communication within and between neurones (2)

Question 1

how long can axons be

Answer 1

a few cm

Question 2

signals need to travel from - to end of -

Answer 2

cell body, axon

Question 3

why is communication not via diffusion of chemicals

Answer 3

we can respond to stimuli very quickly especially in reflexes- communication is fast,
diffusion of chemicals would be far too slow

Question 4

what type of signal occurs in neurones

Answer 4

electrical

Question 5

what type of state is the resting membrane potential

Answer 5

an unstable state

Question 6

what happens while a neurone is in it’s passive state

Answer 6

energy is expended to maintain the unstable state of the resting membrane potential

Question 7

what happens upon a trigger to a neurone

Answer 7

because the neurone is in an unstable state, stored energy is then released

Question 8

what is the release of energy upon trigger of a neurone called

Answer 8

an action potential

Question 9

what is the membrane of a neurone

Answer 9

a phospholipid bilayer

Question 10

what type of ion does the lipid bilayer prevent passing through?

Answer 10

charged molecules/ ions

Question 11

how does the lipid bilayer create an unstable resting membrane potential

Answer 11

membrane creates barrier between inside and outside of neurone, creating a disparity between composition of liquid inside compared to inside

Question 12

what is embedded within the barrier

Answer 12

proteins with various roles

Question 13

what does the sodium/potassium exchange transporter do

Answer 13

moves sodium ions outside of the neurone and moves potassium ions into the neurone

Question 14

do the exchange transporters move more sodium out or more potassium ions in?

Answer 14

more sodium ions out

Question 15

sodium and potassium are both cations, meaning…

Answer 15

they each carry a single positive charge

Question 16

because transporter moves more sodium ions out of the cell than it does potassium ions into the cell, the charge is…

Answer 16

more negative inside the cell, as there is an accumulation of positively charged ions outside of the cell

Question 17

chloride is an…

Answer 17

anion, holds negative charge

Question 18

what is the difference in charges between the inside and outside of a neurone cell?

Answer 18

-70mV (minus as the charge inside of the cell is more negative)

Question 19

what is caused by the difference in charges between the inside and outside of a neurone cell

Answer 19

electrostatic pressure

Question 20

what is electrostatic pressure

Answer 20

the idea that positively charged ions want to move to an area of negative charge

Question 21

what does a transporter do

Answer 21

moves specific ions using energy

Question 22

what forces push sodium back into the cell

Answer 22

electrostatic pressure AND diffusion

Question 23

why does sodium not move back into the cell despite electrostatic pressure and diffusion

Answer 23

it can’t move through the phospholipid bilayer

Question 24

why does a little sodium get back into the cell and what happens to it then

Answer 24

because the lipid membrane is leaky, transporters push them back in

Question 25

what forces act to push K out of the cell

Answer 25

diffusion

Question 26

what forces act to keep K in the cell

Answer 26

electrostatic pressure

Question 27

why does K stay in the cell

Answer 27

the forces of diffusion balance out the force of electrostatic pressure

Question 28

describe the neurone cell at resting state

Answer 28

more sodium outside and more potassium inside, charge more positive outside cell and more negative inside cell, cell has electrical excitability (electrically charged ions would move if we let them), energy is being used by the sodium/ potassium transporter

Question 29

what happens in stage 1 of an action potential

Answer 29

the membrane depolarises

Question 30

why is the membrane said to be polarised when at rest

Answer 30

because there is differential charge inside and outside the cell

Question 31

what does depolarisation refer to

Answer 31

anything that brings the membrane closer to a charge of 0

Question 32

at what point to voltage-gated sodium channels open

Answer 32

-55mV

Question 33

what happens when voltage-gated sodium channels open

Answer 33

the membrane is much more permeable to sodium, and sodium moves into the cell via diffusion and because of electrostatic pressure

Question 34

what happens as sodium moves into the cell

Answer 34

the cell becomes less negatively charged

Question 35

what happens when the cell becomes positively charged

Answer 35

electrostatic pressure works against sodium moving into the cell, however diffusion overcomes this pressure

Question 36

what 2 channels open in stage 1 of an action potential

Answer 36

sodium and potassium

Question 37

what happens in stage 2 of an action potential

Answer 37

the membrane potential gets more positive as cations flood in

Question 38

what ion leaves the cell in stage 2 of an action potential

Answer 38

potassium, as the channels are open and there is no electrostatic pressure opposing them

Question 39

when do voltage-gated sodium channels close again

Answer 39

+40mV

Question 40

what happens in action potential stage 3

Answer 40

membrane repolarisation

Question 41

why does the membrane depolarise in stage 3

Answer 41

sodium ions and potassium leave the cell, so the cell starts becoming negatively charged again

Question 42

what happens in stage 4

Answer 42

membrane hyperpolarisation

Question 43

what is hyperpolarisation and why does it occur in stage 4

Answer 43

it is where the cell membrane becomes extremely negatively charged, it occurs becomes positively charged potassium cations continue to leave the cell

Question 44

what happens in stage 5

Answer 44

potassium channels close and other processes return the balance to resting membrane potential

Question 45

after an action potential is generated, what happens

Answer 45

the action potential is regenerated further down the membrane

Question 46

what makes up the myelin sheath

Answer 46

oligodendrocytes

Question 47

what do glia do

Answer 47

wrap around the neurone forming an insulating layer where an action potential can’t form, forming nodes

Question 48

what do nodes do

Answer 48

force action potentials to jump between nodes

Question 49

what happens to the action potential as it travels underneath the myelin sheath

Answer 49

it decreases, and then is regenerated at the nodes to save energy

Question 50

are action potentials always the same size

Answer 50

yes

Question 51

what is a chemical synapse

Answer 51

a physical gap between the neurones which is around 20nm

Question 52

what is in the terminal of presynaptic neurones

Answer 52

vesicles containing chemicals called neurotransmitters

Question 53

what are the 2 types of post synaptic potentials

Answer 53

excitatory and inhibitory

Question 54

what happens in an EPSP

Answer 54

they make it more likely that an action potential will fire because it brings the membrane potential closer to the threshold

Question 55

what causes an EPSP

Answer 55

Generally happens if we are opening cation channels (positive ion)

Question 56

what causes IPSP

Answer 56

open anion (negatively charged ion) channels

Question 57

what happens in an IPSP

Answer 57

As the membrane becomes less negative it creates less electrostatic pressure, so more chloride will move in- overall makes an action potential less likely to occur

Question 58

what are the 2 types of synapses

Answer 58

chemical and electrical (also called gap junctions)

Question 59

describe an electrical synapse

Answer 59

2 neurones are fused together by a single channel so that ions can move directly from 1 neurone to another

Question 60

when can an electrical charge move in both directions

Answer 60

in an electrical synapse