The petrosal major nerve is a nerve pathway in the face and forms a branch of the facial nerve. For the most part, it carries parasympathetic nerve fibers, but it also carries some sensory fibers. As part of the parasympathetic nervous system, the petrosal major nerve is subject to the action of parasympathomimetics and parasympatholytics.
What is the petrosal major nerve?
The petrosal major nerve is the large petrosal nerve, which is part of the facial nerve. It belongs in part to the parasympathetic nervous system, which humans cannot consciously control and which is primarily responsible for calming and regenerative processes. The parasympathetic nervous system is also of great importance for digestive processes. Other nerve fibers, however, which also run in the greater petrosal nerve, serve to transmit sensory nerve signals. The greater petrosal nerve, like all nerve tracts, is not a smooth structure, but consists of numerous nerve fibers that join together like threads to form a larger bundle. Those filaments are the axons of nerve cells and transmit electrical signals known as action potentials.
Anatomy and structure
The origin of the petrosal major nerve is the facial nerve or nervus facialis. This begins in the brain in the medulla oblongata (medulla oblongata) at the superior salivary nucleus (nucleus salivatorius superior). From there, it runs through the petrous bone to the geniculate ganglion, which is home to the sensory and sensory cell bodies of the nerve. The axons of these neurons form the nerve fibers that make up the entire nerve. The greater petrosal nerve branches off from the facial nerve and passes through the sphenoid bone (Os sphenoidale) to the pterygopalatine ganglion, also known as the wing palatal ganglion. In this collection of nerve cell bodies, the information that the nerve transmits changes to the next (postganglionic) cells. Before the fibers of the petrosal major nerve reach the pterygopalatine ganglion, they converge with fibers of the petrosal profundal nerve. This nerve carries information from the sympathetic nervous system and begins at the internal carotid plexus; this is a plexus of nerves on the internal carotid artery or internal carotid artery. After the pterygopalatine ganglion, the pathway of the petrosal major nerve continues through the facial region to the lacrimal gland, nasal mucosa, nasopharynx, and palate.
Function and Tasks
The petrosal major nerve provides the connection between the brain and other nerves on the one hand and certain organs in the facial area on the other. In the palatal mucosa, the sensory fibers of the nerve are responsible for connecting the taste buds there to the nervous system. They contribute to gustatory perception, although the sensory cells in the palatal mucosa play a subordinate role because of their small number. Signals from the greater petrosal nerve reach the lacrimal gland (glandula lacrimalis) via the lacrimal nerve. It is located obliquely above the orbit, shifted toward the outer side; its secretion consists of proteins and electrolytes in addition to fluid. Part of the lacrimal fluid enters the nose via the lacrimal ducts, where it combines with other components to form nasal mucus or nasal secretion. The mucous membrane of the nose is also connected to the petrosal nerve. However, the nerve does not innervate sensory cells here, but the nasal glands (glandulae nasales). They produce a seromucous secretion that is part of the nasal mucus. This is composed of various secretions and also includes lacrimal fluid, condensed fluid from the air, and mucins from goblet cells. Furthermore, the petrosal major nerve provides a neural connection to the nasopharynx, in whose mucosa other glands are located.
Diseases
Because the petrosal major nerve belongs to the parasympathetic nervous system, parasympathomimetics and parasympatholytics can also have an effect on it. These types of drugs are substances that affect the parasympathetic nervous system. Parasympathomimetics increase the effect of the parasympathetic nervous system. Medicine divides these substances into direct and indirect agents: Indirect parasympathomimetics inhibit the breakdown of neurotransmitters, which thereby trigger a stronger nerve signal in the same amount. Direct parasympathomimetics behave in the synaptic cleft like the transmitter acetylcholine.The substance can dock at the postsynaptic receptors and thus cause an action potential in the downstream nerve cell. The neuron does not distinguish between acetylcholine and the parasympathomimetic, but responds solely to the stimulus mediated by the receptor. An example of a direct parasympathomimetic is the drug pilocarpine. It stimulates the goblet cells in the airways so that they produce more secretions. It also promotes the formation of lacrimal fluid, for which the petrosal major nerve is also relevant. In addition, pilocarpine leads to increased activity of the pancreatic, gastric, intestinal, salivary, and sweat glands. Physicians use the drug in part to treat dry mouth that can occur as a result of radiation therapy, as well as in the treatment of glaucoma and against crabs in the eyelashes. However, the suitability of the drug depends on the individual case. In the diagnosis of cystic fibrosis, the pilocarpine iontophoresis sweat test may find application. Parasympatholytics reduce the action of the parasympathetic nervous system by competitively inhibiting acetylcholine: The agents occupy the receptors but do not trigger a response. Instead, they block the receptors only for acetylcholine, whose release therefore has a reduced effect even though the same amount of neurotransmitter is present. Parasympatholytics are therefore also called anticholinergics. An example of this is atropine, which is used in ophthalmology as well as in emergency medicine. However, it can also act as a poison and is potentially lethal.
