The function of the inner ear is both the conversion of acoustic vibrations into neural impulses for hearing, as well as the detection and transmission of cranial movement for balance. The inner ear is comprised of the vestibular system and the cochlea, both of which have a bony and membranous portion. Pneumatic otoscopy can be used to grossly assess the mobility and compliance of the tympanic membrane if tympanometry is not available. A number of pathologies will result in an abnormal tympanogram, such as fluid within the middle ear or disruption of the ossicular chain. Tympanometry measures impedance to soundwave transmission through the middle ear. The compliance of the middle ear can be measured with tympanometry, which is not part of the standard ear physical examination. During the examination, certain parts of the middle ear can be viewed through the tympanic membrane: the lateral process of the malleus, the incudostapedial junction, and occasionally the cochlear promontory. The middle ear's primary function is to transmit acoustic waves from the tympanic membrane of the external ear to the oval window of the inner ear via the ossicles. The ossicles are termed the malleus, incus, and stapes (from lateral to medial). It is lined with respiratory epithelium, which is continuous with the lining of the Eustachian tube and the upper aerodigestive tract. It contains the three ossicles, the internal (medial) layer of the tympanic membrane, and the Eustachian tube orifice. This is a complex air-filled cavity found within the temporal bone of the skull. The entire external ear can be visualized directly during an ear examination. Incomplete fusion of these Hillocks can lead to the development of preauricular pits, cysts, or sinuses. Embryologically the pinna is formed by the fusion of six mesenchymal proliferations, known as hillocks of His, derivations of the first and second branchial arches. The external ear's function is the funneling of acoustic waves to the tympanic membrane and, therefore, the middle ear. The external ear is made up of the auricle (pinna), the external auditory meatus and canal, and the external (lateral) layer of the tympanic membrane. In general, abnormalities of the external and middle ears will produce conductive hearing loss, and inner ear abnormalities will produce sensorineural hearing loss. The interaction and anatomical proximity of the ear to the brain, skull-base, and cranial nerves must also be appreciated, as certain pathology may involve these structures. Knowledge of the anatomy of the external, middle, and inner ear systems is vital to enable clinicians to interpret what may be vague or misleading symptoms.
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