physiology of autonomic nervous system

 Physiological effects of ANS

(Autonomic nerve stimulation)

Sympathetic stimulation prepares body to deal with exciting and stressful situation. For example; strengthening its defence in times danger and extremes of environmental temperature.

Range of emotion States- fear, embarrassment, anger

Cause sympathetic stimulation

Adrenal glands are stimulated to secrete hormone adrenaline (epinephrine) and noradrenaline (norepinephrine) into bloodstream - these hormone potentiate and sustain effects of sympathetic stimulation.

Parasympathetic stimulation

Has tendency to slow down body processes except digestion and absorption of food and function of genitourinary system.

Normally two function system together, maintaining regular heartbeat, normal temperature and internal environment compatible with immediate external surroundings.

Effects of Autonomic Stimulation

1. Cardiovascular system


A. Accelerates firing of SA node in heart, increasing rate and force of heartbeat.

B. Dilates coronary arteries, increasing blood supply to cardiac muscle.

C. Dilate blood vessel supplying skeletal muscle, increasing supply of oxygen and nutritional materials and removal of metabolic waste product, thus increasing capacity of muscle to work.

D. Constrict blood vessels in secretory gland of digestive system. This raises volume of blood available for circulation in dilated blood vessels.

E. Accelerates blood coagulation because of constriction (narrowing of blood vessel resulting contraction of muscular wall of vessels.

Parasympathetic stimulation

A. Decrease rate and force of hearbeat.

B. Constrict coronary arteries, reducing blood supply to cardiac muscle.

2. Respiratory system

Sympathetic stimulation

This causes smooth muscle relaxation, so

A. Dilation of bronchioles, allowing a greater amount of air to enter lungs at each inspiration, increase respiration rate.

B. In conjunction with increased heart rate, oxygen intake and carbon dioxide output of body are increased to deal with fight or flight situation.

Parasympathetic stimulation

Causes contraction of smooth muscle in leading to bronchoconstriction.

3. Digestive and Urinary stimulation

Sympathetic stimulation

A. Liver increase conversion of glycogen to glucose, making more carbohydrate immediately available to provide energy.

B. Stomach and small intestine

Smooth muscle contraction (peristalsis) and secretion of digestive juices are inhibited, delaying digestion, onward movement and absorption of food, and tone of sphincter muscle is increased.

C. Adrenal (suprarenal) gland are stimulated to secrete adrenaline (epinephrine) and noradrenaline (norepinephrine) which potentiate and sustain effect of sympathetic stimulation throughout body.

D. Urethral and anal sphincter 

The muscle tone of sphincter increased, inhibiting micturition and defecation.

E. Bladder wall relaxes.

F. Metabolic rate is greatly increased.

Parasympathetic stimulation

Liver secretion of bile is increased.

Stomach and small intestine motility and secretion are increased, together with rate of digestion and absorption of food.

Pancreas, secretion of pancreatic juice is increased.

Urethral and anal sphincters

Relaxation of internal urethral sphincter is by contraction of muscle of bladder wall, and micturition occurs.

Relaxation of internal anal sphincter is by contraction of muscle of rectum and defecation occurs. 

There is voluntary relaxation of external sphincter.

Adrenal gland- no effect

Metabolic rate- no effect

5. Eye

Sympathetic stimulation

A. This causes contraction of radiating muscle fibres of iris, dilating pupil.

B. Ciliary muscle that adjusts thickness of lens is slightly relaxed, facilitating distant vision.

Parasympathetic stimulation

This contract the circular muscle fibres of iris, constricting pupil.

Ciliary muscle contract, facilitating near vision.

6. Skin

Sympathetic stimulation

Increase sweat secretion, leading to increased heat loss from body.

Contract muscle in hair follicles of skin, giving appearance of goose flesh. Goose bumps

Constrict peripheral blood vessels, increasing blood supply available to active organs. For example; heart and skeletal muscle.

Parasympathetic stimulation

There is no parasympathetic nerve supply to skin.

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