action potential

Question 1

what is resting membrane potential?

Answer 1

the potential difference that exists across the membrane of all cells

Question 2

what is the range of resting membrane potential?

Answer 2

20-90mV

Question 3

which cellular fluid is more negative?

Answer 3

ICF

Question 4

what causes the polarised ion/charge distribution?

Answer 4

the charge at the very edge of membranes
- inside
+ outside

Question 5

which is the predominant cation in ECF?

Answer 5

sodium

Question 6

what is the principal anion in ECF?

Answer 6

chloride

Question 7

which is the predominant cation in ICF?

Answer 7

potassium

Question 8

which is the principal anion in ICF?

Answer 8

phosphate

Question 9

which directions do Na/K go?

Answer 9

Na into cell

K out of cell

Question 10

which ion is the resting membrane very permeable to?

Answer 10

potassium

Question 11

what causes the resting membrane potential?

Answer 11

diffusion of K leaves excess neg change, potential gradient arising= RMP

Question 12

how is the small amount of Na that leaks into the cell expelled?

Answer 12

the Na/K pump

Question 13

what other factor contributes to RMP?

Answer 13

Na/K pump by exchanging unequal numbers of Na(3 out) and K(2 in)
electrogenic

Question 14

what is the AP threshold?

Answer 14

-55mV

Question 15

what is the rising phase due to?

Answer 15

Na influx

voltage gated Na channels

Question 16

what is the falling phase due to?

Answer 16

K efflux

voltage gated K channels

Question 17

when does Na enter the neuron?

Answer 17

during upstroke

Question 18

when does K move out of the axon?

Answer 18

during downstroke

Question 19

what are ion channels?

Answer 19

transmembrane protein

Question 20

describe the opening of a voltage-gated sodium channel

Answer 20

channel closed
-M-gate closed, h-gate open
channel open
-m&h open
channel closed (refractory)
-m open, h closed

Question 21

describe an AP

Answer 21

at threshold
-voltage gated Na open
-na diffuse in-> further depolarisation
-+ feedback 
at peak
-Na channels close; voltage-gated K channels open
-K diffuse out-> repolarisation 
return to resting membrane potential

Question 22

why is AP an all or none event?

Answer 22

amplitude is independent of stimulus

Question 23

what are the consequences of the refractory period?

Answer 23

limits max firing frequency
ensures unidirectional propagation of AP’s
prevents summation of APs
prevents summation of contractions in cardiac muscle
-cardiac AP lasts as long as ventricular contraction

Question 24

describe propagation of an AP

Answer 24

AP in one section of axon sets up longitudinal current flow
depolarises adjacent resting parts of axon
AP regenerated further along axon
more current flows and next region of axon activated
AP travels along axon as waves of depolarisation

Question 25

how does current flow in ICF & ECF?

Answer 25

from + to - regions

Question 26

how does the AP move with current?

Answer 26

current flow alters membrane potential in adjacent regions

Question 27

what increases the speed of AP propagation?

Answer 27

axon diameter

myelin

Question 28

what is myelin?

Answer 28

many layers of cell membranes wrapped around the axon

Question 29

what cells lay down myelin?

Answer 29

glial-shwann

Question 30

what does myelin do?

Answer 30

forms an insulating layer- reducing leakage of current from axon

Question 31

what are nodes of ranvier?

Answer 31

myelin sheath interrupted at intervals

axon membrane exposed to ECF and ion flow can occur

Question 32

what is saltatory conduction?

Answer 32

in myelinated nerve, the passive currents spread further along the axon
fewer regeneration steps per unit length of axon
so AP propagates more rapidly than in unmyelinated

Question 33

how do peripheral nerve axons differ?

Answer 33

size
-diameter abd cond. velocity
function
-sensory/motor

Question 34

what is the function and myelination of A beta fibres?

Answer 34

myelinated

mechanoreceptors

Question 35

what is the myelination and function of a delta fibres?

Answer 35

myelinated
mechanoreceptors
thermoreceptors(cold)
nociceptors
chemoreceptors (taste)

Question 36

what is the myelination and function of C fibres?

Answer 36

unmyelinated
mechanoreceptors
thermoreceptors (hot)
nociceptors

Question 37

is majority of tooth pulp fibres myelinated or not?

Answer 37

unmyelinated

Question 38

what is the rate and direction of diffusion determined by?

Answer 38

potential and concentration gradients

Question 39

what is the potential difference in a resting state?

Answer 39

inside of cell 70mV more negative than outside

Question 40

what happens if the MP of a neuron is changed from RMP -70mV to -60mV?

Answer 40

depolarisation

Question 41

what is it called if the MP of a neuron is changed from RMP of -70 to -80mV?

Answer 41

hyperpolarisation

Question 42

what is the stimulus for an AP?

Answer 42

depolarisation

Question 43

what kind of feedback is involved when ions enter the cell, depolarisation and more ion channels open?

Answer 43

positive feedback

Question 44

how does the MP return to resting value after the AP peak?

Answer 44

ions move by diffusion

K ions passing out of cell

Question 45

what causes the period of inexitability in the refractory period?

Answer 45

inactivation of sodium channels