Movement of chloride ions across the cell membrane from the the outside of nerve

Question

Movement of chloride ions across the cell membrane from the the outside of nerve cells to the inside has a delta-G of about 1.1 kcal/mol even in the presence of a gradient. Why is the gradient alone not enough to get the ions into the cell? (Think about how delta-G is calculated for movement into a cell.)

a) must also take into consideration other ion concentrations
b) must also take into consideration the membrane potential
c) must also take into consideration the temperature
d) must also take into consideration cotransport

Explanation / Answer

All those 4 factors are relevant, but the most critical is actually b, the membrane potential, which is also the factor that is used by the nervous system, which is able to monitor the membrane potential in a very short time, measurable in nanoseconds, with the added advantage that a change in the resting membrane potential (depolarization of the membrane) may start at one point in a nerve cell surface and may spread to the overall surface, including traveling distances measurable in feet along the axons. The sudden depolarization allows the escape of potassium from the cell in exchange of sodium from the extracellular fluids, accompanied by calcium. At the synapsis (intercellular junctions) the depolarization causes sudden release of neurotransmitters, that cause rapid reactions in the receiving cell. The activation that leads to depolarization is an all-or-nothing reaction that is self-contained and self-limited. Continuous stimuli are necessary for repetition. Repetition could be rapid, but normally one stimulus causes depolarization, and between stimuli, and at the end of the last stimulus, repolarization occurs, meaning the membrane recovers its resting electric potential, which once again, drives potassium in and sodium out. Electrical energy supplements the gradients. Actually it keeps potassium high inside and low outside against gradient, and high sodium out and low sodium in, also against gradient, a precondition for normal neural and neuromuscular tissue functions. That is the function of the so-called "excitable cells", excitable by manipulating electric potential differences across their membrane: mostly nerves and muscles, and nervous system structures.

Related Questions

Navigate

• Browse (All)
• Browse M
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.