Membrane potential
BIOSC 048: Problem Set Questions
1. Given that cell A has significantly more nongated K+ channels than cell B, which cell has the larger resting membrane potential? Explain.
If the permeability to K is higher in A than in B, then the resting membrane potential (rmp) will be closer to the equilibrium potential in cell A, which means the rmp will be more negative in cell A than in cell B; or in other words, the potential difference will be LARGER in cell A.
2. Predict the effect of a reduced extracellular concentration of Na+ on the magnitude of the action potential in an electrically excitable cell.
If there is less Na outside the cell, the equilibrium potential for Na will be less (for example, it will be +25mV instead of +30mV). And the action potential will be smaller in amplitude (smaller magnitude) since it will depolarize to only +25mV instead of +30mV.
3. If the breakdown of rhodopsin occurs rapidly and production is slow, do eyes adapt more rapidly to light or dark conditions? Explain.
Eyes adapt more quickly to bright light because this involves only a change in the conformation of retinal, which happens very quickly. In order to adapt to dark conditions, a lot of rhodopsin (retinal+opsin) needs to build up and that takes time.
4. If the duration of the absolute refractory period of a nerve cell is 1.5msec, how many a.p. are generated in 1sec by a maximal stimulus?
If you can fire an action potential every 1.5msec, then you should be able to generate (1000msec 1.5 msec) or about 667 a.p.s per second.
5. Bethanechol chloride is a drug that binds to muscarinic receptors. Explain why this drug can be used to promote emptying of the urinary bladder. Which of the following side effects would you predict: abdominal cramps -YES, asthmatic attack -YES, decreased tear production, decreased salivation, dilation of the pupils, or sweating -YES
6. You suspect your patient has developed a peripheral neuropathy due to diabetes mellitus.
1. Given that cell A has significantly more nongated K+ channels than cell B, which cell has the larger resting membrane potential? Explain.
If the permeability to K is higher in A than in B, then the resting membrane potential (rmp) will be closer to the equilibrium potential in cell A, which means the rmp will be more negative in cell A than in cell B; or in other words, the potential difference will be LARGER in cell A.
2. Predict the effect of a reduced extracellular concentration of Na+ on the magnitude of the action potential in an electrically excitable cell.
If there is less Na outside the cell, the equilibrium potential for Na will be less (for example, it will be +25mV instead of +30mV). And the action potential will be smaller in amplitude (smaller magnitude) since it will depolarize to only +25mV instead of +30mV.
3. If the breakdown of rhodopsin occurs rapidly and production is slow, do eyes adapt more rapidly to light or dark conditions? Explain.
Eyes adapt more quickly to bright light because this involves only a change in the conformation of retinal, which happens very quickly. In order to adapt to dark conditions, a lot of rhodopsin (retinal+opsin) needs to build up and that takes time.
4. If the duration of the absolute refractory period of a nerve cell is 1.5msec, how many a.p. are generated in 1sec by a maximal stimulus?
If you can fire an action potential every 1.5msec, then you should be able to generate (1000msec 1.5 msec) or about 667 a.p.s per second.
5. Bethanechol chloride is a drug that binds to muscarinic receptors. Explain why this drug can be used to promote emptying of the urinary bladder. Which of the following side effects would you predict: abdominal cramps -YES, asthmatic attack -YES, decreased tear production, decreased salivation, dilation of the pupils, or sweating -YES
6. You suspect your patient has developed a peripheral neuropathy due to diabetes mellitus.