Scrutinization of the Hearing Organ – The Anatomy of Ear
Outer ear contains the pinna, the auditory canal and the tympanic membrane.
Commonly used terms
- Anterior – towards the front of body, eg., the toe lies anterior to leg.
- Posterior – Towards the back of body, eg the leg lies posterior to toe
- Superior – Above, eg., the eye lie superior to mouth
- Inferior – Below, eg., the mouth lie inferior to nose
Also called as Auricle. The main components of the auricle include the helix, antihelix, concha, tragus, antitragus, and lobule. The auricle contains cartilage lined by skin. The lobule contains is the only area with fibrofatty tissue but no cartilage.
The helix and antihelix are 2 ridges. The concha is a depressed area surrounding the external auditory meatus (opening of the auditory canal). The concha on the posterior aspect (towards the back) is surrounded by antihelix. The antihelix is in turn surrounded by helix which forms the outermost boundary of the ear. Between the helix and antihelix in the superior aspect (or in the upper aspect) is a depressed area called the scaphoid fossa. Also, in the superior aspect of the ear, the antihelix splits into two ridges enclosing another triangular depressed area between the 2 ridges. This depressed area is called the triangular fossa and the 2 ridges are called the crura of the antihelix.
The helix contains a small protrusion near the scaphoid fossa called Darwin’s tubercle. As mentioned, the helix lies the outermost prominent ridge, the helix ends in the lobule and starts from the concha just above the external auditory meatus thus forming the hook of the ear, giving the ear its typical appearance. The helix which begins from the concha divides the concha into an upper cymbal concha and lower concha cavum.
Tragus and Anti-Tragus
As mentioned, the helix ends in the lobule, similarly, the antihelix ends in the anti-tragus. The anti-tragus is a flat area above the lobule.
The external auditory meatus in the anterior aspect(towards the front of the body) is surrounded by a projection called the Tragus. The tragus and antitragus are separated by a small depression called inter tragic notch.
In some people, there will be thick hair in the tragus, especially in males. This is due to genetic inheritance in the Y chromosome. The auricle contains certain muscles which are responsible for a moment of the auricle, especially in animals. In some people there would be a rare involuntary moment of the pinna. These muscles are called intrinsic muscles or auricles.
Measures about 24mm. Contains an outer 1/3rd which is cartilaginous and an inner part bony 2/3rd. The common ear wax is produced by the skin covering the outer 1/3rd containing the cartilage. The skin covering bone is thin and is continuous with a tympanic membrane. At about 4mm near the tympanic membrane, the canal is narrowed this narrowing is called the isthmus. This canal is not straight. The outer part goes upwards and posteriorly and the inner part goes downwards and anteriorly.
That’s why during ear examination the pinna is pulled backward and downwards in adults so that the canal is visualized better.
In infants for ear examination, the pinna is pulled backward and downwards, because the bony part of the canal is not well developed and the tympanic membrane is directed downwards.
It is not advised to use earbuds deep inside the ear. Because the wax present in the outer 1/3rd may get displaced inside the bony part, it is very difficult to remove such wax. The wax remains there and progressively accumulates if earbuds are used repeatedly and form into hard wax stones, which block the canal and cause hearing impairment. That is why in the label of earbuds it would be mentioned to be used only in the outer part of the ear.
It is an oval-shaped structure separating the outer ear and middle ear. It faces downwards and makes an angle of 55degee with the floor of the auditory canal. The tympanic membrane is the layer of membrane containing all the 3 germ layers. The membrane contains 3 layers.
- Outer cuticular layer, which is continuous with the skin of the bony part of the canal, corresponds to ectoderm
- Middle fibrous layer, from which the bony handle of malleus originates, corresponds to mesoderm
- Inner mucosal layer, which is continuous with the lining low columnar epithelium of the inner ear, corresponds to the endoderm
OTOSCOPEThe tool used for on-ear examination
On-ear examination using an otoscope, the following things would be seen in a tympanic membrane of normal ear –
- The handle of the malleus
- The Long process of the incus
- Cone of light
- Pars flaccida
- Pars tensa
Malleus and incus are small ear bones in the middle ear.
UMBO – A small portion of the tympanic membrane bulges inward in the middle ear at its center called the umbo, there present is the handle of the malleus. The light from the otoscope is reflected maximum by the umbo towards the anteroinferior region. The anterior wall and the floor of the auditory canal have the largest surface hence the reflected light is seen there. This is reflected light is called the cone of light.
The Pars Pair
The Pars flaccida is the pinkish region seen above the handle of the malleus. It is the region of the tympanic membrane with the middle fibrous layer replaced by loose areolar tissue. This region is also called Sharpenell’s membrane.
The remaining region of the tympanic membrane is called Pars tensa. The Pars tensa is surrounded by a fibrocartilaginous rim which separates the Pars flaccida. This rim at the junction of the Pars tensa and Pars flaccida forms anterior and posterior malleolar folds, in between them lies a notch. From this notch, the lateral process of the malleus gains its attachment.
In the case of pus in the middle ear, the pus drainage is done by a small incision in the posteroinferior region in the tympanic membrane. A nerve called chorda tympani passes in the middle ear behind the handle of the malleus and hence the incision is given below the handle of the malleus, in a way not affecting the cone of light.
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