Topic : Communication

Notes for Communication

Below are the syllabus dot points of Communication. Click on the dot point to expand relvant information. These notes were written by; Emalee Callaghan Click here to donate her

1.1. Identify the role of receptors in detecting stimuli

  • A stimulus is a change in the internal or external environment of an organism. Living organisms detect stimulus by receptors
  • Receptors consist of single cells, scattered all over the body of an organism. They also band together to form sense organs such as the eye and the ear
  • The sense organs contain non-sensory tissue, aside from the special sensory cells that monitor stimuli

1.2. Explain that the response to a stimulus involves ; Stimulus, Receptor, Messenger, Effector, Response

  • The central nervous system (brain and spinal cord) trigger the response
  • Receptors in the sense organ change the stimuli received by a sense organ into electrochemical signals called nerves impulses
  • The impulses travel along the nerves which act as messengers to the central nervous system where they are processed ad interpreted as information and a suitable response is initiated
  • The central nervous system sends messages along the nerves to the effectors that carry out the response

1.3. Identify data sources, gather and process information from secondary sources to identify the range of senses involved in communication

2.1. Describe the anatomy and function of the human eye, including the ; Conjunctiva, Cornea, Sclera, Iris, lens , Optic nerve, Ciliary body , Choroid, Retina , Aqueous and vitreous humour

  • Conjunctiva – Continuation of the epidermis of the skin, this protects the cornea at the front of the eyeball against any inflicted friction
  • Cornea – Transparent to admit light, the cornea refracts light to help focus the image onto the retina
  • Sclera – This is the white of the eye, it consists of a tough coat of fibres, and protects the eyeball against any mechanical damage also maintaining the shape of the eyeball.
  • Choroid – This is a type of membrane that contains certain pigments and blood vessels, this nourishes the retina, and provides a blood supply to the area, also absorbing light to prevent any internal reflection.
  • Retina – The retina contains light and photosensitive light-sensitive receptor cells, these are connected to the sensory neurones, leading to a detection of light.
  • Iris – The iris is the pigmented muscular tissue that surrounds the pupil of the eye this produces the colour of the eye such as blue or green, this can narrow or widen to adjust the amount of light entering the eye.
  • Lens – The lens of the eye is a flexible transparent structure, which enables light to reach the back of the eye; it also refracts light to allow fine focusing of an image onto the retina.
  • Aqueous Humor – The Aqueous Humor is a clear watery fluid found inbetween the cornea and the lens, this allows the eye to maintain the shape of the eye and supplies nutrients to the cornea and lens.
  • Vitreous Humor – This clear jelly-like substance is found behind the lens and in front of the retina, this helps maintain the shape of the back of the eye.
  • Ciliary Body – The Ciliary body consists of muscles; these muscles support the lens and alter the shape of the lens for accurate vision.
  • Optic Nerve The optic nerve consists of bundles of sensory neurons, transmitting impulses that are generated in the retina to the brain

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

The range of wavelengths detected by humans

  • Electromagnetic radiation is made up of large groups of radiation that travel at the same speed (300 000km per second) but all of which have different wave lengths and frequencies.
  • Humans can see visible light – detected by the light sensitive rods and cones
  • Waves of the electromagnetic spectrum are able to travel through a vacuum. When rays of light reach a transparent surface such as glass or plastic or water they are able to travel through it, but they become bent or refracted
    • The splitting of white light into six colours known as dispersion
  • Wavelength is the distance measured between two wave crests. The wavelengths of the electromagnetic spectrum are measured in nanometres nm (1mm = 1 000 000nm)
  • The wavelength of visible light is between 380-760nm
    • Blue or violet light travels as short wavelengths and these are high energy waves.
    • Light in the red part of the spectrum travels as long wavelengths – low energy waves
  • Frequency links the energy of a wave, the shorter the wavelength the greater the frequency
  • Objects absorb some wavelengths and reflect others (dark colours are warmer as they absorb more heat)
  • Humans have trichromatic vision – there are three different types of cone cells sensitive to each colour (blue red and green)
  • We are blind to wavelengths less than 40nm

The range of wavelengths detected by invertebrates and other vertebrates


  • Many insects can detect wavelengths in the ultraviolet range of the spectrum – that is there light sensitive cells can detect shorter wavelengths in the UV range
  • UV patterns on flowers attract bees, they have a bullseye pattern directing bees to the pollen and nectar. Honey bees are unable to detect longer wavelengths in the red part of the spectrum. They see red as black or an absence of colour. Honey Bee’s see a different range


  • Many bird species are able to detect light well into the ultraviolet range.
  • Birds also tend to detect light better in the longer (red and green) spectrum and can also detect sound in the blue range suggesting tetra chromatic vision.
  • Sensitivity to light in the near UV range is also present in some reptiles and some rodents
  • The blue cone receptors in mice are receptive to UV light

Many animals that can fly are able to detect polarised light. This is thought to be used by these animals for navigation during flight – humans cannot see polarised light

2.3. Use available evidence to suggest reasons for the differences in range of electromagnetic radiation detected by humans and other animals

  • Certain types of snakes, such as rattle snakes, can detect infra-red radiation using a pit organ on their body. This means that they will hunt during the night or move into dark burrows and still be able to detect particular endotherms. They can detect prey by using both their eyes and the pit organ.
  • Humans have very different means of hunting these types of food sources for example if we are looking for a food source in the dark we need a source of light that allows us to see the visible spectrum that our eyes can detect, therefore allowing us to see as clear as daylight and expose the food we may be hunting for in the dark.


  • Insects like the honey Bees can detect UV radiation, and as many flowers have patterns of UV light rays as they are exposed to them throughout the day, as a source of food for the honey bees this can be detected easily through the use of their UV radiation, directing them to the nectar helping in the pollination progress as well.
  • Humans are not able to see these particular wavelengths, but for good reason, as we are not a prime pollinator in natural ecosystems

Colour sensitivity

  • Colour sensitivity is related very closely to the structure of the eye. The number of types of colour sensitive 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 the electromagnetic spectrum of radiation.
  • Snakes and some fish that detect infra-red radiation can easily detect their prey at night, as the heat from their bodies will result in infra-red radiation being emitted, pretty much acting as a target for their prey, allowing these fish and snakes to successfully hunt at night. The fish may detect the prey that would normally be hidden by the background or because of camouflage.


3.1. Identify the conditions under which refraction of light occurs

  • In order to be seen an object must reflect light, generate its own light or transmit light into our eyes
  • When light moves from one substance or medium to another medium it is bent or refracted. This leads to a distortion of the image that you see making it difficult to judge the exact location of the object

Conditions under which the refraction of light occurs

  • When light passes through one medium to another of a different density, the speed at which the light is travelling changes.
  • Light will travel more slowly through the water at the bottom of the jar than at the top
  • Because the movement of light in the denser medium is slower, it is refracted to a greater degree than the light travelling through the air
  • When rays of light are passed through a biconvex lens (one that is rounded or bulges on both sides) the rays are refracted towards a central point known as a focal point. The rays then cross over and diverge (spread out) from that point.  

3.2. Identify the cornea, aqueous humour, lens and vitreous humour as refractive media

Refractive media in the mammalian eye

  • The density of the cornea, aqueous humor, lens and vitreous humor are similar to each other and to that of water.
  • All of these structures refract light that passes through the eye, to greater or lesser degrees
  • The refractive power of air, however, through which light travels to reach the eye of terrestrial mammals, is very different from the refractive power of the eye, therefore the greatest degree of refraction occurs when light moves into the eye from the surrounding air into the cornea of the eye
  • The lens has a refractive structure, and is able to refract light into a greater or lesser degree by altering its shape. This is termed accommodation and is useful in allowing the eye to adjust to near or distant vision
  • The lens consists mainly of living protein fibres called crystallins, housed in the lens capsule. These proteins are folded in a particular way to make them transparent, the oval shape of the lens (it’s a degree of curvature) determines the degree to which light can be refracted

3.3. Identify accommodation as the focusing on objects at different distances, describe its achievement through change in curvature of then lens and explain its importance AND 3.4. Compare the change in the refractive power of lens from rest to maximum accommodation

  • If light travels toward the eye from a distant source, the light rays tend to be parallel, this means that they do not have to be refracted much in order to pass through the pupil and fall onto the retina
  • The lens of the eye then therefore remains relaxed and fairly elongated state when viewing distant objects
  • However, if light rays travel from a close source, the light rays tend to diverge. These rays need to be refracted to a greater degree, so that they can converge and can be directed onto the retina
  • For this increased refraction of rays, the lens has to become rounder to result in a more focused image forming on the fovea of the retina
  • The increase in curvature is brought about by muscle action. The muscles are the ciliary muscles, they change the shape of the lens, which in turn affects the tension of the suspensory ligaments that hold the lens
  • Accommodation is the term used to describe the focusing of objects at different distances, brought about by changing the convexity of the lens and as a result its refractive power
  • For distant vision the curvature of the lens must be relatively flat. This occurs when the ciliary muscles are relaxed an they hold the suspensory ligaments taut (stretched)
  • These ligaments pull on the lens keeping it flat and allowing the image to be focused on the retina
  • For near vision the curvature of the lens must be increased, a thicker lens has a greater refractive power and a shorter focal length. The ciliary muscles contract, pulling the sclera forward, causing the suspensory ligaments to slacken. As a result, the lens becomes rounder and the curvature increases refracting the light to a greater degree and allowing a focused image to fall on the retina

3.5. Distinguish between myopia and hyperopia and outline how technologies can be used to correct these conditions

Visual defects including myopia and hyperopia


  • Short sightedness – can see near objects but distant ones appear blurred
  • Distant objects being viewed form a focused image that fall in front of the retina. When near objects are viewed the image falls at the correct depth on the retina, enabling the person to see near objects and not far distance objects
  • There are several causes
    • The eyeball may be too elongated in shape
    • The refractive power of the cornea may be inadequate
    • The lens may not become flat enough when the ciliary muscles contract


  • Long sightedness, when distant things are seen clearly
  • Near objects appear blurry because the image falls behind the retina
  • Causes are
    • The eyeball that is too short from front to back (eyeball is too rounded)
    • A lens that is too flat and is unable to alter its shape therefore can only see long distance
    • The refractive power of the cornea is too great for the shape of the eye


  • a defect in the eye or in a lens caused by a deviation from spherical curvature. Which results in distorted images, as light rays are prevented from meeting at a common focus

Summary of technology to correct myopia and hyperopia

  • Myopic people will have trouble seeing traffic signs, watching television, recognising others and reading signs and playing games. In previous times this would have been hazardous in other ways relating to survival – prohibiting activities like hunting
  • People who have hyperopia can read books, newspapers or computer screens, using tool and machinery and close up hand eye coordination
  • Technologies available to correct these defects are therefore a major advantage in society
  • To compensate for refractive errors in the eye, technologies offer people the opinion of using corrective lenses or more recently laser eye surgery


  • Lens can be made of glass or a clear hard plastic making them lighter and durable
  • Glass however does not scratch as easily as plastic
  • Myopia can be corrected by wearing glasses with concave lenses. These lenses bend the light rays outwards, causing them to diverge before reaching the eye. This extends the focal length of light rays allowing a focused image to fall on the retina
  • Hyperopia can be remedied by wearing glasses with convex lenses. This lens will bend the light rays inwards causing them to begin converging before they reach the eye, shortening the focal length and allowing a focused image to fall on the retina

Contact lenses

  • similar technology to spectacles in terms of shape and lens and refraction of light
  • The basic structure of the lens is a convex or concave shape but the overall lens is shaped to fit the curvature of the eyeball
  • They are worn directly on the surface of the eye – in contact with the eye
  • The first contact lens where made of glass and very uncomfortable for the wearer – further technology led to three types of lens
    • Hard lenses are small, made of glass and cover only the central area of the cornea
    • Soft lenses are larger and, more flexible lenses made of a type of plastic that contains around 30% – 70% water. The lenses cover the cornea and are more comfortable to wear but not as efficient as correcting vision
    • Gas permeable lenses are similar to hard lenses but are porous, allowing an exchange of gases between the surface of the eye and the outside air. This means they can be worn for longer periods of time
  • The advantages of wearing contact lenses compared with spectacles.
    • Contact lenses are used for cosmetic purposes, Advantages when playing sport
    • Use of contact lenses in the entertainment industry
    • Contact lenses that block uv radiation

Refractive laser eye surgery

  • Involves the use pf lasers to change the curvature of the cornea to alter its refractive power, compensating for any visual defects
  • Lasers are computer operated – there are currently two techniques
    • LASIK –laser in situ = involves cutting and lifting a flap of the cornea, leaving it partly intact, allowing them to shape the section under the flap
    • PRK – photorefractive keratectomy – surgery involves the removal of the epithelium and surface of the cornea. The laser is then used to shape the upper most layer of the cornea and the epithelium takes two to three days to grow back
    • Current laser surgery is replacing the previous technique of radial keratectomy where fine surgical instruments rather than lasers where used to shave the cornea surface

3.6. Explain how the production of two different images of a view can result in depth perception

  • Some animals have forward facing eyes, meaning that there is a considerable overlap between the views on the left and the right. Because the two eyes are a few centimetres apart, each eye sees a slightly different view of an object.
  • The brain superimposes images so that they appear correctly, because each view is slightly different, as some objects can appear 2D some can appear 3D

Types of vision:

  • 3D vision: perceptive distance, depth, height and width of vision
  • Binocular vision: occurs when both eyes are focused on the same visual field. As each eye captures its own image of the view and sends the message to the brain, where the images from each eye overlap, and the brain matches the similarities, notes the differences and the combined picture is that of a 3D stereoscopic picture of the view giving a form of depth perception

3.7. Plan, choose equipment and resources and perform a first-hand investigation to model the process of accommodation by passing rays of light through convex lenses of different focal lengths

Bending of light experiment

3.8. Analyse information from secondary sources to describe changes in the shape of the eyes lens when focusing on near and far objects

4.1. 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

The retina

  • The inner most coat of the eyeball is a thin sheet of cells about 1/10mm thick
  • It consists of several layers of nerve cells (one of which is the visual receptors – rods, cones)
  • The rods and cones are the only nerves that respond directly to light (photoreceptors).
  • In humans each retina contains approximately 125 million rods and 6-7 million cones

Position of photoreceptors in the retina

  • The layers of nerve cells are arranged back to front. The rods and cones are the last layer of cells that the light reaches
  • The rods and cones are situated closest to the choroid layer
  • The photoreceptors generate impulses, which travel back alone the various neurone layers of the retina to the optic nerve and then onto the brain
  • There are five main layers of the nerve cells and neurones that are directly involved with the transmission of impulses in the retina: (photo on previous page)
    • The photoreceptor layer
    • Bipolar cell layer
    • Ganglion cell layer
    • Horizontal cells
    • Amacrine cells

Photoreceptor layer

  • Rods and cones when stimulated by light perform three main functions
    • Absorb light energy
    • They convert this energy into electrochemical energy generating a nerve impulse
    • They transmit this nerve impulse towards the bipolar cells

Bipolar cell layer

  • These sensory neurones receive electrochemical signals from the rods and cones and transmit the signal to the ganglion layer

Ganglion layer

  • Receive electrochemical from the bipolar cells. The distal end of ganglion cells is extended into long processes that go on to form the fibres of the optic nerve
  • These neurones are responsible for carrying electrochemical signals from the retina to the brain

Horizontal and Amacrine cells

  • Horizontal cells occur at the junction between photoreceptor cells and bipolar cells. They connect one group of rod and cone cells with another and then link them to bipolar cells
  • Amacrine cells occur at the junction between bipolar and ganglion cells
  • Studies suggest that horizontal cells and Amacrine cells are involved in the process or summarising incoming visual information

Interpretation of the visual signal

  • Some information is processed in the retina, most of the interpretation of visual stimuli occurs in the brain, based on variables such as
    • How strong the light is, how many rods and/or cones are stimulated, contrast enhancement, recognition of horizontal, vertical and diagonal lines, the combination of cones stimulated (leading to colour direction) and the differences in the image hat falls on the retina on the left and right eye (depth perception)

4.2. Describe the differences in distribution, structure and function of the photoreceptor cells in the human eye


  • Both rods and cones are elongated calls that contain an outer segment (closer to the choroid layer of the eye) joined to an inner segment that leads to the conducting part of the cell
  • The conducting part of the cell comprises a cell body containing the nucleus and an extension or process called the foot. This process conducts impulses to the next layer of neurones in the retina
  • Rods and cones are named after the shape of their outer segments. In rods, this segment is long and narrow. Cones tend to have a shorter outer segment that is conical (cone shaped). Most cones are broader than rods
  • Rods and cones contain visual pigments, chemical substances that absorb light energy. These pigments, sometimes collectively terms visual purple are stacked in layers of flattened membranes in the outer segment of each photoreceptor
  • Rhodopsin is the only pigment present in rods. Cones contain iodeosin’s. these are three different types of iodeosin’s, one found in each type of cone cell. Each type is sensitive to a different wavelength of light.
  • the cone cells are therefore responsible for colour vision, while the rod cells can only see black and white.
  • The role of visual pigments is to absorb light energy, which the rod or cone cell then converts into an electrochemical signal that the brain can interpret

Distribution and function

  • Rods are evenly distributed across most of the retina, but are absent from the fovea.
  • As a result, rods are responsible for most peripheral vision, including the detecting of movement
  • The rods are not very tightly packed in the retina and many rods may connect with one bipolar neurone. This retinal convergence results in rods have poorer visual acuity
  • Rods are extremely sensitive to light, responding best to low light intensities and can be stimulated (bleached) by very small quantities of light energy. The pigment can also be rapidly regenerated – the resulting sensitivity allows for operation in semi-darkness and this is why they are used for night vision and light and shadow contrast
  • Cones are distributed in groups throughout the retina but there are fewer around the periphery of the retina, most being concentrated in the macula. This area of retina gives the central 10 degrees of vision.
  • The fovea is a small pit in the middle of the macula and contains cones only. The cones in the fovea are very densely packed and show no retinal coverage. Resulting in a high degree of visual acuity
  • The absence of blood vessels, neuron fibres and rod cells in the fovea lead it to being the area with the most acute vision
  • Cones are responsible for colour vision – each cone containing one of three types of iodopsin pigment – each type of iodopsin is sensitive to one of the primary colours (blue, red and green)
  • The trichromatic colour vision suggests that all colour are a mix of the primary colours
  • Because cones are less sensitive to light than rod they require larger quantities of light to stimulate or bleach them
  • As a result, cones function best in high intensity or bright light, giving day time vision. Cones take longer to regenerate once they have been bleached by light

4.3. Outline the role of rhodopsin in rods

  • The visual pigment rhodopsin’s (previously referred to as visual purple) present in rods, consists of a protein molecule, opsin, combined with a simple, light–absorbing part called the retinal.
  • The retina is a derivative of vitamin A – if this vitamin is lacking, vision is affected and a condition known as night blindness.
  • The retinal exists in an activated or deactivate form

The role of rhodopsin in rods

  • The main role of the photochemical pigments rhodopsin in rods is to absorb light (iodopsin in cones is thought to work in a manner similar to that of rhodopsin in rods)
  • When light strikes the rhodopsin pigment the light energy is absorbed and the rhodopsin changes from its rested state to its excited state. This change is due to the activation of the retinal part of rhodopsin
  • When light strikes the retinal becomes activated causing the rhodopsin to split into its protein opsin and a free retinal part – the split rhodopsin is said to be bleached – but the change is temporary
  • Following this a series of biochemical steps whereby the activated pigment causes a change in electrical charges of the membrane of the cone. This is the start of an electrical impulse that moves along the receptor, triggering the release of a chemical substance known as a neurotransmitter
  • This then stimulates a bipolar cell, generating an impulse in this cell. The signal is then termed electrochemical, because it involves both an electrical change in membrane and a chemical release of a neurotransmitter
  • The bipolar cell transmits the electrochemical signal to the ganglion cells which in turn carry the signal to the brain
  • Rhodopsin, the photochemical pigment which was temporarily bleached or broken down in the presence of light, is then regenerated so that it can be reused: retinal and opsin recombine with the help of enzymes. This allows a new image to be received

4.4. Identify that there are three types of cones, each containing a separate pigment sensitive to either blue, red or green light

Terminology – light sensitive pigments

  • The light sensitive pigments rhodopsin and iodopsin are each made up of two parts
    • A retinal (retinene) molecule (derived from vitamin A)
    • A protein cell opsin
      • It is the difference in the type of opsin molecule that determines whether the visual pigment is rhodopsin (rods) or iodopsin (cones)
    • There are two types of opsins present in photoreceptors
      • Scotopsin – part of rhodopsin
      • Photopsins – part of iodopsin
    • There are three types of photopsins
      • Opsin blue, opsin green, opsin red
    • Components of rhodopsin – opsin and retinal, iodopsin – one of three photopsins and retinal

Rhodopsin and other opsins

  • Because all rods only have one type of pigment rhodopsin, they are not sensitive to different colours. Rhodopsin is a broad spectrum pigment.
  • It peaks sensitivity is in the 500nm wavelength region of the visible light spectrum but rods do not allow us to perceive any colour
  • Each cone contains one of three types of iodopsin pigments and is therefore most sensitive to light in one of three wavelengths
    • The short wavelengths of blue light peak sensitivity being at approximately 445nm
    • The medium wavelengths of green light peak sensitivity at about 530nm
    • The long wavelengths of red light peak sensitivity at 625nm
  • However, the sensitivity of a particular cone cell allows it to direct light to some extent on either side of these peak sensitivities, giving an overlap In some of the colours detected
  • Red cones are actually more sensitive to yellow light (560-565nm) then red light, but they respond to red light before any of the other colours do therefore behaving as red receptors
  • Therefore, light of a particular wavelength may stimulate more than one cone. By comparing the rate at which various receptors respond, as well as the overlap in colours detected, the brain is able to interpret the signals as intermediate colours

4.5. Explain that colour blindness in human’s results from the lack of one or more of the colour-sensitive pigments in the cones

  • As cones are used to detect colour, and the detection of colour comes from the photo pigments in the cones, the lack of one or more of these photo pigments may result in colour blindness.
  • Humans have three different types of opsins present in cones, each coded for by one gene. A mutation in a gene that codes for a cone pigment leads to the inability of this pigment to function properly – being colour deficient or colour blind
  • Inheritance patterns in humans can result in colour blindness, the genes coding for red and green pigment are located on the X chromosome and therefore defects in one or more of these genes can cause colour blindness. The gene for colour blindness is recessive
  • Red and green colour blindness is therefore a sex linked disorder
  • Mutations in the gene for the blue cone pigment are extremely rare.
  • Other non-genetic forms of colour blindness do occur but are also rare. Could arise from disease of the macula or optic nerve or as a result of a bilateral stroke in the optic lobe of the brain

Visual defects as a result of colour blindness

  • Colour blindness is not a serious or dangerous defect but may preclude certain occupations
  • A person who is colour blind is not completely colour blind as they can usually see two of the three primary colours. But because they are unable to detect one of the colours they perceive colours differently and therefore have dichromatic vision
  • Not all people who have defective genes are colour for colour vision are colour blind
  • Some people by be colour deficient. A mutation in a gene for any one of the cone pigments and may simply cause a change in the peak of spectral sensitivity of that cone
  • These people differ in their sensitivity to different wavelengths of light and find it difficult to distinguish between shades of certain colours

Detection of colour blindness and colour deficiency

  • They are detected by showing a person special pictures called ishihara plates, made up of patterns of dot. Certain colours are arranged in a particular pattern often to form a number. A colour blind person will be unable to see the number

4.6. Process and analyse information from secondary sources to compare and describe the nature and functioning of photoreceptors in cells in mammals, insects and in one other animals and compare these with simple light receptors in other animal

  • Eyes in animals range from really simple to extremely complex. Simple eyes are made up of single photoreceptor cells whose function is limited to distinguishing light from dark
  • The most complex eyes form a refraction and a focusing system in animals, involving lenses specialised areas of visual acuity and receptors that can distinguish between a variety of colours
  • Eyes are thought to have evolved many times, so the structures that we call eyes many have originated in different way in several ancestors, rather than one common ancestor and these resulting structures man not be homologous

Simple light receptors in animals – planarians

  • All photoreceptor cells contain the same basic light absorbing pigment molecules
  • The simple eye of animals consists of basic cup shaped structure lined with pigment cells
  • This pigment cup many contain fluid, the only light refracting part of the simple eye. The eye has far fewer pigmented photoreceptor cells than a mammalian or insect eye, resulting in poor visual acuity
  • The simple image that forms on the layer of photoreceptors is unclear and is not inverted
  • The role of the photoreceptors is therefore merely to allow the animal to detect light in the environment and the direction from which it comes

Compound eyes in insects

  • 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 eye. They are also capable of detecting colour
  • Each compound eye is made up of about 8000 units called ommatidia
  • Each ommatidia only sees part of an object. When each section of the object is seen by each ommatidia it is put together, a mosaic type of picture is formed
  • Ommatidia are larger than rods and cones present in mammalian eyes
  • Because of this there are relatively fewer ommatidia in an insect eye than there are rods and cones present in the mammalian eye
  • As a result, the image formed by an insect eye is blurred by human standards
  • A transparent, hexagonal cornea and a clear, crystalline cone refracts the incoming light rays. There is no lens present as in a mammalian eye
  • The crystalline cone provides additional refraction, it is unable to change shape and focus, as does the lends in the mammalian eye
  • After passing through the cornea and crystalline cone, light travels down the rhabdom, an elongated central structure, to the retinal cells that lie below the crystalline cone
  • The retinal cells are light sensitive structures in each ommatidium.
  • There are fewer light sensitive cells in an insect compound eye than there are rods and cone in the mammalian eye
  • The retinal cells contain a light sensitive pigment that undergoes a chemical change to allow a light signal to be transformed into the electrochemical energy of a nerve impulse. nerve fibre from the base of the retinal cells combine to form a tiny nerve that joins with other nerves from adjoining ommatidia, carrying impulses from the compound eye to the insect’s simple brain
  • Each ommatidium is separated from adjacent ones by pigment cells that prevent light from spreading outwards from one ommatidium to the next
  • the time taken for ne ommatidium to receive a light stimulus and generate an impulse and then regenerate is far quicker than that of the mammalian eye, resulting in much higher frequency of flicker fusion than humans
  • if a photoreceptor cells is bombarded with light stimuli in quick succession, the stimuli may be so close together that they do not give the eye time to recover and as a result stimuli are not interpreted separately but as one continuous signal. This allows us to see a series of still images as a moving picture.
  • In humans the flicker fusion is about 50 per second, flicker fusion in an insect’s eye is about 200 per second. This along with the fact that the eye covers such a large area of the head makes the compound eye every efficient at detecting movement over a wide visual range

4.7. 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

Colour communication in humans

  • Humans uses colour for communication in many ways from wearing certain colours for certain events or have coloured wires to show where they connect. We use colours on maps, as targets, sports, flags. Colour can be used as a way of recognition in sports and wars
  • Displays are visual signals that include movements, postures, facial expressions and colours. The signals are often under the voluntary control of the person

Colours communication in animals other than humans

  • Colour communication is important in breeding, recognition of species, opposite sex, sexual maturity and readiness to mate
  • Because of this role colour communication is essential for reproduction and therefore the survival of the species
  • In animal colour communication often takes the form of visual displays for mate attraction. The colouration of animals is genetically determined and is generally species specific
  • Courtship displays are important in ensuring that mates are of the same species as well as to evaluate the quality of the partner
  • Visual displays may also be used as a warning mechanism to defend territory and to ward of possible rivals
  • The advantage of visual displays is that they help to avoid physical battles for mates and territory.
  • Colour displays are important for food recognition. Colouration of flowers is linked to attracting agents of pollen. And with animals it displays If they are edible or poisonous

The occurrence of colour vision is animals

  • Birds
    • Evolved their bright colours and colour vision at the same time. As birds don’t use odour for mating or territory their ability to perceive colour is highly important
    • Many birds are able to distinguish colours in at least four different regions of the colour spectrum – having tetra-chromatic vision
  • Mammals
    • In the past it was believed that mammals where colour blind but recent studies show that many of these mammals have some form of colour vision
    • Most being dichromatic with the blue and green cones
    • In comparison to the group of primate mammals that are trichromatic. Whales, seals and dolphins differ again being dichromatic but lack the visual pigment to see blue light – therefore have green and red cones
  • Insects
    • Bees have three types of cones that are sensitive to blue, green and uv light
  • Other animals
    • Studies have shown that some fish and turtles have tetra-chromatic vision

5.1 Explain why sound is a useful and versatile form of communication

  • Sound bends around objects and travels around corners, it travels through substances – liquids, solids and gases
  • Whatever the habitat an animal is always surrounded by a sound transmitting medium
  • An animal’s resilience on sound, not only for communication but also for the overlapping functions of navigating and hunting is therefore always supported by the environment
  • Animals therefore do not have to be visual or in direct contact to communicate. When other senses are impaired sound can be used as a primary source of communication
  • By changing the tone, pitch, loudness and length a complete message can be conveyed in a short period of time
  • Low frequency sounds travel further distances

5.2 Explain that sound is produced by vibrating objects and that the frequency of the sound is the same od the frequency of the vibration of the source of the sound

  • Sound originates when something vibrates rapidly enough to organise the movement of molecules as to send a compression wave through a medium. As sound can only move through media where the particles can be compressed of spread.
  • The energy is transferred along/through the molecules as the particles move backwards and forwards in the same direction as the flow of energy
  • Waves can be measured in terms of their frequency, wavelength and amplitude.
  • The frequency of vibrations is the number of waves which past a give point per second. Frequency is expressed in cycles per second, one cycle is called a hertz (Hz)
  • Frequency determines the pitch of a sound. High frequency vibrations result in high pitched sounds and low frequency vibrations result in low pitched sounds
  • The wavelength of a sound is the distance between the two centres of two adjacent compressions or refractions. Low frequency sounds have long wavelengths and high frequency sounds have short wavelengths
  • The amplitude of a sound wave is the maximum distance that a particle moves away from its original position. The amplitude terms the volume of the sound

5.3 Outline the structure of the human larynx and the associated structures that assist the production of sound

The larynx

  • The larynx (voice box) is positioned in the throat where the pharynx divides into the respiratory tract (trachea) and the digestive tract (oesophagus).
  • It has two main functions in communication
    • To provide an open air way (when breathing)
    • To provide a mechanism for sound production (e.g. when speaking)
  • A third function is two ensure a closed air channel when eating (swallowing)


  • The larynx is a hallow box which houses the vocal folds / chords
  • In humans its structure mainly consists of a framework of nine cartilages (gristle), joined by membranes and ligaments.
  • These form a box in which sound can be produced and resonate
  • The upper opening of the ‘box’ is called the glottis and is covered by the epiglottis, the uppermost cartilage of the larynx
  • The epiglottis extends from the posterior of the tongue to its anchor point on the anterior rim of the thyroid cartilage. Being flexible and spoon shaped, it tips forwards over the rising larynx during swallowing and prevents food from entering the larynx and the trachea
  • When breathing it is held away from the larynx
  • The large cartilage rings the thyroid cartilage at the top of the larynx is composed of two bands
  • Inferior to this is the cricoid cartilage, which is attached to the trachea at the lower edge. Three pairs of smaller cartilages form part of the lateral and posterior walls of the larynx. The most important of these being the laterally placed arytenoid cartilages because these anchor the vocal cords
  • Muscles connect the cartilages to the head or neck while others alter the position, shape and tension of the vocal cords / folds
  • The interior of the larynx has a mucus-coated lining. Cilia or hairs, on the mucous lining below the vocal cords push substances towards the pharynx, the action of clearing out the throat helps to move mucous up and out of the larynx
  • Lying under the mucus lining, on each side, are the vocal ligaments. These join some of the cartilages to each other, in doing so drawing the mucus lining up to form the vocal folds or the true vocal cords
  • When viewed from above the right and left folds form a V shape. The true vocal cords vibrate and may produce sound as air rushes between them from the lungs through the opening called the glottis
  • Above the true vocal cords there is another set of mucosal folds called the vestibular or the false vocal. Thee play no par in sound production but the mucus produced assists in lubricating the vocal cords.
  • These false vocal cords also shut when they come in contact with liquid preventing liquids from entering the lungs


  • Is the name given to the complicated process of producing intelligible sounds or speech
  • This process can be divided into roughly into three stages
    • Production of airflow
    • Production of sound
    • Articulation of the voice

Production of air flow

  • Air is exhaled from the lungs automatically as we breath and as we speak
  • The force of air must be enough to push open the vocal cords
  • This is achieved by relaxing the diaphragm muscles (to form a dome shape) and the external intercostal muscles so that the pressure inside the chest cavity is higher than that outside the body
  • Thus air is forced out in an attempt to equalise pressure inside and outside the body at a forceful rate
  • The airflow can be altered in various ways, such as by exercising, holding one’s breath and talking and shouting. In fact, a couch can expel a hurricane force airflow

Production of sound

  • The rapid opening and closing of the glottis set up the vibration pattern, which produces sounds
  • This results from the release of air from the lungs and the vibration of the vocal cords
  • The length of the vocal cords/folds and therefore the size of the glottis is controlled by the vagus nerve (the tenth cranial nerve)
  • One of the nerves 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 glottis is wide open when we produce deep notes and just a narrow slip for high pitched
  • The volume or loudness o the voice is controlled by the strength of the airflow. The greater the airflow the stronger the vibrations and the louder the sound

Articulation of the voice

  • The vibration of the vocal cords produces a buzzing sound.
  • The resonance of the voice is determined by other structures situated above the larynx, such as the pharynx and the various sinuses of the cranium
  • In speech, the sounds must be shaped into vowels and consonants by the muscles of the tongue, soft palate, cheeks and lips
  • These are associated structures that assist in the production of sound

5.4 Plan and preform a firsthand investigation to gather data to identify the relationship between wavelength, frequency and pitch of a sound

state the relationship between wavelength, frequency and pitch of a sound???

  • if you have a short wavelength you will have a high frequency which will produce a high pitched sounds
  • if you have a long wavelength you will produce a low frequency which will produce a low pitched sound

Together the tongue along with the larynx and the hard and soft palates, make speech possible, the vocal cord produce vibrations and ultimately sound which can be altered to make different noises normally by the tongue teeth or lips, producing various pitches of sound, that’s why people try and perfect their technique whilst singing in order to manipulate the noises produced.

  • Wavelength is the distance occupied by one complete wave measured in meters per second
  • Amplitude is the maximum distance a point moves from its rest position when a wave passes also measures in meters per second.
  • Frequency is the number of waves that pass a point in one second with the unit of hertz.  1 unit per second

5.5 Gather and process information from secondary sources to outline and compare some of the structures used by animals other than humans to produce sound

All sorts of animals use all sorts of sounds for things such as communication, mating calls and other forms of communication and interaction

  • Crickets and other bugs: Crickets and other bugs use friction of the back legs or rub together the veins on their wings, this form of movement produces sounds, these sounds are then used to communicate with other crickets and predators either to warn them off or draw them in, using their calls.

6.1 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
  • Orthopterans (crickets and lizards) have a tympanum (drum) or ear on ear leg just below the knee. The tympanum is a cavity containing no fluid
  • It is enclosed by the 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
  • Female crickets are deaf to some frequencies and sometimes rely on the smell of given off by the male as he raises highs wing covers to make a call
  • Butterflies and moths have their tympana at the base of their wings
  • Both male and female cicadas possess organs for hearing despite the fact that is it only males that sing
  • A large pair of mirror like membranes, the tympana, are connected to an auditory organ by a short tendon at the base of the abdomen. When a male cicada sings he crinkles his tympana to prevent deafening himself


  • All fish have a lateral line sensory organ, a pronounced pair of sensory canals which run the length of each side of the animal
  • Pressure waves in the surrounding water distort the sensory cells found in the canals, sending a message to the nerves
  • There is a significant link between the lateral line and the true organs of hearing. It has the same type of hair cells and nerves that are found in the inner ear of humans
  • Some fish perceive sound waves by possessing an inner ear that has a sensory chamber composed of passages called the labyrinth
  • It contains an otolith (ear stone) and is lines with hair cells
  • Auditory nerves detect the difference between the hair cells and the otolith. This is recorded as a nerve impulse, which is carried by nerve to the brain
  • The swim bladder may also play a part in transmitting vibrations to the sensory chamber.
  • In many freshwater fish, such as carp, the transmission may be enhanced by a series of small bones called the ossicles which connect the swim bladder to the sensory chamber


  • Some frogs have extremely large tympana on the sides of their heads
  • The size id related to the frequency and wavelength of their call
  • The tympana are connected to the lungs so that when the eardrum vibrates the lung absorbs the vibration, thus preventing pain and injury


  • 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 jaw, the middle ear, inner ear and the auditory nerve to the well-developed auditory cortex of the 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 describe the anatomy and function of the human ear, including ; pinna, tympanic membrane, ear ossicles, oval window, round window, cochlea, organ of corti, auditory nerve

external ear or outer ear:

  • the external ear is comprised of the pinna, the meatus (ear/auditory canal) and the outer layer of the eardrum (tympanic membrane
  • sound waves travel through the ear in the external ear

middle ear:

  • the ear ossicles to the oval window to the round window
  • the middle ear is an air filled cavity
  • separated from the external ear by the tympanic membrane and is connected to the throat via the Eustachian tube
  • the middle ear opens up to the inner ear through the oval window
  • inside the cavity there are three small bones that are connected by true joints to form a system of levers – these bones are easily damaged b noise

inner ear:

  • cochlea, organ of corti, auditory nerve
  • inner ear is formed by a series of bony canals – bony labyrinth but can be divided into three parts
    • the vestibule (entrance)
      • plays no part in hearing but is a three dimensional sensors for balance
    • the semi canals
      • plays no part in hearing but is a three dimensional sensors for balance
    • the cochlea
      • is a spiral bony canal that houses the organ of hearing the organ of corti
      • each hair cell of the OOC has a nerve fibre attached to it
      • these lead to the auditory nerve (VIII nerve) which carries impulses to the hearing centres on the cortex of the brain

6.3 Outline the role of the Eustachian tube

  • The Eustachian tube helps to equalise air pressure on either side of the tympanic membrane by bringing in air from the month

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

external ear

  • sound is transmitted as a wave through air (sound energy) in the auditory canal (meatus) to the outer layer of the tympanic membrane (ear drum)

middle ear

  • vibrations (kinetic energy) from the tympanic membrane are conveyed through this air filled camber via the movement of the interconnecting ear ossicles to the oval window of the inner ear

inner ear

  • the stapes vibrates the oval window setting up a pressure wave in the perilymph of the upper canal. Reissner’s membrane then moves, transferring the kinetic energy to the endolymph of the middle canal.
  • This vibrates the basilar membrane, stimulating the hair cells of the organ of corti. The hair cells send messages along the nerve fibres to the brain where they are interpreted. The pressure waves continue onto the round window at the end of the lowest canal

Energy transformations

  • Sound waves pass in air along the auditory canal.
  • Sound energy is converted into mechanical energy as the vibration is set up in the tympanic membrane
  • The mechanical energy is then transferred through the ossicles to the oval window
  • As it passes into the perilymph as a pressure wave, the mechanical energy is transferred via Reissner’s membrane to the endolymph to the organ of corti
  • Mechanical energy is now converted into electrochemical energy as information is transmitted as nerve impulses from the hair cells by the auditory nerve to the brain

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

distribution of hair cells in the organ of corti

  • the organ of corti rest on the basilar membrane
  • it is composed of supporting cells and about 15 500 hearing receptor cell, called cochlea hair cells
  • there is a finite number and they are not replaced as they die
  • the is one row of inner hair cells and three rows of outer hair cells. These are sandwiched between the tectorial and basilar membranes of the cochlea
  • the fibres of the cochlea nerve are coiled around the bases of the hair cells. The hairs of the hair cells (cilia) protrude into potassium ion rich endolymph and the longest of them are embedded in the overlying gel of the tectorial membrane
  • activation of the hair cells occurs at points of vigorous vibration of the basilar membrane
  • hair cells nearest to the over window (base) are activated by the highest pitched sounds while those furthest away are at the narrow end of the cochlea (apex) are stimulated by low frequency sounds
  • although the outer hair cells are much more numerous, approximately 90% of the fibres of the cochlear nerve service the inner hair cells, which are responsible for sending most of the auditory messages to the brain

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

sound shadows

  • the phenomenon caused by the obstruction or absorption of sound wave by an object in its path is called a sonic or sound shadow
  • this is perceived as a reduction in amplitude or volume
  • the effect will be greatest when the sound source, the absorbing object and the person hearing the sound are all aligned

role of the location of sound

  • as humans are binaural (having two ears), the head creates sonic shadow for the ear further away from the sound source
  • the head absorbs high frequency sounds more readily than the lower frequencies and thus plays a significant role in locating a sound source
  • the effect has been shown to be less important than the split second time differences in each of the two ears receiving the same sound
  • visually impaired people use the sonic shadow effect, together with echolocation and other cues for orientation

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

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

  • the frequency range of humans is limited to 20-20000 cycles per second in children

comparison of the human range of hearing with other mammals

  • animals other that humans can detect sound frequencies lower than 20 Hz. For example, dogs can hear a high pitched whistle which is inaudible to humans
  • dolphins produce in whistles and clicks at 0.25 to 150000 Hz but can only hear from 150-150000 Hz
  • whereas bats use a higher range of frequencies. They produce sounds from 10000-120000 Hz but can hear between 1.000-120000 Hz

possible reasons for difference in hearing

  • the flexibility of the basilar membrane limits the frequency range of human hearing.
  • Because of evolution and human’s ability to modify the environment has resulted in less reliance on the sense of hearing for survival
  • Humans also have effective three dimensional vision which eliminated the need for echolocation
  • Dolphins cannot rely on vision at all times so they produce clicks at high frequency, being a shorter sound wave to find objects and food. They also use low frequency sounds like whistles to communicate – low frequency travels further in water

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

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

chronic exposure to sound and how it effects some hearing

  • some people are born with the inability to hear (congenital)
  • others lose their sense of hearing suddenly or gradually, this can be due to
    • diseases
    • accidents
    • prescription drugs
    • ageing
    • acoustic trauma
    • heredity
  • the most avoidable being acoustic trauma or the chronic exposure to sound
  • noise induced hearing loss (NIHL) can result from one time exposure or repeated sounds
  • the tympanic membrane may rupture and/or the ear ossicles could fracture or be displaced by short exposure to a loud noise such as an explosion. This type off hearing loss and be assisted
  • short term hearing loss is caused by fatigue of the hair ells of the cochlea
  • continual exposure to excessive noise causes damage to the cilia of the hair cells. The hairs cells then die and are not replaced if enough of the hair cells are damaged permanent hearing loss results

7.1 identify that a nerve is a bundle of neurone fibres

structure of neurones

  • neurones are the units that make up the nervous system
    • sensory – transmit impulses from sense organs
    • motor – transmit impulses from the CNS to muscles and glands
    • connector – connect sensory and motor neurones (usually in spinal cord and brain)
  • each neurone has three parts
    • cell body – contain nucleus
    • dendrites – conduct nerve impulses toward cell body (singular is Dendron)
    • axon – one single very long extension, conducts impulses away from cell body
  • dendrites and axons referred to as neuronal fibres – consisting of fluid filled tubes often surrounding by a fatty insulating cover (myelin sheath) which is supported by Schwann cells
  • nerve fibres are able to transmit messages rapidly along their entire length and pass them to a successive neurone, over small gaps known as synapses
  • the myelin sheath has small gaps known as the node of Ranvier
  • the ion channels that function in the action potential are concentrated in the node of ranvier
  • if the impulse travels from a sensory organ or receptor to the CNS the Dendron is called a sensory fibre and if it passes from the CNS to a muscle/gland the axon is a motor fibre

structure of nerves

  • cell bodies of neurones are usually situated in the grey matter of the brain or spinal cord
  • some occur outside the CNS is clusters called ganglia – ganglia coordinate impulses
  • the nervous system is made up of millions of neurones
  • the sensory and motor fibres of neurones are gathered into bundles called nerves
  • the bundle is held together by a connective tissue sheath

7.2 identify neurons as nerve cells that are the transmitters of signals by electrochemical change in their membrane

  • a neuron is a nerve cell that transmits a signal or impulse from one part of the body to another. Neurons send messages electrochemically meaning that chemicals cause electrical signals
  • a nerve impulse can be detected as a change in voltage. The impulse is transmitted as a wave of electrical charges that travel along the cell membrane of the neuron. The electrical changes are cause as sodium ions move into the neuron causing a change in charge therefore being called a electrochemical signal.

7.3 define the term “threshold” and explain why not all stimuli generate an action potential

  • the threshold is the amount of positive change 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 than the resting potential of -70mV
  • no action potential is produced if the depolarisation is below this level
  • this is one of the reasons why not all stimuli generate an action potential
  • also each stimulus produces either a full action potential or none at all
  • each action potential is a separate event and therefore a cell cannot produce another action potential until the previous one is complete

7.4 identify the areas of the cerebrum involved in the perception and interpretation of light and sound

the cerebrum

  • the brains of humans appear to be out of proportion compare with the overall size of the body. This is due to the great enlargement of the cerebrum
  • the cerebrum splits into two hemispheres the left and right. Each hemisphere receives impulses from the opposite site of the body.
  • The hemispheres in turn are divided into five lobes – the frontal, insular, occipital, parietal and temporal lobes
  • Under a tough, protective covering the surface of the cerebrum is drawn up into folds called convolutions thus tripling areas of the brain
  • Most of the activities of the cerebrum occur on its outer surface in a layer of grey matter (cerebral cortex) only a few millimetres thick. Those activities generally fit three categories
    • Motor – movement
    • Sensory – senses
    • Associative – taking up about 95% of the cerebral cortex and is the site of higher mental activities such as reasoning and logic

Light and sound and the cerebrum

  • Optic nerves (cranial nerve II) are the sensory nerves of vision
  • Fibres arise from the retina of the eye to form the optic nerve. Each optic nerve passes through the skull via an opening in the eye socket
  • The optic nerves from each of the eyes partly cross over to form the optic chiasma
  • About half of the nerves cross over to the other side, providing the visual cortex with the same image at a slightly different angle
  • A visual cortex lies within the occipital lobe of each hemisphere
  • Impulses reach this lobe form the retina via the optic nerve. Different sites on the visual cortex process information from different positions on the retina
  • Auditory nerves (cranial nerve VIII) arise from the hearing (cochlea) and equilibrium (vestibule) apparatus within the ear. Two divisions merge to form one nerve now known as the vestibulocochlear nerve. This nerve runs from the organ of corti to the auditory cortex
  • An auditory cortex is found on the temporal lobe of each cerebral hemisphere.
  • Different sites on this cortex receive and interpret different sound frequencies


7.5 explain, using specific examples, the importance of correct interpretation of sensory signals by the brain for the coordination of animal behaviour

short circuits in the brain

  • stimuli must be received and transmitted to the spinal cord or brain before being interpreted and a response given. Reasons that can cause a short circuit
  • lack of stimulus
  • trauma
  • lack of oxygen
  • legal/illegal drug reaction
  • disease
  • pollution
  • age related damage or deterioration


  • Multiple sclerosis
    • Autoimmune disease in which there is an immune attack on the myelin sheath from the body – gradually the myelin sheath and nervous system are destroyed
  • Alcohol, anaesthetics and sedatives
    • These can all impair the transmission of messages by blocking nerve impulses and reducing the plasma membranes permeability to sodium ions
  • Cerebral palsy
    • May be cause by temporary lack of oxygen to a baby during child birth
    • It is neuromuscular damage in which voluntary muscles lack coordination. The brain cells are unable to transmit messages to the muscles