Eustachian tube
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The Eustachian tube (or auditory tube) is a tube that links the pharynx to the middle ear. In adults the Eustachian tube is approximately 35 mm long. It is named after the 16th century anatomist Eustachius. Some modern medical books call this the pharyngotympanic tube.
Functions
Pressure equalization
Normally the Eustachian tube is closed, but it can open to let a small amount of air through to equalize the pressure between the middle ear and the atmosphere. When this happens we hear a small pop, an event familiar to airplane travelers or drivers in mountainous regions. Yawning or swallowing can pull on muscles in the neck, causing the tube to open. Some people are born with the ability to contract just these muscles voluntarily, similar to people who can wiggle their ears. Without this airway, the middle ear would be isolated from the atmosphere, and could be easily damaged by pressure changes.When descending in an aircraft, increase in atmospheric pressure can lock the Eustachian tube. The tube can be reopened by the Valsalva maneuver or politzerization.
Mucus drainage
The Eustachian tube also drains mucus from the middle ear. Upper airway infections or allergies can cause the Eustachian tube to become swollen, trapping bacteria and causing ear infections. This swelling can be reduced through the use of pseudoephedrine. Earaches are more common in children because the tube is more horizontal, making the movement of fluid harder.Embryologic development
The Eustachian tube is derived from the first pharyngeal pouch, which during embryogenesis forms a recess called the tubotympanic sulcus. The sulcus deepens to meet the first pharyngeal cleft forming the tympanic membrane. The distal part of the tubotympanic sulcus gives rise to the tympanic cavity, while the proximal tubular structure becomes the Eustachian tube.Muscles
There are four muscles associated with the function of the eustachian tube:| Sensory system - Auditory system - [http://encycl.opentopia.com/ edit] |
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| Outer ear: Pinna > Ear canal
Middle ear: Eardrum | Ossicles (Malleus, Incus & Stapes) | Stapedius | Tensor tympani | Eustachian tube Inner ear: Cochlea (Scala vestibuli, Scala media & Scala tympani) | Oval window | Helicotrema | Round window | Basilar membrane | Reissner's membrane | Organ of Corti | Hair cells | Stereocilia Brain: Cochlear nerve VIII → Cochlear nuclei → Superior olivary nuclei → Inferior colliculi → Medial geniculate nuclei → Primary auditory cortex |
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