Download Autonomic Nervous System

Autonomic Nervous
System
Keri Muma
Bio 6
Organization of the Nervous System
Efferent Division

Somatic Nervous System
 Voluntary
control
 Effector = skeletal muscles
 Muscles must be excited by a motor neuron or
they are inactive (On or off)
 One motor neuron extends from the CNS all the
way to the effector muscle
Efferent Division

Autonomic Nervous System
 Involuntary control
 Effectors = glands, smooth and cardiac muscles
 Two neuron chain between the CNS and the
effector
Preganglionic neuron
 Postganglionic neuron

Anatomy of the Sympathetic System

Origin sites
 Thoracolumbar
emerges from thoracic
and lumbar regions T1L2

Length of neurons
 Short
preganglionic
 Long postganglionic
Location of Sympathetic Ganglia


Location of ganglia
Close to vertebral column
ganglia –
chain running parallel to the
vertebral column, extends
from C3 to S4
 Collateral (prevertebral)
ganglia – lie anterior to the
vertebral column
 Paravertebral
Path of Sympathetic Neurons



Cell bodies are located in the
lateral gray horns of spinal
segments T1 – L2
White ramus communicans
– pre neuron passes from the
spinal nerve to the
paravertebral ganglia
Gray ramus communicans –
post neuron exits the
paravertebral ganglia
Path of Sympathetic Neurons

Three different routes the preganglion neuron
can take once it enters the paravertebral ganglia
Anatomy of the Parasympathetic
System

Origin sites
 Craniosacral
-
emerges from
brainstem and sacral
regions

Length of neurons
 Long
preganglionic
 Short postganglionic
Location of Parasympathetic
Ganglia

Ganglia close to target
organ
ganglia – very
close to target organ
 Intramural ganglia – within
the walls of the target organ
 Terminal
Structural Differences between
ANS Divisions
Division
Sympathetic
Origin of Fibers
Thoracolumbar
region of the
spinal cord
Parasympathetic Brain and sacral
spinal cord
Length of
Fibers
Location of
Ganglia
Short
preganglionic
and long
postganglionic
Close to the
spinal cord
Long
preganglionic
and short
postganglionic
Close to or in
the visceral
effector
organs
Regulatory Functions of the ANS

Cardiovascular activities


Body fluid chemistry


Motility along digestive tract, mechanical and chemical
digestion
Visceral reflexes


Breathing rate, bronchiole diameter, O2 and CO2 content
Gastrointestinal activities


pH, osmolarity, thirst, water content
Pulmonary activities


Cardiac output, heart rate, blood pressure and distribution
Micturation, defecation, sexual reflexes
Stress

Stimulates various hormones to cope with situation
Autonomic Control Centers
Functions of the ANS

Sympathetic division – fight or flight
 Enables
body to cope rapidly during emergency
situations
 Dominant when excited, frightened, or during exercise









Increase heart rate and blood pressure
Increase respiratory rate, dilates bronchioles
Blood shunted to skeletal muscles, brain, and heart away
from digestive organs and skin
Dilates pupils
Liver releases glucose to meet increased energy needs
Increased cellular metabolism
Initiates sweating to lower body temperature
Increased RBC production and clotting ability
Na+ absorption / K+ secretion, decreased urine production
Functions of the ANS

Parasympathetic division – rest and digest
 Dominant
in non-stressful situations
 Conserves energy and directs maintenance
activities such as digestion and excretion





Blood shunted to visceral organs
Constricts pupils
Increased digestive glandular secretions and activity
Respiratory and lacrimal secretions
Blood pressure, heart rate, respiratory rates at low
normal levels
Divisions of the ANS

Dual Innervation - most internal organs are
innervated by both autonomic divisions
control – the divisions counterbalance
each other by continuously making adjustments
 The ANS either further excites or inhibits the organs
 Antagonistic
Dual Innervation

There are exceptions to dual innervation:
 Most
blood vessels, sweat glands, and
arrector pili muscles are controlled by
sympathetic fibers only

Sympathetic Tone:
 The
sympathetic division controls blood
pressure and keeps the blood vessels in a
continual state of partial constriction
Sympathetic Tone


Increased
sympathetic activity
constricts blood
vessels
Decreased
sympathetic activity
dilates blood vessels
Sympathetic Effects

Some sympathetic metabolic effects are not
reversed by the parasympathetic division
 Increases
the metabolic rate of body cells
 Raises blood glucose levels
 Mobilizes fat as a food source
 Stimulates the reticular activating system (RAS)
of the brain, increasing mental alertness
Sympathetic Effects

The sympathetic nervous system triggers the
release of epinephrine from the adrenal medulla
 Some
preganglion fibers travel to the adrenal medulla
where the synapse with hormone producing cells
 These cells release epinephrine into the blood stream
ANS Neurotransmitters

Acetylcholine (ACh) and norepinephrine (NE) are
the two major neurotransmitters of the ANS
 Neurons
that release ACh are cholinergic fibers
 Neurons that release NE are adrenergic fibers
Cholinergic Fibers



All parasympathetic pre and postganglionic
neurons
All sympathetic preganglionic neurons
Sympathetic postganglionic that innervate sweat
glands and arrector pili muscles
Adrenergic Fibers

Most sympathetic postganglionic neurons
(except sweat glands and arrector pili)
Types of Receptors

Cholinergic receptors – bind Ach
 Nicotinic
 Muscarinic

Adrenergic receptors – binds NE and/or E
 Alpha
 Beta
ANS Receptors

Neurotransmitter effects can be excitatory or
inhibitory depending upon the receptor type they
bind to
Nicotinic Receptors

Nicotinic receptors are found on:
 Motor
end plates (somatic targets)
 All postganglionic neurons of both sympathetic
and parasympathetic divisions
 The hormone-producing cells of the adrenal
medulla

The effect of ACh binding to nicotinic
receptors is always excitatory
Muscarinic Receptors


Muscarinic receptors are found on all effectors
stimulated by postganglionic cholinergic fibers
 Parasympathetic effectors
 Sweat glands and arrector pili
The effect of ACh binding to muscarinic receptors:
 Can be either inhibitory or excitatory depending
on the receptor subtype of the target organ
 Examples – slows cardiac muscle: inhibitory
smooth muscle of digestive: excitatory
Adrenergic Receptors

Alpha receptors– greater sensitivity to NE
1 – binding of NE is stimulatory

Constriction of blood vessels serving the skin
and abdominal viscera
2 – binding of NE is inhibitory
 Inhibits insulin secretion from the pancreas
Adrenergic Receptors

Beta Receptors
 1 – found primarily in the heart, binding of NE
and E is excitatory
 Increases cardiac output, release of renin from
kidneys to increase BP
 2 – binding of E is generally inhibitory
 Dilates coronary blood vessels and bronchioles in
the lungs, relaxes digestive and urinary smooth
muscle
 3 – found in adipose tissue
 Stimulates lipolysis
Localized vs. Wide Spread Effects

Parasympathetic – localized and short lived effect
 Preganglionic
synapse with one or a few
postganglionic
 ACH is quickly destroyed

Sympathetic – longer lasting and body wide
mobilization
 Preganglionic
synapse with many posts at different
levels
 NE is inactivated slower than ACH
 NE and E are indirect neurotransmitters, using a
second-messenger system
 Epinephrine is released into the blood and remains
there until destroyed by the liver
Effects of Drugs on the ANS

Drugs are designed to obtain an inhibitory
or excitatory effect on a target organ by
either blocking or initiating desired effects
of neurotransmitters
agents – enhance
sympathetic response
 Sympatholytic agents – decrease sympathetic
response
 Parasympathomimetic / Parasympatholytic
 Sympathomimetic
Effects of Drugs

Atropine – blocks muscarinic receptors therefore
blocks parasympathetic effects, increase heart
rate and fecal and urinary retention


Tricyclic antidepressants – prolong the activity of
NE on postsynaptic membranes


parasympatholytic
sympathomimetic
Over-the-counter drugs for colds, allergies, and
nasal congestion – stimulate -adrenergic
receptors

sympathomimetic
Effects of Drugs

Beta-blockers – blocks cardiac B1 receptors,
decreases HR and BP


Alpha-blockers - interfere with vasomotor fibers
and are used to treat hypertension


sympatholytic
sympatholytic
Salbutamol – activates B2 receptors, dilates
bronchioles (asthma treatment)

sympathomimetic
Age and the ANS

In old age, ANS efficiency decreases,
resulting in constipation, dry eyes, and
orthostatic hypotension
 Orthostatic
hypotension is a form of low blood
pressure that occurs when sympathetic
vasoconstriction centers respond slowly to
positional changes