1. Chapter 17: The Special Senses
Copyright 2009, John Wiley & Sons, Inc.

2. Comparison of General and Special Senses
General Senses
Special Senses
Include somatic sensations (tactile, thermal, pain, and proprioceptive) and visceral sensations.
Scattered throughout the body.
Simple structures.
Include smell, taste, vision, hearing and equilibrium.
Concentrated in specific locations in the head.
Anatomically distinct structures.
Complex neural pathway.
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3. Olfaction: Sense of Smell
Olfactory epithelium contains million receptors.
Olfactory receptor- a bipolar neuron with cilia called olfactory hairs.
- Respond to chemical stimulation of an odorant molecule.
Supporting cells- provide support and nourishment.
Basal cells- replace olfactory receptors.
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4. Olfactory Epithelium and Olfactory Receptors
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5. Olfactory Epithelium and Olfactory Receptors continued…
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6. Physiology of Olfaction
Can detect about 10,000 different odors.
Odorant binds to the receptor of an olfactory hair→ G-protein activation→ activation of adenylate cyclase→ production of cAMP→ opening of Na+ channels→ inflow of Na+ →generator potential→ nerve impulse through olfactory nerves→ olfactory bulbs→ olfactory tract→ primary olfactory area of the cerebral cortex.
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7. Olfactory transduction
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8. Gustation: Sense of Taste
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9. Anatomy of Taste Buds and Papillae
Taste bud- made of three types of epithelial cells: supporting cells, gustatory receptor cells and basal cells.
About 50 gustatory cells per taste bud. Each one has a gustatory hair that projects through the taste pore.
Taste buds are found in the papillae.
Three types of papillae: vallate (circumvallate), fungiform and foliate.
Copyright 2009, John Wiley & Sons, Inc.

10. Physiology of Gustation
Five types of taste: sour, sweet, bitter, salty and umami.
Tastant dissolves in saliva → plasma membrane of gustatory hair→ receptor potential→ nerve impulse via cranial nerves VII, IX and X→ medulla→ thalamus→ primary gustatory area of the cerebral cortex.
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11. Gustatory Pathway

12. Copyright 2009, John Wiley & Sons, Inc.
Vision or Sight
Visible light: nm.
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13. Accessory Structures of the Eye
Eyelids or palpebrae-
Eyelashes and eyebrows-
Extrinsic eye muscles-
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14. Accessory Structures of the Eye

15. The Lacrimal Apparatus
Tears from the lacrimal apparatus- lacrimal glands→ excretory lacrimal ducts→ lacrimal puncta→ lacrimal canals→ nasolacrimal sac→ nasolacrimal duct.
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16. Copyright 2009, John Wiley & Sons, Inc.
Anatomy of the Eyeball
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17. Copyright 2009, John Wiley & Sons, Inc.
Wall of the Eyeball
Three layers:
Fibrous tunic- outer layer
Sclera “white” of the eye
Cornea-transparent coat
Vascular tunic or uvea- middle layer
Choroid
Ciliary body consists of ciliary processes and ciliary muscle
Iris
Retina- inner layer
Optic disc
Macula lutea- fovea centralis
Copyright 2009, John Wiley & Sons, Inc.

18. Responses of the Pupil to Light
Pupil is an opening in the center of the iris.
Contraction of the circular muscles of the iris causes constriction of the pupil.
Contraction of the radial muscles causes dilation of the pupil.
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19. Interior of the Eyeball
Lens-
lack blood vessels, consists of a capsule with proteins (crystallins) in layers; transparent.
Lens divides the eyeball into two cavities: anterior and posterior.
Anterior cavity- further divided into anterior and posterior chambers. Both are filled with aqueous humor.
Posterior cavity (vitreous chamber)-filled with vitreous body.
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20. Cavities of the Eyeball
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21. Refraction of Light Rays
Refraction is the bending of light rays.
The cornea and lens refract light rays.
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22. Accommodation and the Near Point of Vision
Increase in the curvature of the lens for near vision is called accommodation.
Near point of vision is the minimum distance from the eye that an object can be clearly focused.
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23. Refraction Abnormalities and their Correction
Nearsightedness (myopia)- close objects seen clearly. Image is focused in front of the retina. Correction- use of concave lens.
Farsightedness (hyperopia)- distant objects seen clearly. Image is focused behind the retina. Correction- use of convex lens.
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25. Copyright 2009, John Wiley & Sons, Inc.
Rods and Cones
Named after the shapes of their outer segments.
Rod-
Cones- three types: red, green and blue.
Outer segment- contains photopigments. Transduction of light energy into receptor potential occurs here.
Inner segment- contains the nucleus, Golgi complex and mitochondria.
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26. Structure of Rod and Cone Photoreceptors
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27. Copyright 2009, John Wiley & Sons, Inc.
Photopigments
Two parts: opsin (four types, three in the cones and one in the rod) and retinal (light absorbing part).
Rhodopsin- photopigment in rods.
Cone photopigments- three types.
Absorption of light by a photopigment → structural changes.
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28. Bleaching and Regeneration of Photopigment
Copyright 2009, John Wiley & Sons, Inc.

29. Rod disc in outer segment
Colorless products
Disc
membrane
cis-
retinal
opsin
Cis-retinal
binds to opsin
(regeneration)
Isomerization
of retinal
Light
trans-
Retinal
isomerase
converts trans-
to cis-retinal
Trans-retinal
separates
from opsin
(bleaching)
Rhodopsin
molecule
Colored
photopigment
(rhodopsin) 1 2 3 4
Rod disc in outer segment
Colorless products
Disc
membrane
cis-
retinal
opsin
Isomerization
of retinal
Light
trans-
Retinal
isomerase
converts trans-
to cis-retinal
Trans-retinal
separates
from opsin
(bleaching)
Rhodopsin
molecule
Colored
photopigment
(rhodopsin) 1 2 3
Rod disc in outer segment
Disc
membrane
cis-
retinal
opsin
Isomerization
of retinal
Light
trans-
Trans-retinal
separates
from opsin
(bleaching)
Rhodopsin
molecule
Colored
photopigment
(rhodopsin) 1 2
Rod disc in outer segment
Disc
membrane
cis-
retinal
opsin
Isomerization
of retinal
Light
Rhodopsin
molecule
Colored
photopigment
(rhodopsin) 1

30. Bleaching and Regeneration of Photopigment
Isomerization: In darkness, retinal has a bent shape called cis-retinal. Absorption of photon causes straightening of the retinal (trans-retinal).
Bleaching: trans-retinal separates from opsin.
Regeneration: trans-retinal→ cis-retinal.
Copyright 2009, John Wiley & Sons, Inc.

31. Light and Dark Adaptation
Light adaptation: Dark → light. Faster.
Dark adaptation: Light →dark. Slow.
Cones regenerate rapidly whereas rhodopsin regenerates more slowly.
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32. Operation of Rod Photoreceptors
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33. Color Blindness and Night Blindness
Color blindness- inherited inability to distinguish between certain colors.
Result from the absence of one of the three types of cones.
Most common type: red-green color blindness.
Night blindness or Nyctalopia- vitamin A deficiency.
Copyright 2009, John Wiley & Sons, Inc.

34. Processing of Visual Input
Receptor potential in rods and cones→ graded potentials in bipolar neurons and horizontal cells→ nerve impulses in ganglion cells→ optic nerve→ optic chiasm→ optic tract→ thalamus→ primary visual area of cerebral cortex in occipital lobe.
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35. Copyright 2009, John Wiley & Sons, Inc.
Visual Pathway
Copyright 2009, John Wiley & Sons, Inc.

36. 1 2 4 5 3 1 2 3 4 5 6 1 2 4 3 1 2 3 1 2 1 Visual field of left eye
Temporal
half
right eye
Nasal
Midbrain
Left eye
retina
Optic
radiations
Left eye and its pathways
tract
Primary visual area of cerebral
cortex (area 17) in occipital lobe
Lateral geniculate nucleus
of the thalamus
Right eye
Right eye and its pathways
Nasal retina 1 2 4 5 3
Visual field of
left eye
Temporal
half
right eye
Nasal
Midbrain
Left eye
retina
Optic
radiations
Left eye and its pathways
tract
Primary visual area of cerebral
cortex (area 17) in occipital lobe
Lateral geniculate nucleus
of the thalamus
Right eye
Right eye and its pathways
Nasal retina 1 2 3 4 5 6
Visual field of
left eye
Temporal
half
right eye
Nasal
Midbrain
Left eye
retina
Optic
radiations
Left eye and its pathways
tract
Primary visual area of cerebral
cortex (area 17) in occipital lobe
Lateral geniculate nucleus
of the thalamus
Right eye
Right eye and its pathways
Nasal retina 1 2 4 3
Visual field of
left eye
Temporal
half
right eye
Nasal
Midbrain
Left eye
retina
Optic
radiations
Left eye and its pathways
Primary visual area of cerebral
cortex (area 17) in occipital lobe
Lateral geniculate nucleus
of the thalamus
Right eye
Right eye and its pathways
Nasal retina 1 2 3
Visual field of
left eye
Temporal
half
right eye
Nasal
Midbrain
Left eye
retina
Optic
radiations
Left eye and its pathways
Primary visual area of cerebral
cortex (area 17) in occipital lobe
Lateral geniculate nucleus
of the thalamus
Right eye
Right eye and its pathways
Nasal retina 1 2
Visual field of
left eye
Temporal
half
right eye
Nasal
Midbrain
Left eye
retina
Optic
radiations
Left eye and its pathways
Primary visual area of cerebral
cortex (area 17) in occipital lobe
Lateral geniculate nucleus
of the thalamus
Right eye
Right eye and its pathways
Nasal retina 1

37. Copyright 2009, John Wiley & Sons, Inc.
Anatomy of the Ear
Three main regions:
External (outer) ear- auricle or pinna, external auditory canal, and tympanic membrane.
Ceruminous glands-
Middle ear- auditory ossicles: malleus, incus and stapes.
Auditory (eustachian) tube.
Internal (inner) ear- Labyrinth: bony and membranous. Bony labyrinth- perilymph and membranous labyrinth- endolymph. Oval window and round window- membranous regions.
Copyright 2009, John Wiley & Sons, Inc.

38. Copyright 2009, John Wiley & Sons, Inc.
Anatomy of the Ear
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39. The Middle Ear and the Auditory Ossicles
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40. Copyright 2009, John Wiley & Sons, Inc.
The Internal Ear
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41. Copyright 2009, John Wiley & Sons, Inc.
The Internal Ear
Three parts: the semicircular canals, the vestibule (both contain receptors for equilibrium) and the cochlea (contains receptors for hearing).
Semicircular canals: anterior, posterior and lateral.
Ampulla-
Vestibule consists of two sacs: utricle and saccule.
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42. Semicircular Canals, Vestibule and Cochlea
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43. Semicircular Canals, Vestibule and Cochlea
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44. Copyright 2009, John Wiley & Sons, Inc.
Cochlea
Snail-shaped.
Section through the cochlea shows three channels: cochlear duct, scala vestibuli and scala tympani.
Helicotrema
Vestibular membrane
Basilar membrane
Spiral organ or Organ of Corti- hair cells.
Copyright 2009, John Wiley & Sons, Inc.

45. Copyright 2009, John Wiley & Sons, Inc.
Physiology of Hearing
Audible sound range: 20-20,000 Hz.
Sound waves→ auricle→ external auditory canal→ tympanic membrane→ malleus→ incus→ stapes→ oval window→ perilymph of the scala vestibuli→ vestibular membrane→ endolymph in the cochlear duct→ basilar membrane →hair cells against tectorial membrane → bending of hair cell stereocilia→ receptor potential→ nerve impulse. Sound wave → scala tympani→ round window.
Copyright 2009, John Wiley & Sons, Inc.

46. Events in the Stimulation of Auditory Receptors
Copyright 2009, John Wiley & Sons, Inc.

47. Scala
vestibuli
Cochlear duct
(contains endolymph)
tympani
Perilymph
Basilar
membrane
Cochlea
Sound waves
Helicotrema
Stapes vibrating
in oval window
Malleus
Incus
External auditory
canal
Tympanic
Secondary tympanic
membrane vibrating
in round window
Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ
(organ of Corti) 1 2 3 4 5 6 7
Scala
vestibuli
Cochlear duct
(contains endolymph)
tympani
Perilymph
Basilar
membrane
Cochlea
Sound waves
Helicotrema
Stapes vibrating
in oval window
Malleus
Incus
External auditory
canal
Tympanic
Secondary tympanic
membrane vibrating
in round window
Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ
(organ of Corti) 1 2 3 4 5 6 7 8
Scala
vestibuli
Cochlear duct
(contains endolymph)
tympani
Perilymph
Basilar
membrane
Cochlea
Sound waves
Helicotrema
Stapes vibrating
in oval window
Malleus
Incus
External auditory
canal
Tympanic
Secondary tympanic
membrane vibrating
in round window
Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ
(organ of Corti) 1 2 3 4 5 6 7 8 9
Scala
vestibuli
Cochlear duct
(contains endolymph)
tympani
Perilymph
Basilar
membrane
Cochlea
Sound waves
Helicotrema
Stapes vibrating
in oval window
Malleus
Incus
External auditory
canal
Tympanic
Secondary tympanic
membrane vibrating
in round window
Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ
(organ of Corti) 1 2 3 4 5 6
Scala
vestibuli
Cochlear duct
(contains endolymph)
tympani
Perilymph
Basilar
membrane
Cochlea
Sound waves
Helicotrema
Stapes vibrating
in oval window
Malleus
Incus
External auditory
canal
Tympanic
Secondary tympanic
membrane vibrating
in round window
Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ
(organ of Corti) 1 2 3 4 5
Scala
vestibuli
Cochlear duct
(contains endolymph)
tympani
Perilymph
Basilar
membrane
Cochlea
Sound waves
Helicotrema
Stapes vibrating
in oval window
Malleus
Incus
External auditory
canal
Tympanic
Secondary tympanic
membrane vibrating
in round window
Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ
(organ of Corti) 1 2
Scala
vestibuli
Cochlear duct
(contains endolymph)
tympani
Perilymph
Basilar
membrane
Cochlea
Sound waves
Helicotrema
Stapes vibrating
in oval window
Malleus
Incus
External auditory
canal
Tympanic
Secondary tympanic
membrane vibrating
in round window
Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ
(organ of Corti) 1 2 3
Scala
vestibuli
Cochlear duct
(contains endolymph)
tympani
Perilymph
Basilar
membrane
Cochlea
Sound waves
Helicotrema
Stapes vibrating
in oval window
Malleus
Incus
External auditory
canal
Tympanic
Secondary tympanic
membrane vibrating
in round window
Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ
(organ of Corti) 1 2 3 4
Scala
vestibuli
Cochlear duct
(contains endolymph)
tympani
Perilymph
Basilar
membrane
Cochlea
Sound waves
Helicotrema
Stapes vibrating
in oval window
Malleus
Incus
External auditory
canal
Tympanic
Secondary tympanic
membrane vibrating
in round window
Auditory tube
Vestibular membrane
Middle ear
Tectorial membrane
Spiral organ
(organ of Corti) 1

48. Copyright 2009, John Wiley & Sons, Inc.
The Auditory Pathway
Copyright 2009, John Wiley & Sons, Inc.

49. Physiology of Equilibrium
Two types of equilibrium:
Static- maintenance of the body position relative to the force of gravity.
Dynamic- maintenance of body position (mainly head) in response to rotational acceleration and deceleration.
Receptors for equilibrium are hair cells in the utricle, saccule and semicircular canals and are collectively called vestibular apparatus.
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50. Location and Structure of Receptors in the Maculae
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51. Otolithic Organs: Saccule and Utricle
Macula- small thickened regions within the saccule and utricle.
Sensory structures for static equilibrium.
Also detect linear acceleration and deceleration.
Contain hair cells and supporting cells.
Stereocilia and kinocilium together called hair bundle.
Otolithic membrane rests on the hair cells and contain otoliths.
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52. Physiology of Equilibrium continued
Tilting of the head forward→ sliding of the otolithic membrane bending the hair bundles→ receptor potential→ vestibular branch of the vestibulocochlear nerve.
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53. Location and Structure of the Semicircular Ducts
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54. Copyright 2009, John Wiley & Sons, Inc.
Semicircular Ducts
Crista, a small elevation in the ampulla contain hair cells and supporting cells.
Cupula, a mass of gelatinous material covering the crista.
Head movement→ semicircular ducts and hair cells move with it→ hair bundles bend→ receptor potential→ nerve impulses→ vestibular branch of the vestibulocochlear nerve.
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55. Cupula in Still Position versus Rotation
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56. Copyright 2009, John Wiley & Sons, Inc.
Equilibrium Pathway
Hair cells of utricle, saccule and semicircular ducts→
Vestibular branch of the vestibulocochlear nerve →brain stem → cerebellum and thalamus→ cerebral cortex.
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57. Copyright 2009, John Wiley & Sons, Inc.
End of Chapter 17
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