1. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Chapter 48 Neurons, Synapses, and Signaling

2. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview: Lines of Communication Cone snail kills prey with venom that disables neurons Neurons are nerve cells that transfer information within the body Two types of signals to communicate: electrical (long-distance) chemical (short-distance)

3. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The transmission of information depends on the path of neurons along which a signal travels Processing of information simple clusters of neurons called ganglia more complex organization of neurons called a brain

4. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 48.1: Neuron organization and structure reflect function in information transfer The squid possesses extremely large nerve cells and is a good model for studying neuron function

5. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Introduction to Information Processing Nervous systems process three stages: sensory input, integration, and motor output 1) Sensors detect external stimuli and internal conditions and transmit information along sensory neurons 2) Sensory information is sent to the brain/ganglia, where interneurons integrate the information 3) Motor output leaves the brain or ganglia via motor neurons, which trigger muscle or gland activity

6. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Many animals have a complex nervous system which consists of: – A central nervous system (CNS) where integration takes place; this includes the brain and a nerve cord – A peripheral nervous system (PNS), which brings information into and out of the CNS

7. Fig. 48-3 Sensor Sensory input Integration Effector Motor output Peripheral nervous system (PNS) Central nervous system (CNS)

8. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Neuron Structure and Function Most of a neuron’s organelles are in the cell body Dendrites - highly branched extensions that receive signals from other neurons Axon - a much longer extension that transmits signals to other cells at synapses (connection point between cells where information is passed in the form of chemical messengers called neurotransmitters) An axon joins the cell body at the axon hillock

9. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Information is transmitted from a presynaptic cell (a neuron) to a postsynaptic cell (a neuron, muscle, or gland cell) Most neurons are nourished or insulated by cells called glia

10. Fig. 48-4 Dendrites Stimulus Nucleus Cell body Axon hillock Presynaptic cell Axon Synaptic terminals Synapse Postsynaptic cell Neurotransmitter

11. Fig. 48-5 Dendrites Axon Cell body Sensory neuronInterneurons Portion of axon Cell bodies of overlapping neurons 80 µm Motor neuron Form Fits Function - Variation

12. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Ion pumps and ion channels maintain the resting potential of a neuron Every cell has a voltage (difference in electrical charge) across its plasma membrane called a membrane potential Messages are transmitted as changes in membrane potential The resting potential is the membrane potential of a neuron not sending signals

13. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Formation of the Resting Potential In a mammalian neuron at resting potential, the concentration of K + is greater inside the cell, while the concentration of Na + is greater outside the cell (Overall Negative Internally) Sodium-potassium pumps use the energy of ATP to maintain these K + and Na + gradients across the plasma membrane These concentration gradients represent chemical potential energy

14. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The opening of ion channels in the plasma membrane converts chemical potential to electrical potential A neuron at resting potential contains many open K + channels and fewer open Na + channels; K + diffuses out of the cell Anions trapped inside the cell contribute to the negative charge within the neuron Animation: Resting Potential Animation: Resting Potential

15. Fig. 48-6 OUTSIDE CELL [K + ] 5 mM [Na + ] 150 mM [Cl – ] 120 mM INSIDE CELL [K + ] 140 mM [Na + ] 15 mM [Cl – ] 10 mM [A – ] 100 mM (a)(b) OUTSIDE CELL Na + Key K+K+ Sodium- potassium pump Potassium channel Sodium channel INSIDE CELL

16. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Modeling of the Resting Potential Resting potential can be modeled by an artificial membrane that separates two chambers – The concentration of KCl is higher in the inner chamber and lower in the outer chamber – K + diffuses down its gradient to the outer chamber – Negative charge builds up in the inner chamber At equilibrium, both the electrical and chemical gradients are balanced

17. Fig. 48-7 Inner chamber Outer chamber –90 mV 140 mM 5 mM KCI K+K+ Cl – Potassium channel (a) Membrane selectively permeable to K + (b) Membrane selectively permeable to Na + +62 mV 15 mM NaCI Cl – 150 mM NaCI Na + Sodium channel E K = 62 mV ( log 5 mM 140 mM ) = –90 mV E Na = 62 mV ( log 150 mM 15 mM = +62 mV )

18. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The equilibrium potential (E ion ) is the membrane voltage for a particular ion at equilibrium and can be calculated using the Nernst equation: E ion = 62 mV (log[ion] outside /[ion] inside ) The equilibrium potential of K + (E K ) is negative, while the equilibrium potential of Na + (E Na ) is positive

19. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings In a resting neuron, the currents of K + and Na + are equal and opposite, and the resting potential across the membrane remains steady

20. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Action potentials are the signals conducted by axons Neurons contain gated ion channels that open or close in response to stimuli = membrane potential changes. When gated K + channels open, K + diffuses out, making the inside of the cell more negative Hyperpolarization, an increase in magnitude of the membrane potential

21. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Other stimuli trigger a depolarization, a reduction in the magnitude of the membrane potential For example, depolarization occurs if gated Na + channels open and Na + diffuses into the cell Graded potentials are changes in polarization where the magnitude of the change varies with the strength of the stimulus

22. Fig. 48-9 Stimuli +50 Stimuli 00 Membrane potential (mV) –50 Threshold Resting potential Resting potential Hyperpolarizations –100 0 123 4 5 Time (msec) (a) Graded hyperpolarizations Time (msec) (b) Graded depolarizations Depolarizations 0 1 234 5 Strong depolarizing stimulus +50 0 Membrane potential (mV) –50 Threshold Resting potential –100 Time (msec) 01 2 3 4 56 (c) Action potential Action potential

23. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Production of Action Potentials Voltage-gated Na + and K + channels respond to a change in membrane potential When a stimulus depolarizes the membrane, Na + channels open, allowing Na + to diffuse into the cell The movement of Na + into the cell increases the depolarization and causes even more Na + channels to open A strong stimulus results in a massive change in membrane voltage called an action potential

24. Fig. 48-9c Strong depolarizing stimulus +50 Membrane potential (mV) –50Threshold Resting potential –100 02 3 4 Time (msec) (c) Action potential 1 5 0 Action potential 6 Action Potential Occurs if a stimulus causes the membrane voltage to cross a particular threshold

25. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Brief all-or-none depolarization of a neuron’s plasma membrane Action potentials are signals that carry information along axons (Not to other cells) Hundreds of action potentials per second Frequency of action potentials = strength of a stimulus An action potential can be broken down into a series of stages Action Potential

26. Fig. 48-10-5 Key Na + K+K+ +50 Action potential Threshold 0 1 4 5 1 –50 Resting potential Membrane potential (mV) –100 Time Extracellular fluid Plasma membrane Cytosol Inactivation loop Resting state Sodium channel Potassium channel Depolarization Rising phase of the action potential Falling phase of the action potential 5 Undershoot 2 3 2 1 3 4

27. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings At resting potential 1.Most voltage-gated Na + and K + channels are closed, but some K + channels (not voltage- gated) are open

28. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings When an action potential is generated 2.Voltage-gated Na + channels open first and Na + flows into the cell 3.During the rising phase, the threshold is crossed, and the membrane potential increases 4.During the falling phase, voltage-gated Na + channels become inactivated; voltage-gated K + channels open, and K + flows out of the cell

29. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 5.During the undershoot, membrane permeability to K + is at first higher than at rest, then voltage-gated K + channels close; resting potential is restored Refractory period after an action potential, a second action potential cannot be initiated Result of a temporary inactivation of the Na + channels

30. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Useful Simulations BioFlix: How Neurons Work BioFlix: How Neurons Work Animation: Action Potential Animation: Action Potential

31. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Conduction of Action Potentials Travels long distances by regenerating itself At the site where the action potential is generated, usually the axon hillock, an electrical current depolarizes the neighboring region of the axon membrane Inactivated Na + channels behind the zone of depolarization prevent the action potential from traveling backwards Only travels toward the synaptic terminals

32. Fig. 48-11-3 Axon Plasma membrane Cytosol Action potential Na + Action potential Na + K+K+ K+K+ Action potential K+K+ K+K+ Na +

33. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Conduction Speed The speed of an action potential increases with the axon’s diameter In vertebrates, axons are insulated by a myelin sheath, which causes an action potential’s speed to increase Myelin sheaths are made by glia— oligodendrocytes in the CNS and Schwann cells in the PNS

34. Fig. 48-12a Axon Myelin sheath Schwann cell Nodes of Ranvier Schwann cell Nucleus of Schwann cell Node of Ranvier Layers of myelin Axon Myelinated axon (cross section)

35. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Action potentials are formed only at nodes of Ranvier, gaps in the myelin sheath where voltage-gated Na+ channels are found Jump between the nodes of Ranvier in a process called saltatory conduction Cell body Schwann cell Depolarized region (node of Ranvier) Myelin sheath Axon

36. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Neurons communicate with other cells at synapses Electrical synapses, the electrical current flows from one neuron to another Chemical synapses, a chemical neurotransmitter carries information across the gap junction Most synapses are chemical synapses

37. Fig. 48-14 Postsynaptic neuron Synaptic terminals of pre- synaptic neurons 5 µm

38. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The presynaptic neuron synthesizes and packages the neurotransmitter in synaptic vesicles located in the synaptic terminal The action potential causes the release of the neurotransmitter The neurotransmitter diffuses across the synaptic cleft and is received by the postsynaptic cell Animation: Synapse Animation: Synapse

39. Fig. 48-15 Voltage-gated Ca 2+ channel Ca 2+ 1 2 3 4 Synaptic cleft Ligand-gated ion channels Postsynaptic membrane Presynaptic membrane Synaptic vesicles containing neurotransmitter 5 6 K+K+ Na +

40. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Postsynaptic Potential Binding of neurotransmitters to ligand-gated ion channels in the postsynaptic cell Neurotransmitter binding causes ion channels to open, generating a postsynaptic potential – Excitatory postsynaptic potentials (EPSPs) are depolarizations that bring the membrane potential toward threshold – Inhibitory postsynaptic potentials (IPSPs) are hyperpolarizations that move the membrane potential farther from threshold

41. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings After release, the neurotransmitter – May diffuse out of the synaptic cleft – May be taken up by surrounding cells – May be degraded by enzymes End of a neurotransmitter…or is it?

42. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Summation of Postsynaptic Potentials Unlike action potentials, postsynaptic potentials are graded and do not regenerate Most neurons have many synapses on their dendrites and cell body A single EPSP is usually too small to trigger an action potential in a postsynaptic neuron If two EPSPs are produced in rapid succession, an effect called temporal summation occurs

43. Fig. 48-16ab E1E1 E2E2 Postsynaptic neuron I Terminal branch of presynaptic neuron E2E2 0 –70 Threshold of axon of postsynaptic neuron Resting potential Membrane potential (mV) E1E1 E1E1 (a) Subthreshold, no summation (b) Temporal summation E1E1 E1E1 Action potential I Axon hillock E1E1

44. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings In spatial summation, EPSPs produced nearly simultaneously by different synapses on the same postsynaptic neuron add together The combination of EPSPs can trigger an action potential IPSP can counter the effect of an EPSP May or may not reach threshold and generate an action potential

45. Fig. 48-16cd E1E1 E2E2 Membrane potential (mV) Action potential I E 1 + E 2 (c) Spatial summation (d) Spatial summation of EPSP and I PSP E1E1 E1E1 E 1 + I I I E2E2 0 –70

46. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Modulated Synaptic Transmission Indirect synaptic transmission - A neurotransmitter binds to a receptor that is not part of an ion channel Second messenger in the postsynaptic cell is activated ex) cAMP Effects of indirect synaptic transmission have a slower onset but last longer

47. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Neurotransmitters Same neurotransmitter can produce different effects in different types of cells 5 major classes of neurotransmitters (~100): 1) acetylcholine 2) Biogenic amines 3) Amino acids 4) Neuropeptides 5) Gases

48. Table 48-1

49. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Acetylcholine Acetylcholine is a common neurotransmitter in vertebrates and invertebrates In vertebrates it is usually an excitatory transmitter. Ex) muscles (except Heart) Bacteria produce toxins that causes botulism Botox

50. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Biogenic Amines – Derived from Animo Acids Include epinephrine, norepinephrine, dopamine, and serotonin They are active in the CNS and PNS LSD binds like serotonin to produce hallucinatory effects. Parkinson’s lack of dopamine Treat depression with drugs to increase concentration of Bio Amines.

51. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Amino Acids Two amino acids are known to function as major neurotransmitters in the CNS: Gamma-aminobutyric acid (GABA) – Inhibitory by increasing the Cl - movement. Glutamate – Most common n.t. in brain, excitatory.

52. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Neuropeptides Relatively short chains of amino acids, also function as neurotransmitters Neuropeptides include substance P (Mediates) and endorphins (Decreases Pain), which both affect our perception of pain Opiates bind to the same receptors as endorphins and can be used as painkillers (Euphoria)

53. Fig. 48-17 EXPERIMENT RESULTS Radioactive naloxone Drug Protein mixture Proteins trapped on filter Measure naloxone bound to proteins on each filter

54. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Gases Gases such as nitric oxide and carbon monoxide are local regulators in the PNS Produced on demand (as needed), stimulates production of a second messenger) – Sexual Arousal

55. Fig. 48-UN1 Action potential Falling phase Rising phase Threshold (–55) Resting potential Undershoot Time (msec) Depolarization –70 –100 –50 0 +50 Membrane potential (mV)