Detection of Environment

1. Detection of Environment Eye Ear Skin

2. stimuli: changes in internal and external environments to living organisms sensory system: system perceives stimuli so organisms can respond to changes correctly irritability: ability to respond to stimuli

3. receptors: organs used to detect stimuli, specific, consists one or many sensory cells which they will send impulses to brain through nerve fibres effectors: part of body that reacts to a stimulus or produces responses

4. receptor central nervous system ATP response effector stimulus

5. tear gland orbit oblique muscle eyelash optic nerve pupil iris muscle attachment to skull eyelid oblique muscle rectus muscles eyeball Location of the Eye

6. Location of the Eye • responsible for detecting light • eyeball is a spherical structure which is protected in a bony socket in the skull called orbit • eyeball attached to orbit by six muscles • rotation of eye is brought about by contraction of the muscles

7. Structure around the Eye • blinking helps to keep the surface of eyeball moist and clean by distributing tears produced by tear glands over the eyeball • tears contain sodium chloride, hydrogencarbonate and lysozyme which is used to kill bacteria

8. rate of tear flow and blinking will increase when foreign substance reaches eye surface • excess tear can drain away into nasal cavity through duct in the corner of the eye • eyelashes also help to stop dirt and sweat from running into eyes

9. suspensory ligaments ciliary muscle eye muscle sclera conjunctiva choroid aqueous humour retina yellow spot pupil lens blind spot cornea optic nerve vitreous humour iris Structures and Functions of Eye

10. wall of eyeball is made up of three layers: sclera,choroid and retina Sclera • The outer layer of wall • white, tough and opaque coat to protect eyeball • keeps shape of eye and provides anchorage for eye muscles

11. Cornea • a transparent layer continue from sclera • allows light to pass through • light is refracted into interior of eye as it is curved • protected by a transparent layer called conjunctiva

12. Choroid • middle layer of eyeball • deeply pigmented to absorb light and prevent internal reflection of light • contains lots of blood vessels to supply eye with food and oxygen and removes waste

13. Lens Lens • within ring form by ciliary body • transparent biconvex in shape • compose of living cells

14. ciliary muscle suspensory ligaments Suspensory ligaments and ciliary body • suspensory ligaments are used to hold lens in position. They are run from free edge of ciliary body • ciliary body contains ciliary muscles which can change thickness of lens by alternate contraction and relaxation during focusing

15. Iris • continuous with choroid • lies just over ciliary body • coloured part of eye as it is pigmented Pupil • hole in the centre of iris • size of it is controlled by radial muscles and circular muscles of iris

16. aqueous humour vitreous humour Aqueous and Vitreous Humour • watery fluid filled the anterior chamber in front of the lens inside the eyeball is aqueous humour • jelly-like substance filled the posterior chamber behind the lens is vitreous humour

17. they help in refracting light and maintaining shape of eyeball • aqueous humour also helps cornea and lens to obtain food and oxygen from blood vessels in choroid layer by diffusion

18. Retina • the innermost layer in eye • contains many light-sensitive cells, rods and cones, and nerve fibres • cones are sensitive to light of high intensity and responsible for colour vision. There are three types of cones which sensitive to blue, red and green

19. yellow spot is the part in the centre of retina which possesses cones only and it lies on the optical axis of eye • rods are sensitive to light of low intensity and abundant in the periphery of retina

20. Yellow Spot • densely packed with cones • no rod is present • gives the most distinct image and the greatest colour discrimination

21. Optic Nerve • optic nerve is a nerve which contains nerve fibres from rods and cones • it leaves the eyeball at the blind spot • no sensitive cells at blind spot but only nerve fibres • no nerve impulse can be generated when light falls on the blind spot although image is formed on it, so it is incapable of detecting images

22. blind spot optic nerve Blind spot • the point where the nerve fibres leave the eye-ball • no photo-receptors cannot detect any image

23. image window frame hand lens cardboard What can you tell about the image ? Ans: The image is smaller than the object but the shape remains the same and it is laterally inverted.

24. front view of the lens of the projector plasticine water with sodium fluorescein projector convex lens convex lens Does the light beam bend after passing through the attached lens ? Ans:Yes.

25. front view of the lens of the projector plasticine water with sodium fluorescein projector convex lens convex lens Does the light beam meet at a point ? (This point is the focus of the lens) Ans:Yes.

26. front view of the lens of the projector plasticine water with sodium fluorescein projector convex lens convex lens What is the shape of the image ? Ans:The image is inverted and smaller than the object.

27. front view of the lens of the projector plasticine water with sodium fluorescein projector convex lens convex lens What do the water and the back of the flask represent ? Ans:The water represents vitreous humour while the back of flask represents retina.

28. Change of Pupil Size • pupil is the hole in iris which allows light to pass through • pupil limits amount of light entering the eye • two kinds of iris muscle control size of pupil:-circular iris muscle: makes pupil constrict as they contract - radial iris muscle: pupil dilates as they contract

29. radial muscles relax reduce amount of light pass through pupil size decrease • change of size of pupil is a reflex action and automatic Under Bright Light circular muscles contract

30. circular muscles relax increase amount of light pass through pupil size increases Under Dim Light radial muscles contract

31. shorter focal length longer focal length Accommodation • thick lens • thin lens • accommodation is the ability of the eye to adjust thickness of lens for viewing near and distant objects • helped by the action of ciliary muscles

32. more light rays bend and image of near objects formed on retina ring of ciliary body moves inwards and becomes smaller in diameter lens becomes thicker and more curved tension of suspensory ligaments reduces Focusing Near Objects ciliary muscles contract

33. circular ciliary muscle contracts decrease in circumference tensionof suspensory ligament decreases lens becomes more convex

34. Focusing near object Light from near object

35. image of distant objects formed on retina ring of ciliary body moves outwards and becomes wider in diameter lens becomes thinner and more flattened tension of suspensory ligaments increases Focusing Distant Objects ciliary muscles relax

36. circular ciliary muscle relaxes increase in circumference tension of suspensory ligament increases lens becomes less convex

37. Focusing far away object Light from far away object

38. front view of the lens of the projector water with sodium fluorescein projector convex lens thinner convex lens How is the distance between the lens and the projector related to the thickness of the lens? Ans: The thicker the lens, the shorter is the distance between the lens and the projector.

39. Common Eye Defects -- Short Sight • it occurs when light of distant object focused in front of retina • may be due to eyeball too long or lens becomes too curved • only near object can be seen clearly • corrected by wearing concave lenses which diverge light from distant object before reaching the eye to ensure its image fall on retina sharply

40. Short sight Light from distant object

41. Diverging lens ( Concave lens ) Correction of short sight Light from distant object

42. Common Eye Defects -- Long Sight • it occurs when light from near objects focused behind the retina • may due to eyeball too short or lens becomes too thin • only distant object can be seen clearly • corrected by wearing convex lenses which converge light from near object before reaching the eye

43. Long sight Light from near object

44. Converging lens ( Convex lens ) Correction of long sight Light from near object

45. Common Eye Defects -- Colour Blindness • cone cells are responsible for colour vision • there are three kinds of cone cells responsible for detecting red, green and blue lights • relative number of cones presents and being stimulated determined the colour perceived • colour blindness is a hereditary defect and cannot be corrected by wearing glasses

46. Can You See? Ans: 5 Ans: 8 Ans: Nothing Ans: A line

47. Function of Mammalian Ear • enable mammal to hear so that they can escape from danger • detect changes in position during movement

48. middle ear inner ear outer ear Structure and Functions of Different Parts of Ear • ear is divided into three parts: outer ear,middle ear and inner ear Outer Ear • outer ear includes pinna and an auditory canal

49. pinna • pinna • a flap of cartilage covered with skin • serve to collect sound waves and detect direction of the sound • in some mammals, pinnae are movable so they can detect sound source efficiently as they can move their pinnae to the direction of sound source

50. auditory canal eardrum • lined with hairs and wax-secreting cells to prevent entry of dust or small insects • a membrane present at the end of auditory canal and it is called eardrum (typanum) • eardrum serve as a device to convert sound waves into vibrations as when sound waves strike it, they are translated into mechanical waves auditory canal