Human Anatomy & Physiology I Special Senses Human Anatomy & Physiology I Dr. Rivera

Anatomy of the Ear

Anatomy of Cochlea cochlea has three fluid-filled chambers separated by membranes: scala vestibuli – superior chamber filled with perilymph begins at oval window and spirals to apex scala tympani – inferior chamber begins at apex and ends at round window secondary tympanic membrane – membrane covering round window scala media (cochlear duct) – triangular middle chamber filled with endolymph separated from: scala vestibuli by vestibular membrane scala tympani by thicker basilar membrane contains spiral organ - organ of Corti - acoustic organ – converts vibrations into nerve impulses

Cochlea, and Spiral Organ Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Oval window Figure 16.13 Vestibular membrane Cochlear duct (scala media) Spiral ganglion Cochlear nerve (a) Scala vestibuli (with perilymph) Vestibular membrane Tectorial membrane Cochlear duct (with endolymph) Hairs (stereocilia) Scala tympani (with perilymph) Outer hair cells Supporting cells Tectorial membrane Basilar membrane Spiral organ Inner hair cell Basilar membrane Fibers of cochlear nerve (b) (c) 4

Spiral Organ (Organ of Corti) The spiral organ has epithelium composed of hair cells and supporting cells The hair cells have long, stiff microvilli called stereocilia on apical surface gelatinous tectorial membrane rests on top of stereocilia

Organ of Corti Inner Ear 16-6 6

Physiology of Hearing The auricle directs sound wanes into the external auditory canal. When sound waves strike the eardrum, the alternating high and low pressure of the air causes the eardrum to vibrate back and forth. The eardrum vibrates slowly in response to low-pitched sounds and rapidly in response to high-pitched sounds.

Physiology of Hearing 3. The central area of the eardrum connects with to the ossicles. The vibration is transmitted from the malleus to the incus and then to the stapes. 4. As the stapes moves back an forth, it pushes the membrane of the oval window in and out.

Physiology of Hearing 5. The oval window vibrates about 20 times more vigorously than the eardrum (because the ossicles are very efficient at transmitting the vibrations). 6. The movement of the oval window sets up fluid pressure waves in the perilymph. As the oval window bulges inward, it pushes on the perilymph of the scala vestibuli. 7. Pressure waves are trasmitted from the scala vestibuli to the scala tympani and eventually to the round window, causing it to bulge outward into the middle ear.

Physiology of Hearing 8. As the pressure wave deform the walls of the scala vestibuli and tympanic, they also push the vestibular membrane back and forth, creating pressure waves in the endolymph inside the cochlear duct.

Physiology of Hearing 9. The pressure wave in the endolymph cause the basilar membrane to vibrate, which moves the hair cells of the spiral organ against the tectorial membrane. 10. Bending of the stereocilia produces receptor potentials that ultimately lead to the generation of nerve impulses.

Potassium Gates Figure 16.16 16-12 12 Unstimulated Stimulated Tip link Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Unstimulated Stimulated Tip link Mechanically gated K+ channel Stereocilia K+ Surface of hair cell K+ K+ gate closed K+ gate open Figure 16.16 16-12 12

Equilibrium Equilibrium – coordination, balance, and orientation in three-dimensional space Static equilibrium – the perception of the orientation of the head when the body is stationary Dynamic equilibrium - perception of motion or acceleration linear acceleration - change in velocity in a straight line (elevator) angular acceleration - change in rate of rotation (car turns a corner)

Anatomy of the Eye

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