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By the end of this section, you will be able to:
  • Describe the relationship of amplitude and frequency of a sound wave to attributes of sound
  • Trace the path of sound through the auditory system to the site of transduction of sound
  • Identify the structures of the vestibular system that respond to gravity

Audition , or hearing, is important to humans and to other animals for many different interactions. 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. On the other hand, although it is physically linked to the auditory system, the vestibular system is not involved in hearing. Instead, an animal’s vestibular system detects its own movement, both linear and angular acceleration and deceleration, and balance.

Sound

Auditory stimuli are sound waves, which are mechanical, pressure waves that move through a medium, such as air or water. There are no sound waves in a vacuum since there are no air molecules to move in waves. 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.

As is true for all waves, there are four main characteristics of a sound wave: frequency, wavelength, period, and amplitude. Frequency is the number of waves per unit of time, and in sound is heard as pitch. High-frequency (≥15.000Hz) sounds are higher-pitched (short wavelength) than low-frequency (long wavelengths; ≤100Hz) sounds. Frequency is measured in cycles per second, and for sound, the most commonly used unit is hertz (Hz), or cycles per second. Most humans can perceive sounds with frequencies between 30 and 20,000 Hz. Women are typically better at hearing high frequencies, but everyone’s ability to hear high frequencies decreases with age. 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. Those frequencies above the human range are called ultrasound    .

Amplitude, or the dimension of a wave from peak to trough, in sound is heard as volume and is illustrated in [link] . The sound waves of louder sounds have greater amplitude than those of softer sounds. For sound, volume is measured in decibels (dB). The softest sound that a human can hear is the zero point. Humans speak normally at 60 decibels.

A graph shows a regularly repeating sine wave that goes gradually up, then down, then up again. The distance between two crests is the wavelength. The amplitude is the height of the wave. On the graph, two waves with different wavelengths but the same amplitude are superimposed on one another.
For sound waves, wavelength corresponds to pitch. Amplitude of the wave corresponds to volume. The sound wave shown with a dashed line is softer in volume than the sound wave shown with a solid line. (credit: NIH)

Reception of sound

In mammals, sound waves are collected by the external, cartilaginous part of the ear called the pinna    , 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 [link] ). Interior to the tympanum is the middle ear    . The middle ear holds three small bones called the ossicles , which transfer energy from the moving tympanum to the inner ear. The three ossicles are the malleus    (also known as the hammer), the incus    (the anvil), and stapes    (the stirrup). The aptly named stapes looks very much like a stirrup. The three ossicles are unique to mammals, and each plays a role in hearing. The malleus attaches at three points to the interior surface of the tympanic membrane. The incus attaches the malleus to the stapes. In humans, the stapes is not long enough to reach the tympanum. If we did not have the malleus and the incus, then the vibrations of the tympanum would never reach the inner ear. These bones also function to collect force and amplify sounds. 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. Many animals (frogs, reptiles, and birds, for example) use the stapes of the middle ear to transmit vibrations to the middle ear.

Questions & Answers

different between human being and animals
Habeeb Reply
what is fat soluble drugs
Acho Reply
drugs that dissolve mostly in fatty tissues
shea
what is cell
Sesay Reply
cell is the basic unit of life.
ibtisam
how many double bond present in arachidonic acid?
Rekha
what is the source of the homologous chromosomes and the importance of its event?
Tani Reply
what is biology
Habeeb
chemical, cellular, tissue, organ, organ system, organisms
Saleema Reply
chemical, tissue, cellular, organ, organism, organ system
Saleema
yes, both parts are apart of the reproductive and endocrine system because they function in both
Saleema
du antigen
gambo
what is antigenic
gambo
how many bones are there in a human
Tih Reply
206
Shivani
206 when they fused together
gambo
206 bones
Kate
206bones
R0se
206
Mahmmad
define ornithology
Aniowo
ornithology is the study of birds in every aspect.
Hemamalene
chemical which makes a person to lose appetite
milton Reply
name the matrix from which bone is made?
Vaibhav Reply
hydroxyapatite
Tani
whats the nuclear pore ?
Tani Reply
tell me about the nuclear pore or nuclear membrane I don't quite understanding
Tani
The nuclear pore is a protein-lined channel in the nuclear membrane that regulates the transportation of molecules between thenucleus and the cytoplasm.
Jack
The nuclear pore is a protein lined channel in the nuclear membrane (nuclear envelope) that regulates the transportation of molecules between the nucleus and the cytoplasm.
Jack
Thank you...
Tani
what is cell?
Shashi Reply
cell is a small building block that make everything in the body. Other words known as the smallest unit of life
Cheryl
cell is the basics unit of life, in words it's enablement of life process
Dumbari
what is diffusion
kambani
diffusion is the net movement of a particles from an area of high concentration to an area of low concentration down a concentration gradient
linadora
What is the meaning of the word cell?
hafsa Reply
unit
Samiullah
who discovered cell and in what year.
Jonathan
Robert hook discovered cell in 1665.
Alisohai
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gambo
bioLoGy is tHe bRanCH oF SCIENce, anD iTs dEals witH tHe stUdy oF liFe ..
Alisohai
what happened when the hand accidentally touches a hot abject
Tumbu Reply
quickly removes its hand
hafsa
a stimuli is sent to the central nervous system by neurons which in turn send back a response which makes that person to quickly remove his hand from the hot object.
Ofang
what is cell
Ernest Reply
cell can be defined as the smallest unit of life
alhassan
what is a hormone
Michael Reply
hormones are the body's chemical messengers and are part of the endocrine system,.
Nisa
hormone are the chemical messanger that are produce by ductless gland to act on a target organ.
Luqman
why are the pictures showing
Anasili Reply
I don't get your question well
Prophet

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Source:  OpenStax, Human biology. OpenStax CNX. Dec 01, 2015 Download for free at http://legacy.cnx.org/content/col11903/1.3
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