15.3 lecture 2019

1. Chapter 15, section 3:
Sight and Hearing
How do your eyes enable you to see?
How do you hear and maintain your sense of
balance?

2. Standards
• 7.5.g Students know how to relate the
structures of the eye and ear to their
functions.
• 7.6.b Students know that for an object to be
seen, light emitted by or scattered from it
must be detected by the eye.

3. Vision
• Vision: your eyes
respond to the
stimulus of light.
• They convert that
stimulus into
impulses that your
brain interprets,
enabling you to see.

4. How Light Enters Your Eye
• Cornea- a clear tissue
that covers the front of
the eye
• Pupil-the opening
through which light
enters the eye
• Iris-A circular struture
that surrounds the
pupil and regulates the
amount of light
entering the eye.

5. How Light is Focused
• Lens-Flexible structure that focuses light
• The image it produces is upside down and
reversed.
• Muscles attached to the lens adjust its shape,
focusing the image.

6. How You See an Image
• Retina-After light enters the lens, it goes to the retina, a
sheet of light-sensitive cells that lines the back of the
eye.
• Retina has 130 million cells
• Rod cells- dim light and enable you to see black, white
and shades of gray.
• Cone cells-allows you to see colors
• This is why you see colors best in bright light, but you see
only shadowy gray images in dim light.
• Optic Nerve-rods and cones send electrical impulses to
the brain through the nerve.
• First the brain turns it right-side up then it combines both
images.

7. Seeing in Depth
• Humans have both eyes in front of their head
– BUT they see slightly different images.
• This comparison, interpreted by your brain,
gives you three-dimensional vision.

8. Hearing and Balance
• Your ears are the sense organs that respond to the
stimulus of sound.
• The ears convert sound to nerve impulses that your
brain interprets.

9. How Sound Is Produced
• Sound is produced by vibrations that travel as
waves.
• The vibrations move outward from the source
of the sound, like ripples moving out from a
drop of water.
• The sound waves cause air particles to
vibrate and this is how sound is carried.
• Sound waves can also travel through liquids,
such as water and solids, such as wood.

10. (1) The External Ear
• Shaped like a funnel.
• This enables the external ear to collect sound
waves, which then travel down the ear canal.

11. (2) The Middle Ear
• Sound waves
strike the
eardrum.
• Eardrum
• Hammer, anvil
and stirrup.

12. (3)The Inner Ear
• Stirrup vibrates
against thin
membrane, labyrinth
and cochlea
• Sensory neurons
send nerve impulses
to the cerebrum.

13. The Inner Ear and Balance
• Structures in your inner ear control your sense of
balance.
• Semicircular canals
• Filled with fluid
• Lined with tiny cells that have hair-like extensions
• Movement of the fluid causes hair-like extensions
to bend
• This produces nerve impulses that travel to the brain
• Dizziness