1. Sensations and Special Senses

2. Specialized structures of the
Senses
Specialized structures of the
nervous system which provide information about the environment in which we live to help maintain homeostasis

3. Accessory Structures of the Eye
Eyelids - protects the anterior surface
Conjunctiva - the mucous membrane of the eyelid
Helps moisten and lubricate the eyeball
Lacrimal Apparatus - secretes tears
lacrimal gland - lacrimal sac
lacrimal canals - nasolacrimal duct
moistens and lubricates the eyeball
fights against infection (enzymes in tears)
Extrinsic Muscles of the Eyeball (6)
skeletal muscles that move the eyeball

4. Structure of the Eye
The wall consists of three layers of tissue or tunics
Fibrous Tunic - outer layer
Vascular Tunic - middle layer
Nervous Tunic - inner layer

5. Fibrous Tunic Thick, outermost layer of the eyeball
Sclera - the posterior “white” portion
Forms most of the fibrous tunic
The “whites” of the eye
Cornea - the anterior transparent portion of the fibrous tunic
Bulges outward slightly

6. Vascular Tunic Extremely vascular
Lens
Extremely vascular
Supplies blood to numerous structures of the eye
Choroid: A thin, dark brown membrane that lines most of the internal surface of the sclera
Ciliary Body: Attaches to the lens by ligaments. Changes the thickness and shape of the lens.
Iris: Contraction of it’s smooth muscle accounts for dilation or constriction of the Pupils (openings to the inner cavities of the eyes)
Lens: special tissue which focuses and directs light entering the eye

7. Nervous Tunic The inner layer of the eye
Retina - a thin fragile layer of neurons that forms the inner lining of the eyeball’s posterior wall
Lines the posterior cavity and contains the photoreceptor cells (rods and cones), bipolar neurons, and ganglion cells
Optic Nerve - axons and ganglion cells
Transmits images to the occipital lobe of the brain for interpretation of what we see

8. Rods and Cones
Rods - elongated cylindrical dendrites that are sensitive to varying light conditions
Allows us to see under varying light intensities (night vision)
Cones - dendrites with tapered ends
Color sensitive
Determines the “sharpness” of vision

9. Other Structures of the Nervous Tunic
Optic Disc - blind spot where the optic nerve exits the retina
Fovea Centralis - an area of the retina containing many cone cells
the area of sharpest vision

10. Optic Chiasm

11. Hearing Dependent upon special organs within the ear
The ears are also associated with maintaining equilibrium and balance
Three Regions of the Ears
Outer Ear
Middle Ear
Inner Ear

12. Outer Ear Direct sound waves toward the eardrum
Auricle - the outer appendage
Auditory Canal - a tube that extends into the temporal bone

13. Middle Ear An air-filled space within the temporal bone
Tympanic Cavity - contains the auditory ossicles
Malleus (hammer)
Incus (anvil)
Stapes (stirrup)
Auditory (Eustachian) Tube - a tube from the middle ear to the pharynx- Equalization
Tympanic Membrane (Eardrum) - thin, semitransparent membrane
Vibrates in response to and then transmitted to the auditory ossicles
The tympanic membrane and auditory ossicles convert sound waves into mechanical movement “oval window” cochlea of the inner ear vibrations of the stapes causes the fluid within the inner ear to move stimulating the receptors for hearing

14. The Three Regions of the Inner Ear
Formed by the canals of the bony labyrinth and the series of sacs of the membranous labyrinth
Involved in both the sense of hearing and the maintenance of balance and equilibrium
Cochlea
Vestibule
Semicircular Canals

15. The Cochlea - shape resembles a snail shell
The Semicircular Canals - three loops that lie at right angles to each other
The Vestibule - the chamber between the cochlea and the semicircular canals
Both the semicircular canals and the vestibule are involved with maintaining balance or equilibrium
The Cochlea - shape resembles a snail shell
Contains the organs of hearing (Corti)
Receptor cells that move in response to endolymph motion
Releases neurotransmitters that stimulate nerve impulses

16. Physiology of Hearing

17. Clinical Terms Diseases and Disorders

18. Presbyopia
Presbyopia - a defect in vision in advancing age involving loss of accommodation or recession of near point (results in farsightedness)

19. Presbyopia You Tube Video called ‪presbyopia. mpg‬ found at http://www

20. Myopia
Myopia - nearsightedness
Imaged focused in front of the retina

21. Myopia Prevention found at http://www. youtube. com/watch

22. Hyperopia Hyperopia - farsightedness
Image focused in back of the retina

23. Hyperopia
You Tube Video called Hyperopia- Overview (3D Medical Animation) found at

24. Cataracts Abnormal loss of transparency of the lens
Vision becomes blurry or cloudy
Can be removed and have an artificial lens inserted
Most often occurs to individuals over the age of 50. Exposure to sunlight and smoking increases the risk.

25. Cataract You Tube video called “What is a cataract” found at

26. Conjunctivitis
Conjunctivitis - inflammation of the conjunctiva, the mucous membrane that lines the eyelid and is reflected to the eyeball. Also known as “Pink Eye”

27. Conjunctivitis You Tube Video called “The Problem with Pink Eye (College Health Guru) found at

28. Strabismus You Tube Video called Strabismus Surgery found at
Strabismus – “cross-eyed”

29. Glaucoma
A group of eye diseases characterized by elevated intraocular pressure in the eye resulting in atrophy of the optic nerve which may lead to blindness
Caused by an obstruction of the outflow of the aqueous and vitreous humor
Minor cases can be treated with eye drops
More severe cases may require a surgical incision into the iris of the eye

30. Glaucoma You Tube Video called “Glaucoma- Effects of Glaucoma- Causes of Blindness” found at

31. Macular Degeneration
The destruction or tearing away of the retina from the back of the eye
Commonly occurs in the region of the retina known as the macula lutea
Can be caused by:
Vascular diseases (diabetes)
Chronic increased pressure (glaucoma)
Sudden blow or impact to the head or eye (Detached Retina)

32. Macular Degeneration You Tube Video called “Age Related Macular Degeneration” found at

33. Vertigo A condition of dizziness and spatial disorientation
In some individuals it is due to heights or fear of high places
A spinning sensation that may result in loss of balance and equilibrium

34. Vertigo You Tube Video called “What is Vertigo/Signs and Symptoms/Video/Veria Living” found at

35. Tinnitus
Ringing or tinkling sounds or sensations in the ear

36. What Does Tinnitus Sound Like
What Does Tinnitus Sound Like? You Tube Video called “What Does tinnitus Sound Like” found at

37. Middle Ear Infection
Infection of the tympanic membrane or other structures associated with the middle ear (Otitis Media)

38. Otitis Media You Tube Video called “Ostitis Media: Patologias” found at

39. Deafness Loss of the ability to hear
Conductive Deafness: deafness resulting from any condition that prevents sound waves from being transmitted to the auditory receptors
Sensorineural Deafness: deafness due to defective function of the cochlea, organ of Corti, or the auditory nerve

40. Deafness You Tube Video called “Helen Keller Speaks Out” found at