Ion Gradients and Membrane Potential

What are recording electrodes for…

they are used to measure the difference in electrical potential (created by the charge of ions) relative to the reference electrode

In other terms, they are used to measure the flux/change of the cumulative ion charge near or inside a neuron (this is a method to measure neuron signals)

The two electrodes involved in studying the electrical signals of neurons

1. Stimulating Electrode is used to inject current (Charge) into the neuron

2. The Recording electrode is used to measure the changes in the membrane potential that occur due to the actions of the stimulating electrode

What is waters of hydration

This is the close association of H20 Molecules with ions that prevents diffusion of ions across the hydrophobic regions of the phospholipid bilayer

Traits of Active Transporters

Traits

• Actively Move selected ions against their concentration gradient

• They can also be used to create ion concentration gradients

Traits of Ion channels

Traits

• Allows for ions to diffuse down their concentration gradient

• They are selectively permeable to certain ions

• (exhibit membrane selectivity)

What are some common ion gradients for the mammalian Cell (SODIUM)

Sodium Concentration is typically higher on the extracellular side of the membrane, as compared to the inner side of the cell

What are some common ion gradients for the mammalian cell (POTASSIUM)

Neurons typically have a much higher intracellular potassium concentration as compared to of their extracellular concentration

What are some common ion gradients for the mammalian cell (Chloride)

Neurons typically have a much higher concentration of chloride on the extracellular side of the membrane as compared to that of their intracellular

What establishes an opposing electrical gradient

This is formed by the flow/flux of ions across the membrane (through ion channels)

Electricla potential always opposes the membrane potential that is created by the flow of ions

The flow of ions down the concentration gradient establishes a local charge difference directly adjacent to the membrane. An opposing electrical gradient will then be charged, to counteract the problem.

The movement of ions with the chemical gradient establishes an electrical potential (gradient) in the immediate vicinity of the cell membrane that balances the chemical gradient

in other words it is seen as a simple balancing mechanism for the chemical gradient to return to its balanced state, by using counteract sources from the movement of ions from one area to another.

What is the Nernst Equation and what is it used for

This equation is used to 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

• It is used to calculate the electrochemical equilibrium

Formula: Ek = RT/zF * ln ([K]out / [K]in)

Formula = 58 log 10 ([k]out / [k]in)

What are some common potential values for RT/zF

at room temp, the RT/zF is 58 mV

at around 37 C, the RT/zf is 61.5 mV

What is the effect of ion gradient on equilibrium potential

As assumed changing the ion gradient will as assumed change the membrane potential

What is the effect of changing the membrane potential

This will result in a change in the flow of ions

if the absolute value of the membrane potential produced from the battery, or specific device, it can result in the driving of flux against or up the concentration gradient, go against or in the opposite direction.

what are the trends of mV values and what will they cause to the gradient of a specific chemical?

Example:

• If [Na']out = 10mM and [Na]in = 1mm

• E_Na = 58log10 (10mM / 1mM) = 58 mV

• Any mV value below 58 will drive the Na+ with the gradient, in the normal direction

• Any mV value above 58 will drive the Na+ against the gradient

The opposite is true for negative values

• Any value below negative 58 in K, wil cause it to drive against the gradient

• Any value higher than negative 58 in K, will cause it to drive with the gradient

What is interesting, and or fascinating about the Giant Squid Axon

The Giant Squid has a very famous axon that is very very very wide, as compared to a regular axon that has myelin to increase conduction-velocity. So this wide diameter enables or makes up for some conduction velocity.

• This enables a fast retreat from prey