1. Human Biology Sylvia S. Mader Michael Windelspecht
Chapter 14
Senses
Lecture Outline
Part 2
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2. 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

3. 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

4. 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.

5. The lens 14.4 Sense of Vision ciliary muscle relaxed lens flattened
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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 Focusing light on the retina of the eye. 5

6. 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.

7. 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

8. © 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 The structure of the retina.

9. 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.

10. 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 The two types of photoreceptors in the eye.

11. Summary of eye structures
14.4 Sense of Vision
Summary of eye structures

12. 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

13. 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

14. Abnormalities of the eye that are corrected with lenses
14.4 Sense of Vision
Abnormalities of the eye that are corrected with lenses
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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 How corrective lenses correct vision problems.
Uneven cornea;
rays do not focus evenly.
Uneven lens allows subject
to see objects clearly.
c. Astigmatism

15. 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