Chapter 34 Opener

Concept 34.1 Nervous Systems Consist of Neurons and Glia Parts of a neuron Working in pairs, draw two neurons that meet at a synapse. Label on your diagram: Axon Axon hillock Axon terminal Cell body Dendrite Nucleus Presynaptic cell Postsynaptic cell Synapse Take turns defining each term and describing the function of each part. INSTRUCTOR NOTES: Students can draw their own neurons, or they can be provided with an unlabelled diagram of a neuron on which they can add their own labels. If time permits, drawing a diagram themselves, and adding labels themselves, often helps students retain information better than by just looking at a fully labeled diagram. 2

Concept 34.1 Nervous Systems Consist of Neurons and Glia What do axons do? a. The major function of an axon is to transmit electrical signals from one location to another. b. Axons are the primary location where a neuron receives information from other neurons. c. Axons manufacture neurotransmitter. d. Axons are the primary location where a neuron releases neurotransmitter. e. All of the above Answer: a (Some axons do actually receive information [b] and some do release neurotransmitter [d] at synapses that occur in the middle of the axon. But typically an axon’s major role is simply to transmit electrical impulses from the cell body to the axon terminal.) 3

Figure 34.1 A Generalized Neuron

Figure 34.1 A Generalized Neuron

Figure 34.2 Wrapping Up an Axon

Figure 34.2 Wrapping Up an Axon

Figure 34.2 Wrapping Up an Axon (Part 1)

Figure 34.2 Wrapping Up an Axon (Part 2)

Figure 34.3 Nervous Systems Vary in Size and Complexity

Figure 34.3 Nervous Systems Vary in Size and Complexity

Figure 34.3 Nervous Systems Vary in Size and Complexity (Part 1)

Figure 34.3 Nervous Systems Vary in Size and Complexity (Part 2)

Figure 34.3 Nervous Systems Vary in Size and Complexity (Part 3)

Figure 34.4 Measuring the Membrane Potential

Figure 34.4 Measuring the Membrane Potential

Figure 34.4 Measuring the Membrane Potential (Part 1)

Figure 34.4 Measuring the Membrane Potential (Part 2)

Figure 34.5 Ion Transporters and Channels

Figure 34.5 Ion Transporters and Channels (Part 1)

Figure 34.5 Ion Transporters and Channels (Part 2)

Nernst Equation

Goldman-Hodgkin-Katz Equation

These data were recorded from the large axon of a squid These data were recorded from the large axon of a squid. They show the concentrations of four ions both inside the axon’s cytoplasm and outside the cell, in a sea water bath. Use the Nernst equation to predict the equilibrium potential for each of the four ions. The measured resting potential of this axon is -66 mV. How can you explain that resting potential on the basis of the equilibrium potentials you calculated. Another equation, the Goldman-Hodgkin-Katz equation, includes a relative permeability of the membrane for each ion. Why is this necessary for accurately predicting membrane potential?

Apply the Concept, Ch. 34, p. 677

Figure 34.6 Membranes Can Be Depolarized or Hyperpolarized

Figure 34.6 Membranes Can Be Depolarized or Hyperpolarized

Figure 34.7 The Course of an Action Potential

Figure 34.7 The Course of an Action Potential

Figure 34.7 The Course of an Action Potential (Part 1)

Figure 34.7 The Course of an Action Potential (Part 2)

Figure 34.8 Saltatory Action Potentials

Figure 34.8 Saltatory Action Potentials

Figure 34.8 Saltatory Action Potentials (Part 1)

Figure 34.8 Saltatory Action Potentials (Part 2)

Concept 34.2 Neurons Generate and Transmit Electrical Signals Using the Nernst equation to predict membrane potentials Suppose a cell has the following ion concentrations: Calcium (Ca2+): 1 mM outside, 0.0001 mM inside Chloride (Cl–): 100 mM outside, 10 mM inside Potassium (K+): 5 mM outside, 150 mM inside 1. Working individually, calculate the equilibrium potential of each ion. Then check with your neighbors to see if you all got the same result. 2. Working in small groups, suppose that while at rest, the membrane is much more permeable to chloride than to any other ion. What will the cell’s resting membrane potential be (approximately)? 3. Now suppose the chloride channels close and a large number of calcium channels open, such that the cell membrane becomes much more permeable to calcium than to any other ion. Which way will calcium move? Will the cell depolarize, hyperpolarize, or neither? What will be the new membrane potential (approximately)? Answers: 1. E (calcium) = 116 mV E (chloride) = –58 mV E (potassium) = –86 mV The cell’s resting membrane potential will be close to –58mV, which is the equilibrium potential of chloride. Calcium will move into the cell, causing depolarization. The new membrane potential will be near +116mV, the equilibrium potential of calcium. INSTRUCTOR NOTE: Before doing this exercise, some students may benefit from a short review of logarithms. 37

Concept 34.2 Neurons Generate and Transmit Electrical Signals If calcium channels suddenly open, a. there will be a net movement of calcium into the cell. b. there will be a net movement of calcium out of the cell. c. there will be no net movement of calcium. d. the cell will hyperpolarize. e. Both a and d Answer: a (There will be a net movement of calcium into the cell, and the cell will depolarize.) 38

Concept 34.2 Neurons Generate and Transmit Electrical Signals How does the pufferfish kill? The Japanese pufferfish produces a highly potent neurotoxin called tetrodotoxin (TTX). TTX binds to voltage-gated sodium channels. Ingestion of TTX causes numbness of the lips and tongue, followed rapidly by weakness, loss of coordination, and a sensation of limpness and weakness throughout the body. Relatively small doses of TTX can kill a person. Working in pairs, develop a hypothesis to explain the symptoms of TTX poisoning in terms of TTX’s effect on sodium channels. How exactly do you think TTX kills? Answer: When TTX binds to voltage-gated sodium channels, it prevents them from opening as they usually would when a graded potential passes threshold. As a result, neurons and muscles cannot fire action potentials. TTX essentially blocks communication, both from neuron to neuron, and from neuron to muscle. This causes paralysis in the affected muscles. If a fatal dose has been ingested, death occurs by paralysis of the respiratory muscles. 39

Concept 34.2 Neurons Generate and Transmit Electrical Signals Blockage of voltage-gated sodium channels in a neuron will cause which of the following? a. The neuron’s resting membrane potential will become more negative. b. The neuron’s resting membrane potential will become less negative. c. The neuron will be unable to produce action potentials. d. Both a and c e. Both b and c Answer: c (The resting membrane potential will be unaffected, but the neuron will be unable to generate action potentials.) 40

Figure 34.9 Chemical Synaptic Transmission

Figure 34.9 Chemical Synaptic Transmission

Figure 34.10 Chemically Gated Channels

Figure 34.10 Chemically Gated Channels

Figure 34.11 The Postsynaptic Neuron Sums Information

Figure 34.11 The Postsynaptic Neuron Sums Information

Neurons Communicate with other cells at synapses How do we know that Ca2+ influx into the presynaptic nerve ending causes the release of neurotransmitter? Because the squid giant axon and its nerve endings are so large, they are a convenient system for experiments. It is possible to inject substances into both the presynaptic and postsynaptic cells near the synapse. Some of the substances that can be injected are Ca2+ ions and BAPTA, a substance that binds Ca2+ ions. Also, channel blockers can be added to the culture medium. For example, cadmium blocks Ca2+ channels. Here are the results of a series of experiments using these substances.

Apply the Concept, Ch. 34, p. 683

1. What is happening during the delay between the pre- and post synaptic membrane events in the control condition? 2. Explain the postsynaptic response in the absence of a presynaptic response in experiment 1? 3. Explain why there is a presynaptic but no postsynaptic response in experiment 2? 4. Why are there no pre- or postsynaptic responses in experiment 3?

Concept 34.3 Neurons Communicate with Other Cells at Synapses An acetylcholinesterase inhibitor would cause which of the following? a. No action potentials in the postsynaptic cell b. Too many action potentials in the postsynaptic cell c. No change in action potentials in the postsynaptic cell d. I don’t know. Answer: b [NOTE TO THE INSTRUCTOR: It can be useful to include an “I don't know” choice with clickers, because it can help you discover how many students really haven’t understood the concept at all. Use of this option may depend on whether you assign participation-only points or performance points (or some combination) to clicker questions in your course. If you only assign participation points, it may be useful to leave the “I don't know” choice in the question, as it gives students a penalty-free way of indicating that more time may be needed on this concept.] 50

Concept 34.3 Neurons Communicate with Other Cells at Synapses Sequence of events at a synapse Working in pairs, put the following steps in the correct sequence: a. ACh binds to membrane receptors. b. Vesicles containing ACh fuse with the cell membrane. c. A graded potential spreads through the postsynaptic cell. d. Action potential arrives at the axon terminal. e. Na+ and K+ enter the postsynaptic cell. f. Postsynaptic cell fires an action potential. g. Calcium enters the presynaptic cell. h. Voltage-gated calcium channels open. i. ACh diffuses across the synaptic cleft. j. Ligand-gated channels on the postsynaptic cell open. Answer: d-h-g-b-i-a-j-e-c-f INSTRUCTOR NOTES: After pairs of students have had a few minutes to work out the sequence on their own, have the whole class participate in putting together a consensus sequence. This exercise can also be done as a whole-class activity, with ten volunteers standing up front holding signs that depict all of the steps. Have the volunteers stand in the wrong order at first; then ask the class how to physically rearrange the volunteers until they are standing in the correct order. If time is short, simply show the class the whole list of steps and ask the class to name the first step, then the second step, etc. 51

Concept 34.3 Neurons Communicate with Other Cells at Synapses Biology of a weapon of mass destruction In Tokyo, Japan, on a Monday morning in 1995, at rush hour, five terrorists dropped bags containing a chemical compound called sarin into five subway cars. The perpetrators punctured the bags with sharpened umbrella tips, and then left the cars. Over 5,000 people were affected. Thirteen people died, several dozen became critically ill, and several hundred more suffered vision impairment (in some cases lasting over a decade). Sarin is classified as a weapon of mass destruction. Sarin forms a covalent bond with the enzyme acetylcholinesterase. In small groups, discuss: How exactly could sarin kill a person? (What is the cause of death?) What might the symptoms of sarin poisoning be? Contrast sarin’s mechanism of action with that of pufferfish toxin. Answers: Sarin is an acetylcholinesterase inhibitor. When it forms a covalent bond with acetylcholinesterase, it blocks the enzyme’s active site, and the enzyme can no longer break down ACh. The result is that ACh builds up in neuromuscular junctions and continues to act. Respiration stops - death is caused by suffocation. Muscles go into a tetanic seizure and cannot relax. Early symptoms include constriction of pupils, drooling (due to constriction of salivary gland smooth muscle), difficulty breathing (due to constriction of respiratory muscles), and nausea (due to seizures of smooth muscle throughout the entire digestive tract, stopping peristalsis). Victims who die usually die of suffocation during convulsions. Interestingly, sarin and TTX (pufferfish toxin) both cause death by suffocation, but they stop respiration by opposite means. TTX blocks action potentials, so that respiratory muscles are paralyzed (i.e., become limp). Sarin causes the opposite problem - too many action potentials - causing respiratory muscles to seize up in a tetanic contraction during convulsions. Either way, respiration stops. INSTRUCTOR NOTE: Several other toxins are also acetylcholinesterase inhibitors, including sea slug toxin, the insecticide malathion, and toxic compounds in certain plants (especially lilies). 52

Figure 34.12 Organization of the Nervous System

Figure 34.13 The Autonomic Nervous System

Figure 34.14 The Spinal Cord Coordinates the Knee-jerk Reflex

Figure 34.14 The Spinal Cord Coordinates the Knee-jerk Reflex

Figure 34.15 The Limbic System

Figure 34.15 The Limbic System

Figure 34.16 The Human Cerebrum

Figure 34.16 The Human Cerebrum

Figure 34.16 The Human Cerebrum (Part 1)

Figure 34.16 The Human Cerebrum (Part 2)

Figure 34.17 The Body Is Represented in Primary Motor and Primary Somatosensory Cortexes

Figure 34.17 The Body Is Represented in Primary Motor and Primary Somatosensory Cortexes

Reviewing the divisions of the nervous system Concept 34.4 The Vertebrate Nervous System Has Many Interacting Components Reviewing the divisions of the nervous system Working in pairs and not looking at your notes, make a chart showing the relationships of these parts of the nervous system: Sympathetic nervous system Parasympathetic nervous system Central nervous system Enteric nervous system Peripheral nervous system Autonomic nervous system Brain Spinal cord Voluntary division Afferent pathways Efferent pathways Sensory nerves Motor nerves INSTRUCTOR NOTES: The purpose of this exercise is simply to review the many divisions of the nervous systems and their relationships to each other. Students often do not grasp, for example, that the autonomic nervous system is part of the peripheral nervous system, or how sensory and motor nerves fit into the overall framework. Students should, with some guidance, come up with something like the following framework: 1. Central nervous system a. Brain b. Spinal cord 2. Peripheral nervous system a. Afferent pathways = sensory nerves b. Efferent pathways i. Voluntary division = motor nerves ii. Autonomic nervous system - Sympathetic nervous system - Parasympathetic nervous system c. Enteric nervous system 65

The sympathetic nervous system is a part of the Concept 34.4 The Vertebrate Nervous System Has Many Interacting Components The sympathetic nervous system is a part of the a. autonomic nervous system. b. peripheral nervous system. c. parasympathetic nervous system. d. Both a and b e. All of the above Answer: d 66

Inability to move the right side of her body Concept 34.4 The Vertebrate Nervous System Has Many Interacting Components Where was the damage? Suppose a woman suffers a stroke (bleeding within the brain) and suffers some brain damage. Her symptoms are as follows: Inability to speak Inability to move the right side of her body Some deficits in sensation on the right side of the body Inability to recognize faces She still retains the following abilities: Normal sensation on the left side of her body Normal vision in both sides of both eyes Unchanged personality Normal ability to plan and reason Which lobes of her cerebrum were most likely affected by the stroke? On what side? Explain. Answers: The damage was most likely on the left side of her cerebrum. Three lobes were affected: frontal, parietal, and temporal. Inability to move the right side of the body indicates damage to the left primary motor cortex (part of the frontal lobe), but luckily most of the rest of the frontal lobe seems to have been spared (as indicated by no change in personality and ability to plan/reason). The deficits in sensation on the right side of the body indicate some damage to the left primary somatosensory cortex (part of the parietal lobe). Inability to speak or recognize faces indicates damage to the temporal lobe. The occipital lobe appears to have been unaffected since her vision is normal. 67

Which of the following is associated with the parietal lobe? Concept 34.4 The Vertebrate Nervous System Has Many Interacting Components Which of the following is associated with the parietal lobe? a. Control of the voluntary muscles b. The sense of vision c. The sense of hearing d. Ability to make decisions e. Perception of three-dimensional space Answer: e 68

Figure 34.18 Imaging Techniques Reveal Active Parts of the Brain

Figure 34.19 Stages of Sleep

Figure 34.19 Stages of Sleep (Part 1)

Figure 34.19 Stages of Sleep (Part 2)

Concept 34.5 Specific Brain Areas Underlie the Complex Abilities of Humans Which of the following brain areas is associated with understanding of speech in humans? a. Broca’s area b. Wernicke’s area c. The hippocampus d. The insula e. The thalamus Answer: b 73

Concept 34.5 Specific Brain Areas Underlie the Complex Abilities of Humans A new ape Suppose a previously unknown species of ape is discovered in Africa. To everybody’s astonishment, the new apes turn out to use a fairly complex form of verbal communication - something never before observed in any non-human ape. Tests reveal that the new apes appear capable of highly advanced planning and decision-making, and appear to recognize themselves in a mirror. What brain areas would you predict might be especially well-developed in these apes, compared to other mammals and compared to other apes (chimpanzee, gorilla)? Why? Finally, would your answer be the same if the new species were an intelligent bird, rather than an intelligent mammal? Why or why not? Answers: We could expect speech areas, especially Broca’s and Wernicke’s areas, to be especially well-developed in the new apes - both compared to all other mammals and compared to other apes, since no other apes use complex speech. [Note: It is possible that the new apes might have evolved novel areas for control of speech, but apes do have precursors to Broca’s and Wernicke’s areas that are used in gesture recognition. So it is (arguably) likely that they would use these same areas for speech.] The frontal lobes (decision-making/planning) and the insula (putative site of self-awareness) will also likely be larger in the new apes than in other mammals, though not necessarily larger than in other apes, since other apes also have the capabilities of decision-making/planning and self-awareness. The cerebral areas described in the text are found only in mammals. Therefore, intelligent non-mammals would not necessarily use the cerebral cortex for advanced cognitive abilities. They might instead use different brain regions entirely. (As it happens, this seems to have happened in birds. The most intelligent birds - parrots and corvids - have brain/body ratios similar to the apes, and similar or even slightly superior cognitive abilities. But these birds appear to use entirely different brain regions for advanced cognition. In general, birds have not elaborated the cerebral cortex as mammals have, and instead have elaborated the underlying neostriatum, a region that is relatively undeveloped in mammals. Additionally, birds in general tend to use a much higher degree of learned vocal communication than do mammals, and birds have evolved a novel set of brain regions for this ability.) 74

Figure 34.20 Source of the Fear Response