axon podcats part 1

Understanding Gradients

• Definition of Gradient: A gradient exists when there is a disparity between two levels or points, which indicates a difference or change in a particular variable.

• Degree of Disparity: The greater the difference between the two points, the stronger the gradient. Comparing an incline, such as a hill versus a mountain, illustrates varying gradients.

Types of Gradients

Electrical Gradient

• Also known as electrostatic pressure or electrostatic force.

• Charged particles, like ions, experience forces due to their electrical charges: like charges repel each other, while opposite charges attract.

• Behavior of Charges: Opposite charges line up along membranes, creating regions of high and low potential, impacting ion movement.

Concentration Gradient

• Defined by the movement of particles from an area of high concentration to an area of low concentration until equilibrium is reached.

• Example: In a beaker with colored fluids, molecules will naturally move to equalize concentration, yielding a mixed color (e.g., green).

• This movement occurs in situ, meaning in the natural, undisturbed condition.

Action Potential Overview

• Ion Movement: Understanding gradients is crucial to understanding how ions such as sodium and potassium move during an action potential.

• Axon Structure: Key areas include the axon hillock and the initial segment, where action potentials are measured and start.

• Charged Particles: Positive charges moving into the axon hillock influence other ions, particularly affecting potassium (K+) and sodium (Na+) ions.

Function of Ions in Action Potential

• Anions: Large negatively charged molecules trapped in the axon, contributing to the negative internal charge.

• Cations: Potassium (K+) and sodium (Na+) are positive ions that respond to the gradients, moving according to the electrical and concentration gradients.

Ion Dynamics in Response to Charges

• When a wave of positive charges reaches the axon hillock, potassium ions may exit the axon or move along it due to repulsive forces.

• This creates a chain reaction, as movements influence neighboring ions, ultimately depolarizing sections of the axon and propagating the action potential along the length of the axon.

Action Potential Measurement

• Resting Membrane Potential: The potential difference between the extracellular and intracellular environments is observed, typically around -70 mV for neurons.

• Events of hyperpolarization (more negative) or depolarization (less negative) occur depending on ion movements.

The Role of Postsynaptic Potentials

• Inhibitory Postsynaptic Potential: Negative charges entering the axon hillock can hyperpolarize the initial segment, blocking action potential formation.

• Excitatory Postsynaptic Potential: Positive influences on the axon hillock can lead to depolarization, increasing the potential for action potentials.

Period of Latent Addition

• This refers to the phase where changes in membrane potential occur due to the influence of charges in the axon hillock and initial segment.

• The magnitude of depolarization varies; however, a certain threshold is required for an action potential to occur, which is probabilistic in nature.

• The initial segment is critical since it is where action potentials are generated and will propagate down the axon rapidly, following an all-or-none principle.