1. Special Senses
Eye and Ear

2. Eye and Vision

3. 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

4. External Eye
Eyelid
Eyelashes
Medial canthus
Lateral canthus

5. 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)

6. Internal Eye Anatomy

7. 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

8. Tunics Sclera: outermost tunic Thick, white covering
Anterior portion modified into cornea (window where light can enter the eye)
No blood vessels

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

10. 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

11. Lens Biconvex structure Behind cornea, iris, pupil
Bends to focus on objects
Humors: fluid filled areas in eye
Anterior: aqueous humor
Fluid gives anterior portion shape
Constantly replaced to bring nutrients to areas without blood supply
Posterior: vitreous humor
Constant pressure to give eye shape (intraocular pressure)

12. 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

13. Problems within the Eye
Conjuctivitis
Nearsightedness – distant objects are blurry
Farsightedness – close objects are blurry
Astigmatism
Glaucoma

14. The Ear, Hearing, and Balance

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

17. Outer Ear Pinna or 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 cerumen to protect ear

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

19. 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

20. 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

21. Hearing Video

22. 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
Crista ampularis – tuft of hair cells with cupula (gel cap)
Movement bends hairs and cupula
All send signals to brain through vestibular nerve to cerebellum