6.4 Nerve impulses

Question 1

what are nerve impulses

Answer 1

electrical charges transmitted along a neurone

Question 2

how are nerve impulses created

Answer 2

movement of sodium potassium ions

Question 3

what charge is the outside of the membrane when the cell is resting

Answer 3

postive
(more positive ions outside of the cell than inside)

Question 4

what is the membrane if there are more postive ions outside than inside

Answer 4

polarised > difference in charge across it (PD)

Question 5

what is the voltage at resting potential

Answer 5

-70mV

Question 6

how is the resting potential created and maintained

Answer 6

sodium potassium pumps
potassium ion channels

Question 7

what are sodium potassium pumps

Answer 7

use active transport to move 3 NA+ out of the neurone for every 2K+ moved in
- ATP required

Question 8

what are potassium ion channels

Answer 8

allow facilitated diffusion of K+ out of the neurone down the concentration gradient

Question 9

is the membrane permeable or impermeable to sodium ions

Answer 9

impermeable

Question 10

how is a sodium ion electrochemical gradient created

Answer 10

• sodium ions can’t move back into the membrane
• more postive sodium ions outside than inside

Question 11

what channels are open when the cells at rest

Answer 11

potassium ion channels

Question 12

is the membrane permeable or impermeable to potassium ions

Answer 12

permeable so some diffuse back out through potassium ion channels

Question 13

what ion channels open when a neurone is stimulated

Answer 13

sodium ion channels

Question 14

what happens during stimulus

Answer 14

• membrane becomes excited
• NA+ channels open
• membrane becomes more permeable to NA+ so they moved down the NA+ electricocjemical gradient
• inside of neurone is less negative

Question 15

what happens in depolarisation

Answer 15

• if PD reaches threshold more NA+ channels open so more NA+ diffuses in

Question 16

what happens in repolarisation

Answer 16

• at 30mV NA+ channels close, K+ opens
• membrane is more permeable to K+ so K+ diffuses out down K+ ion concentration gradient
• membrane gets back to resting

Question 17

what mV is threshold

Answer 17

-55mV

Question 18

what happens in hyper polarisation

Answer 18

• K+ ion channels close slowly so slight period of time where too many diffuse out of neurone
• PD BECOMES MORE NEGATIVE TJAN RESTING

Question 19

what happens in resting potential

Answer 19

• sodium potassium pump returns membrane to resting potential by pumping sodium ions out and potassium ions in

Question 20

what is a refractory period

Answer 20

• time no action potential can be made
• NA+ closed during repolarisation and K+ closed during hyper polarisation

Question 21

what does the refractory period allow

Answer 21

action potentials to be seperate from each other

Question 22

what is a wave of depolarisation

Answer 22

• some NA+ diffuse sideways which causes NA+in next region to open and they diffuse into there

Question 23

what does propagate mean

Answer 23

wave like movement

Question 24

what is the all or nothing principle

Answer 24

once threshold reached, an action potential will always fire with the same change in voltage not matter size of stimulus

Question 25

what are 3 factors that affect the speed of conduction

Answer 25

myelination axon diameter temperature

Question 26

what is the myelin sheath

Answer 26

electrical insulator

Question 27

what is the myelin sheath made from in the personal nervous system

Answer 27

schwann cells

Question 28

where are the sodium ion channels concentration

Answer 28

nodes of ranvier

Question 29

what is saltatory conduction

Answer 29

in a myelinated neurone depolarisation only happens at the nodes of ranvier - neurons cytoplasm conducts enough electrical charge to depolarise the next node, so the impulse jumps from node to node

Question 30

how do impulses travel in a non myelinated neuron

Answer 30

as a wave across the whole length of the acon membrane — depolarisation across whole membrane —- slower than saltatory conduction

Question 31

how does axon diameter affect action potentials

Answer 31

action potentials are conducted quicker across axons with bigger diameter as there is less resistance to the flow of ions than in cytoplasm of smaller axon — less resistance means depolarisation can reach different parts of membrane quicker

Question 32

how does temperature affect action potentials

Answer 32

speed of conduction increases with temperature as ions diffuse faster — only until 40 as proteins start to denature (pumps and channels