Middle ear, with auditory tube at bottom right.
|Latin||Tuba auditiva, tuba auditivea,
|Precursor||first branchial pouch|
The Eustachian tube //, also known as the auditory tube or pharyngealtympanic tube, is a tube that links the nasopharynx to the middle ear. It is a part of the middle ear. In adult humans the Eustachian tube is approximately 35 mm (1.4 in) long. It is named after the sixteenth-century anatomist Bartolomeo Eustachi. Some modern medical books call this the pharyngotympanic tube.
The Eustachian tube extends from the anterior wall of the middle ear to the lateral wall of the nasopharynx, approximately at the level of the inferior nasal concha. A portion of the tube (≈1/3) proximal to the middle ear is made of bone; This bony part of pharyngotympanic tube is about 12 mm. in length. It begins in the carotid wall of the tympanic cavity, below the septum canalis musculotubarii, and, gradually narrowing, ends at the angle of junction of the squama and the petrous portion of the temporal bone, its extremity presenting a jagged margin which serves for the attachment of the cartilaginous portion of the rest of the tube, and this raises a tubal elevation, the torus tubarius, in the nasopharynx where it opens.
In the equids (horses) and some rodent-like species such as the desert hyrax, an evagination of the eustachian tube is known as the guttural pouch and is divided into medial and lateral compartments by the stylohyoid bone of the hyoid apparatus. This is of great importance in equine medicine as the pouches are prone to infections, and, due to their intimate relationship to the cranial nerves (VII, IX, X, XI) and the internal and external carotid artery, various syndromes may arise relating to which is damaged. Epistaxis (nosebleed) is a very common presentation to veterinary surgeons and this may often be fatal unless a balloon catheter can be placed in time to suppress bleeding.
There are four muscles associated with the function of the Eustachian tube:
- Levator veli palatini (innervated by the vagus nerve)
- Salpingopharyngeus (innervated by the vagus nerve)
- Tensor tympani (innervated by the mandibular nerve of CN V)
- Tensor veli palatini (innervated by the mandibular nerve of CN V)
The Eustachian tube is derived from the first pharyngeal pouch, which during embryogenesis forms the tubotympanic recess. The distal part of the tubotympanic sulcus gives rise to the tympanic cavity, while the proximal tubular structure becomes the Eustachian tube. It helps transformation of sound waves.
Under normal circumstances, the human Eustachian tube is closed, but it can open to let a small amount of air through to prevent damage by equalizing pressure between the middle ear and the atmosphere. Pressure differences cause temporary conductive hearing loss by decreased motion of the tympanic membrane and ossicles of the ear. Various methods of ear clearing such as yawning, swallowing, or chewing gum, may be used intentionally to open the tube and equalize pressures. When this happens, humans hear a small popping sound, an event familiar to aircraft passengers, scuba divers, or drivers in mountainous regions. Devices assisting in pressure equalization include an ad hoc balloon applied to the nose, creating inflation by positive air pressure. Some people learn to voluntarily 'click' their ears, together or separately, when deliberating doing a pressure equalizing routine by opening their Eustachian tubes where pressure changes are experienced (as in ascending/descending in aircraft flight, mountain driving, elevator lift/drops, etc.). Some even are able to deliberately keep their Eustachian tubes open for a brief period, and even increase or decrease air pressure in the middle ear. The 'clicking your ears' can actually be heard audibly if one puts one's ear to another person's ear for them to hear the clicking sound. Those that are borderline on learning this voluntary control first discover this via yawning or swallowing or other means (above); which later on discover can be done deliberately without force even when there are no pressure issues involved, by 'clicking one's ears'. When the Eustachian Tubes are deliberately held open voluntarily, one's voice sounds louder in one's head than when they are closed.
The Eustachian tube also drains mucus from the middle ear. Upper respiratory tract infections or allergies can cause the Eustachian tube, or the membranes surrounding its opening to become swollen, trapping fluid, which serves as a growth medium for bacteria, causing ear infections. This swelling can be reduced through the use of decongestants such as pseudoephedrine, oxymetazoline, and phenylephrine. Ear infections are more common in children because the tube is horizontal and shorter, making bacterial entry easier, and it also has a smaller diameter, making the movement of fluid more difficult. In addition, children's developing immune systems and poor hygiene habits make them more prone to upper respiratory infections.
Otitis media, or inflammation of the middle ear, commonly affects the Eustachian tube. Children under 7 are more susceptible to this condition and one theory is that this is because the Eustachian tube is shorter and at more of a horizontal angle than in the adult ear. Others argue that susceptibility in this age group is related to immunological factors and not Eustachian tube anatomy.
Barotitis, a form of barotrauma, may occur when there is a substantial difference in air or water pressure between the outer inner and the inner ear, for example in a rapid ascent while scuba diving, or a sudden decompression of an aircraft at high altitude.
Some people are born with a dysfunctional Eustachian tube, which is much slimmer than the usual human Eustachian tube. This may be genetic, but it has also been suggested to be a condition in which the patient did not fully recover from the effects of pressure on the middle ear during birth (retained birth compression). It is suggested that Eustachian tube dysfunction can result in a large amount of mucus accumulating in the middle ear, often impairing hearing to a degree. This condition is known as otitis media with effusion, and may result in the mucus becoming very thick and glue-like, a condition known as glue ear.
A patulous Eustachian tube is a rare condition, in which the Eustachian tube remains intermittently open, causing an echoing sound of the person's own heartbeat, breathing, and speech. This may be temporarily relieved by moving into a position where the head is upside down.
Smoking can also cause damage to the cilia that protect the Eustachian tube from mucus, which can result in the clogging of the tube and a buildup of bacteria in the ear, leading to a middle ear infection in some cases.
Eustachian tube dysfunction can be caused by recurring and chronic cases of sinus infection. This results from excessive mucus production which causes obstruction to the openings of the Eustachian tubes.
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|Wikimedia Commons has media related to Eustachian tube.|
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