Corpus: Cranial nerve: Unterschied zwischen den Versionen

The term cranial nerves refers to nerves whose fibers emerge directly from the brain or radiate into the brain. This distinguishes them from the spinal nerves, which arise from the spinal cord. Most cranial nerves are connected to specialized nerve cell collections in the brain stem, the cranial nerve nuclei. Cranial nerves always have at least one passageway within the bony structure of the skull.

Half of the cranial nerves are mixed nerves that carry different fiber qualities. This means, for example, that one nerve can be responsible for controlling muscles and transmitting sensations at the same time. The other half carries only one fiber quality. A distinction is made between

Efferent fibers

• Somatomotor fibers (GSE, general somatic efferent)
• general visceromotor fibers (GVE, general visceral efferent, parasympathetic)
• special visceromotor fibers (SVE, special visceral efferent, branchiomotor)

Afferent fibers

• general somatosensory fibers (GSA, general somatic afferent)
• special somatosensory fibers (SSA, special somatic afferent, sensory)
• general viscerosensitive fibers (GVA, general visceral afferent)
• special viscerosensitive fibers (SVA, special visceral afferent, sensory)

In simple terms, "general" means that the fiber qualities correspond to the conditions in the rest of the peripheral nervous system, while "special" describes fiber qualities that only occur in the cranial nerves (sensory perceptions, supply of the gill arch muscles).

The 12 cranial nerves are numbered with Roman numerals in the order in which they emerge from the brain, from rostral to caudal. The classification was introduced in 1788 by Samuel Thomas von Soemmerring.

The fila olfactoria, which radiate into the olfactory bulb, are predominantly regarded as the first cranial nerve. Deviating from this, the rudimentary Jacobson's organ in humans is also referred to as the 1st cranial nerve. The 2nd cranial nerve is the optic nerve.

Today there is a consensus that the 1st and 2nd cranial nerves are upstream parts of the brain. They are therefore not to be regarded as nerves in the proper sense, but are still referred to as such.

The accessorius nerve (XI) also has a special position among the cranial nerves because part of its fibers (ramus externus) originate from the spinal cord.

The cranial nerves V, VII, IX and X are also classified as gill arch nerves due to their embryonic developmental history. Their motor fiber qualities are described as special visceromotor or branchiomotor. They supply muscles that have developed from the muscles of the gill arches.

In some textbooks, nerve XI (nervus accessorius) is also categorised as a gill arch nerve. However, this only applies to its cranial part ("internal ramus"), which is a continuation of the vagus nerve (nerve X).

Regarding the 7th cranial nerve: its classification is also not standardised. Sometimes a part of the 7th cranial nerve, the nervus intermedius, is referred to as the "13th cranial nerve". This concept is useful for understanding the function of the parasympathetic nervous system in the head area.

In addition to the 12 cranial nerves mentioned above, the terminal nerve, which was only discovered in 1913, can also be counted among the cranial nerves as the "zeroth cranial nerve" (nerve 0).

All cranial nerves are arranged in pairs. After emerging from the nerve cell mass of the brain, the fibers of the cranial nerves initially run intracranially and then emerge from the skull via differently dimensioned channels (foramina, fissures). Their extracranial section then begins.

Table: Passage points of the cranial nerves in the skull

Cranial nerves in the narrower sense with afferent parts (V, VII, VIII, IX, X) carry sensitive or sensory fibers whose cell bodies are located in nerve cell collections (ganglia) outside the brain. These cranial nerve ganglia (ganglia nervorum cranialum) correspond to the spinal ganglia of the spinal nerves. These include:

• trigeminal ganglion (trigeminal nerve)
• Geniculate ganglion (facial nerve)
• Cochlear ganglion (vestibulocochlear nerve)
• Vestibular ganglion (vestibulocochlear nerve)
• Ganglion superius nervi vagi (vagus nerve)
• Ganglion inferius nervi vagi (vagus nerve)
• Ganglion superius nervi glossopharyngei (glossopharyngeal nerve)
• Ganglion inferius nervi glossopharyngei (glossopharyngeal nerve)

Some cranial nerves also carry fibers from nerve cells in the parasympathetic head ganglia:

• ciliary ganglion (oculomotor nerve)
• Pterygopalatine ganglion (maxillary nerve)
• Ganglion oticum (glossopharyngeal nerve)
• Submandibular ganglion (lingual nerve)

Brain stem with cranial nerves

Cranial base with cranial nerves

The loss of a cranial nerve is called cranial nerve palsy. This is caused by lesions, e.g. due to trauma, infections, tumours or ischaemia. The lesion can be localised centrally, i.e. in the cranial nerve nucleus, or peripherally, i.e. in the course of the nerve. Examples are facial nerve palsy and oculomotor nerve palsy.

Pain syndromes can originate from the sensitive cranial nerves, the most prominent of which is trigeminal neuralgia. Other forms are glossopharyngeal neuralgia and intermedius neuralgia.

Mnemonic devices for the 12 cranial nerves:

• "O'hne O'nkel O'swald t'anzen t'ausend A'natomen f'ür v'iele g'ute V'enen a'm H'imalaya.'
• "'O'ma o'ben o'hne t'anzt t'ropfnass, a'ber f'roh, v'or G'rossv'ater A'lberts H'aus."
• "O'nkel O'tto o'niert T'ag t'äglich, a'ber f'reitags v'ernascht er g'erne v'iele a'lte H'ausfrauen."

Mnemonic for the 12 fiber qualities of the cranial nerves (s=sensitive; m=motor; b=both):

• ''S'ome s'ay m'oney m'atters b'ut m'y b'rother s'ays b'ig b'oobs m'atter m'ore"
• "S''ome s'tudents m'ake m'oney b'ut m'y b'rother s'ays B'oris B'ecker m'akes m'ore"

• 3D model: Dr Claudia Krebs (Faculty Lead) University of British Columbia