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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
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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.
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
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)
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?
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)?
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
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?
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
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.
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.
