The ear ossicles are homologous to bones in a fish mouth: the bones that support gills in fish are thought to be adapted for use in the vertebrate ear over evolutionary time. These bones also function to collect force and amplify sounds. If we did not have the malleus and the incus, then the vibrations of the tympanum would never reach the inner ear.

In humans, the stapes is not long enough to reach the tympanum. The incus attaches the malleus to the stapes. The malleus attaches at three points to the interior surface of the tympanic membrane. The three ossicles are unique to mammals, and each plays a role in hearing. The aptly named stapes looks very much like a stirrup. The three ossicles are the malleus (also known as the hammer), the incus (the anvil), and stapes (the stirrup). The middle ear holds three small bones called the ossicles, which transfer energy from the moving tympanum to the inner ear. Interior to the tympanum is the middle ear. In mammals, sound waves are collected by the external, cartilaginous part of the ear called the auricle, then travel through the auditory canal and cause vibration of the thin diaphragm called the tympanum or ear drum, the innermost part of the outer ear (illustrated in Figure 27.13). The sound wave shown with a dashed line is softer in volume than the sound wave shown with a solid line. Amplitude of the wave corresponds to volume.

Humans speak normally at 60 decibels.įigure 27.12 For sound waves, wavelength corresponds to pitch. The softest sound that a human can hear is the zero point. For sound, volume is measured in decibels (dB). The sound waves of louder sounds have greater amplitude than those of softer sounds. Those frequencies above the human range are called ultrasound.Īmplitude, or the dimension of a wave from peak to trough, in sound is heard as volume and is illustrated in Figure 27.12. Dogs detect up to about 40,000 Hz cats, 60,000 Hz bats, 100,000 Hz and dolphins 150,000 Hz, and American shad ( Alosa sapidissima), a fish, can hear 180,000 Hz. Women are typically better at hearing high frequencies, but everyone’s ability to hear high frequencies decreases with age. Most humans can perceive sounds with frequencies between 30 and 20,000 Hz. Frequency is measured in cycles per second, and for sound, the most commonly used unit is hertz (Hz), or cycles per second. High-frequency (≥15.000Hz) sounds are higher-pitched (short wavelength) than low-frequency (long wavelengths ≤100Hz) sounds. Frequency is the number of waves per unit of time, and in sound is heard as pitch. The speed of sound waves differs, based on altitude, temperature, and medium, but at sea level and a temperature of 20º C (68º F), sound waves travel in the air at about 343 meters per second.Īs is true for all waves, there are four main characteristics of a sound wave: frequency, wavelength, period, and amplitude. There are no sound waves in a vacuum since there are no air molecules to move in waves. SoundĪuditory stimuli are sound waves, which are mechanical, pressure waves that move through a medium, such as air or water. Instead, an animal’s vestibular system detects its own movement, both linear and angular acceleration and deceleration, and balance. On the other hand, although it is physically linked to the auditory system, the vestibular system is not involved in hearing. It enables an organism to detect and receive information about danger, such as an approaching predator, and to participate in communal exchanges like those concerning territories or mating.

What are the structures of the vestibular system that respond to gravity?Īudition, or hearing, is important to humans and to other animals for many different interactions.

What path does sound travel within the auditory system to the site of transduction of sound?.

What is the relationship of amplitude and frequency of a sound wave to the attributes of sound?.

In this section, you will explore the following questions:

Auditory nerve ap psychology