Human Biology Sylvia S. Mader Michael Windelspecht Chapter 14 Senses Lecture Outline Part 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

1. Layers of the eye: Sclera 14.4 Sense of Vision 1. Layers of the eye: Sclera _______ – the white of the eye that maintains eye shape Cornea: transparent portion of the sclera that is important in refracting light Pupil: a hole that allows light into the eyeball

2. Layers of the eye: Choroid 14.4 Sense of Vision 2. Layers of the eye: Choroid Choroid – middle layer that absorbs light rays not absorbed by the retina ____: donut-shaped, colored structure that regulates the size of the pupil _______ body: structure behind the iris that contains a muscle that controls the shape of the lens Lens – attached to the ciliary body; refracts and focuses light rays

The lens The lens is a flexible, transparent, and concave structure. 14.4 Sense of Vision The lens The lens is a flexible, transparent, and concave structure. Visual accommodation occurs when the lens changes shape to focus light on the retina and form an image. As we age, the lens loses elasticity, and we use glasses to correct for this.

The lens 14.4 Sense of Vision ciliary muscle relaxed lens flattened Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ciliary muscle relaxed lens flattened light rays suspensory ligament taut a. Focusing on distant object ciliary body ciliary muscle contracted lens rounded suspensory ligament relaxed b. Focusing on near object Figure 14.7 Focusing light on the retina of the eye. 5

3. Layers of the eye: Retina 14.4 Sense of Vision 3. Layers of the eye: Retina The retina contains photoreceptors called rods and cones. _____ are sensitive to light. ______ require bright light and respond to wavelengths of light (color). The ______________ is an area of the retina densely packed with cones where images are focused.

3. Layers of the eye: Retina 14.4 Sense of Vision 3. Layers of the eye: Retina Sensory receptors from the retina form the optic nerve that takes impulses to the brain. The ___________ is where the optic nerve attaches; it lacks photoreceptors. 7

© Biophoto Associates/Photo Researchers, Inc. 14.4 Sense of Vision Anatomy of the retina Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. sclera choroid rod cell and cone cell layer bipolar cell layer retina optic nerve ganglion cell layer axons of ganglion cells b. Micrograph of retina blind spot © Biophoto Associates/Photo Researchers, Inc. to optic nerve light rays a. Location of retina Figure 14.9 The structure of the retina.

Photoreceptors of the retina 14.4 Sense of Vision Photoreceptors of the retina Rods They contain a visual pigment called rhodopsin. Rods are important for peripheral and night vision. Vitamin A is important for proper functioning. Cones They are located mostly in the fovea. Cones allow us to detect fine detail and color. 3 different kinds of cones containing red, green, and blue pigments.

Rods and cones in the retina 14.4 Sense of Vision Rods and cones in the retina Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. membrane of disk ion channels close cascade of reactions rod cell light rays outer segment cone cell ion channels in plasma membrane retinal inner segment cell body opsin nucleus membrane of disk rhodopsin molecule (opsin + retinal) synaptic vesicles synaptic endings a. 20 μm b. © Lennart Nilsson, from The Incredible Machine/Scanpix Figure 14.8 The two types of photoreceptors in the eye.

Summary of eye structures 14.4 Sense of Vision Summary of eye structures

Abnormalities of the eye 14.4 Sense of Vision Abnormalities of the eye _______________ – genetic abnormality in which colors, usually red and green, cannot be distinguished; most common in males __________ – lens of the eye is cloudy __________ – fluid pressure builds up in the eye

Abnormalities of the eye 14.4 Sense of Vision Abnormalities of the eye Astigmatism – condition in which the cornea or lens is uneven, leading to a fuzzy image ____sightedness – eyeball is too long, making it hard to see far away objects ____sightedness – eyeball is too short, making it hard to see near objects 13

Abnormalities of the eye that are corrected with lenses 14.4 Sense of Vision Abnormalities of the eye that are corrected with lenses Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. normal eye Long eye; rays focus in front of retina when viewing distant objects. Concave lens allows subject to see distant objects. a. Nearsightedness normal eyeball Short eye; rays focus behind retina when viewing close objects. Convex allows subject to see close objects. b. Farsightedness Figure 14.11 How corrective lenses correct vision problems. Uneven cornea; rays do not focus evenly. Uneven lens allows subject to see objects clearly. c. Astigmatism

Anatomy of the ear The ear functions in hearing and balance. 14.5 Sense of Hearing Anatomy of the ear The ear functions in hearing and balance. 3 divisions Outer ear: functions in hearing; filled with air Middle ear: functions in hearing; filled with air Inner ear: functions in hearing and balance; filled with fluid