Download Option – Communication Humans, and other animals, are able to

Option – Communication
1. Humans, and other animals, are able to detect a range of stimuli from the external
environment, some of which are useful for communication
1.2.1 Identify the role of receptors in detecting stimuli
Sensory structures that detect changes in the environment are called receptors. Animals, including
humans, use all five senses to communicate. The skin haspressure, pain, heat and cold receptors, in
taste buds there are five main types of receptors; salt, sour, sweet, bitter and umami, and there are
about 1000 different smell receptors that can detect up to 10 000 different odours. Effective
methods of communication rely on a corresponding development of visual, acoustic, tactile and
chemical receptors.
1.2.2 Explain that the response to a stimulus involves
- stimulus
- receptors
- messenger
- effector
- response
Stimulus – Reflects change in the environment
Receptor – Detects the stimulus. Each type of receptor is responsible for detecting a certain
type of stimulus. They change the stimuli received into electrochemical signals called nerve
impluses
Messengers – Sensory nerve carrying nerve impulses from the receptors to the CNS where
they are processed and interpreted.
CNS – Brain and spinal cord triggers the response
Messengers – Motor nerve carrying nerve impulses to the effector organ
Effectors – Usually muscles or glands that receive the message and carries out the response
Response – Reaction to the stimulus, triggered by the CNS.
1.3.1 Identify data sources, gather and process information from secondary sources to identify the
range of senses involved in communication.
Visual (sight) – This includes communication by colour, pattern, posture, body movement, facial
expression. It used in courtship behaviour, to signal threat and defend territory. This form of
communication is very effective because light travels in straight lines and extremely fast, which also
makes it effective in providing details about the distance from an object and the speed at which it is
travelling. Most human communication relies on symbols, for example numbers or words, making
sight an extremely important form of communication in this regard, particularly through allowing
information to reach those who are not within range of hearing or sight.
Olfactory (smell) – This is communication via specific chemical signals. It is used in marking
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territories, to search for and identify food, water, and species, sex recognition and to detect and
avoid harmful substances.
Auditory
(hearing) – This is communication by sound. Used to defend territory, alert others to danger,
distress calls and used in breeding.
Tactile
(touch) – Used to avoid obstacles, fighting, defence mechanisms, friendship behaviour and
copulation.
Taste –
Animals that have a poor sense of smell may rely on taste as a form of communication. Bees and
blowflies have “tastebuds” on their feet helping to locate food and chameleons rely on taste in
marking territory.
Other – Detecting
electric fields (platypus), polarised light (bees) and gravity.
2. Visual communication involves the eye registering changes in the immediate
environment
2.2.1 Describe the anatomy and function of the human eye including the:
Conjunctiva –Fine transparent membrane that covers and protects the surface of the
cornea. This membrane is continuous with the inner layer of the eyelid.
Cornea– The transparent front window through which light enters the eyeball. The
curvature of the cornea helps to bend or refract the incoming light, doing much of the initial
focussing of images, so that they converge and land at the back of the eyeball on the inside.
Sclera – The outermost layer of the eye. It is opaque, forming the white part of the eye. It is
composed of tough, non-elastic tissue that protects the delicate inner layers of the eye and it helps
to maintain the shape of the eyeball.
Chloroid – Underneath the sclera is the chloroid, a sheet of blood vessels that carry oxygen
and nutrients to the eye and remove carbon dioxide and wastes. It also prevents scattering or
reflection of light within the eye.
Retina– Complex structures of photoreceptors (rods and cones) on the back of the eye.
Photoreceptors allow us to see shape, movement and colour; retinal nerve cells convert incoming
light into nerve impulses.
Iris– The coloured part of the eye. It is made up of connective tissue and smooth muscle
which brings about its main function; to control the size of the pupil by controlling the amount of
light entering the eye (pupil dilates or contracts).
Lens– The lens refracts light rays and directs them onto the retina where a focused image
will be formed. The lens has highly elastic properties that enable it to change shape, varying from a
rounded to a flatter structure, allowing the eye to accommodate to near and far vision respectively.
Aqueous and Vitreous Humor – The aqueous humor is a transparent, watery fluid that has a
similar composition to blood plasma and provides nutrients for the lens and cornea, which do not
have their own blood supply. The Vitreous humor is a clear, jelly-like material filling the remainder of
the eyeball. It contains dissolved nutrients, refracts light and helps to maintain the shape of the eye.
Ciliary body – Circular, muscular ring that focuses the lens. It is responsible for secreting the
aqueous humor.
Optic nerve – contains a million nerve fibres that conduct the nerve impulses to the vision
centres in the brain.
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2.2.2 Identify the limited range of wavelengths of the electromagnetic spectrum detected by
humans and compare this range with those of other vertebrates and invertebrates.
Human eye can detect wavelengths between 380 and 750nm, the “visible light” range on the
electromagnetic spectrum. This is compared to the colours of red, orange, yellow, green, blue,
indigo and violet.
The honey bees (invertebrates) can detect wavelengths in the UV range but are unable to
detect some longer wavelengths in the red part of the spectrum. This assists them in finding the
pollen and nectar.
The Pit Viper snake (vertebrate), detects infra-red radiation. This enables them to detect
endotherms, such as mice, for prey.
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2.3.2 Use available evidence to suggests reasons for the differences in the range of
electromagnetic radiation detected by humans and other animals
Colour sensitivity is related to the structure of the eye. The number of types of coloursensitive cones and their sensitivity range in many vertebrates determines their colour vision. Some
organisms with compound eyes, such as bees, also have visual cells sensitive to different ranges of
electromagnetic radiation.
Colour vision is related to evolution. Most nocturnal animals have vision that is less sensitive
to colour. It is believed that humans and our primate line have evolved from a nocturnal ancestor, so
our colour vision evolved separately from many of the other placental mammals. Colour vision can
be important for the recognition of food sources. This is particularly the case in some birds, bees and
herbivorous primates. Bees, for example, can often see patterns on flowers that humans cannot.
These patterns guide the insect to the pollen or nectar source in the flower. Birds that are sensitive
to red and infra-red will be able to compete to visit red coloured flowers as a source of food. Snakes
and some fish that detect infra-red radiation will be able to easily detect their prey, as the heat will
allow the snake to hunt successfully at night. The fish may detect prey that would normally be
hidden by the background or because of camouflage. Orientation and navigation in some birds have
been linked to a dependence of the presence of blue and green light. Monarch butterflies, which can
migrate over long distances, navigate by ultraviolet light in the sky.
3. The clarity of the signal transferred can affect interpretation of the intended visual
communication
3.2.1 Identify the conditions under which the refraction of light occurs
When light passes from one medium to another medium with a different density, the speed at which
the light is travelling changes. As a result, the light rays are bent or refracted.
3.2.2 Identify the cornea, aqueous humor, lens and vitreous humor as refractive media
Each of these structures is made up of substances with differing optical density and refract light that
passes through the eye, to a greater or lesser extent. Most of the refraction takes place at the
cornea. Here there is the largest change in the index of refraction, as light leaves the air and enters
the cornea. Because the ciliary muscles can change the shape of the lens, the amount that the lens
refracts the light varies. This enables focussing on objects at differing distances.
3.2.3 Identify accommodation as the focussing on objects at different distances, describe its
achievements through the change in curvature of the lens and explain its importance.
Accommodation is the process by which the lens changes convexity, and as a result, its
refractive power, to focus images from objects different distances away from the retina.
For distant objects/vision, the curvature of the lens must be relatively flat. When the ciliary
muscles are relaxed, they hold the suspensory ligaments taught. These ligaments pull on the lens,
keeping it relatively flat and allowing the image of distant objects to be focussed on the retina.
For near vision, the curvature of the lens must be increased; a thicker lens has greater
refractive power and a shorter focal length. The ciliary muscles contract, pulling the sclera forward,
causing the suspensory ligaments to slacken. The lens becomes rounder, refracting the light to a
greater degree and allowing a focussed image to fall on the retina.
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3.2.4 Compare the change in the refractive power of the lens from rest to maximum
accommodation
The refractive power of the lens changes from low (in a flatter lens) when at rest, to high (in a
rounder lens) at maximum accommodation. The refractive power of lenses can be compared using
the SI unit dioptre. A dioptre is inversely proportional to the focal length of a lens (i.e. the larger the
number of dioptres, the less the refraction).
3.3.2 Analyse information from secondary sources to describe changes in the shape of the eye’s
lens when focusing on near and far objects
3.2.5 Distinguish between myopia and hyperopia and outline how technologies can be used to
correct these conditions
Myopia is short-sightedness. This is when a person can see near objects clearly, but distant
objects appear blurred. In the eye, the distance between the lens and the retina is too great or the
lens is too strong, so the image is focussed in front of the retina.
Hyperopia is long-sightedness. This is when distant objects are seen clearly but near objects
cannot be seen in focus because the image falls behind the retina.
Eyeglasses/spectacles – nowadays made of hard plastic. They are lighter in weight and less
easily broken and shattering them does not carry the risk of glass splinters, however glass does not
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scratch as easily and does not become hazy with time. Myopia can be corrected with concave lenses,
Hyperopia with convex.
Contact lenses – can be concave or convex, but the overall lens is shaped to fit the curvature
of the eyeballs. They have advantages cosmetically, playing sport, in entertainment industry and
ones that block UV light. There can however be issues with infection.
Refractive Laser Eye surgery is a treatment that involves reshaping the curvature of the
cornea. A thin flap of corneal tissue is cut. This tissue is then folded back and a laser beam is applied
to the exposed corneal tissue. When the laser is finished, the flap is returned.
3.2.6 Explain how the production of two different images of a view can result in depth perception
Depth perception depends on binocular vision, where the fields of vision overlap. In predatory
animals, eyes are placed towards the front of the head, giving greater distance and depth
perception. Animals that are preyed on need to know what is approaching them. Their eyes are
found on the side of their head, giving them wider fields of view but little depth perception.
3.3.3 Process and analyse information from secondary sources to describe cataracts and the
technology that can be used to prevent blindness from cataracts and discuss the implications of
this technology for society
A cataract is a clouding or thickening of the lens of the eye. This results in loss of
transparency and therefore loss of vision.
The lens of the eye is composed of water and folded proteins called crystallins. The main
structures of the lens are lens fibres (the crystallins). Lens fibres are continually replaced throughout
life, enlarging the lens slightly so that it becomes denser and less elastic. As the lens becomes
denser, nutrients in the lens fibres become insufficient. The crystalline protein fibres become
oxidised, therefore clumping together forming the cloudiness or thickening and so preventing some
light from reaching the retina and interfering with vision.
Cataract surgery removes the natural, clouded lens of the eye and replaces it with a clear,
artificial one. It is usually performed under anaesthesia and the entire process usually takes less than
an hour. There are several variations in the both the removal and replacement portions of the
surgery, with the most commonly used type called phacoemulsification. This procedure enables the
removal of the cataract and implantation of the artificial lens through the micro incision (less than
3mm) around the pupil. Once the incision is made, a small tip is inserted to break the cataract into
small fragments via ultrasonic vibration. These are then removed by suction via the incision. The
artificial lens is usually a foldable intraocular lens and can be folded to less than half its size, allowing
insertion through the incision. Once inserted, the lens unfolds to its normal full size. There are
generally no stiches required and after surgery the eye is covered with a shield for protection.
In the past, cataract surgery involved the removal of the entire lens from the eye, leaving the
patient functionally blind unless they wore extremely thick glasses to compensate. Modern
techniques obviate this need for glasses post-surgery.
This technology has meant that thousands of people, who are cataract blind, can now see.
With the surgery, people can live more independent lives, particularly as it affects, predominantly,
older people. The Fred Hollows foundation worked tirelessly to bring affordable, sight-restoring
surgery to indigenous Australians, particularly in remote and isolated communities, and to very poor
communities in other parts of the world such as Nepal, Eritrea, Vietnam and Africa. The implications
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for these societies are enormous. For example, an estimated 3.5 million people are cataract blind in
sub-Saharan Africa and many of these people will die within four years of going blind. The availability
of the simple surgery can save the lives of these people.
4. The light signal reaching the retina is transformed into an electrical impulse
4.2.1 Identify photoreceptor cells as those containing light sensitive pigments and explain that
these cells convert light images into electrochemical signals that the brain can interpret
Photoreceptor cells are specialised neurones, or nerve cells, that contain light sensitive
pigments found in the retina. These cells convert light images into electrochemical signals/impulses
that the brain can interpret. There are two main types of receptors; rods and cones, which contain
photosensitive chemical substances that undergo reactions when they absorb light energy. There
are five main layers of nerve cells or neurones that are directly involved in the transmission of
impulses in the retina; the photoreceptor cell layer, bipolar cell layer ad ganglion cell layer, as well as
associated horizontal cells and amacrine cells.
The rods and cones in the photoreceptor cell layer, when stimulated by light, perform three
main functions:
1)
They absorb light energy (this involves the visual pigments)
2) They convert this light energy into electrochemical energy, generating a nerve impulse
3) They transmit this nerve impulse towards the bipolar cells of the retina.
The signals are then transmitted to the Ganglion cells which, at the distal end of the cells,
are extended and go on to form the fibres of the optic nerve that are responsible for carrying the
electrochemical signals to the brain
Horizontal cells occur at the junction between photoreceptors and bipolar cells. They
connect one group of rod and cone cells to another.
Amacrine cells occur at the junction between bipolar cells and ganglion cells.
4.2.2 Describe the differences in distribution, structure and function of the photoreceptor cells in
the human eye
Rods and cones are responsible for the formation of an image.
Rhodopsin is the only pigment present in rods. Cones contain iodopsin.
Cones are more densely concentrated in the central fovea, a small depression in the centre
of the macula lutea at the back of the eyeball. They are stimulated by bright light and are specialised
for colour vision and visual activity.
Rods are more evenly distributed across most of the retina and respond best to low light
intensities. They allow us to detect shape and movement and to discriminate between shades of
light and dark.
4.2.3 Outline the role of rhodopsin in rods
When rhodopsin absorbs a sufficient amount of light energy, it splits into two parts. This reaction
produces activity in the nerve cell. In bright light, the rhodopsin in rods is broken down faster than it
can be manufactured. In dim light, production is able to keep pace with the rate of breakdown.
Therefore rods are specialised for night vision.
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4.2.4 Identify that there are three types of cones, each containing a separate pigment sensitive
either blue, red or green light
The pigments are almost the same as those in rods but require bright light and re-form quickly. The
three iodopsin pigments are sensitive to the short wavelengths of blue light, medium wavelengths of
green light and the long wavelengths of red light, and therefore cones are responsible for colour
vision. The sensitivity of a particular cone cell allows it to detect light to some extent on either side
of these peak sensitivities, giving an overlap in some of the colours detected.
4.2.5 Explain that colour blindness in humans results from the lack of one or more of the coloursensitive pigments in the cone
Because cones detect colour, any defect or damage to the cones will affect the ability of the eye to
perceive colour. A mutation in a gene that codes for a cone pigment leads to the inability of this
pigment to function properly. As a result, the person is unable to perceive colour in the normal
trichromatic manner and is said to be either colour deficient or colour blind, depending on how the
mutation affects the pigment.
The gene for colour blindness is recessive to the gene for normal vision. Because the X
chromosome is a sex chromosome, red-green colour blindness is a sex-linked disorder.
4.3.1 Process and analyse information from secondary sources to compare and describe the nature
and functioning of photoreceptor cells in mammals, insects and in one other animal
Eyes in animals range from really simple structures to extremely complex ones.
The main photoreceptors in mammals are rods and cones. Depending on the number of
types of cones in each mammal, they may be sensitive to a range of colours. Humans and primates
are in the minority of mammals that have full colour vision. Nocturnal animals have a higher
proportion of rods to cones and, in fact, rats do not even possess cones and so see only black and
white.
Some invertebrates, such as planarians (e.g. flatworms) have simple light receptors or
eyespots. These are patches of light sensitive cells in a concave cup lined with pigment cells and are
used to distinguish light from dark. This may contain fluid, the only light-refracting part of the eye.
The simple “image” that forms on the layer of the photoreceptors is unclear and is not inverted. The
role of the photoreceptors is therefore merely to allow the animal to detect light.
Insects have a pair of more complex light-sensitive structures called compound eyes. They
are able to detect light, movement and form a clearer image than the simple eyes of planarians.
Each eye is made up of 8000 units called omatidia. Each ommatidium only sees part of an object.
When each section of the object is put together, it forms a mosaic type of picture.
A transparent, hexagonal cornea and a clear, crystalline cone refract the incoming light rays.
There is no lens present as in the mammalian eye. After passing through the cornea and crystalline
cone, lights travels down the rhabdom, an elongate central structure, to the retinal cells. These are
the light sensitive structures in each ommatidium. Nerve fibres from the base of the retinal cells
combine to form a tiny nerve that joins with other nerves from other ommatidium, carrying impulses
to the insects simple brain.
The time taken for one ommatidium to receive a light stimulus, generate an impulse in
response and then regenerate is far quicker than for a rod in a mammalian eye, resulting in a much
higher frequency of flicker fusion than humans.
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4.3.2 Process and analyse information from secondary sources to describe and analyse the use of
colour for communication in animals and relate this to the occurrence of colour vision in animals
Humans are familiar with many forms of colour communication in everyday life. Examples
include; the colour coding of electrical wires for electricians, the use of colour for map markers to
signify different countries and states, targets in archery, team recognition in sports clubs and colours
used in flags of different countries. The use of colour may also be important for survival such as the
recognition of soldiers being allies or enemies or may be trivial like in board games.
In animals other than humans, colour is an essential form of communication for breeding,
used for recognition of members of the same species, members of the opposite sex, sexual maturity
and readiness to mate.
Colour communication in animals often takes the form of visual displays for mate attraction.
Courtship displays in animals are important to ensure that mates are of the same species, as well as
to evaluate the quality of the partner. These rely on colouration, for example male angelfish are
brightly coloured to attract females.
Visual displays may be used as a warning mechanism to defend a territory or to ward of
possible enemies. For example, the display of large, colourful feathers by the male peacock is not
only for mate attraction, but is also a common sign when they are threatened.
Colour plays an important role in food recognition. Colouration of flowers is linked to
attracting agents of pollination such as bees and birds. Warning colouration also plays a role in food
recognition. One example is that of the yellow and black markings of the Monarch butterfly. These
colours warn birds that the insect is poisonous.
The use of colour for communication is only effective if the animal receiving the message has
colour vision. Mammals with poor colour vision, such as dogs, depend more on their senses of smell
and hearing for communication.
5. Sound is also a very important communication medium for humans and other
animals
5.2.1 Explain why sound is a useful and versatile form of communication
Sound bends around objects and travels around corners. It travels through all substances;
solids, liquids and gases and animals do not have to be in visual or direct contact to communicate.
When visual, touch and alfactory senses are impaired or absent, sound can be used as a primary
method of communication. A complete message can be conveyed in a short space of time. Therefore
it is a useful, versatile form of communication.
5.2.2 Explain that sound is produced by vibrating objects and that the frequency of the sound is
the same as the frequency of the vibration of the source of the sound
Sound originates when something vibrates rapidly enough to organise the movement of
molecules so as to spread a compression wave through a medium.
The frequency of vibrations is the number of waves that pass a given point in one second.
High frequency results in high pitch and low frequency results in low-pitched sounds. Low frequency
sounds have long wavelengths while high-frequency sounds have short wavelengths.
The amplitude (height of the wave) determines the volume of the sound; the greater the
amplitude, the louder the sound.
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5.3.1 Plan and perform a first-hand investigation to gather data to identify the relationship
between wavelength, frequency and pitch of a sound
Aim: To determine the relationship between wavelength, frequency and pitch of a sound.
Method: You will need to use a cathode ray oscillator (CRO) and audio oscillator to generate and
detect sound waves of varying frequencies.
Alternatively, a microphone attached to the CRO could be used and generate sounds of
varying pitches and frequencies using tuning forks or other musical instruments.
Conclusion: A high-pitched sound has a high frequency and a short wavelength. The loudness of the
sound is determined by the energy carried by the wave. The larger the amplitude, the larger the
sound.
5.2.3 Outline the structure of the human larynx and the associated structures that assist the
production of sound
The larynx (voice box) is positioned in the throat where the pharynx divides into the
respiratory tract (trachea) and the digestive tract (oesophagus).
The larynx is a hollow box which houses the vocal folds/vocal cords. In humans, its structure
basically consists of nine cartilages, joined by membranes and ligaments, to form the voice box in
which sound can be produced and resonate. The upper opening of the box is called the glottis, and is
often covered by the epiglottis. Being
flexible and spoon shaped, it tips
forward over the rising larynx during
swallowing and prevents food from
entering the larynx and trachea.
Cartilage surrounds the larynx
and muscles connect this to the head or
neck while others alter the position,
shape and tension of the vocal
cords/vocal folds.
The interior of the larynx has a
mucus-coated lining. Lying under this
mucous lining, on each side, are the
vocal ligaments. These join some of the
cartilage together and in doing so, draw
the mucous lining up from the vocal cords or true vocal cords. The true vocal cords vibrate and may
produce sound as air rushes between them from the lungs through the glottis. The rapid opening
and closing of the glottis set up the vibration pattern which produces sound. Above the true vocal
cords, there is another set of vestibular, or false, vocal cords. These play no part in sound production
however the mucous produced here assists in lubricating the true vocal cords.
The length of the vocal cords, and therefore the size of the glottis is controlled by the vagus
nerve. One of this nerve’s functions is the contraction and relaxation of the muscles and
consequently the movement of the attached ligaments and cartilage. The shorter and tenser the
vocal folds, the faster they vibrate and the higher the pitch.
The volume or loudness of the voice is controlled by the strength of the airflow; the greater
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the airflow, the stronger the vibrations and the louder the sound.
The vibration of the vocal cords only produces a buzzing sound. This sound is resonated and
amplified through the action of the pharynx, tongue,soft palate, cheeks, lips and nasal cavity. The
soft palate acts as a valve and directs the airflow from the larynx to the mouth and nose. The nasal
cavity is responsible for the unique voice produced by each person. Different speech sounds are
produced by the movement of the tongue, lips and jaw.
5.3.2 Gather and process information from secondary sources to outline and compare some of the
structures used by animals other than humans to produce sound
Some insects communicate via sound. Crickets and Katydids produce sound by lifting the
wing covers to 45 degrees and rubbing the front of one wing cover over the rough area of the other
front wing. They can alternate wings to reduce wear and tear. This is called Stridulation.
Male cicadas are renowned for being one of the noisiest insects. The organs which produce
the sound are called the tymbals. These are a pair ribbed membranes at the base of the abdomen.
Muscles attached to the tymbals contract, causing them to buckle and produce a pulse of sound.
When the muscles relax, the tymbals resume their usual position.
Fish can produce sound, for example the sea catfish, by vibrating a bone against their swim
bladder, producing a noise similar to a giant aerator bubbler on a fish tank.
A bird’s sound producing organ is called the syrinx. It is situated at the base of the trachea
where it splits into the two bronchi. Elastic membranes of connective tissue inside the syrinx open
and close as the bird exhales. The pressure of the air entering the syrinx, the size of the syrinx and
the elasticity of the folds determine how the sound is produced.
The dolphin’s larynx does not possess vocal cords and current research suggests that all of
the clicks, grunts, squeaks and whistles are produced in the tissue complex of the nasal region.
Sound results from movements of air in the trachea and nasal sacs as well as the release of air from
the blowhole.
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6. Animals that produce vibrations also have organs to detect vibrations
6.2.1 Outline and compare the detection of vibrations by insects, fish and mammals
The tactile bristles on an insect’s cuticle and on its antennae respond to low frequency
vibrations. But many insects have more specialised structures for hearing.
Orthopterans (such as crickets and katydids) have a tympanum (drum) or ear on each leg
just below the knee. The tympanum is a cavity containing no fluid. It is enclosed by an eardrum on
the outer side and a pressure release valve on the other. Nerve fibres are connected to the eardrum
and pick up the vibrations directly.
The hearing abilities in fish vary between species. They have two main systems for
underwater detection of sound;
- A labyrinth (an inner ear that has a sensory chamber composed of passages) that contain
sound receptors.
- A visible lateral line that runs along the body. Disturbances in the surrounding water distort
the sensory cells found in the canals, sending a message to the nerves.
Hearing is most developed in mammals. Killer whales have an acute sense of hearing. Sound
is received by the lower jawbone. This contains a fat-filled cavity which extends back to the auditory
bulla (ear-bone complex). Sound waves are received and conducted through the lower jax, the
middle ear, inner ear and the auditory nerve to the well developed brain.
Dolphins close their ear canals when diving. They detect vibrations through special organs in
the head and some low-frequency sounds through the stomach.
6.2.2 Describe the anatomy and function of the human ear
Pinna – Collects sound waves from a wide area and funnels the sound into the external ear
passage. It is made of cartilage.
Tympanic membrane – Sound waves cause it to vibrate which are then conveyed to the oval
window by the ossicles. It is stretched across the end of the auditory canal.
Ear Ossicles – Hammer (Malleus), Anvil (Incus) and Stirrup (Stapes), act as a compound lever,
amplifying the waves as they transmit them to the inner ear.
Oval Window – A membrane between the middle ear and the inner ear. It holds the fluid in
the cochlea. As the stapes vibrates, the oval window vibrates, sending waves through the peilymph
(fluid).
Round Window – A membrane located in the round window niche at the base end of the
lower canal of the cochlea. It allows the release if the hydraulic pressure of the perilymph that is
caused by the vibration of the stapes on the oval window.
Cochlea – Contains the receptors for sound and the vestibular apparatus that is associated
with a sense of balance.
Organ of Corti – Contains the auditory receptor cells.
Auditory Nerve – Transmits the sound waves to the brain in the form of electrochemical
impulses.
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6.3.1 Gather, process and analyse information from secondary sources on the structure of a
mammalian ear to relate structure to function
Part
Pinna
Tympanic
membrane
Ear Ossicles
Malleus (hammer)
Incus (anvil)
Structure
This, together with the auditory
canal and the outer layer of the
eardur,. Forms the outer/external
ear. Composed of cartilage and has
a relatively poor blood supply.
Found on each side of the head
This taut membrane consists of
three layers, the outer layer being
continous with the outer layer of
the auditory canal.
Its shape resembles a hammer. The
“handle” is attached to the inner
layer of the tympanic membrane.
Resembles a blacksmith’s anvil. It is
attached to the malleus and the
long process is attached to the
stapes
Function
Healps to localise sound waves coming
to the ears. Glands in this cartilaginous
part of the ear produce cerumen
(earwax) that traps dust etc.,
preventing it from reaching the
eardrum, thus helping the ear to be
water repellent and self-cleaning.
Airborne sound waves set up
vibrations in the tight membrane. The
pars tensa provides the active vibrating
area in response to sound. This
membrane grow continually which
allows it to self-repair after damage.
When the tympanic membrane
vibrates in response to sound, the
malleus also vibrates, passing these
vibrations to the incus.
Incoming sound is given a small boost.
This is due to the long process of the
incus being shorter than the long
process of the malleus.
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Stapes (stirrup)
Resembles a stirrup on a saddle.
The “footplate” of the stirrup rests
on the oval window
Oval Window
A membrane, between the middle
ear and the inner ear, covering an
opening in the bony case of the
cochlea.
Round Window
Membrane located in the round
window niche at the base end of
the lower canal of the cochlea
Cochlea
A snail-shaped structure containing
three canals, filled with fluid and
separated from each other by two
membranes.
Organ of Corti
Situated in the middle canal of the
cochlea, is consists of:
Tectorial membrane: A delicate,
gelatinous membrane which covers
the inner and outer hair cells
Outer hair cells: each cell contains
a muscle-like filament.
Auditory nerve
Inner hair cells: each cell has a
nerve fibre attached.
Basilar membrane: separated
middle canal and lowest canal. It is
a tapering, ribbon-like structure
with the broader, stiffer end
towards the oval window.
Pillars of Corti: cells which bound
the tunnel of Corti and run the
entire length of the cochlear
partition.
Leads from the cochlea and the
sense organ of balance to the
correct perception centre of the
brain.
Incoming sound is given a significant
boost as the long process of the incus
vibrates so does the footplate of the
stapes. The boost is the result of the
vibrating tympanic membrane being
larger than the vibrating area of the
stapes.
This separates the middle ear from the
perilymph (fluid) of the inner ear. It
holds the fluid in the cochlea. As the
footplate of the stapes vibrates, the
oval window vibrates, sending waves
through the perilymph.
Allows the release of the hydraulic
pressure of the perilymph that is
caused by the vibration of the stapes
on the oval window.
Vibrational wave patterns from the
stapes set up a vibration in the
membranes and a travelling wave
pattern in the perilymph and
endolymph of the cochlea.
The sense organ of hearing which
changes mechanical energy to
electrochemical energy.
Holds the cilia of the outer hair cells
The basilar membrane changes
position in response to a travelling
wave causing movement of the cilia,
causing the muscle-like filaments to
contract.
Prime responsibility for producing our
sensation of hearing.
Because of the changes in broadness
and stiffness, high frequencies are
coded at the end nearer the oval
window (base) and lower frequencies
at the narrow end (apex).
Cells which provide support
The transmission of neural energy from
the cochlea to the brain.
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6.2.3 Outline the role of the Eustachian tube
The Eustachian tube connects the middle ear to the pharynx (the chamber at the back of the mouth
and nose). The tube is usually closed, but can be opened by yawning or swallowing. The role of the
Eustachian tube is to equalise the pressure on the two sides of the ear drum.
6.2.4 Outline the path of a sound wave through the external, middle and inner ear and identify the
energy transformations that occur
The Pinna collects the sound waves (sound energy) and directs them into the ear. These vibrations
continue along the external Auditory Canal until they reach the eardrum which vibrates at the same
frequency as the entering waves (mechanical energy). These vibrations are transferred to the ear
ossicles; Hammer, Anvile and Stirrup, which act as a compound lever, amplifying the vibrations. The
stirrup connects with the oval window so when it vibrates, it pushes on the window, causing fluid in
the inner ear to move. These are transmitted to the three chambers of the Cochlea. The hair cells,
located in the Organ of Corti, detect the vibrations and bend and generate nerve impulses that go to
the brain, via the auditory nerve (electrochemical energy).
6.2.5 Describe the relationship between the distribution of hair cells in the Organ of Corti and the
detection of sounds if different frequencies
The Organ of Corti rests on top of the basilar membrane. The sound receptor cells in the Organ of
Corti are hair cells. The hair cells synapse immediately with endings of the cochlear nerves. The
movement of hair cells varies with the frequency of vibrations. Hair cells nearest the oval window
(base) are activated by the highest pitched sounds, while those furthest away at the narrow end of
the cochlea (apex) are stimulated by low frequency sounds.
6.2.6 Outline the role of the sound shadow cast by the head in the location of the sound
The phenomenon caused by the obstruction or absorption of a sound wave by an object in its path is
called a sonic or sound shadow. One ear, therefore, receives less sound than the other. This plays a
significant role in locating a sound source.
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6.3.2 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
Human – 20 – 20 000Hz
- the flexibility of the Basilar Membrane limits frequency range. During evolution,
the ability to modify the environment has reduced the reliance on hearing. Effective vision
eliminates the need for echolocation.
Dolphins – 200 – 200 000Hz
- The cannot rely on vision all the time, for instance in murk or dark water,
therefore they use sound to detect objects and locate food. Changes in frequency, intensity,
duration and quality provide details about shape, size, texture, velocity, distance away and
movement of an object. They also use it for communication.
Bats – 10 000 – 100 000Hz
- bats are crepuscular (active in dim light – dawn or dusk) and/or nocturnal. They,
therefore, rely on echolocation for navigation and detection of prey. The higher the frequency sound
wave, being short, produces more detailed messages for the bat regarding its surroundings.
6.3.3 Evaluate a hearing aid and a cochlear implant in terms of; the position and type of energy
transfer occurring; conditions under which each technology will assist hearing; and limitations of
each
Hearing aids work by amplifying the sounds. They are battery operated devices that fit in the
hollow just outside the ear canal. The device consists of a microphone to capture sounds, an
amplifier to magnify them and a earphone to channel them into the ear. Hearing aids restore quality
of life to recipients and prevent them from becoming socially isolated which could ultimately lead to
mental health issues. A hearing aid is non-invasive. They may, however, have problems with
background noise and feedback received in the hearing aid, as well as a limited distance if hearing,
which is approximately 3 metres.
A cochlear implant is an artificial hearing device. It is designed to bypass dead hair cells and
electrically stimulate the auditory nerve directly. They consist of a cochlear implant package and
receiver-stimulator, a speech processor and a headset.
The receiver is implanted into the patients skull. A fine wire attaches the receiver to the
cochlea. A transmitting coil is implanted and held against the skin by a magnet on the outside of the
skull. A microphone behind the patient’s ear picks up sounds. These are passed to a sound
processor, usually worn on a belt or in a pocket. The processor then transmits the signals to the
receiver.
This technology assists who are profoundly or totally deaf. The limitations to the technology
include that it requires surgery to place the electrode array in the inner ear. This is quite significant
surgery due to it being in close proximity to the brain, and opening up the susceptibility to disease.
There can be post-operative side effects such as a droopy face and numbness of the tongue. It is
expensive, with on-going costs and programming needs to be adjusted for different situations as
well as it can also take time to adjust to it.
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7. Signals from the eye and ear are transmitted as electro-chemical changes in the
membranes of the optic and auditory nerves
7.2.1 Identify that a nerve is a bundle of neuronal fibres
The basic unit of the nervous system is the neurone, or nerve cell. A neurone is made of dendrites, a
cell body containing the nucleus, and an axon. The long axon fibre is usually covered in a myelin
sheath that insulates the fibre. A nerve is a bundle of neuronal fibres or axons. There are three types
of neurones:
- Sensory neurones – transmit impulses from sense
organs to other neurones in the CNS
-
Motor Neurones – transmit impulses
from the CNS to muscles and glands
-
Connector Neurones – connect sensory neurones
with motor neurones, usually in the brain and
spinal cord
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- Structure of a typical Nuerone
7.2.2 Identify neurones as nerve cells that are the transmitters of signals by electrochemical
changes in their membrane
Neurones are nerve cells that transmit signals by electrochemical changes in their
membrane. The signals travel like a wave from dendrites, through the cell body to the axon and then
have to cross synapses to other neurones. The signals are electrical in that they can be detected as
changes in voltage. They are regarded as chemical because it is actually the movement of charged
atoms that brings about the signal.
The voltage is always measured between two points and is called the potential difference or
simply potential. A potential exists across every cell’s plasma membrane. The side of the membrane
exposed to the cytoplasm is negative while the side exposed to the extracellular fluid is positive. The
differences on either side of the membrane result in a cellular voltage, which is called the resting
membrane potential. This measures about -70mV, which indicates that the inside of the membrane
is negative. The membrane is then said to be polarised.
Cell membranes are selectively permeable to Sodium, Potassium and Chloride ions because
of ion channels.
The electrical charges are caused as Sodium ions move into the neurone when the ion
channel pores are open. After the signal has been transmitted, potassium ions move to the outside
of the cell to restore the original of the neurones.
A positive shift in membrane potential, from -70mV to -40mV for example, is called
depolarisation. If depolarisation is strong enough, this flow of ions causes the neurone to generate a
nerve impulse or action potential.
7.2.3 Define the term “threshold” and explain why not all stimuli generate an action potential
The threshold is the amount of positive charge in membrane potential which is required
before an action potential is produced. The depolarisation must reach a threshold which is at least
15mV more positive that the resting potential of -70mV. No action potential is produced if the
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depolarisation is below this level. This is one reason why not all stimuli generate an action potential.
There may also be an insufficient influx of Sodium ions across the membrane, insufficient release of
neurotransmitter to depolarise the synaptic nerve or insufficient time for the nerve to reset for the
next action potential.
Each stimulus produces either a full action potential or none at all, known as the “all or
nothing” response.
7.3.2 Perform a first-hand investigation to examine an appropriate mammalian brain or model of a
human brain to gather information to distinguish the cerebrum, cerebellum and medulla
oblongata and locate the regions involved in speech, sight and sound perception
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7.2.4 Identify those areas of the cerebrum involved in the perception and interpretation of light
and sound
Perception and interpretation of light
A visual cortex lies within the Occipital lobe of each cerebral hemispheres. Impulses are
received from the retina via the optic nerve. The optic nerves from each of the eyes partly cross over
to form the optic chiasma. About half of the nerves cross to the other side, providing each visual
cortex with the same image as viewed by both eyes, but each eye receives the image at a slightly
different angle.
Perception and Interpretation of Sound
An auditory nerve is found on the Temporal lobe of each cerebral hemisphere. Different
sites on this cortex receive and interpret different sound frequencies. Auditory nerves arise from the
hearing (cochlea) and equilibrium (vestibule) apparatus within the ear. This merges to form the
vestibulocochlear nerve which runs from the Organ of Corti to the Temporal lobe.
7.2.5 Explain, using specific examples, the importance of correct interpretation of sensory signals
by the brain for the coordination of animal behaviour
Signals from the environment are only meaningful if they can be interpreted correctly by the
brain and then used to bring about a coordinate response. Sensory signals can be wrongly
interpreted, however, such as with optical illusions. Certain species of orchids are able to “deceive”
some male wasps into believing the flower is a receptive female wasp. The male attempts to mate
with the flower and in doing so, pollinates it.
Sometimes the transmission of the stimuli to the spinal cord and brain is short-circuited,
preventing the interpretation to be made and a response given. A variety of reasons can cause this,
including; lack of stimulus (e.g due to cataracts), trauma (severing of or damage to nerves), lack of
oxygen or disease.
An example of when things go wrong is Multiple Sclerosis (MS). It is an autoimmune disease
in which there is an immune attack by the body on its own myelin protein. Gradually the myelin
sheath in the CNS are destroyed and become hard substances called scleroses. As the insulating
layer becomes non-functional, the impulses are sort circuited and finally conduction of the impulses
cease. There are problems with controlling muscles (weakness, clumsiness and urinary incontinence)
and visual disturbances (including blindness).
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