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Subject: Neurophysiology
The neuron for this experiment is in a bath with [K+] = 2 mM and [Na+] = 150 mM.
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- Calculate the Nernst Equilibrium potential for each ion.
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- What is your estimate for the gNa and for gK? If you are more comfortable, use PNa and PK. Remember, these values should be between 0 and 1.
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- What is the resting membrane potential for this cell?
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- Draw an action potential for this neuron in this solution. Keep in mind that this neuron is in unusual solutions. Label each axis and indicate inward and outward currents. Be absolutely certain to label the peak voltage and threshold for the AP!
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- Patch clamp recording of a single ion channel yields the following results: Holding Potential (mV) Measured Current (pA) -100 -1.0 -50 0.0 0 +1.0 +50 +2.0 +100 +3.0 part a.) Calculate the membrane potential at the instant when a neuron has the following relative permeabilities: PK+ = 1.0, PNa+ = 1.0, PCl- = 1.0. Use the ionic concentration values in the picture included. a.) -12 mv b.) -35mv c.) -60 mv d.) +20 mv e.) 0 mv part b.) What would be the equilibrium potential for K+ in neurons under such circumstances? a.) -11 mv b.) +30 mv c.) +75 mv d.) -35 mv e.) 0 mv part c.) What would be the new resting potential, discounting the effects of non-gated chloride channels (just give an approximate value – no calculation is necessary)? a.) about +20 to +25 mV b.) about -30 to -40 mV c.) about +1 to +5 mV d.) close to ENa+ e.) about -10 to -15 mVThe typical distribution of K+ and Na+ ions inside and outside the cell is: [K+]in = 150 mM; [K+]out = 5 mM; [Na+]in = 10 mM; [Na+]out = 150 mM What are reversal potentials for Na+ and K+ at 25oC ? What should be the ratios of PNa/PK at (i) rest (-60 mV) and (ii) during the action potential (+20 mV) to generate a spike from -60 to +20 mV. Use the short form of Goldman equation.Calculate the free energy of transport for the movement of potassium by the sodium/potassium pump under normal physiological conditions: 4 mM serum potassium, 135 mM intracellular potassium, 37.1 °C, and resting potential -82 mV. Express your answer in kJ/mol. Show all work. Calculate the free energy of transport for the movement of potassium by the sodium/potassium pump under disturbed conditions of 2 mM serum potassium. Assume all other parameters remain the same. Express your answer in kJ/mol. Show all work. What factors could limit the continued action of the sodium/potassium pump when only 2 mM potassium is present in the blood plasma? Note that under normal physiological conditions, the cell interior contains 11 mM sodium and the blood contains 140 mM sodium.
- Myasthenia gravis is a disease that leads to a marked decrease in the number of acetylcholine (Ach) receptors at the neuromuscular junction. As a result, suppose only about 200 (instead of 2000) Ach receptor-channels are opened by each quantum of Ach. The Ach-gated channels that survive operate normally and each cause a depolarization of about 0.25 x 10-3 mV when open. The function of the presynaptic terminal is normal and an action potential will cause the release of 100 quanta of neurotransmitter. For a patient with myasthenia gravis, what would be the magnitude of the depolarization (in mV) associated with opening of one Ach-gated channel? a.) 0.25x10^-2 mv b.) 0.25x10^-3 mv c.) 0.25x10^-4 mv d.) 0.5x10^-1 mv e.) 0.5 mvTable Q1(a) shows typical values for the intracellular and extracellular concentrations of the major ion species (in millimoles per litre) for frog skeletal muscle. Table Q1(a) Permeability (cm/s) 2 x 10-8 2х 10 Ions Intracellular Extracellular Na* 12 145 K+ 155 4 4 120 4 x 106 By referring to Table Q1(a), compute the equilibrium resting potential for this membrane by assuming the room temperature is 20° C. Given the Boltzman's constant, k = 1.38 x 1023 J/K and an electronic charge, q = 1.602 x 10-19 C.Myasthenia gravis is a disease that leads to a marked decrease in the number of acetylcholine (Ach) receptors at the neuromuscular junction. As a result, suppose only about 200 (instead of 2000) Ach receptor-channels are opened by each quantum of Ach. The Ach-gated channels that survive operate normally and each cause a depolarization of about 0.25 x 10-3 mV when open. The function of the presynaptic terminal is normal and an action potential will cause the release of 100 quanta of neurotransmitter. Part a.) For a patient with myasthenia gravis, what would be the size (in mV) of a miniature excitatory post-synaptic potential (or that associated with one quantum of Ach)? a.) 0.05 mv b.) 0.25x10-4 mv c.) 0.25x10-3 mv d.) 0.5x10-3 mv e.) 0.5 mv Part b.) For a patient with myasthenia gravis, what would be the size (in mV) of the full excitatory post synaptic potential consequent to the entry of an action potential into the presynaptic terminal of the neuromuscular junction? a.) 70 mv…
- What is the intracellular voltage for Cl- if the intracellular concentration was 5 mM and the extracellular concentration was 130 mM. Write the voltage as a number in mV inside the cell relative to that outside, eg. -72 or + 90. Question 2. What is the intracellular voltage for Ca++ if the intracellular concentration was 0.0008 mM and the extracellular concentration was 0.6 mM. Write the voltage as a number in mV inside the cell relative to that outside, eg. -72 or +90. Round to the nearest milli Volt.One of the important uses of the Nernst equation is in describing the flow of ions across plasma membranes. Ions move under the influence of two forces: the concentration gradient (given in electrical units by the Nernst equation) and the electrical gradient (given by the membrane voltage). This is summarized by Ohms law: Ix=Gx(VmEx) which describes the movement of ion x across the membrane. I is the current in amperes (A); G is the conductance, a measure of the permeability of x, in Siemens (S), which is I/V;Vm is the membrane voltage; and Ex is the equilibrium potential of ion x. Not only does this equation tell how large the current is, but it also tells what direction the current is flowing. By convention, a negative value of the current represents either a positive ion entering the cell or a negative ion leaving the cell. The opposite is true of a positive value of the current. a. Using the following information, calculate the magnitude of Na [ Na+ ]0=145mM,[ Na+ ]i=15mM,Gna+=1nS,Vm=70mV b. Is Na+ entering or leaving the cell? c. Is Na+ moving with or against the concentration gradient? Is it moving with or against the electrical gradient?Separately, draw a table using arrows to depict the appropriate magnitude and direction of the forces and ion fluxes at different membrane potentials for a ligand-gated channel that is equally permeable to both ion X+ and ion Y+. The equilibrium potential for ion X+ is -60 mV, and the equilibrium potential for ion Y+ is -20 mV. Which item best represents the forces and fluxes for a membrane potential of -40 mV (a, b, c, or d)? Upwards arrows means outward direction and downwards arrow means inward direction. The length of the arrow determines the magnitude.
- Separately, draw a table using arrows to depict the appropriate magnitude and direction of the forces and ion fluxes at different membrane potentials for a ligand-gated channel that is equally permeable to both ion X+ and ion Y+. The equilibrium potential for ion X+ is -60 mV, and the equilibrium potential for ion Y+ is -20 mV. Which item best represents the forces and fluxes for a membrane potential of -40 mV?What happens to membrane potential during manipulation 4 in the attached figure (Figure 4.13 of the textbook)? 1 Efflux of Nat Nat efflux (logarithmic scale) 0 3 Recovery when K+ is restored 2 Nat efflux reduced by removal of external K 50 100 4 Efflux decreased by metabolic inhibitors, such as dinitrophenol, which block ATP synthesis 150 Time (min) 200 5 Recovery when ATP is restored " I 250 TATI 122 O Membrane potential does not change, because the Na+-K+ ATPase does not contribute to membrane potential. O Membrane potential is hyperpolarized, because the Na+-K+ ATPase is electrogenic and hyperpolarizes membrane potential when it is active. O Membrane potential is depolarized, because the Na+-K+ ATPase is electrogenic and hyperpolarizes membrane potential when it is active. 300Separately, draw a table using arrows to depict the appropriate magnitude and direction of the forces and ion fluxes at different membrane potentials for a ligand-gated channel that is equally permeable to both ion X+ and ion Y+. The equilibrium potential for ion X+ is -60 mV, and the equilibrium potential for ion Y+ is -20 mV. Which item (a, b, c, or d) best represents the forces and fluxes for a membrane potential of +20 mV? Upwards arrows means outward direction and downwards arrow means inward direction. The length of the arrow determines the magnitude.