Action Potential vs. Resting Potential

Attribute	Action Potential	Resting Potential
Definition	The rapid change in electrical potential that occurs across the cell membrane of a neuron or muscle cell during the transmission of a nerve impulse or contraction of a muscle.	The steady membrane potential of a neuron or muscle cell when it is not transmitting a nerve impulse or contracting.
Membrane Potential	Depolarized state with a positive potential difference compared to the outside of the cell.	Polarized state with a negative potential difference compared to the outside of the cell.
Ion Channels	Voltage-gated sodium (Na+) channels and voltage-gated potassium (K+) channels play a crucial role.	Leak channels and sodium-potassium (Na+/K+) pumps maintain the resting potential.
Threshold	Must reach a certain threshold to trigger an action potential.	No specific threshold required for the resting potential.
Propagation	Action potentials propagate along the axon in an all-or-nothing manner.	Resting potential does not propagate.
Duration	Short-lived, typically lasting a few milliseconds.	Long-lasting, maintained as long as the cell is at rest.
Role	Transmits signals between neurons and initiates muscle contractions.	Prepares the neuron for the transmission of signals and maintains cell homeostasis.

Introduction

The nervous system is a complex network of cells that allows us to perceive and respond to the world around us. At the core of this system are neurons, specialized cells that transmit electrical signals called nerve impulses or action potentials. These action potentials are crucial for communication between neurons and the overall functioning of the nervous system. However, before we delve into the attributes of action potential, it is important to understand its counterpart, the resting potential.

Resting Potential

Resting potential refers to the electrical charge across the membrane of a neuron when it is not actively transmitting signals. In this state, the neuron is said to be polarized, with a negative charge inside the cell compared to the outside. The resting potential is typically around -70 millivolts (mV) and is maintained by the selective permeability of the neuron's membrane to different ions, such as sodium (Na+), potassium (K+), and chloride (Cl-).

One of the key factors contributing to the resting potential is the sodium-potassium pump, a protein complex that actively transports three sodium ions out of the cell for every two potassium ions it brings in. This process helps maintain the concentration gradients of these ions, which are essential for generating action potentials. Additionally, the neuron's membrane is selectively permeable to potassium ions, allowing them to diffuse out of the cell more easily than sodium ions, further contributing to the negative charge inside the cell.

Another important aspect of resting potential is the presence of ion channels, which are proteins embedded in the neuron's membrane. These channels allow the passive movement of ions across the membrane, contributing to the overall electrical charge. Specifically, leak channels, which are always open, play a significant role in maintaining the resting potential by allowing the slow leakage of potassium ions out of the cell.

Overall, the resting potential is a stable state that prepares the neuron for the transmission of electrical signals. It provides a baseline from which action potentials can be generated and ensures that the neuron is ready to respond to stimuli.

Action Potential

Action potential, also known as a nerve impulse, is a rapid and transient change in the electrical potential of a neuron. It occurs when the neuron is stimulated above a certain threshold, triggering a series of events that result in the depolarization and subsequent repolarization of the cell membrane. This electrical signal allows for the transmission of information along the neuron and between neurons.

When a neuron receives a strong enough stimulus, it causes the opening of voltage-gated sodium channels in the membrane. This allows an influx of sodium ions into the cell, rapidly reversing the electrical charge from negative to positive. This phase is known as depolarization and is the key characteristic of an action potential. The depolarization spreads along the neuron's membrane, creating a wave-like effect.

Following depolarization, the neuron enters a refractory period, during which it is temporarily unable to generate another action potential. This period allows the neuron to reset and ensures that action potentials propagate in one direction, preventing backward transmission. During the refractory period, voltage-gated potassium channels open, allowing potassium ions to leave the cell. This repolarization phase restores the negative charge inside the neuron, bringing it back to its resting potential.

It is important to note that action potentials are all-or-nothing events. Once the threshold is reached, the action potential is generated with a consistent magnitude and duration, regardless of the strength of the initial stimulus. This property ensures the reliability and efficiency of signal transmission in the nervous system.

In summary, action potentials are rapid and transient changes in the electrical potential of a neuron, allowing for the transmission of information. They are characterized by depolarization, followed by a refractory period and repolarization, and are essential for the functioning of the nervous system.

Comparison of Attributes

While resting potential and action potential are distinct states of a neuron, they are interconnected and rely on each other for proper functioning. Let's compare some of their key attributes:

1. Electrical Charge

Resting potential is characterized by a negative charge inside the neuron, typically around -70 mV. In contrast, action potential involves a rapid change in the electrical charge, with depolarization causing a reversal from negative to positive, followed by repolarization to restore the negative charge.

2. Magnitude and Duration

Resting potential is a relatively stable state, maintaining a consistent negative charge. In contrast, action potentials have a consistent magnitude and duration once the threshold is reached, regardless of the strength of the initial stimulus. This property ensures reliable signal transmission.

3. Initiation

Resting potential is the baseline state of a neuron, maintained by the selective permeability of the membrane and the activity of ion channels. Action potentials, on the other hand, are initiated by a strong enough stimulus that reaches the threshold, causing the opening of voltage-gated sodium channels and subsequent depolarization.

4. Directionality

Resting potential does not have a specific directionality, as it represents the baseline state of the neuron. In contrast, action potentials propagate in one direction along the neuron's membrane, ensuring the efficient transmission of signals.

5. Role in Communication

Resting potential provides the foundation for action potentials and allows neurons to be ready for signal transmission. Action potentials, on the other hand, are the means by which neurons communicate with each other and transmit information throughout the nervous system.

Conclusion

Resting potential and action potential are two essential states of a neuron that work together to enable the transmission of electrical signals in the nervous system. Resting potential provides the baseline charge and prepares the neuron for action potentials, while action potentials allow for the rapid and reliable transmission of information. Understanding the attributes of both states is crucial for comprehending the intricate workings of the nervous system and how neurons communicate with each other.