1. Ear Ossicles The tympanic cavity contains three small bones: the malleus, incus, and stapes The tympanic cavity contains three small bones: the malleus, incus, and stapes Transmit vibratory motion of the eardrum to the oval window Transmit vibratory motion of the eardrum to the oval window Dampened by the tensor tympani and stapedius muscles Dampened by the tensor tympani and stapedius muscles

2. Ear Ossicles Figure 15.26

3. Inner Ear Bony labyrinth Bony labyrinth Tortuous channels worming their way through the temporal bone Tortuous channels worming their way through the temporal bone Contains the vestibule, the cochlea, and the semicircular canals Contains the vestibule, the cochlea, and the semicircular canals Filled with perilymph Filled with perilymph Membranous labyrinth Membranous labyrinth Series of membranous sacs within the bony labyrinth Series of membranous sacs within the bony labyrinth Filled with a potassium-rich fluid Filled with a potassium-rich fluid

4. Inner Ear Figure 15.27

5. The Vestibule The central egg-shaped cavity of the bony labyrinth The central egg-shaped cavity of the bony labyrinth Suspended in its perilymph are two sacs: the saccule and utricle Suspended in its perilymph are two sacs: the saccule and utricle The saccule extends into the cochlea The saccule extends into the cochlea

6. The Vestibule The utricle extends into the semicircular canals The utricle extends into the semicircular canals These sacs: These sacs: House equilibrium receptors called maculae House equilibrium receptors called maculae Respond to gravity and changes in the position of the head Respond to gravity and changes in the position of the head

7. The Vestibule Figure 15.27

8. The Semicircular Canals Three canals that each define two-thirds of a circle and lie in the three planes of space Three canals that each define two-thirds of a circle and lie in the three planes of space Membranous semicircular ducts line each canal and communicate with the utricle Membranous semicircular ducts line each canal and communicate with the utricle The ampulla is the swollen end of each canal and it houses equilibrium receptors in a region called the crista ampullaris The ampulla is the swollen end of each canal and it houses equilibrium receptors in a region called the crista ampullaris These receptors respond to angular movements of the head These receptors respond to angular movements of the head

9. The Semicircular Canals Figure 15.27

10. The Cochlea A spiral, conical, bony chamber that: A spiral, conical, bony chamber that: Extends from the anterior vestibule Extends from the anterior vestibule Coils around a bony pillar called the modiolus Coils around a bony pillar called the modiolus Contains the cochlear duct, which ends at the cochlear apex Contains the cochlear duct, which ends at the cochlear apex Contains the organ of Corti (hearing receptor) Contains the organ of Corti (hearing receptor)

11. The Cochlea The cochlea is divided into three chambers: The cochlea is divided into three chambers: Scala vestibuli Scala vestibuli Scala media Scala media Scala tympani Scala tympani

12. The Cochlea The scala tympani terminates at the round window The scala tympani terminates at the round window The scalas tympani and vestibuli: The scalas tympani and vestibuli: Are filled with perilymph Are filled with perilymph Are continuous with each other via the helicotrema Are continuous with each other via the helicotrema The scala media is filled with endolymph The scala media is filled with endolymph

13. The Cochlea The “floor” of the cochlear duct is composed of: The “floor” of the cochlear duct is composed of: The bony spiral lamina The bony spiral lamina The basilar membrane, which supports the organ of Corti The basilar membrane, which supports the organ of Corti The cochlear branch of nerve VIII runs from the organ of Corti to the brain The cochlear branch of nerve VIII runs from the organ of Corti to the brain

14. The Cochlea Figure 15.28

15. Sound and Mechanisms of Hearing Sound vibrations beat against the eardrum Sound vibrations beat against the eardrum The eardrum pushes against the ossicles, which presses fluid in the inner ear against the oval and round windows The eardrum pushes against the ossicles, which presses fluid in the inner ear against the oval and round windows This movement sets up shearing forces that pull on hair cells This movement sets up shearing forces that pull on hair cells Moving hair cells stimulates the cochlear nerve that sends impulses to the brain Moving hair cells stimulates the cochlear nerve that sends impulses to the brain

16. Properties of Sound Sound is: Sound is: A pressure disturbance (alternating areas of high and low pressure) originating from a vibrating object A pressure disturbance (alternating areas of high and low pressure) originating from a vibrating object Composed of areas of rarefaction and compression Composed of areas of rarefaction and compression Represented by a sine wave in wavelength, frequency, and amplitude Represented by a sine wave in wavelength, frequency, and amplitude

17. Properties of Sound Frequency – the number of waves that pass a given point in a given time Frequency – the number of waves that pass a given point in a given time Pitch – perception of different frequencies (we hear from 20–20,000 Hz) Pitch – perception of different frequencies (we hear from 20–20,000 Hz)

18. Properties of Sound Amplitude – intensity of a sound measured in decibels (dB) Amplitude – intensity of a sound measured in decibels (dB) Loudness – subjective interpretation of sound intensity Loudness – subjective interpretation of sound intensity Figure 15.29

19. Transmission of Sound to the Inner Ear The route of sound to the inner ear follows this pathway: The route of sound to the inner ear follows this pathway: Outer ear – pinna, auditory canal, eardrum Outer ear – pinna, auditory canal, eardrum Middle ear – malleus, incus, and stapes to the oval window Middle ear – malleus, incus, and stapes to the oval window Inner ear – scalas vestibuli and tympani to the cochlear duct Inner ear – scalas vestibuli and tympani to the cochlear duct Stimulation of the organ of Corti Stimulation of the organ of Corti Generation of impulses in the cochlear nerve Generation of impulses in the cochlear nerve

20. Frequency and Amplitude Figure 15.30

21. Transmission of Sound to the Inner Ear Figure 15.31

22. Resonance of the Basilar Membrane Sound waves of low frequency (inaudible): Sound waves of low frequency (inaudible): Travel around the helicotrema Travel around the helicotrema Do not excite hair cells Do not excite hair cells Audible sound waves: Audible sound waves: Penetrate through the cochlear duct Penetrate through the cochlear duct Vibrate the basilar membrane Vibrate the basilar membrane Excite specific hair cells according to frequency of the sound Excite specific hair cells according to frequency of the sound

23. Resonance of the Basilar Membrane Figure 15.32

24. The Organ of Corti Is composed of supporting cells and outer and inner hair cells Is composed of supporting cells and outer and inner hair cells Afferent fibers of the cochlear nerve attach to the base of hair cells Afferent fibers of the cochlear nerve attach to the base of hair cells The stereocilia (hairs): The stereocilia (hairs): Protrude into the endolymph Protrude into the endolymph Touch the tectorial membrane Touch the tectorial membrane

25. Excitation of Hair Cells in the Organ of Corti Bending cilia: Bending cilia: Opens mechanically gated ion channels Opens mechanically gated ion channels Causes a graded potential and the release of a neurotransmitter (probably glutamate) Causes a graded potential and the release of a neurotransmitter (probably glutamate) The neurotransmitter causes cochlear fibers to transmit impulses to the brain, where sound is perceived The neurotransmitter causes cochlear fibers to transmit impulses to the brain, where sound is perceived

26. Excitation of Hair Cells in the Organ of Corti Figure 15.28c

27. Auditory Pathway to the Brain Impulses from the cochlea pass via the spiral ganglion to the cochlear nuclei Impulses from the cochlea pass via the spiral ganglion to the cochlear nuclei From there, impulses are sent to the: From there, impulses are sent to the: Superior olivary nucleus Superior olivary nucleus Inferior colliculus (auditory reflex center) Inferior colliculus (auditory reflex center) From there, impulses pass to the auditory cortex From there, impulses pass to the auditory cortex Auditory pathways decussate so that both cortices receive input from both ears Auditory pathways decussate so that both cortices receive input from both ears

28. Simplified Auditory Pathways Figure 15.34

29. Auditory Processing Pitch is perceived by: Pitch is perceived by: The primary auditory cortex The primary auditory cortex Cochlear nuclei Cochlear nuclei Loudness is perceived by: Loudness is perceived by: Varying thresholds of cochlear cells Varying thresholds of cochlear cells The number of cells stimulated The number of cells stimulated Localization is perceived by superior olivary nuclei that determine sound Localization is perceived by superior olivary nuclei that determine sound

30. Deafness Conduction deafness – something hampers sound conduction to the fluids of the inner ear (e.g., impacted earwax, perforated eardrum, osteosclerosis of the ossicles) Conduction deafness – something hampers sound conduction to the fluids of the inner ear (e.g., impacted earwax, perforated eardrum, osteosclerosis of the ossicles) Sensorineural deafness – results from damage to the neural structures at any point from the cochlear hair cells to the auditory cortical cells Sensorineural deafness – results from damage to the neural structures at any point from the cochlear hair cells to the auditory cortical cells

31. Deafness Tinnitus – ringing or clicking sound in the ears in the absence of auditory stimuli Tinnitus – ringing or clicking sound in the ears in the absence of auditory stimuli Meniere’s syndrome – labyrinth disorder that affects the cochlea and the semicircular canals, causing vertigo, nausea, and vomiting Meniere’s syndrome – labyrinth disorder that affects the cochlea and the semicircular canals, causing vertigo, nausea, and vomiting

32. Mechanisms of Equilibrium and Orientation Vestibular apparatus – equilibrium receptors in the semicircular canals and vestibule Vestibular apparatus – equilibrium receptors in the semicircular canals and vestibule Maintains our orientation and balance in space Maintains our orientation and balance in space Vestibular receptors monitor static equilibrium Vestibular receptors monitor static equilibrium Semicircular canal receptors monitor dynamic equilibrium Semicircular canal receptors monitor dynamic equilibrium

33. Anatomy of Maculae Maculae are the sensory receptors for static equilibrium Maculae are the sensory receptors for static equilibrium Contain supporting cells and hair cells Contain supporting cells and hair cells Each hair cell has stereocilia and kinocilium embedded in the otolithic membrane Each hair cell has stereocilia and kinocilium embedded in the otolithic membrane Otolithic membrane – jellylike mass studded with tiny CaCO 3 stones called otoliths Otolithic membrane – jellylike mass studded with tiny CaCO 3 stones called otoliths Utricular hairs respond to horizontal movement Utricular hairs respond to horizontal movement Saccular hairs respond to vertical movement Saccular hairs respond to vertical movement

34. Anatomy of Maculae Figure 15.35

35. Effect of Gravity on Utricular Receptor Cells Otolithic movement in the direction of the kinocilia: Otolithic movement in the direction of the kinocilia: Depolarizes vestibular nerve fibers Depolarizes vestibular nerve fibers Increases the number of action potentials generated Increases the number of action potentials generated Movement in the opposite direction: Movement in the opposite direction: Hyperpolarizes vestibular nerve fibers Hyperpolarizes vestibular nerve fibers Reduces the rate of impulse propagation Reduces the rate of impulse propagation From this information, the brain is informed of the changing position of the head From this information, the brain is informed of the changing position of the head

36. Effect of Gravity on Utricular Receptor Cells Figure 15.36

37. Crista Ampullaris and Dynamic Equilibrium The crista ampullaris (or crista): The crista ampullaris (or crista): Is the receptor for dynamic equilibrium Is the receptor for dynamic equilibrium Is located in the ampulla of each semicircular canal Is located in the ampulla of each semicircular canal Responds to angular movements Responds to angular movements Each crista has support cells and hair cells that extend into a gel-like mass called the cupula Each crista has support cells and hair cells that extend into a gel-like mass called the cupula Dendrites of vestibular nerve fibers encircle the base of the hair cells Dendrites of vestibular nerve fibers encircle the base of the hair cells

38. Activating Crista Ampullaris Receptors Cristae respond to changes in velocity of rotatory movements of the head Cristae respond to changes in velocity of rotatory movements of the head Directional bending of hair cells in the cristae causes: Directional bending of hair cells in the cristae causes: Depolarizations, and rapid impulses reach the brain at a faster rate Depolarizations, and rapid impulses reach the brain at a faster rate Hyperpolarizations, and fewer impulses reach the brain Hyperpolarizations, and fewer impulses reach the brain The result is that the brain is informed of rotational movements of the head The result is that the brain is informed of rotational movements of the head

39. Rotary Head Movement Figure 15.37d

40. Balance and Orientation Pathways There are three modes of input for balance and orientation There are three modes of input for balance and orientation Vestibular receptors Vestibular receptors Visual receptors Visual receptors Somatic receptors Somatic receptors These receptors allow our body to respond reflexively These receptors allow our body to respond reflexively Figure 15.38

41. Developmental Aspects All special senses are functional at birth All special senses are functional at birth Chemical senses – few problems occur until the fourth decade, when these senses begin to decline Chemical senses – few problems occur until the fourth decade, when these senses begin to decline Vision – optic vesicles protrude from the diencephalon during the fourth week of development Vision – optic vesicles protrude from the diencephalon during the fourth week of development These vesicles indent to form optic cups and their stalks form optic nerves These vesicles indent to form optic cups and their stalks form optic nerves Later, the lens forms from ectoderm Later, the lens forms from ectoderm

42. Developmental Aspects Vision is not fully functional at birth Vision is not fully functional at birth Babies are hyperopic, see only gray tones, and eye movements are uncoordinated Babies are hyperopic, see only gray tones, and eye movements are uncoordinated Depth perception and color vision is well developed by age five and emmetropic eyes are developed by year six Depth perception and color vision is well developed by age five and emmetropic eyes are developed by year six With age the lens loses clarity, dilator muscles are less efficient, and visual acuity is drastically decreased by age 70 With age the lens loses clarity, dilator muscles are less efficient, and visual acuity is drastically decreased by age 70

43. Developmental Aspects Ear development begins in the three-week embryo Ear development begins in the three-week embryo Inner ears develop from otic placodes, which invaginate into the otic pit and otic vesicle Inner ears develop from otic placodes, which invaginate into the otic pit and otic vesicle The otic vesicle becomes the membranous labyrinth, and the surrounding mesenchyme becomes the bony labyrinth The otic vesicle becomes the membranous labyrinth, and the surrounding mesenchyme becomes the bony labyrinth Middle ear structures develop from the pharyngeal pouches Middle ear structures develop from the pharyngeal pouches The branchial groove develops into outer ear structures The branchial groove develops into outer ear structures