1.Consider a skeletal muscle or nerve cell that is bathed in an extracellular an
ID: 220965 • Letter: 1
Question
1.Consider a skeletal muscle or nerve cell that is bathed in an extracellular and intracellular solution containing the same concentration of a cation, i.e. the cation concentration inside the cell = its concentration outside the cell. Regarding the electrochemical forces on this cation, which ONE of the following options is CORRECT?
Select one:
a.When the membrane potential of the cell is +30 mV, an electrochemical force acts on the ion to favour cation efflux.
b.The equilibrium potential for the ion would be approximately -90 mV at 37°C.
c.When the membrane potential of the cell is –70 mV, there is no electrochemical force causing the ion to move across the membrane.
d.When the membrane potential of the cell is –70 mV, a chemical force acts on the ion to cause cation influx.
e.At – 70 mV, no cations would move through a cation selective channel as there is no driving force for cation movement.
2.
A healthy young man drinks a sports supplement containing glucose and creatine which is advertised to “enhance muscle endurance by increasing intracellular ATP and Na-pump activity”. Assuming this “Na-pump” refers to the Na+/K+/ATPase, which ONE of the following options is MOST CORRECT?
Select one:
a.Increased ATP concentration allows a greater passive flux of K+ and Na+ via the Na+/K+/ATPase.
b.The Na+/K+/ATPase will transport glucose (along with K+) into the muscle fibre to generate ATP and Na+.
c.The Na+/K+/ATPase actively transports K+ ions out of a cell and Na+ ions into the cell.
d.A sustained and significant increase in the activity of the Na+/K+/ATPase would not have any effect on the intracellular ion concentrations.
e.An increase in Na+/K+/ATPase activity would be expected to lead to a decrease in the intracellular free Ca2+ concentration due to an increased activity of a secondary active transporter that exchanges Na+ influx for Ca2+ efflux.
3.
A nerve cell contains intracellular K+ and Na+ concentrations of 140 mM and 10 mM, respectively. It is surrounded by an extracellular solution containing K+ and Na+concentrations of 4 mM and 150 mM, respectively. The only open ion channels in the nerve cell are selective for K+. Given that R= the Gas constant, T = temperature in Kelvins, F = Faraday’s constant and z = valence, the nerve cell’s membrane potential can be calculated as:
Select one:
a.(RT) / (zF) multiplied by loge [(150 mM + 4 mM) / (10 mM + 140 mM)]
b.(RT) / (zF) multiplied by loge (140 mM / 4 mM)
c.(RT) / (zF) multiplied by loge (10 mM / 150 mM)
d.(RT) / (zF) multiplied by loge (4 mM / 140 mM)
e.(RT) / (zF) multiplied by loge [(10 mM + 140 mM) / (4 mM + 150mM)]
4.
Which ONE of the following statements regarding action potential propagation in nerve cells is CORRECT?
Select one:
a.Action potentials are initiated in the axon hillock and can then propagate both forward towards the axon terminal and backwards into the nerve dendrites.
b.There is a greater leak of local current flow across the cell membrane in a myelinated axon as compared to an unmyelinated axon.
c.Saltatory conduction is where the action potential “jumps” from node to node and occurs in all mammalian nerve axons.
d.In a normal unmyelinated axon, the action potential amplitude gets progressively smaller as it travels along the axon towards the nerve terminal.
e.Myelination decreases the conduction velocity of action potential propagation
Explanation / Answer
1) Answer is A
Electrochemical force which is applied on the cation ,push the cation out, means efflux.
2) Answer is E
An increase in Na+/K+/ATPase activity increase the pumping out of Na+ and it generates more electrochemical force for Na+/ Ca2+ exchange.
Blocking the Na+/K+/ATPase will increase intracellular Ca2+ and cardiac muscle contraction in congestive heart disease.
3). Answer is D
As by Nernst equation, the cell is only permeable to K+, to make membrane potential will quickly go to the K+ equilibrium potential.
4) Option D is the incorrect statement. The action potential is a regenerative or “all or nothing” response, this means the same amplitude throughout the axon.
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