1.2. The outer ear
The outer ear can be divided into three main structures:
- The auricle (outer ear)
- The ear canal
- The eardrum (‘tympanic membrane’).
These parts are discussed in turn.
The pinna, or ‘auricle’, is the outer ear that is visible and is an external fold of skin, consisting of a skeleton of elastic cartilage; a wavy surface with ridges and cavities; and an appendage, the earlobe (‘lobule’), which has no cartilage skeleton. The outer edge is called the ‘helix’. The deepest impression is the ‘concha’. This is flanked at the front by an elevation, the ‘tragus’. The auricle is located eccentrically around the ear canal opening and is attached to the head at an angle of approximately 30 degrees. The shell is attached to the temporal bone by two ligaments (anterior and posterior).
The cartilaginous auricle continues with the skin covering the outer part of the external auditory canal (the ear canal). This is a tubular duct with a length of about 25 mm and a diameter of 6 to 8 mm. The canal is closed off by the eardrum, the ‘tympanic membrane’. The resonant frequency of the ear canal is 2,000 to 3,000 Hz. This frequency range corresponds to the frequencies that are important for understanding speech.
The first third of the ear canal has a cartilaginous wall. The deeper part (two-thirds) lies in the ‘temporal bone’ and has a bony wall. At the back (posterior), this wall forms part of the mastoid (the ‘mastoid part of the temporal bone). The lining of the first part consists of skin in which sweat and sebaceous glands occur (the ceruminous glands). There are also hairs in the ear canal that can transport the earwax (cerumen) out through their movement.
The ear canal has a slightly S-shaped course. Going from the outside in, the direction is horizontal, first forward towards the nose (‘anterior’), and then backwards (‘posterior’). Then the tube makes a slight bend forward again, but also down to the closing eardrum. The ear canal’s front wall (nasal side) has a direct relationship with the adjacent temporomandibular joint. The clinical significance is that osteoarthritis of the temporomandibular joint often manifests as ear pain. Mechanical movements of the temporomandibular joint can cause deformation of the anterior wall and the displaced air in the ear canal can then be perceived as sound. The ear canal can be inspected completely up to the eardrum by slightly pulling the auricle back and up.
The eardrum closes off the external auditory canal and forms the lateral boundary of the middle ear cavity. It is contained in a cartilaginous (fibrous) ring interrupted at the top. It is set at about 60 degrees in the ear canal, skewed on the anterior-posterior plane, the ‘sagittal’ plane. Seen from the auditory canal, it is viewed obliquely from below. The eardrum is somewhat funnel-shaped with a 135-degree opening with the tip inward. It is smooth and semi-transparent so that the malleus and incus are slightly visible.
Next pages in section 1
1.3 The middle ear
1.4 The inner ear
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