Answers for the LAB Functions of cell membrane channels.pdf

LAB. Function of cell membrane channels (compiuter simulation) Study Questions on Ion Channels: 1. (Page 3.) What controls the movement of ions across the membrane of a neuron? Ion channels control the movement of ions across the neuronal membrane. 2. (Page 3.)...

LAB. Function of cell membrane channels (compiuter simulation) Study Questions on Ion Channels: 1. (Page 3.) What controls the movement of ions across the membrane of a neuron? Ion channels control the movement of ions across the neuronal membrane. 2. (Page 3.) What are four properties of ion channels? The channels are: 1. selective 2. either passive or active 3. regionally located 4. functionally unique 3. (Page 3.) What are ion channels made of? Integral proteins 4. (Page 4.) What three factors determine the selectivity of an ion channel? Channel selectivity depends on: 1. the charge on the ion—that is, whether it is positive or negative 2. on the size of the ion 3. on how much water the ion attracts and holds around it 5. (Page 5.) What's the difference between an active and passive ion channel? Active channels have gates that can open or close the channel. Passive channels, also called leakage channels, are always open and ions pass through them continuously. 6. (Page 6.) Is a resting neuronal cell membrane more positive inside or outside? Cells have slightly more positive ions on the outside of their membranes, and slightly more negative ions on the inside. 7. (Page 6.) What is the result of the charge separation in a resting neuronal membrane? Membrane potential value is -70 mV. 8. (Page 6.) When the neuronal membrane is at rest are the voltage-gated channels opened or closed? When a neuron is at rest, voltage-gated channels are closed. 9. (Page 6.) What happens to the voltage-gated channels when there is a nerve impulse (or action potential) in the neuronal membrane? During an action potential, the voltage across the membrane changes, causing voltage-gated channels to open and close. 10. (Page 6.) Why, when the Na+ voltage-gated channel opens, does the membrane potential goes from -70 mV to less negative values. When the Na+ voltage-gated channel opens, membrane potential goes from -70 mV to less negative values. This is because a positive ion is moving inward, making the inside of the membrane more positive. 11. (Page 6.) Why, when the K+ voltage-gated channel opens, does the membrane potential goes from +30 mV to more negative values (-70). When the K+ voltage-gated channel opens, membrane potential goes from +30 mV to more negative values -70. This is because a positive ion is moving outward, making the inside of the membrane more negative. 12. (Page 7.) Give two general types of active channels. 1. Voltage-gated Channels 2. Chemically-gated Channels 13. (Page 7.) What will open a chemically-gated ion channel in a neuron? Chemically-gated channels have gates controlled by chemicals, in particular by neurotransmitters such as acetylcholine and GABA. When these neurotransmitters bind to chemically-gated channels, they cause the channels to open, thereby permitting ions to move across the membrane. 14. (Page 7.) When a neurotransmitter opens a chemically-gated channel, does the neurotransmitter go into the cell? No, neurotransmitters only open channels. 15. (Page 7.) When acetyl choline binds to its receptor, which ion(s) will move across the membrane? In which direction will they move? Na and K across the membrane move opposite direction: sodium (Na+) inside - potassium (K+) outside. 16. (Page 7.) When GABA binds to its receptor, which ion(s) will move across the membrane? In which direction will they move? Chloride (Cl-) moves inside the cell. 17. (Page 7.) What determines the direction that ions move through an ion channel? The direction that ions move through an ion channel determines ions concentration. 18. (Page 8.) On what parts of the neuron do we find passive channels? Passive channels are located in the cell membrane all over the neuron—on dendrites, the cell body, and the axon. 19. (Page 8.) On what parts of the neuron do we find chemically-gated channels? Chemically-gated channels are located on the dendrites and cell body of the neuron. 20. (Page 8.) On what parts of the neuron do we find voltage-gated channels? Voltage-gated channels are found on the axon hillock, all along unmyelinated axons, and at the nodes of Ranvier in myelinated axons. Study Questions on The Membrane Potential: 1. (Page 3.) Which of Na+, K+, Cl- ions have a high concentration outside the cell and which have a high concentration inside the cell? In the extracellular fluid outside the cell, the concentration of positive sodium (Na+) ions is high. It is balanced by a high concentration of negative chloride (Cl-) ions. Inside the cell, the concentration of positive potassium (K+) ions is high. 2. (Page 4.) What is the only way that ions can get across the cell membrane? They can only cross cell membranes by passing through watery pores called ion channels. 3. (Page 4.) Which ion are most cells in the body permeable to? Many cells in the body are selectively permeable only to potassium. 4. (Page 4.) What's the difference between a neuron's permeability to sodium and potassium? Excitable cells are very permeable to potassium and slightly permeable to sodium. 5. (Page 5.) What two factors will affect the permeability of a cell for a particular ion? The permeability of a cell for a particular ion depends on: 1. The number of channels for that ion. Permeability can be increased by increasing the number of channels for a given ion. 2. The ease with which the ion can move through the channels. If an ion is small compared to the size of an ion channel, it goes through easily. 6. (Page 6.) What mechanism used by the nervous system to produce rapid changes in membrane permeability? The permeability of a cell for a given ion increases when gated channels for that ion are opened. This is the mechanism used by the nervous system to produce rapid changes in membrane permeability. 7. (Page 7.) As opposed to neurons, simple, non-excitable cells are permeable only to one ion. What is that ion? Simple, non-excitable cell is selectively permeable only to potassium (K+) ions. 8. (Page 7.) What major factor causes ions to move through ion channels? The concentration gradient. 9. (Page 7.) What type of force is the concentration gradient? The concentration gradient acts as a chemical force that pushes potassium out of the cell. 10. (Page 8.) How does the cell membrane become more positive outside and more negative inside? As potassium ions diffuse out of the cell, they accumulate on the outside surface of the cell membrane, making it more positive than the inside surface of the membrane. This results in a separation of charge across the cell membrane. 11. (Page 8.) What type of force is the separation of charge? This separation of charge creates an electrical potential across the cell membrane. 12. (Page 9.) As potassium diffuses out of a cell, the outside of the cell becomes more __positive_____ and the inside of the cell becomes more ___negative_____. Since opposite charges attract each other, and potassium is positive, the potassium will __back into the cell________. 13. (Page 9.) The force that is responsible for the movement of positive potassium ions back into the cell, where it is more negative is called the ____ the electrical potential____. 14. (Page 9.) What effect does both the chemical force and the electrical force have on K+? The Concentration Gradient or Chemical Force Causes K+ to diffuse out of the cell. The Electrical potential or Electrical force Pulls K+ in to the cell. 15. (Page 10.) What is a membrane potential? The electrical potential across the cell membrane is called the membrane potential. 16. (Page 10.) In what units is both the concentration and the membrane potential measured? The membrane potential is measured in millivolts. 17. (Page 12.) What is a typical value for the resting membrane potential? 18. (Page 15.) Does the sodium-potassium pump move sodium and potassium with or against their gradients? The sodium-potassium pump move sodium and potassium against their gradients. Three sodium ions are pumped out of the neuron for every two potassium ions that are pumped in. 19. (Page 15.) What provides the energy to pump sodium and potassium against their gradients? This pump uses the energy of ATP to move sodium and potassium against their electrochemical gradients. Study Questions on the Action Potential: 1. (Page 1.) What is another name for an action potential? An electrical signal called a nerve impulse, or action potential. 2. (Page 4.) Where is the action potential generated? The action potential is generated at the axon hillock. 3. (Page 4.) What causes an axon potential to occur at the axon hillock? At the axon hillock, where the density of voltage-gated sodium channels is greatest. 4. (Page 5.) What happens to ion channels when the membrane depolarizes at the axon hillock? The action potential begins when signals from the dendrites and cell body reach the axon hillock and cause the membrane potential there to become more positive, a process called depolarization. 5. (Page 6.) How much does the axon hillock have to depolarize to reach threshold? If the stimulus to the axon hillock is great enough, the neuron depolarizes by about 15 millivolts and reaches a trigger point called threshold. 6. (Page 6.) What happens at threshold? At threshold, an action potential is generated. 7. (Page 6.) What happens if there is a weak stimulus at the axon hillock and threshold is not reached? Weak stimuli that do not reach threshold do not produce an action potential. Thus we say that the action potential is an all-or-none event. 8. (Page 6.) Do action potentials always have the same amplitude and the same duration? Action potentials always have the same amplitude and the same duration. 9. (Page 7.) What happens to sodium voltage-gated channels at threshold? At -55 millivolts the membrane is depolarized to threshold, and an action potential is generated. 10. (Page 7.) Explain how the positive feedback loop maintains the rising phase of the action potential. Threshold is a special membrane potential where the process of depolarization becomes regenerative, that is, where a positive feedback loop is established. 11. (Page 8, 9.) The rising phase of the action potential ends when the positive feedback loop is interrupted. What two processes break the loop? Two processes break the loop: 1. the inactivation of the voltage-gated sodium channels. 2. the opening of the voltage-gated potassium channels. 12. (Page 8.) What are the names of the two gates on the voltage-gated sodium channels? The voltage-gated sodium channels have two gates: 1. A voltage-sensitive gate opens as the cell is depolarized. 2. A time-sensitive inactivation gate stops the movement of sodium through the channel after the channel has been open for a fixed time. 13. (Page 8.) What happens to the voltage gated sodium channels at the peak of the action potential? At the peak of the action potential, voltage-gated sodium channels begin to inactivate. As they inactivate, the inward flow of sodium decreases, and the positive feedback loop is interrupted. 14. (Page 9.) When do the voltage-gated potassium channels open? The voltage-gated potassium channels respond slowly to depolarization. They begin to open only about the time that the action potential reaches its peak. 15. (Page 9.) What happen when the voltage-gated potassium channels open and the potassium moves out of the cell? As potassium moves out, depolarization ends, and the positive feedback loop is broken. 16. (Page 10.) When does repolarization occur? With less sodium moving into the cell and more potassium moving out, the membrane potential becomes more negative, moving toward its resting value. This process is called repolarization. 17. (Page 11.) What is hyperpolarization? In many neurons, the slow voltage-gated potassium channels remain open after the cell has repolarized. Potassium continues to move out of the cell, causing the membrane potential to become more negative than the resting membrane potential. This process is called hyperpolarization. 18. (Page 12.) During the action potential, when does sodium permeability increase rapidly? a. during repolarization b. during the rising phase of the action potential c. during hyperpolarization d. during repolarization 19. (Page 12.) During the action potential, when does sodium permeability decrease rapidly? a. during repolarization b. during the rising phase of the action potential c. during hyperpolarization d. during repolarization 20. (Page 12.) During the action potential, when is potassium permeability the greatest? a. during repolarization b. during the rising phase of the action potential c. during hyperpolarization d. during repolarization 21. (Page 12.) During the action potential, when does potassium permeability decrease slowly? a. during repolarization b. during the rising phase of the action potential c. during hyperpolarization d. during repolarization 22. (Page 13.) Which part of the graph to the right corresponds to the following: hyperpolarization-E depolarization-B rest-A initiation of repolarization-C repolarization-D 23. (Page 13.) Which phase of the action potential does the diagram below best correspond to? a. rest b. depolarization c. peak d. repolarization e. hyperpolarization 24. (Page 13.) Which phase of the action potential does the diagram below best correspond to? a. rest b. depolarization c. peak d. repolarization e. hyperpolarization 25. (Page 13.) Which phase of the action potential does the diagram below best correspond to? a. rest b. depolarization c. peak d. repolarization e. hyperpolarization 26. (Page 13.) Which phase of the action potential does the diagram below best correspond to? a. rest b. depolarization c. peak d. repolarization e. hyperpolarization 27. (Page 14.) What is the absolute refractory period? Just after the neuron has generated an action potential, it cannot generate another one. Many sodium channels are inactive and will not open, no matter what voltage is applied to the membrane. Most potassium channels are open. This period is called the absolute refractory period. 28. (Page 14.) Why can't a neuron generate another action potential during the absolute refractory period? The neuron cannot generate an action potential because sodium cannot move in through inactive channels and because potassium continues to move out through open voltage-gated channels. A neuron cannot generate an action potential during the absolute refractory period. 29. (Page 15.) What is the relative refractory period? Immediately after the absolute refractory period, the cell can generate an action potential, but only if it is depolarized to a value more positive than normal threshold. This is true because some sodium channels are still inactive and some potassium channels are still open. This is called the relative refractory period. 30. (Page 14, 15.) What letter on this graph to the right corresponds to the absolute refractory period? B 31. (Page 14, 15.) What letter on this graph to the right corresponds to the relative refractory period? C 32. (Page 16.) What happens after an action potential is generated at the axon hillock? After an action potential is generated at the axon hillock, it is propagated down the axon. 33. (Page 16.) How is an action potential propagated down the axon? Positive charge flows along the axon, depolarizing adjacent areas of membrane, which reach threshold and generate an action potential. The action potential thus moves along the axon as a wave of depolarization traveling away from the cell body. 34. (Page 17.) What is conduction velocity? Conduction velocity is the speed with which an action potential is propagated. 35. (Page 17.) What two factors does conduction velocity depend on? Conduction velocity depends on two things: 1. The diameter of the axon. As the axon diameter increases, the internal resistance to the flow of charge decreases and the action potential travels faster. 2. How well the axon is insulated with myelin. Recall that myelinated axons have areas of insulation interrupted by areas of bare axon called nodes of Ranvier. 36. (Page 17.) What is the effect of myelin on conduction velocity? In a myelinated axon, charge flows across the membrane only at the nodes, so an action potential is generated only at the nodes. The action potential appears to jump along the axon. This type of propagation is called saltatory conduction. A myelinated axon typically conducts action potentials faster than an unmyelinated axon of the same diameter.