2. How and why do organisms respond to changes in their environment? Can you list what is required for a coordinated response? What makes up the CNS? Can you explain that receptors are used to generate impulses in neurones, resulting in a rapid response? What is a reflex arc?

4. Receptor cells are special cells adapted to detect stimuli. They are found in our sense organs. Light Chemical Pressure/heat Movement of sound waves

6. There are two parts: – The Central Nervous System (CNS) which consists of the brain and spinal cord. – The Peripheral Nervous System which is all the nerves that take information from our sense organs into the CNS and from the CNS out to effectors (muscles or glands).

8. Stimuli are picked up by sensory receptors and passed into the neurone.

9. This generates an impulse which travels along the neurone.

10. Stimuli are picked up by sensory receptors and passed into the neurone. This generates an impulse which travels along the neurone.

11. Stimuli are picked up by sensory receptors and passed into the neurone. This is then passed to the spinal cord or the brain to interpret the initial stimuli.

12. The neurone is surrounded by cells made of a substance called myelin. This insulates the neurone. Myelin sheath

13. The dendron carries the impulse up to the cell body, it then becomes the axon. The cell body contains the nucleus and all the other components that a cell needs to function. Cell body Axon Dendron

14. Cell body Axon Myelin sheath Dendron Junction with sensory receptor Junction with CNS

15. A message is sent out from the brain down the dendrites. The impulse travels down the axon. Cell body Dendron Axon Myelin sheath Dendrites Muscle

16. The impulse arrives at a muscle (effector) causing it to contract. Cell body Dendron Axon Myelin sheath Dendrites Muscle

17. A reflex is a rapid, automatic response to a stimulus. The action often protects the body. The nerve pathway of a reflex is called the reflex arc.

18. A reflex is a rapid, automatic response to a stimulus. The action often protects the body. The nerve pathway of a reflex is called the reflex arc. Iris constricting in bright For example

19. A reflex is a rapid, automatic response to a stimulus. The action often protects the body. The nerve pathway of a reflex is called the reflex arc. Iris constricting in bright Touching something very hot For example

20. Sensory neurone Relay neurone Motor neurone Spinal cord

21. The signal does not go up to the brain, but is processed in the spinal cord via a relay neurone. Sensory neurone Relay neurone Motor neurone Spinal cord

22. Stimulus

23. Receptor

24. Stimulus Receptor Coordinator

25. Stimulus Receptor Coordinator Effector

26. Stimulus Receptor Coordinator Effector Response

28. Stimulus Receptor Coordinator Effector Response Sensory neurone Motor neurone

29. Stimulus Receptor Coordinator Effector Response Sensory neurone Motor neurone The candle

30. Stimulus Receptor Coordinator Effector Response Sensory neurone Motor neurone The candle Temperature receptor in finger

31. Stimulus Receptor Coordinator Effector Response Sensory neurone Motor neurone The candle Temperature receptor in finger Relay neurone in spinal cord Sensory neurone

32. Stimulus Receptor Coordinator Effector Response Sensory neurone Motor neurone The candle Temperature receptor in finger Relay neurone in spinal cord Muscle in arm Sensory neurone Motor neurone

33. Stimulus Receptor Coordinator Effector Response Sensory neurone Motor neurone The candle Temperature receptor in finger Relay neurone in spinal cord Muscle in arm Arm moves away from candle Sensory neurone Motor neurone

34. A reflex is an example of an automatic coordinated response. In a voluntary response the brain would be the coordinator not the spinal cord.