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 Smooth muscle & Glands 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) smooth muscle glands, heart Control of targets slower & much less precise

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 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

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

Organization of the Autonomic Neuroeffector Junction

Skeletal NMJ Autonomic NEJ Motor unit

POSTGANGLIONIC

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

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 15 - 50 m/sec 0.5 m/sec Ach/NE Ach Ach Skeletal Muscle fiber Motor neuron NMJ Pre Post NEJ

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) 1000 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

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