Membrane Potential

NEU 101: Membrane Potential Study Notes

Course Overview

  • Class Topic: Membrane Potential

  • Date: Thursday, February 13, 2025

  • Reminder to students: Understand the global structure of the class and the focus of the upcoming quadrant.

Effective Study Techniques

  • Prioritize Active/Productive Activities:

    • Teach concepts to a teddy bear, pet, or friend to reinforce understanding.

    • Use drawing, coloring, and labeling to visualize concepts.

    • Create mnemonic devices to memorize information.

    • Invent your own exam questions to anticipate potential test items.

    • Develop study guides or concept maps to organize material.

    • Engage in active self-quizzing to assess understanding.

  • Avoid Passive/Receptive Activities:

    • Merely reading books, slides, and notes is not sufficient.

Announcements & Reminders

  • Quiz 1:

    • Grades will be posted on Canvas by the next Tuesday.

    • Students can review their quiz during office hours by appointment starting next week.

    • Book an appointment on the calendar or email a TA with the subject “Quiz 1 review.”

    • “Drop-in” hours for quiz review will take place Thursdays from 3:30 to 4:30 PM.

    • Anticipate at least 48 business hours to set up a review with a TA.

    • The review of Quiz 1 will be available until Quiz 2 is graded.

  • Discussion Opportunities:

    • Open time for questions, comments, and thoughts.

Learning Outcomes

  • Upon completing this segment, students should be able to:

    • Identify sub-components of the phospholipid bilayer.

    • Recognize definitions of atoms, molecules, cations, and anions.

    • Recall the chemical symbols for Potassium (K), Sodium (Na), Chloride (Cl), and Calcium (Ca).

    • Identify relative concentrations of ions inside and outside neurons at rest.

    • Explain the term "membrane potential."

    • Explain how chemical and electrical gradients influence ion movements.

    • Define and identify Inhibitory Postsynaptic Potential (IPSP) and Excitatory Postsynaptic Potential (EPSP).

    • Recognize the function of the sodium-potassium pump, including relevant numerical data.

Membrane Potential & Action Potentials

Overview of Membrane Potential

  • Definition: The voltage difference across a cell membrane at rest due to ionic concentration differences.

  • Importance: Essential for the generation and propagation of action potentials.

Action Potentials

  • Definition: Rapid, transient changes in membrane potential that propagate along the axon of a neuron.

  • Threshold Requirement:

    • An action potential occurs if the threshold is met at the axon hillock; if not met, no action occurs.

    • Final outcome: “Fire” if threshold is met, causing the action potential to travel down the axon.

Neural Communication

  • Neurotransmitter Release:

    • Terminal buttons release neurotransmitters into the synapse, leading to either excitation or inhibition of the subsequent neuron.

Structure of the Neuronal Cell Membrane

  • Composition:

    • Made up of a phospholipid bilayer which acts as a barrier to ions.

    • Consists of hydrophilic heads and hydrophobic tails within the bilayer.

  • Functionality: Generally restricts movement of molecules, exceptions being channel proteins which facilitate ion movement when activated.

Atoms & Molecules

  • Atoms: Basic units of matter consisting of protons, neutrons, and electrons.

  • Molecules: Two or more atoms bonded together, acting as a unit.

    • Example:

    • Water (H₂O): Comprised of one Oxygen atom and two Hydrogen atoms.

Importance of Water in Neurophysiology

  • Water aids in dissolving salts into ions, illustrating its role in cellular processes.

  • Dissolution Example:

    • Shows separation of NaCl into Na⁺ and Cl⁻ ions when in water.

Ions and Their Roles

Ions Defined

  • Ions: Charged atoms or molecules.

    • Cations: Positively charged ions (e.g., Na⁺, K⁺).

    • Anions: Negatively charged ions (e.g., Cl⁻).

Ion Concentration and Equilibrium

  • Driving Forces: Movement of ions is influenced by two primary forces:

    • Chemical Gradient: Difference in concentration of ions across the membrane.

    • Electrical Gradient: Difference in charge, where opposite charges attract and like charges repel.

Transmembrane Proteins and Ion Channels

  • Function of Channel Proteins: Allow selective permeability for specific ions.

  • Types:

    • Gated channels that open/close based on stimulation (voltage-gated, ligand-gated).

Sodium-Potassium Pump

  • Functionality: Maintains resting membrane potential by pumping ions against their concentration gradient:

    • Transports 3 Na⁺ ions out of the cell and 2 K⁺ ions into the cell utilizing ATP for energy.

  • Relative Ion Concentrations at Rest:

    • Sodium (Na⁺): Higher concentration outside the cell.

    • Potassium (K⁺): Higher concentration inside the cell.

    • Calcium (Ca²⁺) and Chloride (Cl⁻) concentrations also favor the extracellular space.

Resting Neuron State

Characteristics of a Resting Neuron

  • More positive ions (Na⁺, Ca²⁺, Cl⁻) outside and negative ions (K⁺, anions) inside contribute to a net negative charge of approximately -65 mV across the membrane, known as the membrane potential.

Maintaining Resting Potential

  • Energy is expended to maintain the ion distribution.

    • Mitochondrial Involvement: Mitochondria power the sodium-potassium pumps that maintain higher K⁺ inside and higher Na⁺ outside the neuron.

Postsynaptic Potentials (PSPs)

Types of Postsynaptic Potentials

  • EPSP: Excitatory Postsynaptic Potential—causes depolarization, making the inside of the cell less negative.

  • IPSP: Inhibitory Postsynaptic Potential—causes hyperpolarization, making the inside of the cell more negative.

Signal Transmission

  • Neurotransmitter binding can lead to changes in the electrical charge of the postsynaptic neuron, influencing whether or not it will fire an action potential based on the cumulative effect of all incoming signals.