1. 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, nose and throat

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. Accessory Structures of Eye
Eyelids or palpebrae
protect & lubricate
epidermis, dermis, CT, orbicularis oculi m., tarsal plate, tarsal glands & conjunctiva
Tarsal glands
oily secretions keep lids from sticking together
Conjunctiva
palpebral & bulbar
stops at corneal edge
dilated BV--bloodshot

4. Eyelashes & Eyebrows
Eyeball = 1 inch diameter
5/6 of Eyeball located 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

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

6. Extraocular Muscles
Six muscles that insert on the exterior surface of the eyeball
Innervated by Cranial Nerve (CN) III, IV or VI.
4 rectus muscles -- superior, inferior, lateral and medial
2 oblique muscles -- inferior and superior

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

8. Fibrous Tunic -- Description of Cornea
Transparent
Helps focus light(refraction)
astigmatism
3 layers
nonkeratinized stratified squamous
collagen fibers & fibroblasts
simple squamous epithelium
Transplants
common & successful
no blood vessels so no antibodies to cause rejection
Nourished by tears & aqueous humor

9. Fibrous Tunic -- Description of Sclera
“White” of the eye
Dense irregular connective tissue layer -- collagen & fibroblasts
Provides shape & support
At the junction of the sclera and cornea is an opening (scleral venous sinus)
Posteriorly pierced by Optic Nerve (CNII)

10. 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

11. 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
Autonomic reflexes
circular muscle fibers contract in bright light to shrink pupil
radial muscle fibers contract in dim light to enlarge pupil

12. Vascular Tunic -- Muscles of the Iris
Constrictor pupillae (circular) are innervated by parasympathetic fibers while Dilator pupillae (radial) are innervated by sympathetic fibers.
Response varies with different levels of light

13. Vascular Tunic -- Description of lens
Avascular
Crystallin proteins arranged like layers in onion
Clear capsule & perfectly transparent
Lens held in place by suspensory ligaments
Focuses light on fovea

14. Vascular Tunic -- Suspensory ligament
Suspensory ligaments attach lens to ciliary process
Ciliary muscle controls tension on ligaments & lens

15. 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

16. Layers of Retina Pigmented epithelium
nonvisual portion
absorbs stray light & helps keep image clear
3 layers of neurons (outgrowth of brain)
photoreceptor layer
bipolar neuron layer
ganglion neuron layer
2 other cell types (modify the signal)
horizontal cells
amacrine cells

17. 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

18. Cavities of the Interior of Eyeball
Anterior cavity (anterior to lens)
filled with aqueous humor
produced by ciliary body
continually drained
replaced every 90 minutes
2 chambers
anterior chamber between cornea and iris
posterior chamber between iris and lens
Posterior cavity (posterior to lens)
filled with vitreous body (jellylike)
formed once during embryonic life
floaters are debris in vitreous of older individuals

19. Aqueous Humor Continuously produced by ciliary body
Flows from posterior chamber into anterior through the pupil
Scleral venous sinus
canal of Schlemm
opening in white of eye at junction of cornea & sclera
drainage of aqueous humor from eye to bloodstream
Glaucoma
increased intraocular pressure that could produce blindness
problem with drainage of aqueous humor

20. 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
Light rays from > 20’ are nearly parallel and only need to be bent enough to focus on retina
Light rays from < 6’ are more divergent & need more refraction
extra process needed to get additional bending of light is called accommodation

21. Accommodation & the Lens
Convex lens refract light rays towards each other
Lens of eye is convex on both surfaces
View a distant object
lens is nearly flat by pulling of suspensory ligaments
View a close object
ciliary muscle is contracted & decreases the pull of the suspensory ligaments on the lens
elastic lens thickens as the tension is removed from it
increase in curvature of lens is called accommodation

22. 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

23. 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

24. Constriction of the Pupil
Constrictor pupillae muscle contracts
Narrows beam of light that enters the eye
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

25. 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
required so that light rays from the object will strike both retinas at the same relative point
extrinsic eye muscles must coordinate this action

26. 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

27. 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

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

29. 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

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

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

32. 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

33. 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
Found on sides of circumvallate & fungiform papillae
3 cell types: supporting, receptor & basal cells

34. 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.

35. 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
Mechanism
dissolved substance contacts gustatory hairs
receptor potential results in neurotransmitter release
nerve impulse formed in 1st-order neuron

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. Cranial nerves of the Ear Region
Vestibulocochlear nerve = CN VIII
ampullary, utricular & saccular brs. form vestibular branch
cochlear branch has spiral ganglion in bony modiolus

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. Physiology of Equilibrium (Balance)
Static equilibrium
maintain the position of the body (head) relative to the force of gravity
macula receptors within saccule & utricle
Dynamic equilibrium
maintain body position (head) during sudden movement of any type--rotation, deceleration or acceleration
crista receptors within ampulla of semicircular ducts

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

48. Detection of Rotational Movement
When head moves, the attached semicircular ducts and hair cells move with it
endolymph fluid does not and bends the cupula and enclosed hair cells
Nerve signals to the brain are generated indicating which direction the head has been rotated

49. Equilibrium Pathways in the CNS
Fibers from vestibulocochlear nerve (VIII) end in vestibular nuclei and the cerebellum
Fibers from these areas connect to:
cranial nerves that control eye and head and neck movements (III,IV,VI & XI)
vestibulospinal tract that adjusts postural skeletal muscle contractions in response to head movements
Cerebellum receives constant updated sensory information which it sends to the motor areas of the cerebral cortex
motor cortex can adjust its signals to maintain balance