Ch 11 HW Focus Figure 11.1: Resting Membrane Potential 20113 Part F. Conclusion/Synthesis: Resting Membrane Potential, Parti Na+ Nark Pump Na Cell Interior -70 V You Are Going To Record RMP From A Calling An Electrode You Place Your Electrode And Record A Resting Membrane Potential Every Millisecond You Record An Initial Value Of MV, However, Over Time You Notice
The Correct Answer and Explanation is:
Sure! Based on your description, this question involves recording the Resting Membrane Potential (RMP) from a cell with an electrode, where initially you record a value around -70 mV (millivolts), which is typical for many cells (like neurons). Over time, you notice changes in the recorded potential.
Likely Question:
You are recording the resting membrane potential from a cell using an electrode. You record an initial value of about -70 mV. However, over time, the potential drifts toward 0 mV. Why does this happen?
Correct Answer:
The resting membrane potential drifts toward 0 mV over time because the cell membrane is damaged or the electrode is causing leakage of ions, disrupting the ionic gradients that maintain the RMP.
Explanation (300+ words):
The resting membrane potential (RMP) is the voltage difference across the cell membrane when the cell is at rest, typically about -70 mV in neurons. This negative potential inside the cell is primarily maintained by the uneven distribution of ions, especially sodium (Na⁺), potassium (K⁺), chloride (Cl⁻), and negatively charged proteins, along with the activity of the sodium-potassium (Na⁺/K⁺) pump.
How the RMP is generated:
- The cell membrane is selectively permeable to ions, with potassium channels being the most permeable at rest.
- K⁺ tends to move out of the cell down its concentration gradient, leaving behind negatively charged proteins, which creates a negative charge inside.
- The Na⁺/K⁺ pump actively moves 3 Na⁺ ions out of the cell and 2 K⁺ ions in, maintaining the concentration gradients essential for RMP.
- This ionic imbalance results in a stable, negative resting membrane potential.
Why does the recorded RMP drift toward 0 mV over time?
When you place an electrode inside the cell to measure the RMP, the cell membrane must remain intact for accurate recordings. Over time, if:
- The membrane is damaged by the electrode insertion or by the electrode itself:
- This can create a leak pathway for ions.
- The ionic gradients begin to collapse because ions move freely across the membrane instead of being selectively controlled.
- Ionic leakage occurs through the electrode or damaged membrane:
- The difference in ion concentration between inside and outside the cell diminishes.
- Without these gradients, the electrical potential difference disappears.
- The Na⁺/K⁺ pump cannot maintain gradients effectively:
- If the cell is compromised, the pump may not work properly, leading to dissipation of ion gradients.
As a result, the inside of the cell becomes less negative and eventually approaches 0 mV, which represents no voltage difference across the membrane. This drift indicates the loss of the cell’s resting electrical state, often signaling that the cell is dying or that the recording technique is damaging the cell.
Summary:
The initial -70 mV reading reflects a healthy, functioning membrane potential. A gradual drift toward 0 mV signifies loss of membrane integrity or ionic gradients, which invalidates the RMP measurement. This phenomenon highlights the delicate balance of ion channels, pumps, and membrane permeability that underlies the resting membrane potential.
If you want, I can also help explain the physiological roles of the Na⁺/K⁺ pump or why RMP is crucial for cell function!