Lecture 3: Neuron Electrical Properties and Resting Potential

100 vocabulary flashcards covering the resting potential, action potential, membrane dynamics, and historical experiments of Hodgkins and Huxley from PSYC2200 Lecture 3.

Hodgkins and Huxley

English scientists who published landmark neurophysiology experiments in the 1950s studying neuron electrical activity and won the Nobel Prize in 1963.

1963 Nobel Prize

The Nobel Prize awarded to Hodgkins and Huxley for demonstrating the relationship between electrical activity and neuronal function.

Squid Giant Axon

A specialized axon running the length of a squid that is exceptionally large, measuring approximately $1\text{ mm}$ in diameter, used to study neuronal electrical properties.

Model Organism

An animal species chosen for study because its specific adaptations make it uniquely suited to answer a research question.

Conduction Velocity

The speed at which an electrical signal travels down the length of an axon.

Cross-Sectional Area

The interior diameter or gauge of an axon, which is directly proportional to signal conduction speed.

Oligodendro Sites

Glial cells in the central nervous system that wrap around vertebrate axons to provide myelin insulation.

Myelin

An insulating wrapping around vertebrate axons that accelerates the speed of electrical impulse transmission down the axon.

Invertebrate Axon Adaptation

The evolution of giant axons with large diameters to increase message conduction speed in organisms lacking substantial myelin.

Jet Propulsion Mechanism

An escape mechanism in squids activated by the giant axon when the squid is touched on its nose.

Principle of Electrical Charges

The fundamental electrical rule stating that opposite charges attract one another and like charges repel.

Electrical Disturbance

A change in the distribution of positive and negative charges across two locations in the brain or neuron.

Microelectrodes

Extremely small wire electrodes designed to record localized electrical activity inside and outside an axon.

Number of Electrodes Needed

Two electrodes, necessary to record and compare the relative electrical charge difference between two points.

Size of Squid Giant Axon

Approximately $1\text{ mm}$ in diameter, which is giant compared to human axons.

Amplifier

A custom-built device using telephone tubes created by Hodgkins and Huxley to boost tiny electrical signals so they could be registered.

Oscilloscope

A measuring box device with a display screen used by Hodgkins and Huxley to register electrical oscillations and voltage directions.

Cathode Ray TV Technology

Display technology using a beam of light moving across a screen, deflecting upward for positive voltage changes and downward for negative voltage changes.

Experiment #1 (Hodgkins & Huxley)

Control experiment where both electrodes were placed outside the axon, detecting zero electrical potential difference.

Experiment #2 (Hodgkins & Huxley)

Passive recording experiment placing one electrode inside and one outside the axon, revealing a resting potential of about $-70\text{ mV}$.

Resting Potential

The steady negative membrane potential of $-70\text{ mV}$ detected inside an axon relative to the outside when at rest.

-70 Millivolts

The measured baseline electrical charge difference across a resting neuron membrane, written as $-70\text{ mV}$.

Experiment #3 (Hodgkins & Huxley)

Stimulation attempt where current sent through the giant axon caused it to jump, knocking into and destroying the amplifier and oscilloscope.

Experiment #4 (Hodgkins & Huxley)

Electrical stimulation experiment showing the full chain of events during an action potential, spiking positive and returning to baseline.

Action Potential

The rapid, standard sequence of electrical changes occurring across a neuron membrane when stimulated with electricity.

Synaptic Conduction

The process by which an electrical signal at the end of an axon is transmitted to another nerve cell across a synapse.

Chemical Equilibrium

A state achieved when chemical molecules become evenly distributed across an available space over time.

Diffusion

The net movement of chemical molecules from an area of higher concentration to lower concentration until balanced.

Chanel #5 Perfume Example

An analogy illustrating diffusion, where perfume molecules escape an open bottle and disperse across a room until evenly distributed.

Chemical Gradient

A change or difference in the concentration of a chemical substance over a given area or space.

Electrical Equilibrium

A balanced state accounting for both uniform molecular spacing and equal distribution of positive and negative charges.

Battery Example

An illustration of an electrical gradient created by separating positive and negative charges to power a component like a light.

Diode

A semiconductor indicator forming part of a closed circuit through which electric current moves.

Dead Battery

A state reached when charge distribution achieves exact equilibrium, leaving no electrical force to drive current.

Sodium Chloride

Table salt ($NaCl$), which ionizes into positively charged sodium ions and negatively charged chloride ions when dissolved in water.

Ionized

The state where a chemical compound breaks apart into separate positively and negatively charged ions in liquid.

Selectively Permeable Membrane

A barrier containing small pores that allows small molecules or ions to cross while blocking larger ones.

Relative Size of Sodium vs Chloride

Sodium ions are small enough to pass through membrane pores, whereas chloride ions are too large to cross.

Intracellular Proteins

Large, mostly negatively charged molecules trapped inside the axon that cannot pass through the membrane, contributing to internal negativity.

Resting Sodium ($Na^+$) Distribution

Positively charged sodium ions are preferentially concentrated on the outside of the axon membrane when at rest.

Resting Potassium ($K^+$) Distribution

Positively charged potassium ions are preferentially concentrated on the inside of the axon membrane when at rest.

Symbol for Potassium

The chemical symbol $K$ (or $K^+$ for potassium ion).

Symbol for Sodium

The chemical symbol $Na$ (or $Na^+$ for sodium ion).

Resting Chloride ($Cl^-$) Distribution

Negatively charged chloride ions that maintain a differential distribution across the cell membrane at rest.

Phospholipid Bilayer

The double-layer structure of jellyfish-like lipid molecules forming the plasma membrane of an axon.

Ion Channels

Protein tubes or pores embedded in the phospholipid bilayer that selectively allow ions to pass through the cell membrane.

Sodium Potassium Pump

A membrane transport mechanism that actively pumps 3 sodium ions out of the cell and 2 potassium ions into the cell.

Sodium Pump Movement

Transports 3 positive sodium ions ($Na^+$) out of the axon during each operational cycle.

Potassium Pump Movement

Transports 2 positive potassium ions ($K^+$) into the axon during each operational cycle.

Cause of Negative Resting Potential

Lower positivity inside the cell relative to outside, caused by pumping out 3 positive sodiums for every 2 positive potassiums brought in.

ATP (Adenosine Triphosphate)

The cell's energy molecule that powers the sodium potassium pump against concentration gradients.

ADP (Adenosine Diphosphate)

The molecule formed when ATP loses one phosphate group to release energy for the sodium potassium pump.

Phosphate Bond Energy

The energy stored in phosphate-phosphate bonds released when ATP breaks down into ADP.

Weight of Human Brain

Approximately $3\text{ lbs}$.

Brain Energy Percentage

The brain consumes $20\text{\%}$ of the human body's total energy needs.

Majority Use of Brain Energy

The majority of the brain's $20\text{\%}$ energy share goes directly to powering the sodium potassium pump.

Baseline Voltage Reading

A $0\text{ mV}$ difference measured when both recording microelectrodes are placed in the same fluid medium.

Positive Electrical Change

An upward deflection of the cathode ray light beam on an oscilloscope screen.

Negative Electrical Change

A downward deflection of the cathode ray light beam on an oscilloscope screen.

Electrode #1 Location in Exp 2

Inserted into the center of the squid giant axon.

Electrode #2 Location in Exp 2

Placed outside the squid giant axon.

Passive Recording

Monitoring electrical baseline voltage differences without delivering external electrical stimulation.

Potential Difference Value at Rest

$-70\text{ mV}$ across the membrane when the cell is hanging out and not active.

Nobel Prize Discovery Significance

Hodgkins and Huxley were the first to describe and mechanically explain the exact electrical steps occurring in a neuron.

Rebuilding Lab Equipment

The necessity for Hodgkins and Huxley to rebuild their custom amplifier and oscilloscope after the squid giant axon destroyed them in Experiment #3.

Resting Membrane Potential Value

$-70\text{ mV}$, indicating higher positivity outside the axon relative to the inside.

Synapsed End of Axon

The terminal end of the axon where signals transition from electrical potentials to synaptic conduction.

Concentration Gradient

A continuous change in the density of solute particles over a distance within a solution or space.

Kool-Aid Example

An illustration showing how concentrated powder mix dissolves and spreads throughout water until chemical equilibrium is reached.

Equilibrium in Fluid Salt

The uniform distribution of dissolved sodium and chloride ions throughout a volume of water.

Partitioned Vessel Experiment

A demonstration showing that impermeable partitions prevent dissolved ions from moving to balanced equilibrium across water.

Charge Attraction Rule

Opposite electrical charges ($+\text{ and }-$) attract, while identical electrical charges ($+\text{ and }+, -\text{ and }-$) repel.

Dual Forces on Molecules

The simultaneous combination of chemical concentration forces and electrical charge forces governing ion movement.

Plasma Membrane

An alternate term for the semi-permeable cell membrane surrounding an axon.

Untapped Energy Source

An unbalanced chemical or electrical gradient across a membrane that acts like stored battery power.

Axon

The long fiber projection of a neuron that conducts electrical impulses away from the cell body.

Wires

Simple metallic conductors that make up recording electrodes.

Signal Boosting Purpose

Amplifying microscopic electrical voltage changes in neurons so they are large enough to be registered visually.

Amazon Amplifiers

Reference made by the instructor noting that commercially pre-made amplifiers could not be bought in the 1940s and 1950s.

Telephone Tube Amplifiers

Vacuum tube electronics adapted from early telephone systems to construct custom signal amplifiers.

Oscillation

A rhythmic back-and-forth or up-and-down movement of electrical voltage.

Graph X-Axis

The horizontal axis on neuron electrical recordings representing time.

Graph Y-Axis

The vertical axis on neuron electrical recordings representing voltage in millivolts.

Unit of Membrane Potential

Millivolts ($\text{mV}$).

Initial Dip in Voltage

The sudden negative deflection to $-70\text{ mV}$ observed when an electrode penetrates the axon interior.

Positive Overshoot

The high point of an action potential spike where electrical potential swings past $0\text{ mV}$ into positive values.

Undershoot Phase

The brief hyperpolarizing dip where voltage drops below $-70\text{ mV}$ before recovering.

Restabilization Phase

The return of the neuronal membrane potential back to its stable $-70\text{ mV}$ baseline state.

Three Parts of Neuron Electrical Study

Understanding resting membrane potential, action potential, and synaptic conduction.

Perfume Bottle Cork

A physical barrier preventing perfume molecules from escaping into the surrounding room air.

Time Lag in Diffusion

The time delay between opening a perfume bottle and distant individuals smelling the dispersed molecules.

Equal Air Distribution State

The final outcome of diffusion where identical air sample volumes from anywhere in a room contain equal amounts of perfume particles.

Circuit Light Indicator

A bulb in a battery circuit that stays illuminated while an electrical charge gradient drives current.

Block of Salt Dissolution

The process where solid table salt in water breaks apart into separate, moving sodium and chloride ions.

Small Holes in Membrane Partition

Selective pores that permit tiny sodium ions to cross while trapping larger chloride ions on one side.

Balanced Gradient Trade-off

The equilibrium state where chemical concentration and electrical attraction forces reach an optimal balance.

Yellow Ions in Slide Diagram

Potassium ($K^+$) ions shown inside the cell membrane at rest.

Orange Hexagon Ions in Slide Diagram

Sodium ($Na^+$) ions shown outside the cell membrane at rest.

Phospholipid Jellyfish Appearance

Visual description of the lipid molecules forming the plasma membrane bilayer.

Energy-Consuming Brain Function

Continually burning ATP to pump ions against natural gradients and maintain an uneven resting potential.