Biology, Eighth Edition (Raven)

Chapter 45: Sensory Systems

Effect of Sound Waves on Cochlear Structures

What determines the range of sound frequencies a person can hear? Sound travels through the air and through water as waves of changing pressure. The volume of a sound is determined by the amplitude of the sound waves, taller waves are louder sounds than shorter waves. The frequency of sound is determined by the wavelength of the sound waves. Short waves are high-pitched sounds, long waves are low-pitched sounds. The cochlea varies in structure so that different wavelengths stimulate different areas in the basilar membrane. Some wavelengths do not stimulate any area of the basilar membrane and are not detectable. In general, smaller ear structures are able to detect higher pitched sounds. Human children are able to hear higher pitched sounds that adults cannot detect. Both cats and dogs are able to hear higher frequency sounds than humans.

View the animation below, then complete the quiz to test your knowledge of the concept.


1.	During hearing, which of the following is the first to vibrate?

		A)	basilar membrane
		B)	tympanic membrane
		C)	hair cells of spiral organ
		D)	oval window
		E)	stapes

2.	During hearing, which of the following is the last to vibrate?

		A)	basilar membrane
		B)	tympanic membrane
		C)	hair cells of spiral organ
		D)	oval window
		E)	stapes

3.	The foot plate is part of the

		A)	malleus.
		B)	spiral organ.
		C)	incus.
		D)	tympanic membrane.
		E)	stapes.

4.	The middle ear has four bones.

		A)	True
		B)	False

5.	Short wavelengths, from high pitched sounds, cause displacement of the basilar membrane near the oval window.

		A)	True
		B)	False