1. The Nervous System Ian Matmungal 1

2. Objectives: You should be able to: define the terms “receptors” and “effectors”; explain the relationship between the receptor, the central nervous system and the effector; and describe the role of the sensory, relay and motor neurones. Ian Matmungal 2

4. Integrates input of stimuli from receptors

5. Responds to stimuliIan Matmungal 3

7. The peripheral nervous system (PNS) consists of two sets of nerves - the cranial nerves from the brain and the spinal nerves from the spinal cord. The PNS links the CNS with the receptors and effectors. Ian Matmungal 4

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9. Ian Matmungal 6 The nerve cell is known as a neurone.

11. one long thin nerve fibre called an axon which transmits impulses away from the cell body

12. one or more short nerve fibres called dendronsthat conduct impulses to cell body

13. nerve endings (dendrites at the end of dendrons and axon terminals at the end of axons).

14. The myelin sheath which serves as an insulating layer for nerve fibres

15. Nodes of Ranvier separating the myelin sheath to speed up impulse transmissionIan Matmungal 7

16. There are three main functional types of neurones – sensory neurones, motor neurones and intermediate or relay neurones. Ian Matmungal 8

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18. Synapses – the connection between neurones A synapse is found at the point where an axon of one neurone comes into very close contact with the dendrite of another neurone. Transmission across a synapse is by chemical means – known as neurotransmitters. Ian Matmungal 10

19. Ian Matmungal 11 Synapses – the connection between neurones

20. The Pathway of Nervous Transmission Components of a general neural pathway: Receptors detect stimuli Information is sent via sensory neurones to spinal cord Relay neurones in spinal cord conduct nerve impulses to the brain Motor neurones signal effectors to respond Ian Matmungal 12

21. The Central Nervous System You should be able to: describe the functions of the main regions of the brain; and describe the role of the autonomic nervous system. Ian Matmungal 13

23. Grey matter – contains cell bodies of neurons

25. Midbrain

26. Hindbrain – consists of cerebellum and medulla oblongataIan Matmungal 14

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30. Peripheral Nervous System Somatic nervous system Consists of peripheral nerves linking the sense organs and skeletal muscles to the CNS. Under conscious control Autonomic nervous system Responsible for the regulation of involuntary actions, such as heart rate, breathing rate, digestion and pupil dilation. Brings about homeostasis Ian Matmungal 18

31. The Reflex Action You should be able to: describe a reflex arc; and distinguish between a cranial reflex and a spinal reflex. Ian Matmungal 19

33. The shortest pathway of nerve impulses from the receptor to the effector is known as the reflex arc. Ian Matmungal 20

35. Receptor (sense organ)

36. Sensory or receptor neurone

37. Reflex centre (CNS)

38. Motor or effectorneurone

39. Effector (muscle or gland)Ian Matmungal 21

40. There are two main types of reflex actions: Spinal reflexes Controlled by spinal cord E.g. withdrawal reflex E.g. knee-jerk reflex Cranial reflexes Controlled by the brain and occur in the head region (but not under conscious control) E.g. blink reflex, pupil reflex and salivation Ian Matmungal 22

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43. Our Five Senses You should be able to: identify the main sense organs and the stimuli to which they respond. Ian Matmungal 25

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47. explain how the eye produces a focused image of near and distant objects on the retina;

48. describe the pupil reflex in response to bright and dim light; and

49. explain sight defects and their corrections.Ian Matmungal 28

50. Ian Matmungal 29 External structure of the human eye

51. Ian Matmungal 30 Side view of the human eye

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53. The Cells Which Enable Us to SeeRetina is the innermost, light-sensitive layer on which images are formed Photoreceptors convert light waves into nerve impulses which relay the information to the brain. There are two kinds of photoreceptor cells – rods and cones. Rods Important for vision in dim light Cones Used for vision in bright light Ian Matmungal 32

54. Fovea centralis- shallow depression of the retina with the highest concentration of cones Blind spot – where the optic nerve joins the eyeball. No photoreceptors are located here, so light rays falling on this spot would not be detected. Ian Matmungal 33

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57. Ian Matmungal 37 Looking at a close object

58. Ian Matmungal 38 Looking at a distant object

59. Pupil Reflex A cranial reflex The automatic change in the size of the pupil in response to changes in light intensity. The pupil size is controlled by the action of the circular and radial muscles of the iris. Ian Matmungal 39

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62. Ian Matmungal 42 Vision defects People with short-sightedness are unable to see distant objects clearly.

63. Ian Matmungal 43 People with long-sightedness are unable to see near objects clearly.

64. Ian Matmungal 44 Vision defects Astigmatism Caused by irregular curvature of the cornea or lens, so light cannot be focused at one point, causing blurred vision Glaucoma Buildup of pressure of fluid in eyeball can damage optic nerve and cause vision loss

65. Ian Matmungal 45 Cataracts Clouding of the lens, causing blurred vision