Change in Membrane Potential: Videos & Practice Problems

Membrane potential changes are crucial for neural communication, involving resting membrane potential at -70 millivolts. Neurons can undergo depolarization, where the inside becomes more positive, and repolarization, returning to resting potential. Hyperpolarization occurs when the membrane potential dips below -70 millivolts. Understanding these terms—polarized, depolarization, repolarization, and hyperpolarization—facilitates comprehension of graded and action potentials, essential for neuronal signaling and overall nervous system function.

Change in Membrane Potential

Understanding changes in membrane potential is crucial for grasping how neurons communicate. Initially, neurons exist in a state known as resting membrane potential, which is typically around -70 millivolts, indicating that the inside of the neuron is negatively charged compared to the outside. This state is referred to as being polarized.

When a neuron receives a stimulus, it can undergo a process called depolarization, where the membrane potential becomes less negative, moving towards a more positive value. This is often described as a temporary decrease in membrane potential, as the inside of the neuron becomes more positive. Following depolarization, the neuron will eventually return to its resting state through a process called repolarization, where the membrane potential decreases back towards -70 millivolts, restoring the negative charge inside the neuron.

However, during repolarization, a neuron may sometimes become overly negative, resulting in a state known as hyperpolarization. This occurs when the membrane potential dips below the resting level, indicating an excess of negativity. Hyperpolarization can be thought of as a temporary increase in membrane potential, where the inside of the neuron becomes more negative than its resting state.

To summarize, the key terms related to membrane potential changes include:

• Polarized: Resting state at -70 millivolts.
• Depolarization: Membrane potential becomes more positive.
• Repolarization: Membrane potential returns to resting state.
• Hyperpolarization: Membrane potential becomes more negative than resting state.

Familiarity with these concepts will enhance your understanding of neural communication, making it easier to follow discussions about graded and action potentials in future studies.

Change in Membrane Potential Example 1

In the study of neuronal activity, understanding the changes in membrane potential is crucial. The resting potential of a neuron is typically around -70 millivolts, a state known as polarization. This indicates that the neuron is at rest and ready to transmit signals.

As the neuron becomes activated, the membrane potential begins to increase, moving towards a more positive value. This process is referred to as depolarization. During depolarization, the influx of sodium ions causes the interior of the neuron to become less negative, leading to the generation of an action potential if the threshold is reached.

Following depolarization, the neuron must return to its resting state, which is achieved through repolarization. This phase involves the outflow of potassium ions, which helps to bring the membrane potential back down towards the resting level of -70 millivolts.

However, in some cases, the membrane potential can overshoot the resting level, resulting in a state known as hyperpolarization. This occurs when the membrane potential becomes more negative than the resting potential, briefly exceeding -70 millivolts. The term "hyper" indicates an excess, reflecting the neuron’s temporary state of being overly negative.

In summary, the sequence of events in neuronal membrane potential includes polarization at resting potential, depolarization as the neuron becomes more positive, repolarization as it returns to resting potential, and hyperpolarization when it dips below resting potential. Understanding these phases is essential for grasping how neurons communicate and transmit signals effectively.

A neuron's membrane potential goes from -90 mV to -10 mV. Which of the following terms describes this change?

• A. Hyperpolarization.
• B. Polarization.
• C. Depolarization.
• D. Repolarization.

Answer: (C)

Here’s what students ask on this topic:

What is the resting membrane potential and why is it important?

The resting membrane potential is the electrical potential difference across the neuronal membrane when the neuron is not actively sending a signal. It is typically around -70 millivolts (mV). This negative charge inside the neuron is crucial because it sets the stage for the generation and propagation of electrical signals, such as action potentials. The resting membrane potential is maintained by ion channels and pumps, particularly the sodium-potassium pump, which helps to keep the inside of the neuron negatively charged relative to the outside. Understanding this concept is fundamental for grasping how neurons communicate and process information.

What happens during depolarization in a neuron?

During depolarization, the inside of the neuron's membrane becomes more positive compared to the resting membrane potential. This occurs when sodium (Na⁺) channels open, allowing Na⁺ ions to flow into the cell. As a result, the membrane potential moves closer to zero and can even become positive. Depolarization is a critical step in the generation of an action potential, which is the electrical signal that neurons use to communicate. This process is essential for the transmission of information within the nervous system.

What is repolarization and how does it occur?

Repolarization is the process by which the neuron's membrane potential returns to its resting state after depolarization. This occurs when potassium (K⁺) channels open, allowing K⁺ ions to flow out of the cell. As K⁺ exits, the inside of the membrane becomes more negative, moving back toward the resting membrane potential of -70 millivolts (mV). Repolarization is crucial for resetting the neuron's membrane potential, allowing it to be ready for the next action potential.

What is hyperpolarization and what causes it?

Hyperpolarization is when the membrane potential becomes more negative than the resting membrane potential, typically dipping below -70 millivolts (mV). This occurs when there is an excessive outflow of potassium (K⁺) ions or an influx of chloride (Cl^-) ions. Hyperpolarization makes it more difficult for the neuron to reach the threshold needed to generate an action potential, thus temporarily inhibiting neuronal activity. This process is important for regulating the excitability of neurons and ensuring proper neural function.

How do graded potentials differ from action potentials?

Graded potentials and action potentials are two types of electrical signals in neurons. Graded potentials are changes in membrane potential that vary in size and are not all-or-nothing. They occur in the dendrites and cell body and can be either depolarizing or hyperpolarizing. In contrast, action potentials are all-or-nothing events that occur when the membrane potential reaches a certain threshold, typically around -55 millivolts (mV). Action potentials are generated at the axon hillock and propagate along the axon without decreasing in amplitude, ensuring reliable signal transmission over long distances.