NEU Exam 1

Question 1

What are the four principles of action potentials?

Answer 1

1. The All-or-None Phenomenon: An AP either happens completely, or it does not happen at all
2. Refractory Periods: Refractory periods are caused by: potassium continuing to leave the cell, and voltage-gated sodium channels unable to open again
3. Forward Movement: once an action potential is initiated→ it will travel in a ONE-WAY direction (axon hillock→the axon terminal).
4. Rate Code: Coding for Stimulus Intensity
   - No strong or weak APs, all the same regardless of stimulus strength
   - Strong stimuli cause action potentials to occur more frequently
   - CNS determines stimulus intensity by the frequency of impulses
   Higher frequency means stronger stimulus

Question 2

The All-or-None Phenomenon:

Answer 2

An AP either happens completely, or it does not happen at all

Question 3

Refractory Periods:

Answer 3

Refractory periods are caused by: potassium continuing to leave the cell, and voltage-gated

Question 4

Forward Movement:

Answer 4

once an action potential is initiated→ it will travel in a ONE-WAY direction (axon hillock→the axon terminal).

Question 5

Rate Code:

Answer 5

Coding for Stimulus Intensity
- No strong or weak APs, all the same regardless of stimulus strength
- Strong stimuli cause action potentials to occur more frequently
- CNS determines stimulus intensity by the frequency of impulses
Higher frequency means stronger stimulus

Question 6

What is the threshold the membrane potential needs to reach to fire an action potential?

Answer 6

-55mV

Question 7

For the following steps of the action potential

Answer 7

Resting state:-70mV, the inside of the cell is NEGATIVELY charged relative to the outside
Action potential begins when a depolarization increases the membrane potential so that threshold is reached→-55mV
At threshold: VG Na+ channels open, Na+ flow into the cell
This influx of Na+ makes the membrane potential INC (LESS NEG/MORE POS) → +40mV
This is DEPOLARIZATION
SODIUM channels self-inactivate (close), ABSOLUTE REFRACTORY PERIOD (ABSOLUTELY CANNOT GENERATE AN AP, impossible to generate AP)
Potassium channels open→ K+ leaves the cell→going down its concentration gradient→ REPOLARIZATION→RMP decreases→bringing it back towards the normal RMP
The continual K+ leaving the cell→ causes cell to be MORE AND MORE negative→hyperpolarization
RELATIVE REFRACTORY PERIOD (another AP can be generated but would require a stronger stimulus to reach threshold).
Back to resting membrane potential: -70mV
Sodium/Potassium Pump: restores electrical conditions
3Na+ OUT: 2K+ IN (remember KIN)

Question 8

Nernest Equation

Answer 8

One ion can cross
concentraion of in and out

Question 9

K+

Answer 9

In 150
Out 5

Question 10

GHK Equation

Answer 10

more than one can cross
concentration of ion and peremabiilty of an ion

Question 11

Na+

Answer 11

In 10
Out 145

Question 12

Establishing RMP

Answer 12

membrane more permeibale to K+
Rmp is closer to GHK than Nerenst

Question 13

What affects action potential conduction velocity?

Answer 13

*Axon diameter (THICKNESS): larger axon diameter→faster conduction. This is because a larger diameter reduces the resistance to ion flow→enables the AP to propagate more quickly.
- *Myelation: is a fatty substance, wraps around the axon, protecting the sheath.
— Myelinated axons have a SALTATORY CONDUCTION: where the AP jumps from one node of Ranvier to the next→ speeding conduction velocity.
— This is because myelin insulation PREVENTS LEAKAGE and allows for a RAPID propagation at the nodes.

Temperature: higher temperature generally increases the speed of AP conduction
– This is due to the increased kinetic energy of ions→leading to faster movement through ion channels.

Axon length: longer axons experience a DECREASE in conduction velocity due to increased resistance along the length of the axon
— Please note: this effect is relatively small compared to the influence of the axon diameter & myelination

Ion channel properties: opening & closing kinetics. Faster opening & closing if Na+ channels→ FASTER CONDUCTION.

Question 14

Explain the difference between action potential propagation in unmyelinated versus myelinated neurons

Answer 14

Unmyelinated Neurons:
- Continuous conduction
- Depolarization occurs step by step, throughout the axon
- VG Na+ channels are distributed along the entire length of the axon
- The action potential is regenerated at each step

Myelinated Neurons:
- Saltatory Conduction
- Depolarization: only happens at NODES OF RANVIER
- VG Na+ channels are concentrated at nodes of ranvier
- The action potential is regenerated only at the nodes of ranvier

Question 15

Which statement correctly differentiates between the passive and active current in a myelinated axon?

Answer 15

The active current flows only in the nodes of Ranvier, unlike the passive current

• Passive flow is just movement of sodium ions that is passive depolarization
• Active when voltage gated channels are open and sodium is rushing in

Question 16

Nodes of Ranvier represent

Answer 16

gaps in myelin wrapping

Question 17

Changes in membrane potential

Answer 17

way to receive, integrate, send information

Question 18

Changes produce two types of signals

Answer 18

Graded potentials - Incoming signals operating over SHORT distances

Action potentials - Long-distance signals of axons

Question 19

Action Potentials (AP)

Answer 19

Principal way neurons send signals
Occur only in axons of neurons, and muscle cells (skeletal, cardiac, smooth)
Brief reversal of membrane potential

Question 20

Make predictions on what you think might happen if a toxin were to bind to and stop the activity of the sodium-potassium pump?

Answer 20

RMP will get depolarized and during AP reset ionic conditions → might affect refractory period

Question 21

The refractory period is responsible for what other principle of action potentials?

Answer 21

Forward movement

Question 22

Recent research has explored whether myelin thickness can change over time based on experience, and emerging evidence indicates this is possible. If an axon for a neuron important for motor learning increases the number of layers of myelin, thus increasing myelin thickness, what will happen to capacitance, internal resistance, membrane resistance, and propagation velocity?

Answer 22

Capacitance (charges are further apart) - less

Internal - same bc diameter hasn’t changed

Membrane - same

Prop - increases

Question 23

A neuron has increased its production of Na+ leak channels, increasing the permeability of the membrane so that it is now twice as permeable to Na+ as it is to K+ RMP is now +14.5mV. Which direction will Na+ move with the above RMP?

Answer 23

In, primarily due to concentration gradient - only changed permeability not ions

Question 24

A newly discovered species of lizard is found to have a unique central nervous system. The neurons of this lizard have a resting membrane potential that is -83 mV. Why might the RMP of these neurons be so much more negative than in a human neuron?

Answer 24

The membrane is more permeable to potassium than in a human neuron

Question 25

Opioid receptors (such as those that allow for morphine to bind), are metabotropic/G-protein coupled receptors. Binding of morphine to these receptors elicits an IPSP in the postsynaptic cell (hyperpolarize), by activating G- proteins that then act on nearby potassium channels to open them. What might be the mechanism of how inhibition of the postsynaptic cell is occurring, based on this information?

Answer 25

Potassium is able to flow out of the cell, with its concentration gradient, hyperpolarizing the cell