Module 1 The Nervous System

1.1.6 page 6

Read

Hearing Pitch and Loudness

You have likely been to a concert, listened to your iPod, or perhaps you play a musical instrument, so you are probably familiar with high and low pitch sounds. However, do you know how or why you are able to hear high or low pitch sounds? How are you able to distinguish between yelling and whispering? To understand how we hear, read pages 421 – 424. When you have finished, make summary notes, a concept map, or a flow chart for your course folder.

Try This

To assure your understanding of the concepts of pitch and loudness, answer the following questions in full sentences. If you are unsure of any of the concepts, consult with your instructor. File your exercise in your course folder.

1. Define frequency.
2. What is pitch? What is the relationship between pitch and frequency?
3. What is the amplitude of a sound wave? How is the intensity or loudness of a sound related to the amplitude of a sound wave?
4. Each of the sounds described below predominantly illustrates either pitch or loudness. Classify each as one or the other according to its main feature.

1. whine of a mosquito
2. sound of a low note on the piano
3. sound of a jackhammer breaking up a cement sidewalk
4. sound of jet plane taking off
5. growl of a dog

Read

Loudness, Pitch, and the Organ of Corti

As you have read on pages 421 to 424, the hair cells in the organ of Corti are sensitive to the frequency (pitch) as well as to the amplitude (loudness) of sound waves. The basilar membrane closest to the oval window (where frequency is 20,000) is narrow and stiff as shown in the diagram below. It responds to high frequency sound waves.The basilar memrane by the apex of the cochlea (where frequency is 20) is wide and flexible. It responds to low frequency sound waves.

In the lab, you will be examining the differences between pitch and loudness. Notice in the diagram that the wider basilar membrane furthest from the oval window and closest to the apex or tip of the cochlea responds to lower frequency sound waves. Different hair cells are stimulated by different frequencies. In the diagram, the numbers correspond to the range of frequencies that humans can hear. In comparison to humans, dogs can hear very high sounds in the range of 40,000 Hz Reflect on how we use this knowledge in the use of a dog whistle. Mice can hear in the range of 80,000 Hz. And elephants can hear sounds as low as 16 Hz. Hair cells at either end of the basilar membrane can be damaged over the years and they do not regenerate. How would this damage affect the range of your hearing as you age? If you guessed that the ability to hear high and low sounds deteriorates, you were right.

Try This (optional)

You may choose from one of the following exercises:

Demonstrate your understanding of the concepts on how sound is perceived by answering the following questions in complete sentences.

1. How is the brain able to perceive sounds of higher or lower pitch and softer or louder sounds?

2. Mice and dogs can hear sounds in the range of 40, 000 - 80,000 Hz whereas elephants hear sounds as low as 16 Hz. Describe how the cochlea of these animals might be modified as compared to the human cochlea.

3. Why are elderly people often not able to hear very high pitched sounds?

OR

Do questions 6, 18, and 19 on page 432 of the textbook.