The nervous system can be divided in the central nervous system [CNS] аnd the peripheral nervous system. The central nervous system consists of the brain, the brainstem аnd the spinal cord. The peripheral nervous system consists of afferent nerves, which transmit information from the receptors to the CNS, аnd efferent nerves, which transmit information from the CNS to smooth muscles, the heart muscle, skeletal muscles аnd glands. The nervous sytem can also be divided in the voluntary аnd involuntary nervous sytem.
The voluntary system takes care of the interaction of the body with the environment. The involuntary nervous system, also called the autonomic nervous system is involved in the innervation of the heart, the glands аnd the blood vessels: in short, the visceral system. It is involved in the maintenance of general homeostasis. The autonomic nervous sytem consists of 2 different working parts; 1.) The parasympathetic аnd the sympathetic nervous system. Nearly all innervated organs are innervated by both systems. The peripheral blood vessels аnd the adrenal аnd sweat glands, however, are only innervated by the sympathetic system.
Parasympathetic аnd sympathetic nervous system
The parasympathetic nerves are located in the brain stem аnd in the sacral part of the vertebral column, also called the craniosacral part. An important parasympathetic nerve, the nervus vagus, leaves from the brain stem. It innervates, among others, the heart, the lungs, аnd the stomach. The nerves from the sacral part drive the bladder, the genitals, аnd lower intestines. The sympathetic nerves are situated in the thoracolumbar part of the autonomic nervous system. The nerves for head аnd neck start from the upper thoracal segments.
The nerves in the thoracal as well as the lumbal part innervate the organs in the breast аnd abdomen. Table I illustrates the influence of parasympathetic resp. sympathetic system on some organs. An action potential is transferred from one nerve to another nerve through a synapse. Such a transfer takes place in clusters of nervous cells, ganglia. There is a clear difference between the sympathetic аnd the parasympathetic nervous system.
In contrast to the sympathetic nervous system, in the parasympathetic nervous system the ganglia are located close to the effector organs. The sympathetic part they located close to the spinal cord. The sympathetic part forms a network, in contrast to the parasympathetic that goes directly to the organs to be innervated. The parasympathetic system works within several tenth of a second, while the sympathetic system works only after several seconds.
Effects of symphatic аnd parasymphatic nerves on various organs
Organ sympathetic effect parasympathetic effect
- Heart acceleration retardation
- Arterioles constriction generally no effect
- Bronchi dilatation constriction
- Iris pupil dilatation pupil narrowing
- Bladder relaxation contraction