Central and peripheral
The human nervous system consists of a central and a peripheral part. The central nervous system (CNS) includes the brain and spinal cord; from the latter, nerve tracts extend to all regions of the body – they form the peripheral nervous system. In functional terms, this can be subdivided into two areas, the vegetative (autonomic) and the somatic nervous system.
Two halves of the brain in a team
Registering, processing and forwarding stimuli
After all, the brain also sends electrical signals in turn, for example to trigger body movements (e.g., winking, raising hands) or to regulate the function of internal organs (such as the secretion of gastric juice). And let’s not forget: Thinking, laughing, reading, learning – all of these and much more also keep the brain constantly on its toes and cause the neurons to fire countless impulses through the network every millisecond – an endless fireworks display.
The brain consists of about 100 billion neurons; some experts estimate the number to be as high as 1 trillion (1,000,000,000,000)! But there are no space problems in the head because the individual nerve cell bodies are only a maximum of 150 micrometers (µm) in size. For comparison: 1 µm is one millionth of a meter.
– Cell body with processes
– Myelin sheath
To ensure that information is not transmitted too slowly at this length, the axon is enclosed in sections by so-called myelin sheaths – special cells that wrap around the axon several times and insulate it electrically. The axon and sheath together form a (medullary) nerve fiber.
The insulation of the axons can be defective due to various diseases: In the autoimmune disease multiple sclerosis (MS), for example, the misguided immune system attacks the myelin sheaths and destroys them in places. As a result, the transmission of information along the affected axon no longer functions smoothly, leading to symptoms such as paralysis, sensory and visual disturbances.
– Synapses
