Question

Which ion most readily leaks across a neuron's membrane, helping to establish the resting potential? a. \(\mathrm{Ca}^{2+}\) b. \(\mathrm{K}^{+}\) c. \(\mathrm{Na}^{+}\) d. \(\mathrm{Cl}^{+}\)

Short answer

The ion that most readily leaks across a neuron's membrane, helping to establish the resting potential, is \(\mathrm{K}^{+}\) (potassium ions).

Step-by-step solution

Understanding the resting potential

The resting potential is the electrical potential difference across a neuron's membrane in a resting state. This potential is typically around -70mV. It is primarily established by the passive diffusion of potassium ions (\(\mathrm{K}^{+}\)) and the action of the sodium-potassium pump, which actively transports sodium ions (\(\mathrm{Na}^{+}\)) out of the cell and potassium ions into the cell.

Analyzing the role of ions in establishing the resting potential

In order to maintain the resting potential, the neuron's membrane must be permeable to certain ions. The neuron's selective permeability causes an unequal distribution of ions across its membrane, leading to the electrical potential difference. Let's examine the role of each ion in the given exercise: a. \(\mathrm{Ca}^{2+}\): Calcium ions are important for regulating the release of neurotransmitters. However, they don't significantly contribute to the resting potential. b. \(\mathrm{K}^{+}\): Potassium ions are the primary ion responsible for establishing the resting potential as they are the ions that leak across the membrane the most. c. \(\mathrm{Na}^{+}\): Sodium ions are involved in generating action potentials in neurons, but their role in establishing the resting potential is limited to being pumped out of the cell by the sodium-potassium pump. d. \(\mathrm{Cl}^{+}\): Chloride ions, though involved in maintaining the overall balance of charges across the membrane, do not contribute significantly to the establishment of the resting potential.

Identifying the correct ion

Based on the analysis of each ion's role in establishing the resting potential, it's clear that the correct answer is: b. \(\mathrm{K}^{+}\) Potassium ions most readily leak across the neuron's membrane, helping establish the resting potential.

Key concepts

Neuron Membrane

The neuron membrane is a complex and dynamic structure that plays a crucial role in maintaining the resting potential. At its core, the membrane is composed of a lipid bilayer, which creates a barrier between the inside and outside of the neuron. This barrier is selectively permeable, meaning it allows certain ions to pass through while blocking others.

There are various protein channels within the membrane that aid in this process. For example, ion channels specific to potassium (\(\mathrm{K}^{+}\)) and sodium (\(\mathrm{Na}^{+}\)) ions regulate their movement. The unequal distribution of these ions across the neuron membrane results in a difference in electrical charge, thus creating the resting potential.

The interaction between these ion movements and the properties of the neuron membrane results in a stable resting potential, which is essential for the neuron’s ability to respond to stimuli and communicate with other neurons.

Potassium Ions

Potassium ions (\(\mathrm{K}^{+}\)) play a pivotal role in establishing the neuron's resting potential. Their movements across the neuron membrane are chiefly responsible for the electrical potential difference.

Potassium ions are more highly concentrated inside the neuron than outside. Due to this concentration gradient, \(\mathrm{K}^{+}\) ions tend to move out of the cell through potassium channels, which are more permeable compared to channels for other ions. This outflow contributes to a negative charge inside the neuron relative to the outside.

Furthermore, the selective permeability of the membrane to \(\mathrm{K}^{+}\) is why they are the main ions that leak across, contributing significantly to the resting potential. This constant movement helps maintain the potential at around -70mV, which is crucial for normal neuronal function.

Sodium-Potassium Pump

The sodium-potassium pump is an essential component of the neuron membrane that operates to maintain the resting potential. This pump is a type of active transport mechanism using energy from ATP to move ions across the membrane against their concentration gradients.

For every cycle it completes, the sodium-potassium pump actively transports three sodium ions (\(\mathrm{Na}^{+}\)) out of the cell and two potassium ions (\(\mathrm{K}^{+}\)) into the cell. This exchange is crucial in maintaining the high concentration of \(\mathrm{K}^{+}\) inside the cell and \(\mathrm{Na}^{+}\) outside the cell.

Without the sodium-potassium pump, the concentration gradients would diminish over time, leading to the loss of the resting potential. Its active transport role ensures that the neuron remains ready to fire action potentials, maintaining the delicate balance necessary for nerve impulse transmission.