Synonyms

Latin: Aruis externa

English: external ear

definition

In addition to the middle ear, the outer ear represents the first level of the sound conduction apparatus. The outer ear includes the auricle (Auricula), the external ear canal (Meatus acousticus externus) and the eardrum (Tympanic membrane), which forms the border with the middle ear.

Anatomy and function

Figure outer ear

The auricle:

The first important component of the outer ear is the auricle.
she includes an elastic cartilage plate (Cartilago auriculae) a. Her skin lies close to her. From the outside, an individual shape of the auricle can be seen in every person. This is made up of the cartilaginous structures Helix, anthelix, tragus and Antitragus educated.

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For more information about ear cartilage, please also read: The ear cartilage - the function and piercing

The earlobe (Auricular lobe ) is the only part free of cartilage and can be grown together or hang down freely as a bulge.
The muscles of the ear are part of the facial muscles and are made up of the 7th cranial nerve (Facial nerve) innervated. Most of the time, however, they are severely regressed and have no function. Therefore, very few people can consciously wiggle their ears. The auricle is very well supplied with blood, which is used for temperature regulation. If the body temperature is too high, more blood is directed into the auricle and cooled by the external air flow. Everyone knows the phenomenon of "red ears" in embarrassing or fearful situations. Since there is no insulating layer of fat around the auricle, frostbite can quickly occur, especially in the upper area.The temperature-regulating effect via the ears is certainly of secondary importance in humans, since sweat glands and other mechanisms can regulate body temperature more effectively. In the animal kingdom e.g. with elephants the success is more evident.

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At the outer ear are also diverse Lymph nodesthat can be swollen with inflammatory processes.
The auricle collects the incoming sound as a kind of funnel, which then passes through the external ear canal continues on its way. This funnel function is particularly important for directional hearing. A distinction is made between "top / bottom" and "front / back", which is ensured by the folds of the auricle, as these reflect or amplify the various sound frequencies differently. Central neurons evaluate this information.

Figure ear

Figure hearing and balance organs

A - outer ear - Auris externa
B - middle ear - Auris media
C - inner ear - Auris interna

  1. Ear strip - Helix
  2. Counter bar - Antihelix
  3. Auricle - Auricula
  4. Ear corner - Tragus
  5. Earlobe -
    Lobulus auriculae
  6. External ear canal -
    Meatus acousticus externus
  7. Temporal bone - Temporal bone
  8. Eardrum -
    Tympanic membrane
  9. Stirrups - Stapes
  10. Eustachian tube (tube) -
    Tuba auditiva
  11. Slug - Cochlea
  12. Auditory nerve - Cochlear nerve
  13. Equilibrium nerve -
    Vestibular nerve
  14. Inner ear canal -
    Meatus acousticus internus
  15. Enlargement (ampoule)
    of the posterior semicircular canal -
    Ampulla membranacea posterior
  16. Archway -
    Semicircural duct
  17. Anvil - Incus
  18. Hammer - Malleus
  19. Tympanic cavity -
    Cavitas tympani

You can find an overview of all Dr-Gumpert images at: medical illustrations

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The external ear canal:

The outer ear canal (part of the outer ear) is approx. 3 cm long and has a mean diameter of 0.6 cm. In the beginning it consists mainly of elastic cartilage. Towards the eardrum, the walls are increasingly formed by a bony wall. It has an S-shaped course, which is particularly important when examining the eardrum with an otoscope. The auricle has to be pulled back and upwards so that the cartilaginous part is stretched and directed straight ahead, the funnel of the otoscope can be inserted and the view of the eardrum is exposed. There are more sebum and ceruminal glands, especially in the front section. The latter produce a thin liquid secretion which, together with the sebum and dead cells, forms ear wax (cerumen). Normally this lard serves as protection against the ingress of foreign bodies and against drying out of the skin in the ear canal. However, with excessive production, it can reduce hearing performance. A swelling of the secretion on contact with water and the following hearing loss is also possible.

The eardrum:

The healthy eardrum (component outer ear) has a pearl-gray color, is round-oval and has an area of ​​approx. 75 mm2. It can be divided clockwise into four quadrants:

  1. I: front top
  2. II: front lower
  3. III: back below
  4. IV: back top.

This division is made along a light strip (Stria mellearis), to which the translucent hammer handle can be assigned, and a vertical line on this line that passes through the navel (Umbo) runs. The navel forms the lower end of the eardrum that has grown together with the hammer handle. This classification is clinically important, as pathological changes can be described better in their localization. With a normal eardrum, a light reflex occurs in the 2nd quadrant, which provides information about the eardrum tension. In principle, however, the eardrum can be divided into a small, flaccid part (Pars flaccida, shrapnel membrane) and a larger, stretched part (Pars tensa)organize. The middle of the eardrum is drawn in like a funnel towards the navel.
The task of the eardrum is to transmit sound to the ossicular chain and thus into the tympanic cavity (middle ear). The incoming sound sets the eardrum into mechanical vibrations, which are carried to the oval window via the hammer, anvil and stirrup, thus causing the inner ear fluid to vibrate. in the Inner ear Then the actual conversion of the sound waves into electrical impulses takes place.

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Summary

The subdivision into the outer ear, middle ear and inner ear is of great importance, since in the case of hearing impairment exactly between the sound conduction (outer ear and middle ear) and sensorineural hearing loss (Inner ear) must be decided. This means that a precise differentiation and localization of the cause can and should be undertaken.


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