Action Potentials

Question 1

what is the resting membrane potential

Answer 1

about -70mV

Question 2

the ICF or the ECF more negative?

Answer 2

ICF

Question 3

which ion is most abundant in the ECF?

Answer 3

Na

Question 4

which ion is most abundant in the ICF?

Answer 4

K

Question 5

which ion can move through the membrane more?

Answer 5

K

Question 6

how is the resting membrane potential brought about?

Answer 6

potassium diffuses OUT of the cell which leaves an excess of -ve charges inside the cell. The potential gradient that arises from this is the resting membrane potential

Question 7

what does the sodium potassium pump do?

Answer 7

move 3Na out and 2K in

Question 8

does the sodium potassium pump require energy?

Answer 8

yes as it moves the ions from a low to high concentration

Question 9

what is the threshold voltage during the AP?

Answer 9

-55mV

Question 10

what is the rising phase during the action potential due to?

Answer 10

Na+ influx through voltage gated Na channels

Question 11

what is the falling phase during the action potential due to?

Answer 11

K+ efflux through voltage gated K channels

Question 12

what type of protein is an ion channel?

Answer 12

transmembrane protein

Question 13

how many gates does the sodium channel have?

Answer 13

2 - H and M

Question 14

what is the action of the sodium gates?

Answer 14

the channel opens when the M gate opens as H gate is already open. The channel closes when the H gate closes (refractory period)

Question 15

at resting membrane potential what is the state of the Na gate?

Answer 15

H gate open, M gate closed

Question 16

at the threshold until hyperpolarisation what is the state of the Na gate?

Answer 16

M gate and H gate open

Question 17

at the refractory stage what is the state of the Na gate?

Answer 17

M gate open, H gate closed

Question 18

how many gates are there for K

Answer 18

1

Question 19

what is the first step of the AP?

Answer 19

stimulus applied - depolarisation - MP moves towards threshold, gated ion channels closed

Question 20

what is the second step of the AP?

Answer 20

MP reaches threshold (-55mV) - Na channels start opening, Na influx, more depolarisation, K+ channels still closed

Question 21

what is the third step of the AP?

Answer 21

all Na channels open, maximum Na influx, MP overshoots 0mV

Question 22

what is the fourth step of the AP?

Answer 22

MP reaches +35mV - Na channels shut, inactivation, H gate closes, K+ channels open and K+ efflux begins

Question 23

what is the fifth step of the AP?

Answer 23

AP downstroke (recovery phase) - Na+ channels shut, refractory period, K+ channels open, K+ efflux continues

Question 24

what is the sixth step of the AP?

Answer 24

MP returns to resting level, ion channels return to resting state (H gate open, M gate closed), excitability restored

Question 25

what happens at the threshold of the AP?

Answer 25

voltage gated Na channels open, Na+ diffuse in, further depolarisation, positive feedback involved

Question 26

what happens at the peak of the AP?

Answer 26

Na+ channels close, voltage gated K+ channels open, K+ diffuse out - repolarisation

Question 27

what is the refractory period

Answer 27

after an AP is initiated the neuron cannot generate another AP until the first one has ended (period of inexcitability)

Question 28

what is the refractory period due to?

Answer 28

inactivation of the voltage gated sodium channels (H gate closed)

Question 29

what are the consequences of the refractory period?

Answer 29

limits maximum firing frequency, ensures unidirectional propagation of action potentials, prevents summation of AP, prevents summation of contractions in cardiac muscle

Question 30

describe AP propagation

Answer 30

AP set up in one section of axon, depolarises adjacent part, AP regenerated further along, it moves along the axon as waves of depolarisation

Question 31

what increases AP propagation?

Answer 31

myelination and large axons

Question 32

what does myelination do?

Answer 32

increases speed of AP propagation for given diameter of axon, forms an insulating layer which reduces leakage of current from axons

Question 33

what is myelin laid down by?

Answer 33

glial cells

Question 34

what are the spaces where the myelin sheath is interrupted called?

Answer 34

Nodes of Ranvier

Question 35

what occurs at the nodes of Ranvier?

Answer 35

axon membrane is exposed to ECF and ion flow can occur

Question 36

what is saltatory conduction

Answer 36

AP jumps from one node of Ranvier to the next which increases speed so fewer regeneration steps meaning more rapid AP propagation

Question 37

what is the tissue layer surrounding axons?

Answer 37

endoneuron

Question 38

what layer protects a bunch of axons?

Answer 38

perineuron

Question 39

what layer protects lots of bunches of axons?

Answer 39

epineuron

Question 40

what do A beta fibres do?

Answer 40

mechanoreceptors

Question 41

what do A delta fibres do?

Answer 41

mechanoreceptors, thermoreceptors, nociceptors, chemoreceptors

Question 42

what do C fibres do?

Answer 42

mechanoreceptors, thermoreceptors, nociceptors

Question 43

are tooth fibres myelinated or unmyelinated?

Answer 43

most are unmyelinated as when myelinated fibres move closer to odontoblasts they lose myelination