Action potentials

Question 1

what is the advantage of passive conduction

Answer 1

direct coding

Question 2

what is direct coding

Answer 2

coded strength directly indicates the signal strength

Question 3

what are the two disadvantages of passive conduction

Answer 3

attenuation

noise

Question 4

what is attentuation

Answer 4

coded signal decreases with distance

Question 5

what are three advantages of active conduction

Answer 5

high amplitude
noise resistant
quite fast

Question 6

what is the basis of an action potential

Answer 6

changing the relative na and k conductances the membrane potential can change from -75 to +55

Question 7

what are 4 points about leakage channels

Answer 7

always open
relatively low conductance
channels not affected by voltage or ligand

Question 8

what are the two examples of voltage dependent channels for an action potential

Answer 8

na and k

Question 9

what activates voltage dependent channels for an action potential?

Answer 9

depolarisation
at resting potential (low conductance) channels tend to be closed
open (high conductance) when membrane depolarises- gets more positive

Question 10

describe opening and closing of na and k channels during action potential

Answer 10

na open (active) rapdily but then shut automatically (inactive) even if membrane stays depolarised - self limiting
k channels open (active) more slowly and do not shut while membrane stays depolarised

Question 11

what is it that determines the action potential slope on a graph

Answer 11

feedback loops

Question 12

what are the two feedback loops of an action potential

Answer 12

positive and negative

Question 13

describe the positive feedback loop of an action potentual

Answer 13

depolarisation
increased sodium conductance
increase inflow of sodium

Question 14

describe the negative feedback loop of an action potential

Answer 14

depolarisation
increased potassium conductance
k outflow
leads to hyperpolarisation

Question 15

what does hyperpolarisation do

Answer 15

counteracts the depolarisation

Question 16

what is an action potential threshold

Answer 16

all or none factor

if stimulus is not big enough, increased sodium conductance cant overcome leakage of potassium

Question 17

what is a refractory period

Answer 17

second stimulus elicited shortly after a first spike fails to initatiate a response

Question 18

what does refractory period set

Answer 18

an upper limit to spike frequency

Question 19

what does the refractory period ensure

Answer 19

uni directional propagation

Question 20

what are the two types of refractory periods

Answer 20

absolute

relative

Question 21

what is the absolute refractory period

Answer 21

cannot get another spike with second stimulus
after na active, takes them a while to deactive
until fully deactiveted, they cannot open the channel

Question 22

what is the relative refractory period

Answer 22

needs bigger than normal stimulus to get another spike
after membrane repolarises, k channels close slowly
residual excess k conductance after spike
makes membrane more difficult to depolarise

Question 23

how do spikes propagate

Answer 23

through passive conduction

Question 24

what reduces the space constant for propagation

Answer 24

excess potassium conductance

Question 25

what is important for travelling far distances (AP)

Answer 25

conduction velocity

Question 26

how can we increase conduction velocity

Answer 26

increase axon diameter

Question 27

what are two disadvantages of fat axons

Answer 27

expensive

cant fit too many into small nerve bundles

Question 28

what is myelination

Answer 28

myelin wrap around neurons

Question 29

what does myelination do

Answer 29

blocks membrane leaks increasing the time constant and reduces capacitance meaning membranes charge faster

Question 30

what is saltatory conduction

Answer 30

action potential jumps from node to node (nodes of ranvier)

Question 31

what is mutiple sclerosis

Answer 31

immune system destroys central myelin

reduces space constant

Question 32

when will current flow

Answer 32

if there is a driving force and a conducting path

Question 33

what was the main aim of hodgkin and huxleys work

Answer 33

to explain the ionic basis of action potentials

Question 34

what are two useful drugs for HH experiments

Answer 34

tetrodotoxin (TTX)
tetraethyl ammonium (TEA)

Question 35

what does TTX do

Answer 35

blocks na channels

Question 36

what does TEA do

Answer 36

blocks k channels