Learning Objectives

2. Learning Objectives • 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?

3. Responding to change • In order for living organisms to find food, avoid danger, find a mate they need to be able to respond to changes in their environment. • These changes are called STIMULI.

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

5. Impulses • Information from these receptors passes as electrical impulses along nerve cells (neurones) to the brain. • The brain then coordinates the response. • Some responses are voluntary, some are automatic. • Some responses bypass the brain altogether, these are called reflex actions.

6. The structure of the nervous system • 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).

7. Neurones • Neurones transmit impulses around the body. • Impulses travel at speeds of between 10 and 100 m/s • Sensory neurones carry impulses from the receptor to the brain. • Motor neurones carry impulses from the brain to the effector.

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

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

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

11. Sensory neurone • 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. Direction of impulse

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

13. Sensory neurone • 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 Dendron Axon

14. Sensory neurone Direction of impulse Cell body Dendron Junction with sensory receptor Myelin sheath Junction with CNS Axon

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

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

17. Reflex Action • 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. Reflex Action • 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. For example Iris constricting in bright

19. Reflex Action • 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. For example Iris constricting in bright Touching something very hot

20. Reflex arc Spinal cord Sensory neurone Relay neurone Motor neurone

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

22. Reflex arc Stimulus

23. Reflex arc Receptor Stimulus

24. Reflex arc Coordinator Receptor Stimulus

25. Reflex arc Coordinator Receptor Effector Stimulus

26. Reflex arc Response Coordinator Receptor Effector Stimulus

27. Reflex arc

28. Reflex arc Stimulus Receptor Sensory neurone Coordinator Motor neurone Effector Response

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

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

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

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

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

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