The diagram below shows a schematic nerve cell bathed in intracellular and extra
ID: 221077 • Letter: T
Question
The diagram below shows a schematic nerve cell bathed in intracellular and extracellular solutions at 37°C and with the concentrations of Na and K as shown. The cell membrane contains a population of K -selective ion channels and a separate population of Na selective ion channels as indicated. An electrode is inserted into the cell that measures the membrane potential (V The Nernst equation for ion x at 37 "C, can be simplified to: Ex 62 mV log10 ion ionarsidel outside] Vm K+ selective channels Na+ selective channels Extracellular concentrations: DK loutsido 14 mM [NaTinside 140 mM Intracellular concentrations: KHoutside 140 mM Na inside 4 mM If initially (at rest) only the K channels are open, and then the Na channels also open, which ONE of the following options MOST CLOSELY describes the membrane potential (V Select one Resting Vm +62 mV, when the Na' channels open, Vm becomes hyperpolarized Resting VI 0 mV, no change when Na channels open Resting Vm +62 mV, when the Na' channels open, Vm becomes depolarized Resting Vm -62 mv, when the Na channels open, Vm becomes depolarized Resting Vm -62 mV, when the Na channels open, Vm becomes hyperpolarized X This is incorrect. When the Nat channels open the vm will become depolarizedExplanation / Answer
The correct options are
1)
Resting Vm=-62mV, when the Na+ channels open, Vm becomes depolarized
Initially, in response to the nerve stimulus, sodium channels open and move the sodium ions to inside of the nerve cell causing depolarization.
2)
Touch causes the membrane potential of this sensory nerve cell to cross the threshold for activation of voltage-dependent Na+ and K+ channels.
3)
Here both first and second options are correct. They are
The voltage dependent sodium channels are inactivated when the action potential threshold is reached.
Voltage-dependent potassium channels are open during the repolarization phase.
4)
In a normal unmyelinated axon, the action potential amplitude gets progressively smaller as it travels along the axon towards the nerve terminal.