The pictures in this series illustrate the enormous variations in size of the structures necessary for hearing.

The pictures do not include all the cells, tissues, or organs necessary for a person to hear, but they do show that small things are made of small things that are made of small things ...........

The first picture is a transverse section of several cilia. A cilium is a minute hair-like process that either causes motion or interprets motion. With hearing, the cilia are sensors that are responsive to movement of the liquid that vibrates in the cochlea. The cilia are composed of slender, protein tubules that are in a 9 + 2 arrangement. The left cilium in the picture clearly shows the arrangement.

1. Using the scale that accompanies the microphotograph, determine the width of a single cilium: ________________nm.

2. Using a ruler and devising a scaled ratio of your own choosing, determine the width of a single pair of microtubules from the first cilium.
________________nm.

The second picture is a scanning electron micrograph (SEM) of an organ-pipe-like arrangement of stereocilia that stick out of the hair cells of the cochlea, an organ of the inner ear. These cilia are shaken by the vibrations (oscillations) of the fluid within the cochlea which was originally stimulated by mechanical vibrations from the bones of the middle ear.

The hairs convert the mechanical energy into electrical impulses which are carried from the inner ear, along the auditory nerve, to the cerebral cortex of the cerebrum. They are then recognized as sound.

3. Using the scale that accompanies the picture, determine the size of the group of cilia: _________________micrometer ( m)

4. What is the width of a single cilia? _____________ micrometer ( m)

5. Convert your answer to nanometers to see if it is similar to your answer to number 2 above.

The third picture shows an enlargement of the inner ear. The organ shaped like a snail is the cochlea. It is lined with membranes containing more than 20,000 sterocilia tuned to vibrate at different frequencies (Hz).
If the cochlea was uncoiled, it would be nearly 4 centimeters long, but when coiled, it is no bigger than a pea.

The hair cells at one end respond to high pitched vibrations up to 20,000 vps and in the center of the coil are the bass receptors that respond to vibrations as little as 16 vps.

6. Use the scale to determine the size of the cochlea. _____________
Remember, the cochlea is about the size of a pea.

7. What is the width of the entire inner ear as shown? Include the distance from the right end of the stapes to the right end of the cochlea.
_____________________

The fourth picture shows the 3 compartments of the ear and the arrangement of the important organs.

8. Use the scale in picture 3 to determine the length of the inner ear. ___________
(Compare to your answer in #7)

9. Determine the length of the middle ear. _______________________

10. Determine the length of the outer ear region. _________________

11. Determine the length of the auditory canal. ___________________

12. Determine the length of the pinna. _________________________

13. Is this picture the actual size of a human ear? (This is not a yes or no question)


14. Is your ear larger or smaller than this one?


15. Change the size of your answer for the middle ear from millimeters to micrometers.