1 Hole’s Human Anatomy and Physiology Twelfth Edition Shier  Butler  Lewis Chapter 12 Nervous System III: Senses Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2 Sense of Hearing Ear Organ of hearing Three (3) sections: External ear Middle ear Inner ear

3 External Ear Auricle Collects sounds waves External auditory meatus Lined with ceruminous glands Carries sound to tympanic membrane Terminates with tympanic membrane Tympanic membrane Vibrates in response to sound waves Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Round window Pharynx Auditory tube Auricle Oval window (under stapes) Cochlea Malleus Incus Stapes External acoustic meatus Semicircular canals Vestibulocochlear nerve Tympanic cavity Tympanic membrane

4 Middle Ear Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Round window Pharynx Auditory tube Auricle Oval window (under stapes) Cochlea Malleus Incus Stapes External acoustic meatus Semicircular canals Vestibulocochlear nerve Tympanic cavity Tympanic membrane Tympanic cavity Air-filled space in temporal bone Auditory ossicles Vibrate in response to tympanic membrane Malleus, incus and stapes Hammer, anvil and stirrup Oval window Opening in wall of tympanic cavity Stapes vibrates against it to move fluids in inner ear

5 Auditory Tube Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Round window Pharynx Auditory tube Auricle Oval window (under stapes) Cochlea Malleus Incus Stapes External acoustic meatus Semicircular canals Vestibulocochlear nerve Tympanic cavity Tympanic membrane Also known as the Eustachian tube Connects middle ear to throat Helps maintain equal pressure on both sides of tympanic membrane Usually closed by valve- like flaps in throat

Inner Ear Complex system of labyrinths Osseous labyrinth Bony canal in temporal bone Filled with perilymph Membranous labyrinth Tube within osseous labyrinth Filled with endolymph Cochlear nerve Maculae Utricle (a) Cochlea Saccule Ampullae Endolymph Perilymph Membranous labyrinth Bony labyrinth Vestibular nerve Scala vestibuli (cut) Scala tympani (cut) Cochlear duct (cut) containing endolymph VestibuleOval window Round window Semicircular canals Bony labyrinth (contains perilymph) Membranous labyrinth (contains endolymph) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6

Inner Ear Cochlear nerve Maculae Utricle (a) Cochlea Saccule Ampullae Endolymph Perilymph Membranous labyrinth Bony labyrinth Vestibular nerve Scala vestibuli (cut) Scala tympani (cut) Cochlear duct (cut) containing endolymph VestibuleOval window Round window Semicircular canals Bony labyrinth (contains perilymph) Membranous labyrinth (contains endolymph) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7 Three (3) parts of labyrinths: Cochlea Functions in hearing Semicircular canals Functions in equilibrium Vestibule Functions in equilibrium

8 Cochlea Scala vestibuli Upper compartment Leads from oval window to apex of spiral Part of bony labyrinth Scala tympani Lower compartment Extends from apex of the cochlea to round window Part of bony labyrinth Stapes vibrating in oval window Scala vestibuli filled with perilymph Vestibular membrane Basilar membrane Scala tympani filled with perilymph Round window Helicotrema Membranous labyrinth Cochlear duct filled with endolymph Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

9 Cochlea Cochlear duct Portion of membranous labyrinth in cochlea Vestibular membrane Separates cochlear duct from scala vestibuli Basilar membrane Separates cochlear duct from scala tympani Spiral organ (organ of Corti) Basilar membrane (a) Scala vestibuli (contains perilymph) Vestibular membrane Cochlear duct (contains endolymph) Scala tympani (contains perilymph) Branch of cochlear nerve Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Clinical Application Getting a Cochlear Implant

11 Organ of Corti Group of hearing receptor cells (hair cells) On upper surface of basilar membrane Different frequencies of vibration move different parts of basilar membrane Particular sound frequencies cause hairs of receptor cells to bend Nerve impulse generated Spiral organ (organ of Corti) Hair cells Basilar membrane (a) (b) Scala vestibuli (contains perilymph) Cochlear duct (contains endolymph) Scala tympani (contains perilymph) Branch of cochlear nerve Tectorial membrane Basilar membrane Supporting cells Nerve fibers Branch of cochlear nerve Vestibular membrane Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

12 Organ of Corti Cochlear duct Scala tympaniHair cells (a) (b) Basilar membrane Tectorial membrane Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a: © John D. Cunningham/Visuals Unlimited; b: © Fred Hossler/Visuals Unlimited

13 Auditory Nerve Pathways Midbrain Pons Thalamus Auditory cortex (temporal lobe) Medial geniculate body of thalamus Superior olivary nucleus Medulla oblongata Vestibulocochlear nerve Cochlear nuclei Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Clinical Application Hearing Loss

15 Summary of the Generation of Sensory Impulses from the Ear

16 Sense of Equilibrium Static equilibrium Vestibule Senses position of head when body is not moving Dynamic Equilibrium Semicircular canals Senses rotation and movement of head and body

17 Vestibule Utricle Communicates with saccule and membranous portion of semicircular canals Saccule Communicates with cochlear duct Macula Hair cells of utricle and saccule Saccule Utricle Cochlea Maculae Ampullae of semicircular canals Vestibulocochlear nerve Cochlear duct Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Vestibule

Macula Responds to changes in head position Bending of hairs results in generation of nerve impulse Hair cells Sensory (afferent) nerve fiber Supporting cells Otoliths (a) Head upright(b) Head bent forward Macula of utricle Hairs of hair cells bend Gelatinous material sags Gravitational force Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18

19 Semicircular Canals Three (3) canals at right angles Ampulla Swelling of membranous labyrinth that communicates with the vestibule Crista ampullaris Sensory organ of ampulla Hair cells and supporting cells Rapid turns of head or body stimulate hair cells Saccule Utricle Cochlea Maculae Ampullae of semicircular canals Vestibulocochlear nerve Cochlear duct Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Vestibule

20 Crista Ampullaris Hair cell Supporting cells Sensory (afferent) nerve fibers Hairs Cupula Crista ampullaris (a) Head in still position (b) Head rotating Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (c) Crista ampullaris Semicircular canal Endolymph Ampulla Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.