The visceral system of the Peripheral Nervous System is known as the Autonomic Nervous System. The sensory (afferent) and motor (efferent) nerves connecting the surface of the body with the central nervous system constitute the peripheral nervous system. In other words, rest of the nervous system, other than the brain Autonomic Nervous system.
The nerve fibers of the Autonomic Nervous System are connected with the function of blood vessels, endocrine glands, heart, lungs, stomach, intestines, in and bladders etc. The Autonomic Nervous System is controlled by the old brain, and is not under the functional control of the cortex. The synapse of system is situated outside of both the spinal column and central nervous system.
Physiologists have discovered two divisions of the autonomic nervous system, i.e., sympathetic division and parasympathetic division. These two divisions never function together. Either of the two functions at a time.
The Sympathetic Division
The spinal nerves emerge from the middle portions of the spinal cord. These spinal nerves emerging on both the sides of the spinal cord run a series of ganglia. Ganglia are the nerve centers present in both the sides of the spinal cord. These nerve fibers run up and down the body synapse with the effect or neurons that go into muscles, glands, skin, and viscera. These fibers coming from thoracolumbar segments of the spinal column finally reach organs from the head to toes - all parts of the body. This part of the autonomic system is called sympathetic nervous division because they make the visceral organs function in 'sympathy' during emergency conditions of serious effort or exercise, states of fear and anger.
The sympathetic division acts in three major events, such as during (a) excitement, emotion of fear, anger and elation, (b) violent exercise and bodily activities and (c) extreme cold when the life is endangered.
Owing to the function of the sympathetic division during emotion such as anger and rage, medulla of the adrenal gland pours excess amount of its “adrenaline" secretion to the blood stream. This secretion in the blood stream is associated with strong emotional experiences. This leads to release of stored sugar from the liver into the blood.
There are chemical changes in the blood as a result of which the blood clots easily and quickly. Blood pressure increases, pulse beats become rapid and vigorous. The passages of the lungs enlarge and more air is admitted due to heavy breathing. The pupils of the eyes are dilated and thus more light enters into the eyes. Heavy sweating occurs throughout the body. Palms and hands are full with sweating. The temperature of the skin sometimes rises and at times falls several degrees.
The adrenal medulla also secretes another hormone called "noradrenaline” which constricts the blood vessels at the surface of skin. Bloods are chanalised from stomach and sex organs to the motor organs, such as, muscles of and arms. The digestive functions come to stop. There is cessation of digestive juices due to inhibitive function of the sympathetic division. The blood from these is diverted to the muscles.
Hairs stand on their roots. The adrenaline secreted from adrenal glands expedites the actions and reinforces emergency-facing processes. There is evidence that the thyroids and pituitary glands also secrete hormones during emotion. During joy, the stomach maximum visceral changes, where as in fear and anger, the adrenal functions vigorously. During sorrow, the gall bladder becomes most active. These glandular responses in emotion are adaptive in nature, which means individual becomes able to cope physically with emergency situation.
The visceral activities as well as the neural activities are involving emotion. Almost the total nervous system is involved in emotional response. Electrical responses are also closely associated with the visceral and the activities during emotion. The electrical responses, such as galvanic responses and brain potentials undergo changes during emotion. The autonomic activities energizing sweat glands lead to perspiration, which produces changes in the electrical properties of the skin. The tissues –of the skin generate electromotive force and the electrical resistance of the skin is changed.
The Parasympathetic Division
From the two end segments of the spinal cord, i.e., from the upper and the lower segments, the nerves of the parasympathetic division emerge on both the sides. The upper division of the spinal column is called cranial part and the lower segment is called the sacral part. These nerves then pass the rough series of ganglia and reach the visceral organs structures having synapses outside the central nervous system.
Thus, parasympathetic division of the autonomic nervous system is situated from the above and below the sympathetic division. This division is thus know “cranio-sacral division' of the autonomic nervous system. Parasympathetic nerves like the sympathetic division reach almost all the organs of the body from head to toes. When sympathetic division is active, the parasympathetic division takes rest and vice-versa. Whether a particular division accelerates or inhabits a particular organ or system depends on the welfare of the organism at that moment depending on the situation.
Parasympathetic division is involved in the ordinary vital ions of life. The parasympathetic division maintains the ordinary processes of life. Protection of the eyes from the bright light is the work of this division. The constrictions of the pupils of the eyes are done by this division for protection purpose. It adjusts the lens of the eye for new vision.
The construction of food, its digestion and the excretion are done by parasympathetic on. During sexual union more blood supply to the sex organs are made is division. It meets the physiological demands of the body to maintain. It stores up energy in abundance for future use by the sympathetic division during emergency.
But owing to prolonged emotion, if both the divisions of the Autonomic nervous system become overactive that may lead to organic pathology, parasympathetic over activity may lead to peptic ulcer, backache, and headache etc. The sympathetic over activity may lead to psychosomatic diseases, such as asthma, tuberculosis, migraine etc. for which psychosomatic medicines are prescribed by the physicians.