1. The Special Senses Smell, taste, vision, hearing and equilibrium
Housed in complex sensory organs

2. Tunics (Layers) of Eyeball
Fibrous Tunic (outer layer, cornea and sclera)
Vascular Tunic (middle layer)
Nervous Tunic (inner layer)

3. Vascular Tunic -- Iris & Pupil
Colored portion of eye
Contains melanin
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

4. Vascular Tunic -- Muscles of the Iris

5. 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 (back surface of eye)

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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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 cornea and the lens

15. 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 > 6 m are nearly parallel and only need to be bent enough to focus on retina
Light rays from < 6 m are more divergent & need more refraction
extra process needed to get additional bending of light is called accommodation

16. 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

17. 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

18. 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

19. Convergence of the Eyes
Binocular vision in humans has both eyes looking at the same object
Allows for the perception of depth
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

20. Photoreceptors Named for shape of outer segment
Transduction of light energy into a receptor potential in outer segment
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

21. 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
difficulty seeing in low light
inability to make normal amount of rhodopsin
possibly due to deficiency of vitamin A

22. Photopigments Isomerization Bleaching Regeneration
light cause cis-retinal to straighten & become trans-retinal shape
lead to production of receptor potential
Bleaching
enzymes separate the trans-retinal from the opsin
colorless final products
Regeneration
in darkness, an enzyme converts trans-retinal back to cis-retinal (resynthesis of a photopigment)

23. Formation of Receptor Potentials
In darkness
Na+ channels are held open and photoreceptor is always partially depolarized (-30mV)
continuous release of inhibitory neurotransmitter onto bipolar cells
In light
enzymes cause the closing of Na+ channels producing a hyperpolarized receptor potential (-70mV)
release of inhibitory neurotransmitter is stopped
bipolar cells become excited and a nerve impulse will travel towards the brain

24. Release of Neurotransmitters

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

26. 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

27. 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

28. Anatomy of the Ear Region

29. 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

30. Middle Ear Cavity

31. 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 to membrane of oval window
Auditory tube leads to nasopharynx
helps to equalize pressure on both sides of eardrum

32. 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

33. 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

34. Cranial nerves of the Ear Region
Vestibulocochlear nerve = CN VIII

35. Cochlear Anatomy 3 fluid filled channels found within the cochlea
scala vestibuli, scala tympani and cochlear duct
Vibration of the stapes upon the oval window sends vibrations into the fluid of the scala vestibuli

36. Tubular Structures of the Cochlea
Stapes pushes on fluid of scala vestibuli at oval window
At helicotrema, vibration moves into scala tympani
Fluid vibration dissipated at round window which bulges
The central structure is vibrated (cochlear duct)

37. Section thru one turn of Cochlea
Partitions that separate the channels are Y shaped
vestibular membrane above & basilar membrane below form the central fluid filled chamber (cochlear duct)
Fluid vibrations affect hair cells in cochlear duct

38. 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

39. 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

40. Overview of Physiology of Hearing

41. Hair Cell Physiology
Hair cells convert mechanical deformation into electrical signals
As microvilli are bent, mechanically-gated channels in the membrane let in K+ ions
This depolarization spreads & causes voltage-gated Ca+2 channels at the base of the cell to open
Triggering the release of neurotransmitter onto the first order neuron
more neurotransmitter means more nerve impulses

42. 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

43. 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

44. Vestibular Apparatus
Notice: semicircular ducts with ampulla, utricle & saccule

45. Otolithic Organs: Saccule & Utricle
Thickened regions called macula within the saccule & utricle of the vestibular apparatus
Cell types in the macula region
hair cells with stereocilia (microvilli) & one cilia (kinocilium)
supporting cells that secrete gelatinous layer
Gelatinous otolithic membrane contains calcium carbonate crystals called otoliths that move when you tip your head

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

47. Crista: Ampulla of Semicircular Ducts
Small elevation within each of three semicircular ducts
anterior, posterior & horizontal ducts detect different movements
Hair cells covered with cupula of gelatinous material
When you move, fluid in canal bends cupula stimulating hair cells that release neurotransmitter

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