FoM:L4+5 - Ion distribution

Question 1

What is ion distribution?

Answer 1

the location and concentration of biologically important ions both inside and immediately outside a cell

Question 2

What is membrane potential (Vm)?

Answer 2

• difference in electrical potential between interior and exterior of a cell
• measured in mV

Question 3

Describe the relative amounts/concentrations of the following ions inside and outside the cell: Na+ , K+ , Cl- , Ca2+ , A-

Answer 3

Na+: higher outside
K+ : lower outside
Cl- : higher outside
Ca2+ : higher outside
A- : lower outside

Question 4

Why is the distribution of ions important?

Answer 4

• cells would shrink or swell by osmosis
• response and survival
• create charge difference

Question 5

Outline resting membrane potential…

Answer 5

• all cells have Vm which is negative compared to ECF
• excitable cells have larger Vm
• dependent on ion distribution and permeability

Question 6

Describe the distribution of ions around a membrane

Answer 6

• negative ions attracted to inner surface of membrane
• positive ions attracted to outer surface
• region around the membrane is essential for Vm

Question 7

What 2 forces are acting on each ion?

Answer 7

• concentration gradient
• electrical gradient
  forms electrochemical gradient

Question 8

What is equilibrium potential?

Answer 8

The membrane potential at which
equilibrium would occur for an individual Ion (i.e. if cell were only permeable to that ion)
- balance between electrical and chemical gradients

Question 9

How do ions move through membranes?

Answer 9

• do not move through cell membranes directly (CHARGED)
• open channels or other processes

Question 10

Describe membrane permeability to potassium at rest

Answer 10

• potassium channels are open
• allow potassium to move
• which makes [K+] the main determinant of resting membrane potential

Question 11

What is resting membrane potential?

Answer 11

The steady state membrane potential at rest and is generated from interactions of multiple ion species

Question 12

What can alter the membrane potential?

Answer 12

changes in intracellular and extracellular concentrations of ions

Question 13

How can membrane permeability be altered by gated ion channels?

Answer 13

• ligand gated: typically closed, when an agonist binds to binding site, they open and allow ions in
• voltage gated: typically closed, when Vm changes, they open and allow ions in

Question 14

What are graded potentials?

Answer 14

• excitatory post-synaptic potential (EPSPs)
• inhibitory PSPs
• changes in non-synaptic ion channels
• differ in size
• summation can occur

Question 15

What are action potentials?

Answer 15

• depolarisation past the threshold point
• all or nothing