Transcript The Ear
The Eye and Vision • Most of eye protected by cushion of fat and bony orbit • Accessory Structures protect eye and aid eye function – Eyebrows, Eyelids, Conjunctiva, Lacrimal apparatus – Extrinsic eye muscles BIOL 105--Lab 12—Eye 1 Conjunctiva: Transparent mucous membrane – Produces lubricating mucous secretion – Conjunctiva covers white of eyes but not cornea Lacrimal Apparatus • Lacrimal glands secrete tears and drain them via ducts into nasolacrimal duct • Lacrimal gland in orbit above lateral end of eye • Tears are dilute saline solution containing mucus, antibodies, and lysozyme – Blinking spreads tears toward medial commissure BIOL 105--Lab 12—Eye 2 Extrinsic Eye Muscles • Six extrinsic eye muscles attach to scleral layer and move eyeball – Originate from bony orbit; insert on eyeball – Enable eye to follow moving objects; maintain shape of eyeball; hold in orbit – Four rectus muscles originate from common tendinous ring; names indicate movements • Superior, inferior, lateral, medial rectus muscles – Two oblique muscles move eye laterally and rotate eyeball • Superior and inferior oblique muscles BIOL 105--Lab 12—Eye 3 Structure of Eye: • Outermost layer; dense avascular connective tissue – Two areas: sclera and cornea 1. Sclera--Opaque region • Protects, shapes eyeball; anchors extrinsic eye muscles • Continuous with dura mater of brain posteriorly 2. Cornea--Transparent anterior area • Bends light as it enters eye • Pain receptors contribute to blinking and tearing reflexes • Corneal transplants typically are not rejected by immune system because cornea has no blood vessels BIOL 105--Lab 12—Eye 4 Choroid---Middle pigmented layer • Contains: choroid, ciliary body, and iris 1. Choroid • Supplies blood to all layers of eyeball • Black pigment absorbs light to prevent it scattering within eye which makes focusing impossible 2. Ciliary body • Ring of smooth muscle surrounding lens • Ciliary muscles relax and contract to control lens shape to allow lens to focus light • Capillaries of ciliary processes secrete fluid • Suspensory ligament holds lens in position BIOL 105--Lab 12—Eye 5 3. Iris-anterior to ciliary body • Colored part of eye • Pupil—central opening that regulates light entering eye – Close vision and bright light —pupils constrict – Distant vision and dim light —pupils dilate – Changes in emotional state—pupils dilate when subject matter is appealing or requires problem-solving skills • Intrinsic eye muscles = ciliary muscle and iris BIOL 105--Lab 12—Eye 6 Lens • Biconvex, transparent, flexible, and avascular • Changes shape to precisely focus light on retina – filled with transparent protein crystallin – becomes more dense, convex, less elastic with age • Cataracts (clouding of lens) consequence of aging, diabetes mellitus, heavy smoking, frequent exposure to intense sunlight BIOL 105--Lab 12—Eye 7 Innermost Layer: Retina • Delicate 2-layered membrane – Outer pigmented layer • Absorbs light and prevents its scattering • Phagocytize photoreceptor cell fragments • Stores vitamin A – Inner Neural layer • Transparent • Composed of 3 types of neurons – Photoreceptors, bipolar cells, ganglion cells • Signals spread from photoreceptors bipolar cells ganglion cells • Ganglion cell axons exit eye as optic nerve BIOL 105--Lab 12—Eye 8 The Retina • Optic disc (blind spot) – Lacks photoreceptors – Site where optic nerve leaves eye • Photoreceptors (quarter-billion) of two types – Rods-black and white vision – Cones-color vision BIOL 105--Lab 12—Eye 9 • Rods – Dim light, peripheral vision receptors – More numerous, more sensitive to light than cones – Used for peripheral vision because numbers greatest at periphery • Cones – Receptors for color vision which function better in bright light (daytime vision) – Macula lutea • Mostly cones • Fovea centralis – Tiny pit in center of macula with all cones; best vision BIOL 105--Lab 12—Eye 10 Internal Chambers and Fluids • Anterior area contains Aqueous humor • Plasma like fluid continuously formed • Drains via canal of Schlemm (at sclera-cornea junction) • Supplies nutrients and oxygen mainly to lens and cornea but also to retina, and removes wastes • Helps maintain shape and pressure of eye • Glaucoma: blocked drainage of aqueous humor increases pressure and causes compression of retina and optic nerve blindness BIOL 105--Lab 12—Eye 11 • Posterior area contains vitreous humor that – Transmits light – Supports posterior surface of lens – Holds neural layer of retina firmly against pigmented layer – Contributes to intraocular pressure and maintains shape of eye – As you get older, may get floaters— • caused by age-related changes and/or changes in vitreous consistency becomes more liquid causes shrinking and pulling away from interior surface of eye. This can cast shadows on your retina, which you interpret as eye floaters. • If you notice a sudden increase in number of floaters, contact an eye doctor immediately — especially if you see flashes of light or lose your peripheral vision; may be caused by retinal detachment. BIOL 105--Lab 12—Eye 12 LABWORK 1. Dissect sheep eye 2. Using eye models and charts, locate the following: sclera, choroid, cornea, retina, iris, pupil, ciliary body, lens, aqueous humor, vitreous body, optic disk, optic nerve. 3. Perform eye tests for visual acuity, astigmatism, and other tests in your lab book, time permitting. BIOL 105--Lab 12—Eye 13 The Ear: Hearing and Equilibrium (Balance) • Three major areas of ear 1. External (outer) ear – hearing only 2. Middle ear (tympanic cavity) – hearing only 3. Internal (inner) ear – hearing and equilibrium • Receptors for hearing and balance respond to separate stimuli BIOL 105--Lab 12—Eye 14 External Ear • Auricle (pinna) – Funnels sound waves into auditory canal – Sound is form of energy transmitted in waves; different sounds have different wavelengths • External acoustic meatus (auditory canal) – Short tube lined with skin ceruminous glands – Transmits sound waves to eardrum BIOL 105--Lab 12—Eye 15 • Tympanic membrane (eardrum) – Boundary between external and middle ears – Connective tissue membrane that vibrates in response to sound – Transfers sound energy to bones of middle ear Middle Ear – Small, air-filled, mucosa-lined cavity in temporal bone – Eardrum at lateral border and medially is bony wall containing oval (vestibular) and round (cochlear) windows BIOL 105--Lab 12—Eye 16 • Eustachian or Pharyngotympanic (auditory) tube—connects middle ear to nasopharynx – Equalizes pressure in middle ear cavity with external air pressure Ear Ossicles • Three small bones in tympanic cavity: the malleus (hammer), incus (anvil), and stapes (stirrup) – Suspended by ligaments and joined by synovial joints – Transmit vibratory motion of eardrum to oval window BIOL 105--Lab 12—Eye 17 Inner Ear (has sound and equilibrium receptors) • Bony labyrinth --filled with perilymph – Three regions: vestibule, semicircular canals, and cochlea • Membranous labyrinth -filled with endolymph – Series of membranous sacs and ducts • Vestibular apparatus – Equilibrium receptors in semicircular canals and vestibule – Vestibular receptors monitor static equilibrium – Semicircular canal receptors monitor dynamic equilibrium BIOL 105--Lab 12—Eye 18 Vestibule • Central cavity of bony labyrinth • Contains two membranous sacs 1. Saccule: continuous with cochlear duct 2. Utricle: continuous with semicircular canals • Sacs responsible for static or linear equilibrium – Maculae contain equilibrium receptor regions – Responds to gravity and changes in position of head BIOL 105--Lab 12—Eye 19 Semicircular Canals • Three canals (anterior, lateral, and posterior) lie in three planes of space –Membranous ducts line canals and communicate with utricle • Ampulla of each canal houses equilibrium receptor region called crista ampullaris – Receptors respond to angular (rotational) movements of head BIOL 105--Lab 12—Eye 20 The Cochlea--hearing • spiral, conical, bony chamber; size of split pea – Extends from vestibule – Coils around bony pillar – Contains cochlear duct, which contains Organ of Corti (spiral organ) • "roof" of cochlear duct is vestibular membrane • • External wall secretes endolymph "Floor" of cochlear duct composed of basilar membrane which supports organ BIOL 105--Lab 12—Eye 21 Auditory Processing • Pitch perceived by impulses from specific hair cells in different positions along basilar membrane • Loudness detected by increased numbers of action potentials that result when hair cells experience larger deflections • Localization of sound depends on relative intensity and relative timing of sound waves reaching both ears BIOL 105--Lab 12—Eye 22 Maculae • Sensory receptors for static equilibrium • One in each saccule wall and one in each utricle wall • Monitor position of head in space, necessary for control of posture • Respond to linear acceleration forces, but not rotation • Contain supporting cells and hair cells • Stereocilia and kinocilia are embedded in otolith membrane studded with otoliths (tiny CaCO3 stones) BIOL 105--Lab 12—Eye 23 The Ear: 1. Find the following structures in your lab book and the human ear models: Pinna, pharyngotympanic (auditory) tube, Tympanic membrane (eardrum), malleus, Incus, Stapes, Cochlea, Vestibule, Semicircular canals, Auditory canal, Round/oval windows, Vestibulocochlear nerve. 2. View slide of the cochlea and note the three fluidfilled chambers and the organ of Corti. 3. Perform hearing/balance tests in lab book. BIOL 105--Lab 12—Eye 24