W3- Resting Membrane Potential

Question 1

How can you measure the membrane potential of a cell?

Answer 1

Use a very fine micropipette or microelectrode (

Question 2

What is the range of resting membrane potentials in animal cells?

Answer 2

-20 to -90mV

Question 3

Which two cell types have the largest resting membrane potential?

Answer 3

Cardiac and skeletal cells

Question 4

What is the range of resting membrane potentials in nerve cells?

Answer 4

-50 to -75mV

Question 5

How are membrane potentials always expressed?

Answer 5

As the potential inside relative to the EC fluid

Question 6

How does selective permeability allow membrane potentials to be set up?

Answer 6

Membrane potentials are set up because the membrane is selectively permeable to different ions

Question 7

What are the 3 characteristics of an ion channel?

Answer 7

Selectivity (for ion/s), gating (channel opened or closed by conformational change), rapid ion flow (down electrochemical gradient)

Question 8

What does A- represent?

Answer 8

Anions other than Cl- (P, aa’s, charged groups on proteins)

Question 9

What gives a membrane selective permeability?

Answer 9

The ion selectivity of channels and the types of channels that are open

Question 10

How does the membrane potential arise? Which ion is important?

Answer 10

Arises because the membrane is selectively permeable to K+.

Question 11

At rest, which channels is open in the membrane? Which ion diffuses which way? What does this do to the charge of the cell?

Answer 11

K+ channels- K+ diffuses out of the cell down it’s c.g causing cell to become negatively charged inside

Question 12

At eq, is there a net driving force for K+? Why?

Answer 12

No net driving force because electirical and chemical gradients for K+ are balanced

Question 13

How is the K+ eq potential Ek calculated? When does it occur?

Answer 13

Using the Nernst eq- need IC and EC K+ values, occurs when chemical and electrical gradients for K+ are equal so no net driving force

Question 14

What is the resting membrane potential for Ek?

Answer 14

-95mV, often resting membrane potential of a cell is very close to this because open K+ channels dominate at rest

Question 15

What is the resting membrane potential?

Answer 15

The electrical potential difference across the p.m of a cell

Question 16

Which two ions make the RMP slightly less negative and make it lie somewhere between ECl and Ek?

Answer 16

Na+ and Ca2+

Question 17

Which two ions is the RMP highly permeable to?

Answer 17

K+ and Cl-

Question 18

Is the membrane perfectly selective for K+?

Answer 18

No- other channel types are open

Question 19

What does a lower selectivity for K+ do to the RMP?

Answer 19

Lowers the RMP

Question 20

Define depolarisation

Answer 20

A decrease in the size of membrane potential from its normal value- cell becomes less negative e.g -70 to -50mV

Question 21

Define hyperpolarisation

Answer 21

An increase in the size of the membrane potential from its normal value- cell interior becomes more negative e.g -70 to -90mV

Question 22

How do you move the membrane potential towards a particular ion equilibrium potential?

Answer 22

Increase the membrane permeability for it

Question 23

What does opening K+ or Cl- channels do to the state of the cell?

Answer 23

HyperpolariZation

Question 24

What does opening Na+ of Ca2+ channels do to the state of he cell?

Answer 24

Depolarization

Question 25

What does the Goldman-Hodgkin-Katz eq approximate?

Answer 25

The contribution of each ion to the membrane potential of a cell- depends on membrane permeability for each ion

Question 26

What is the membrane potential of the nicotinic AChR when ACh activates it, why?

Answer 26

0mV because channels let Na+ and K+ thorough so membrane potential is intermediate between Ek and ENa so 0mV

Question 27

What are the three types of gating that can control channel activity?

Answer 27

Ligand (opens/closes in response to ligand), voltage (opens/closes in response to change in membrane potential), mechanical (opens/closes in response to membrane deformation)

Question 28

Between which cells might synaptic connections occur?

Answer 28

Nerve to nerve/muscle/gland cell or sensory cell to nerve cell

Question 29

How does a LGIC lead to a synaptic potential?

Answer 29

NT binds to post synaptic membrane, Na+ influx through channel

Question 30

In fast synaptic transmission, what is the R also?

Answer 30

A LGIC- NT binds opening channel

Question 31

What is an excitatory post-synaptic potential?

Answer 31

Cause depolarisation. Cations flow through channel when opened leading to excitation of cell and change in membrane potential

Question 32

Is an EPSP longer or shorter than and a.p?

Answer 32

Longer- graded with amount of NT

Question 33

What is an IPSP?

Answer 33

Causes hyperpolarisation. K+ or Cl- enter cell via channel and lead to inhibition and change in membrane potential- more negative

Question 34

What 2 NTs are associated with EPSP?

Answer 34

ACh and glutamate

Question 35

Which two NT's are associated with IPSP?

Answer 35

Glycine and GABA

Question 36

In slow synaptic transmission, how are the R and channel arranged? What do they require?

Answer 36

As separate proteins (GPRC). Require GTP binding

Question 37

What are the 2 basic patterns that GPCRs can activate an ion channel?

Answer 37

Direct binding of the G-protein to channel (localised, rapid) or via IC messenger (G-protein activates enzyme causing amplifying signalling cascade that may activate channel, effect throughout cell)

Question 38

What two other factors can influence membrane potential?

Answer 38

Changes in ion conc (most important is EC K+), electrogenic pumps (Na/K+ATPase may contribute to more negative

Question 39

What is indirectly responsible for the entire membrane potential?

Answer 39

Active transport of ions as they set up and maintain the ionic gradients needed