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This system regulates the different involuntary activities as contraction of cardiac muscle and smooth (involuntary) muscles in addition to secretion of glands.
The autonomic nervous system includes two divisions:
1) Sympathetic nervous system:
The nerve fibres of this system originate form the thoracic and lumbar regions of the spinal cord. This system is important as an emergency system which enables the body to confront emergency situations.
2) Parasympathetic nervous system:
The nerve fibers of this system arise from the brain (stem) and the sacral region of the spinal cord. Most of the internal parts of the body receive nerve fibres related to both sympathetic and parasympathetic systems and in most cases the effort of one system antagonize the effect of the other.
The following table summarizes the effects of the sympathetic and parasympathetic system on some parts of the body:
| Effector organ | Effect of Sympathetic system | Effect of Parasympathetic system |
| Heart | Increases heart beat rate and force of contraction. | Decreases heart beat rate and force of contraction. |
| Blood vessels | Vaso constriction of blood vessels of skin, viscera, salivary glands, brain, external genetalia and lungs. | Vaso relaxation of salivary glands and external genetalia. |
| Alimentary canal | Relaxation of the wall of stomach, intestine and colon. | Contraction of the wall of stomach, intestine and colon. |
| Respiratory system | Dilatation (relaxation) of bronchioles and decreases secretions. | Constriction (contraction) of bronchioles and increases secretions. |
| Urinary bladder | Relaxation of the wall. | Contraction of the wall. |
| Eyes | Dilatation of the eye pupils. | Constriction of the eye pupils. |
| Glands: | ||
| 1. Salivary | Stimulates small quantity of secretion. | Stimulates large quantity of secretion. |
| 2. Gastric (of the stomach) | Inhibits secretion. | Stimulates secretion. |
| 3. Liver | Break down of Glycogen and increases Glucose level in blood. | No Parasympathetic fibres. |
| 4. Pancreas | Inhibits secretion of enzymes. | Stimulates secretion of enzymes. |
| 5. Adrenal medulla | Stimulates the secretion of the adrenaline hormone (epinephrine) which increases blood pressure, increases heart beat rate, and increases the Glucose level in the blood. | No Parasympathetic fibres. |
Effects of autonomic nervous system on some parts of the body
Sensory System – Sense Organs
Sensation is the ability of Man to recognize different external and internal stimuli. Sensation takes place through specialized sense organs and sensory receptors which each can be stimulated by a single type of stimuli. The receptor can detect a single type of energy and the transduction of this energy into an action potential (nerve impulse) which can be transmitted to the central nervous system which in turn gives the proper response.
Types of sensory receptors:
1) According to their site in the body, receptors are of two types:
a. Exterceptors:
Present on body surface and stimulated by external stimuli as light, sound, and temperature (hot and cold). Usually called sense organs and include the eye, the ear, the nose, the tongue, and the skin.
b. Interceptors:
Date: 2015-12-17; view: 1381