passage of an action potential

Question 1

what is an refractory period

Answer 1

period during which the membrane of the axon of a neurone cannot be depolarised and no new action potential can be intiated

Question 2

why can’t neurone be stimulated straight away (after A.P) ?

Answer 2

• Na+ ion channel closed during repolarisation
• K+ ion channel closed during hyperpolarisation

Question 3

why is the refractory period important

Answer 3

delaying time between one a.p and next

ensuring a.p pass as discrete impulses

AP travels in 1 direction from cell body to axon terminal

limiting the frequency of impulses transmitted

Question 4

explain the passage of an action potential along an unmyelinated axon

Answer 4

1. stimulus - Na+ ions move into the axon via voltage gated sodium channels
   causing membrane to depolarise (Action Potential)
2. movement of action potential - Na+ ions diffuse sideways (forming localised electric current) causes the Na+ voltage gated channels to open further along the membrane causing the next section to become depolarised
3. start of repolarisation - on reaching +30mV Na+ voltage gated channels close and K+ channels open and K+ moves out of axon while action potential moves along axon
4. return to resting potential - Na+/ K+ pump restores membrane potential to -70mV

Question 5

explain how an action potential travels along a myelinated neurone

Answer 5

• Na+ ion channels are concentrated at the nodes of Ranvier
• depolarisation occurs
• local current can only act at nodes of Ranvier so depolarisation only occurs at the nodes where Na+ ions can get through the membrane

Question 6

what is the name of the conduction that takes place in a myelinated neurone

Answer 6

saltatory conduction

Question 7

define saltatory conduction

Answer 7

action potential jumps from node to node of Ranvier as depolarisation only occurs at the nodes of ranvier

or

localised circuits occur between adjacent nodes and cause action potential to jump from node to node

Question 8

define myelinate axon

Answer 8

wrapped in schwann cells
the layers of membrane act as an insulator increasing the speed of electrical transmission

myelin accelerates electrical impulses along the axon

Question 9

define the refractory period

Answer 9

period during which the membrane of the axon of a neuron cannot be depolarised and no new action potential can be intiated

Question 10

why can’t neurone be stimulated straight away after an action potential

Answer 10

• Na+ ion channels closed during repolarisation
• K+ ion channels closed during hyperpolarisation

Question 11

what are the 4 reasons for why the refractory period so important

Answer 11

• delaying time between 1 action potential and the next
• ensuring action potentials pass as discrete impulses
• AP travels in 1 direction from cell body to axon terminal
• limiting the frequency of impulses transmitted

Question 12

what is a node of ranvier

Answer 12

breaks in myelin sheath at intervals of 1-3 mm

action potentials only occur at this point