which term describes the difference in electrical charge across a membrane?
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Membrane potential (resting membrane potential) (article)
How the resting membrane potential is established in a neuron.
The neuron and nervous system
The membrane potential
How the resting membrane potential is established in a neuron.
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Key points:
A resting (non-signaling) neuron has a voltage across its membrane called the resting membrane potential, or simply the resting potential.
The resting potential is determined by concentration gradients of ions across the membrane and by membrane permeability to each type of ion.
In a resting neuron, there are concentration gradients across the membrane for
\text {Na}^+ Na +
start text, N, a, end text, start superscript, plus, end superscript
and \text K^+ K +
start text, K, end text, start superscript, plus, end superscript
. Ions move down their gradients via channels, leading to a separation of charge that creates the resting potential.
The membrane is much more permeable to
\text K^+ K +
start text, K, end text, start superscript, plus, end superscript
than to \text {Na}^+ Na +
start text, N, a, end text, start superscript, plus, end superscript
, so the resting potential is close to the equilibrium potential of
\text K^+ K +
start text, K, end text, start superscript, plus, end superscript
(the potential that would be generated by
\text K^+ K +
start text, K, end text, start superscript, plus, end superscript
if it were the only ion in the system).
Introduction
Suppose you have a dead frog. (Yes, that's kind of gross, but let's just imagine it for a second.) What would happen if you applied an electrical stimulus to the nerve that feeds the frog's leg? Creepily enough, the dead leg would kick!
The Italian scientist Luigi Galvani discovered this fun fact back in the 1700s, somewhat by accident during a frog dissection. Today, we know that the frog's leg kicks because neurons (nerve cells) carry information via electrical signals.
How do neurons in a living organism produce electrical signals? At a basic level, neurons generate electrical signals through brief, controlled changes in the permeability of their cell membrane to particular ions (such as
\text{Na}^+ Na +
start text, N, a, end text, start superscript, plus, end superscript
and \text K^+ K +
start text, K, end text, start superscript, plus, end superscript
). Before we look in detail at how these signals are generated, we first need to understand how membrane permeability works in a resting neuron (one that is not sending or receiving electrical signals). [What is permeability?]
In this article, we'll see how a neuron establishes and maintains a stable voltage across its membrane – that is, a resting membrane potential.
The resting membrane potential
Imagine taking two electrodes and placing one on the outside and the other on the inside of the plasma membrane of a living cell. If you did this, you would measure an electrical potential difference, or voltage, between the electrodes. This electrical potential difference is called the membrane potential.
[Is this the same as a voltage in a wire?]
Diagram of a voltmeter measuring the membrane potential. One electrode is outside the cell. The other electrode is in the interior of the cell. The voltmeter shows a -70 mV voltage across the membrane.
_Image modified from "How neurons communicate: Figure 2," by OpenStax College, Biology (CC BY 4.0)._
Like distance, potential difference is measured relative to a reference point. In the case of distance, the reference point might be a city. For instance, we can say that Boston is
190 190 190 \text{miles} miles
start text, m, i, l, e, s, end text
northeast, but only if we know that our reference point is New York City.
For a cell’s membrane potential, the reference point is the outside of the cell. In most resting neurons, the potential difference across the membrane is about
30 30 30 to 90 90 90 \text{mV} mV
start text, m, V, end text
(a \text{mV} mV
start text, m, V, end text
is 1/1000 1/1000 1, slash, 1000
of a volt), with the inside of the cell more negative than the outside. That is, neurons have a resting membrane potential (or simply, resting potential) of about
-30 −30 minus, 30 \text{mV} mV
start text, m, V, end text
to - 90 −90 minus, 90 \text{mV} mV
start text, m, V, end text
.
Because there is a potential difference across the cell membrane, the membrane is said to be polarized.
If the membrane potential becomes more positive than it is at the resting potential, the membrane is said to be depolarized.
If the membrane potential becomes more negative than it is at the resting potential, the membrane is said to be hyperpolarized.
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Biology Ch. 48 Key Concepts and Mastering Bio
Describe the basic pathway of info flow through neurons that causes you to turn your head when someone calls your name
Click card to see definition 👆
Sensors in your ear transmit info to your brain. There the activity of interneurons in processing centers enables you to recognize your name. In response, signals transmitted via motor neurons cause contractions of muscles that turn your neck
Click again to see term 👆
How might increased branching of an axon help coordinate responses to signals communicated by the nervous system?
Click card to see definition 👆
Increased branching would allow control of a greater number of postsynaptic cells, enhancing coordination of responses to nervous system signals
Click again to see term 👆
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Terms in this set (25)
Describe the basic pathway of info flow through neurons that causes you to turn your head when someone calls your name
Sensors in your ear transmit info to your brain. There the activity of interneurons in processing centers enables you to recognize your name. In response, signals transmitted via motor neurons cause contractions of muscles that turn your neck
How might increased branching of an axon help coordinate responses to signals communicated by the nervous system?
Increased branching would allow control of a greater number of postsynaptic cells, enhancing coordination of responses to nervous system signals
Under what circumstances could ions flow through ion channels from regions of low ion concentration to regions of high ion concentraion?
Ions can flow against a chemical concentration gradient if there is an opposing electrical gradient of greater magnitude
Suppose a cell's membrane potential shifts from-70 mV to -50 mV. What changes in the cell's permeability to K+ or Na+ could cause such a shift?
A decrease in permeability of K+, an increase to permeability of Na+, or both
Ouabain, a plant substance used in some cultures to poison hunting arrows, disables the sodium-potassium pump. What change in the resting potential would you expect to see if you treated a neuron with ouabain?
The activity of the sodium-potassium pump is essential to maintain the resting potential. With the pump inactivated, the sodium and potassium gradients would gradually disappear, resulting in a greatly reduced resting potential
In multiple sclerosis, myelin sheaths harden and deteriorate. How would this affect nervous system function?
Loss of the insulation provided by myelin sheaths leads to a disruption of action potential propagation along axons
Suppose a mutation cause gated sodium channels to remain inactivated longer after an action potential. How would this affect the frequency at which action potentials could be generated?
The maximum frequency would decrease because the refractory period would be extended
How is it possible for a particular neurotransmitter to produce opposite effects in different tissues?
It can bind to different types of receptors, each triggering a specific response in postsynaptic cells
Organophosphate pesticides work by inhibiting acetylcholinesterase, the enzyme that breaks down the neurotranmitter acetylocholine. Explain how these toxins would affect APSPs produced by acetylcholine
These toxins would prolong the EPSPs that acetylcholine produces because the neurotransmitter would remain longer in the synaptic cleft
Which term describes the difference in electrical charge across a membrane?
Membrane potential-the difference in electrical charge across a membrane.
Resting neurons are most permeable to which of the following ions?
K+, Resting neurons are most permeable to K+ ions
True or false? The potential energy of a membrane potential comes solely from the difference in electrical charge across the membrane.
False-The potential energy of a membrane potential comes both from the difference in electrical charge and from the concentration gradient of ions across a membrane.
Which channel is mainly responsible for the resting potential of a neuron?
Potassium leak channel- K+ ions flow along their concentration gradient to maintain the resting potential of a neuron.
Which term describes an electrical signal generated by neurons?
Action potential-a rapid electrical signal generated by neurons.
Which channel maintains the concentration gradients of ions across a neuronal membrane?
The sodium potassium pump moving Na+ ions out and K+ ions in-channel maintains the ion concentration gradients across a neuronal membrane.
What behavior is observed if the voltage across a neuronal membrane is set to -20 mV?
The sodium channel opens, and Na+ ions flow in- Sodium ions flow into the cell when the membrane potential is between -20 mV and 30 mV.
Which structure is not part of a neuron? cell body, dendrite, myelin sheath, axon
myelin sheath- layer of Schwann cells wrapped around a neuron.
Which event triggers the creation of an action potential?
The membrane depolarizes above a certain threshold potential-Influx of Na+ ions into the neuron can lead to membrane depolarization above the threshold potential; this event triggers the creation of an action potential.
What term describes how a neuronal membrane's potential is altered in the presence of inhibitory signals?
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25 Cards in this Set
Describe the basic pathway of info flow through neurons that causes you to turn your head when someone calls your name
Sensors in your ear transmit info to your brain. There the activity of interneurons in processing centers enables you to recognize your name. In response, signals transmitted via motor neurons cause contractions of muscles that turn your neck
How might increased branching of an axon help coordinate responses to signals communicated by the nervous system?
Increased branching would allow control of a greater number of postsynaptic cells, enhancing coordination of responses to nervous system signals
Under what circumstances could ions flow through ion channels from regions of low ion concentration to regions of high ion concentraion?
Ions can flow against a chemical concentration gradient if there is an opposing electrical gradient of greater magnitude
Suppose a cell's membrane potential shifts from-70 mV to -50 mV. What changes in the cell's permeability to K+ or Na+ could cause such a shift?
A decrease in permeability of K+, an increase to permeability of Na+, or both
Ouabain, a plant substance used in some cultures to poison hunting arrows, disables the sodium-potassium pump. What change in the resting potential would you expect to see if you treated a neuron with ouabain?
The activity of the sodium-potassium pump is essential to maintain the resting potential. With the pump inactivated, the sodium and potassium gradients would gradually disappear, resulting in a greatly reduced resting potential
In multiple sclerosis, myelin sheaths harden and deteriorate. How would this affect nervous system function?
Loss of the insulation provided by myelin sheaths leads to a disruption of action potential propagation along axons
Suppose a mutation cause gated sodium channels to remain inactivated longer after an action potential. How would this affect the frequency at which action potentials could be generated?
The maximum frequency would decrease because the refractory period would be extended
How is it possible for a particular neurotransmitter to produce opposite effects in different tissues?
It can bind to different types of receptors, each triggering a specific response in postsynaptic cells
Organophosphate pesticides work by inhibiting acetylcholinesterase, the enzyme that breaks down the neurotranmitter acetylocholine. Explain how these toxins would affect APSPs produced by acetylcholine
These toxins would prolong the EPSPs that acetylcholine produces because the neurotransmitter would remain longer in the synaptic cleft
Which term describes the difference in electrical charge across a membrane?
Membrane potential-the difference in electrical charge across a membrane.
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Guys, does anyone know the answer?