Topic 6 - Nervous Coordination

Question 1

What is the function of the sodium-potassium ion pump

Answer 1

The sodium potassium ion pump actively transports 2 potassium ions into the axon and 3 sodium ions out of the axon. This results in an overall negative charge inside the axon
It also restores resting potential

Question 2

what happens at resting potential

Answer 2

around -70mV
Sodium ions should diffuse back in and potassium ions should diffuse back out through voltage gated ion channels. However the movement of sodium ions back in is much less than the movement of potassium ions.

Question 3

what happens during depolarisation

Answer 3

an action potential occurs and some voltage gated sodium ion channels open so sodium ions diffuse into the axon.
The chnage in charge causes more sodium ion channels to open so more sodium ions diffuse into the axon.
Once the action potential of around 40mV has been established, the voltage gated sodium ion channels close
Voltage gated potassium ions open

Question 4

what happens during re polarisation

Answer 4

potassium ions diffuse out making the inside of the cell more negative

Question 5

what happens during hyperpolarisation

Answer 5

there is a slight overshoot in the movement of potassium ions so the inside of the axon is more negative than usual. The voltage gated potassium ion channels close

Question 6

what happens during the refractory period

Answer 6

short period of time where the axon cannot be excited again.
limits number of action potentials a nerve cell can produce

Question 7

what happens during repolarisation of the resting potential

Answer 7

the resting potential is restored by the sodium potassium ion pump.
the axon is repolarised

Question 8

what are the stages off activity in a motor neurone

Answer 8

resting potential
de polarisation
re polarisation
hyperpolarisation
restoration of resting potential

Question 9

what are dendrites on a nerve cell

Answer 9

highly branched fibres that conduct impulses

Question 10

what are Schwan cells on a nerve cell

Answer 10

a cell wrapped around the axon forming the myelin sheath

Question 11

what is the myelin sheath on a nerve cell

Answer 11

a thick insulating layer around the axon

Question 12

what is the node of Ranvier on a nerve cell

Answer 12

gap in the myelin sheath where the axon is exposed

Question 13

what is the axon on a nerve cell

Answer 13

a long single fibre that carries nerve impulses

Question 14

what is the all or nothing nature

Answer 14

action potentials have an all or nothing nature, once the threshold level is reached, an action potential will always fire with the same change in voltage no matter how big the stimulus is.
A bigger stimulus wont cause a bigger action potential, but it will cause them to fire more frequently

Question 15

what 3 factors affect the speed of conduction of action potentials

Answer 15

myelination
axon diameter
temperature

Question 16

what does it mean if a neurone is myelinated

Answer 16

they have a myelin sheath

Question 17

what is found at the node of ranvier

Answer 17

sodium ion channels

Question 18

how does myelination increase the speed of conduction of an action potential

Answer 18

in a myelinated neurone, depolarisation only happens at the nodes of ranvier so the impulses jump from node to node this is called salatory conduction and its really fast.
in a non myelinated neurone the impulse travels as a wave along the whole length of the axon membrane this is slower.

Question 19

how does axon diameter affect speed of conduction of action potentials

Answer 19

action potentials are conducted quicker along axons with bigger diameter becauuse there’s less resistance to the flow of ions, with less resistance depolarisation reaches other parts of th neurone cell membrane quicker

Question 20

how does temperature affect the speed of conduction of an action potential

Answer 20

the speed of conduction increases as the temperature increases because ions are given more kinetic energy so can diffuse faster.