Lecture: Physiology 2: Neuronal signalling: Ions, action potentials and the synapse

Question 1

What is voltage (DV)?

Answer 1

The difference in electric potential energy per unit charge between two points.

Question 2

What is voltage used to signal?

Answer 2

Voltage across membrane is used to signal changes, ie. ion movements across the membrane.

Question 3

What is current (I)?

Answer 3

The flow of electric charge through a medium.

Question 4

What is resistance (R)?

Answer 4

The opposition to the passage of an electric current.

Question 5

What is electrical conductance (g)?

Answer 5

Inverse of resistance; measuring how easily electricity flows along a certain path.

Question 6

Equation for Ohm’s Law

Answer 6

V = I x R

Question 7

Equation for conductance (g)

Answer 7

g = 1/R or current/voltage

Question 8

What is meant by ‘selectively permeable’?

Answer 8

cell membrane is a “selectively permeable membrane” whereby some ions can pass through, but others cannot

Question 9

What effects ionic permeability?

Answer 9

Ionic permeabilities (and related conductance) depend on ion channels being open, so selectivity can vary over time.

Question 10

What is transmembrane potential (Vm)?

Answer 10

Measurement of the overall electrical potential energy across the membrane

Question 11

What determines transmembrane potential (Vm)?

Answer 11

The relative electrical currents and conductance’s of different ions.

Question 12

What are the 4 steps of an action potential?

Answer 12

1. At rest, K+ is going out of cell; -ve membrane potential (e.g. -70 mV)
2. External factor causes the membrane to depolarise slightly.
3. If the voltage reaches threshold, then Na+ enters cell and membrane potential depolarises and becomes positive (+40 mV). Positive Feedback Loop.
4. Eventually Na+ conduction diminishes, K+ conductance increases; membrane repolarises, becomes slightly more negative and then returns to resting.

Question 13

Describe the ‘all or nothing’ model for action potentials

Answer 13

An action potential is not trigger unless there is an appropriate force from a stimuli to trigger an action potential; depolarisation of the cell must reach a certain limit, otherwise the action potential will not follow through.

Question 14

What is the refractory period?

Answer 14

Period within an action potential whereby new action potentials cannot be initiated.

Question 15

What are neurotransmitters?

Answer 15

Neurotransmitters are endogenous chemicals that are released extracellularly by neurons across a synaptic junction.

Question 16

What are the purpose of neurotransmitters in signalling?

Answer 16

Synapses use neurotransmitters to transfer action potentials between cells to propagate signalling.

Question 17

How do neurotransmitters send signals across a synapse?

Answer 17

1. Neurotransmitter is synthesised and moved to the cell membrane via vesicles.
2. AP causes depolarisation which opens calcium channels and causes increase in free calcium ions.
3. Increase in free calcium causes neurotransmitter to be released when vesicle fuses with membrane.
4. Neurotransmitter diffuses across synaptic cleft and binds to and activates specific post-synaptic receptors which will typically open an ion channel.

Question 18

What happens to neurotransmitters after they have triggered an action potential?

Answer 18

Neurotransmitter diffuse away and are either metabolised or transported back to terminal.

Question 19

What is gating?

Answer 19

Biochemical changing of a protein to open or close channels. Channels open when there is a positive change inside the membrane.

Question 20

What is the equilibrium potential of sodium?

Answer 20

+60 mV

Question 21

What is the equilibrium potential of potassium?

Answer 21

-90 mV

Question 22

What is the equilibrium potential of calcium?

Answer 22

+123 mV

Question 23

What is the equilibrium potential of chloride?

Answer 23

-40 mV

Question 24

How does the equilibrium potential dictate the movement of ions?

Answer 24

Membrane potential is driven towards the equilibrium potential of particular ion if there is great permeability (or conductance) for that ion

Question 25

What are some examples of neurotransmitter?

Answer 25

Glutamate
Dopamine
Acetylcholine