Exam 4 Review:  Chapter 15:  Spiral Organ of Corti

Cross-Section of the Cochlea and Spiral Organ of Corti:

cochlea - A spiral-shaped cavity of the inner ear that resembles a snail shell (it has 2 1/2 turns) and contains a specialized organ containing mechanoreceptors (hair cells) and nerve endings essential for hearing; a part of the membranous labyrinth anterior to the vestibule where sound vibrations are converted into special sensory nerve impulses by the spiral organ of Corti; these special sensory nerve impulses are transferred to the vestibulocochlear (eighth) cranial nerve.

modiolus - The central, conical, bony core of the cochlea; a part of the bony labyrinth.

cochlear duct = scala media - The middle of the three scalae of the membranous labyrinth of the inner ear; a spiral tube enclosed in the bony canal of the cochlea, which contains a plasma filtrate termed endolymph; bounded by the tectorial membrane and scala vestibuli above and by the basilar membrane and scale tympani below; harmonic vibrations in the endolymph stimulate the hair cells of the spiral organ of Corti for the transduction of sound.

spiral organ of Corti - The true organ of hearing, a spiral sensory structure within the cochlea containing hair cells (mechanoreceptors) which are stimulated indirectly by sound vibrations; the hair cells convert the vibrations created in the cochlear duct and basilar membrane into nerve impulses which are transmitted by the cochlear branch of the vestibulocochlear (eighth) cranial nerve to the primary sensory cortex for hearing in the temporal lobes of the brain; high notes are detected at the base and low notes are detected at the apex of the cochlea.

hair cells - Specialized mechanoreceptor cells with hairlike processes (stereocilia and kinocilia) found in the sensory epithelium of certain parts of the membranous labyrinth of the internal ear which convert vibrations of the basilar and tectorial membranes into nerve impulses which will be interpreted as sound.

spiral lamina - The thin spiral bony ledge, an extension of the modiolus, which serves as the medial support for the basilar membrane.

scala vestibuli - The superior compartment of the cochlea within the membranous labyrinth of the inner ear; containing perilymph; it leads from the oval window (point of attachment for the stapes/stirrup) to the apex of the spiral and the helicotrema which is the opening to the scala tympani.

scala tympani - The inferior compartment of the cochlea within the membranous labyrinth of the inner ear, containing perilymph; it extends from the apex of the cochlea and the helicotrema which is the opening from the scala vestibuli to a membrane-covered opening in the wall of the inner ear called the round window.

helicotrema - The opening by which the two scalae, vestibuli and tympani, connect at the top of the cochlea of the ear.

vestibular membrane - The two-squamous-cell-thick membrane that separates scala vestibuli (perilymph) from scala media (endolymph) in the cochlea within the membranous labyrinth of the inner ear; this tissue assists in the transmission of sound vibrations from the perilymph of the scala vestibuli to the endolymp of the scala media (cochlear duct) where the vibrations can stimulate the spiral organ.

basilar membrane - A thin, homogeneous layer of connective tissue covered on its surfaces above and below with a layer of epithelium; the spiral organ of Corti rests upon the basilar membrane; differences in the width and flexibility of this membrane determine where within the spiral organ of Corti the hair cells will be stimulated and this difference is a function of the frequency of the sound vibrations so that high notes are detected at the base and low notes are detected at the apex of the cochlea.

tectorial membrane - The acellular, gelatinous membrane covering the spiral organ of Corti and resting on the hairlike processes (stereocilia and kinocilia) of its hair cells and bathed in the endolymph of the scala media/cochlear duct within the membranous labyrinth of the inner ear.

cochlear nerve - The division of the vestibulocochlear (eighth) cranial nerve which conducts auditory sensory information from the spiral organ of Corti within the membranous labyrinth of the inner ear to the primary sensory cortex for hearing in the temporal lobes of the brain.

Animated Longitudinal Diagram of the Cochlea to Illustrate Perilymph Vibrations

Animated Cross-sectional Diagram of the Cochlear Duct to Illustrate Endolymph and Tectorial Membrane Vibrations

Sketch and Label:

4. a cross section of one turn (spiral) of the cochlea. Identify the chambers, membranes, cells, and fluids found in each part.

 

Use Part (b) below as your model for your sketch.  Label accordingly.