Action Potential

Question 1

Action potential process

Answer 1

1) Stimulus-gated ion channels open, membrane depolarises slightly
2) Membrane potential increases to -50mV
3) Voltage gated Na+ channels open and increase permeability to Na+
4) Voltage gated K+ channels open increase permeability to K+
5) Voltage gated Na+ channels close and deactivate
6) Voltage gated K+ channels close
7) Membrane potential returns to -70mV

Question 2

All or nothing principle

Answer 2

• Action potential will always fire once threshold potential is met
• All action potentials are the same size

Question 3

Absolute refractory period

Answer 3

• Cell is completely resistant to initiating a second action potential
• Large number of voltage gated ions are inactivated only open when cells are in refactory period

Question 4

Relative refractory period

Answer 4

• Stimulus of grater than nomal intensity can elicit a response
• Some voltage gated Na+ inactivated stronger stimulus required for another response
• More permeable to K+ ions

Question 5

Propagation of action potential

Answer 5

• Polarity is briefly reversed producing local currents that cause depolarisation in arwa of action potential
• When threshold is reached Na+ channels open and action potential formed in new place
• self propogation of action potential along axon

Question 6

Myelin sheath

Answer 6

• Insulate axon reduce loss of electrical impulse
• Decreases membranes ability to store electrical energy increase membrane resistance

Question 7

Nodes of Ranvier

Answer 7

• Change of membrane permeability at node
• Node has a high conentration of Na+ channels action potential jump (saltatory conduction)

Question 8

Resting potential maintained

Answer 8

• Na+/K+ pump requires ATP and 3 Na+ move outside of cell to 2 K+ inside of cell
• Leak channel K+ channel with high basal activity more permiable to K+ leave than Na+ enter
• Resulting negative net movement

Question 9

Electromotive force (EMF)

Answer 9

• Potential energy that can be released to make an electrial current (movement of charge carried by ion)
• Concentration difference between the inside and the outside of the cell

Question 10

What does Resting potential concider?

Answer 10

• Resting potention accounts for the net movement of all ions
• Ca2+ moves into the cell
• Na+ moves into the cell
• Cl- moves into cell
• K+ moves out of the cell

Question 11

Voltage dependancy

Answer 11

• Probability the Na+ channels will open increases as the voltage applied increases

Question 12

Time-dependancy and threshold

Answer 12

• Channel opens allowing influx of Na+ down concentration gradient from outside cell
• Channel close after 1 millisecond due to cell inactivation
• Most Na+ channels stop conducting by 1.5 milisecond

Question 13

Opening of Na+ voltage gated ion channel

Answer 13

• Na+ channels move from closed to open conformation when exposed to the threashold
• Depolarisation causes neigbouring section to become positve than resting
• Increase in voltage is sufficient enough to trigger voltage sensitive Na+ channel to open causing influx from outside

Question 14

Depolarisation

Answer 14

• Influx of Na+ entering cell causes large rate of flow into cell (capacitence)
• Lots of positive charge enters cell and polarity of cell reverses

Question 15

Inactive Na+ channel

Answer 15

• After the Na+ enters cell the voltaged gated Na+ channel resets
• doesnt allow Na+ through and requires a significant negative voltage before moving to closed

Question 16

Difference between ligand gated and voltage gated ions

Answer 16

• Ligand-gated ion channels open when a chemical ligand such as a neurotransmitter binds to the protein
• Voltage channels open and close in response to changes in membrane potential

Question 17

Repolarisation

Answer 17

• More positive potentials are required to generate an eflux of K+
• loss of positive K+ ions cause membrane potential back down to below resting
• not time dependant stay open when potential is high enough

Question 18

Hyperpolarisation

Answer 18

• Kenetics of closing the K+ channel is slower than the Na+ causing repolarisation to overshoot
• Resting potentional becomes more negative helps increase proportion of voltage sensitive Na+ channels to move to closed form

Question 19

Recovery from action potential

Answer 19

• Ecess Na+ needs to be pumped out and K+ needs to be pumped back
• requires energy to form ATP to pump high levels of Na+ out