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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 1|Page 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. 2|Page 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. 3|Page 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. 4|Page 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 5|Page 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 6|Page 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. 7|Page 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. 8|Page 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. 9|Page 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 10 | P a g e 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. 11 | P a g e 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. 12 | P a g e 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. 13 | P a g e 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. 14 | P a g e 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. 15 | P a g e 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. 16 | P a g e 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 17 | P a g e - 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 18 | P a g e 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 19 | P a g e 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). 20 | P a g e