Transmembrane Potential Flashcards

1
Q

A resting cell’s Em is negative or positive?

A

Inside negative

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2
Q

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

A
  • Inside the cell:
    • K+ & Pr- are high
    • Na+ & Cl- are low
  • Outisde the cell :
    • K+ is low, no Pr-
    • Na+ & Cl- are high
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3
Q

Nernst equation

A

Transmembrane potential generated by diffusion of a single ion speices

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4
Q

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

A

Conc gradient wants to move K+ out

Electrical force keeps K+ inside.

Ek is negative (inside-negative)

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5
Q

Concentration gradient of Na+ favors

A

it moving inwards

ENa+ is inside positive

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6
Q

Nernst potential/Equilibrium potential

A

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

Ek= -95mV

ENa= +65mV

ECl= - 89mV

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7
Q

Goldman-Hodgkin Katz equation shows that

A

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 Em

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8
Q

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.

A

Na,K pumps

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9
Q

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

A

Increasing/decreasing membrane permeability

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10
Q

Depolarization

A

Em becomes more positive than -60mV

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11
Q

Hyperpolarization

A

Em becomes more negative

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12
Q

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

A

Passive electrical responses depend on membrane resistance and capacitance

Active electrical responses require activation of voltage-gated ion channels

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13
Q

How does membrane resistance determine transmembrane potential?

A

V = I R

Ohm’s law

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14
Q

Electrotonic potentials vs Action potentials

A
  • 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
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15
Q

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

A

Decremental: allowing for signaling only over very short distances

Graded: amplitude of response is porportional to intensity of stimulus

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16
Q

Local responses

A

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

17
Q

Action potential threshold

A

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

18
Q

Local circuit current flow

A

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
19
Q

____ of action potentials ensure the bidirecitonal travel of AP propagation

A

Refractory periods of APs after dpolarization

20
Q

Saltatory conduction

A

Action potential propagation in myelinated axons

21
Q

Why is saltatory conduction faster than local circuit current flow?

A

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.

22
Q

Conduction velocity in unmyelinated fibers is proportional to…

Conduction velocity in myelinated fibers is proportional to…

A
  • Unmyelinated - Diameter
    • Larger diameters are faster, more excitable, and have lower AP thresholds
  • Myelinated -
    • diameter
    • resistance of myelin sheath
    • internodal length
23
Q

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

A

Na+ at the nodes

K+ under the sheath

24
Q

Impact of demyelination on conduction

A

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

25
Q

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

A

Ek

Em= -73.5mV

26
Q

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

A

It gets closer to Eion

27
Q

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

A

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

28
Q

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

A

Depolarize because Em would move towards ENa

29
Q

Changes in EK+ have a strong effect on Em because

A

Pk>PNa