In human, there are 31 pairs of spinal nerves. Each spinal nerve is of mixed type and arise from the roots of the horns of grey matter of the spinal cord.
Spinal nerves are divided into 5 groups according to its position:

1. Cranial spinal nerve – 8 pairs
2. Thoracic spinal nerve – 12 pairs
3. Lumber spinal nerve – 5 pairs
4. Sacral spinal nerve – 5 pairs
5. Coccygeal nerve – 1 pairs

Autonomic nervous system
The autonomic nervous system controls activities inside the body that are involuntary e.g. heart rate, sweating, peristalsis etc. It consists of motor neurons passing to the smooth muscle of internal organs. Autonomic nervous system plays an important role in maintaining homeostasis. It is divided into two parts: 1) Sympathetic and 2) Para-sympathetic.
Sympathetic system is related with such intuitive reaction which increases the protection of body in adverse atmospheric condition along with energy consumption. Whereas para-sympathetic system is linked with those reactions in which energy is conserved.
Measurement of nerve conduction
A nerve conduction study (NCS) is a medical diagnostic test. It is used to estimate the function and the capability of electrical conduction, of the motor nerves and sensory nerves of the human body. Nerve conduction velocity (NCV) is frequently measured during this test.
NCS laterally with electromyography measure nerve and muscle function. Diagnosis of defective spinal nerve compression, or any other neurologic disorder or injuries are undertaken for study by NCS process. Evaluation of numbness of limbs, weakness of the legs and arms as well tingling or burning sensation in certain areas of the body are the central area of diagnosis.. Nerve conduction study mainly comprise of the following studies.

1. Motor NCS: It is performed by electrical stimulation of a peripheral nerve and recording from a muscle to which these nerve supplies. Latency is defined as the time taken for the electrical impulse to travel from the stimulation to that muscleand is usually measured in milliseconds. The target muscle generates a response whose size is called the amplitude. Motor amplitudes are measured in millivolts. Determination of NCV across different segments of the nerve is a primary goal of the Motor NCS study. It is done by the stimulation of two or more different locations along the same nerve.With the help ofthe difference in latencies from the two points of stimulation as well as the distance between the different stimulating electrodes, one can calculate the NCVs across different segments.?