Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
The neural membrane contains selective ion channels that are differentially permeable to various ions like and .
Resting Membrane Potential: In a resting neuron, the axonal membrane is more permeable to and nearly impermeable to . This results in a high concentration of and negatively charged proteins inside, and high outside, creating a potential difference of approximately .
The Pump: An active transport mechanism that moves ions outwards for every ions into the cell to maintain the ionic gradient.
Depolarization: When a stimulus is applied, VGCs (Voltage-Gated Channels) open, leading to a rapid influx of . The polarity is reversed (inside becomes positive), generating an Action Potential ( to ).
Repolarization: Shortly after depolarization, channels close and channels open. diffuses outside the membrane, restoring the resting potential.
Saltatory Conduction: In myelinated nerve fibers, the impulse 'jumps' from one Node of Ranvier to the next, significantly increasing the speed of conduction.
📐Formulae
💡Examples
Problem 1:
During the resting state of a nerve fiber, if the pump is inhibited by a toxin like Ouabain, what will happen to the resting membrane potential?
Solution:
The resting membrane potential will gradually disappear, and the cell will depolarize (move towards ).
Explanation:
The resting potential of is maintained by the active transport of ions. Without the pump moving out and in, the ionic gradients dissipate due to leakage, and the electrical charge across the membrane neutralizes.
Problem 2:
Calculate the ratio of sodium ions pumped out to potassium ions pumped in during the maintenance of the ionic gradient across the axolemma.
Solution:
The ratio is .
Explanation:
The ATPase pump utilizes energy from to transport ions out of the cytoplasm into the extracellular fluid and ions into the cytoplasm, contributing to the electrogenic nature of the membrane.