The peripheral nervous system consist of 3 parts-
- 31 pairs of spinal nerves
- 12 pairs of cranial nerves
- autonomic nervous system
Autonomic Nervous System
ANS is a involuntary part of nervous system and controls involuntary body activities. Stimulation of ANS is not voluntarily; but its effects are sometimes sensed by an individual. ANS is divided in two divisions: sympathetic and parasympathetic.
Both these divisions works together in a complementary manner(opposite effect) to maintain involuntary functions and homeostasis. Sympathetic activity predominates during stressful condition; that is during exercise, exertion and excitement. While, the parasympathetic activity predominates during rest time and digestion.
There are some similarities and some differences between the two division. On comparing with other parts of nervous system; the effect of ANS is more rapid. Its effector organ are: skeletal muscles, cardiac muscle and glands. Each division have 2 efferent (motor) neurons between the central nervous system and the effector organ. these neurons are
- Preganglionic neurons
- Postganglionic neurons
1. Sympathetic Nervous system
The preganglionic neuron originate in the spinal cord; at the thoracic and lumber levels. Hence sympathetic division is also known as thoraco-lumber outflow. The sympathetic division has different parts which are as follows:
- Preganglionic neuron:- It has its cell body in the lateral column of grey matter in the spinal cord. The nerve fibers of the cell leaves the cord meet the cell body of the postganglionic neuron at one of the sympathetic ganglia. Acetylcholine is a neurotransmitter at the sympathetic ganglia.
- Postganglionic neuron:- It has its cell body in the ganglia. Its axons then terminates in the effector organ. Norepinephrine is a neurotransmitter at the effector organ.
- Sympathetic ganglia:- these are the sites of synapses between the sympathetic preganglionic neuron and sympathetic postganglionic neurons. It is of two types-
1. Sympathetic trunk ganglia: also known as vertebral chain ganglia. these extends from upper cervical to the sacrum. It lies in vertical rows on the two either sides of the vertebral column. postganglionic axons from this ganglia usually supplies to the organs above the diaphragm.
Sympathetic ganglia of neck have names like-
- middle and
- inferior cervical ganglia.
2. Prevertebral ganglia: It lies anterior to the vertebral column. The postganglionic axons from this ganglia usually supplies the organs below diaphragm.
There are five major prevertebral ganglia-
- celiac ganglia,
- superior mesenteric ganglia,
- inferior mesenteric ganglia,
- aorticorenal ganglia
- renal ganglia.
Parasympathetic Nervous system
Like the sympathetic division, parasympathetic division also have 2 neurons- preganglionic neuron and postganglionic neuron. In this case, the neurotransmitter at both the synapse is acetylcholine. Parts of parasympathetic division are:-
- Preganglionic neuron- preganglionic neuron of parasympathetic division is longer that the preganglionic neuron of sympathetic division. It has its cell body either in the nuclei of four cranial nerves (lll, Vll, lX , X) or in the lateral column of grey matter of spinal cord.
- Postganglionic neuron- This is usually shorter than the postganglionic neuron of sympathetic division. It has its cell body either in the parasympathetic ganglia or in the walls of organ supplied.
- Parasympathetic ganglia- also known as terminal ganglia. The terminal ganglia of head have specific names like: ciliary ganglia, pterygopalatine ganglia, submandibular ganglia and otic ganglia.
Physiology Of ANS
As studied earlier, both the divisions of ANS work in opposite effect to maintain the homeostasis; and also to fulfill the need of the body at that particular time. Like, during exercise, we need more energy. for this, oxygen supply should be increased; skeletal muscles to be provided with more blood and more glycogen to glucose conversion. The effects of both the division during their stimulation is described in below table:-
|Effect of sympathetic stimulation
|Effect of parasympathetic stimulation
|Pupil dilate, circular muscle contracted
|Pupil constricted and radial muscle contracted
|Heart rate and force of contraction increased
|Heart rate and force of contraction decreased
|Glycogen to glucose conversion increased
|Glycogen to glucose conversion decreased
|4. Blood vessels
|Skeletal blood vessels dilated
|Skeletal blood vessel constricted
|Urine secretion decreased
|Urine secretion increased
|6. Sex organs
|Male and female: increased glandular secretion
Female: variable effect, depending on stage of the cycle.
Multiple choice questions(MCQs)
1. ANS is a part of which nervous system?
A. central nervous system B. somatic nervous system
C. peripheral nervous system D. all of the above
2. How does the two divisions of ANS work?
A. works with similar effects B. works with opposite effect
C. does not work together D. both A and B
3. Which of the following is the part of sympathetic division?
A. sympathetic preganglionic neuron B. trunk ganglia
C. sympathetic postganglionic neuron D. all of the above
4. What effect occur on the trachea and bronchi during sympathetic stimulation
A. Trachea and bronchi dilate B. remains constant
C. trachea and bronchi constrict D. no effect
5. Which organs are supplied from the sympathetic postganglionic axons coming from prevertebral ganglia?
A. below the diaphragm B. only lower limbs
C. above the diaphragm D. only upper limbs
6. Match the effect of following organs-
a. trunk ganglia 1. Parasympathetic stimulation
b. prevertebral ganglia 2. Sympathetic ganglia
c. pupil dilate 3. Pterygopalatine ganglia
d. pupil constrict 4. Superior cervical ganglia
7. What is other the name of parasympathetic division?
A. thoracolumbar outflow B. thoracosacral outflow
C. craniosacral outflow D. craniolumber outflow
8. Which of the following statement is true?
A. Sympathetic ganglia is also known as thoracolumber outflow
B. prevertebral ganglia is a parasympathetic ganglia
C. Otic ganglia is a trunk ganglia
D. during sympathetic stimulation, kidney increases urine secretion
9. Which of the following structure is supplied with parasympathetic division?
A. sweat glands B. blood vessels of skeletal muscle
C. skin D. none of the above
10. Which of the following is not the type of prevertebral ganglia?
A. celiac ganglia B. ciliary ganglia
C. renal ganglia D. superior mesenteric ganglia
1. peripheral nervous system
2. works with opposite effect
3. all of the above
4. trachea and bronchi dilate
5. below the diaphragm
6. a – 4 b – 3 c – 2 d – 1
7. craniosacral outflow
8. sympathetic division is also known as thoraco-lumber outflow
9. none of the above
10. ciliary ganglia
REFERENCE: 1. Ross and Wilson-Anatomy and physiology in health and illness; 12th edition; page no.-: 173-177.
2. Gerard J. Tortora -Principles of anatomy and physiology; edition twelfth ; page no.-: 549-552.