Ions move in the direction opposite to that favored by the chemical concentration gradient when _____.
answer
they are pumped by proteins that require ATP hydrolysis and when the electrical charge gradient repulses or attracts them
Active pumping moves ions against their chemical concentration gradients and the Nernst equation describes how membrane potentials can yield electrical gradients to motivate ion movement.
question
Choose the set that includes the most charged compounds that are more abundant inside neurons, in the cytosol, than outside the neurons, in the extracellular fluid.
answer
potassium ions and proteins
Proteins are abundant in all cells of the body and are mostly anions, thus contributing significantly to the membrane potential; and potassium ions are actively pumped into the cytosol of all cells in the body.
question
The simultaneous arrival of graded depolarization and a graded hyperpolarization of equal but opposite magnitude at a particular location on the dendritic membrane is likely to _____.
answer
cancel each other out, making it appear as if there was no change in membrane potential
Grade potentials are summable, so a depolarization and a hyperpolarization can offset each other to make it appear that there were no changes in membrane potential at that location.
question
In a neuron, during the depolarization phase that may trigger an action potential _____.
answer
some voltage-gated sodium channels are open
When a stimulus depolarizes the membrane, some gated sodium channels open, causing further depolarization. If the threshold is reached, most gated sodium channels open, triggering an action potential.
question
Of these choices, neuronal communication between the brain and the muscles of the leg is best conceptualized as _____.
answer
electrical and chemical signaling
A neuron propagates action potentials as a consequence of ion movements across its membranes (the electrical part), but is also requires chemical signaling at its synapses, via neurotransmitters, to be able to function properly.
question
The plasma membrane of a neuron has voltage-gated sodium and potassium channels. What is the effect of membrane depolarization on these channels?
answer
Membrane depolarization first opens sodium channels and then opens potassium channels.
Membrane depolarization opens both types of channels, but they respond independently and sequentially. Sodium channels open first, initiating the action potential. As the action potential proceeds, the sodium channels become inactivated and remain inactivated until after the membrane returns to the resting potential and the channels close. Potassium channels open more slowly than sodium channels but remain open and functional throughout the action potential. Read about the generation of action potentials.
question
If the membrane potential of a neuron decreases, the membrane potential _____.
answer
becomes less negative.
Your answer shows that you understand that the membrane potential measures the difference in the electrical potential (voltage) across the neuron's plasma membrane. When the membrane potential of a neuron decreases, the negative value of the electrical potential across the plasma membrane is reduced and the membrane potential becomes more positive. Read about membrane potential.
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