Ear canal

The external auditory canal ( external auditory meatus ) starts at the ear and extends to the eardrum. It is therefore part of the outer ear. The external auditory canal in humans has a length of about 2 to 2.5 cm with a diameter of about 7 mm and shows a slight angle forward / down, so check with the investigation with the otoscope for a better view by gentle straightening train the ear is back, trying to reach the top.

The wall of the external auditory canal is formed in the outer third of cartilage ( cartilage meatus acustici ), which forms a part (lamina tragi ) and the projection on the front of the ear canal entrance ( tragus ). The wall of the remaining two-thirds is the bony canal of the temporal bone. The external auditory canal is completely lined by skin, which is relatively thick in the outer part, but in the bony part, especially in the vicinity of the tympanic membrane, it is very thin and immovably connected with the periosteum. On the tympanic ear canal skin goes into the outer layer (stratum cutaneum ) of the tympanic membrane. The sensory innervation of the ear canal is made by the vagus meatus acustici externi, a branch of the nerve auriculotemporal, and the auricular branch of the vagus nerve. The blood supply is via the auricular artery profunda.

Exclusively in the outer cartilaginous part of the ear canal are special protective hair that tragi. It is a special type of bristle hair. The secretion of special glands in the ear canal, the so-called ball glands ( glands ceruminosae ), together with sebum, which originates from associated with hair glands, and scales of epidermis earwax ( cerumen).

The ear reinforced by its self-resonance of the incoming sound within the range of 2000 to 4000 Hz, and therefore the man of these frequencies is more sensitive than others. This effect, also called Open Ear Gain, is responsible among other things for the frequency-dependent perception of loudness.

In addition, the outer ear canal acts as a 4 resonator, as it is flush with the tympanic membrane, that is, the ear canal acts as an organ pipe, stopped. The resonances are - as with gedackten pipes - at λ / 4, 3 λ / 4, λ 5 /4, etc., and can be calculated as follows:

First response: λ / 4 = 0.025 m = length of the ear canal → λ = 0.10 m → f = c / λ = 343 / 0.10 = 3430 Hz

The second and third resonance is obtained analogously:

For the third resonance is already at the outer end of the range of human hearing - all other resonances are outside the audible range.

In the " curves of the same volume level" to make the first two resonances by an increased sensitivity at about 4 kHz and 12 kHz noticeable. It must be noted that even small differences in the length of the ear canal (such as are common in humans) produce large variations in the position of the resonant frequencies.

Pictures of Ear canal

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