the resting membrane potential

Question 1

the inside of the cell is ____vely charged compared to the outside

Answer 1

negatively

Question 2

where in the cell can you find more sodium, chlorine and calcium?

Answer 2

outside

Question 3

where in the cell can you find more potassium and proteins?

Answer 3

inside

Question 4

sum up the ion distribution in the cell membrane

Answer 4

most potassium ions are inside the neuron, whilst most sodium, chlorine and calcium are in the extracellular fluid (outside). Protein remains inside the cell.

Question 5

why does this particular ion distribution occur?

Answer 5

particles always move from high to low concentration gradients.
- there is a diffusion of potassium (k+)

Question 6

what is the purpose of the sodium/potassium pump? Na-/K+ (what does it do and why is this useful)

Answer 6

it is a mechanism that pumps 3 Na+ ions out of the cell for every 2 K+ ions that pump in.
useful because sodium channels are not open usually, so it maintains the resting membrane potential

Question 7

what is the resting membrane potential?

Answer 7

• 60mV.

- a result of the selective permeability of the membrane and the activity of the Na/K pump

Question 8

how are voltage gated sodium channels opened?

Answer 8

by neurotransmitters which bind to the receptors on the ion channels

Question 9

what is an action potential?

Answer 9

= a very brief but large change in neural polarisation

the propagated electrical message that travels along the axon to the presynaptic axon terminals

Question 10

what causes an action potential?

Answer 10

the opening of the voltage gated sodium channels at the axon hillock.

Question 11

what is hyperpolarisation?

Answer 11

an increased negativity of the membrane potential.

- goes further from 0.

Question 12

what ion channels cause hyperpolarisation?

Answer 12

potassium or chlorine

Question 13

what is depolarisation?

Answer 13

a decreased polarization of the membrane potential in the cell.
- makes the inside of the cell more like the outside, bringing it closer to 0.

Question 14

what ion channels cause depolarization?

Answer 14

sodium

Question 15

at what mV does the charge reach threshold, causing an action potential?

Answer 15

-40mV

Question 16

name 4 characteristics of a voltage gated action potential

Answer 16

• passive
• fast
• multidirectional
• decremental

Question 17

what is the postsynaptic potential?

Answer 17

when a neurotransmitter briefly alters the membrane potential of the postsynaptic cell.

Question 18

what characteristics are there of a postsynaptic potential?

Answer 18

• passive

- decremental (decrease in strength with time and distance)

Question 19

what is an EPSP?

Answer 19

a DEPOLARIZING potential in the post synaptic neuron

• an increase of charge closer to zero.
• these INCREASE the probability that the postsynaptic neuron will fire an action potential.

Question 20

what is an IPSP?

Answer 20

a HYPERPOLARIZING potential in the postsynaptic neuron.

• a charge further from zero.
• this DECREASES the probability that the postsynaptic neuron will fire an action potential.

Question 21

what does the cell membrane reflect at any one time?

Answer 21

the spatial and temporal summation of all the EPSP/IPSPs at that time

Question 22

where does summation of information occur?

Answer 22

at the axon hillock

Question 23

when do voltage gated ion channels open in the postsynaptic neuron?

Answer 23

when the membrane potential reaches threshold. these remain open during a voltage window, then close automatically.

Question 24

what is the absolute refractory period?

Answer 24

a period of time after which an action potential has taken place where an ion channel will not open again, regardless of the charge.

Question 25

describe propagation of the action potential down the axon (5 parts)

Answer 25

1. a voltage gated ion channel is opened at the top of the axon due to summation at the axon hillock.
2. this depolarization will travel to the other channels adjacent to it, which will then open.
3. action potentials travel down the axon, regenerating at each ion channel. it does not get weaker as it travels along.
4. the previous voltage gated channel cannot be repolarised due to the absolute refractory period.
5. propagation is therefore a unidirectional flow

Question 26

name 4 features of propagation down an axon

Answer 26

• non-decremental (doesnt decrease)
• passive (does not need any energy)
• slow (takes some time)
• unidirectional

Question 27

what role does myelin play on the axon?

Answer 27

increases the speed of action potentials

Question 28

describe propagation over the presynaptic membrane

Answer 28

1. action potentials travel down the axon and arrive at the axon terminal
2. this depolarization opens voltage-gated calcium channels in the membrane of the terminal
3. the calcium causes synaptic vesicles filled with neurotransmitters to bind to the presynaptic cell membrane.
4. this releases neurotransmitter molecules into the synaptic cleft.
5. the transmitter molecules cross the cleft to bind to the receptor molecules in the postsynaptic membrane which opens the ion channels.
6. this flow creates local EPSP/IPSPs in the postsynaptic neuron.