Neuron Function Worksheet

25 July 2022
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question
what is the job of a neuron
answer
to move an electrical signal from one place to another in order to send sensory messages throughout the body
question
Which of the gated embedded proteins in Model 1 allow sodium ions ( O ) through the membrane?
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gates A, B, D and F allow sodium ions through the membrane
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Which of the gated embedded proteins in Model 1 allow potassium ions ( triangles ) through the membrane?
answer
Gates C, E, and G allow potassium ions through the membrane
question
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?
answer
A signal Ligand has bound to the ligand-gated embedded protein and the gate has opened
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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.
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No, diagram 2 does not show a ligand bound to embedded protein B. The gate may have opened because of the change in membrane potential from the flood of ions nearby
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When a signal moves down the axon of the neuron, which direction do sodium ions move through the voltage-gated embedded proteins?
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sodium ions move into the cell when the sodium gates are opened
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What does the movement of sodium ions across the membrane do to the membrane potential near the open embedded protein?
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the membrane potential increases (gets more positive) as the sodium ions move into the cell
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When a signal moves through the axon of the neuron, which direction do potassium ions move through the voltage-gated embedded proteins?
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potassium ions move out of the cell when the potassium gates are opened
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What does the movement of potassium ions across the membrane do to the membrane potential near the open embedded protein?
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the membrane potential decreases ( gets more negative) as the potassium ions move out of the cell
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how is the degree of polarization measured?
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the degree of polarization is measured by the cell membrane potential
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the gated embedded proteins in the axon of a neuron are triggered to open by changes in electrical potential across the membrane.
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the voltage at which they open is called the threshold potential
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Looking at model 1 What is the threshold potential that causes the sodium ion gates to open?
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the sodium ion gates open at -55 mV
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Looking at model 1 At what potential are the potassium ion gates fully open?
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the potassium ion gate open at +35 mV
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looking at model 1 at what potential are the sodium ion gates closed
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the sodium ion gates close when the membrane potential reaches +35 mV
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At what potential are the potassium ion gates closed?
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The potassium ion gates close when the membrane potential reaches -80 mV
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Describe how the electrical signal in the neuron moves
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the gates open one at a time from left to right in model 1. the high concentration of sodium ions inside the cell moves from left to right in model 1
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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?
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The sodium and potassium ions eventually move back to their original position
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B. Propose a mechanism that the cell might use to accomplish the change you describe in part A
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The sodium and potassium ions move through embedded proteins in the membrane to reinstate the resting membrane potential
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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?
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No, the neuron cannot transmit another signal until the ions are returned because the concentration gradients for the ions are going in the wrong direction
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Define depolarized
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When an action potential is in progress the cell membrane is depolarized. The potential difference between the two sides of the membrane is decreased
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Define refractory period
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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 hyperpolarizaton and and repolarization
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define hyperpolarization
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hyper means beyond normal. Hyperpolarization means there is a difference in membrane potential that is GREATER than normal
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Define repolarization
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Occurs immediately after depolarization and is the movement of positively charged ions back to the outside of the cell, returning the cell back to its original polarized state. A cell must repolarize before it can depolarize again.
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define polarization
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polarization refers to the difference in potential on either side of the membrane
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according to model 1 ,what is the membrane potential near sodium ion gates during the refractory period ?
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the lowest potential in model 1 is -80mv
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nerve impulses always move in one direction. Explain how the refractory period for a voltage gated embedded protein is necessary to make this possible
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if the gated protein could open again immediately after closing, the nerve "signal" would end up moving in both directions. Once the sodium ions diffused out of the immediate area and raised the potential to -55mv , the protein would open again
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Not every signal that a neuron receives is acted upon and transmitted to the next nerve cell. In some cases the signal is too weak to make the membrane potential reach the threshold potential. What advantage does the organism have when there is a minimum signal required that may have influenced the evolution of this mechanism?
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organisms receive alot of sensory input. Not all of it is important. The necessity of a minimum signal to fire off an impulse saves resources to react to sensory information that is vital for survival.
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One student described the diagrams in Model 1 by saying "As more gates open the concentration of sodium inside the cell increases and this causes even more gates to open." Is this an example of a positive or negative feedback loop?
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This is a positive feedback because the end result of the process makes the process happen again and escalates the response. The response, opening of gated embedded proteins, amplifies the stimulus, a change in cell membrane potential.
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For a neuron to function, an input of free energy from ATP is required to set up the sodium and potassium ion concentration gradients such that a signal can be propagated down the axon of a neuron without the necessity of ATP. The system could have worked the opposite way. The neuron could have used ATP to move ions across when a signal was being propagated and then allow natural diffusion to return the ions to their respective sides of the membrane. What advantage does the organism have using ATP up front?
answer
During times of stress, such as running from a predator, a lack of ATP would slow the nerve response if it was required to create the action potential. In the current form the ATP is needed slowly during rest periods and the natural flow of ions used when quick response is necessary.