Understanding the Resting Membrane Potential of Neurons

What is the typical resting membrane potential of a neuron?

• A. -50 mV
• B. -70 mV
• C. -90 mV
• D. 0 mV

Answer: (B)

The typical resting membrane potential of a neuron is around -70 mV. This value indicates that the inside of the neuron is more negatively charged compared to the outside, which is primarily due to the distribution of ions across the cell membrane. At rest, neurons have a higher concentration of potassium ions (K+) inside the cell and a higher concentration of sodium ions (Na+) outside the cell. The uneven distribution of these ions, maintained by the sodium-potassium pump, contributes significantly to the negative charge inside the neuron. Additionally, the membrane is more permeable to K+ than Na+ at rest, allowing K+ to flow out of the cell, which further contributes to the negative membrane potential. As a result, -70 mV is considered the standard resting state for most neurons, providing a baseline from which action potentials can occur when the neuron is stimulated. This value is crucial for the proper functioning of neuronal communication and transmission of signals throughout the nervous system.

When it comes to neurons, understanding their resting membrane potential is like peeking behind the curtain of how they work. Have you ever wondered why they seem to have a magic number? The answer usually floats around -70 mV, which gives you an insight into how these tiny powerhouses of our nervous system operate.

Why does this number matter? Well, it’s all about the charges inside and outside the neuron. The inside of a neuron is like a quiet library filled with potassium ions (K+), while the outside is a bustling street loaded with sodium ions (Na+). This uneven distribution isn't random; it’s meticulously maintained by the famous sodium-potassium pump, which actively pushes sodium out while pulling potassium in. You see, the neuron prefers its cozy -70 mV setting. It's almost like the perfect balance in a game of tug-of-war—no one feels overly strained, and everything functions smoothly.

But hold on a second. What makes these K+ ions feel so right at home inside the neuron? The secret lies in the neuron’s membrane, which is much more permeable to K+ ions than Na+ at rest. Picture this: like a well-guarded fortress, the neuron's membrane allows potassium ions to slip through more freely, leaving behind a negative charge. It's a vital process because the negative potential is the home base for sending signals that evoke everything from reflex actions to deep thoughts.

So, every time your neurons fire up an action potential—bam!—think about how they sprint away from their resting state. Those action potentials are crucial for communication in the central nervous system. It's almost poetic how a resting state of -70 mV is transformed into exciting electrical signals that travel along nerves and make everything happen.

Now, to be clear, while the -70 mV resting membrane potential is the expected norm for many neurons, not all neurons are identical, and some can have variations depending on types and conditions. But like a classic song that doesn’t lose its charm, this resting potential remains a cornerstone for understanding how neurons connect, communicate, and function as vital parts of our biological systems. So, when you sit down to study for the Biological Systems MCAT, remember this number. It’s not just random—it’s a piece of the bigger puzzle that keeps our nervous system performing harmoniously.