1-3 Action Potential

Study Notes

Resting Membrane Potential and Changes

Resting membrane potential typically ranges from -60 to -90 mV, commonly around -70 mV.
Depolarization occurs when the membrane potential becomes more positive.
Overshoot is when the membrane potential exceeds zero during depolarization.
Hyperpolarization refers to the membrane potential dropping below the resting state.
Repolarization is the process of returning to the resting state after depolarization.

Action Potential Overview

Action potential represents a rapid change in membrane potential crucial for cellular communication.
Triggered by alterations in ion permeability, especially for sodium (Na+) and potassium (K+).
Involves voltage-gated ion channels specific to sodium and potassium.

Graded Potentials

Graded potentials are small, localized changes in membrane potential initiated by ligand binding, such as neurotransmitters.
Excitatory graded potentials (e.g., sodium influx) result in depolarization.
Inhibitory graded potentials (e.g., chloride influx or potassium efflux) cause hyperpolarization.
The strength of graded potentials is proportional to the stimulus intensity, demonstrating a graded response.
Signals experience decremental decay, with strength diminishing over distance from the stimulus site.

Threshold and Action Potential Generation

Threshold potential is the membrane potential level that triggers an action potential due to graded potentials.
At threshold, voltage-gated sodium channels rapidly open, causing a sharp depolarization (upstroke).
Voltage-gated potassium channels open more slowly, facilitating potassium efflux for repolarization.

Ion Channel Dynamics

Sodium channels contain two gates: the M-gate (activation gate) and the H-gate (inactivation gate).
Sodium channels open in response to depolarization via the M-gate, then inactivate quickly through the H-gate to prevent further sodium influx.
Potassium channels open more slowly than sodium channels, allowing potassium to exit the cell, promoting repolarization.
Potassium channels remain open longer, leading to after-hyperpolarization, where the membrane potential temporarily becomes more negative.

Phases of Action Potential

Resting state is maintained by potassium leak channels.
During depolarization, voltage-gated sodium channels open, increasing membrane positivity.
Repolarization occurs when sodium channels inactivate and potassium channels open.
Hyperpolarization happens when potassium channels remain open briefly, resulting in a more negative membrane potential.
Return to resting membrane potential occurs as potassium channels close, re-establishing resting conditions.

Key Testing Concepts for Pharmacy School

Understanding ion permeability changes is critical during the action potential, specifically the roles of Na+ and K+.
Recognizing the function of voltage-gated channels in depolarization and repolarization processes is essential.
Differentiating between graded and action potentials, particularly the decremental nature of graded potentials, is important.
The inactivation of sodium channels is crucial for the action potential cycle.
Distinguishing the effects of excitatory and inhibitory neurotransmitters on membrane potential is vital for comprehending neuronal signaling.
These concepts are foundational for understanding neuron and excitable cell signaling, relevant in physiology and pharmacology studies.

Description

Test your understanding of action potentials and the various states of membrane potential. This quiz covers key definitions and concepts such as resting membrane potential, depolarization, overshoot, hyperpolarization, and repolarization. Challenge yourself to apply these concepts in neurological contexts.