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Understanding Eye and Ear Anatomy: Quick Facts on Vision and Hearing

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Discover essential facts about the anatomy and functions of the eye and ear. The eye, comprising various structures, processes light and forms images, while the ear is crucial for hearing and balance. Explore the roles of the sclera, retina, cochlea, and more, and learn about common problems like nearsightedness and ear infections. This concise overview highlights key components like the tunics of the eye, mechanics of hearing, and the vestibular apparatus, shedding light on how these special senses contribute to our interactions with the world.

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Understanding Eye and Ear Anatomy: Quick Facts on Vision and Hearing

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  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 • Supplies blood to eye • 2 parts: • Choroid (posterior) • Ciliary body (anterior) attaches lens using ciliaryzonule • 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)

  16. 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

  17. 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

  18. 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

  19. 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

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

  21. 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

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