Action Potentials A stimulus causes the nerve cell membrane to become [ ] (more / less) permeable to Na+. Na+ can then enter the cell as voltage-gated Na+ channels become activated and open. At rest, the membrane had a potential of - [ ] (please write a number) mV. As Na+ enters the cell, the inside of the membrane becomes more [ ] (positive / negative). The potential will tend to go toward [ ] (-80 / -55 ) mV. The process of [ ] (polarization / depolarization ) is occurring. This process causes changes in more Na+ channels so that even more Na+ enters. This is an example of a [ ] (positive / negative) feedback mechanism. The result is a nerve impulse. The membrane is completely depolarized at exactly [ ] (-50 / 0 / +30 ) mV. Na + channels stay open until the inside of the membrane potential is [ ] (reversed / hyperpolarized) at + 30 mV.
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When a neuron is stimulated sufficiently to cause an action potential, which of the following events occurs first in the axon? If you are uncertain of the answer, revisit the lecture video or refer to pages 930 and 931 in your text. gated ion channels close, preventing the movement of Na+ across the cell membrane K+ floods out of the cell via diffusion, depolarizing the cell membrane and initiating an action potential gated ion channels in the cell membrane open up, allowing Na+ ions to enter the cell K+ exits the cell via the Na+/K+ pump (with the help of ATP), thereby triggering an action potential True or False: the magnitude of an action potential, measured in mV across the cell membrane of a neuron, increases with increasing stimulus intensity.
Sri K.
Conduction of Action Potentials and Synapses "How does an action potential get from one cell to another?" Model 1: There are multiple types of ion channels in excitable cells. 1. Stimulus arrives at Stimulus-gated ion channel (sensory input or a neurotransmitter like Ach) 2. Stimulus-gated Na channel opens and Na floods the inside of the cell 3. Influx of Na+ causes the voltage near the channel to rise 4. The increased intracellular voltage causes the voltage-gated Na channel to open. Critical Thinking Questions 1. According to the model, what are some examples of stimuli that can cause a stimulus-gated Na channel to open? 2. According to the model, what causes the voltage-gated Na channels to open? a. Small increases in potential will not cause these channels to open. What do you (the group) think is the term for the actual potential value that will cause these channels to open (the point of no return)?
Supreeta N.
The resting membrane potential in neurons requires: a. membrane transport channels to be constantly open for $\mathrm{Na}^{+}$ and $K^{+}$ flow. b. the inside of neurons to be positive relative to the outside. c. the diffusion of $\mathrm{K}^{+}$ out of the cell and a charge difference between the inside and outside of the axon set up by this movement of $\mathrm{K}^{+}$ d. an active $\mathrm{Na}^{+} / \mathrm{K}^{+}$ pump, which pumps $\mathrm{Na}^{+}$ and $\mathrm{K}^{+}$ into the neuron. e. three $\mathrm{Na}^{+}$ ions to be pumped through three Na $^{+}$ gates and two $\mathrm{K}^{+}$ ions to be pumped through two $\mathrm{K}^{+}$ gates.
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