Membrane Potentials Flashcards Preview

BS1060 Physiology, Pharmacology & Neuroscience > Membrane Potentials > Flashcards

Flashcards in Membrane Potentials Deck (29):
1

Membrane potential

The potential difference between the inside and outside of a cell (measured in millivolts: mV).

2

Membrane potential of extracellular fluid

0 mV by definition

3

Microelectrode

-Fine glass pipette
-Tip diameter < 1 μm
-Can penetrate cell membrane
-Filled with conducting solution (KCl)

4

Animal cell resting membrane potential

-20 to -90 mV

5

Cardiac and skeletal muscle cell resting membrane potential

-80 to -90 mV

6

Nerve cell resting membrane potential

-50 to -75 mV

7

Effect of -70 mV membrane potential

Outward chemical gradient exceeds inward electrical gradient resulting in net efflux of K+ ions.

8

Effect of -90 mV membrane potential

Equilibrium potential- chemical and electrical gradients equal but opposite- no net flow of K+.

9

The Nernst equation

Ek = (61/z)log([K+]o/[K+]i
Ek: membrane potential at which K+ at eqm
z: valency (+1 for K+)
[K+]o,[K+]i: concentrations

10

Setting up the resting potential

-Open K+ channels dominate membrane ionic permeability at rest
-At eqm no net movement of K+ but -ve membrane potential
-Resting membrane potential arises as membrane more permeable to K+ at rest than other ions

11

Depolarisation

-Decrease in the size of membrane potential from normal value
-Cell interior less negative

12

Hyperpolarisation

-Increase in the size of membrane potential from normal value
-Cell interior more negative

13

Effect of increasing membrane permeability to a particular ion

Membrane potential moves towards the equilibrium potential for that ion

14

Equilibrium potential for K+ (Ek)

-90 mV

15

Equilibrium potential for Cl- (Ecl)

-70 mV

16

Equilibrium potential for Na+ (Ena)

+70 mV

17

Equilibrium potential for Ca2+ (Eca)

+120 mV

18

Movement of Na+ ions

Na+ moves into the cell to move Vm closer to Ena

19

Movement of K+ ions

K+ moves out of the cell

20

Movement of Cl- ions

Cl- moves into cell (has a -ve charge)

21

Ligand gating

Channel opens or closes in response to binding of a chemical ligand e.g. channels at synapses that respond to extracellular transmitters.

22

Voltage gating

Channel opens or closes in response to changes in membrane potential e.g. channels involved in action potentials.

23

Mechanical gating

Channel opens or closes in response to membrane deformation e.g. channels in mechanoreceptors.

24

Where can synaptic connections occur between?

nerve cell - nerve cell
nerve cell - muscle cell
nerve cell - gland cell
sensory cell - nerve cell

25

Basic synaptic mechanism

Chemical transmitter released from presynaptic cell binds to receptors on postsynaptic membrane.

26

Excitatory synapses

-Excitatory transmitters open ligand-gated channels that cause membrane depolarisation
-Permeable to Na+, Ca2+ or cations in general
-Resulting change called excitatory post-synaptic potential (EPSP)
-Excitatory transmitters include acetylcholine, glutamate

27

Inhibitory synapses

-Inhibitory transmitters open ligand-gated channels that cause hyperpolarisation
-Permeable to K+ or Cl-
-Resulting change called inhibitory post-synaptic potential
-Inhibitory transmitters include glycine, ɣ-aminobutyric acid

28

Factors that influence membrane potential

1. Changes in ion concentration
-most important extracellular K+ conc (~5mM)
2. Electrogenic pumps - Na+/K- ATPase
-contributes very little to potential
-one +ve charge moved out per cycle

29

Significance of active transport of ions on membrane potential

Indirectly responsible for entire membrane potential, because it sets up and maintains ionic gadients.