And Auditory Canal

ry organ of sound reception, the organ of Corti. Waves of vibration are conveyed from the perilymph to the walls of the scala media, from which, through the en-dolymph, they affect the sensory cells of the organ of Corti.

The cochlear duct communicates with the vestibular endolymph-containing sacs through two fine canals so that the endolymphatic system of the cochlea and vestibule is continuous, like the perilymphatic one. Gravitational acceleration of the head is detected in a sensory organ arranged within endolymph-con-taining sacs in the vestibule (the utricle and saccule), and angular acceleration is detected within tubes emanating in three dimensions from the utricle (lateral, posterior and superior semicircular canals). The sensory cells are located as a thickened portion of epithelium, the macula, in the saccule and utricle and a raised prominence of epithelium, the crista, in expansions of each semicircular canal, the ampullae. The vestibular aqueduct contains the endolymphatic duct and sac, which constitute a blind offshoot of the endolymphatic system, probably functioning to absorb endolymph. The cochlear aqueduct is a communication between the cerebrospinal fluid in the subarachnoid space to the perilymph of the scala tympani near the round window. Cochlea, vestibule and semicircular canals are surrounded by very dense bone, the otic capsule.

The cochlear and vestibular sensory structures are supplied by a double nerve, the audiovestibular nerve or eighth cranial nerve, which enters the temporal bone through the internal auditory meatus. The facial nerve or seventh cranial nerve, enters the temporal bone through the same canal, and after a right-angled bend in the genu, where the geniculate ganglion is located, reaches the posterior wall of the middle ear, from which it passes down through the mastoid to emerge in the region of the parotid salivary gland, after which it provides motor nerve supply for the muscles of the face.

The ear and temporal bone are composed of many different tissues, the normal histology of which is best considered when describing the pathologic appearances of these parts.

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