What is a gradient?

A change in value or quantity

What is a chemical gradient?

Chemical gradient is a gradient created when high concentration of particles is separated from an area of low concentration.

What is the direction of particles in a chemical gradient?

Particles flow from high concentration to low concentration

What are some chemical gradients found in the cell (2 examples)?

Example 1: Extracellular fluid has high concentration of sodium (Na+), calcium (Ca2+), & chloride (Cl-) relative to cytosol.

Example 2: Intracellular fluid has high concentration of potassium (K+), phosphate (PO43-), & proteins (e- charged) relative to outside of cell.

What is the charge inside the cell?

Cytosol (liquid inside cell) is negatively charged.

What is the charge outside the cell?

Outside the cell is positively charged.

Why are ions unable to cross the cell membrane?

Ions are polar molecules; since phospholipid bilayer has non-polar region, ions cannot cross that environment

How can ions cross cell membrane?

Ions cross membrane via carrier protein.

What is an electrical gradient?

Electrical gradient is the difference in electrical charge across the cell membrane due to extracellular and intracellular concentration of ions.

What is the direction of charged particles (ions) in an electrical gradient?

Positive ions move inside of the cell (cell is negatively charged)

Negative ions move outside of the cell (outside is positively charged)

What is an ion?

An ion is a molecule or atom that is electrically charged

What is a cation?

A cation is an ion that has lost electrons, and is positively charged.

What is an anion?

An anion is an ion that has gain electrons, and is negatively charged.

What is electrochemical gradient?

Sum of chemical and electrical force (vector sum of chemical and electrical force= net movement of particles)

What is membrane potential?

The potential of the membrane to do work

What is resting membrane potential (in voltage) of the cell?

-70mV

Define equilibrium potential EM (or membrane potential)?

It is the membrane potential at which chemical gradient = electrical gradient, WITH opposing driving force

(when there is no net flux of ion: chemical gradient brings 2 molecules of sodium in the cell, electrical gradient brings 2 sodium out)

What is the ultimate condition for an ion to have an equilibrium potential?

The ion must be permeable to the cell (it must be able to cross the membrane through channels or pores)

What is the equilibrium potential of an impermeable ion (cannot diffuse through cell membrane)?

There is no equilibrium potential for impermeable ions (different from equilibrium potential=0)

Describe how sodium ion reaches its equilibrium potential and the value of EM.

Concentration of Na+ is higher outside of the cell relative to inside, thus chemical gradient moves Na+ down its gradient, into the cell

Cytosol is negatively charged, sodium ion positively charged, electrical gradient moves ion inside the cell (opposite charges attract).

Influx of Na+ makes cytosol less negative (more positive), electrical gradient repels Na+ out of the cell

Na+ has reach its equilibrium potential when membrane potential reads +65mV

Describe how potassium ion reaches its equilibrium potential and the value of EM.

Concentration of K+ is higher inside of the cell relative to the outside, thus chemical gradient moves K+ down its gradient, out of the cell

Cytosol is negatively charged, K+ is positively charged, electrical gradient moves ion inside the cell (opposite charges attract).

K+ has reach its equilibrium potential when membrane potential reads -95mV

Describe how chlorine ion reaches its equilibrium potential and the value of EM.

Concentration of Cl- is higher outside of the cell relative to the inside, thus chemical gradient moves Cl- down its gradient, into the cell

Cytosol is negatively charged, Cl- is negatively charged, electrical gradient moves ion outside of cell (same charges repel).

Cl- has reach its equilibrium potential when membrane potential reads -91mV

Describe how calcium ion reaches its equilibrium potential and the value of EM.

Concentration of Ca2+ is higher outside of the cell relative to inside, thus chemical gradient moves Na+ down its gradient, into the cell

Cytosol is negatively charged, Ca2+ is positively charged, electrical gradient moves ion inside the cell (opposite charges attract).

Influx of Ca2+ makes cytosol less negative (more positive), electrical gradient repels Ca2+ out of the cell

Ca2+ has reach its equilibrium potential has membrane potential reads +132mV

What is the Nernst Equation?

For permeable ions only, the Nernst equation predicts the equilibrium potential based on ion concentration and ion valence:

What is the valence of Na+? the valence of K+? the valence of Cl-? the valence of Ca2+?

Na+ valence: +1K+ valence: +1Cl- valence: -1Ca2+ valence: +2

What are 3 factors the magnitude of equilibrium potential depends on?

1. Permeability of ion2. Concentration gradient; greater the gradient, greater potential3. Valence of ion (z)

What is hyperkalemia?

High levels of potassium in blood.

Describe the levels of k+ in hyperkalemia?

Chemical gradient for potassium is still outward (more slowly)Electrical gradient is inward (more quickly)

Cell is more positive

What is hypokalemia?

Low levels of potassium in blood.

Describe the levels of k+ in hypokalemia?

Chemical gradient for potassium is still outward (more quickly)Electrical gradient is inward (more slowly)

Cell is more negative

What is hypernatremia?

High levels of sodium in blood.

Describe the levels of k+ in hyperkalemia?

Chemical gradient for sodium is still outward (more quickly)Electrical gradient is inward (more quickly)

Cell is more + (more excited to do work)

What is hyponatremia?

Low levels of sodium in blood.

Describe the levels of k+ in hyponatremia?

Chemical gradient for sodium is still outward (more slowly)Electrical gradient is inward (more slowly)

Cell is more negative

What is hypercalcemia?

High levels of calcium in blood.

Describe the levels of Ca2+ in hyperkalemia?

Chemical gradient for sodium is still outward (more quickly)Electrical gradient is inward (more quickly)

Cell is more positive (more excited to do work)

What is hypocalcemia?

Low levels of calcium in blood.

Describe the levels of Ca2+ in hypokalemia?

Chemical gradient for calcium is still outward (more slowly)Electrical gradient is inward (more slowly)

Cell is more negative

What is the cell charge in Hyperchloremia?

Negative

What is the cell charge in Hypochloremia?

Positive

What is the Na+/K+ ATpase pump?

Pump that drives ions against their concentration gradient.

3 Na+ ions is pump out of cell and 2 K+ ions are pump inside the cell

Why is the Na+/K+ ATpase pump electrogenic?

Pump is electrogenic because it causes chemical gradient (which causes electrical gradient) by pumping more positive ions out of cell.

What is the function of the Na+/K+ ATpase pump?

It keeps the concentration of intracellular K+ high.

If Na+/K+ ATpase pump is defective, what happens to the membrane potential?

Only a small, insignificant change would occur. K+ will still diffuse inside the membrane attracted to the negative charged cytosol, and would exit the cell via leakage channel down its concentration gradient until equilibrium potential is reached.

How does K+ influence the membrane potential? *****check with teacher

1. K+ is the ion closest to being in electrochemical equilibrium when the cell is at rest (-95mV vs -71mV)2. Cell membrane of resting neuron is more permeable to K