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LESSON 17

Outer ear anatomy

Year 1
Fall semester
Anatomy I
Ear anatomy
Duration: 9:41

The outer ear is where sound first enters the ear. In this lesson we cover the auricle (pinna) and its landmarks, the length and curve of the ear canal, and the differences between its cartilaginous and bony parts. We also look at cerumen and clinical links such as collapsing ear canals in audiometry.

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Hello, and welcome to the AIHEAR Audiology Academy.
In this lesson we will get to know the part where sound first enters the ear: the outer ear.
We will learn the parts of the pinna, the shape of the ear canal and its two different wall structures.
The outer ear is the part of the ear that is visible from outside and collects sound inward.
Its first part is the auricle, also called the pinna.
Its second part is the external auditory canal, the meatus acusticus externus.
The ear canal begins at the hollow in the middle of the pinna and ends inside at the tympanic membrane.
The tympanic membrane is the border between the outer and middle ear; we will study it in detail in the next lesson.
The outer ear collects sound, boosts certain frequencies and protects the deeper parts of the ear.
The auricle is made of thin skin covering a frame of elastic cartilage.
The only exception is the lobule, the earlobe, at the bottom; it has no cartilage, only fat and connective tissue.
That is why the earlobe is soft and easily changes shape.
There are small muscles that move the pinna, but in humans these muscles are very weak.
In the embryo, the pinna develops from six small hillocks on the first and second pharyngeal arches.
Small irregularities in how these hillocks fuse can lead to preauricular pits, seen in front of the ear.
The surface of the pinna has fixed landmarks that we use in examinations and when taking earmold impressions.
The fold that forms the outer rim of the pinna is called the helix.
The ridge running parallel to it on the inner side of the helix is the antihelix; at its upper end it splits into two crura.
The small flap just in front of the ear canal is the tragus.
Opposite the tragus, above the earlobe, lies the antitragus.
The deep bowl around the canal entrance is called the concha; sound is directed into the canal from here.
The concha and the tragus are the main areas where earmolds and in-the-ear hearing aids sit.
The ear canal is a tube that runs from the concha to the tympanic membrane.
In adults it is about two and a half centimeters long.
Its diameter is about seven millimeters, but this varies between people and along the canal.
The canal is not straight; it follows a curved path that looks like a gentle letter S.
Because the tympanic membrane sits at a slant, the anterior inferior wall of the canal is longer than the posterior superior wall.
This leaves a narrow recess between the lower front edge of the eardrum and the canal floor, where debris can collect.
The wall of the ear canal is made of two different parts.
The outer third is made of cartilage and is about eight millimeters long.
The skin of this part is thick; it holds the hairs and the glands that produce earwax.
The cartilaginous part is flexible; its shape changes when the pinna is pulled or the jaw moves.
The inner two thirds lie within the temporal bone and are about sixteen millimeters long.
The skin of the bony part is very thin, attached directly to the periosteum, and has no glands or hairs.
This thin skin is very sensitive to touch; the patient may feel pain if an otoscope or probe tip touches it.
Because the canal curves, we need to straighten it to see the eardrum during otoscopy.
In adults the canal changes direction several times; its inner part slopes forward and slightly downward toward the eardrum.
So in adults, the canal is straightened by gently pulling the pinna up and back.
In infants the bony part has not yet developed; the canal is short, soft and largely cartilaginous.
For this reason, in infants the pinna is gently pulled down and back.
The narrowest point of the canal lies just medial to the junction of the cartilaginous and bony parts; it is called the isthmus.
Foreign bodies or earwax pushed beyond this narrowing can be hard to remove.
Cerumen, or earwax, forms when the secretion of glands in the cartilaginous part mixes with oil and shed skin cells.
Cerumen is produced only in the outer part of the canal; the inner part has no glands.
Genetically there are two types, wet and dry; the dry type is more common especially in East Asian populations.
Cerumen moisturizes the canal skin, traps dust and small particles, and protects against microbes.
Because the canal skin migrates from the inside outward, cerumen is normally carried out on its own.
When cerumen builds up and blocks the canal, it is called impaction; hearing is rarely affected much unless the canal is fully blocked.
When impacted cerumen fully blocks the canal, a mild conductive loss can appear, as in this example.
There is more than one valid removal method; drops that soften the wax and irrigation with warm water are two of them.
Suction under a microscope or cleaning with small instruments is also common; each method suits different situations.
In Türkiye, cerumen removal is done by a physician; in the audiological assessment the finding is recorded and the person is referred.
When the test is repeated after removal, we can see whether the thresholds have improved.
The anterior wall of the canal lies next to the jaw joint, the temporomandibular joint.
So jaw movements change the shape of the canal; this is why an earmold can shift during speaking and chewing.
The posterior wall lies next to the mastoid, the bony prominence behind the ear.
The superior wall of the bony part is separated from the middle cranial fossa by a thin plate of bone.
Sensation of the canal skin comes from branches of the fifth, tenth and seventh cranial nerves.
When the auricular branch of the tenth nerve is stimulated, some people cough while the ear is being cleaned.
The flexible cartilaginous part of the ear canal can cause an unexpected problem in audiometry.
A supra-aural earphone pressing on the pinna can close the canal entrance, especially in older adults and infants: a collapsing ear canal.
In this example, right ear air conduction thresholds are poorer at high frequencies, while bone conduction looks normal.
This picture creates a false air-bone gap without any real middle ear problem.
When canal collapse is suspected, the test is repeated with insert earphones or with the canal entrance held open.
The false gap then largely disappears, which is why it is important to look at the canal entrance during the examination.
A tip from practice: before starting otoscopy, inspect the pinna and the canal entrance with the naked eye.
Note any differences in the shape of the pinna, small pits in front of the ear, or narrowing at the canal entrance.
In older patients, press gently on the pinna to check whether the canal entrance closes.
If you see it close, testing with insert earphones from the start prevents a false conductive loss.
The auricle is elastic cartilage covered by skin; only the lobule has no cartilage.
The helix, antihelix, tragus, antitragus and concha are the main landmarks of the pinna.
In adults, the ear canal is a curved tube about two and a half centimeters long.
The outer third of the canal is cartilage and the inner two thirds are bone; cerumen is produced only in the outer part.
Test yourself: In which part of the ear canal are the glands that produce earwax?
The correct answer is B: in the cartilaginous outer third.
The skin of the bony part is thin, without glands or hairs, so earwax forms only in the outer part of the canal.
In the next lesson we will study the tympanic membrane at the end of the ear canal, its parts and its otoscopic landmarks.
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Prerequisites

LESSON 16 The Temporal Bone: Where the Ear Lives Coming soon

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