Central and peripheral nerves
A distinction is made between a central nervous system (CNS) and a peripheral nervous system (PNS) and thus also between central and peripheral nerve cells. The nerve cells of the CNS include, for example, the motoneurons, which are found in both the brain and the spinal cord. In terms of numbers, however, the neurons make up only a small proportion of the CNS, the far greater proportion being made up of the so-called glial cells or supporting cells.
In PNS, there are two main types of nerves. The first one: The cranial nerves – even if their name suggests otherwise – with the exception of the 1st and 2nd cranial nerve, do not belong to the CNS, but only originate in the area of the CNS in so-called cranial nerve nuclei. A distinction is made between 12 cranial nerves, which control essential bodily functions, especially those in the head and neck region.
These include – among others – The second large group of nerves of the PNS are the spinal nerves. They originate at the spinal cord and are formed from Where the efferent fibers enter the body via the front root and transmit signals generated in the CNS to the body periphery, while the afferent fibers with information from the body enter the spinal cord via the rear root. There are 31-32 spinal nerves, which are arranged in pairs and each exit between two vertebral bodies.
Each spinal nerve belongs to a specific spinal cord segment. The actual spinal nerve is only about one centimeter long and then releases nerve fibers that either mix in nerve plexuses (plexus) or supply the chest wall with nerves without remixing. Each spinal nerve – and thus each spinal cord segment – can be assigned to a specific body region, which it supplies.
This area is called the dermatome. In the area of the chest wall, the dermatomes are regular belt-shaped areas. Thus the area of the So also a formation of nerve plexuses (plexus) occurs only in these areas: While the nerves to supply the chest wall are moving to their destination without prior mixing.
A disease that manifests itself by attacking certain dermatomes is shingles (herpes zoster). It is caused by the reactivation of the varicella zoster virus. After a chickenpox infection in childhood, which is caused by this virus, the virus remains in the body at very specific locations of one or sometimes several spinal nerves, the dorsal root ganglia.
The virus remains there for years to decades without causing any symptoms. Such viruses, which have a high affinity to nerve structures, are called neurotropic viruses. These include, among others, When the immune system is weakened, the varicella zoster virus triggers a second infection, which manifests itself differently than the first.
Typical of shingles is a painful skin rash (whereby the pain usually occurs a few days before the rash), which is limited to a specific area. Namely, the dermatome of the spinal nerve where the virus is located.In most cases, the thoracic spinal nerves are affected, so that the rash is a belt-like structure on the trunk, which gave the disease its name. In rare cases, however, the eye (zoster ophthalmicus), ear (zoster oticus) and other structures may also be affected.
- The cranial nerves.
- The facial nerve (cranial nerve VII), which, among other things, innervates the facial mimic muscles,
- The nervus vestibulocochlearis (cranial nerve VIII), which controls essential functions of the hearing and balance organs and
- The oculomotor nerve (III), which innervates a large part of the eye muscles and thus enables eye movements.
- Afferents and
- Efferent nerve fibers.
- 8neck spinal nerves (cervical),
- 12 chest wall spinal nerves (thoracic),
- 5Lumbar spinal vertebrae (lumbar),
- 5Sacral spinal nerves (sacral) and
- 1-2 coccygeal spinal nerves (coccygeal).
- Navel to the Th (thoracic) 10 dermatome (it is thus supplied by the 10th thoracic spinal nerve), while the area of the
- Nipples Th 4 to 5. To
- In the arms and legs, the dermatomes appear somewhat more disordered, this is related to processes in embryonic development.
- The arms (brachial plexus) and
- The legs (Plexus lumbosacralis).
- The Herpes Simplex Virus and
- The Borrelia.
