1. Chapter 8 Special Senses
Essentials of Human Anatomy & Physiology
Seventh Edition
Elaine N. Marieb
Chapter 8 Special Senses
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

2. The Senses General senses of touch Special senses Temperature Pressure
Pain
Special senses
Smell
Taste
Sight
Hearing
Equilibrium
Slide 8.1
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3. The Eye and Vision
70 percent of all sensory receptors are in the eyes, only see 1/6th of eye
Each eye has over a million nerve fibers
Protection for the eye
Most of the eye is enclosed in a bony orbit
A cushion of fat surrounds most of the eye
Slide 8.2
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4. Accessory Structures of the Eye
Eyelids
Meets at medial and lateral canthus (crease)
Eyelashes
Figure 8.1b
Slide 8.3a
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5. Accessory Structures of the Eye
Eyelashes
Meibomian glands - modified sebacious glands produce an oily secretion to lubricate the eye
Figure 8.1b
Slide 8.3b
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6. Accessory Structures of the Eye
Ciliary glands – modified sweat glands between the eyelashes
Figure 8.1b
Slide 8.3c
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7. Accessory Structures of the Eye
Conjunctiva
Membrane that lines eyelids
Connects to the surface of eye
Secretes mucus to lubricate eye
When inflamed, conjunctivitis
Slide 8.4a
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8. Accessory Structures of the Eye
Lacrimal apparatus
Glands, ducts, (eye), canals, sac, nasolacrimal duct
Tears: antibodies, lysozymes, stress?
Figure 8.1a
Slide 8.4b

9. Extrinsic Eye Muscles Muscles attach to the outer surface of the eye
Produce eye movements
Figure 8.2
Slide 8.6
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10. Structure of the Eye The wall is composed of three tunics
Sclera & Cornea fibrous outside layer
Choroid – middle layer
Sensory tunic – (retina) inside layer
Figure 8.3a
Slide 8.7
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11. The Fibrous Tunic Sclera Cornea White connective tissue layer
Seen anteriorly as the “white of the eye”
Cornea
Transparent, central anterior portion
Allows for light to pass through
Repairs itself easily
The only human tissue that can be transplanted without fear of rejection
Slide 8.8
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12. Choroid Layer Blood-rich, nutritive tunic
Pigment prevents light from scattering
Modified interiorly into two structures
Ciliary body – smooth muscle
Iris
Pigmented layer that gives eye color
Pupil – rounded opening in the iris
Slide 8.9
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13. Sensory Tunic (Retina)
Contains receptor cells (photoreceptors)
Rods- Most are found towards the edges of the retina
Allow dim light vision and peripheral vision
Perception in gray tones
Cones – 3 types detect different colors
Densest in the center of the retina
Fovea centralis – area of the retina with only cones
Lack of one type = color blindness
Signals pass from photoreceptors; leave the retina toward the brain through the optic nerve
No photoreceptor cells are at the optic disk, or blind spot

14. Neurons of the Retina Slide 8.11 Figure 8.4
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15. Lens Biconvex crystal-like structure
Held in place by a suspensory ligament attached to the ciliary body

16. Internal Eye Chamber Fluids
Aqueous humor in Anterior Segment
Watery fluid found in chamber between lens and cornea
Similar to blood plasma
Helps maintain intraocular pressure
Provides nutrients for the lens and cornea
Reabsorbed into venous blood
Blocked drainage = inc pressure = glaucoma

17. Internal Eye Chamber Fluids
Vitreous humor in Posterior Segment
Gel-like substance behind lens
Keeps the eye from collapsing
Lasts a lifetime and is not replaced
Slide 8.15b
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18. Lens Accommodation
Light must be focused to point on retina for optimal vision
The eye is set for distance vision (over 20 ft away)
The lens must change shape to focus for closer objects

19. Correcting the Eye Correct Focus = emmetropia Nearsightedness = myopia
Focus of light in front of retina
Eyeball too long or lens too strong
Distant objects are blurry
Farsightedness = hyperopia
Focus of light beyond the retina
Short eyeball or lazy lens
Near objects are blurry.

20. Emmetropia

22. Hyperopia

23. Astigmatism
Unequal curvatures in cornea & lens

24. The Ear Houses two senses Receptors are mechanoreceptors Hearing
Equilibrium (balance)
Receptors are mechanoreceptors
Slide 8.20
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25. Anatomy of the Ear The ear is divided into 3 areas
Outer (external) ear
Middle ear
Inner ear

26. The External Ear Involved in hearing only Structures of external ear
Pinna (auricle)
External auditory canal

27. The External Auditory Canal
Narrow chamber in the temporal bone
Lined with skin
Ceruminous (wax) glands present
Ends at the tympanic membrane (ear drum)
Slide 8.23
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28. The Middle Ear or Tympanic Cavity
                          
Air-filled cavity within temporal bone
Only involved in sense of hearing
Slide 8.24a
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29. The Middle Ear or Tympanic Cavity
2 tubes are associated with the ear
opening from auditory canal is covered by the tympanic membrane
auditory tube (Eustachian tube) connecting middle ear with throat
equalizing pressure during yawning or swallowing
otherwise collapsed

30. Bones of the Tympanic Cavity
Three bones span cavity
Malleus (hammer)
Incus (anvil)
Stapes (stirrip)
Figure 8.12
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31. Bones of the Tympanic Cavity
Vibrations from eardrum move malleus
These bones transfer sound to inner ear
Figure 8.12
Slide 8.25b
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32. Inner Ear or Bony Labyrinth
Includes sense organs for hearing and balance
Filled with perilymph (liquid)
Figure 8.12
Slide 8.26a
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33. Inner Ear or Bony Labrynth
Maze of bony chambers within temporal bone
Cochlea
Vestibule
Semicircular canals

34. Organs of Hearing Organ of Corti Located within cochlea
Receptors = hair cells on basilar membrane
Gel-like tactorial membrane is capable of bending hair cells
Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe

35. Organs of Hearing Slide 8.27b Figure 8.13
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36. Mechanisms of Hearing
Vibrations from sound waves move tectorial membrane
Hair cells are bent by the membrane
An action potential starts in the cochlear nerve
Continued stimulation can lead to adaptation
Slide 8.28
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37. Mechanisms of Hearing Slide 8.29 Figure 8.14
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38. Mechanisms of Hearing
Uncoiled cochlea: sound waves below level of hearing travel w/o exciting hair cells
1- Higher pitched sounds make pressure waves that penetrate through cochlea and reach scala tympani
2- Membrane vibrates and response to frequencies of sound, stimulating hair cells
Figure 8.14
Slide 8.29
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39. Organs of Equilibrium Receptor cells are in two structures Vestibule
Semicircular canals
Figure 8.16a, b
Slide 8.30a
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40. Organs of Equilibrium Equilibrium has two functional parts
Static equilibrium – sense of gravity at rest
Dynamic equilibrium – angular and rotary head movements
Figure 8.16a, b
Slide 8.30b
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41. Static Equilibrium - Rest
Maculae – receptors in the vestibule
Report on position of head
Send information via vestibular nerve
Anatomy of the maculae
Hair cells are embedded in otolithic membrane
Otoliths (tiny stones) float in a gel around hair cells
Movements cause otoliths to bend hair cells
Slide 8.31
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42. Function of Maculae Slide 8.32 Figure 8.15
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43. Dynamic Equilibrium - Movement
Crista ampullaris – receptors in the semicircular canals
Tuft of hair cells
Cupula (gelatinous cap) covers hair cells
Figure 8.16c
Slide 8.33a
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44. Dynamic Equilibrium Action of angular head movements
The cupula stimulates hair cells
An impulse is sent via vestibular nerve to cerebellum
Figure 8.16c
Slide 8.33b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

45. Chemical Senses Taste and Smell
Both senses use chemoreceptors
Both stimulated by chemicals in solution
Taste has 4 types of receptors
Smell can differentiate a large range of chemicals
Both senses complement each other and respond to many of same stimuli!
Slide 8.34
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46. Olfaction – The Sense of Smell
Olfactory receptors are in roof of the nasal cavity
Neurons with long cilia
Chemicals must be dissolved in mucus for detection

47. Olfaction – The Sense of Smell
Impulses are transmitted via olfactory nerve
Interpretation of smells made in cortex

48. The Sense of Taste Taste buds house the receptor organs
Location of taste buds
Most are on the tongue
Soft palate
Cheeks
Figure 8.18a, b
Slide 8.37
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49. The Tongue and Taste The tongue is covered w/ projections,or papillae
Filiform papillae sharp w/ no taste buds
Fungifiorm papillae rounded w/ taste buds
Circumvallate papillae large w/ taste buds

50. The Tongue and Taste
Taste buds are found on the sides of papillae

51. Structure of Taste Buds
Gustatory cells are the receptors
Have gustatory hairs (long microvilli)
Hairs stimulated by chemicals dissolved in saliva

52. Facial, Glossopharyngeal & Vagus nerves
Structure of Taste Buds
Impulses carried to gustatory complex by several cranial nerves b/c taste buds found in different areas
Facial, Glossopharyngeal & Vagus nerves

53. Taste Sensations Sweet receptors Sugars Saccharine Some amino acids
indicates energy-rich nutrients
Slide 8.41
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54. Taste Sensations
Sour receptors
Acids
Slide 8.41

55. Taste Sensations Bitter receptors allows sensing diverse
natural toxins

56. Taste Sensations Salty receptors allows modulating
diet for electrolyte
balance

57. Developmental Aspects of All Special Senses
Formed early in embryonic development
Eyes are outgrowths of the brain
All special senses are functional at birth

58. Short taste intro
Relationship between smell and taste