Electrophysiological properties of neurons

Question 1

Describe the properties of the neuronal membrane.

Answer 1

Composed of fatty chains with hydrophilic heads facing outside and hydrophobic chains towards the center to prevent the movement of charged ions (lipid bilayer). Proteins are imbedded in membrane for active transport/channels
Hydrophobic center doesn’t allow charged ions to cross
Vm results from the separation of positive and negative ions
At rest, Vm is typically between -60 and -70 mV

Question 2

Describe the properties of ion channels and how they contribute to the dynamic properties of membranes.

Answer 2

They recognize specific ions (p-loop), open and close in response to electrical, chemical, or mechanical signals, conduct ions across the membrane. (ligand, voltage, phosphorylation, stretch) These properties give membrane dynamic properties.

Question 3

Define the difference between channels and transporters

Answer 3

Channels are passive flow of ions across an ionic gradient (Na in). Transporters require ATP and can be used against a concentration gradient.

Question 4

List 3 fundamental factors that account for the resting membrane potential

Answer 4

Separation of positive and negative ions that create a negative intracellular and positive extracellular environment. The driving force of the ions on each side. Sodium potassium pumps

Question 5

Define the factors that cause ions to move across a membrane (or not).

Answer 5

Ions can move across the membrane through a channel via ligand binding, voltage gating, phosphorylation, or stretching/pressure. Movement depends on concentration of ion on each side, voltage of membrane, and membrane permeability to the ion

Question 6

Estimate the membrane potential based on individual ion conductances

Answer 6

Nernst equation.
Vm = 61 * log (Ion(out)/Ion(in) 
K: low out, high in, -88.3
Na: High out, low in, +61.5
Cl-: High out, low in, -70.3 (changes in permeability won't do much 
Ca++: High out, Low in, +184.0

Question 7

Compare the two different types of synaptic membrane potentials.

Answer 7

Ligand gated Na channels lead to depolarization (Vm more positive), K hyperpolarization (Vm negative). Excitatory Post-Synaptic Potential (EPSP):
Excitatory
Membrane depolarizes allowing cations (Na+ and Ca2+) to flow into the cell
Thus, makes an action potential more likely
Common in glutamatergic neurons
Inhibitory Post-Synaptic Potential (IPSP):
Inhibitory
Membrane hyperpolarizes leading to the outward flow of cations (K+) and inward flow of anions (Cl-)
Thus, makes it more difficult to perform an action potential
Common in GABAergic cells

Question 8

Describe the passive properties of membranes.

Answer 8

When a small patch of membrane depolarizes it spreads locally and depolarizes adjacent membranes. This is reduced over space as current leaks through the membrane due to capacitance and permeability

Question 9

Which ion contributes most to the resting membrane potential

Answer 9

K+

Question 10

Describe the relative permeability for each ion (K+ Na+ Cl- and Ca++)

Answer 10

At rest, the membrane is permeable to K+ but not Na+ or Cl

Question 11

What happens to the Nernst potential of K if you double the extracellular concentration?

Answer 11

It becomes less negative

Question 12

How does doubling extracellular K impact the membrane potential

Answer 12

It becomes depolarized

Question 13

What happens to the resting membrane potential if you increase Cl- permeability?

Answer 13

Nothing. Maybe small hyper polarization but driving force is very small

Question 14

What happens to resting membrane potential if you decrease Na+ permeability?

Answer 14

It would be very slightly hyper polarized. It’s not nothing because there are small leak channels even though the membrane is not permeable to Na

Question 15

What happens to the resting membrane potential if you increase Na+ permeability

Answer 15

Depolarization

Question 16

If the resting membrane potential is more negative than the Nernst potential of K+ what direction is the K+ current?

Answer 16

In. Cell is already hyper polarized which is what happens when K+ leaves so the K+ will want to counteract that and flow in

Question 17

What happens to the membrane potential if you eliminate extracellular Na+?

Answer 17

The cell would hyper polarize

Question 18

How many ions do the Na/K pump transport at a time?

Answer 18

3 Na+ and 2K+ against their concentration gradient

Question 19

All neurons have large ____ which gives the intracellular environment a ____ charge and attracts _____

Answer 19

anions, negative, cations

Question 20

Define positive and negative driving force

Answer 20

Positive driving force= cation efflux/anion influx Negative driving force=cation influx/anion efflux

Question 21

Define driving force

Answer 21

The degree to which the membrane potential deviates from an ion’s equilibrium potential. Without driving force, ion will not generate current

Question 22

Compare IPSP and EPSP

Answer 22

EPSP: depolarizing, Na+/Ca2+, Glutamate
IPSP: hyper polarizing, K+/Cl-, GABA/glycine

Question 23

What happens to the resting membrane potential if you decrease Cl- permeability

Answer 23

Nothing. Cl- is close to resting potential.