Problem 3 - Biology of Humans: Concepts, Applications, and Issues

Question

In a resting neuron a. potassium ions are more concentrated outside the membrane than inside. b. the inside is more negative than the outside. c. sodium ions are more concentrated inside than outside. d. action potentials are being generated.

Step-by-Step Solution

Answer

b. the inside is more negative than the outside.

Step 1: Understand the Resting Neuron

In a resting neuron, the concentration and electrical gradients of ions are crucial. Resting potential refers to when a neuron is not sending a signal.

Step 2: Examine Potassium Ion Concentration

Evaluate statement (a): 'potassium ions are more concentrated outside the membrane than inside.' This is incorrect because potassium ions are more concentrated inside the neuron.

Step 3: Examine the Electrical Gradient

Evaluate statement (b): 'the inside is more negative than the outside.' This is correct. During resting potential, the inside of the neuron is more negative relative to the outside.

Step 4: Examine Sodium Ion Concentration

Evaluate statement (c): 'sodium ions are more concentrated inside than outside.' This is incorrect because sodium ions are more concentrated outside the neuron.

Step 5: Examine Action Potentials

Evaluate statement (d): 'action potentials are being generated.' This is incorrect because action potentials are only generated when the neuron is activated, not when it is in a resting state.

Key Concepts

Potassium Ion Concentration

In a resting neuron, potassium ions play a significant role in maintaining the resting potential. Potassium ions (K+) are primarily found inside the cell. This creates what's called a concentration gradient between the inside and outside of the neuron. To put it simply, there are more potassium ions on the inside than on the outside. However, the cell membrane has potassium channels that allow a small amount of these ions to move out of the cell. This movement is one part of what maintains the electrical gradient in the cell at rest.

Electrical Gradient

The electrical gradient in a resting neuron indicates that the inside of the cell is more negative compared to the outside. Imagine this like a tiny battery, where one side is negative and the other is positive. The difference in charge across the cell membrane is known as the resting membrane potential, typically sitting around -70 millivolts (mV). This negative charge inside the neuron is mainly due to negatively charged proteins and other molecules that cannot cross the membrane, along with the movement of potassium ions.

Sodium Ion Concentration

Sodium ions (Na+) are also crucial but behave differently from potassium ions. In resting neurons, sodium ions are concentrated outside the cell. This is the opposite of potassium, where most are inside. The neuron keeps sodium ions out by using sodium-potassium pumps, which move three sodium ions out for every two potassium ions they bring in. This pump relies on energy to work properly. Keeping sodium ions outside and potassium ions inside maintains the correct balance necessary for the neuron to function.

Action Potentials

Action potentials are the electrical signals neurons use to communicate. But these do not occur when the neuron is resting. For an action potential to happen, the neuron must be stimulated to a certain level known as the threshold. When this happens, sodium channels open rapidly, allowing sodium ions to rush into the cell. This sudden influx of sodium ions changes the electrical charge inside the neuron from negative to positive, generating an action potential. Once the signal has passed, the cell quickly works to restore its resting potential by moving sodium out and potassium back in.