Practical 2. Simulation of Resting Membrane Potential and Action Potential using Metaneuron

Question 1

What is neurotransmission ?

Answer 1

The conversion of an electrical signal which passes down a neuron, into a chemical messenger that passes this signal to the next neuron

Question 2

What are synapses filled with ?

Answer 2

Neurotransmitters

Question 3

What is the release of neurotransmitters triggered by ?

Answer 3

The activation of the presynaptic cell

Question 4

What does the action of the neurotransmitter at the post synaptic site lead to ?

Answer 4

Either an activation or an inhibition of the post synaptic neuron

Question 5

What is on either side of the neuronal membrane ?

Answer 5

Positive and negative ions

Question 6

What is the resting membrane potential determined by ?

Answer 6

The distribution of positively and negatively charged ions on either side of the neuronal membrane

Question 7

What is the resting membrane potential with respect to the extracellular medium ?

Answer 7

-65 mV

Question 8

Where does the local net positive charge on the outside of the neuronal cell membrane and a local negative charge on the inside occurr ?

Answer 8

Really close to the membrane

Question 9

How is a net positive charge outside the cell maintained with respect to the inside ?

Answer 9

Positive ions have to be pumped out of the cell

Question 10

How are positive ions pumped into the cell ?

Answer 10

Sodium/potassium ATPase

Question 11

What is the function of the sodium/potassium ATPase ?

Answer 11

Exports three sodium ions out for every 2 potassium ions it pumps into the cell

Question 12

What does the pumping of the sodium/potassium ATPase do ?

Answer 12

Leaves a net negative charge on the inside of the cell

Question 13

How does the neuron maintain high intracellular potassium and high extracellular sodium ?

Answer 13

Sodium/potassium ATPase

Question 14

What does the sodium/potassium ATPase pump consume ?

Answer 14

ATP

Question 15

What is the cells principle energy source ?

Answer 15

ATP

Question 16

How much of the neurons energy budget does the sodium/potassium ATPase use up ?

Answer 16

2/3

Question 17

What is energy used for ?

Answer 17

To maintain the polarised state

Question 18

What must happen for the neuron to fire ?

Answer 18

The membrane potential has to become less negative ie. depolarise

Question 19

What can depolarise the membrane potential ?

Answer 19

Stimulation of the neuron

Question 20

What is the most important type of stimulation ?

Answer 20

The arrival of the action potentials

Question 21

What is depolarisation typically initiated by ?

Answer 21

The sodium influx

Question 22

How is sodium influxed ?

Answer 22

Through a ligand gated sodium channel

Question 23

What opens or gates the sodium channel ?

Answer 23

Neurotransmitter binding

Question 24

What is the ligand ?

Answer 24

The neurotransmitter

Question 25

What opens the sodium channel ?

Answer 25

When the ligand binds to the receptor

Question 26

What does the neuron have to depolarise to if its going to achieve an action potential ?

Answer 26

At least -55mV

Question 27

What is the neuromuscular junction ?

Answer 27

The junction between the neuron and the muscle

Question 28

What is a failed initiation ?

Answer 28

Initiations where there is some depolarisation but it is insufficient to trigger an action potential

Question 29

What type of phenomenon is the triggering of an action potential ?

Answer 29

An all or nothing phenomenon

Question 30

What is a depolarisation ?

Answer 30

A change in voltage

Question 31

What opens behind the sodium channels ?

Answer 31

The voltage gated potassium channels

Question 32

What does the opening of the voltage gated potassium channels allow ?

Answer 32

Potassium ions to flow out to rapidly restore the charge separation

Question 33

How much intracellular potassium is there in the resting membrane potential verses the action potential ?

Answer 33

400mM verses 20

Question 34

How much extracellular sodium is there in the resting membrane potential verses the action potential ?

Answer 34

440mM verses 50

Question 35

What is the chemical trigger for neurotransmitter release ?

Answer 35

Calcium

Question 36

What is an excitatory post synaptic potential ?

Answer 36

The signal at the post synaptic site

Question 37

What happens when sodium channels are blocked with tetrodotoxin ?

Answer 37

The post synaptic and presynaptic potentials are progressively diminished across the time course of the tetrodotoxin treatment

Question 38

What contains tetrodotoxin ?

Answer 38

Puffer fish

Question 39

What does tetrodotoxin cause and why ?

Answer 39

Paralysis as it blocks all function at neuromuscular junctions

Question 40

What is an example of a potassium block ?

Answer 40

Tetraethylammonium

Question 41

How can the sodium influx be bypassed ?

Answer 41

By electrically depolarising the cell and the neurotransmitter still gets released and still stimulates the post synaptic cell

Question 42

What does the potassium block result in ?

Answer 42

The prevention of the normal repolarisation of the synaptic membrane

Question 43

What is potassium important in?

Answer 43

Repolarisation

Question 44

What are sodium and potassiums role in the release of neurotransmitters ?

Answer 44

Electrical

Question 45

What does depolarisation not produce in a calcium free medium ?

Answer 45

A post synaptic response

Question 46

What does increasing extracellular calcium increase ?

Answer 46

Neurotransmitter release

Question 47

As well as sodium and potassium channels, what other channels are there ?

Answer 47

Voltage dependent calcium channels

Question 48

Where must calcium be present to facilitate neurotransmitter release ?

Answer 48

Before or during the action potential

Question 49

What does dendrotoxin do ?

Answer 49

Blocks potassium channels

Question 50

Where is dendrotoxin found ?

Answer 50

Black mamba

Question 51

Where is latrotoxin found ?

Answer 51

Black widow spider

Question 52

What does latrotoxin produce ?

Answer 52

Massive acetylcholine release

Question 53

Where is alpha bungarotoxin found ?

Answer 53

Snake venom

Question 54

What does alpha bungarotoxin do ?

Answer 54

Blocks acetylcholine nicotinic receptor on skeletal muscle resulting in paralysis

Question 55

What are the steps in neurotransmitter release ?

Answer 55

1. Sodium channels open 2. Voltage change above 40mV - depolarisation 3. Voltage dependent calcium channels open 4. Low affinity calcium sensors in the active zone bind calcium 5. Calcium dependent exocytosis 6. Rapid turn off as calcium diffuses away from active zone

Question 56

Why does the concentration of calcium go very high for a short time ?

Answer 56

The synapse can rapidly buffer calcium - therefore must trigger its response quickly

Question 57

What are the four main factors influencing intracellular and extracellular concentrations ?

Answer 57

1. Electrical gradients 2. Chemical gradients 3. Membrane permeability and leak channels 4. Sodium/potassium ATPase

Question 58

What is equilibrium potential ?

Answer 58

The potential at which the chemical and electrical forces on a given ion are balanced and therefore is the potential at which this ion would cease to move across the membrane

Question 59

What is the phospholipid bilayer of the cell membrane highly impermeable to ?

Answer 59

Ions

Question 60

What is in the phospholipid bilayer of the cell membrane ?

Answer 60

Proteins embedded in the lipid bilayer

Question 61

What are ion channels ?

Answer 61

Proteins embedded in the lipid bilayer

Question 62

What do ion channels do ?

Answer 62

Allow for the highly specific passage of ions

Question 63

What do leak potassium channels allow ?

Answer 63

Potassium to flow through the membrane in response to the disparity in concentrations inside and outside the cell

Question 64

What contributes to the resting membrane potential of about -65mV ?

Answer 64

1. Sodium/potassium ATPase | 2. Potassium leak channels

Question 65

What is the threshold potential ?

Answer 65

The critical level to which a membrane potential must be depolarised to initiate an action potential