Neuron Function pogil

Neuron Function How does a signal travel across and between neurons? Why? Just as the coaxial cables that run down your street or through your house carry television and Internet signals, the job of a neuron is to move an electrical signal from one place to another in order to send sensory messages throughout the body. In a previous activity you saw how a membrane potential is formed both at rest and during an inflow of ions. In this activity you will explore how changes in membrane potentials can propagate a signal down the axon of a neuron. 1. Which of the gated embedded proteins in Model 1 allow sodium ions ( ) through the membrane? 2. Which of the gated embedded proteins in Model 1 allow potassium ions ( ) through the membrane? 3. The neuron illustrated in Model 1 has received a signal from either a sensory cell (taste bud, skin cell, retinal cell, etc.) or from another neuron. What evidence do you find in diagram 1 of the model that indicates a signal has been received? 4. In diagram 2 of Model 1, gated embedded protein B has opened. Was this opening triggered by the arrival of a signal ligand? If no, propose an alternate stimulus that might have triggered the gate to open. 5. Consider Model 1. a. When a signal moves down the axon of the neuron, which direction do sodium ions move through the voltage-gated embedded proteins? b. What does the movement of sodium ions across the membrane do to the membrane potential near the open embedded protein? 6. Consider Model 1. a. When a signal moves through the axon of the neuron, which direction do potassium ions move through the voltage-gated embedded proteins? b. What does the movement of potassium ions across the membrane do to the membrane potential near the open embedded protein? GatesA BDandFallowsodiumionsthroughthemembrane GatesC EandGallowpotassiumionsthroughthemembrane Asignalligandhasboundtotheligandgatedembeddedproteinandthegatehasopened Nodiagram2doesnotshowaligandboundtoembeddedproteinBThegatemayhave openedbecauseofthechangeinmembranepotentialfromthefloodofionsnearby Sodiumionsmoveintothecellwhenthesodiumgatesareopened Themembranepotentialincreasesgetsmorepositiveasthesodiumionsmoveintothecell Potassiumionsmoveoutofthecellwhenthepotassiumgatesareopened Themembranepotentialdecreasesgetsmorenegative asthepotassiumionsmoveoutof thecell This study source was downloaded by from CourseH on :15:30 GMT -06:00 2 POGIL™ Activities for AP* Biology Model 1 – An Action Potential 1 4 Outside of cell Inside of cell –60 mV –70 mV –70 mV A B C D E F G –55 mV +30 mV +35 mV A B C D E F G 2 5 –60 mV –55 mV –70 mV A B C D E F G +30 mV +35 mV –80 mV A B C D E F G 3 6 –60 mV –55 mV +30 mV A B C D E F G +35 mV –80 mV –70 mV A B C D E F G This study source was downloaded by from CourseH on :15:30 GMT -06:00 Neuron Function 3 Read This! When a neuron is resting, the cell membrane is said to be polarized. The degree of polarization is measured by the cell membrane potential. The gated embedded proteins in the axon of a neuron are triggered to open by changes in electrical potential across the membrane. The voltage at which they open is called the threshold potential. 7. Refer to Model 1. a. What is the threshold potential that causes the sodium ion gates to open? b. At what potential are the potassium ion gates fully open? c. At what potential are the sodium ion gates closed? d. At what potential are the potassium ion gates closed? 8. A nerve impulse is said to “move along” the length of the cell. In one or more complete sentences, describe how the electrical signal in the neuron moves. Discuss this with your group members before writing an answer. 9. Consider the diagrams in Model 1. a. When the gated embedded proteins (either sodium or potassium) close, do the sodium and potassium ions remain on the side of the membrane that they are on, or do they move back to their original position? b. Propose a mechanism that the cell might use to accomplish the change you described in part a. c. Could another signal be sent down the length of the neuron cell if the sodium ions and potassium ions were not returned to their original position? Explain. Thesodiumiongatesopenat 55mV Thepotassiumiongatesopenat 35mV Thesodiumiongatesclosewhenthemembranepotentialreaches 35mV Thepotassium iongatesclosewhenthemembranepotentialreaches 80mV Thegatesopenone at atimefromlefttoright Thesodiumandpotassiumionseventuallymovebacktotheiroriginalposition Thesodiumandpotassiumionsmovethroughembeddedproteins inthemembrane to reinstatetherestingmembranepotential Notheneuroncannottransmitanothersignaluntiltheions arereturned becausetheconcentrationgradients fortheionsaregoing inthewrong direction This study source was downloaded by from CourseH on :15:30 GMT -06:00 4 POGIL™ Activities for AP* Biology Read This! When the action potential is in progress the cell membrane is depolarized—the potential difference between the two sides of the membrane is decreased. After a sodium ion gate has been opened and closed, it is in a refractory period where the membrane potential in the immediate vicinity is very low and the embedded protein cannot be opened again. This is called hyperpolarization and repolarization. 10. Consider the parts of the word “hyperpolarization” and write a definition of this state of the neuron. 11. According to Model 1, what is the membrane potential near sodium ion gates during the refractory period? 12. Nerve impulses always move in one direction. Explain how the refractory period for a voltagegated embedded protein is necessary to make this possible. 13. The graph below shows the voltages near embedded protein B of Model 1 versus time. Identify the points on the graph where each of the diagrams (1–6) in Model 1 occurred.