BIOL 109 1st Edition Lecture 18Outline of Last Lecture I. Parts of ear and role of each part of hearing II. Pitch and loudness III. How receptors responsible for hearing (hair cells) workIV. Perceive and maintain balance Outline of Current Lecture I. Describe wall of Eyeball (layers, structures etc.) II. Describe fluid-filled chambers (difference between vitreous and aqueous) III. How do we focus? IV. Explain how we visualize an object using eyes. V. Describe common visual impairments. VI. Explain how photoreceptors work. VII. Differentiate between rods and cones. VIII. Explain what can cause color blindnessCurrent LectureStructure of the eyeI. Theouter layer is tough and fibrous - Sclera – the white of the eye, protects and shapes the eye, serves as attachment site for muscles- Cornea- transparent area at the front of the eye, allows light to enterVision II. The middle layer is vascular - Choroid – contains blood vessels that supply eye tissue with nutrients and oxygen- Ciliary body- muscular ring former by the choroid toward the front of the eye, holds lens in place and changes its shapeThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Iris – colored portion of the eye, muscular part of the choroid in front of the ciliary body, regulated pupil size. III. The inner layer is light sensitive tissue - Retina – lines the eyeball, contains several layers of neurons, location of photoreceptors. IV. Pupil - an opening in the center of the iris- allows light to enter the eye and reach the retina- action – dilated( opens) in dim light- constricts (closes) in bright lightRetina – the innermost layer that contains photoreceptors. Photoreceptors respond to light by generating electrical signals. Types of photoreceptors: - rods – dim light- cones – bright light and color visionFovea – region of the retina with the greatest concentration of cones. Objects are focused here for sharp vision. Optic nerve – carries visual information from the eye to the brain for interpretation - blind spot- region where the optic nerve leaves the retina. The retina lacks photoreceptors here. An image that strikes the blind spot cannot be seen. Function of Lens: Focusing - theciliary muscles can change the shape of the lens, allowing the image to befocused on the retina. - Light rays must converge onto retina. - The elasticity of the lens allows it to change the shape to change the bending of light- accommodation -> can focus on near and distant objects - With age the lens becomes less elastic-> harder to focus on close objects- A cataract – a lens that has become cloudy, usually due to aging Vision - Over 70% of all sensory receptors of the body are in the eye- Rods and cones are the two types of photoreceptors - All photoreceptors respond to light with a neutral message sent to the brain - Rods allow us to see in dim light, seeing black and white. - They are more numerous than cones, contain the pigment rhodopsin which is broken down in bright light, resynthesized in dark.- Cones - responsible for color vision. Three types – red, blue, and green allow us to see color. Produce sharp images. A reduced number or lack of one of the types of cones results in color