week 2

Question 1

can neurones extend over long distances

Answer 1

yes

Question 2

why cant signals move via diffusion

Answer 2

its too slow

Question 3

what are the signals in nature

Answer 3

electrical

Question 4

what is the fundamental concept of action potentials

Answer 4

electrical excitability

Question 5

what do action potentials depend on

Answer 5

the resting membrane potential

Question 6

what is the resting membrane potential (description)

Answer 6

electrical excitablity, when a neurone is not active (in a passive state) energy is used to maintain an unstable state

Question 7

what happens to the resting membrane potential when there is a trigger?

Answer 7

as the neurone is unstable upon a trigger energy is released which is the actoin potential

Question 8

what is the order of an action potential being released?

Answer 8

trigger - release of energy - signal (action potential)

Question 9

describe the cell membrane

Answer 9

• barrier
• leaky
• lipid bilayer
• mostly keeps ions out of the cell
• charged ions cant pass through very well

Question 10

what is the resting membrane potential

Answer 10

-70mV

Question 11

What ion moves out of the cell membrane more?

Answer 11

More Na goes out than K in

Question 12

what do transporters do?

Answer 12

moves Na+ cations out of the cell

Question 13

why is the resting membrane potential -70mV?

Answer 13

• less k+ going inside the cell means there are more positive ions outside of the cell
  -the inside of the neurone is more negative than the outside

Question 14

what are the forces involved in resting membrane potential

Answer 14

• diffusion
• electrostatic pressure - attraction and repulsion between ions e.g. positive ions want to move to are more negative area
• transporters - use energy to move specific ions

Question 15

what happens to the resting membrane potential at rest?

Answer 15

• Na tends to move into the cell as the cell membrane is only leaky for cations, but the transporter pushes them back out

Question 16

what does cl- do at rest?

Answer 16

wants to go inside the cell via diffusion but cannot due to electrostatic pressure

Question 17

what charge is the inside and outside of the cell at rest

Answer 17

outside = positive
inside = negative

Question 18

what does K+ do at rest?

Answer 18

wants to leave via diffusion but cannot due to electrostatic pressure

Question 19

what does na+ do at rest?

Answer 19

wants to enter via diffusion and can due to electrostatic pressure

Question 20

how is the resting membrane potential maintained?

Answer 20

by the sodium pump which requires energy

Question 21

how does an action potentil happen?

Answer 21

energy is stored up within a neurone at rest and the release constitutes an electrical signal (action potential)

Question 22

is the resting potential key to allowing activity?

Answer 22

yes

Question 23

what is stage 1 of the activation of an action potential called?

Answer 23

membrane depolarisation

Question 24

what happens during depolarisatoin?

Answer 24

• the voltage becomes closer to zero
• if the membrane depolarises to -55mV or closer to zero the sodium channels open
• causes more sodium to go inside, making the inside of the neurone more positive and depolarising it even more
• K+ channels also open

Question 25

what happens at stage 2 of the activation of action potentials?

Answer 25

- sodium cations flood into the neurone via diffusion and electrostatic pressure - the membrane potential becomes less negative

Question 26

what happens at stage 3 in the activation of action potentials?

Answer 26

- membrane potential turns positive - potassium ions can now leave the cell as there is no more electrostatic pressure - however there is more Na going in than k coming out - the sodium channels close at +40mV - K is still leaving the cell making the inside less positive

Question 27

what happens at stage 4 in the activation of action potentials?

Answer 27

- potassium channels remain open - K+ continue to leave the cell due to diffusion and electrostatic pressures - MEMBRANE REPOLARISATION

Question 28

what happens at stage 5 in the activation of action potentials?

Answer 28

- membrane hyperpolarisation - loads of k+ leaves making the inside negative (k+ keep leaving the cell) again = hyperpolarisation as it goes beyond -70 mV

Question 29

what happens in stage 6 in the activation of action potentials?

Answer 29

- potassium channels close - other processes restores the balance to the resting membrane potential

Question 30

does the activation of an action potential happen in a non localised manner?

Answer 30

no, it happens in a localised manner

Question 31

how big is the absolute movement of ions?

Answer 31

very small

Question 32

although the absolute movement od ions is small how does the shift in concentrations compare?

Answer 32

the shift in concentration is significant near the membrane - however only a small part of the membrane changes in voltage

Question 33

why is communication within the neurone fast?

Answer 33

- myelin sheath made from oligodendrocytes - action potentials jump between nodes - action potentials decrease as the travel underneath the sheath (due to insulating properties of the myelin sheath ions cannot go through) - the full action potentual is regenerated at the nodes - this saves energy

Question 34

why are action potentials important in brain function

Answer 34

- they are the basic code for information in the brain - the movement of ions creates an electrical signal which is the code for informational processing in our nervous system