HSES 375 Exam 1 - Study Guide

Explain how the input conductance of a neuron affects the amount of current needed to change the membrane potential at a given amount (hint - use Ohms law).

-As conductance goes up, current must go up. -Greater density of Na+ channels deltaV=I/g. -The more conductance (g input), the more current is needed.

Describe the flow of Na+ and K+ ions in the process of an action potential (include depolarization, repolarization, and afterhyperpolarization).

-Depolarization: Na+ starts to flow in making the cell more positive. -Repolarization: K+ starts to flow in. -Afterhyperpolarization: K+ has not started to leak out and is open longer. Refractory period.

Explain the difference between voltage and ligand gated ion channels.

Ligand gating: chemical binding to receptor (e.g, neurotransmitter) Voltage gating: change in membrane potential opens or closes channels.

Describe the location (both outside and inside the cell) of ions involved in establishing the resting membrane potential of a neuron

Na+ outside. K+/ - anions/ - amino acids inside

How does the Na+-K+ pump maintain resting membrane potential? Is the pumping action an active or passive process?

Uses energy (ATP) to pump ions against electrochemical gradients. One cycle of the pump uses one ATP, and moves 3 Na+out and 2 K+ in. Electrogenic action of the pump: unequal ion transfer contributes ~ -5.6mV to resting membrane potential. - Pump action is an active process.

What is the approximate threshold (in millivolts) that must be reached during depolarization for a neuron to generate an action potential?

-55mV

What is the approximate potential difference (i.e., in millivolts) across the membrane of a neuron at rest?

-65 to -70mV

Differentiate between depolarization and repolarization.

-Depolarization: membrane potential becomes less negative. -Hyperpolarization: membrane potential become more negative

How does neuron size affect input conductance of a neuron? How does the relationship between neuron size and input conductance affect the ease of changing the membrane potential? What is the importance of this in terms of generating action potentials?

-Small neurons: small input conductance (g), therefore larger change in membrane potential (V) with a given current (V=I/g), easier to get to threshold. -Large neurons: all else being equal, for any given current → more capacitive current, less ionic current → harder to change membrane potential ("...the change in membrane potential parallels the change in ionic current").

What is an action potential?

A transient reversal in the potential difference across the membrane that is transmitted rapidly along an excitable membrane.

Do myelinated neurons propagate action potentials faster or slower than unmyelinated neurons?

Faster

State Ohm's law with respect to: a) resistance, and b) conductance.

I = gV. Current (I) = conductance (g) x potential difference (V). Resistance (R) = 1/g = reciprocal of conductance g = 1/R. I= V/R; current = voltage / resistance.

What is occurring during the afterhyperpolarization phase of the action potential? Is the membrane potential during this period more or less negative than the resting membrane potential prior to depolarization?

K+ is coming in. It is more negative than the resting membrane potential

Is the outside (extracellular space) of a neuron at rest more positive or negative in comparison to the inside of the cell?

More positive

What happens to the myelin sheath as a result of multiple sclerosis? Will the propagation of action potential be impaired in a patient diagnosed with multiple sclerosis?

Myelin sheath is under attack, "foreign". T-cells destroy myelin sheath and this affects conduction (see example 5.2 on next page)

During intense exercise, why does the plasma K+ concentration increase?

Na+ is going in the cell and K+ is kicked out of the cell into blood. Also, if Na+/K+ pump is not working well and having a harder time pulling Na+ out.

Describe the structure of a cell membrane. How does this structure contribute to the development of the resting membrane potential?

Phospholipid Bilayer does not allow ions to cross membrane unless thru ion channels, thus causing different membrane potentials

Which positively charged ion tends to "leak" from inside a neuron to the extracellular space through resting ion channels? Does the inside of the neuron become more negative or positive as a result of this outward ion "leak?"

Potassium (K+) tends to leak. The inside of the neuron becomes more negative.

Define potential difference, current, conductance, and capacitance

Potential difference - A measure of the potential energy that must be used to move a a positive charge from one location to another; units=Mili-volts; electromotive force. mV=J/C Current - the rate at which positive charges move between the two locations that represent a potential difference. I=Q/t=charge/time Conductance - Capacity to conduct electric current. unit=siemens (S). Ratio of charge stored (Q) to the potential difference (V); units=farad (F). C=Q/V

What is the relationship between conductance and resistance?

Resistance (R) is the inverse of conductance. R = 1/g. g = 1/R