Download autonomic nervous system i

AUTONOMIC NERVOUS
SYSTEM I
Dr Margaret Biber
January 14, 2009
AUTONOMIC NERVOUS
SYSTEM
Involuntary motor system
Visceral efferent (motor) system
CENTRAL NERVOUS SYSTEM
Brain
Spinal Cord
PERIPHERAL NERVOUS SYSTEM
Somatic N.S.
Autonomic N.S.
Sympathetic
Parasympathetic
Skeletal Muscle
(voluntary muscle)
Enteric N.S
Heart
Smooth Muscle
Glands
Smooth muscle &
Glands of GI tract
Not under voluntary control
TARGETS OF INNERVATION BY THE ANS
• HEART MUSCLE & specialized conducting
tissue
• SMOOTH MUSCLE – walls of all hollow organs
(except heart)
–
–
–
–
–
Blood vessels
Digestive tract
Urinary tract
Reproductive organs
Airways
• GLANDULAR TISSUE
– Sweat glands
– Digestive glands
– Glands of the respiratory tract
Functions of the ANS:
Regulation of visceral organ function
EXAMPLES
• CV system: Arterial blood pressure
– Diameter of blood vessels
– Mechanical performance of the heart: heart rate, force of
contraction
• Digestive system: controls & coordinates gastrointestinal
motility and secretions (in conjunction with hormones)
• Emptying of the urinary bladder
• Respiratory tract secretions and airway resistance
(diameter of bronchi and bronchioles)
HOMEOSTASIS (maintenance of the
internal environment)
Function of the ANS: Adaptive
responses to environmental stimuli
• Light
• Temperature
• Threatening stimuli - Stress
Function of the ANS: Adaptive
responses to environmental stimuli
• Light - constriction of the pupil to bright light (miosis)
- dilation of the pupil in low light (mydriasis)
• Temperature
- cutaneous vasodilation and sweating in a
warm environment
- cutaneous vasoconstriction and goose
pimpling in the cold
• Stress - rapid, coordinated response to threatening
or stressful stimuli
FEAR
SIGNS OF FEAR
• POUNDING HEART – heart rate & force of
contraction increases
• DILATED PUPILS – wide eyed with fear
• PALLOR – pale with fear – ashen faced
• GOOSEPIMPLING – hair standing on end;
chills down the spine
• COLD SWEAT – clammy hands
• DRY MOUTH
STAY AND FIGHT
TAKE TO YOUR HEELS IN FLIGHT
FIGHT OR FLIGHT RESPONSE
• Anticipatory – triggered the
moment the possibility of
trouble is detected
• Allows immediate & sustained
physical exertion
• Critical for survival
SUMMARY OF FUNCTION OF ANS
• Exerts overall control of function of visceral
organs – key contribution to homeostasis
• Produces important adaptations to
environmental stimuli:
• Level of illumination
• Ambient temperature
• Stressful, alarming or dangerous situations
• Proper function essential for survival
Characteristics of autonomic control
1. Speed of onset
• heart rate can double within 3-5 seconds
• sweating can occur within a few seconds to a
rise in temperature or in response to fear (cold
sweat).
• goose pimpling appears in seconds in cold or
fearful situations
• involuntary emptying of the bladder, when it
occurs, does so in seconds
• marked changes in blood pressure (rise or fall)
can take place in about 5 secs. A precipitous fall
in blood pressure causes fainting.
2. Tonic activity
• Basal rate of neuronal firing - sympathetic
or parasympathetic tone.
• Consists of low frequency bursts of action
potentials averaging ~ 1 Hz (impulses per
sec).
• Sets up a baseline level of effector organ
activity
• Permits basal activity to be increased or
decreased.
3. Reflex control of autonomic activity
• Not under voluntary control
• Reflexes are stereotyped responses
triggered by specific sensory stimuli
• Sensory stimuli that trigger autonomic
reflexes do not reach consciousness
• Autonomic reflexes are sensitive to &
altered by emotional state
ORGANIZATION OF THE
ANS
Physiological Anatomy
Somatic motor neuron
Spinal cord
Alpha motor neurons:
Axons: Wide diameter, myelinated;
Conduct APs at high speeds
15-50 m/sec& at high frequency.
 Fast precise control of skeletal muscle
Skeletal muscle
Autonomic neurons
Spinal cord
preganglionic
postganglionic
Fine axons:
Conduct APs at low speeds (0.5 m/sec)
& at low frequency (~20 Hz)
Control of targets slower & much less precise
smooth muscle
glands, heart
FIG 1
P 174
Fig 2
P 175
FIG 1
Fig 2
Diffusely
distributed
targets
FIG 1
Diffusely
distributed
targets
FIG 1
1. Cervical ganglia
are fused
Diffusely
distributed
targets
2. Prevertebral or
collateral ganglia
(coeliac, superior &
inferior mesenteric
ganglia) innervate
abdominal organs &
the enteric NS
3. Preganglionic
sympathetic nerves
innervate adrenal
medullary chromaffin
cells (= modified
postganglionic
sympathetic neurons)
Synaptic Organization of Sympathetic
Ganglia: Divergence
Spinal cord
Sympathetic ganglion
Postganglionic nerve
Sympathetic chain
Preganglionics
Synaptic Organization of Sympathetic
Ganglia: Convergence
Spinal cord
Sympathetic ganglion
Postganglionic nerve
Sympathetic chain
Preganglionic nerve
Divergence and Convergence at
the level of single neurons
Divergence
Convergence
Post
Pre
ANATOMICAL FEATURES OF
THE SYMPATHETIC NS
•
•
•
•
Thoraco-lumbar outflow
Short preganglionic axon
Long postganglionic axon
Distinct ganglion system with much
divergence and convergence of
inputs
Fig 3
Key Features of Parasympathetic
Postganglionic nerves lie in or near
target tissues 
• Long pre, short
postganglionic neurons
• Ratio of pre to postganglionic
neurons 1:1 or 1: 2
• Control is highly targeted
ANATOMICAL FEATURES OF
THE PARASYMPATHETIC NS
• Cranial-sacral outflow
• Relatively long preganglionic axon
• Little branching of preganglionic axons
(little divergence)
• Ganglion, if present, located at or near
target organ (cranial region)
• Short postganglionic axon
post
pre
Parasympathetic
Cranial
Spinal cord
T1
pre
post
Sympathetic
pre
Adrenal
Splanchnic nerve
L3
pre
Parasympathetic
Sacral
post
S2
S3
S4
Schematic ANS
Organization of the Autonomic
Neuroeffector Junction
Skeletal NMJ
Motor unit
Autonomic NEJ
POSTGANGLIONIC
Sympathetic postganglionic nerve terminal:
Branching terminal network with varicosities
Synaptic vesicle
COMPARISON OF SOMATIC AND AUTONOMIC
NERVOUS SYSTEMS
Target:
SOMATIC
AUTONOMIC
skeletal muscle
smooth muscle
heart
glands
Control: precise; rapid (msecs)
less so (100 msecs to
secs)
Anatomy:
two neurons
one neuron
Ach
Motor neuron
NMJ
Skeletal
Muscle
fiber
Properties of motor neurons:
wide diameter
myelinated
rapidly conducting
15 - 50 m/sec
Ach/NE
Ach
Pre
Post
NEJ
fine diameter
2nd neuron unmyelinated
slow conducting
0.5 m/sec
COMPARISON OF SOMATIC AND AUTONOMIC
NERVOUS SYSTEMS
SOMATIC
Neuroeffector
junction:
well organized
nerve terminals close to
muscle endplate
(15 nm gap)
Ach receptors tightly
packed in endplate
Receptors:
ligand gated ion channels
Transmitter:
acetylcholine
AUTONOMIC
branching, diffuse terminals
with variable distances from
effector cell membrane (80 1000 nm)
receptors not organized into a
localized chemosensitive area
G-protein coupled signaling on
the effector cells
acetylcholine - parasympathetic
norepinephrine- sympathetic
(exception generalized sweat glands)
Effects:
excitation
one to one relay
excitation or inhibition
modulatory
END