Process of Eyesight and Hearing

Eye Structure Layers Eye composed of three layers Outside Layer: Sclera – white of the eye Muscles attached to the sclera allow the eye to move Front of the sclera curves outward to form the cornea – transparent and permits light into the eye Optic Nerve – transmits visual information to the brain Conjunctiva – thin, moist membrane / covers front part of sclera and inside the eyelid

Eye Structure Layers Middle Layer – Choroid Choroid – mostly blood vessels, just inside the sclera and ends at the front of the eye in two structures: Iris – colored disk with the opening in the center / determines color of eye Pupil – opening of the iris / determines amount of light entering the eye from the cornea Bright light – muscles of the iris contract, causing the pupil to narrow and let in less light Dim light – muscle fibers relax, pupil becomes larger, letting more light in Ciliary Body – produces water fluid between cornea and the lens Small muscles in the ciliary body contract or relax to change the shape of the lens Lens – behind the iris, ciliary muscles help lens to focus on objects at various distances

Eye Structure Layers Inner Layer – Retina Retina – light-sensing portion of eye, containing thousands of light receiving cells and nerve cells Two types of light receiving cells: Rods – dim light, allow to see black and white Cones – bright light, enable you to see color Rods and cones convert images focused on the retina to nerve signals, which are transmitted to the brain by the optic nerve

How Vision Occurs Light passes through the cornea, the lens, and vitreous humor before reaching the retina Light receptor cells (Rods and Cones) convert the light images to signals traveling through the optic nerve to be interpreted in the brain

Structure of the Ear Outer Ear Ear lobes and exposed portions of the ear funnel sound waves into the ear canal End of the ear canal is the eardrum Eardrum vibrates when sound waves strike it

Structure of the Ear Middle Ear Eardrum sends vibrations into the middle ear Vibrations are processed by three tiny bones called the hammer (malleus), anvil (incus), and stirrup (stapes) These bones magnify gentle sounds and soften loud ones

Structure of the Ear Inner Ear Vibrations from the bones in the middle ear transmit sound vibrations to the cochlea Cochlea – hollow, fluid-filled, coiled tube with special vibration sensing cells These vibration cells send out nerve signals that travel through the auditory nerve to the brain, where they are interpreted as sound