AUTONOMOUS NERVOUS SYSTEM, SYMPATHETIC NERVOUS SYSTEM AND PARASYMPATHETIC NERVOUS SYSTEM

Published in Zoology
Monday, 29 May 2017 22:50
AUTONOMOUS NERVOUS SYSTEM

The name autonomous (Gr. autos = self, nomos = governing) indicates that it is a self-governing nervous system. It is a partly independent system. It is not under the voluntary control of nervous system. The activities of some of the organs which are not under the control of the will of an organism are controlled by this system. The autonomous nervous system controls activities like heartbeat, peristalsis in alimentary canal, contraction of urinary bladder, secretion of digestive juices from digestive glands, etc. The autonomous nervous system is also known as "visceral nervous system".
 
The central nervous system generally, regulates various visceral organs and movements of involuntary muscles. Though it is involuntarily controlled by the nerve centres located in the central nervous system, it has connection with spinal nerves and some cranial nerves.
 
The autonomous nervous system consists of visceral sensory and visceral motor fibres. It has two divisions:
  1. Sympathetic nervous system and
  2. Para-sympathetic nervous system.
 
They ensure smooth functioning of the various organs.
 
SYMPATHETIC NERVOUS SYSTEM

It consists of a pair of slender longitudinal chains of ganglia, which lie on either side of the dorsal aorta. These chains are called sympathetic nerve chains or cords. They continue forward along the outer sides of systemic arches. Anteriorly, each sympathetic nerve cord enters the skull through jugular foramen and finally ends in vagus or gasserian ganglion. The sympathetic nerve chain is connected with corresponding spinal nerve by a narrow branch called ramus communicans.
 
Several nerves arise from sympathetic ganglia, which innervate various visceral organs like stomach, intestine, spleen, kidneys, urinary bladder, gonads etc. The nerve endings of the sympathetic nervous system secrete a chemical substance called sympathin which is functionally similar to adrenalin. This sympathin has an accelerating effect on the activities of various visceral organs.
 
PARASYMPATHETIC NERVOUS SYSTEM
 
This is a functionally different component of the autonomous nervous system. The nerve fibres of parasympathetic nerves are found in third, seventh, ninth and tenth cranial nerves and the spinal nerves of the sacral region. The ganglia of the parasympathetic system are located in the wall of heart, stomach, lungs, urinary bladder etc. The nerve endings of parasympathetic system secrete acetylcholine. This substance has inhibiting effect which retards the over activity of the organs. Thus the normal working of the body is ensured by opposing functions of two components (sympathetic and parasympathetic) of autonomous nervous system.
 
The opposing functions of sympathetic and parasympathetic sys­tems are given below:
 

Organ & Activities

Sympathetic control

Parasympathetic control

1. Rate of heart beat

Increases

Decreases

2. Stomach

a) Tonus and motility

b) Secretions

a) Decrease

b) Decrease

a) Increase

b) Increase

3. Intestine

Tonus and motility

Decrease

Increase

4. Bronchial muscles

Dilate

Constrict

5. Blood vessels

Constrict

Dialate

6. Urinary bladder

Relaxation of muscles occur

Contraction of the muscles occur

7. Peristalsis of alimentary canal

Decreases

Increases

8. Secretions of salivary and gastric glands

Decrease

Increase

NERVOUS SYSTEM OF RABBIT

Published in Zoology
Monday, 29 May 2017 19:35
 
All the functions of any organism are regulated and integrated by the nervous system.All the systems are coordinated with one another to perform normal functioning of the body. This co-ordination is by two systems. They are nervous and endocrine systems. Study of nervous and endocrine systems together called Cybernetics. The main and fast co-ordinating system is nervous system. For example the sensory organs first receive external stimuli. These are carried to the centres of brain through the sensory nerves. The centres of the brain take decessions. These decessions are carried to the muscles for contraction and to the glands for secretion. The entire nervous system is derived from embryonic ectoderm. The structural and functional units are neurons.
 
The nervous system is divided into three parts. These are i. Central ii. Peripheral and iii. Autonomous nervous system.
 
CENTRAL NERVOUS SYSTEM
 
It lies dorsally in the mid longitudinal axis of the body. The central nervous system contains two parts. They are brain and spinal cord.
 
PERIPHERAL NERVOUS SYSTEM
 
The peripheral nervous system includes cranial nerves and spinal nerves.
 
The nerves which arise from brain are cranial nerves and that of spinal cord are spinal nerves. The cranial nerves come out of cranial cavity through cranial foramina. Spinal nerves come out of the neural canal through the inter-vertebral foramina. The nerves of the peripheral nervous system innervate different parts of the body.
 
Based on the function, the nerves are of 3 types.
 
A. SENSORY NERVES
 
The sensory nerves are also known as afferent nerves. These nerves carry impulses from sense organs like nose, tongue, skin etc to the central nervous system.
 
B. MOTOR NERVES
 
These nerves are also known as efferent nerves. These nerves carry orders from central nervous system to the effectors ( muscles and glands).
 
C. MIXED NERVES
 
These nerves conduct impulses in both directions. They contain both afferent and efferent fibres.
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