1. Special Senses
Chapter 8

2. Special Senses Smell, taste, sight, and hearing Equilibrium
Special sense receptors:
large, complex sensory organs (eyes, ears)
localized clusters of receptors (taste buds and olfactory epithelium)
Senses blend to give us our sensations

3. The Eye & Vision

4. External Anatomy of the Eye
Only anterior 1/6 of eye’s surface can normally be seen
Accessory structures:
Extrinsic eye muscles
Eyelids
Conjunctiva
Lacrimal apparatus

5. Accessory Structures Extrinsic eye muscles
Six muscles are attached to outer surface of each eye
Produce gross eye movements

6. video

7. Accessory Structures Eyelids
4 layers: skin, muscle, connective tissue, conjunctiva (mucous membrane)
Moved by orbicularis oculi muscles (close) and levatator palpebrae superioris (open)

8. Accessory Structures Lacrimal apparatus
Consists of lacrimal gland & ducts that drain lacrimal secretions into nasal cavity
Lacrimal glands: continuously secrete dilute salt solution (tears) onto anterior surface of eyeball
Secretion contains mucus, antibodies, and lysozyme which is an enzyme that destroys bacteria
Cleans and protects eye surface as it moistens & lubricates it

9. link

11. Internal Structures Eyeball is a hollow sphere
Wall composed of three layers:
Fibrous layer
Sclera
Cornea
Vascular layer
Choroid
Ciliary body
Iris
Sensory layer
Retina
Pigmented layer (prevent light from scattering)
Neural layer (photoreceptors)

12. Fibrous Layer
Sclera: thick, white connective tissue (“white of the eye”)
Opaque due to large, disorganized collagenous and elastic fibers
For protection & attachment
Cornea: clear “window” through which light enters eye
anterior portion of eye
many nerve endings (pain fibers), easily repairs itself
avascular, so only tissue in the body that can be transplanted without fear of rejection
helps focus entering light rays
Connective tissue with thin layer of epithelium; unusually regular fiber pattern

13. Fibrous Layer: Sclera & Cornea

14. LASIK
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15. Vascular Layer
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Choroid: blood-rich nutritive tunic that contains a dark pigment
Prevents light from scattering inside the eye
Modified anteriorly to form ciliary body & iris
Produces melanin to absorb light
Contains blood vessels
Ciliary body: two smooth muscle structures to which the lens is attached with the ciliary zonule (ligament)
Forms internal ring around front of eye (muscle fibers & ligaments)
Iris: pigmented, has an opening called the pupil through which light passes
Thin diaphragm composed of muscle tissue and connective tissue
Circular and radial muscle fibers control size of pupil (stimulated by photons of light)
Regulates the amount of light which enters the eye

16. Choroid

17. Ciliary Body

18. Sensory Layer: Retina
Retina – two layers which extends anteriorly only to the ciliary body
Pigmented layer
composed of pigment cells that absorb light and prevent light from scattering inside the light
act as phagocytes to remove dead or damaged receptor cells
store vitamin A needed for vision

19. Sensory Layer: Retina
Neural layer – contains millions of receptor cells
Photoreceptors (rods & cones): respond to light, bipolar neurons
70% of sensory receptors are in the eyes
Rods: more sensitive in low light, gives general outline, seen as black and white
Cones: less sensitive in low light, sharp picture, color
Electrical impulse leaves the retina via the optic nerve & nerve impulses are transmitted to the optic cortex which results in vision
Fovea: all cones, sharpest vision (visual acuity)
Optic disc (“blind spot”) – where optic nerve leaves eyeball

20. Retina

21. Sensory Layer: Retina
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Night blindness: fewer working rods (lack of vitamin A)
Day blindness: lack of working cones

22. Age-related Macular Degeneration

23. Retinitis Pigmentosa Genetic disorder
FDA approval
Genetic disorder
involves abnormalities in photoreceptors or retinal tissue that leads to progressive vision loss
Bionic Eye (Argus II Retinal Prosthesis System)
Mostly restores black & white vision
Did restore color vision in some

24. Sensory Layer: Retina Read pg. 286
Rods: rhodopsin breaks down into opsin & retinal when struck by photons; initiates chemical reaction (action potential) which is sent to visual cortex (occipital lobe)
In bright light, nearly all rhodopsin I broken down, reducing rod sensitivity
Cones: three different light sensitive proteins connected to retinal – each most sensitive to a particular wavelength of visible light
Depending on which is stimulated, brain interprets that color
Erythrolabe: red
Chlorolabe: green
Cyanolabe: blue
Mixing & interpretation of color occurs in the brain, not the retina! (i.e. red light in one light & green light in another eye will be seen as yellow)
Read pg. 286

25. Visual Pigments
If all are stimulated at once, see white!

26. Color Blindness Total color blindness: lack of all three cones
Partial color blindness: lack of one cone type (lack of red or green receptor is most common)
Sex-linked condition (carried on X chromosome)

27. Color Blindness 1. Normal Color Vision: A: 29, B: 45, C: --, D: 26
4 Sex-Linked Traits:
 1. Normal Color Vision:  A: 29,  B: 45,  C: --,  D: 26
 2. Red-Green Color-Blind:  A: 70,  B: --,  C: 5,  D: --
 3. Red Color-blind:  A: 70,  B: --,  C: 5,  D: 6
 4. Green Color-Blind:  A: 70,  B: --,  C: 5,  D: 2

28. Internal Structures: Lens
Lies directly behind iris & pupil
Focuses light entering the eye on the retina (changes shape to focus)
Held upright in the eye by a suspensory ligament (ciliary zonule) attached to ciliary body
Epithelial cells (cytoplasm
is transparent part)

29. Cataracts With age, lens becomes increasingly hard and opaque
Cataracts result from this process and cause vision to become hazy and distorted
Can eventually cause blindness in affected eye
Treatment: surgical removal of lens and replacement with lens implant or special cataract glasses

30. Internal Structures: Humors
Aqueous humor
Anterior to the lens, clear watery fluid
Fills space between cornea and lens
Nourishes, helps hold shape
Vitreous humor
Reinforces
eyeball internally
Posterior to lens

32. Glaucoma
aqueous humor made more quickly than can be removed or drainage is blocked
pressure builds, damage results from compression of retina and optic nerve

33. Link
Medicinal Marijuana
for Glaucoma

35. Physiology of Vision
Light rays are bent (refracted) as light encounters the cornea, aqueous humor, lens, and vitreous humor
Refractory power of the lens can be changed by changing its shape (ciliary body controls shape of lens)
Accommodation: ability of eye to focus for close objects (less than 20 ft. away)
Image formed on retina is a real image (inverted)

36. Vision

38. Astigmatism

40. Visual Pathways
Axons carrying impulses from retina are bundled together at posterior aspect of eyeball and issue from back of eye as optic nerve
Optic chiasma: fibers from medial side of eye cross over to opposite side of brain
Fiber tracts that result are optic tracts
Each optic tract contains fibers from the lateral side of the eye on the same side and the medial side of the opposite eye
Optic tract fibers synapse with neurons in the thalamus, whose axons form the optic radiation which runs to the occipital lobe of brain (visual interpretation occurs)
Each side of brain receives visual input from both eyes
Visual fields overlap to give humans binocular vision

42. The Ear: Hearing & Balance

43. Anatomy of the Ear Divided into three major areas External (outer) ear
Middle ear
Internal (inner) ear

44. External (Outer) Ear Auricle (pinna) – “ear”
Collects and directs sound waves into the auditory canal (function largely lost in humans)
External acoustic meatus (auditory canal)
Short, narrow chamber carved into temporal bone of skull
Ceruminous glands – secrete cerumen (earwax)
Tympanic membrane (eardrum) – vibrate when sound waves strike it; separates external & middle ear

45. Swimmer’s Ear
Otitis Externus

46. Middle Ear Small, air-filled, mucosa-lined cavity within temporal bone
Transfers vibrations via the ossicles (smallest bones in body)
malleus (hammer), incus (anvil), and stapes (stirrup)
Stapes passes vibration to the oval window of the inner ear
Pharyngotympanic tube (auditory tube): pressure needs to be equalized to enable eardrum to vibrate

47. Middle Ear

48. Otitis Media Inflammation of the middle ear
Pharyngotympanic tubes run more horizontally in children
Ear tubes – implanted in ear drum to allow pus to drain into external ear canal
Infants with bottles “propped” or fed lying flat can get fluid in their ears through the pharyngotympanic tube

49. Internal (Inner) Ear
Bony (osseous) cavity located behind the eye socket
Filled with perilymph (fluid)
Membranous labyrinth suspended in perilymph, contains endolymph
Three subdivisions
Cochlea
Vestibule
Semicircular canals
Lined with hair cells
(mechanoreceptors)

50. Equilibrium Vestibular apparatus: equilibrium receptors of ear
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Vestibular apparatus: equilibrium receptors of ear
Static equilibrium: maculae receptors
Report on changes in position of head when body not moving (keep head erect)
Otoliths: tiny stones that roll in response to changes in pull of gravity
Dynamic equilibrium: bending of cupula indicates rotation (gelatinous cap)
Report on changes when body moving (i.e. spinning)
Receptors stimulate hair cells, which send impulses via the vestibular nerve to the cerebellum
Work together with proprioceptors for control & balance

51. Hearing
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Spiral organ of corti – contains hair cells (hearing receptors)
Vibrations set cochlear fluids in motion, pressure waves cause vibrations
impulses are sent via cochlear nerve to temporal lobe (auditory cortex)

53. Loud Sounds
and
Hair Cell Damage

54. Cochlear implant
link

55. Chemical Senses: Smell & Taste

56. Olfaction
Olfactory receptors (chemoreceptors): receptors for sense of smell, occupy a postage stamp-size area in roof of each nasal cavity
10-100,000,000 receptors in nose
Olfactory filaments (axons) make up olfactory nerve (cranial nerve I) which conducts impulses to olfactory cortex of brain
Olfactory lobes of brain (gray matter) – situated over nose (bottom of frontal lobe)
Olfactory impulses closely tied to limbic system
Sensitive receptors, just a few molecule can activate them (thousands of smells)
Adapt rather quickly when exposed to unchanging stimulus

57. Link 1
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58. Gustation: Taste
Taste buds: specific receptors for taste widely scattered in the oral cavity
Live 7-10 days!
protection (low threshold – bitter)
10,000 taste buds (mostly on tongue)
Five tastes: sweet, salty, sour, bitter, and umami (savory)
Flavors: combination of 5 tastes and olfactory and touch sensations
1st order neuron  medulla  hypothalamus or thalamus (limbic)  parietal lobe (conscious perception of taste)

59. link
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