w-1 ion gradients and membrane potential Flashcards
How can we measure neuron signals?
- Recording electrodes measure the difference in electrical potential (created by the
charge of ions) relative to reference electrode - Used to measure the flux/change of cumulative ion charge near or inside a neuron
Define stimulating/recording electrical signals in neurons
- Stimulating electrode is used to inject current (charge) into the neuron
- Changes in membrane potential are measured with the recording electrode
Membrane potential in neurons:
Electrical potential (membrane potential or Vm)
caused by differences in ion concentration across
the cell membrane
How are ion gradients established?
- Ion gradients are maintained by active transport proteins that move ions against their concentration gradients using ATP.
- Key Players:
- Na⁺/K⁺ ATPase (Sodium-Potassium Pump): Pumps 3 Na⁺ out, 2 K⁺ in, creating high Na⁺ outside and high K⁺ inside.
- Calcium Pumps (Ca²⁺ ATPase): Actively remove Ca²⁺ from the cytoplasm, keeping intracellular Ca²⁺ levels low.
- Cl⁻ Transporters: Help regulate chloride ion distribution across the membrane.
How do ion gradients create membrane potential?
- The membrane potential is the electrical charge difference across the neuronal membrane, created by ion gradients and selective permeability.
- Resting Membrane Potential (RMP) (~ -70 mV):
- More Na⁺ outside, K⁺ inside (due to Na⁺/K⁺ pump).
- K⁺ leak channels allow some K⁺ to exit, making the inside more negative.
- Large anionic proteins inside the neuron contribute to the negative charge.
- Key Concepts:
- Selective permeability: More permeable to K⁺ than Na⁺, causing net negative charge inside.
- Electrochemical gradient: Balances diffusion forces and electrical attraction/repulsion of ions.
- Nernst Equation & Goldman Equation help calculate membrane potential based on ion distribution.
__________ __________ and ____ ________ enable
ion movements across cell membranes
Active transporters and ion channels
the flow/flux of ions across the membrane (through ion channels)…
establisheds an opposing electrical gradient (membrane potential)
the movement of ions with the chemical gradient establishes an…
electrical potential (gradient) in the immidiete vicinity of the cell membrane that balances the chemical gradient
the nerst equation:
lets you figure out what the equilibrium potential is for each ionic species, which is necessary for predicting the flow of current through an ion channel under varying conditions
membrane potential influences ion fluxes:
- changing the membrane potential changes the flow of ions
- can drive the flux against (up) the gradient
Why don’t ions diffuse freely across the cell membrane?
- The lipid bilayer of the cell membrane is hydrophobic, preventing ion movement.
- Ions require ion channels or transporters to cross the membrane.
- Selective permeability ensures controlled ion movement, essential for neural signaling.
How are ion gradients formed and maintained?
Active transporters:
Na⁺/K⁺ ATPase – Moves 3 Na⁺ out, 2 K⁺ in (requires ATP).
Ca²⁺ pumps – Maintain low intracellular calcium.
Ion channels:
K⁺ leak channels – Allow some passive K⁺ movement.
Voltage-gated channels – Open in response to signals, helping regulate ion flow.
These mechanisms establish the resting membrane potential (~ -70mV).
What is the equilibrium potential of an ion and how can it be calculated?
Why does the net charge of all the ions in the cytoplasm/extracellular space differ from the charge difference across the membrane?
Why doesn’t the measured resting membrane potential of a neuronal membrane perfectly match the slope of the Nernst equation for potassium?
The Nernst equation considers only one ion (K⁺), but resting membrane potential (Vm) is influenced by multiple ions (Na⁺, Cl⁻, K⁺, etc.).
Na⁺ leak channels allow some Na⁺ entry, slightly depolarizing Vm above E_K.
The Goldman-Hodgkin-Katz equation is more accurate because it accounts for multiple ion contributions.
