Human Cochlea

Buried deep in the petrous part of the
temporal bone lies the hearing organ, the cochlea. It’s central axis is horizontally oriented
in relation to the axis of the skull The shell shaped part of the internal ear
the cochlea lies antero-medial to the semicircular canals
and vestibule. About 35 millimeters in length, when straightened the human cochlea spirals two-and-a-half times around its central bony modulus
starting with a wide nasal coil and tapering to a tighter apical coil. A bony shelf called the osseous spiral lamina coils around the modulus
like the threads of a corkscrew projecting outwards towards
the outer wall of the cochlea. The bone of the osseous spiral lamina,
like that of the modulus, is porous allowing nerve fibers
and blood vessels to travel within. The spiro modular artery and vein travel
on the modulus and follow the spiral of the chochlea. Arterial sprint off from the spiral modeler artery forming capillary beds and the osseous spiral lamina
and the osseous spiral lamina Radiating arterioles extend laterally
within the bony partition to form a capillary bed in
the lateral wall of the cochlea. Radiating venules which empty into the spiral modular vein drain these capillary beds the cochlea consists of the membranous labyrinth of our scale and medea suspended from the osseous spiral lamina within the bony labyrinth the scale and Medea divides the bony labyrinth into two fluid filled compartments the apical scale of vestibuli and basal Scylla symphony the scale of Medea contains the organ of Corti which is responsible for transmitting sound impulses to fibers of the cochlear nerve enclosing its own unique fluid called endolymph the scale and Medea consists of a roof called reissner’s membrane a lateral wall and a floor called the basilar membrane the basilar membrane supports the sensory structure of the cochlea the organ of Corti which consists of sensory cells support cells and the gelatinous tectorial membrane the apical surface of the hair cells and their support cells fit tightly together forming the reticular lamina the inner hair cells are closer to the modulus and line up in a single continuous row following the spiral of the cochlea the stereocilia on their epical surface form an almost continuous wall located further from the modulus the outer hair cells outnumber the inner hair cells four to one there stereocilia are arranged in a V or W formation surrounding the hair cells a variety of cells such as inner and outer pillar cells and phalangeal cells offer structural support the pillar cells also form the walls of the tunnel of Corti inner hair cells receive sensory nerve fibers from the cochlear nerve some sensory nerve fibers cross the floor the tunnel of Corti and contact 6 to 100 outer hair cells usually in the same row however outer hair cells primarily receive modern nerve fibers which cross the tunnel of Corti edna level and synapse with the base of an outer hair cell this arrangement of the components of the organ of Corti changes from the base of the cochlea to the apex at the base of the cochlea where higher frequencies of sound are sonst there are 3 rows of outer hair cells this increases to 4 or 5 rows of the apex where lower frequencies are sensed Sal and stereocilia length also increases of the apex causing a more severe angle in the epical surface of the organ of Corti from its interior composition to its outer spiral shape the design of the cochlea accounts for the ability of the human ear to distinguish between many different frequencies and provides us with the gift of hearing you

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