. Bronchospasm.
E. None of the above.