Electrochemical Gradient

Electrochemical Gradient

electrical & chemical components- (see notes on transportation)

Electrical Gradient

inside negative at rest…. outside positive (electrical gradients) - more potassium inside, more sodium (& calcium and chloride) on outside (chemical gradients)

Electrical Potential

difference in charge on inside and outside of cell.

Chemical Gradient

difference in concentration of ions inside vs outside of a cell - at rest more Sodium and Chloride outside and more Potassium inside

Current

influx or efflux of ions

Ion

an atom or molecule with a positive or negative charge.

Cation

ion with a positive charge- If a neutral atom or molecule loses and electron with it’s negative charge it becomes positive - like Na+ (Sodium) or K+ (Potassium), Ca++ (Calcium) and Mg++ (Magnesium) have lost 2 electrons so have a plus 2 charge - if a cation enters a cell (influx) the cell becomes more positive inside- if a cation leaves a cell (efflux) the cell becomes more negative inside

Anion

ion with a negative charge so it will have an extra electron ( or more) - Cl is an important example - if it floods into a cell, it makes the cell more negative - if it leaves the cell, it becomes more positive

End Plate Potential

the difference between the “charge” at the Motor End Plate inside the cell compared to the outside of the cell - together the chemical + electrical gradients = electrochemical gradient

The Resting Cell

has more Na+ outside, more K+ inside and the cell is positive on the outside and negative on the inside - so if Na+ channel opens, Na+ floods (diffuses) in to depolarize the cell and must be pumped back out. - If K+ channel opens, K+ floods (diffuses) out to repolarize the cell and must be pumped back in

Sodium - Potassium- ATPase Pump (Na+ - K+ - ATPase)= The Sodium Pump

pumps 3 Na+ back out of cell and pumps 2 K+ back in cell - returning the electrochemical gradient to the resting state - So the resting cell is polar (polar for charge and polar for Na+ and K+) - what happens to the inside of the cell if K+, Na +, or Cl is pumped IN or OUT

Action Potential (AP)

from axon hillock to terminal- if the local potential is strong enough ( stimulus is strong enough), enough Positive sodium enters to bring the cell to Threshold - the point-of-no-return and an action potential (AP) is generated

Stages of Action Potentials (AP’s)

1. Resting State

more sodium outside, more potassium inside- and negative inside, positive outside - so the resting cell is Polarized -Action Potential

2. Depolarization

sodium influx so inside Pos-Pos on inside and outside so the cell membrane is now Depolarized

3. Repolarization

potassium efflux so inside becomes negative again but now the chemical gradient is all messed up

Hyperpolarization

- too much potassium goes out so more negative than normal resting cell

The Sodium Pump

will restore the chemical gradient and help keep inside negative because, 3”+” Na’s out for every 2 “+” K’s in