topic 6 neurons/action potential

Question 1

are nerve cells polarised or depolarised at rest?

Answer 1

polarised

Question 2

why is the inside of a neuron negative compared to the outside?

Answer 2

imbalance of sodium and potassium ions

Question 3

what is the resting potential of a neuron?

Answer 3

-70mV

Question 4

how is the resting potential maintained and generated?

Answer 4

by the sodium potassium pump

Question 5

how is the inside of a neuron made negative compared to the outside?

Answer 5

sodium potassium pump moves sodium out, creating an electrochemical gradient. higher conc of sodium outside the membrane and the membrane is not permeable to sodium.
moves potassium ions into the axon, these can also move by faciliated diffusion. there are more potassium channels and these are mainly open, whereas sodium channels are mainly shut.

Question 6

how many sodium ions are pumped out of the axon?

Answer 6

3

Question 7

how many potassium ions are pumped into the axon?

Answer 7

2

Question 8

what is needed for active transport to occur?

Answer 8

ATP

Question 9

what does Na+ stand for?

Answer 9

sodium ion

Question 10

what does K+ stand for?

Answer 10

potassium ion

Question 11

what is an action potential?

Answer 11

when the neuron’s voltage increases beyond a set point, resulting in a nervous impulse

Question 12

why does a neuron’s voltage increase/depolarisation occur?

Answer 12

membrane becomes more permeable to sodium

Question 13

what happens in an action potential when a stimulus is detected?

Answer 13

excites the cell membrane of the neuron, which causes sodium ion channels to open
membrane becomes more permeable to sodium, so sodium ions diffuse into the neuron down the electrochemical gradient
inside of the neuron becomes less negative

Question 14

what happens in an action potential during depolarisation?

Answer 14

potential differences reaches the threshold at around -55mV
more sodium ion channels open
more sodium ions rapidly diffuse into the neuron

Question 15

what happens in an action potential during repolarisation?

Answer 15

potential difference of around 30mV
sodium channels close and potassium channels open
membrane becomes more permeable to potassium
potassium ions diffuse out of the neuron down the potassium ion concentration gradient
begins to return to resting potential

Question 16

what happens in an action potential during hyperpolarisation?

Answer 16

potassium channels are slow to close
overshoot happens where too many potassium ions diffuse out of the neuron
potential difference becomes more negative than resting potential

Question 17

how does an action potential go from hyperpolarisation to resting potential?

Answer 17

ion channels reset

sodium potassium pump returns membrane to resting potential

Question 18

what is the ‘all or nothing’ principle?

Answer 18

there is a -55mV threshold
if a stimulus does not exceed this threshold then an action potential is not produced
bigger stimulus increases the frequency of action potentials
only respond to large enough stimuli to prevent someone becoming overwhelmed

Question 19

what is the refractory period?

Answer 19

after the action potential is generated, the membrane enters the refractory period where it cannot be stimulated
sodium channels are recovering and cannot be opened

Question 20

why is the refractory period important?

Answer 20

results in discrete impulses- no overlap allows separate action potentials to be processed
action potential travels in one direction- if it is spread in different directions a response is prevented
limits the number of impulse transmissions, prevents over reaction to stimuli and overwhelming the sense

Question 21

what are waves of depolarisation?

Answer 21

action potential occurs
some sodium ions entering the neuron diffuse sideways
sodium ion channels in the next region of the neuron open
sodium ions diffuse into the next part of the neuron
wave of depolarisation travels along the neuron
wave moves away from parts of the neuron in the refractory period

Question 22

what is the myelin sheath?

Answer 22

electrical insulator, made up of Schwann cells with Nodes of Ranvier

Question 23

how can the myelin sheath act as an electrical insulator?

Answer 23

made of lipids so no charged ions can pass through

Question 24

where are sodium ions concentrated?

Answer 24

at the Nodes of Ranvier

Question 25

is an action potential quicker with myelinated or non-myelinated neurons?

Answer 25

myelinated

Question 26

how does conduction occur in myelinated neurons?

Answer 26

depolarisation only happens at the Nodes of Ranvier
cytoplasm conducts enough electrical charge to depolarise the next node
impulse jumps, known as saltatory conduction

Question 27

how does conduction occur in non-myelinated neurons?

Answer 27

slower
impulse is a wave along the axon membrane so there is depolarisation all along
has to generate an action potential along the whole length

Question 28

what is an axon?

Answer 28

long fibre that conducts/carries nerve impulses

Question 29

how does axon diameter impact speed of conduction?

Answer 29

bigger diameter means a quicker action potential
less resistance to flow of ions and depolarisation reaches other parts of the cell membrane faster
less leakage of ions

Question 30

how does temperature impact speed of conduction?

Answer 30

speed of conduction increases as temperature increases
ions diffuse faster
enzymes involved in respiration are faster so more ATP produced for sodium-potassium pump
however if too high denatures