Chapter 12: Nervous System

1. UNIT B Chapter 12: Nervous System In this chapter, you will learn about the structure and function of the nervous system. Chapter 12: Nervous System • How might a researcher study the effects of frequent head trauma? • How might one determine which part of the brain has been affected by repeated blunt impacts? • Given the available information about CTE, what steps do you feel should be taken to prevent its occurrence (if any)? Sport-Related Head Trauma and Brain Function. Neurosurgeon Dr. Robert Cantu has studied the brains of many deceased athletes, including hockey and football players. He has found that these players often suffered from chronic traumatic encephalopathy (CTE), a degenerative brain disease caused by repeated blunt impact to the head. TO PREVIOUS SLIDE

2. Reflex Arc: nerve pathway followed by a reflex action

3. Action potential • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html

4. UNIT B Chapter 12: Nervous System Section 12.2 Nerve impulse: used by the nervous system to convey information . Voltage: the electrical potential difference between two points: measured in millivolts (mV); studied using a voltmeter called an oscilloscope 12.2 Transmission of Nerve Impulses TO PREVIOUS SLIDE

5. Resting and Action Potential

6. UNIT B Chapter 12: Nervous System Section 12.2 The resting potential is the potential difference across the membrane in a resting neuron -70mV Resting Potential TO PREVIOUS SLIDE

7. UNIT B Chapter 12: Nervous System Section 12.2 The polarity of the resting axonal membrane is due to a difference in ion distribution on each side. Greater [ Na+] outside Greater [K+] inside Why? TO PREVIOUS SLIDE

8. UNIT B Chapter 12: Nervous System Section 12.2 Potential Difference Across a Membrane Sodium-potassium pumpsactively transport Na+ out of the axon and K+ into the axon membrane is permeable to Na+ and K+ more permeable to K+, therefore there are always more positive ions outside the membrane than inside TO PREVIOUS SLIDE

9. UNIT B Chapter 12: Nervous System Section 12.2 Rapid change in polarity across axonal membrane. Requires two gated channel proteins in the membrane: Na+ to pass into the axon K+ to pass out of the axon Action Potential: TO PREVIOUS SLIDE

10. Animation: How Sodium-Potassium Pump works • http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.htmlv • BLM 12-14 Worksheet

11. Animation: Nerve Impulse • http://highered.mheducation.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html • BLM 12-15 WS

12. All-or-none phenomenon: • A certain level of stimulus (threshold) must be reached before the voltage gated channels will open. • The strength of an action potential does not change, but an intense stimulus can cause an axon to fire (start an action potential) more often

13. UNIT B Chapter 12: Nervous System Section 12.2 Figure 12.4 Action Potential. c. The changes in the transmembrane potential of the axon are a result of sodium ions flowing into the axon and potassium ions flowing out. An action potential lasts only a few seconds. TO PREVIOUS SLIDE

14. UNIT B Chapter 12: Nervous System Section 12.2 1. Sodium Gates Open (Depolarization) Na+ flows down its concentration gradient into the axon  membrane potential changes from -70 mV to +35 mV Called depolarization because the charge inside the axon changes from negative to positive Action Potential: Sequence of Events TO PREVIOUS SLIDE

15. UNIT B Chapter 12: Nervous System Section 12.2 Figure 12.4 Action Potential. a. The action potential begins as the sodium gates (purple) open and Na+ ions move into the axon through facilitated diffusion. This is depolarization as the membrane potential jumps from −70 to +35 millivolts. TO PREVIOUS SLIDE

16. UNIT B Chapter 12: Nervous System Section 12.2 2. Potassium Gates Open (Repolarization) K+ flows down its concentration gradient  the action potential becomes more negative again (repolarization) During this time, it briefly becomes slightly more negative that its original resting potential (hyperpolarization) Action Potential: Sequence of Events TO PREVIOUS SLIDE

17. UNIT B Chapter 12: Nervous System Section 12.2 Figure 12.4 Action Potential. b. The repolarization of a neuron occurs as the potassium gates (orange) open and K+ ions move out of the axon through facilitated diffusion. TO PREVIOUS SLIDE

18. Animation: Action Potential Propagation in unmyelinated neuron • http://highered.mheducation.com/sites/0072943696/student_view0/chapter8/animation__action_potential_propagation_in_an_unmyelinated_axon__quiz_2_.html • BLM 12-16

19. UNIT B Chapter 12: Nervous System Section 12.2 Action potentials in non-myelinated axons: Travels down axon one small section at a time, depolarizing and repolarizing. What stops the signal from going both ways? Conduction of an Action Potential TO PREVIOUS SLIDE

20. What stops the signal from going both ways? • Refractory period: • Period of time when sodium gates are unable to open • Prevents action potential from moving backward; it always moves down an axon

21. UNIT B Chapter 12: Nervous System Section 12.2 Action potentials in myelinated axons The gated ion channels that produce an action potential are concentrated at the nodes of Ranvier Ion exchange only occurs at these nodes, therefore the action potential travels faster than in non-myelinated axons The action potential appears to “jump” from node to node (saltatory conduction) TO PREVIOUS SLIDE

22. Myelin Sheath • Increases speed nerve impulse, • helps in reduces energy expenditure over the axon membrane as a whole, (less Na+ and K+ needed to be pumped to bring the concentrations back to the resting state after each action potential)

23. How does the action potential get to the next neuron?

24. How does the action potential get to the next neuron?

26. UNIT B Chapter 12: Nervous System Section 12.2 axon terminal – small swelling at end of axon terminal lies closed to another neuron, muscle cell, or gland synapse - region of close proximity (chemical or electrical) presynaptic membrane- membrane of the first neuron postsynaptic membrane - membrane of the second neuron: synaptic cleft – gap between Transmission Across a Synapse TO PREVIOUS SLIDE

27. How does the message cross the synaptic cleft? • http://highered.mheducation.com/sites/0072943696/student_view0/chapter8/animation__chemical_synapse__quiz_1_.html

28. UNIT B Chapter 12: Nervous System Section 12.2 An action potential cannot cross a synapse. neurotransmitters (chemicals stored in the synaptic vesicles in axon terminals) Figure 12.5 Structure and function of a synapse. Transmission across a synapse from one neuron to another occurs when an action potential causes a neurotransmitter to be released at the presynaptic membrane. TO PREVIOUS SLIDE

29. Neurotransmitters • Amino acids: • glutamate, aspartate, D-serine, GABA), glycine. • Monoamines: • dopamine (DA), norepinephrine, epinephrine , histamine, serotonin (SER,) • Peptides; • Opioids, endorphins • Gasotransmitters: • nitric oxide (NO), carbon monoxide (CO), hydrogen sulfide (H2S) • Other: • Acetylcholine

30. UNIT B Chapter 12: Nervous System Section 12.2 When an action potential arrives at an axon terminal: Gated channels for Ca2+ open, Ca2+ enters the terminal, Ca2+ binds to contractile proteins, which contract and pull the synaptic vesicles to the presynaptic Membrane synaptic vesicles merge with the presynaptic membraneexocytosis TO PREVIOUS SLIDE

31. UNIT B Chapter 12: Nervous System Section 12.2 TO PREVIOUS SLIDE

32. UNIT B Chapter 12: Nervous System Section 12.2 Depending on the neurotransmitter, the postsynaptic neuron can either be excited (causing an action potential) or inhibited (stopping an action potential) TO PREVIOUS SLIDE

33. Transmission across a synapse animation • http://highered.mheducation.com/sites/0072495855/student_view0/chapter14/animation__transmission_across_a_synapse.html • http://highered.mheducation.com/sites/0072943696/student_view0/chapter8/animation__chemical_synapse__quiz_2_.html

34. UNIT B Chapter 12: Nervous System Section 12.2 Neurons can receive messages from many other neurons. Synapticintegration is the summing up of the excitatory and inhibitory signals in a postsynaptic neuron. Synaptic Integration Figure 12.6 Synaptic integration. TO PREVIOUS SLIDE

35. Integration

36. UNIT B Chapter 12: Nervous System Section 12.2 Some may be either: Excitatory signals: cause a depolarizing effect Inhibitory signals: cause a hyperpolarizing effect If the combined signals cause membrane potential to rise above threshold, an action potential occurs TO PREVIOUS SLIDE

37. UNIT B Chapter 12: Nervous System Section 12.2 To prevent continuous stimulation, neurotransmitter needs to be removed: Enzymes in the postsynaptic membrane Or presynaptic membrane reabsorbs Neurotransmitters TO PREVIOUS SLIDE

38. UNIT B Chapter 12: Nervous System Section 12.2 Enhance or block the release of neurotransmitters Mimic the neurotransmitter Block the receptor for the neurotransmitter Interfere with the removal of the neurotransmitter Example: Sarin gas is a chemical weapon that inhibits acetylcholinesterase (AChE), an enzyme that is responsible for the breakdown of acetylcholine (ACh) Leads to prolonged ACh activity (convulsive spasms) Drugs TO PREVIOUS SLIDE

39. Opioids • Block pain receptors. • Morphine, heroin  analgesia • Inhibit pain signa at multiple steps in the pathway (brain, spinal cord and periphery) . In the brain opioids have mood altering effects, cause sedation, and can even decrease emotional response to pain. • ENDOPHINS (ENDO genous moRPHIN e) • Body gets used to the the

40. Pain • https://www.youtube.com/watch?v=GmHGUTNoL-I

41. Addiction • SciShow • https://www.youtube.com/watch?v=ukFjH9odsXw

42. Agonists and Antagonists • Agonist • chemical that binds to a receptor and activates the receptor to produce a biological response. • causes an action. • Antagonist blocks action

43. Golden poison frog (Phyllobates terribilis) Harbours enough poison to kill 10 grown men.

44. Neurotoxins: Neurotransmittor inhibition • Botox prevents the release of the chemical acetylcholine

45. Sydney Funnel Web Spider • atracotoxin does the opposite. It hyper-stimulates the nervous system to the point of overload. As the toxin works its way through a victim’s body, it elevates blood pressure, eventually causing the millions of air sacs in the lungs to burst (pulmonary edema), a condition which causes you to effectively drown on dry land. 



46. Brazilian Wandering Spider

47. Muscle ParalysisFound in the Cone Snail

48. Puffer Fish

49. Reuptake Inhibitor • A reuptake inhibitor (RI) • type of reuptake modulator which inhibits the plasmalemmal transporter-mediated reuptake of a neurotransmitter from the synapse into the pre-synaptic neuron, leading to an increase in the extracellular concentrations of the neurotransmitter and therefore an increase in neurotransmission.

50. UNIT B Chapter 12: Nervous System Section 12.2 Describe the activity of the sodium-potassium pump present in neurons. Explain how the changes in Na+ and K+ ion concentrations that occur during an action potential are associated with depolarization and repolarization. Define refractory period, saltatory conduction, and synaptic integration. Check Your Progress TO PREVIOUS SLIDE