thru fall2018 lecture04
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ackman678
@@ -27,7 +27,7 @@ as well as general molecular signaling within neurons as any living cell might h
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<div style="font-size:0.7em; width:600px">
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<div></div>
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* For intracellular recordings, an electrode is placed inside a cell such that the inside of the pipette is contiguous with the inside of the cell. If this electrode is connected to a voltmeter, which records transmembrane voltage across the cell membrane, one can determine the difference in voltage between the inside and outside of the cell.
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* For intracellular recordings, an electrode is placed inside a cell such that the inside of the pipette is contiguous with the inside of the cell. If this electrode is connected to a voltmeter, which records transmembrane voltage across the cell membrane, one can determine the difference in voltage between the inside and outside of the cell.
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* When one does this in neurons, the microelectrode reports a negative potential called the resting potential. Always a fraction of a volt (-40 to -90 mV).
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* Volts are a unit of electrochemical potential energy. 1 Volt will drive 1 coulomb of charge (6.24x10<sup>18</sup> electrons) through a resistance of 1 ohm in 1 second.
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@@ -37,7 +37,7 @@ as well as general molecular signaling within neurons as any living cell might h
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Note:
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To understand the basis of electrical excitability in neurons, we first need to understand that neurons, like other excitable cells, have a difference in electrical potential across the cell membrane when it is at rest.
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To understand the basis of electrical excitability in neurons, we first need to understand that neurons, like other excitable cells, have a difference in electrical potential across the cell membrane when it is at rest.
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To learn this physiologists stick electrodes inside of cells, including neurons. This electrode is hooked up to a voltmeter and another electrode sits outside the cell as a ground or reference electrode to complete the circuit. The difference in voltage between the inside of the cell and the outside of the cell is monitored over time and displayed on an oscilloscope.
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@@ -68,7 +68,7 @@ Flow rate ~ Current (amperes) = `I`
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Note:
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And recall from physics that voltage is related to the resistance and current in an electrical circuit as described by Ohm’s law. This analogy of a water pump/water wheel circuit helps us understand these relationships better.
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And recall from physics that voltage is related to the resistance and current in an electrical circuit as described by Ohm’s law. This analogy of a water pump/water wheel circuit helps us understand these relationships better.
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Voltage
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: is the potential difference, or electromotive force measured across the conductor in units of volts.
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@@ -124,17 +124,17 @@ Note:
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Signals in neurons can be generated by changing the membrane potential.
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This includes receptor potentials inside your body’s sensory neurons for touch, heat, light, and sound.
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This includes receptor potentials inside your body’s sensory neurons for touch, heat, light, and sound.
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And synaptic potentials are the changes in membrane potential at synapses that underly the transfer of information from neuron to neuron.
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Action potentials are the large electrical spikes or impulses that allow neuronal signals to propagate over long distances, including nerves centimeters to meters long.
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Action potentials are the large electrical spikes or impulses that allow neuronal signals to propagate over long distances, including nerves centimeters to meters long.
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---
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## Types of electrical signals in neurons
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<figure><img src="figs/Neuroscience5e-Fig-02.01-0_63cc814.png" height="500px"><figcaption>Neuroscience 5e Fig. 2.1</figcaption></figure>
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<figure><img src="figs/Neuroscience5e-Fig-02.01-0_63cc814.png" height="500px"><figcaption>Neuroscience 5e/6e Fig. 2.1</figcaption></figure>
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Note:
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@@ -145,7 +145,7 @@ This figure shows these 3 types of neuronal signals.
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- Here is a synaptic potential recorded in a postsynaptic neuron.
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- Here is an action potential in a motor neuron. **Look as the y-axes here**— the action potential has a much larger amplitude change than receptor or synaptic potentials.
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- Here is an action potential in a motor neuron. **Look as the y-axes here**— the action potential has a much larger amplitude change than receptor or synaptic potentials.
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To understand the basis of these electrical signals we first need to learn about how this baseline membrane potential is generated, which is the neurons membrane potential while it is at rest. We will spend most of today's class learning about the neurons resting membrane potential and which will lead into how the action potential is generated that we'll continue with next class.
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@@ -159,7 +159,7 @@ To understand the basis of these electrical signals we first need to learn about
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* The membrane of a nerve cell maintains an electrical polarization
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* The cell is polarized– at rest, an electrical gradient is maintained across the plasma membrane (negative charge is greater inside the cell)
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* The cell has a resting potential– difference in voltage across the membrane of a cell (~ -70 mV)
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* The cell has a concentration gradient– difference in distribution of ions between the inside and outside of a membrane
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* The cell has a concentration gradient– difference in distribution of ions between the inside and outside of a membrane
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</div>
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@@ -206,14 +206,14 @@ Just remember that a neuron not eliciting any electrical signals is ‘resting
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</div>
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<div style="margin:0 15px"><img src="figs/Neuroscience5e-Fig-02.02-1R_f6f9bef_b7eea85.png" height="400px"><figcaption>Neuroscience 5e Fig. 2.2</figcaption></div>
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<div style="margin:0 15px"><img src="figs/Neuroscience5e-Fig-02.02-1R_f6f9bef_b7eea85.png" height="400px"><figcaption>Neuroscience 5e/6e Fig. 2.2</figcaption></div>
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Note:
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Now we already saw that we can stick an electrode into a cell, and hook it up to an oscilloscope and passively record its resting membrane potential on the slide from earlier.
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Now we already saw that we can stick an electrode into a cell, and hook it up to an oscilloscope and passively record its resting membrane potential on the slide from earlier.
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Now what if do the same recordings, but also electrically stimulate the cell so that positive or negative charge is added—
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Now what if do the same recordings, but also electrically stimulate the cell so that positive or negative charge is added—
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--
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@@ -226,20 +226,20 @@ Now what if do the same recordings, but also electrically stimulate the cell so
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</div>
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<div style="margin:0 15px"><img src="figs/Neuroscience5e-Fig-02.02-2R_3b5b1ef.png" width="500px"><figcaption>Neuroscience 5e Fig. 2.2</figcaption></div>
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<div style="margin:0 15px"><img src="figs/Neuroscience5e-Fig-02.02-2R_3b5b1ef.png" width="500px"><figcaption>Neuroscience 5e/6e Fig. 2.2</figcaption></div>
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Note:
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So we insert the microelectrode into the cell and find that this neuron is resting at -65 mV.
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So we insert the microelectrode into the cell and find that this neuron is resting at -65 mV.
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Then we inject a small amount of negative current (less than 1 nA) so that we hyperpolarize the cell and we see that the membrane responds passively, meaning that the membrane potential changes and recovers with an exponential relationship.
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* 1-(1/e) = 63% (rise) Vm and 1/e (37%) (decat) of Vm
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If we depolarize the cell membrane from rest by injecting pulses of positive current we get corresponding passive responses with exponential rises and decays of membrane potential– **unless that cell is a neuron and we’ve exceeded the threshold potential (shown by the red dotted line) for generating an action potential in that neuron.
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If we depolarize the cell membrane from rest by injecting pulses of positive current we get corresponding passive responses with exponential rises and decays of membrane potential– **unless that cell is a neuron and we’ve exceeded the threshold potential (shown by the red dotted line) for generating an action potential in that neuron.**
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Notice if we inject stronger current pulses, we get more action potentials, also known as a higher spiking or firing rate, rather than different action potential amplitudes. If the depolarization is sufficient to generate an AP, that AP amplitude stays largely the same within each individual neuron.
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Notice if we inject stronger current pulses, we get more action potentials, also known as a higher spiking or firing rate, rather than different action potential amplitudes. If the depolarization is sufficient to generate an AP, that AP amplitude stays largely the same within each individual neuron.
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We will go over more detail each of these components later on...
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@@ -252,18 +252,18 @@ We will go over more detail each of these components later on...
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Note:
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All electrical signals are the due to the flow of charge, positive or negative. In this case of neurons the charge is due to the movement cations such as Na and K and anions such as Cl and neuronal membranes are selectively permeable to some of these ions giving rise to the flow of charge or current across the cell membrane.
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All electrical signals are the due to the flow of charge, positive or negative. In this case of neurons the charge is due to the movement cations such as Na and K and anions such as Cl and neuronal membranes are selectively permeable to some of these ions giving rise to the flow of charge or current across the cell membrane.
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---
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## Ionic movements across neuronal membranes
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<figure><img src="figs/Neuroscience5e-Fig-02.04-0R_cf6b01f.png" height="400px"><figcaption>Neuroscience 5e Fig. 2.4</figcaption></figure>
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<figure><img src="figs/Neuroscience5e-Fig-02.04-0R_cf6b01f.png" height="400px"><figcaption>Neuroscience 5e/6e Fig. 2.4</figcaption></figure>
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Note:
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there are active ion transporters like the Na-K ATPase and there are ion channels. For example you could pretend this is a Na channel that opens when the neuron is depolarized.
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there are active ion transporters like the Na-K ATPase and there are ion channels. For example you could pretend this is a Na channel that opens when the neuron is depolarized.
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---
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@@ -277,7 +277,7 @@ there are active ion transporters like the Na-K ATPase and there are ion channel
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Note:
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So how do ions get across the lipid cell membrane bilayer? Remember there are proteins in the cell membrane. Some of these are selective ion transporters, remember the Na-K ATPase from cell biology. These work to create concentration gradients.
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So how do ions get across the lipid cell membrane bilayer? Remember there are proteins in the cell membrane. Some of these are selective ion transporters, remember the Na-K ATPase from cell biology. These work to create concentration gradients.
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There are also ion channels that form pores in the cell membrane that are selectively permeable for certain kinds of ions to cross the membrane. These allow ions move across the membrane
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@@ -311,7 +311,7 @@ Here is one these ion transporters— the Na-K pump that moves 3 Na out of the c
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Note:
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Ion channels span the membrane and act as pores. They can open and close, often in a voltage-dependent fashion as we will learn thursday. And ion channels even show selectively such that there are different types of Na, K channels as well as others.
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Ion channels span the membrane and act as pores. They can open and close, often in a voltage-dependent fashion as we will learn thursday. And ion channels even show selectively such that there are different types of Na, K channels as well as others.
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And they can be additionally regulated or ‘gated’ by different mechanisms including voltage or binding of ligands such as neurotransmitters. We will learn much more about the selectivity and function of ion channels a couple lectures from now.
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@@ -327,11 +327,11 @@ Note:
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We actually can predict what the resting membrane potential is by knowing the concentrations of ions inside and outside the cell and knowing the relative permeability of these ions to move across the cell membrane.
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If a cell membrane is largely permeable to just one ion species, we can use the Nernst equation to predict the membrane potential for all kinds of cells.
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If a cell membrane is largely permeable to just one ion species, we can use the Nernst equation to predict the membrane potential for all kinds of cells.
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If a cell membrane is permeable to more than one ion, we can use the Goldman equation.
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We will come back to these in a minute.
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We will come back to these in a minute.
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*Walther Nernst (1864-1941), West Prussia, 1920 Nobel Prize in chemistry*
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@@ -341,15 +341,15 @@ We will come back to these in a minute.
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## Electrochemical equilibrium
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<figure><figcaption class="big">orange dots K⁺, green dots Cl⁻. This simulated membrane is only permeable to K⁺</figcaption><img src="figs/Neuroscience5e-Fig-02.05-1R-2_163131c.png" height="500px"><figcaption>Neuroscience 5e Fig. 2.5</figcaption></figure>
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<figure><figcaption class="big">orange dots K⁺, green dots Cl⁻. This simulated membrane is **only permeable to K⁺**</figcaption><img src="figs/Neuroscience5e-Fig-02.05-1R-2_163131c.png" height="500px"><figcaption>Neuroscience 5e/6e Fig. 2.5</figcaption></figure>
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Note:
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First let’s discuss **electrochemical** equilibrium, which is the balance of two driving forces— electrical AND chemical diffusion– across a cell membrane.
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First let’s discuss **electrochemical** equilibrium, which is the balance of two driving forces— electrical AND chemical diffusion– across a cell membrane.
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Imagine the following experiment. We have a cell and record intracellular membrane potential with electrodes and a voltmeter.
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Imagine the following experiment. We have a cell and record intracellular membrane potential with electrodes and a voltmeter.
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If this membrane is only permeable to K⁺, and KCl concentration is the same inside and outside the cell, there is no net flux of K⁺
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@@ -378,7 +378,7 @@ Note:
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## Resting membrane potential video
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<div><video height=400px controls src="figs/Animation02-01TheRestingMembranePotential.mp4"></video><figcaption>Neuroscience 5e Animation 2.1</figcaption></div>
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<div><video height=400px controls src="figs/Animation02-01TheRestingMembranePotential.mp4"></video><figcaption>Neuroscience 5e Animation 2.1</figcaption></div>
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Note:
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@@ -410,7 +410,7 @@ Note:
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Note:
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So I stated that the Nernst equation is how we can calculate the equilibrium potential for a cell membrane permeable to one type of ion.
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So I stated that the Nernst equation is how we can calculate the equilibrium potential for a cell membrane permeable to one type of ion.
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And here is the Nernst equation is:
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@@ -437,7 +437,7 @@ ln
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: ln(e) = 1, where e =~ 2.718
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Now many of the classical experiments recording membrane potential in squid axon or other preparations were conducted at room temperature, which is 20ºC or about 68ºF.
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Now many of the classical experiments recording membrane potential in squid axon or other preparations were conducted at room temperature, which is 20ºC or about 68ºF.
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Thus to make calculations simpler in the classic scientific papers (often from the 1930s and 1940s before computers) this equation for experiments carried out at room temperature (20ºC = 68ºF = 20ºC+273ºK = 293ºK) is often simplified to the following of:
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@@ -450,14 +450,14 @@ ln(x) / log10(x) = 2.30
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—> 2.30 * log10(x) = ln(x)
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logarithm slope example:
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x = seq(0,10,0.10);
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plot(x,log(x), asp=1);
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plot(x,log10(x), asp=1);
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x = seq(0,10,0.10);
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plot(x,log(x), asp=1);
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plot(x,log10(x), asp=1);
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R = 8.3 J/K*mol, T = 37ºC + 273ºC = 310 K, F = 9.6*10^4 J/mol*V
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E =
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E =
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@@ -474,15 +474,15 @@ log(7) / log10(7)
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<div style="font-size:0.7em">
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<div></div>
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Open up your browser's javascript console `cmd-alt-j (or View-->Developer-->). Copy/paste the following lines:
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Open up your browser's web developer javascript console (shift-ctrl-k (Firefox) or cmd-alt-j (Chrome)). Copy/paste the following lines:
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```javascript
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R = 8.3 //Gas constant
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F = 9.6 * Math.pow(10,4) //Faraday constant
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F = 9.6 * 10**4 //Faraday constant
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T = 20+273 //Room temperature in Kelvins
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```
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Relation of the natural lograrithm (base ~2.718...) to the base 10 logarithm is always `ln(x) = 2.30 * log10(x)` or `ln(x) / log10(x) = 2.30`. ln() is `Math.log()` and log10() is `Math.log10()` in js. Copy/paste the following lines. Try varying *x* a few times and re-calculate:
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Relation of the natural logarithm (base *e* 2.718...) to the base 10 logarithm is always `ln(x) = 2.30 * log10(x)` or `ln(x) / log10(x) = 2.30`. ln() is `Math.log()` and log10() is `Math.log10()` in javascript. Copy/paste the following lines. Try varying *x* a few times and re-calculate:
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```javascript
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x = 5
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@@ -539,14 +539,14 @@ For CaCl₂: (58/2)log10(10/1) = +29 mV
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Since the Nernst equation is really just a linear equation of the form y = mx, you can think of this first term at the slope and the equilibrium potential for an ion varies linearly with the log of the concentration gradient. In other words there is 58 mV per tenfold change in the concentration gradient when we are talking about our potassium examples above, which is depicted here -->
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<!--
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<!--
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## Electrochemical equilibrium
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<div><img src="figs/Neuroscience5e-Fig-02.05-2R_c30075c.png" height="500px"><figcaption>Neuroscience 5e Fig. 2.5</figcaption></div>
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This plot depicts this equilibrium relationship for a hypothetical cell permeable only to potassium.
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This plot depicts this equilibrium relationship for a hypothetical cell permeable only to potassium.
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-->
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@@ -562,9 +562,9 @@ This plot depicts this equilibrium relationship for a hypothetical cell permeabl
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Note:
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Remember that electrochemical equilibrium is the:
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Remember that electrochemical equilibrium is the:
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I = g(Vm-Ex). g = conductance, no. of open channels. (Vm-Ex) = driving force causing either positive or negative current.
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I = g(Vm-Ex). g = conductance, no. of open channels. (Vm-Ex) = driving force causing either positive or negative current.
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@@ -572,7 +572,7 @@ I = g(Vm-Ex). g = conductance, no. of open channels. (Vm-Ex) = driving force ca
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## Electrochemical equilibrium video summary
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<div><video height=400px controls src="figs/Animation02-02ElectrochemicalEquilibrium.mp4"></video><figcaption>Neuroscience 5e Animation 2.2</figcaption></div>
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<div><video height=400px controls src="figs/Animation02-02ElectrochemicalEquilibrium.mp4"></video><figcaption>Neuroscience 5e Animation 2.2</figcaption></div>
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Note:
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@@ -583,7 +583,7 @@ Note:
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## Membrane potential influences the flux of ions
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<div><figcaption class="big">Simulated cell at room temperature</figcaption><img src="figs/Neuroscience5e-Fig-02.06-1R_5d1ff2f.png" height="350px"><figcaption>Neuroscience 5e Fig. 2.6</figcaption></div>
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<div><figcaption class="big">Simulated cell at room temperature</figcaption><img src="figs/Neuroscience5e-Fig-02.06-1R_5d1ff2f.png" height="350px"><figcaption>Neuroscience 5e/6e Fig. 2.6</figcaption></div>
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Note:
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@@ -597,7 +597,7 @@ If our hypothetical battery holds the membrane at -58 mV, the equilbrium potenti
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At more negative membrane potentials than the nernst equilbrium potential we get net inward flow due to the stronger electrical driving force which in the case of potassium here is causing it to move against its chemical gradient.
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<!--
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<!--
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## Membrane potential influences ion fluxes
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<figure><img src="figs/Neuroscience5e-Fig-02.06-2R_1ec257b.png" height="400px"><figcaption>Neuroscience 5e Fig. 2.6</figcaption></figure>
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@@ -622,7 +622,7 @@ The results of this thought experiment are displayed here, displaying the net mo
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</div>
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So to summarize, remember that both the direction (inward vs outward) and magnitude of charge flow or current depends on membrane potential.
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So to summarize, remember that both the direction (inward vs outward) and magnitude of charge flow or current depends on membrane potential.
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Just remember Ohm’s law, I = V/R and rewrite it as Ix = (Vm - Ex)/R
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@@ -657,9 +657,9 @@ So imagine we have 10 mM KCl and 1mM NaCl inside the cell and 1 mM KCl and 10mM
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If we have a simplified situation like earlier where the membrane is permeable to just K we can use Nernst eqn to show that the Veq will be -58mV at room temp. If just permeable to Na we can use Nernst to show the Veq will be +58mV
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Now imagine the cell membrane is permeable to both K and Na and that these permeabilities or ability of ions to pass across the membrane are not equal for K and Na, then we have to use the Goldman eqn.
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Now imagine the cell membrane is permeable to both K and Na and that these permeabilities or ability of ions to pass across the membrane are not equal for K and Na, then we have to use the Goldman eqn.
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Which looks like a more complex version of the Nernst equation but with added terms that take into account the concentrations and relative membrane permeabilities of multiple ion species.
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Which looks like a more complex version of the Nernst equation but with added terms that take into account the concentrations and relative membrane permeabilities of multiple ion species.
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There is no valence term, thus since choride is an anion, its concentration terms are flipped.
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@@ -690,7 +690,7 @@ For a typical neuron at rest, pK : pNa : pCl = 1 : 0.05 : 0.45. Note that becaus
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Note:
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Cells are a bit like a semipermeable bag of electrolytes with different concentrations of ionic species inside and outside.
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Cells are a bit like a semipermeable bag of electrolytes with different concentrations of ionic species inside and outside.
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---
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@@ -769,7 +769,7 @@ Alan Hodgkin, Andrew Huxley, Bernard Katz
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## K⁺ concentration gradient determines resting membrane potential
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<figure><img src="figs/Neuroscience5e-Fig-02.08-0_40bc007.png" height="400px"><figcaption>Neuroscience 5e fig. 2.8</figcaption></figure>
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<figure><img src="figs/Neuroscience5e-Fig-02.08-0_40bc007.png" height="400px"><figcaption>Neuroscience 5e/6e fig. 2.8; Hodgkin and Katz *J. Physiol* 1949</figcaption></figure>
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Note:
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@@ -823,14 +823,14 @@ Their experiment was to lower Na concentrations in the extracellular medium—
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## The action potential as measured by Hodgkin, Huxley, and Katz
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<figure><img src="figs/hodkin-huxley-nature-1939-AP_d30dfee.png" height="400px"><figcaption>Adapted from Hodgkin Huxley *Nature* 1939</figcaption></figure>
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<figure><img src="figs/hodkin-huxley-nature-1939-AP_d30dfee.png" height="400px"><figcaption>Adapted from Hodgkin and Huxley *Nature* 1939</figcaption></figure>
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Note:
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Hodgkin and Huxley, Nature 1939 squid giant axon
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Image adapted from Principles of Neurobiology, L. Luo Garland Fig 2-19 which in turn adapted from Nature 1939.
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Image adapted from Principles of Neurobiology, L. Luo Garland Fig 2-19 which in turn adapted from Nature 1939.
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Capacitance (farads) is the ability of a body to store an electrical charge. Any object that can be electrically charged exhibits capacitance. Dielectric materials. Storage of electrical energy temporarily in an electric field. **Unlike a resistor, an ideal capacitor does not dissipate energy. Instead, a capacitor stores energy in the form of an electrostatic field between its plates.**
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@@ -838,7 +838,7 @@ Capacitance (farads) is the ability of a body to store an electrical charge. Any
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## Role of sodium in the generation of an action potential
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<figure><figcaption class="big">Lowering Na⁺ decreases both the rate and the rise of an action potential</figcaption><img src="figs/Neuroscience5e-Fig-02.09-1R_2c02203.png" height="400px"><figcaption>Neuroscience 5e Fig. 2.9</figcaption></figure>
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<figure><figcaption class="big">Lowering Na⁺ decreases both the rate and the rise of an action potential</figcaption><img src="figs/Neuroscience5e-Fig-02.09-1R_2c02203.png" height="400px"><figcaption>Neuroscience 5e/6e Fig. 2.9; Hodgkin and Katz *J. Physiol* 1949</figcaption></figure>
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Note:
|
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@@ -849,7 +849,7 @@ When Hodgkin and Katz did this low extracellular Na experiment, the AP had a sma
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## Role of sodium in the generation of an action potential
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<figure><img src="figs/Neuroscience5e-Fig-02.09-2R_6ca6c4f.png" height="400px"><figcaption>Neuroscience 5e Fig. 2.9</figcaption></figure>
|
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<figure><img src="figs/Neuroscience5e-Fig-02.09-2R_6ca6c4f.png" height="400px"><figcaption>Neuroscience 5e/6e Fig. 2.9; Hodgkin and Katz *J. Physiol* 1949</figcaption></figure>
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Note:
|
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@@ -875,7 +875,7 @@ So a summary of the Hodgkin and Katz experiment conclusions...
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## Resting membrane and action potentials entail permeabilities to different ions
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<figure><img src="figs/Neuroscience5e-Fig-02.07-0_caebcb8.png" height="400px"><figcaption>Neuroscience 5e Fig. 2.7</figcaption></figure>
|
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<figure><img src="figs/Neuroscience5e-Fig-02.07-0_caebcb8.png" height="400px"><figcaption>Neuroscience 5e/6e Fig. 2.7</figcaption></figure>
|
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|
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|
||||
Note:
|
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@@ -894,10 +894,7 @@ Note:
|
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And this is just a overall summary of what we have been discussing
|
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|
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|
||||
|
||||
|
||||
<!--
|
||||
<!--
|
||||
|
||||
## Action potential form and nomenclature
|
||||
|
||||
@@ -938,5 +935,3 @@ AHP due to voltage-gated K⁺ channels, including Ca²⁺ activated potassium ch
|
||||
|
||||
Llinas Sugimori J Physiol 1980 Purkinje neurons
|
||||
-->
|
||||
|
||||
---
|
||||
|
||||
Reference in New Issue
Block a user