Membrane potentials

Question 1

What does EPSP mean?

Answer 1

Excitatory post synaptic potential. This is where there is an influx of positive ions into the cell causing depolarisation (causes the membrane potential to rise above the resting potential)

Question 2

What does IPSP mean?

Answer 2

Inhibitory post synaptic potential. This is an influx of negative ions (e.g. Cl-) causing the cell to become more negatively charged (repolarisation)

Question 3

Where are concentrations of Na+, Ca2+, K+ and Cl- higher?

Answer 3

Outside the cell: Higher conc of Na+, Ca2+ and Cl-
Inside the cell: Higher conc of K+

Question 4

What is an inactivated sodium voltage gated channel?

Answer 4

This is where, after depolarisation of the membrane, sodium voltage gated channel are inactivated which prevents sodium ions from entering into the membrane until repolarisation has occurred.

This prevents sodium ions from moving backwards too.

Question 5

What happens during the repolarisation period?

Answer 5

sodium potassium pump works to pump 3 sodium ions out of the cell for every 2 potassium ions into the cell.
Potassium ions move out of the cell by facilitated diffusion via potassium voltage gated channels.
Sodium potassium pumps are inactivated.

Question 6

What is the importance of the refractory period?

Answer 6

Prevents action potentials from happening too closely.
Prevents action potentials from moving backwards along a neuron.

Question 7

What causes hyperpolarization?

Answer 7

Potassium channels remain open while sodium channels are closed.

Question 8

How does fatty myelin speed up the rate of nerve conduction?

Answer 8

There are no ion channels on the membrane inside myelin sheath. Instead the action potentials move rapidly down the membrane by saltatory conduction from node to node (Node of Ranvier).

Question 9

What is the resting membrane potential? Threshold Potential? and peak of the action potential?

Answer 9

Resting= -70mv
Threshold= -55mv
Action peak= +30mv

Question 10

What mechanism maintains the uneven distribution of ions across a membrane?

Answer 10

Sodium/potassium ATPase

Question 11

What factor is most important in creating the resting potential?

Answer 11

Relative permeability of Na+ and K+ ions

Question 12

What is the Nernst equation?

Answer 12

This is an equation that defines the relationship between the concentrations of an ion on either side of the membrane to give us the magnitude of the electrical gradient.

Question 13

What is the Goldman-Hodgkin-Katz equation tell us?

Answer 13

Used to calculate the potential across a cell’s membrane taking into account all of the ions and their permeability across the membrane

Question 14

Why is the resting potential closer to potassium than sodium?

Answer 14

This is because the membrane is much more permeable to K+ than to Na+.

Question 15

What happens to cause an action potential?

Answer 15

Electrical impulses causes an influx of sodium ions into the membrane via sodium channels. If the influx reaches the threshold potential, then sodium voltage gated channels open causing an action potential (all or nothing principle)/

Question 16

What is temporal summation?

Answer 16

When 2 separate impulses (from same source) work together to cause depolarization of a membrane

Question 17

What is spatial summation?

Answer 17

When 2 impulses from different sources add together to hit the threshold potential.

Question 18

What is the difference between convergence and divergence?

Answer 18

Convergence is when impulses from 2 or more fibres converge on a single neuron (spatial summation).

Divergence is when one neuron sends impulses that are divided into several branches of an axon.

Question 19

What is the absolute and relative refractory period?

Answer 19

Absolute- Axon membrane is incapable of producing another action potential (prevents impulses moving backwards)
Relative- Axon membrane can produce another action potential, but requires a stronger stimulus.