The term nervous system (Latin Systema nervosum ) is the sum of all nerve and glial cells in an organism. It is an organ system of the higher animals, which has the task to include information about the environment and the organism, to process and to cause reactions of the organism to respond optimally to changes. The nervous system implements one of the basic properties of life, irritability ( irritability ).
In the course of evolution, and with the higher development of individual departments of the animal kingdom is a clear tendency towards concentration and concomitant specialization of parts of the nervous system can be observed. While in primitive animals still some single neuron specific functions fall (eg, pacemaker neurons that set the pace for elementary body movements of worms ), perform in highly complex nervous systems up to several billion neurons in the network specific tasks.
In systems with central nervous ganglia, the conduction of neurons in afferent fibers ( from the sensors to the brain ) and efferent fibers are divided ( from the brain to the effectors such as muscles).
As most primitive nervous systems, the relatively homogeneous neural networks of cnidarians apply. In cnidarians are found medullary cords ( See also: coelenterates, polyp ).
Platt and nematodes
Platt and nematodes possess a strand-like nervous system.
In arthropods it is already in the formation of higher processing centers in the form of several ganglia ( ganglia). These ganglia are connected by two nerve strands rope-ladder- like manner, which is why this is called a rope ladder nervous system. For most of these animals, the Oberschlundganglion is formed very large. It already takes over the functions of a " brain ", in particular the processing of sensory stimuli. The ganglia of the body segments often control the movements of the leg and wing muscles largely autonomous. The rope ladder nervous systems are ( with the exception of the upper pharyngeal ganglion ) below the digestive system. Therefore, one also speaks of the ventral nerve cord.
Cephalopods and vertebrates
Particularly strong are the centralized nervous systems of cephalopods and vertebrates. In great many functions of the nervous system and muscles are controlled centrally. One therefore speaks of a central nervous system. This consists of the brain and the spinal cord, which are surrounded by bone. Located outside of the central nervous system neuronal structures are referred to as peripheral nervous system and have a connective tissue sheath on. Apart from this topographic classification the nervous system can also be functional in the somatic nervous system (also called animalistic nervous system ) and the autonomic nervous system (including visceral or autonomic nervous system ) are divided. Here, the somatic nervous system is responsible for the perception of external stimuli and the execution of arbitrary motion, while the autonomic nervous system is mainly responsible for the control of the business of running outside of consciousness bodily functions. The autonomic nervous system consists of the sympathetic and parasympathetic nervous than their opponents and the enteric nervous system.
The nervous system corresponds to the totality of an organism present in nerve tissue. It consists of cross-linked nerve cells (neurons ), and glial cells.
In higher organisms, the nerve tissue is composed of a network of neurons and glial cells in many places dock. The latter support the activity of nerve cells. Depend by modulating the extra-cellular concentrations of ions and transmitters as well as the regulation of local blood flow, hormonal of the oxygen supply and the availability neuromodulators (ex. NO), they affect the conduction of electrical impulses from neuron to neuron.
Nervous system disorders usually occur until later in life, often they are innate. They usually have far-reaching consequences and limit the sufferers strong in its freedom of action.
Some relatively well-known examples:
- Amyotrophic lateral sclerosis (or amyotrophic lateral sclerosis, myatrophe lateral, English and Motor Neuron Disease, also known as Lou Gehrig's disease or after first described Charcot 's disease ), short ALS, is a degenerative disease of the motor nervous system.
- Parkinson's disease is a disease of the central nervous system that is associated with the loss of specific dopamine-producing brain cells.
- Multiple sclerosis ( MS), often disseminated encephalomyelitis, is a chronic inflammatory demyelinating disease of the central nervous system (CNS), the cause of which is still unclear despite major research efforts.