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9.5 Option – Communication: 6. Detection of Sounds

Syllabus reference (October 2002 version)
6. Animals that produce vibrations also have organs to detect vibrations

Students learn to:


Extract from Biology Stage 6 Syllabus (Amended October 2002). © Board of Studies, NSW

Background: If oral communication is to be effective, it is essential that the organism has a way of producing sounds and that those receiving these oral messages have a way to detect them.

outline and compare the detection of vibrations by insects, fish and mammals

Structures used to detect vibrations

Tympanic membranes; sensory hairs

Internal ear; lateral line system; swim bladder


Receptor cells

Mechanoreceptor cells

Hair cells in the inner ear; neuromasts in the lateral line

Hair cells in the organ of Corti

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gather, process and analyse information from secondary sources on the structure of a mammalian ear to relate structures to functions

Description of Anatomy


large fleshy external part of the ear

collects sound and channels it into the ear

tympanic membrane

the eardrum - a membrane that stretches across the ear canal

vibrates when sound waves reaches it and transfers mechanical energy into the middle ear

ear ossicles

three tiny bones, the hammer, anvil and stirrup

amplify the vibrations from the tympanic membrane

oval window

region that links the ossicles of the middle ear with the cochlea in the inner ear

picks up the vibrations from the ossicles and passes them onto the fluid in the cochlea

round window

membrane between cochlea and middle ear

bulges outward to allow pressure differences in the cochlea


circular fluid filled chamber

changes mechanical energy into electrochemical

organ of Corti

a structure within the cochlea

location of the hair cells that transfer vibrations into electrochemical signals

auditory nerve

the nerve that travels from the ear to the brain

Transmits electrochemical signals to the brain

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describe the anatomy and function of the human ear, including:

  • pinna
  • tympanic membrane
  • ear ossicles
  • oval window
  • round window
  • cochlea
  • organ of Corti
  • auditory nerve

Structure of the ear

Structure of the ear
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outline the role of the Eustachian tube

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process information from secondary sources to outline the range of frequencies detected by humans as sound and compare this range with two other mammals, discussing possible reasons for the differences identified

Mammal Lowest frequency detected (Hz)
Highest frequency detected (Hz)
23 000
45 000
123 000
1 000
91 000
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outline the path of a sound wave through the external, middle and inner ear and identify the energy transformations that occur

Path of sound and energy transformations that occur

You can view some of the processes involved in this pathway at How the ear works Bupa, UK.

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describe the relationship between the distribution of hair cells in the organ of Corti and the detection of sounds of different frequencies

Organ of Corti
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outline the role of the sound shadow cast by the head in the location of sound

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process information from secondary sources to evaluate a hearing aid and a cochlear implant in terms of:

  • the position and type of energy transfer occurring
  • conditions under which the technology will assist hearing
  • limitations of each technology


Hearing aids and cochlear implants are both devices designed to improve deafness.

A hearing aid is an electronic, battery-operated device that amplifies and changes sound to allow for improved communication. Hearing aids receive sound through a microphone, which then converts the sound energy to electrical energy. The amplifier increases the loudness of the signals and then converts the electrical energy back to sound. This sound leaves the hearing aid through a speaker which directs the sound down the auditory canal. Most hearing aids are placed in or near the external auditory canal.

Hearing aids are particularly useful in improving the hearing and speech comprehension of people with sensorineural hearing loss. Sensorineural hearing loss develops when the auditory nerve or hair cells in the inner ear are damaged by aging, noise, illness, injury, infection, head trauma, toxic medications, or an inherited condition. Hearing aids will not restore normal hearing or eliminate background noise.

A cochlear implant is a small, complex electronic device that can help to provide a sense of sound to a person who is profoundly deaf or severely hard of hearing. It bypasses damaged parts of the inner ear and electronically stimulates the auditory nerve. Part of the device is surgically implanted in the skull behind the ear and tiny electrode wires are inserted into the cochlea. The other part of the device is external and has a microphone, a speech processor (to convert sound into electrical impulses), and connecting cables.

An implant does not restore or create normal hearing. Instead, it can give a deaf person a useful auditory understanding of the environment and help him or her to understand speech. Unlike a hearing aid which amplifies sound, cochlear implants compensate for damaged or non-working parts of the inner ear. It electronically finds useful sounds and then sends them to the brain.

A person with a cochlear implant must learn to interpret the sounds created by an implant. This process takes time and practice. The person may also have to use the implant in conjunction with lip reading. It has been shown that individuals who receive the implant after they have learnt to speak perform better than those who have never spoken. The implant is also very expensive.

Hearing aid
Cochlear implant
The position and type of energy transfer occurring    
Conditions under which the technology will assist hearing    
Limitations of each technology    
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