Irritability

1. Irritability • The ability to detect stimuli (internal/external changes) is referred to as irritability • Stimuli are detected by receptors/sensorycells/senseorgans (there are different receptors for different types of stimuli) • Appropriate responses will be produced in respond to the stimuli

2. Irritability • Receptors generate nerve impulses after being stimulated • Nerve impulses are sent to the nervous system for interpretation via sensory nerve fibres • The brain generates nerve impulses carrying suitable responses to effectors (muscles or glands) • A particular sensation is produced

3. Nervous System Stimulus Receptor Response Effector

4. What are the major sense organs of our body??? • There are FIVE main sense organs (mostly on our head) • These organs are distributed unevenly around the body

5. Sense Organs • Eyes - sense of sight - detect light

6. Sense Organs • Eyes • Ears – sense of hearing - detect sound vibrations - sense of balance - detect body movements

7. Sense Organs • Eyes • Ears • Tongue – sense of taste - detect chemicals in food

8. Sense Organs • Eyes • Ears • Tongue • Nose – sense of smell - detect chemicals in air

9. Sense Organs • Eyes • Ears • Tongue • Nose • Skin – sense of touch - sense of pressure - sense of pain - sense of heat/cold

10. The eyeball is located in a socket of the skull called the orbit Three pairs of eye muscles connect the eyeball to the orbit Contraction of the eye muscles allows the eyeball to rotate inside the orbit The Human Eye

12. The eyeball is protected by the eyelid and eyelashes The movable upper lid makes blinking possible – this allows the distribution of tears over the surface of the eyeball (to moisten and clean the eye) The Human Eye

13. Tears – solution containing sodium hydrogencarbonate and sodium chloride Tears are produced by tear glands located under the upper eyelid Tears contain an enzyme (lyzozyme) that can kill bacteria Tears are drained into the nasal cavity via the tear duct The Human Eye

15. The Human Eye The wall of the eyeball consists of 3 layers: • 1.Sclera • The outermost layer • White, opaque and tough • Maintain the shape of the eyeball

16. The Human Eye The wall of the eyeball consists of 3 layers: • 1.Sclera • It protects the inner structures • It provides anchorage for eye muscles

17. The Human Eye Cornea • Front of the sclera • It is transparent to allow light to pass through • It is curved and therefore light is refracted as it enters the eye (to focus light)

18. The Human Eye Conjunctiva - Thin, protective layer covering the cornea

19. The Human Eye • Choroid • The middle layer • With many blood vessels and pigment

20. The Human Eye • Choroid • Blood vessels supply nutrients and oxygen to the eyes, and also remove metabolic wastes

21. The Human Eye • Choroid • - Pigment absorbs extra light to prevent reflection of light inside the eyeball which may blur the image

22. The Human Eye Pupil - The opening which allows light to enter the eyeball

23. The Human Eye Iris • Disc-like structure at the front part of the choroid • Contains different kinds of pigment to give the colour to the eyes

24. The Human Eye Lens • Behind the iris • Transparent, elastic, biconvex structure • Consists of living cells - To focus light rays onto the back of the eye by changing its convexity

25. The Human Eye Suspensory ligaments - Attach the lens to the ciliary body and hold it in position

26. Ciliary body The front part of the choroid Regulates the curvature of the lens by contraction and relaxation of the ciliary muscles The Human Eye

27. The Human Eye Anterior chamber • In front of the lens • Filled with a watery fluid called aqueous humour • Refracts light • Maintain the shape of the eyeball • Supply nutrients to the conjunctiva, cornea and lens

28. The Human Eye Posterior chamber - Behind the lens - Filled with a jelly-like fluid called vitreous humour - Refracts light - Maintain the shape of the eyeball Posterior chamber

29. The Human Eye • 3. Retina • The innermost layer • Contains light sensitive cells (photo-receptors) and nerves fibres • a) Rods for black-and-white vision • b) Cones for colour vision (red, blue and green cones)

31. The Human Eye Rods Cones More abundant at the periphery of retina More abundant at the center of retina Sensitive to bright light Sensitive to dim light Responsible for black & white vision Responsible for colour vision Rod shape Cone shape About 1.25 x 108 About 6 x 106

32. The Human Eye • Yellow Spot (Fovea) • At the centre of the retina • Densely packed with cones • No rod is present • Gives the most distant image and the greatest colour discrimination

33. The Human Eye • Blind Spot • - The light sensitive cells are all connected to nerve fibres • The point where the nerve fibres exit the eyeball • No rods/cones at this spot and therefore cannot detect any image

35. The Human Eye • Optic Nerve • At the back of the eyeball • Transmits nerve impulses from the retina to the optic centre in the brain (cerebrum) for interpretation

36. The Human Eye Ciliary body Eye muscle Suspensory ligaments Sclera Choroid Conjunctiva Retina Cornea Pupil Yellow spot Lens Iris Blind spot Aqueous humour Optic nerve Vitreous humour

37. Eye Model

38. Dissection of an Ox’s Eye

39. Changes in Pupil Size • The iris is made of circular muscles and radial muscles • The size of the pupil can be increased or decreased by antagonistic contraction and relaxation of circular and radial muscles • Changes in pupil size regulate the amount of light entering the eye

40. Increase in Pupil Size • Relaxation of the circular muscles makes the pupil larger in size

41. Increase in Pupil Size • Contraction of the radial muscles also makes the pupil larger in size

42. Increase in Pupil Size In dim light : circular muscles relax; radial muscles contract • increase in size of pupil allows more light to enter eye to ensure clear vision in the dark

43. Increase in Pupil Size

44. Decrease in Pupil Size • Contraction of the circular muscles makes the pupil smaller in size

45. Decrease in Pupil Size • Relaxation of the radial muscles also makes the pupil smaller in size

46. Decrease in Pupil Size In bright light : circular muscles contract; radial muscles relax • decrease in size of pupil reduces amount of light entering to prevent over-stimulation

47. Decrease in Pupil Size

48. Colour Vision Three types of cones: • Red cones • Green cones • Blue cones - All cones are stimulated by white light

49. Colour Vision

50. Colour Vision • The degree of stimulation of each type of cones determines the colour of the object Light from the apple falls on the retina. The red cones are stimulated. Nerve impulse are sent to the brain. Therefore we see the apple as “red”