6.5 Nerves, Hormones and Homeostasis

1. 6.5 Nerves, Hormones and Homeostasis

2. Assessment Statements 6.5.1 State that the nervous system consists of the central nervous system (CNS) and peripheral nerves, and is composed of cells called neurons that can carry rapid electrical impulses. 6.5.2 Draw and label a diagram of the structure of a motor neuron. 6.5.3 State that nerve impulses are conducted from receptors to the CNS by sensory neurons, within the CNS by relay neurons, and from the CNS to effectors by motor neurons. 6.5.4 Define resting potential and action potential (depolarization and repolarization). 6.5.5 Explain how a nerve impulse passes along a non-myelinated neuron. 6.5.6 Explain the principles of synaptic transmission.

3. Why do we need control systems? Response to stimuli is essential for survival Multicellular organisms need coordination Nervous versus endocrine systems Both work together e.g. rabbit running from fox – what systems involved?

4. Sense organs detect change (receptors) Effectors respond Distance between two Every sensor and effector has at least 1 link to CNS Spinal cord links brain to rest of body

5. 6.5.1 State that the nervous system consists of the central nervous system (CNS) and peripheral nerves

8. 6.5.1... cells called neurons that can carry rapid electrical impulses.

9. 6.5.2 Draw and label a diagram of the structure of a motor neuron Dendrites transmit impulses to cell body Nodes of Ranvier Impulses leave via axon Myelin sheath composed of Schwann cells Cell body with nucleus direction of impulse Axon terminal passes signal to effector

10. Neurones packed and wrapped to form nerves May contain sensory, effector or mixture

11. 6.5.3 State that nerve impulses are conducted from receptors to the CNS by sensory neurons, within the CNS by relay neurons, and from the CNS to effectors by motor neurons.

12. Relay neurone Sensory neurone Motor neurone

13. Sensory neurons carry messages from receptors in sense organs to CNS. Relay neurones connect sensory neurons to motor neurones in the CNS. Motor neurons connect the CNS to the effector.

14. A Receptor in skin B Sensory neurone C Relay neurone D Motor neurone E Effector

18. 6.5.4 Define resting potential and action potential (depolarization and repolarization). Neurons have an electrical potential (voltage) across the cell membrane, i.e. membrane is polarised. The inside of the cell is more negative than the outside This is called the Resting Membrane Potential = 70mV

19. Definitions Resting potential - the electrical potential across the cell membrane of a cell that is not conducting an impulse Action potential - is the reversal (polarisation) and restoration (depolarisation) of the electrical potential across the plasma membrane as an impulse passes along a neurone

20. Concentration of Na+ is high outside the neuron This results in the inside being more negative than outside Sodium/potassium cation pumps transport Na+ out and K+ in Difference in concentration of ions maintained by active transport against concentration gradient Membrane is more permeable to K+ than Na+ This requires ATP Concentration of K+ inside 20x greater so K+ ions rapidly diffuse out until equilibrium reached Concentration of K+ is high inside the neuron

22. 6.5.5 Explain how a nerve impulse passes along a non-myelinated neuron. Stimulation can reverse the charge on a neuron (-70 to +40 mV) Membrane becomes depolarised If stimulus exceeds certain threshold value an action potential results Action potential - rapid reversal of the resting membrane potential that travels down the axon

27. The nervous impulse

29. 6.5.6 Explain the principles of synaptic transmission.

30. Synapses occur where neurons meet

38. Outline the use of four method of membrane transport in nerves and synapses (8)

39. Assessment Statements: 6.5.7 State that the endocrine system consists of glands that release hormones that are transported in the blood. 6.5.8 State that homeostasis involves maintaining the internal environment between limits, including blood pH, carbon dioxide concentration, blood glucose concentration, body temperature and water balance. 6.5.9 Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms. 6.5.10 Explain the control of body temperature, including the transfer of heat in blood, and the roles of the hypothalamus, sweat glands, skin arterioles and shivering. 6.5.11 Explain the control of blood glucose concentration, including the roles of glucagon, insulin and α and β cells in the pancreatic islets. 6.5.12 Distinguish between type I and type II diabetes.

40. 6.5.7 State that the endocrine system consists of glands that release hormones that are transported in the blood.

41. The endocrine system consists of glands. Glands secrete chemicals called hormones directly into the blood. Hormones travel in the blood to a target organ (effector) and bring about a response. The response becomes a feedback stimuli.

42. 6.5.8 State that homeostasis involves maintaining the internal environment between limits Homeostasis literally means “same state” - refers to the process of keeping the internal body environment in a steady state. Very important - a great deal of the endocrine system and autonomicnervous system is dedicated to homeostasis.

43. What needs to be controlled? 7.35 to 7.45 • Blood pH • Blood carbon dioxide levels • Blood glucose concentration • Body temperature • Water balance All of these factors are maintained between limits within the blood and tissue fluid. 70 - 100 mg/dL 37.0oC

44. 6.5.9 Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms.

45. Negative feedback loops All homeostatic mechanisms use negative feedback to maintain a constant value (called the set point). Negative feedback means that whenever a change occurs in a system, the change automatically causes a corrective mechanism to start, which reverses the original change and brings the system back to normal.

46. The bigger the change the bigger the corrective mechanism. Applies to electronic circuits and central heating systems as well as to biological systems. In a system controlled by negative feedback the level is never maintained perfectly, but constantly oscillates about the set point. An efficient homeostatic system minimises the size of the oscillations.

47. 6.5.10 Explain the control of body temperature, including the transfer of heat in blood, and the roles of the hypothalamus, sweat glands, skin arterioles and shivering. Homeotherms - animals that maintain a fairly constant body temperature (birds and mammals) Animals with variable body temperature (all others) are called poikilotherms Homeotherms maintain body temperature at around 37°C (warm-blooded) Poikilothermic animals can also have very warm blood during the day by basking in the sun.

48. In humans temperature is controlled by the thermoregulatory centre in the hypothalamus. Receives input from two sets of thermoreceptors Receptors in the hypothalamus monitor the temperature of the blood as it passes through the brain (core body temperature) Receptors in the skin monitor the external temperature. The thermoregulatory centre sends impulses to several different effectors to adjust body temperature.

50. The skin and temperature control