Exploring the Brain: Chapter 3

When the brain is deprived of oxygen, the mitochondria within neurons cease producing ATP. What effect would this have on the membrane potential? Why?

It would cause Na+ and K+ pumps to stop working which would allow the membrane potential to unbalanced.

At rest, what ion is the most permeable?

K+

What are the structures that regulate extracellular K+?

The brain blood barrier, astrocytes that take up extracellular K+ whenever concentrations rise.

What is the resting potential of a typical neuron?

-65mV

What would the membrane potential be if the membrane was only permeable to K+?

-80mV

What would the membrane potential be if the membran was only permeable to Na+?

62mV

What is the structure of phospholipids?

A long chain nonpolar of carbon atoms bonded to hydrogen atoms ("tail") attached to a polar phosphate group ("head").

Why is it important to know that the phospholipid bilayer is thin?

Because that is why ions on one side of the membrane can interact electrostatically with ions on the other side. The negative charges inside the neuron and the positive charges outside the neuron tend to be mutually attracted to the cell membrane.

There is much greater K+ concentration inside the cell than outside. Why, then, is the resting membrane potential negative?

Because there is a much higher concentration of Na+ outside than there is K+ inside the cell.

How are ion channels and ion pumps different?

Channels are passive and pumps are active (use ATP)

What would the membrane potential be if the membrane were 40 times more permeable to K+ than Na+?

It would be between ENa (-80mV) and EK (62mV), but closer to EK. The weighted average.

What is stronger, diffusion or electrical force?

Electrical force

What do hydrophobic and hydrophilic mean? Give an example for both.

Hydrophobic means "water fearing" or unable to dissolve in water (nonpolar).

The Weaver mouse has a genetic mutation that allows Na+ and K+ to pass through K+ channels. What does this cause?

Increased sodium permeability causes thee membrane potential to become less negative which disrupts neuronal function.

What are other mechanisms that decrease intracellular Ca2+?

Intracellular calcium binding proteins and organelles: mitochondria and ER which sequester cytosolic calcium ions.

What are ionic bonds?

Ions held together with opposingly charged ions. (ex: sodium chloride Na+ and Cl-)

What does a change of extracellular K+ from 5mM to 50mM cause?

It causes the membrane potential from the normal resting value (65mV), to a less negative value (-17mV). It causes a depolarizing effect.

How does the sodium potassium pump work?

It is an eenzyme ethat breaks down ATP in the presence of internal Na+. The chemical energy released by this reaction drives the pump which exchanges internal Na+ for external K+.

How do calcium pumps work?

It is an enzyme that transports Ca2+ out of the cytosol across the cell membrane to keep internal Ca2+ levels incredibly low.

Which ions are more concentrated inside the cell than outside and vice versa?

K+ is 20 times more concentrated inside the cell, Na+ is 10 times moree concentrated outside the the cell, Ca2+ is 10,000 times more concentrated outside the cell, Cl- is 11.5 times more concentrated outside the cell.

What is the molecular basis for K+ channels?

K+ selectivity is caused by the arrangement of amino acid residues that line the pore regions of the channels. There is a pore loop that contributes to the selectivity filter that makes thee channel permeable mostly to K+.

On which side of the neuronal membrane are Na+ ions more abundant?

On the outside.

When the membrane is at the potassium equilibrium potential, in which direction (in or out) is there a net movement of potassium ions?

Out.

What are the four levels of protein structure?

Primary: a chain of amino acids linked my peptide bonds Secondary: shaping the chain (ex: alpha helix) Tertiary: folding the protein into complex 3-D shapes Quaternary: bonding of multiple polypeptide chains

What is diffusion?

Random movement that causes equal distribution of stuff. Moves down the concentration gradient: stuff goes to where it is less concentrated.

What are the important properties of most ion channels?

Size of the pore, nature of the R groups lining it (ion sensitivity- what ions can get through). Gating: the ability to open and close based on changes in the membrane.

What is electrical potential (voltage)?

The force exeereted on a charged particle, reflecting the difference in charge between anode and cathode. More current will flow as this difference is increased.

When a membrane is at rest, is the inside of the cell more negative or positive than the outside of the cell? What is this state called?

The inside of the cell is more negative. This is called resting membrane potential.

How do you calculate the equilibrium potential for an ion with the concentration difference across the membrane?

The nerst equation

What is electrical conductance?

The relative ability of an electrical chase to migrate from one point to another.

What two functions do proteins in the neuronal membrane perform to establish and maintain the resting membrane potential?

They allow specific ions in and out of the cell to regulate membrane potential.

What is potassium spatial buffering?

They have membrane potassium pumps and potassium channels that concentrate K+ in their cytosol. When extracellular K+ increases, K+ enters thee astrocyte through the potassium channels, causing the astrocyte membrane to depolarize. The K+ inside the the astrocyte are dissipated over a large ara by astrocytic processes.

Why is water polar? What does this allow water to do?

Water is polar because the two hydrogen atoms are covalently bonded to the oxygen. The oxygen atom holds a net negative charge because of the extra electrons while the hydrogen atoms hold a net positive charge. This allows water to be a solvent of other charged/polar molecules.

What is the equilibrium state?

When the electrical force pulling ions exactly counterbalances the force of diffusion and net movement of ions across the membrane ceases.

What does it mean when the membrane potential is increased? Decreased?

When the inside of the cell becomes more negative (hyperpolarization), membrane potential is decreased. When the inside of the cell becomes more positive (depolarization), membrane potential increases

When do ions flow across the membrane by diffusion?

When the membrane has channels permeable to the ions and there is a concentration gradient across the membrane.

How do you calculate resting membrane potential?

With the Goldman equation

What would be the membrane potential if it were equally permeable to Na+ and K+? How do you calculate that?

You calculate the average between the two separate membrane potentials: -9mV.

What are cations and anions?

cations are positively charged ions and anions are negatively charged ions.

What is the membrane potential?

the difference of electric charge across the membrane

What is ionic equilibrium potential?

the electrical potential difference that exactly balances an ionic concentration gradient.

What is the purpose of ions pumps?

they work in the background to ensur that ionic concentration gradients aree established and maintained.

What is the structure of the phospholipid bilayer membrane? Why is it structured this way?

two chains of phopholipids, the hydrophobic tails pointing towards eachother, hydrophilic heads pointing outwards. This is because the hydrophobic tails are repelled from the water in the cytosol and the hydrophilic heads are attracted to the water in the cytosol.