Transmembrane Potential

Question 1

A resting cell’s E_m is negative or positive?

Answer 1

Inside negative

Question 2

Concentrations of K+, anionic proteins (Pr-), Na+, and Cl- inside and outside the cell

Answer 2

• Inside the cell:
  
  • K+ & Pr- are high
  • Na+ & Cl- are low
• Outisde the cell :
  
  • K+ is low, no Pr-
  • Na+ & Cl- are high

Question 3

Nernst equation

Answer 3

Transmembrane potential generated by diffusion of a single ion speices

Question 4

Two opposing forces across the membrane for K+, which plays the most important role in determining resting transmembrane potential

Answer 4

Conc gradient wants to move K+ out

Electrical force keeps K+ inside.

E_k is negative (inside-negative)

Question 5

Concentration gradient of Na+ favors

Answer 5

it moving inwards

E_Na+ is inside positive

Question 6

Nernst potential/Equilibrium potential

Answer 6

Transmembrane potential (electrical force) that exactly counterbalances the concentration force

E_k= -95mV

E_Na= +65mV

E_Cl= - 89mV

Question 7

Goldman-Hodgkin Katz equation shows that

Answer 7

Em is determined by

• Concentration gradients of the ions
• Relative permability of the membrane to each ion species

The more permeable a given ion is, the more its Nernst potential will influence E_m

Question 8

The diffusion required to produce the transmembrane potential does not result in any observable concentration changes, though K+ tends to leak out and Na+ tends to leak in. ___ obviates this to maintain ionic concentration gradients to generate the transmembrane potential.

Answer 8

Na,K pumps

Question 9

Most physiological conditions that alter the transmembrane potential of a cell do so by

Answer 9

Increasing/decreasing membrane permeability

Question 10

Depolarization

Answer 10

Em becomes more positive than -60mV

Question 11

Hyperpolarization

Answer 11

Em becomes more negative

Question 12

Passive vs active responses to application of electric current ot a cell membrane

Answer 12

Passive electrical responses depend on membrane resistance and capacitance

Active electrical responses require activation of voltage-gated ion channels

Question 13

How does membrane resistance determine transmembrane potential?

Answer 13

V = I R

Ohm’s law

Question 14

Electrotonic potentials vs Action potentials

Answer 14

• Depolarizing or hyperpolarizing vs Depolarizing
• Subthreshold initiation vs threshold or suprathreshold
• Passive vs Active
• Graded vs All-or-none
• Amplitude decreases with distance vs Constant
• Faster conduction vs Slower

Question 15

Passive electrical responses (e.g. synaptic potentials) are conducted decrementally and are graded.

Answer 15

Decremental: allowing for signaling only over very short distances

Graded: amplitude of response is porportional to intensity of stimulus

Question 16

Local responses

Answer 16

Weak, subthreshold active responses; the membrane is somewhat depolarized, but not sufficiently to trigger an action potential.

Results from a local increase in membrane conductance to Na+; amplitude decays as it propagates according to the passive electrical propertie so fthe membrane

Question 17

Action potential threshold

Answer 17

Membrane potential at which dpeolarization is sufficient to trigger a Hodgkin cycle: regenerative increase in membrane conductance to Na+; all-or-none

Question 18

Local circuit current flow

Answer 18

Active & passive conduction of APs /depolarization along excitable membranes and non-myelinated axons

1. Na+ ions enter the cell when threshold stimulus is applied
2. The membrane becomes inside-positive while adjacent regions are inside negative
3. Current can passive flow outward across, depolarizing these areas

Question 19

____ of action potentials ensure the bidirecitonal travel of AP propagation

Answer 19

Refractory periods of APs after dpolarization

Question 20

Saltatory conduction

Answer 20

Action potential propagation in myelinated axons

Question 21

Why is saltatory conduction faster than local circuit current flow?

Answer 21

Myelin sheath is high resistance –> current flows down axoplasm and outward across the membrane at the adjacent node; this reduces membrane capacitance because only the capacitance at the nodes need to be charged.

Question 22

Conduction velocity in unmyelinated fibers is proportional to…

Conduction velocity in myelinated fibers is proportional to…

Answer 22

• Unmyelinated - Diameter
  
  • Larger diameters are faster, more excitable, and have lower AP thresholds
• Myelinated -
  
  • diameter
  • resistance of myelin sheath
  • internodal length

Question 23

__ channels are 25x more concentrated at the nodes, whereas __ channels are more concentrated under the myelin sheath

Answer 23

Na+ at the nodes

K+ under the sheath

Question 24

Impact of demyelination on conduction

Answer 24

Demyelination exposes regions of the axonal membrane that can’t sustain APs because they don’t have Na+ channels concentrated there

–> conduction is slowed or blocked

Question 25

In the resting transmembrane potential, E_m is closer to Ek or Ena?

Answer 25

Ek

Em= -73.5mV

Question 26

If you increase the permeability of the cell membrane to [ion] what happens to E_m?

Answer 26

It gets closer to E_ion

Question 27

What would be teh value of Em if the permeability of the cell membrane was increased to Na+ such that Pk=Pna?

Answer 27

Em would lie halfway between Ek and ENa if Pk=Pna

Question 28

If the membrane permeability to K+ was decreased, then the membrane would

Answer 28

Depolarize because Em would move towards ENa

Question 29

Changes in E_K+ have a strong effect on E_m because

Answer 29

P_k>P_Na