1. AUTONOMIC NERVOUS SYSTEM I
Dr Margaret Biber
January 14, 2009

2. AUTONOMIC NERVOUS SYSTEM
Involuntary motor system
Visceral efferent (motor) system

3. 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 Smooth muscle &
Glands Glands of GI tract
Not under voluntary control

4. 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

5. 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)

6. Function of the ANS: Adaptive responses to environmental stimuli
Light
Temperature
Threatening stimuli - Stress

7. 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

8. FEAR

9. 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

10. STAY AND FIGHT

11. TAKE TO YOUR HEELS IN FLIGHT

12. FIGHT OR FLIGHT RESPONSE
Anticipatory – triggered the moment the possibility of trouble is detected
Allows immediate & sustained physical exertion
Critical for survival

13. 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

14. Characteristics of autonomic control

15. 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.

16. 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.

17. 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

18. ORGANIZATION OF THE ANS
Physiological Anatomy

19. 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

20. Autonomic neurons Spinal cord preganglionic postganglionic Fine axons:
Conduct APs at low speeds (0.5 m/sec)
& at low frequency (~20 Hz)
smooth muscle
glands, heart
Control of targets slower & much less precise

21. FIG 1
P 174

22. Fig 2
P 175

23. FIG 1

24. Fig 2
Diffusely
distributed
targets

25. FIG 1
Diffusely
distributed
targets

26. 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)

27. Synaptic Organization of Sympathetic Ganglia: Divergence
Spinal cord
Sympathetic ganglion
Postganglionic nerve
Sympathetic chain
Preganglionics

28. Synaptic Organization of Sympathetic Ganglia: Convergence
Spinal cord
Sympathetic ganglion
Postganglionic nerve
Sympathetic chain
Preganglionic nerve

29. Divergence and Convergence at the level of single neurons
Post
Pre

30. 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

31. Fig 3

32. 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

33. 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

34. Schematic ANS post pre Parasympathetic Cranial Spinal cord pre T1 post
Adrenal
Splanchnic nerve L3
Parasympathetic
post
pre
Sacral S2 S3 S4
Schematic ANS

35. Organization of the Autonomic Neuroeffector Junction

36. Skeletal NMJ Autonomic NEJ
Motor unit

37. POSTGANGLIONIC

38. Sympathetic postganglionic nerve terminal: Branching terminal network with varicosities
Synaptic vesicle

40. COMPARISON OF SOMATIC AND AUTONOMIC NERVOUS SYSTEMS
SOMATIC AUTONOMIC
Target: skeletal muscle smooth muscle
heart
glands
Control: precise; rapid (msecs) less so (100 msecs to secs)
Anatomy: one neuron two neurons
Properties of motor neurons:
wide diameter fine diameter
myelinated 2nd neuron unmyelinated
rapidly conducting slow conducting
m/sec m/sec
Ach/NE
Ach
Ach
Skeletal
Muscle
fiber
Motor neuron
NMJ
Pre
Post
NEJ

41. COMPARISON OF SOMATIC AND AUTONOMIC NERVOUS SYSTEMS
SOMATIC AUTONOMIC
Neuroeffector
junction:
well organized branching, diffuse terminals
nerve terminals close to with variable distances from
muscle endplate effector cell membrane (80 -
(15 nm gap) nm)
Ach receptors tightly receptors not organized into a
packed in endplate localized chemosensitive area
Receptors:
ligand gated ion channels G-protein coupled signaling on the effector cells
Transmitter:
acetylcholine acetylcholine - parasympathetic
norepinephrine- sympathetic
(exception generalized sweat glands)
Effects:
excitation excitation or inhibition
one to one relay modulatory

42. END