Chapter 3: Neural Conduction and Transmission

Question 1

How does information flow within a neuron?

Answer 1

Through electrical signals known as Action Potential.

Question 2

How does information flow between neurons?

Answer 2

Through chemical signals known as Neurotransmission.

Question 3

What is Resting Membrane Potential?

Answer 3

A difference in electrical potential across the membrane of a nerve cell during an inactive period.
The inside of the cell (intercellular fluid) is negatively charged in comparison to the the outside of the cell (extracellular fluid).

Question 4

Identify and describe the 3 important aspects of Resting Membrane Potential.

Answer 4

1. Electrochemical Equilibrium (Concentration Gradient and Electrostatic Pressure)
As anions (-) move to the outside of the cell due to the concentration gradient, there is an opposing force from electrostatic pressure that pushes them back in - thus keeping the RMP negative.

2. Selective Permeability of the Cell Membrane
   Ions move through Ion Channel Proteins according to the concentration gradient.
   a) Leak Channels are always open, leading to passive transport of ions through the cell membrane.
   b) Gated Channels only open by voltage, mechanical or ligand stimulus.

3. Sodium/Potassium Ion Pumps
Active transport (needs energy) of sodium and potassium occurs through the Na+/K+ ion pump.

Question 5

What is Electrochemical Equilibrium Potential?

Answer 5

Voltage difference across the cell membrane to counterbalance the movement of molecules down their concentration gradient and the opposing electrostatic pressure.

Question 6

What’s a Ligand gated channel protein?

Answer 6

Needs neurotransmitter to bind to it for it to open.

Question 7

How much Na+ to the outside of the cell and K+ to the inside of the cell respectively are displaced by a Sodium Potassium Pump during RMP?

Answer 7

The pump displaces 3 Na+ molecules out of the cell, and brings 2 K+ molecules into the cell.

Question 8

What’s the mV of RMP?

Answer 8

Around -65mV.

Question 9

True or false; there is more K+ inside the cell than Na+, Cl- and Ca+ during RMP.

Answer 9

True.

Question 10

True or false; neurons have far more K+ leak channels than Na+ leak channels.

Answer 10

True.

Question 11

What causes a neuron at rest to be slightly negative compared to the surrounding fluid?

Answer 11

The movement of K+ ions out of the cell through Leak channel proteins.

Question 12

How is RMP achieved? (3)

Answer 12

1) Na+ and K+ freely move in and out of the cell and aim to maintain a balanced concentration gradient through Leak Channel proteins on the cell membrane. The cell has more K+ leak channels and as a result K+ flows out of the cell faster than Na+ flows in, making the charge negative.
2) Through Active Transport, Sodium potassium pump proteins displace 3 Na+ out and 2 K+ molecules into the cell, maintaining the net charge as negative.
3) This is how a RMP of -65mV is maintained.

Question 13

What is Action Potential?

Answer 13

The propagated electrical message of a neuron that travels along the axon to the presynaptic axon terminals.

Question 14

What’s the difference between Depolarization and Polarization?

Answer 14

Depolarization: Membrane potential decreases (the difference between the charge on the inside of the cell and outside of the cell decreases), thus the cell has a more + value.
Polarization: Membrane potential increases, thus the cell has a more - value.

Question 15

At what part of the neuron does the decision to fire or not occur?

Answer 15

the Axon Hillock.

Question 16

Identify and describe the 0/5th stage of the Action Potential process.

Answer 16

5) Resting Stage: neuron is at RMP.

There is more K+ in the cell than Na+ due to difference in number of leak channels on cell membrane.

Question 17

Identify and describe the 1st stage of the Action Potential process.

Answer 17

1) Stimulus: Initial depolarization of neuron due to stimuli.
Here, Na+ enters the cell through Gated channels that open due to the stimuli.
If the influx of ions is enough to cause an AP (if it reaches the Threshold mV) then the cell will fire moving to the next stage, if not, it fails.

Question 18

Identify and describe the 2nd stage of the Action Potential process.

Answer 18

2) Depolarization: AP fires.
If stimulus-provoked depolarization brings cell potential to -55 mV threshold, action potential fires.
Voltage-gated Na+ channels open. Na+ moves down its concentration gradient into the cell, further depolarizing the cell.

Question 19

What’s the Threshold potential mV for an AP to occur?

Answer 19

-55 mV

Question 20

Identify and describe the 3rd stage of the Action Potential process.

Answer 20

3) Repolarization: membrane potentials falls after a peak.
Depolarization reaches peak of +40 mV. This triggers Voltage-Gated Na+ channels to CLOSE and become temporarily inactivated.
At the same time, voltage-gated K+ channels OPEN.

Question 21

What’s the peak potential mV before repolarization?

Answer 21

+40mV

Question 22

Identify and describe the 4th stage of the Action Potential process.

Answer 22

4) Hyperpolarization: potential overshoots below resting to about -90mV.
Voltage-gated Na+ channels remain CLOSED.
Voltage-gated K+ channels remain OPEN, driving membrane potential closer to the electrochemical equilibrium of K+.

Question 23

Identify and describe the 5th and final stage of the Action Potential process.

Answer 23

5) Resting State: neuron returns to resting membrane potential.
All Voltage-gated ion channels CLOSE.
K+ and Na+ Leak channels remain OPEN. Remember, Number of K+ leak channels&raquo_space;> number of Na+ leak channels.

Question 24

Identify at which stage there is an Absolute Refractory period.

Answer 24

The 2nd and 3rd stages where the potential reaches its peak.

Question 25

Identify at which stage there is a Relative Refractory period.

Answer 25

Between the 3rd and 4th stages where Repolarization and Hyperpolarization take place.

Question 26

What is a Refractory period?

Answer 26

A period of time during which a cell is incapable of repeating an action potential.

Question 27

Describe the stages of Action Potential in a neuron. (6)

Answer 27

0/5) Resting state
Neuron potential is at -65mV, at RMP. This is bc of more K+ channels than Na+ and the Na+/K+ pump.
1) Stimulus
Beginning of depolarization of cell due to a stimulus that causes Na+ to enter the cell through Gated channels.
2) Depolarization
If potential of cell reaches threshold of -55mV, action potential fires. Voltage gated Na+ channels OPEN and Na+ moves into the cell further depolarizing it.
3) Repolarization
Membrane potential falls after a peak of +40mV. This makes Voltage gated Na+ channels CLOSE and Voltage gated K+ channels OPEN.
4) Hypepolarization
Potential of cell overshoots to -90mV bc Voltage-gated Na+ channels remain CLOSED and Voltage-gated K+ channels remain OPEN, trying to reach the electrochemical equilibrium of K+.
5) Resting State
Neuron potential is back at -65mV. All Voltage gated channels CLOSE.

Question 28

How is the intensity of a stimulus ‘measured’?

Answer 28

By how many APs are fired. But neurotransmission has more to do with that!

Question 29

What are neurotransmitters?

Answer 29

Chemical messengers of the brain; either Small Molecule NTs or Peptide NTs.

Question 30

True or False: Neurons can only produce

one type of neurotransmitter.

Answer 30

False, a neuron can co-transmit and co-release different

types of neurotransmitters.

Question 31

Describe how Neurotransmission takes place. (8)

Answer 31

1) Action potential arrives at Axon Terminal.
2) Voltage gated Ca2+ channels open due to Depolarization.
3) Ca2+ enters PreSynaptic Neuron.
4) Ca2+ signals to neurotransmitter Vesicles.
5) Vesicles move to membrane and dock.
6) Neurotransmitters released with exocytosis.
7) Neurotransmitters bind to Receptors.
8) Signal started in PostSynaptic cell.

Question 32

Name 2 functions of Ca2+ in neurotransmission.

Answer 32

1) Signals vesicles with neurotransmitters to move to membrane
2) Helps vesicles fuse with the membrane and release to the synaptic cleft.

Question 33

What are 2 types of Receptors on the PostSynaptic Membrane?

Answer 33

1) Ionotropic (Ligand gated ion channel; FAST)

2) Metabotropic (G protein coupled receptor; SLOW)

Question 34

Describe how an Ionotropic receptor works.

Answer 34

1) NT binds to channel protein (Ionotropic receptor)
2) Channel opens immediately
3) Ions flow through for a brief time.

Question 35

Describe how a Metabotropic receptor works.

Answer 35

1) NT binds to G protein coupled receptor, activates it.
2) G protein subunit binds to channel protein, so there is a slight delay.
3) Channel opens, ions flow through for a longer time.

Question 36

What is an Excitatory Post Synaptic Potential (EPSP)?

Answer 36

A temporary Depolarization of the cell.

Question 37

What is an Inhibitory Post Synaptic Potential (IPSP)?

Answer 37

A temporary Hyperpolarization of postsynaptic membrane caused by the flow of negatively charged ions into the postsynaptic cell.

Question 38

Where does Summation occur in the neuron?

Answer 38

At the Axon Hillock.

Question 39

What is Spatial Summation?

Answer 39

It is the summing of potentials from different areas of input to lead to an AP usually on the dendrites.
(like multiple mini firings from the different neurons until it reaches threshold)

Question 40

What is Temporal Summation?

Answer 40

Subthresholds generated by a single presynaptic neuron over a period of time are responsible for the generation of an action potential on the postsynaptic neuron.
(like multiple mini firings from the same neuron until it reaches threshold)

Question 41

How is Ca2+ used in research? (2)

Answer 41

1) To measure Ca2+ in response to behavior:
Ca2+ tagged with Fluorescent Protein and infused into a Virus to be put into a specific brain region. This way we have a visual depiction.
2) Optogenetics:
Virus with light sensitive protein injected into rat’s brain region. If the protein comes into contact with light it creates an INHIBITORY or EXCITATORY response.
This is how they stop fear responses.