Memrane Physiology

Question 1

Function of cell membrane

Answer 1

Defines boundaries of cell
Enclose cell organelles
Enables cell to create an internal environment

Question 2

Describe the compartment within confines of the cell membrane

Answer 2

Intracellular environment
Largely aqueous

Question 3

Describe the compartment outside the cell membrane

Answer 3

Extracellular compartment:
Interstitial space
Largely aqueous

Question 4

Examples of charge carrying particles in the intracellular environment

Answer 4

Organelles
Proteins
Anions or cations

Question 5

Chemical gradient?

Answer 5

Concentration gradient of ions between the Intracellular and extracellular compartments of the cell

Question 6

Electrical gradient?

Answer 6

Known as membrane potential
Electrical polarity between inside and outside of cells due to charged particles

Question 7

Electrochemical gradient?

Answer 7

Combined electrical and chemical gradients
Standing electrochemical gradient because continuously present

Question 8

What is Resting membrane potential?

Answer 8

Cells of different tissue have different resting potentials
Electrical gradient between inside and outside of the cell
Maintained via ion pump
Leak channels open

Question 9

RMP of nerve cell?

Answer 9

-70 mv

Question 10

Characteristic of electrically excitable tissues?

Answer 10

They able to momentarily discharge the standing electrical potential between the Intracellular and extracellular compartments

Question 11

What is death in terms of electrically excitable tissue?

Answer 11

The permanent discharge of resting membrane potentials

Question 12

Factors that decide what can cross cell membrane

Answer 12

Size
Polarity
Solubility in water
Ion channel/ protein

Question 13

Types of ion channels

Answer 13

Selective
Leak

Question 14

Transmembrane spanning proteins?

Answer 14

Protein assemblies that span the full thickness of the cell membrane

Question 15

Common on ion channels

Answer 15

Voltage gated - generate AP
Ligand gated - generate Em at synapse with NT
Leak - set RMP
Mechanically gated

Question 16

What is the function Ion pumps in nerve cells?

Answer 16

Maintain resting potential, dont set it up
Require ATP

they provide the starting point for the ability of the cell to generate electrical signals.

Question 17

What is a Graded depolarisation?

Answer 17

Depolarisation is proportional to the strength of stimulation applied
Once threshold reached same AP always generated

Question 18

What is level of membrane potential at which graded depolarisations become an action potential known as?

Answer 18

‘Threshold level’
Different neuronal cell types have different threshold levels
~ -55mV in neurones

Question 19

Value of Resting membrane potential

Answer 19

-70mV

Question 20

Nerst equation used for

Answer 20

Calculates membrane potential at eqm for each of the ions in question

Need to know relative conc of ion intracellularly and extracellularly

Question 21

Epm potential of K+

Answer 21

-80mV

Question 22

Eqm potential of Na+

Answer 22

+60mV

Question 23

What is conductance of ion channels

Answer 23

Represents the activity of ion channels
Directly proportional to how many channels are opening in membrane
Each ion has its own conductance

Question 24

When are voltage gates channels open

Answer 24

RMP closed
Depolarisation Na+ open
Repolarisation K+ open

Question 25

Goldman Hodgkin Katz equation

Answer 25

Modification of the nerst equation Takes into account relative permeabilities of ions in question

Question 26

What happens during depolarisation

Answer 26

Na+ enters the cell Membrane depolarises Depolarisation reaches threshold More Voltage gated Na+ channels open

Question 27

Repolarisation events

Answer 27

K+ channels open - K+ efflux Na+ channels closed - Na+ influx stopped

Question 28

Extracellular voltage?

Answer 28

Zero mV

Question 29

Channels that determine resting membrane potential?

Answer 29

Leak channels control permeability at rest

Question 30

Electrogenic?

Answer 30

Many active transport mechanisms are electrogenic Produce change in voltage because there is net movement of anions/ cations to one side of membrane

Question 31

Chemical force

Answer 31

Differences in ion concentration

Question 32

Electrical force?

Answer 32

Due to electrical charge intracellularly/ extracellularly Membrane potential of the cell

Question 33

What is eqm potential?

Answer 33

When chemical force = electrical force Equal and opposite

Question 34

Resting membrane potential will be equal to eqm potential if membrane permeable to one ion only. True/ False?

Answer 34

True Skeletal muscle cells/ glial cells only permeable to k+ So membrane potential = K+ eqm potential

Question 35

Ion composition of Na and K

Answer 35

• K+ concentration is high inside the cell, low outside • Na+ concentration is low inside the cell, high outside

Question 36

Driving an ion across the membrane electrically requires:

Answer 36

• the membrane possesses channels permeable to that ion to provide conductance • There is an electrical potential difference across the membrane

Question 37

How does Em remain constant

Answer 37

Na influx = K efflux - Driving force of K small and cell has large permeability to K - Driving force of Na large but small permeability to Na

Question 38

Why is the Na driving force large at Em (resting membrane potential)

Answer 38

Na influx due to chemical and electrical force Big electrical difference. Na eqm is +60mV and Em is -65mV. More Na outside due to pump so steep Chemical gradient.

Question 39

What does resting potential depend on

Answer 39

Permeability of the ions The ions driving forces

Question 40

What is a nerve cell more permeable to?

Answer 40

K More K leak channels

Question 41

Why is there a small K driving force at RMP

Answer 41

Eqm potential of K+ is -80mV and Em is -65m. So small difference. Chemical gradient (causing efflux) is greater than electrical force (causing influx)

Question 42

Which ion is resting membrane most permeable to

Answer 42

K+

Question 43

What are the permeabilities of ions during hyperpolarisation

Answer 43

Increased k+ permeability Decreased Na+ permeability

Question 44

What is the conductance of ions during depolarisation

Answer 44

Sodium has higher conductance than potassium So sodium influx

Question 45

What is refractory period caused by

Answer 45

Inactivation of na+ channels Delayed closing of K+ channels

Question 46

Do AP spread backwards?

Answer 46

No