Membrane potentials

Question 1

What is the membrane potential?

Answer 1

• Voltage across the plasma membrane

Question 2

What is the resting potential?

Answer 2

• The membrane potential of a cell not sending signals

Question 3

Resting potential of a neuronal membrane

Answer 3

-70mV

Question 4

Resting potential of cardiac membrane

Answer 4

-90mV

Question 5

Formation of the resting potential

Answer 5

• Concentration of potassium greater in the cell than outside the cell
• Concentration of sodium greater outside the cell than inside the cell
• Concentration of chloride greater outside the cell than inside the cell
• Sodium and potassium concentration maintained by sodium-potassium pump
• Three Na+ out for every two K+ in
• K+ channel always open at resting potential(K+ leak)
• Net outflow of K+ and negative net charge inside cell
• At equilibrium, both electrical and chemical gradients are balanced

Question 6

Nernst equation

Answer 6

• Used to calculate equilibrium potential

* Log[ion]outside/Log[ion]inside

Question 7

Difference in resting potentials between neurone and cardiac cells

Answer 7

• Neuron:
	○ Many more K+ channels than Na+ channels
	○ Slight compromise between Ek and Ena
• Cardiac:
	○ Majority K+ channels
	○ Resting potential is similar to Ek

Question 8

What is The goldman equation used for?

Answer 8

Used to calculate resting potential of a cell taking into account multiple ion permeabilities

SEE EQUATION

Question 9

Why does change in membrane potential occur?

Answer 9

Change in membrane potential occurs due to certain stimuli causing ion gated channels to open or close

Question 10

What occurs in hyperpolarisation?

Answer 10

○ When gated K+ channels open:
§ K+ diffuse out
§ Inside of cell becomes more negative
Graded hyperpolarisation produced by two stimuli that increase membrane permeability to K+

Question 11

What occurs in depolarisation?

Answer 11

○ When gated Na+ channels open:
§ Na+ diffuse in
§ Inside of cell becomes more positive
○ Graded depolarisations produced by two stimuli that increase membrane permeability to Na+

Question 12

How is an action potential generated and move?

Answer 12

• When depolarisation shifts membrane potential sufficiently resulting in a massive change in voltage
• Action potential generated as Na+ flows inwards across the membrane at one location
• Depolarisation of action potential spreads reinitiating the action potential there
• Region before is repolarising as K+ flows outwards
• Depolarisation moves onto the next region and therefore these local currents propagate action potential along the length of axon

Question 13

What is not possible during the refractory period?

Answer 13

second action potential cannot be initiated

Question 14

Relation between action potential speed and axon diameter

Answer 14

• Speed of an action potential increases with the axons diameter

Question 15

What do vertebrates have that increases the speed of the action potential?

Answer 15

A myelin sheath

Question 16

What do oligodendrocytes provide to the CNS?

Answer 16

provide support and insulation to axons

Question 17

What makes up the myelin sheath in the PNS?

Answer 17

Schwann cells

Question 18

What is the grey area in the brain?

Answer 18

Cell bodies

Question 19

What is the white area in the brain?

Answer 19

Axons

Question 20

In saltatory conduction, where do action potentials occur on the myelin sheath?

Answer 20

Only occur at the nodes of ranviers

Question 21

In saltatory conduction, how do action potentials travel down the membrane?

Answer 21

Action potentials jump between nodes of ranvier

Question 22

Action potential in cardiac cell

Answer 22

• Rapid Na+ inactivation
• Plateau phase
• Ca2+ elicits further Ca2+ release from sarcoplasmic reticulum leading to muscle contraction
• Rapid repolarisation
• Diastole
• Increase in action potential frequency increases heart rate
• Plateau phase shortens due to quicker inactivation of Ca2+ channels