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Special Senses

Special Senses. Eye and Ear. Eye and Vision. 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. External Eye. Eyelid Eyelashes Medial canthus Lateral canthus.

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Special Senses

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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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