neurones

Question 1

in a neurones resting state, what is the relative charge on the inside and outside of the membrane, what does this mean

Answer 1

the outside is positively charged compared to the inside - this is due to more positive ions outside the cell than the inside, this means the membrane is polarised, there’s a difference in charge across it

Question 2

what is the voltage across the membrane at resting potential

Answer 2

-70mV

Question 3

what is the resting potential created and maintained by

Answer 3

sodium-potassium ions and potassium ion channels

Question 4

what happens in the sodium-potassium pump

Answer 4

the pump used active transport to 3 sodium ions out of the membrane for every 2 potassium ions moved inside. ATP is needed for this.

Question 5

what happens in the potassium ion channel

Answer 5

these channels allow facilitated diffusion of potassium ions down their concentration gradient out of the neurone

Question 6

what is an electrochemical gradient

Answer 6

a concentration gradient of ions

Question 7

what creates a sodium ion electrochemical gradient across the membrane

Answer 7

there’s more sodium ions on the outside of the membrane

Question 8

what are the 5 stages of an action potential

Answer 8

1) stimulus - the neurone is excited by a stimulus, this causes the sodium ion channels to open so more sodium ions move into the membrane making it less negative down the electrochemical gradient
2) depolarization - if the potential difference reaches the threshold of -55mV more sodium ion channels open which causes more sodium ions to rapidly diffuse in
3) repolarization - at +30mV the sodium channels close and potassium ion channels open so the potassium ions diffuse out of the neurone down the potassium ion concentration gradient
4) hyperpolarization - potassium ions are slower to close which causes too many potassium ions to diffuse out, the potential difference becomes less than -70mV for about 0.5 millisecond
5) resting potential - the ion channels are reset, the sodium- potassium ion pump returns the membrane to its resting potential.

Question 9

what causes a wave of depolarisation

Answer 9

some of the sodium ions that enter the neurone diffuse sideways which causes the sodium ions in the next region of the neurone to open and sodium ions diffuse into that part which causes a wave of depolarisation to travel along the neurone

Question 10

how are action potentials discrete and unidirectional

Answer 10

action potentials don’t overlap which means they pass along as discrete impulses. they’re unidirectional because they only travel in one direction

Question 11

what’s the difference between a big and small stimulus in terms of action potentials

Answer 11

an action potential always fires at the same voltage, a bigger stimulus doesen’t mean a higher voltage, a bigger stimulus means the action potential will fire more often - at a higher frequency

Question 12

what is a myelin sheath

Answer 12

some neurones have a myelin sheath, its an electrical insulator

Question 13

in the peripheral nervous system, what is the sheath made of

Answer 13

a type of cell called Schwann cell

Question 14

what 3 factors affect the speed of conduction of action potentials

Answer 14

1) myelination
2) axon diameter
3) temperature

Question 15

what is between the Schwann cells

Answer 15

tiny patches of bare membrane called nodes of Ranvier, sodium ions are concentrated at the nodes

Question 16

in a myelinated neurone, where does depolarization occur

Answer 16

only occurs in the nodes of Ranvier

Question 17

how does the electrical charge go from node to node

Answer 17

the neurone cytoplasm conducts enough electrical charge to depolarize the next node so the impulse jumps from node to node - this is called saltatory conduction

Question 18

in a non-myelinated neurone, how does the impulse travel

Answer 18

as a wave along the whole length of the axon membrane so depolarisation occurs along the whole length of the membrane

Question 19

do action potentials occur quicker in axons with bigger diameters, or smaller diameters and why

Answer 19

they conduct quicker in axons with bigger diameters because there is less resistance to the flow of ions, with less resistance, depolarization reaches other parts of the neurone cell membrane quicker

Question 20

does the speed of conduction increase or decrease as the temperature goes up and why

Answer 20

the speed of conduction increases as temperature increases because ions diffuse faster, but only up to about 40°C, after this proteins start to denature