Lesson 3: The Action Potential

Question 1

What is the basic structure of the neuron? (5)

Answer 1

1. Soma (cell body)
2. Dendrites
3. Myelin Sheath
4. Axon
5. Terminal Buttons

Question 2

Neurons have a resting membrane potential of how much voltage (in mV)?

Answer 2

-40 to -90 mV

Question 3

Why do neurons have a negative voltage?

Answer 3

Electrostatic pressure across the membrane promotes movement of positively charged ions into the cell and negatively charged ions out of the cell

Question 4

What are cations? Anions?

Answer 4

Cations: positively charged ions
Anions: negatively charged ions

Question 5

What are ion channels?

Answer 5

Specialized protein molecules that sit in the cell membrane
- they have a pore in them through which specific ions cna enter or leave cells

Question 6

What is a leak channel?

Answer 6

An ion channel protein that is in the membrane and has a pore that is always open
- only the specific protein can move through it (ex: in the potassium leak channel, only the potassium ion is comfortable to move through it)

Question 7

In the atomic composition of cells (CHNOPS), which are positively charged ions? Negatively charged ions?

Answer 7

Cations
- sodium
- potassium
- calcium
- magnesium
Anions
- chloride

Question 8

Which of the cations and anions are more abundant outside of the cells (in extracellular space)?

Answer 8

Sodium, calcium, magnesium, and chloride

Question 9

Which atom is more abundant inside of the cell (in intracellular space)?

Answer 9

Potassium

Question 10

How do neurons generate a resting membrane potential?

Answer 10

The lipid bilayer is impermeable to ions
- there is an equal concentration of positively and negatively charged ions on either side of the membrane

Question 11

Which are the two proteins that are responsible for setting up and maintaining the resting membrane potential of neurons?

Answer 11

Sodium and potassium

Question 12

What is a sodium-potassium pump (from the sodium-potassium transporter)?

Answer 12

A protein that pumps Na+ atoms out of the cell and K+ atoms in

Question 13

What are the steps of the sodium-potassium pump?

Answer 13

1. The sodium-potassium pump binds three sodium ions and a molecule of ATP
2. The splitting of ATP provides energy to change the shape of the channel. The sodium ions are driven through the channel
3. The sodium ions are released to the outside of the membrane, and the new shape of the channel allows two potassium ions to bind
4. Release of the phosphate allows the channel to revert to its original form, releasing the potassium ions on the inside of the membrane

Question 14

What are the concentration gradients of K+ ions and Na+ ions inside and outside of the cell?

Answer 14

Inside of the cell: K+ ions are 30x more concentrated

Outside of the cell: Na+ ions are 15x more concentrated

Question 15

What is the force of diffusion?

Answer 15

If there is a concentration gradient and no forces or barriers to prevent free movement of molecules, then molecules will move, on average, from regions of high concentration to regions of low concentration

Question 16

How does the membrane potential become -90 mV?

Answer 16

If millions of potassium ions leave the cell

Question 17

What is the range (in mV) of the resting membrane potential of a neuron?

Answer 17

From -40 to -90 mV. This is because ions are always sneaking through other leak channels

Question 18

What is membrane potential?

Answer 18

Electrical charge across a cell membrane; difference in electrical potential inside and outside the cell

Question 19

What is resting potential?

Answer 19

Membrane potential of a neuron when it is at rest (i.e., when not actively receiving or transmitting messages)

Question 20

T/F: Potassium leak channels are always open

Answer 20

True. Potassium can always flow through them (in either direction). The abundance of leak channels in the membrane ensures that the membrane potential never deviates from its resting state for very long

Question 21

Which proteins does the action potential involve? (3)

Answer 21

1. Voltage-gated sodium channel (to initiate and propagate the action potential)
2. Voltage-gated potassium channel (to restore the resting membrane potential)
3. Voltage-gated calcium (located in the axon terminal; triggers release of neurotransmitter)

Question 22

When does the voltage-gate sodium channel open/activate? How does it open? When does it close?

Answer 22

When the membrane potential becomes more positive than -40 mV
- opens because the activation of receptor protein ion channels let in sodium
- closes when membrane potential gets back down to -70 mV

Question 23

What is the action potential?

Answer 23

A brief electrical impulse that provides the basis for conduction of information along the axon. It is a rapid change in the membrane potential caused by the opening and closing of voltage-gated ion channels

Question 24

What is the threshold of excitation?

Answer 24

The value of the membrane potential that must be reached to produce an action potential (+40 mV)

Question 25

Which ion channel opens to counteract the sodium channel?

Answer 25

Voltage-gated potassium channels
- additional to the potassium leak channels, which are always open, but are slow

Question 26

When do the voltage-gate potassium channels open?

Answer 26

When the membrane potential is more positive than 0 mV. The opening helps bring the membrane potential back down to -70 mV

Question 27

When do the voltage-gated calcium channels open?

Answer 27

When an action potential reaches the end of an axon (axon terminal/terminal buttons)

Question 28

What happens when the voltage-gated calcium channel opens?

Answer 28

The release of signaling molecules (neurotransmitters) into the synapse

Question 29

What is the primary means of communication between neurons?

Answer 29

Synaptic transmission: tranmission of messages from one neuron to another via the release of signaling molecules (neurotransmitters) into the synapse

Question 30

What is the all-or-none law?

Answer 30

The action potential occurs or does not occur, and once triggered, will propagate down the axon without diminishing or growing in size, to the end of the axon