Nerve Impulses

Question 1

resting potential

Answer 1

has a potential difference of -70mV
outside positive charge, inside negative charge
maintained by Na+K+ pump

higher conc of K+ inside so they diffuse out
and higher conc of Na+ outside so they diffuse in
membrane is more permeable to K+ ions

active transport of Na+ out axon (low to high)- ATP
and diffusion of K+ into of axon

more K+ channels than Na+ channels

Question 2

potential difference

Answer 2

caused movement of sodium and potassium ions
Na+ and K+ ion channels are always open and membrane is more permeable to K+ ions ( more channels)
Na+ and K+ VGIC that open and close at specific voltages
Na+ K+ pump actively transports Na+ out and K+ in

Question 3

depolarisation

Answer 3

energy from stimulus cause Na+ VGIC to open
Na+ diffuse into axon down conc gradient (from outside) down electrochemical gradient
triggers more Na+ VGIC to open
more positive on inside compared to outside
PD becomes positive

Question 4

repolarisation

Answer 4

when PD reaches +40mv
Na+ VGIC shut and K+ VGIC open 
K+ move from inside to outside the axon down electrochemical gradient 
causes outside to become more positive
PD= -70mv

Question 5

hyperpolarisation

Answer 5

K+ VGIC are slow to close so PD becomes -75mv rather than -70mv
Na+K+ pump rectifies this and returns PD to -70mv

Question 6

action potential

Answer 6

process from rest to depol to repol to hyperpol is an action potential
meaning the neurone is transmitting a nerve impulse

Question 7

threshold

Answer 7

stimulus must create pd of -55mv to trigger an action potential
if stimulus is too weak and the influx of Na+ is too little, normal polarity is quickly reestablished
all or nothing responses

Question 8

intensity

Answer 8

amplitude of action potential is always the same

intensity is detected by frequency of action potentials eg how many per second

Question 9

action potential moving

Answer 9

axon becomes depolarised
creates local currents
cause more Na+ VGIC to open causing depol
more positively charged regions (depol regions as it is positive in axon) move to more negatively charged regions
depolarises next part of region and depol travels along axon
lots of energy needed to restore whole membrane

Question 10

speed- non myelinated

Answer 10

continuous conduction, lots of energy needed to restore to rest as there is more of membrane so it is slower
depol occurs across whole of the axon

Question 11

speed- myelinated

Answer 11

saltatory conduction, there are only Na+K+ pumps and ion channels at the nodes so depol only occurs at nodes
Na+ ions move to adjacent node which depolarises it
action potential jumps from node to node so is faster
- uses less energy as only membrane at nodes need to be restored to rest (by Na+K+ pump)

Question 12

refractory period

Answer 12

when the axon is hyperpolarised and in state of recovery and trying to get back to resting potential
membrane cannot be depolarised + no impulse can travel down
ensures- action potential can only travel in one direction
each act pot is separate/ discrete

Question 13

temperature

Answer 13

act pots travel faster at higher temperatures as the ions diffuse faster across the membrane

Question 14

axon diameter

Answer 14

wide axons transmit act pot faster than narrow ones

as they offer less resistance to the flow of local currents so adjacent areas of axon reach threshold more quickly