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Home > Biology > Options > Communication > Communication: 6. Detection of Sounds

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: outline and compare the detection of vibrations by insects, fish and mammals   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 outline the role of the Eustachian tube   outline the path of a sound wave through the external, middle and inner ear and identify the energy transformations that occur   describe the relationship between the distribution of hair cells in the organ of Corti and the detection of sounds of different frequencies   outline the role of the sound shadow cast by the head in the location of sound	Students: gather, process and analyse information from secondary sources on the structure of a mammalian ear to relate structures to functions   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   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

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

• Many insects have a pair of membranes, called the tympanic membranes, located on the abdomen or legs. The tympanic membranes act in a similar way to eardrums by vibrating when sound waves reach them. Sensory cells called mechanoreceptor cells detect the vibrations and send a message to the brain.
   
• Many insects also have hairs on the exterior of the body which vibrate in response to sound waves of specific frequencies, depending on the stiffness and length of the hairs. The hairs are often tuned to frequencies of sounds produced by the same or other species. These hairs may be used to detect mates or predators.
   
• Fish do not have external ears, but have internal ears located near the brain. There is no eardrum or cochlea, but the semicircular canals are present. Vibrations of water caused by sound waves are conducted through the skeleton of the head to the inner ear. Hair cells in the semicircular canals vibrate in response and send a message to the brain.
   
• Fish also detect low frequency vibrations with the lateral line system. This consists of a long fluid-filled canal which runs just under the skin down each side of the fish. There are pores at frequent intervals which connect the canals to the exterior. Vibrations in the surrounding water are transmitted to the fluid in the canals, and are detected by groups of sensitive cells called neuromasts. These neuromasts have hairs which project into the canal fluid and detect vibrations by a mechanism similar to that used in the cochlea of the mammalian ear. Messages from the neuromasts are sent to the brain.
   
• Fish also have an air-filled swim bladder, located in the abdomen, which vibrates in response to sound or vibrations. Some fish have a series of bones which conduct vibrations from the swim bladder to the inner ear.
   
• See above for a description for the detection of vibrations by the mammalian ear.
   
• To compare the detection of vibrations by insects, fish and mammals we can use the table shown below.

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

• Try to gather information from a range of resources, including popular scientific journals, digital technologies like CD-ROMs and the Internet. When processing and analysing information you need to ensure that you relate the anatomy of each structure to its function. The web site, Ear Wikipedia, the free encyclopedia, is a useful starting point.
   
• A table like the one below is an effective tool to assist you to gather information.

Structure	Description of Anatomy	Function
pinna	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
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

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

outline the role of the Eustachian tube

• The Eustachian tube connects the middle ear with the throat. Usually this opening is kept closed, but it opens when we swallow or yawn.
• Air can pass through this opening, thus equalising the pressure between the middle ear and the atmosphere.

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

• The range of frequencies that can be detected by humans is 20-23,000 Hz.
• The range of frequencies that can be detected as sounds differs from species to species. These ranges can be easily accessed via the Internet. Record the lowest and highest frequencies detected for humans and two other mammals. Here is a useful starting point Frequency hearing ranges Louisiana State University, Baton Rouge, Louisiana, USA.

• A table like the one below is an effective tool to assist you to record information.

• Compare the results from another source and account for any differences. Hearing (sense)Wikipedia, the free encyclopedia, scroll down to Hearing in animals.
   
• The frequency of sounds produced is related to the hearing frequency of the animal and whether the animal is using sonar for navigation.

outline the path of a sound wave through the external, middle and inner ear and identify the energy transformations that occur

• Sound waves are collected by the pinna and travel down the auditory canal to the tympanic membrane, which vibrates at the same frequency as the sound.
• The first of the ossicles is attached to the tympanic membrane, and this bone begins to vibrate, amplifies the vibration and then passes the vibration on to the other two ossicles, which also amplify the vibration.
• The last ossicle is attached to the oval window, which begins to vibrate and causes the fluid in the cochlea to vibrate.
• The hair cells of the organ of Corti detect the vibration and pass a message to the brain via the auditory nerve.
• Different sounds move the hair cells in different ways, thus allowing the brain to distinguish various sounds.
• We can summarise as shown below:

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

• Passing along the length of the cochlea is a ribbon-like structure, the organ of Corti. This has three main components: the basilar membrane, hair cells and the tectorial membrane.
• The basilar membrane is composed of transverse fibres of varying lengths. Vibrations received at the oval window are transmitted through the fluids of the cochlea causing the transverse fibres of the membrane to vibrate at certain places according to the frequency.
• High frequency sounds cause the short fibres of the front part of the membrane to vibrate and low frequency sounds stimulate the longer fibres towards the far end.
• As the basilar membrane vibrates, the hairs of the hair cells are pushed against the tectorial membrane. This causes the hair cells to send an electrochemical impulse along the auditory nerve to the brain.
• The region of the basilar membrane vibrating the most at any instant sends the most impulses along the auditory nerve.

• The actual perception of pitch depends on the mapping of the brain. Nerves from particular parts of the organ of Corti stimulate specific auditory regions of the cerebral cortex of the brain. When a particular part of the cortex is stimulated, we perceive a sound of a particular pitch.

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

• Many animals can use their two ears to judge the position from which a sound comes. They can move each ear independently until each ear receives the maximum sound.
• Humans cannot move their ears, but can locate the direction of a sound nevertheless. This is because the sound is heard more loudly by the ear nearest to it and also fractionally earlier.
• The pinna is mostly skin and cartilage with some muscles attached to the back, which is what allows some animals to "wiggle" their ears.
• The brain uses reflections from the twists and folds of the pinna to determine the direction of sounds. Sounds coming from the front and sides become enhanced as they are directed into the auditory canal while sounds from behind are reduced. This helps an animal to hear what they are looking at while reducing some of the distracting background noise.

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

• When processing, use the table below to organise your information and then look for patterns and trends.

• You can find more information on cochlear implants at The Bionic Ear Institute.
• Also at Cochlear Implants NIDCD, Bethesda, Maryland, USA