Passage of action potential

Question 1

How is action potential similar to a Mexican wave?

Answer 1

Although wave of people standing up and raising their hands (action potential) moves around the stadium

People themselves do not move from seat to seat wtih wave (i.e do not physically pass around the stadium until they reach their orginal seat)

Instead their indvidiual actions of standing and raising their hands are stimulated by the action of the person on side of them are reproduced by person on the other side

Question 2

Instructions of passage of action potnetial on unmyelinated axon

First step

Answer 2

At resting potential, the concentration of Na+ outside is high than inside, K+ is high on inside relative to outside

Overall concentration of positive ions, greater on outside making it positive compared to inside, axon is polarised

Mexican wave - equvialent to whole stadium seated at rest

Question 3

Instructions of passage of action potnetial on unmyelinated axon

Second step

Answer 3

• Stimulus causes a sudden influex of Na+ hence a change on charge of axon membrane
• Action potential and membrane depolarised
• Mexican wave - a prompt leads to a vertical line of people to stand and wave their arms and stimulated into action

Question 4

Instructions of passage of action potnetial on unmyelinated axon

Third step

Answer 4

• Localised of electrical current estbalished influex of Na+ opening voltage-gated channel a little further along axon - depolarisation
• Potassium ones open
• K+ began to leave the axon along the electrical chemical gradient , once initated the depolarisation moves along the membrane
• Mexican wave - sight of people standing and waving prompts the person to adjacent to seat to wave

Question 5

Instructions of passage of action potnetial on unmyelinated axon

Fourth step

Answer 5

• Action potential (depolarisation) is propagated in the same way further along the axon
• The outward of movement of K+ ions have continued the extent of axon membrane behind the action potential has return to original ( + in outside , - on inside) - repolarisation
• Mexican wave - second line of people standing and waving prompts the third line of people to do the same
• Meanwhile first line resumed at original positions - re-seated

Question 6

Instructions of passage of action potnetial on unmyelinated axon

Fifth step

Answer 6

• Repolarisation of axon allows Na+ ions to be actively transported out , once again returning the axon to its resting potential , readiness for new stimulus
• Mexican wave - people who have settle back in seats readjust themselves in readiness to repeat process when prompted to do so

Question 7

What does myelin act around myelinated axon?

Answer 7

Act as an electrical insulator around axon

Prevents the action potentials from forming

Prevents depolarisation

Prepares the movement of ions in and out of membrane

Question 8

What are the breaks between myelin called?

Answer 8

Nodes of Ranvier

Question 9

Where can action potential occur in myelinated axon?

Answer 9

At nodes of Ranvier

Question 10

What is saltatory conduction?

Answer 10

When an axon potential jumps between nodes of Ranvier

Question 11

Advantages of salatory conduction?

Answer 11

• Speeds up transmission of nerve impulses
• Cytoplasm conducts enough electrical charge to depolarise the next node

Question 12

Properties of node of Ranvier

Answer 12

• Gaps in myelin sheath
• Lots of Na+ and K+ ion channel
• Depolarisation can only happen at the nodes
• Action potential can jump between the nodes in process called salatory conduction