Lecture 3- The action potential

Question 1

Explain the usage of the Golgi stain mixture:

Answer 1

The Golgi stain is a mixture of silver nitrate and potassium chromate that causes 2% of brain cells to darken in colour. Silver chromate crystallizes inside of every nook causing a “snowflake”.

Question 2

As part of the basic structure if neurons, explain the usage of the
1. Soma (cell body)
2. Dendrites
3. Axon
4. Axon terminal
5. Synapse

Answer 2

Soma: is where the nucleus is located

Dendrites: are branches, extensions from soma, responsible for sensing external environment.

Axon: Is responsible for rapidly transmitting messages.

Axon terminal: End of axon, receives a message from soma and releases signalling molecules which are then detected by downstream neurons.

Synapse: Small space between axon terminal of cell and dendrite of next cell.

Question 3

What is voltage? How does a voltmeter work?

Answer 3

Voltage refers to a difference in electric charge between two points or “electrostatic potential”.

A voltmeter allows a negligible amount of flow from one wire to another. The amount of resistance needed to let just a little electricity flow indicated the charge difference across the two wires.

Question 4

What is the charge of solutions outside of neurons?
What is the charge of a neurons resting membrane potential? What does it signify?

Answer 4

-0 mV

-40 mV to -90 mV,
meaning that electrostatic pressure promotes movement of POSITIVE charged ions INTO the cell and NEGATIVE charge ions OUT of the cell.

Question 5

An ion is a charged atom or molecule, what is a cation and a Anion

Answer 5

Cation: + charged
Anion: - charged

Question 6

What is electrostatic pressure?

Answer 6

An ATTRACTIVE force between molecules that are positively charged (+ and -)
or
a REPULSIVE force between molecules that are similar charged (+ and +)

Question 7

What are ion channels?

Answer 7

Specialized protein molecules that sit in the cell membrane. They have pores in them where only specific ions can enter of leave cells.

Question 8

What is a leak channel?

Answer 8

An ion channel protein that is in the membrane and has a pore that is always open (ie. potassium leak channel)

Question 9

Name the positively charged ions (cations) that are monovalent (2) and divalent (2):

Answer 9

Monovalent: Sodium (Na+), Potassium (K+)

Divalent: Calcium (Ca+2), Magnesium (MG2+)

Question 10

Name the negatively charged ion (anions) that is monovalent (2):

Answer 10

Chloride: (CI -)

Question 11

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

Answer 11

1. Sodium- potassium transporter
2. Leak potassium channels

Question 12

What is the use of a sodium-potassium pump?

Answer 12

It is known as a transporter, its function of this protein is to pump NA+ atoms OUT and K+ atoms IN.

Question 13

Name the 4 steps of the sodium potassium pump:

Answer 13

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

Question 14

As the sodium potassium pump creates concentration gradients, what is the ratio of K+ ions in and NA+ ions out?

Answer 14

It cause K+ 30x more concentrated in than out
and
Na+ ions to be 15x more concentrated out than in.

Question 15

What is diffusion?

Answer 15

If there is a concentrated gradient and no force or barrier to prevent free movement of molecules, they will move from regions of HIGH concentration to regions of LOW concentration.

Question 16

What is membrane potential?
What is resting potential?

Answer 16

Membrane potential: Electrical charge across a cell membrane; the difference in electrical potential inside and out of the cell.

Resting potential: The membrane potential of a neuron when it is at rest (not actively receiving or transmitting messages). At rest, neurons have a resting potential between -40 and -90 mV.

Question 17

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

Answer 17

1) the sodium potassium transporter (requires ATP; concentrates sodium outside the cell and potassium inside the cell.

2) Leak Potassium channels (always open; the number of these channels largely determines the resting membrane potential)

Question 18

What is the use of the sodium potassium transporter?

Answer 18

-These pumps make it so that there is 30x more K+ inside the cell than out and 15x more Na outside than in. (These concentrations never ever change)

Question 19

What is the use of the leak potassium channel?

Question 20

Neurons put receptor proteins on their dendrites to sense the external world, what do the sensors often detect?

Answer 20

-Presence of certain molecules
-Physical pressure (movement/touch)
-Electrical pressure (voltage)
-Temperature
-PH (acidity, basicity)
-Electromagnetic radiation (light)

Question 21

What is depolarization?

Answer 21

When the membrane potential of a cell becomes less negative than it normally is at rest.

ie, when positive sodium ions enter a cell through s receptor protein ion channel, they might depolarize an ion from -70 to -60 mV.

Question 22

Why does the abundance of leak channels in the membrane help the membrane potential?

Answer 22

The abundance ensures that the membrane potential never deviated from its resting state for too long.
(Na+ in = K+ out = restore membrane potential)

Question 23

What are the 3 voltage gated ions that the action potential involves?

Answer 23

3) Voltage gated SODIUM channel (initiate and propagate the action potential)

4)voltage gated POTASSIUM channel (to restore the resting membrane potential)

5) voltage gated CALCIUM channel (triggers release of neurotransmitter)

Question 24

Explain how the voltage gated sodium channel becomes closed, open and inactive:

Answer 24

Closed: at resting potential the channel is closed.

Open: With nerve impulses, the gate opens and Na+ enters.
It opens when the membrane potential becomes less negative than -40 mV.

Inactivated: Following activation, the channel does not open in response to new signal. Lasts until the membrane potential gets back down to -70 mV.

Question 25

What is the action potential?

Answer 25

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

Question 26

The value of the membrane potential that must be reached to produce an action potential is called the…?

Answer 26

The threshold of excitation

Question 27

When does the voltage gated potassium channel open?
How does it close?

Answer 27

Open: It opens when the membrane potential is more positive than 0.

Close: It closes when the membrane potential gets back down to rest.

Question 28

What happens when the voltage gated potassium ion channel open?

Answer 28

The outflow of K+ ions is driven by diffusion and electrostatic energy, forcing to restore the resting membrane potential.

Question 29

What is the refractory period?

Answer 29

It is the post action potential hyper polarization.

Question 30

When does the voltage gated calcium channel open? Where is the calcium more concentrated?

Answer 30

When the axon terminal becomes depolarized.

It is 1000x more concentrated outside the cell than in.

Question 31

What is the primary means of communication between neurons, via releasing molecules into the synapse called?

Answer 31

Synaptic transmission

Question 32

What are the 5 rules of the conduction of action potential:

Answer 32

1. Conduction of the action potential (movement of info)
2. Occurs is a unidirectional manner
3. The size of action potential stay constant.
4. All or none law it will propagate down the axon without changing size.
5. Rate law states that strength is represented by rate of firing axon.