1. Chapter 16 The Special Senses
Smell, taste, vision, hearing and equilibrium
Housed in complex sensory organs
Ophthalmology is science of the eye
Otolaryngology is science of the ear

2. Chemical Senses Interaction of molecules with receptor cells
Olfaction (smell) and gustation (taste)
Both project to cerebral cortex & limbic system
evokes strong emotional reactions

3. Olfactory Epithelium
1 square inch of membrane holding million receptors
Covers superior nasal cavity and cribriform plate
3 types of receptor cells

4. Olfaction: Sense of Smell
Odorants bind to receptors
Na+ channels open
Depolarization occurs
Nerve impulse is triggered

5. Adaptation & Odor Thresholds
Adaptation = decreasing sensitivity
Olfactory adaptation is rapid
50% in 1 second
complete in 1 minute
Low threshold
only a few molecules need to be present
methyl mercaptan added to natural gas as warning

6. Gustatory Sensation: Taste
Taste requires dissolving of substances
Four classes of stimuli--sour, bitter, sweet, and salty
10,000 taste buds found on tongue, soft palate & larynx

7. Anatomy of Taste Buds
An oval body consisting of 50 receptor cells surrounded by supporting cells
A single gustatory hair projects upward through the taste pore
Basal cells develop into new receptor cells every 10 days.

8. Physiology of Taste Complete adaptation in 1 to 5 minutes
Thresholds for tastes vary among the 4 primary tastes
most sensitive to bitter (poisons)
least sensitive to salty and sweet

9. Accessory Structures of Eye
Eyelids or palpebrae
protect & lubricate
Tarsal glands
oily secretions keep lids from sticking together
Conjunctiva
stops at corneal edge
dilated BV--bloodshot

10. Eyelashes & Eyebrows
Eyeball = 1 inch diameter
5/6 of Eyeball inside orbit & protected
Eyelashes & eyebrows help protect from foreign objects, perspiration & sunlight
Sebaceous glands are found at base of eyelashes (sty)
Palpebral fissure is gap between the eyelids

11. Lacrimal Apparatus
About 1 ml of tears produced per day. Spread over eye by blinking. Contains bactericidal enzyme called lysozyme.

12. Extraocular Muscles
Six muscles that insert on the exterior surface of the eyeball .
4 rectus muscles -- superior, inferior, lateral and medial
2 oblique muscles -- inferior and superior

13. Tunics (Layers) of Eyeball
Fibrous Tunic (outer layer)
Vascular Tunic (middle layer)
Nervous Tunic (inner layer)

14. Fibrous Tunic -- Description of Cornea
Transparent
Helps focus light(refraction)
astigmatism
Transplants
common & successful
no blood vessels so no antibodies to cause rejection

15. Fibrous Tunic -- Description of Sclera
“White” of the eye
Dense irregular connective tissue layer -- collagen & fibroblasts
Provides shape & support

16. Vascular Tunic -- Choroid & Ciliary Body
pigmented epithilial cells (melanocytes) & blood vessels
provides nutrients to retina
black pigment in melanocytes absorb scattered light
Ciliary body
ciliary processes
folds on ciliary body
secrete aqueous humor
ciliary muscle
smooth muscle that alters shape of lens

17. Vascular Tunic -- Iris & Pupil
Colored portion of eye
Shape of flat donut suspended between cornea & lens
Hole in center is pupil
Function is to regulate amount of light entering eye

18. Vascular Tunic -- Description of lens
Avascular
Crystallin proteins arranged like layers in onion
Clear capsule & perfectly transparent

19. Nervous Tunic -- Retina
Posterior 3/4 of eyeball
Optic disc
optic nerve exiting back of eyeball
Central retina BV
fan out to supply nourishment to retina
visible for inspection
hypertension & diabetes
Detached retina
trauma (boxing)
fluid between layers
distortion or blindness
View with Ophthalmoscope

20. Rods & Cones--Photoreceptors
Rods----rod shaped
shades of gray in dim light
120 million rod cells
discriminates shapes & movements
distributed along periphery
Cones----cone shaped
sharp, color vision
6 million
fovea of macula lutea
densely packed region
at exact visual axis of eye
2nd cells do not cover cones
sharpest resolution or acuity

21. Pathway of Nerve Signal in Retina
Light penetrates retina
Rods & cones transduce light into action potentials
Rods & cones excite bipolar cells
Bipolars excite ganglion cells
Axons of ganglion cells form optic nerve leaving the eyeball (blind spot)
To thalamus & then the primary visual cortex

22. Aqueous Humor Continuously produced by ciliary body
Flows from posterior chamber into anterior through the pupil
Glaucoma
increased intraocular pressure that could produce blindness
problem with drainage of aqueous humor

23. Major Processes of Image Formation
Refraction of light
by cornea & lens
light rays must fall upon the retina
Accommodation of the lens
changing shape of lens so that light is focused
Constriction of the pupil
less light enters the eye

24. Definition of Refraction
Bending of light as it passes from one substance (air) into a 2nd substance with a different density(cornea)
In the eye, light is refracted by the anterior & posterior surfaces of the cornea and the lens

25. Refraction by the Cornea & Lens
Image focused on retina is inverted & reversed from left to right
Brain learns to work with that information
75% of Refraction is done by cornea -- rest is done by the lens

26. Near Point of Vision and Presbyopia
Near point is the closest distance from the eye an object can be & still be in clear focus
4 inches in a young adult
8 inches in a 40 year old
lens has become less elastic
31 inches in a 60 to 80 year old
Reading glasses may be needed by age 40
presbyopia
glasses replace refraction previously provided by increased curvature of the relaxed, youthful lens

27. Correction for Refraction Problems
Emmetropic eye (normal)
can refract light from 20 ft away
Myopia (nearsighted)
eyeball is too long from front to back
glasses concave
Hypermetropic (farsighted)
eyeball is too short
glasses convex (coke-bottle)
Astigmatism
corneal surface wavy
parts of image out of focus

28. Constriction of the Pupil
Constrictor pupillae muscle contracts
Prevents light rays from entering the eye through the edge of the lens
Sharpens vision by preventing blurry edges
Protects retina very excessively bright light

29. Convergence of the Eyes
Binocular vision in humans has both eyes looking at the same object
As you look at an object close to your face, both eyeballs must turn inward.
convergence

30. Photoreceptors
Photopigment is integral membrane protein of outer segment membrane
photopigment membrane folded into “discs” & replaced at a very rapid rate
Photopigments = opsin (protein) + retinal (derivative of vitamin A)
rods contain rhodopsin
cone photopigments contain 3 different opsin proteins permitting the absorption of 3 different wavelengths (colors) of light

31. Color Blindness & Night Blindness
inability to distinguish between certain colors
absence of certain cone photopigments
red-green color blind person can not tell red from green
Night blindness (nyctalopia)
difficulty seeing in low light
inability to make normal amount of rhodopsin
possibly due to deficiency of vitamin A

32. Light and Dark Adaptation
Light adaptation
adjustments when emerge from the dark into the light
Dark adaptation
adjustments when enter the dark from a bright situation
light sensitivity increases as photopigments regenerate
during first 8 minutes of dark adaptation, only cone pigments are regenerated, so threshold burst of light is seen as color
after sufficient time, sensitivity will increase so that a flash of a single photon of light will be seen as gray-white

33. Brain Pathways of Vision
synapse in thalamus & visual cortex

34. Processing of Image Data in the Brain
Visual information in optic nerve travels to
occipital lobe for vision
midbrain for controlling pupil size & coordination of head and eye movements
hypothalamus to establish sleep patterns based upon circadian rhythms of light and darkness

35. Visual fields
Left occipital lobe receives visual images from right side of an object through impulses from nasal 1/2 of the right eye and temporal 1/2 of the left eye
Left occipital lobe sees right 1/2 of the world
Fibers from nasal 1/2 of each retina cross in optic chiasm

36. Anatomy of the Ear Region

37. External Ear Function = collect sounds Structures
auricle or pinna
elastic cartilage covered with skin
external auditory canal
curved 1” tube of cartilage & bone leading into temporal bone
ceruminous glands produce cerumen = ear wax
tympanic membrane or eardrum
epidermis, collagen & elastic fibers, simple cuboidal epith.
Perforated eardrum (hole is present)
at time of injury (pain, ringing, hearing loss, dizziness)
caused by explosion, scuba diving, or ear infection

38. Middle Ear Cavity

39. Middle Ear Cavity Air filled cavity in the temporal bone
Separated from external ear by eardrum and from internal ear by oval & round window
3 ear ossicles connected by synovial joints
malleus attached to eardrum, incus & stapes attached by foot plate to membrane of oval window
stapedius and tensor tympani muscles attach to ossicles
Auditory tube leads to nasopharynx
helps to equalize pressure on both sides of eardrum
Connection to mastoid bone =mastoiditis

40. Inner Ear---Bony Labyrinth
Vestibule
canals
ampulla
Bony labyrinth = set of tubelike cavities in temporal bone
semicircular canals, vestibule & cochlea lined with periosteum & filled with perilymph
surrounds & protects Membranous Labyrinth

41. Inner Ear---Membranous Labyrinth
Membranous labyrinth = set of membranous tubes containing sensory receptors for hearing & balance and filled with endolymph
utricle, saccule, ampulla, 3 semicircular ducts & cochlea

42. Anatomy of the Organ of Corti
16,000 hair cells have stereocilia(microvilli )
Microvilli make contact with tectorial membrane (gelatinous membrane that overlaps the spiral organ of Corti)
Basal sides of inner hair cells synapse with 1st order sensory neurons whose cell body is in spiral ganglion

43. Sound Waves
Vibrating object causes compression of air around it = sound waves
audible range is 20 to 20,000 Hz
hear best within 500 to 5000 cycles/sec or Hz
speech is 100 to 3000 Hz
Frequency of a sound vibration is pitch
higher frequency is higher pitch
Greater intensity (size) of vibration, the louder the sound measured in decibels (dB)
Conversation is 60 dB; pain above 140dB
OSA requires ear protection above 90dB

44. Deafness Nerve deafness Conduction deafness
damage to hair cells from antibiotics, high pitched sounds, anticancer drugs
the louder the sound the quicker the hearing loss
fail to notice until difficulty with speech
Conduction deafness
perforated eardrum
otosclerosis

45. Physiology of Hearing Auricle collects sound waves Eardrum vibrates
slow vibration in response to low-pitched sounds
rapid vibration in response to high-pitched sounds
Ossicles vibrate since malleus attached to eardrum
Stapes pushes on oval window producing fluid pressure waves in scala vestibuli & tympani
oval window vibration 20X more vigorous than eardrum
Pressure fluctuations inside cochlear duct move the hair cells against the tectorial membrane
Microvilli are bent producing receptor potentials

46. Overview of Physiology of Hearing

47. Cochlear Implants If deafness is due to destruction of hair cells
Microphone, microprocessor & electrodes translate sounds into electric stimulation of the vestibulocochlear nerve
artificially induced nerve signals follow normal pathways to brain
Provides only a crude representation of sounds

48. Physiology of Equilibrium (Balance)
Static equilibrium
maintain the position of the body (head) relative to the force of gravity
Dynamic equilibrium
maintain body position (head) during sudden movement of any type--rotation, deceleration or acceleration

49. Detection of Position of Head
Movement of stereocilia or kinocilium results in the release of neurotransmitter onto the vestibular branches of the vestibulocochler nerve

50. Detection of Rotational Movement
When head moves, the attached semicircular ducts and hair cells move with it
Nerve signals to the brain are generated indicating which direction the head has been rotated