Lecture 26: Membrane potentials

Question 1

What are the components of a neuron?

Answer 1

Dendrites
Cell body
Axon
Axon terminals

Question 2

What is the function of dendrites?

Answer 2

Receives electrical input

Question 3

What is the function of cell body?

Answer 3

Passively conducts electrical signals

Question 4

What is the function of axon?

Answer 4

Propagate action potentials

Question 5

What is the function of axon terminals?

Answer 5

Release chemical signals

Question 6

What are the two types of signals used for communication by neurons?

Answer 6

Electrical and chemical signals

Question 7

What is the resting membrane potential?

Answer 7

Difference in potential between inside and outside of a cell

Question 8

What is the resting membrane potential of neurons?

Answer 8

-50 to -70mV

Question 9

What is special about neurons and muscle fibres compared to other cells in the body?

Answer 9

These cells are able to respond to sudden transient change of the potential (an action potential) in response to a stimuli - they are known as excitable tissues

Question 10

What generates the resting membrane potential?

Answer 10

1) Unequal concentrations of sodium and potassium ions inside and outside the cell
2) Unequal permeability of the cell membrane to certain ions

Question 11

What is the relative concentration of sodium and potassium ions at RMP?

Answer 11

Higher sodium ion concentration outside the cell and higher potassium ion concentration inside the cell

Question 12

How is the concentration gradient of the sodium and potassium ions maintained?

Answer 12

By sodium/potassium pump (pumps 3 Na+ out for every 2 K+ in)

Question 13

What components of the membrane control permeability to ions?

Answer 13

1) Non-gated ion channels (leak channels)

2) Gated channels (voltage, ligand, or mechanically gated)

Question 14

What is the permeability of neurons at rest?

Answer 14

There are many leak K+ ion channels but very few leak Na+ ion channels therefore the membrane is a lot more permeable to potassium ions

40x more permeable to K+

Question 15

What is equilibrium potential?

Answer 15

An intracellular potential at which the net flow of ions is zero, in spite of a concentration gradient and permeability

Question 16

What is the nernst equation?

Answer 16

Eion = 2.3RT/zF x log [ion]outside/[ion]inside
Eion = 61.5mV x log [ion]outside/[ion]inside

Question 17

When does the nernst equation apply?

Answer 17

When a cell membrane is only permeable to a single ion - hence this equation can be used to calculate RMP for that membrane

Question 18

What is the relationship between permeability and RMP?

Answer 18

The more permeable a membrane is to an ion the closer the RMP of that membrane will be to the equilibrium potential of that ion

Question 19

What is the Goldman equation?

Answer 19

A way of calculating RMP that takes both concentration gradients and relative permeability into account

Vm = 61.5mV x log( Pk[K+]o + Pna[Na+]o/Pk[K+]i + Pna[Na+]i)

Question 20

If more K+ ion channels are activated how would this affect sensitivity to pain?

Answer 20

Activation of K+ leaky channels means that K+ ions will flow out of the cell causing membrane potential to become more negative -> this requires greater stimuli for action potentials to occur therefore sensitivity will decrease