1. © 2014 Pearson Education, Inc. PowerPoint ® Lecture Presentations prepared by Leslie Hendon University of Alabama, Birmingham 16 PART 1 The Special Senses Pages 488-502, 506- 514

2. © 2014 Pearson Education, Inc. The Special Senses Taste, smell, sight, hearing, and balance Touch—a large group of general senses Special sensory receptors Localized—confined to the head region Receptors are not free endings of sensory neurons Special receptor cells Are neuronlike epithelial cells or small peripheral neurons Transfer sensory information to other neurons in afferent pathways

3. © 2014 Pearson Education, Inc. The Chemical Senses: Taste and Smell Taste—gustation Smell—olfaction Receptors—classified as chemoreceptors Respond to chemicals Food dissolved in saliva Airborne chemicals that dissolve in fluids of the nasal mucosa

4. © 2014 Pearson Education, Inc. Taste—Gustation Taste receptors Occur in taste buds Most are found on the surface of the tongue Located within tongue papillae Two types of papillae (with taste buds) Fungiform papillae Vallate papillae

5. © 2014 Pearson Education, Inc. Taste Buds Collection of 50–100 epithelial cells Contain two major cell types Gustatory epithelial cells supporting cells Basal epithelial cells gustatory cells Contain long microvilli—extend through a taste pore to the surface of the epithelium Cells in tastebuds replaced every 7–10 days

6. © 2014 Pearson Education, Inc. Taste Buds Figure 16.1 (a)Taste buds associated with fungiform and vallate papillae (b)Enlarged section of a vallate papilla Fungiform papillae Taste bud Vallate papilla Epiglottis Palatine tonsil Lingual tonsil Taste fibers of cranial nerve Connective tissue Gustatory epithelial cells Taste pore Gustatory hair Stratified squamous epithelium of tongue (c)Enlarged view of a taste bud (micrograph, 160 X ) Basal epithelial cells

7. © 2014 Pearson Education, Inc. Smell (Olfaction) Olfactory receptors are part of the olfactory epithelium Olfactory epithelium is pseudostratified columnar and contains three main cell types Olfactory sensory neurons Supporting epithelial cells Basal epithelial cells

8. © 2014 Pearson Education, Inc. Smell (Olfaction) Cell bodies of olfactory sensory neurons Located in olfactory epithelium Have an apical dendrite that projects to the epithelial surface Ends in a knob from which olfactory cilia radiate Olfactory cilia act as receptive structures for smell Mucus captures and dissolves odor molecules

9. © 2014 Pearson Education, Inc. Smell (Olfaction) Axons of olfactory epithelium Gather into bundles—filaments of the olfactory nerve Pass through the cribriform plate of the ethmoid bone Attach to the olfactory bulbs and synapse with mitral cells Mitral cells transmit impulses along the olfactory tract to 1.Limbic system 2.Piriform lobe of the cerebral cortex

10. © 2014 Pearson Education, Inc. Olfactory Receptors Figure 16.3 Mitral cell (output cell) Olfactory gland Olfactory tract Olfactory epithelium Filaments of olfactory nerve Cribriform plate of ethmoid bone Lamina propria connective tissue Basal cell Supporting cell Dendrite Olfactory cilia Olfactory bulb Glomeruli Axon Olfactory sensory neuron Mucus Route of inhaled air containing odor molecules Nasal conchae Route of inhaled air Olfactory epithelium Olfactory tract Olfactory bulb (a) (b)

11. © 2014 Pearson Education, Inc. The Eye and Vision Visual organ—the eye 70% of all sensory receptors are in the eyes 40% of the cerebral cortex is involved in processing visual information Anterior one-sixth of the eye’s surface is visible

12. © 2014 Pearson Education, Inc. Accessory Structures of the Eye Eyebrows—coarse hairs on the superciliary arches Eyelids (palpebrae)—separated by the palpebral fissure Meet at the medial and lateral angles (canthi) Lacrimal caruncle—reddish elevation at the medial canthus Tarsal plates—connective tissue within the eyelids Tarsal glands—modified sebaceous glands

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14. Accessory Structures of the Eye Conjunctiva— transparent mucous membrane Palpebral conjunctiva Bulbar conjunctiva Conjunctival sac Figure 16.4b (b) Lateral view; some structures shown in sagittal section Levator palpebrae superioris muscle Orbicularis oculi muscle Eyebrow Tarsal plate Palpebral conjunctiva Tarsal glands Cornea Palpebral fissure Eyelashes Bulbar conjunctiva Conjunctival sac Orbicularis oculi muscle

15. © 2014 Pearson Education, Inc. Accessory Structures of the Eye Lacrimal apparatus—keeps the surface of the eye moist Lacrimal gland— produces lacrimal fluid Lacrimal sac— fluid empties into nasal cavity Figure 16.5 Lacrimal gland Excretory ducts of lacrimal glands Lacrimal punctum Lacrimal canaliculus Nasolacrimal duct Inferior meatus of nasal cavity Nostril Lacrimal sac

16. © 2014 Pearson Education, Inc. Extrinsic Eye Muscles Six muscles that control movement of the eye Originate in the walls of the orbit Insert on outer surface of the eyeball Annular ring—origin of the four rectus muscles The six extrinsic eye muscles are Lateral rectus and medial rectus Superior rectus and inferior rectus Superior oblique and inferior oblique

17. © 2014 Pearson Education, Inc. Extrinsic Eye Muscles Figure 16.6a, b Inferior rectus muscle Common tendinous ring Inferior oblique muscle Superior oblique muscle Trochlea Superior oblique tendon Superior rectus muscle Lateral rectus muscle (a) Lateral view of the right eye(b) Anterior view of the right eye Trochlea Superior oblique Inferior rectus Inferior oblique Lateral rectus Superior rectus Medial rectus

18. © 2014 Pearson Education, Inc. Summary of Muscle Actions (c) Summary of muscle actions and innervating cranial nerves Lateral rectus Medial rectus Superior rectus Inferior rectus Inferior oblique Superior oblique Moves eye laterally Moves eye medially Elevates eye and turns it medially Depresses eye and turns it medially Elevates eye and turns it laterally Depresses eye and turns it laterally VI (abducens) III (oculomotor) IV (trochlear) MuscleActionControlling cranial nerve Figure 16.6c

19. © 2014 Pearson Education, Inc. Anatomy of the Eyeball Components of the eye Protect and support the photoreceptors Gather, focus, and process light into precise images Anterior pole—most anterior part of the eye Posterior pole—most posterior part of the eye External walls—composed of three tunics Internal cavity—contains fluids (humors)

20. © 2014 Pearson Education, Inc. The Fibrous Layer Most external layer of the eyeball Composed of two regions of connective tissue Sclera—posterior five-sixths of the tunic White, opaque region Provides shape and an anchor for eye muscles Cornea—anterior one-sixth of the fibrous tunic Epithelial stem cells Transparent Avascular but rich with nerve endings

21. © 2014 Pearson Education, Inc. Medial View of the Eye Figure 16.7a Ora serrata (a) Diagrammatic view. The vitreous humor is illustrated only in the bottom part of the eyeball. Ciliary body Ciliary zonule (suspensory ligament) Cornea Iris Anterior pole Pupil Anterior segment (contains aqueous humor) Lens Scleral venous sinus Posterior segment (contains vitreous humor) Optic nerve Posterior pole Fovea centralis Macula lutea Retina Choroid Sclera Central artery and vein of the retina Optic disc (blind spot)

22. © 2014 Pearson Education, Inc. Figure 16.7b Internal structure of the eye (sagittal section). Photograph of the human eye Vitreous humor in posterior segment Retina Choroid Sclera Fovea centralis Optic disc Optic nerve Ciliary zonule (suspensory ligament) Cornea Lens Anterior segment Margin of pupil Iris Ciliary processes Ciliary body

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24. The Vascular Layer The middle coat of the eyeball Composed of choroid, ciliary body, and iris Choroid—vascular, darkly pigmented membrane Forms posterior five-sixths of the vascular tunic Brown color—from melanocytes Prevents scattering of light rays within the eye Choroid corresponds to the arachnoid and pia maters

25. © 2014 Pearson Education, Inc. The Vascular Layer Ciliary body—thickened ring of tissue, which encircles the lens Composed of ciliary muscle & ciliary processes Ciliary processes—posterior surface of the ciliary body Ciliary zonule (suspensory ligament) Attached around entire circumference of the lens

26. © 2014 Pearson Education, Inc. The Vascular Layer Figure 16.7a Ora serrata (a) Diagrammatic view. The vitreous humor is illustrated only in the bottom part of the eyeball. Ciliary body Ciliary zonule (suspensory ligament) Cornea Iris Anterior pole Pupil Anterior segment (contains aqueous humor) Lens Scleral venous sinus Posterior segment (contains vitreous humor) Optic nerve Posterior pole Fovea centralis Macula lutea Retina Choroid Sclera Central artery and vein of the retina Optic disc (blind spot)

27. © 2014 Pearson Education, Inc. The Iris Visible colored part of the eye Attached to the ciliary body Composed of smooth muscle Pupil—the round, central opening Sphincter pupillae muscle Dilator pupillae muscle Act to vary the size of the pupil Pupillary light reflex Protective response of pupil constriction when a bright light is flashed in the eye

28. © 2014 Pearson Education, Inc. Figure 16.8 Pupil dilation and constriction, anterior view. Sphincter pupillae muscle contracts: Pupil size decreases. Iris (two muscles) Sphincter pupillae Dilator pupillae Dilator pupillae muscle contracts: Pupil size increases. Parasympathetic  Sympathetic 

29. © 2014 Pearson Education, Inc. The Inner Layer (Retina) Retina—the deepest tunic Composed of two layers Pigmented layer—single layer of melanocytes Neural layer—sheet of nervous tissue Contains three main types of neurons Photoreceptor cells Bipolar cells Ganglion cells

30. © 2014 Pearson Education, Inc. Posterior Aspect of the Eyeball Figure 16.9a (a) Posterior aspect of the eyeball Neural layer of retina Pigmented layer of retina Central artery and vein of retina Optic nerve Sclera Choroid Optic disc Pathway of light

31. © 2014 Pearson Education, Inc. Microscopic Anatomy of the Retina Figure 16.9b, c Pigmented layer of retina Pathway of light Pathway of signal output (b) Cells of the neural layer of the retina Amacrine cell Horizontal cell Rod Photoreceptors Cone Bipolar cells Ganglion cells Choroid Pigmented layer of retina Axons of ganglion cells Outer segments of rods and cones Nuclei of ganglion cells Nuclei of rods and cones Nuclei of bipolar cells (c) Photomicrograph of retina

32. © 2014 Pearson Education, Inc. The Inner Layer Photoreceptor cells signal bipolar cells Bipolar cells signal ganglion cells to generate nerve impulses Axons from ganglion cells run along internal surface of the retina Converge posteriorly to form the optic nerve

33. © 2014 Pearson Education, Inc. Photoreceptors Figure 16.10 Process of bipolar cell Outer fiber Apical microvillus Discs containing visual pigments Melanin granules Discs being phagocytized Pigment cell nucleus Inner fibers Rod cell body Cone cell body Synaptic terminals Rod cell body Nuclei Mitochondria Connecting cilia Basal lamina (border with choroid) Light Inner segment Outer segment Pigmented layer Two main types Rod cells—more sensitive to light Allow vision in dim light Cone cells—operate best in bright light Enable high-acuity, color vision Considered neurons

34. © 2014 Pearson Education, Inc. Photoreceptors Rods and cones have an inner and outer segment Outer segments are receptor regions Light absorbing pigments are present Light particles modify the visual pigment and generate a nerve impulse Vulnerable to damage by light or heat Cannot regenerate if destroyed Continuously renew and replace their outer segments

35. © 2014 Pearson Education, Inc. Regional Specializations of the Retina Ora serrata retinae Neural layer ends at the posterior margin of the ciliary body Pigmented layer covers ciliary body and posterior surface of the iris Macula lutea—contains mostly cones Fovea centralis—contains only cones Region of highest visual acuity Optic disc—blind spot

36. © 2014 Pearson Education, Inc. Medial View of the Eye Figure 16.7a Ora serrata (a) Diagrammatic view. The vitreous humor is illustrated only in the bottom part of the eyeball. Ciliary body Ciliary zonule (suspensory ligament) Cornea Iris Anterior pole Pupil Anterior segment (contains aqueous humor) Lens Scleral venous sinus Posterior segment (contains vitreous humor) Optic nerve Posterior pole Fovea centralis Macula lutea Retina Choroid Sclera Central artery and vein of the retina Optic disc (blind spot)

37. © 2014 Pearson Education, Inc. Figure 16.11 Blood Supply of the Retina Retina receives blood from two sources Outer third of the retina—supplied by capillaries in the choroid Inner two-thirds of the retina— supplied by central artery and vein of the retina Macula lutea Central artery and vein emerging from the optic disc Optic disc Retina

38. © 2014 Pearson Education, Inc. Internal Chambers and Fluids The lens and ciliary zonules divide the eye Posterior segment (cavity) Filled with vitreous humor Clear, jelly-like substance Transmits light Supports the posterior surface of the lens Helps maintain intraocular pressure

39. © 2014 Pearson Education, Inc. Internal Chambers and Fluids Anterior segment Divided into anterior and posterior chambers Anterior chamber—between the cornea and iris Posterior chamber—between the iris and lens Filled with aqueous humor Renewed continuously Formed as a blood filtrate Supplies nutrients to the lens and cornea

40. © 2014 Pearson Education, Inc. Internal Chambers and Fluids Figure 16.12 Aqueous humor is formed by filtration from the capillaries in the ciliary processes. Sclera Bulbar conjunctiva Scleral venous sinus Posterior chamber Anterior chamber Anterior segment (contains aqueous humor) Corneoscleral junction Cornea Corneal epithelium Corneal endothelium Aqueous humor Iris Lens Lens epithelium Lens Posterior segment (contains vitreous humor) Ciliary zonule (suspensory ligament) Ciliary processes Ciliary muscle Ciliary body Aqueous humor flows from the posterior chamber through the pupil into the anterior chamber. Some also flows through the vitreous humor (not shown). Aqueous humor is reabsorbed into the venous blood by the scleral venous sinus. 1 2 3 1 2 3

41. © 2014 Pearson Education, Inc. Vision The Lens A thick, transparent, biconvex disc Held in place by its ciliary zonule Lens epithelium—covers anterior surface of the lens Lens fibers form the bulk of the lens New lens fibers are continuously added Lens enlarges throughout life PLAY

42. © 2014 Pearson Education, Inc. The Eye as an Optical Device Structures in the eye bend light rays Light rays converge on the retina at a single focal point Light bending structures (refractory media) are The lens, cornea, and humors Accommodation—curvature of the lens is adjustable Allows for focusing on nearby objects

43. © 2014 Pearson Education, Inc. The Eye as an Optical Device Figure 16.13 Lens Inverted image Ciliary zonule Ciliary muscle Nearly parallel rays from distant object (a) Lens is flattened for distant vision. Sympathetic input relaxes the ciliary muscle, tightening the ciliary zonule, and flattening the lens. Sympathetic activation (b) Lens bulges for close vision. Parasympathetic input contracts the ciliary muscle, loosening the ciliary zonule, allowing the lens to bulge. Divergent rays from close object Inverted image Parasympathetic activation

44. © 2014 Pearson Education, Inc. The Ear: Hearing and Equilibrium The ear—receptor organ for hearing and equilibrium Composed of three main regions Outer ear—functions in hearing Middle ear—functions in hearing Internal ear—functions in both hearing and equilibrium

45. © 2014 Pearson Education, Inc. The Outer (External) Ear Composed of The auricle (pinna) Helps direct sounds External acoustic meatus Lined with skin Contains hairs, sebaceous glands, and ceruminous glands Tympanic membrane Forms the boundary between the external and middle ear

46. © 2014 Pearson Education, Inc. Structure of the Ear Figure 16.16a External acoustic meatus Auricle (pinna) (a) The three regions of the ear Helix Lobule Pharyngotympanic (auditory) tube Tympanic membrane External ear Middle ear Internal ear (labyrinth)

47. © 2014 Pearson Education, Inc. The Middle Ear Composed of The tympanic cavity A small, air-filled space Located within the petrous portion of the temporal bone Medial wall is penetrated by Oval window Round window Pharyngotympanic tube (auditory or eustachian tube) Links the middle ear and pharynx

48. © 2014 Pearson Education, Inc. Structures of the Middle Ear Figure 16.16b Pharyngotympanic (auditory) tube Auditory ossicles Entrance to mastoid antrum in the epitympanic recess Tympanic membrane Semicircular canals Cochlea Cochlear nerve Vestibular nerve Oval window (deep to stapes) Round window Incus (anvil) Malleus (hammer) Stapes (stirrup) (b) Middle and internal ear Vestibule

49. © 2014 Pearson Education, Inc. Pharyngotym- panic tube Tensor tympani muscle Tympanic membrane (medial view) Stapes Malleus View Superior Anterior Lateral IncusEpitympanic recess Stapedius muscle Figure 16.17 The Middle Ear Ear ossicles— smallest bones in the body Malleus—attaches to the eardrum Incus—between the malleus and stapes Stapes—vibrates against the oval window Tensor tympani and stapedius Two tiny skeletal muscles in the middle ear cavity

50. © 2014 Pearson Education, Inc. The Internal Ear Internal ear—also called the labyrinth Lies within the petrous portion of the temporal bone Bony labyrinth—a cavity consisting of three parts Semicircular canals Vestibule Cochlea

51. © 2014 Pearson Education, Inc. The Internal Ear Figure 16.16b Pharyngotympanic (auditory) tube Auditory ossicles Entrance to mastoid antrum in the epitympanic recess Tympanic membrane Semicircular canals Cochlea Cochlear nerve Vestibular nerve Oval window (deep to stapes) Round window Incus (anvil) Malleus (hammer) Stapes (stirrup) (b) Middle and internal ear Vestibule

52. © 2014 Pearson Education, Inc. The Internal Ear Membranous labyrinth Series of membrane-walled sacs and ducts Fit within the bony labyrinth Consists of three main parts Semicircular ducts Utricle and saccule Cochlear duct

53. © 2014 Pearson Education, Inc. The Internal Ear Membranous labyrinth (continued) Filled with a clear fluid—endolymph Confined to the membranous labyrinth Bony labyrinth is filled with perilymph Continuous with cerebrospinal fluid

54. © 2014 Pearson Education, Inc. The Internal Ear Figure 16.18 Anterior Semicircular ducts in semicircular canals Posterior Lateral Cristae ampullares in the membranous ampullae Utricle in vestibule Saccule in vestibule Stapes in oval window Temporal bone Facial nerve Vestibular nerve Superior vestibular ganglion Inferior vestibular ganglion Cochlear nerve Maculae Spiral organ (of Corti) Cochlear duct in cochlea Round window

55. © 2014 Pearson Education, Inc. The Cochlea A spiraling chamber in the bony labyrinth Coils around a pillar of bone—the modiolus Spiral lamina—a spiral of bone in the modiolus The cochlear nerve runs through the core of the modiolus

56. © 2014 Pearson Education, Inc. Figure 16.19 Anatomy of the cochlea. Helicotrema at apex Modiolus Cochlear nerve, division of the vestibulocochlear nerve (VIII) Spiral ganglion Osseous spiral lamina Vestibular membrane Cochlear duct (scala media) Vestibular membrane Tectorial membrane Stria vascularis Spiral organ Basilar membrane Osseous spiral lamina Spiral ganglion Cochlear duct ( scala media ; contains endolymph) Scala vestibuli (contains perilymph) Scala tympani (contains perilymph) Outer hair cells Tectorial membraneInner hair cell Basilar membrane Hairs (stereocilia) Supporting cells Afferent nerve fibers Fibers of cochlear nerve Inner hair cell Outer hair cell

57. © 2014 Pearson Education, Inc. The Cochlea Figure 16.19b, c (b) Cochlear duct (scala media; contains endolymph) Tectorial membrane Vestibular membrane Scala vestibuli (contains perilymph) Scala tympani (contains perilymph) Basilar membrane Spiral organ (of Corti) Stria vascularis Spiral ganglion Osseous spiral lamina (c) Tectorial membrane Inner hair cell Outer hair cells Hairs (stereocilia) Afferent nerve fibers Basilar membrane Fibers of cochlear nerve Supporting cells

58. © 2014 Pearson Education, Inc. The Cochlea The cochlear duct (scala media)—contains receptors for hearing Lies between two chambers The scala vestibuli The scala tympani The vestibular membrane—the roof of the cochlear duct The basilar membrane—the floor of the cochlear duct

59. © 2014 Pearson Education, Inc. The Cochlea The cochlear duct (scala media)—contains receptors for hearing Spiral organ (of Corti)—the receptor epithelium for hearing Consists of Supporting cells Inner and outer hair cells (receptor cells) Inner hair cells are the receptors that transmit vibrations of the basilar membrane Outer hair cells actively tune the cochlea and amplify the signal

60. © 2014 Pearson Education, Inc. Figure 16.19 Anatomy of the cochlea. Helicotrema at apex Modiolus Cochlear nerve, division of the vestibulocochlear nerve (VIII) Spiral ganglion Osseous spiral lamina Vestibular membrane Cochlear duct (scala media) Vestibular membrane Tectorial membrane Stria vascularis Spiral organ Basilar membrane Osseous spiral lamina Spiral ganglion Cochlear duct ( scala media ; contains endolymph) Scala vestibuli (contains perilymph) Scala tympani (contains perilymph) Outer hair cells Tectorial membraneInner hair cell Basilar membrane Hairs (stereocilia) Supporting cells Afferent nerve fibers Fibers of cochlear nerve Inner hair cell Outer hair cell

61. © 2014 Pearson Education, Inc. The Role of the Cochlea in Hearing Figure 16.20 Sound waves vibrate the tympanic membrane. MalleusIncus Auditory ossicles Stapes Oval window Scala vestibuli Helicotrema Cochlear nerve Scala tympani Cochlear duct Basilar membrane Round window Tympanic membrane Auditory ossicles vibrate. Pressure is amplified. Pressure waves created by the stapes pushing on the oval window move through fluid in the scala vestibuli. Sounds with frequencies below hearing travel through the helicotrema and do not excite hair cells. Sounds in the hearing range go through the cochlear duct, vibrating the basilar membrane and deflecting hairs on inner hair cells. 1 2 3 4a 4b 1 2 3 4a 4b

62. © 2014 Pearson Education, Inc. The Vestibule The central part of the bony labyrinth Lies medial to the middle ear Utricle and saccule—suspended in perilymph Two egg-shaped parts of the membranous labyrinth House the macula—a spot of sensory epithelium

63. © 2014 Pearson Education, Inc. The Vestibule Macula—contains receptor cells Monitor the position of the head when the head is still Contains columnar supporting cells Receptor cells—called hair cells Synapse with the vestibular nerve Tips of hair cells are embedded in otolithic membrane Contains crystals of calcium carbonate called otoliths

64. © 2014 Pearson Education, Inc. The Maculae in the Internal Ear Figure 16.21a Macula of saccule Otoliths Hair bundle Kinocilium Stereocilia Otolithic membrane Vestibular nerve fibers Hair cells Supporting cells (a) Macula of utricle

65. © 2014 Pearson Education, Inc. The Maculae in the Internal Ear Figure 16.21b (b) Head uprightHead tilted Hair cell Otoliths Otolithic membrane Force of gravity

66. © 2014 Pearson Education, Inc. The Semicircular Canals Lie posterior and lateral to the vestibule Anterior and posterior semicircular canals Lie in the vertical plane at right angles Lateral semicircular canal Lies in the horizontal plane

67. © 2014 Pearson Education, Inc. The Semicircular Canals Figure 16.18 Anterior Semicircular ducts in semicircular canals Posterior Lateral Cristae ampullares in the membranous ampullae Utricle in vestibule Saccule in vestibule Stapes in oval window Temporal bone Facial nerve Vestibular nerve Superior vestibular ganglion Inferior vestibular ganglion Cochlear nerve Maculae Spiral organ (of Corti) Cochlear duct in cochlea Round window

68. © 2014 Pearson Education, Inc. The Semicircular Canals Semicircular duct—snakes through each semicircular canal Membranous ampulla—located within bony ampulla Houses a structure called a crista ampullaris Cristae contain receptor cells of rotational acceleration Epithelium contains supporting cells and receptor hair cells

69. © 2014 Pearson Education, Inc. Structure and Function of the Crista Ampullaris Figure 16.22a, b Fibers of vestibular nerve Hair bundle (kinocilium plus stereocilia) Hair cell Supporting cell Membranous labyrinth Crista ampullaris Crista ampullaris Endolymph Cupula (a) Anatomy of a crista ampullaris in a semicircular canal (b) Scanning electron micrograph of a crista ampullaris (45X)

70. © 2014 Pearson Education, Inc. Figure 16.22c Structure and Function of the Crista Ampullaris Fibers of vestibular nerve At rest, the cupula stands upright. Section of ampulla, filled with endolymph (c) Movement of the cupula during rotational acceleration and deceleration CupulaFlow of endolymph During rotational acceleration, endolymph moves inside the semicircular canals in the direction opposite the rotation (it lags behind because of inertia). Endolymph flow bends the cupula and excites the hair cells. As rotational movement slows, endolymph keeps moving in the direction of the rotation, bending the cupula in the opposite direction from acceleration and inhibiting the hair cells.