16.14
Resting Potential Decay
The resting membrane potential of a neuron (-70mV) is sustained due to the selective ion permeability of the membrane. At the resting potential, the m…
A neurons' resting membrane potential is maintained because of the differences in the ionic composition and permeability of two essential ions — sodium and potassium.
In the resting state, potassium ions move out through the potassium leak channels, creating an internal negative potential.
To balance the charges, sodium ions enter the cell through sodium leak channels and increase the membrane potential to negative 70 millivolts.
Thus, a cell at rest is like a leaky boat as the ions are being moved in and out of the cell. The sodium-potassium pump moves three sodium ions out and two potassium ions back into the cell to maintain the ionic gradient.
Suppose the sodium-potassium pump fails to function or is inhibited for more than 10 seconds.
The leak channels would continue to move ions until the equilibrium state is reached, where no further net movement of ions occurs.
So, the membrane potential falls or decays to zero in the absence of the gradient. With the loss of the membrane potential, the cell quickly loses its viability.
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Q1: What is resting potential and why does it matter for neurons?
Resting potential is the stable electrical voltage across a neuron's membrane when it is not actively firing, typically around -70 millivolts. This negative charge inside the cell relative to outside is maintained by the sodium-potassium pump and is essential for neuronal excitability, allowing neurons to respond to stimuli and generate electrical signals.
Q2: How does the sodium-potassium pump maintain resting potential?
The sodium-potassium pump actively transports three sodium ions out of the cell and two potassium ions into the cell using ATP energy. This unequal exchange creates and maintains the concentration gradients that establish the negative resting potential, compensating for passive ion leakage across the membrane.
Q3: What role do ion channels play in resting potential stability?
Ion channels allow selective passive movement of ions across the membrane based on concentration and electrical gradients. The electrochemical gradient and channel proteins determine which ions flow and at what rate, with potassium channels being more permeable at rest, contributing to the negative resting potential.
Q4: How does resting potential relate to action potential generation?
Resting potential provides the baseline electrical state from which neurons can generate action potentials. When stimulated, the membrane depolarizes from resting potential toward threshold, triggering the rapid voltage changes characteristic of action potential phases of stimulation that propagate signals along the axon.
Q5: What happens to resting potential if the sodium-potassium pump fails?
Without the sodium-potassium pump, sodium accumulates inside the cell and potassium leaks out, causing the resting potential to become less negative and eventually depolarize. The neuron loses its ability to maintain stable electrical conditions and cannot generate normal action potentials, impairing neuronal communication.
Q6: Why is potassium more important than sodium for establishing resting potential?
At rest, the neuronal membrane is more permeable to potassium than sodium because more potassium channels are open. Since potassium ions flow out of the cell down their concentration gradient, this outward movement of positive charge makes the inside more negative, establishing the characteristic negative resting potential.