What are nerves?Schematic representation of the anatomy and structure of a nerve cell. Click to enlarge.
The totality of all nerve cells (neurons) and glial cells (isolation and connection of neurons) is called the nervous system. The brain and spinal cord constitute the central nervous system (CNS), and all nerves outside the CNS belong to the peripheral nervous system (PNS).
The simplest nerves are unipolar nerves - simple sensory cells such as those of the eyes, whereas biopolar nerve cells transmit sensory impulses. The most common nerve cells are so-called multipolar cells, which mainly occur in the spinal cord. Afferent nerves conduct signals from sensory neurons, such as the mechanoreceptors in the skin, to the central nervous system.
Efferent nerves in turn conduct signals from the central nervous system to the muscles and glands. The PNS includes the spinal nerves (connection to the spinal cord through the spine), the cranial nerves (connection to the brain stem) as well as the nerves of the intestinal nervous system (enteric nervous system).
Anatomy & Construction
Neurons have special structures for quickly and accurately sending signals to other cells. Each nerve cell forms a cord-like structure, which consists of a cell body with extensions, so-called axons (nerve fibers).
Within a nerve, each axon is surrounded by a layer of connective tissue (endoneurium). This endoneurium consists of an inner envelope of glycocalix and an outer delicate network of collagen fibers. Within the endoneurium, the individual nerve fibers are surrounded by a protein liquid, similar to the cerebrospinal fluid in the central nervous system.
The nerve fibers are bundled in groups (fascicles) and again covered by connective tissue (perineurium). The connective tissue surrounding the entire nerve is called epineurium. Nerve growth usually ends at puberty, but can be re-stimulated with a molecular mechanism.
Functions & Tasks
The primary function of the nerves and the nervous system is to control the body sensomotorically. This is done by extracting information from the environment using sensory receptors, sending signals that encode that information into the central nervous system, processing the information for an appropriate response, and sending output signals to muscles or glands for the reaction in question to activate.
Even in the nervous system of a single species, such as humans, there are hundreds of different types of neurons, with a wide variety of morphologies and functions. The exchange between them occurs in the form of electrochemical nerve impulses with speeds up to 120 m / s.
They migrate from one neuron to the next, crossing a synapse, the message in question is converted from an electrical impulse to a chemical message (neurotransmitters) and then back into an electrical impulse.
The connections between the neurons form neuronal circuits that create a perception and determine the behavior of the organism.
The nervous system as well as the rest of the organism is susceptible to failure, whether due to genetic defects, physical damage due to trauma or poison, infections or simple aging processes. The medical department of neurology deals with the causes of malfunction of the nervous system and their treatment or prevention.
In the peripheral nervous system, the most common type of problem is a failure of the nerve conduction velocity, which can have a variety of causes. These include diabetic neuropathy and demyelinating diseases such as multiple sclerosis and amyotrophic lateral sclerosis. A pinched nerve occurs when pressure is applied to a nerve, for example due to swelling in an injury or pregnancy.
Nerve damage or pinched nerves are usually accompanied by pain, numbness, weakness, or paralysis, some of which can be felt far from the actual site of injury. When a nerve is damaged, radiating pain occurs in all areas from which the nerve cell receives input. Nerve disorders are usually diagnosed by a physical examination, including the examination of reflexes, running and other directed movements, muscle reactions and sensory evaluation in addition to an EMG.
Typical & common diseases