Comprehensive Review of the Eye and Ear: Anatomy, Function, and Disorders

1. Semester 1 Review • Anatomical directional terms • Cells and tissues • Skin and the integumentary system • Nervous system

2. Special Senses Eye and Ear

3. Eye and Vision

4. Quick Facts about the Eye • 70% of all sensory receptors are in the eye • Approx. 1 inch in diameter • Uses light to gather information about environment

5. External Eye • Eyelid • Eyelashes • Medial canthus • Lateral canthus

6. Accessory Structures of the Eye • Tarsal glands (within eyelids) • Conjuctiva • Lacrimal apparatus • Lacrimal glands Lacrimal canals and lacrimal sac Nasolacrimal duct  nasal cavity • Lacrimal secretions are made up of a dilute salt solution and lysozyme (antibiotic)

7. Internal Eye Anatomy (from above)

8. Eye Overview • Made of tunics and humors • Tunics: layers surrounding the eye and it’s parts • Humors: fluid areas within the tunics to give eye pressure and keep it’s shape

9. Tunics • Sclera: outermost tunic • Thick, white covering • Anterior portion modified into cornea • No blood vessels

10. Tunics • Vascular tunic: middle tunic • Supplies blood to eye • 2 parts: • Choroid (posterior) • Ciliary body (anterior) attaches lens using ciliaryzonule • Iris • Pupil

11. Tunics • Sensory tunic: innermost tunic • Retina: contains photoreceptors • Rods: black, white and shades of gray in dim light, peripheral vision • Cones: color receptors • Signals sent from retina to optic nerve to brain

12. Retina • Macula lutea: yellowish area near back of the eye • Fovea Centralis: depression in the center of Macula lutea • High concentration of cones • Produces sharpest vision • Optic disc: nerve fibers and blood vessels enter and leave the eye • Contains a blind spot

13. Humors • Humors: fluid filled areas in eye • Aqueous humor • Anterior to lens • Constantly replaced to bring nutrients to areas without blood supply • Secreted by choroid • Scleralvernous sinus (canal of Schlemm) – at junction of sclera and cornea • Vitreous humor • Posterior to lens • Constant pressure to give eye shape (intraocular pressure)

16. Lens • Biconvex structure • Behind cornea, iris, pupil • Bends to focus on objects

17. Muscles of the Eye (right eye)

18. Muscles of the Eye (front)

19. How does the eye work? • Light is refracted by each layer it moves through • Humors, lens, cornea • Image is shown on retina (upside-down) and sent to brain • Brain flips the image and uses other cues to make sense of image

21. How does the eye work? • Nerve impulses from the retina leave the eye through the optic nerve. • Optic nerves from each eye meet at the optic chiasma.

22. How does the eye work? • At the optic chiasma, the impulses from the medial portion of each retina cross over to the opposite side; • Leaving the optic chiasma are the optic tracts, which fuse in the thalamus; • Leaving the thalamus are the optic radiations, which then join to the occipital lobe (visual cortex) of the brain where interpretation occurs;

23. How does the eye work? • Result is that each side of the brain receives input from both eyes. • Binocular vision – each eye sends an image to the brain, resulting in 3-dimensional vision.

24. Problems within the Eye • Cateracts • Conjunctivitis • Nearsightedness – distant objects are blurry • Farsightedness – close objects are blurry • Astigmatism • Glaucoma

26. The Ear, Hearing, and Balance

27. Overview of the Ear • 3 parts: outer, middle, inner • Mechanoreceptor: respond to physical forces (sound vibrations, movement of the head)

29. Outer Ear • Pinnaor auricle – external ear • Surrounds auditory canal into ear canal • External acoustic meatus(external auditory canal) – skin lined canal between outside of the head and the eardrum • Glands in skin (ceruminous canals) secrete cerumento protect ear

30. Middle Ear • Tympanic membrane • Tympanic cavity • Ossicles (hammer/malleus, anvil/incus, stirrup/stapes) • Oval window • Round window • Pharyngotympanic tube (auditory/Eustachian tube)– connects ear and throat and will open and close to keep pressure within ear the same as external pressure

31. Inner Ear • Made up of bony chambers called the osseous (bony) labyrinth • 3 divisions: • Cochlea • Vestibule • Semicircular canals • Filled with fluid called perilymph • Within labyrinth are membranes (membranous labyrinth) • Filled with endolymph

32. Hearing • Organ of Corti • Within the cochlea • Contain hair cells to detect vibrations which cause cochlear fluid to move • Send sound signals along cochlear nerve to the temporal lobe (auditory cortex) • Two ears help us determine where sounds are coming from • Over-stimulation of cochlear nerve allows us to “tune out” certain sounds

33. Hearing Video • http://www.youtube.com/watch?v=ahCbGjasm_E

34. Equilibrium and Balance • Vestibular Apparatus: equilibrium detectors in the vestibule and semicircular canals • Static equilibrium – detects up and down • Maculae: otolithic membrane with a gel-like material with otoliths (calcium salt stones) detect movement of head • Dynamic equilibrium – movement in all directions • Cristaampularis – tuft of hair cells with cupula (gel cap) • Movement bends hairs and cupula • All send signals to brain through vestibular nerve to cerebellum