Question

The most important diffusible ion in the establishment of the membrane potential is a. \(\mathrm{K}^{+}\). b. \(\mathrm{Na}^{+}\). c. \(\mathrm{Ca}^{2+}\). d. \(\mathrm{Cl}^{-}\).

Short answer

The most important diffusible ion in the establishment of the membrane potential is a. \(\mathrm{K}^+\). Potassium ions (\(\mathrm{K}^+\)) are primarily responsible for the resting membrane potential and play a significant role in cell signaling.

Step-by-step solution

Membrane potential is the difference in voltage between the inside and outside of a cell membrane, due to the uneven distribution of ions. It plays a critical role in cell signaling, such as in nerve impulses and muscle contractions. #Step 2: Role of Potassium ions (\(\mathrm{K}^+\))#

Potassium ions (\(\mathrm{K}^+\)) are responsible for the establishment of the resting membrane potential in cells. When a cell is at rest, there is a higher concentration of \(\mathrm{K}^+\) ions inside the cell than outside. These ions tend to diffuse out of the cell, leading to a negative charge inside the cell relative to the outside. This creates the resting membrane potential, which is around -70mV. #Step 3: Role of Sodium ions (\(\mathrm{Na}^+\))#

Sodium ions (\(\mathrm{Na}^+\)) are involved in the propagation of action potentials, such as in nerve cells. When an action potential is triggered, \(\mathrm{Na}^+\) ions influx into the cell, resulting in the depolarization of the cell membrane. However, they are not primarily responsible for establishing resting membrane potential. #Step 4: Role of Calcium ions (\(\mathrm{Ca}^{2+}\))#

Calcium ions (\(\mathrm{Ca}^{2+}\)) are important for many cellular processes, such as muscle contractions and neurotransmitter release. They are not the primary ions responsible for establishing resting membrane potential. #Step 5: Role of Chloride ions (\(\mathrm{Cl}^{-}\))#

Chloride ions (\(\mathrm{Cl}^{-}\)) also play a role in the maintenance of the resting membrane potential; however, their contribution is minor compared to \(\mathrm{K}^+\). In some cases, chloride ions can have an inhibitory effect on the cell membrane potential. #Step 6: Determine the most important ion#

Based on the roles of each ion, it is clear that the most important diffusible ion in the establishment of the membrane potential is Potassium ions (\(\mathrm{K}^+\)). They are primarily responsible for the resting membrane potential and play a significant role in cell signaling. #Answer# a. \(\mathrm{K}^+\).

Key concepts

Potassium Ions

Potassium ions, denoted as \(\mathrm{K}^+\), are vital in maintaining the membrane potential in cells. When dealing with membrane potential, we focus on how ions move across the cell membrane. Potassium ions have an essential role because they are heavily concentrated inside the cell compared to outside.
This imbalance drives the process of diffusion where \(\mathrm{K}^+\) ions move out of the cell through potassium channels. Since positive ions are leaving, the inside of the cell becomes more negatively charged relative to the outside.
This process is crucial for cells, especially in nerves and muscles, where a stable membrane potential is needed for signaling.

• Potassium ions help establish a negative charge inside the cell.
• They diffuse out because they are more concentrated inside the cell than outside.
• This movement of ions is key to maintaining the resting membrane potential.

This makes potassium ions the most influential in establishing the resting membrane potential, creating the foundation for further electrical activity in cells.

Resting Membrane Potential

The resting membrane potential is the voltage across the cell membrane when the cell is idle, not sending any signals. It is usually about -70mV, meaning the inside of the cell is negatively charged compared to the outside.
This voltage results from the differential distribution and movement of ions across the cell membrane primarily involving sodium (\(\mathrm{Na}^+\)) and potassium (\(\mathrm{K}^+\)) ions.
Potassium ions move out of the cell more easily than sodium ions move in, leading to a net negative charge inside. The cell's membrane is more permeable to \(\mathrm{K}^+\) ions, which contributes greatly to the resting potential.

• The membrane potential is a result of ion gradients across the cell membrane.
• It is essential for cells to maintain this potential for proper function.
• Without this resting state, cells would not be able to respond to stimuli effectively.

In summary, the resting membrane potential is crucial for the normal function of cells, allowing them to be ready to respond to changes in their environment.

Ion Distribution in Cells

In cells, ions such as \(\mathrm{K}^+\), \(\mathrm{Na}^+\), \(\mathrm{Ca}^{2+}\), and \(\mathrm{Cl}^-\) are unevenly distributed. This distribution is crucial because it affects how signals are transmitted within and between cells.
The cell membrane has specialized proteins called ion channels that help maintain different concentrations of these ions inside and outside the cell.

• Potassium ions (\(\mathrm{K}^+\)) are more concentrated inside the cell.
• Sodium ions (\(\mathrm{Na}^+\)) are more concentrated outside the cell.
• This uneven distribution creates a potential difference across the membrane.

The sodium-potassium pump, which actively transports \(\mathrm{Na}^+\) out and \(\mathrm{K}^+\) into the cell, is vital in maintaining this ion distribution. It uses ATP to exchange three \(\mathrm{Na}^+\) ions out of the cell for two \(\mathrm{K}^+\) ions into the cell, contributing to the negative resting membrane potential.
This active transport system ensures that despite passive movements of ions, cells maintain their proper function and readiness to act upon stimulation.