1.3 Membrane And Action Potential

Question 1

Flux

Answer 1

The number of molecules that cross a unit area per unit time

Question 2

Voltage

Answer 2

Potential difference
Unit: volts
Generated by ions to produce a charge gradient

Current x resistance

Question 3

Current

Answer 3

Movement of ions due to a potential difference (voltage)
Unit: amps

Question 4

Resistance

Answer 4

Barrier that prevents the movement of ions
Units: ohms

Question 5

Equation for voltage

Answer 5

Current x resistance

Question 6

How to measure membrane potential

Answer 6

A reference electrode is placed outside the cell (zero-volt level)
Another electrode placed inside the cell

The voltage measured is negative compared with the outside (the zero-volt reference)

Question 7

Membrane potential

Answer 7

Difference in voltage between the inside and outside of the cell

Question 8

Examples of ions that channels can be selective for

Answer 8

K+, Na+, Cl-, Ca2+

Question 9

How is membrane potential generated

Answer 9

Diffusion through a selectively permeable membrane

Question 10

Electrochemical equilibrium

Answer 10

Achieved when electrical force prevents further diffusion across the membrane

Question 11

Depolarisation

Answer 11

Membrane potential becomes more positive

Question 12

Repolarisation

Answer 12

Membrane potential decreases towards resting potentiak

Question 13

Overshoot

Answer 13

Membrane potential is positive

Question 14

Hyperpolarisation

Answer 14

Membrane potential decreases beyond resting potential

Question 15

Graded potential

Answer 15

Change in membrane potential is graded in response to the type or strength of stimulation
Determine (initiate or prevent) action potentials

Question 16

Action potential

Answer 16

Occur when a graded potential reaches the threshold for the activation of Na+ channels, resulting in an all or nothing event

Question 17

In what cells do action potentials occur

Answer 17

Excitable cells, mainly neurons and muscle cells, some endocrine tissues

Question 18

Nerve impulses

Answer 18

An action potential in neurons
Allow transmission of information reliably and quickly over long distances

Question 19

Phase 1 of the action potential

Answer 19

Resting membrane potential (-70mV)

[permeability for K > Na]

Question 20

Phase 2 of the action potential

Answer 20

Depolarising stimulus

Membrane potential moves more positive towards to threshold

Question 21

Phase 3 of the action potential

Answer 21

Upstroke

Starts at the threshold potential
Na+ channels open quickly; influx of Na+ (Inc permeability of Na)
K+ channels open slowly; K+ leaves cell [slower than Na+ enters] (Inc permeability of K+)

Membrane potential moves towards the Na+ equilibrium potential (+72mV)

Question 22

Phase 4 of the action potential

Answer 22

Repolarisation

Na+ channels inactivate/ close (decreased Na+ perm)
K+ channels continue to open and remain open; K+ leagues cell

Membrane potential moves toward K+ equilibrium (-90mV)

Question 23

Phase 5 of the action potential

Answer 23

After - Hyperpolarisation

K+ channels remain open; K+ continues to leave
Membrane potential moves closer to K+ quilibrium (-90mV)
Some K+ channels then close and membrane potential returns to resting potential

Question 24

Absolute refractory period

Answer 24

New action potential cannot be triggered even with a very strong stimulus

(Na channel activation gate is open, inactivation gate is closed at the start of Repolarisation, both closes at end of Repolarisation)

Question 25

Relative refractory period

Answer 25

Stronger than normal stimulus required to trigger an action potential

(Some Na+ channels have recovered from inactivation- gate is open)

Question 26

How is membrane potential restored following passive propagation

Answer 26

Small sub-threshold depolarisations decay along length of axon
More k+ channels open to restore resting potential

Question 27

Where are voltage gated channels located

Answer 27

Nodes

Question 28

What affect conduction velocity

Answer 28

Axon diameter and myelination

Question 29

How to increase velocity of an action potential

Answer 29

Large diameter
Myelinated axons

Question 30

Cause for reduced axon diameter

Answer 30

Re-growth after injury

Question 31

Cause for reduced myelination

Answer 31

Multiple sclerosis
Diphtheria

Question 32

Reduced axon speedcan be due to

Answer 32

Reduced axon diameter
Reduced myelination
Cold
Anoxia
Compression
Drugs
Some anaesthetics

Question 33

What are three main factors that influence the movement of ions across the membrane

Answer 33

Concentration of the ion on both sides of the memb
Charge of the ion
Voltage across the membrane

Question 34

Why is the K+ equilibrium potential negative and the Na+ equilibrium positive when both are positive ions

Answer 34

More K+ inside the cell that out so flow out of the cell (needs a negative equilibrium is needed to to stop net outwards flow)

More Na+ outside the cell so tends to flow in (needs a positive charge to prevent entering the cell)

Question 35

What ion is important for the upstroke and which is important for the falling phase of the action potential, in which direction do these ions flow

Answer 35

Upstroke mediated by Na+ ions moving into the cell

Falling phase mediated by K+ ions moving out of the cell

Question 36

What factors influence the speed of propagation of an action potential along an axon and how

Answer 36

Larger diameter axons have lower resistance and so move faster - conduction velocity is proportional to square root of the axon diameter
Linear relationship between conduction velocity and myelin thickness

Question 37

Relationship between speed of propagation of an action potential and diameter of the axon

Answer 37

Conduction velocity is proportional to the square root of the axon diameter

Question 38

Relationship between speed of propagation of the action potential and myelin thickness

Answer 38

Linear