Lecture 3.1

Question 0

How are membrane potentials expressed?

Answer 0

Inside relative to the outside and in mV

Question 1

How is the MP measured?

Answer 1

Microelectrodes with tips of <1micrometer, that can penetrate cell membranes and are filled with KCl conducting solution - one on the inside of the cell and one on the outside, and a Voltmeter

Question 2

Are animal MPs negative or positive?

What are the ranges for each type of cells?

Answer 2

Negative from -20mV to -90mV
Skeletal muscle -80mV to -90mV
Smooth muscle -40mV to -50mV
Neurones -50mV to -75mV

Question 3

How are membrane potentials established?

Answer 3

Due to the selective permeability of the membrane to different ions. This is achieved through ion channels.

Question 4

State 3 characteristics of an ion channel

Answer 4

1. Selectivity - channel is permeable only to one or very few ions
2. Gating - conformational change in protein molecule leads to opening and closing of the channel
3. Fast rate of ion flow down electrochemical gradient for that ion

Question 5

What is the hydrophobic interior of a bilayer permeable to?

Answer 5

Small uncharged molecules; O2, CO2, H2O, ethanol

Question 6

What are the ionic concentrations of sodium?

Answer 6

Intracellular: 10mM
Extracellular: 145mM

Question 7

What are the ionic concentrations of potassium?

Answer 7

Intracellular: 160mM
Extracellular: 4.5mM

Question 8

What are the ionic concentrations for chloride?

Answer 8

Intracellular: 3mM
Extracellular: 114mM

Question 9

What are the ionic concentrations of anions? What are they?

Answer 9

Intracellular: 167mM
Extracellular: 40mM

Negatively charged ions; phosphate bicarbonate, AAs

Question 10

The action of which ionic channels dominate at rest?

Answer 10

Potassium

Question 11

How is the membrane potential established at rest?

Answer 11

1. Potassium channels in the membrane is open and the membrane is selectively permeable to potassium ions
2. Potassium ions diffuse out of the cell down the concentration gradient
3. Anions can’t follow so cell becomes negatively charged
4. The membrane potential opposes the outward movement of potassium and the system will come into equilibrium

Question 12

How is Ek reached?

Answer 12

When diffusion of potassium ions out of cells down the chemical gradient is opposite and equal to the flow of potassium ions into the cell down the electrical gradient (because as potassium ions flow out down chem gradient, cell becomes more negative and so positive potassium ions are attracted back into cell), and there is no net movement of potassium ions.

Question 13

What is the Nernst equation and what does it tell us?

Answer 13

At 37 degrees, 61/valency of ion x log (outside concentration of ion/inside concentration of ion). It tells us the equilibrium potential of an ion and therefore, the MP for which that ion will be in equilibrium.

Question 14

Why is the resting membrane potential close to Ek?

Answer 14

Open potassium ion channels dominate at rest

Question 15

What is Ek?

Answer 15

-95mV

Question 16

Why aren’t all resting membrane potentials equal to Ek?

Answer 16

Resting membrane is not perfectly selective for potassium ions as other types of channels are also open so the resting potential is usually less negative than Ek

Question 17

Between which two ionic equilibrium potentials does the resting potential of skeletal muscle lie and why?

Answer 17

ECl and Ek as skeletal muscle resting membrane is highly permeable to both chloride and potassium ions

Question 18

Define depolarisation

Answer 18

The inside of a cell becomes less negative and the membrane potential decreases

Question 19

Define hyperpolarisation

Answer 19

Inside of membrane becomes more negative and the membrane potential increases

Question 20

What will happen if you change the membrane permeability to a specific ion?

Answer 20

Changing the selectivity to an ion changes the membrane potential and moves it closer to that ion.

Question 21

What will happen if you open more sodium and calcium channels?

Answer 21

Depolarisation

Question 22

What will happen if you open chloride and potassium channels?

Answer 22

Hyperpolarization

Question 23

What does the GHK equation prediction?

Answer 23

Membrane potential as an average of all the equilibrium potentials for all the ions of which there are ion channels open for.

Question 24

If there are multiple ion channels open, what determines which one influences the membrane potential most.

Answer 24

1. Number of channels open for that specific ion | 2. Ease of which the ion can flow through the channel relative to the other ions

Question 25

In what 3 ways can channels be gated?

Answer 25

1. Voltage gated - channel opens/closes with changes in membrane potential 2. Ligand gated - binding of a chemical molecule can open of close the channel. The chemical molecule can be an intercellular messenger or an extracellular transmitter. 3. Mechanical gating - changes in membrane conformation causes change to ion channels

Question 26

In fast synaptic transmission, what type of ion channel is the receptor?

Answer 26

Ligand-gated ion channel

Question 27

What are the channels that depolarising transmitters open, selective for?

Answer 27

Sodium and calcium (and other cations) - these channels have positive reversal potential

Question 28

What happens as a result of a depolarising transmitter binding to a receptor?

Answer 28

A change in membrane potential known as an EPSP (excitatory post synaptic potential) and excitation of cells

Question 29

What types of channels do hyperpolarising transmitters open?

Answer 29

Channels with negative reversible potential i.e. Channels selective for Potsssium and chloride

Question 30

What does binding of a hyperpolarising transmitter do?

Answer 30

Causes inhibition and change in membrane potential known as IPSP (inhibitory post synaptic potential)

Question 31

Is the receptor is slow transmission an ion channel?

Answer 31

No, it is a molecule associated with a GTP-binding protein. It is a G protein receptor

Question 32

In what two ways can a G protein receptor signal to a channel in slow synaptic transmission?

Answer 32

1. Within membrane - transmitter binds to G protein receptor. G protein binds to channel. Channel opens. 2. Via an Intracellular cascade - transmitter binds to G protein receptor. G protein binds to enzyme. Amplification by signalling cascade. Activates Intracellular messenger or a protein kinase. Channel opens.

Question 33

What is the structure of a nicotinic ACh receptor?

Answer 33

1. Ligand gated intrinsic ion channel 2. ACh binds to it, channel opens 3. Allows sodium and potassium to flow through but not anions 4. Brings MP to 0mV - between Ek and ENa

Question 34

What are the 4 places where synaptic connections can occur?

Answer 34

1. Nerve-nerve 2. Nerve-muscle 3. Nerve-gland 4. Sensory cell-nerve