Membranes

Question 1

What are the main factors that influence the speed of diffusion across a membrane?

Answer 1

• Size
• Diffusion Distance
• Temperature
• Concentration gradient of the molecule
• Surface area of diffusion
• Solubility of the molecule

Question 2

Molecules that are polar or charged must use [] to traverse the plasma membrane?

Answer 2

protein channels

Question 3

What are the two types of protein channels?

Answer 3

Voltage-Gated

Ligand-Gated

Question 4

Why is the cell more positively charged on the cystoplasmic than the extracellular side?

Answer 4

False

Cells are more negative inside, compared to the extracellular space.

Question 5

Where does secondary active transport get its energy from?

Answer 5

• Relies on energy eastablished in Na+ or H+ gradients.
• These molecules travel down their electrochemical gradient - creating the energy to pull the “2nd” molecule with it.

Question 6

At high concentrations, the transport rate of simple diffusion can actually exceed that of [] - [] diffusion.

Answer 6

carrier-mediated.

Question 7

Why do carrier-mediated diffusion proteins become less efficient than simple diffusion at high concentration levels?

Answer 7

• Each carrier protein has a T_m, or its transport maximum. At a certain level of concentration, the protein will not be able to transport all of the solute that it encounters.
• Whereas, simple diffusion can continuously transport solutes across the membrane. Simple diffusion does not have to deal with T_m.

Question 8

70% of most cell’s total energy is used to power the [] - [] pump

Answer 8

Na+ - K+

Question 9

Na - K Pump

• [] Na⁺ are pumped out of the cell
• [] K⁺ are pumped into the cell
• T/F, this pump is inactive during action potentials?

Answer 9

• 3
• 2
• F, this pump is almost always active.

Question 10

Is secondary active transport an active process?

Answer 10

No, it indirectly relies on the use of ATP…..so its passive.

Question 11

In secondary active transport, does the “2nd” molecule being transported go against or with its gradient?

Answer 11

The 2nd molecule goes against its gradient.

Think about Na/Glucose transporters in the intestine (symport) or Na/Ca transporters in muscle cells (antiport)

Question 12

What are the 3 reasons for hte resting membrane potential to be negative?

Answer 12

1. Na⁺/K⁺ pumps keep the inside of the cell slightly more negative because it pumps out 3 cations while pumping in only 2 Cations (imbalance of cations)
2. Leakage channels allow Na⁺ and K⁺ to slowly move down their gradients.
   
   1. K⁺ leakage out of the cell is much larger than Na⁺ leakage into the cell
3. Negatively charged molecules are trapped in the cell.

Question 13

Which transport proteins are active during an action potential?

What type of transport is this?

Answer 13

• Voltage gated Na+ (Fast)
• Voltage gated K⁺ (Slow)

Simple Diffusion! - the ions are moving down their electrochemical gradient?

Question 14

What does our electrochemical gradient say about the movement of the following molecules into/out of a resting membrane cell, if their respective channels were opening?

Na+, K+, Ca2+

Answer 14

• Na^+​
  
  • The gradient is larger outside the cell so Na will flow into the cell
  • The electro gradient will be attracted to the negatively charged cytoplasmic area
  • Therefore Na+ moves into the cell.
• ^​K⁺
  
  • The gradient is larger inside the cell so the K will flow out of the cell
  • The electro gradient will be attacted to the negatively charge cytoplasmic area though…so its fighting the concentration gradient
  • It is a net efflux, so the concentration gradient outweights the electro gradient
• Ca2+
  
  • concentration gradient and electro gradient both pull Ca2+ into the cell.

Question 15

Why does the electrochemical gradient effect the movement of solutes more so than the concentration gradient?

Answer 15

• False.
• The concentration gradient effects the movement more than electricity.
  
  • For Na and K, their corresponding voltages required to coutner act the concentration gradient are almost never met.

Question 16

At what mV number do fast Na⁺ channels open, causing a rapid depolarization?

Answer 16

-55 mV

Question 17

What are the 4 basic phases of an action potential?

Answer 17

Depolarization to threshold

Rapid depolarization

Rapid repolarization

After-hyperpolarization

Question 18

Rapid depolarization is characterized by the function of which ion channel?

Answer 18

The opening of Voltage gated, fast Na⁺ channels

Question 19

At what point during the action potential do voltage gated Na+ channels close?

Answer 19

• Technically they are not “closed” during the action potential.
• These channels are in the inactive state through the majority of the action potential, even through the rapid repolarization

Question 20

What ion channel is responsible for the rapid repolarization of the membrane potential?

Answer 20

K+

Question 21

What causes the “after-hyperpolarization” of an action potential?

Answer 21

Voltage gated K+ channels remain open longer than they should, causing a slightly greater eflux of cations….leading to a “more” negative membrane potential.

Question 22

During the “after-hyperpolarization,” is the membrane potentail more or less negative than the resting membrane potential?

Answer 22

MORE negative

Question 23

During APs depolarization and repolarization, in which direction are Na+ and K+ ions moving?

Answer 23

• Na+ = influx…rushing into the cell
• K+ = eflux….rusing out of the cell

Question 24

[] is a measure of the ease with which ions flow across the membrane

Answer 24

Conductance

Question 25

When do Na+ ions have the most conductance?

When do K+ ions have hte most conductance?

Answer 25

1. Na+ has the most conductance during rapid depolarization
   
   1. the voltage gated channels open, allowing sodium to influx down its electrochemical gradient
2. K+ has the most conducatnce during rapid repolarization
   
   1. the voltage gated channels open, allowing K+ to eflux, out of the cell, down its electrochemical gradient.

Question 26

Digitalis (from the foxglove plant)

1. inhibits []/ [] pumps
2. Results in a more [] resting membrane potential
3. Causes a [] to APs

Answer 26

1. Na+/K+
2. Positive
3. “Desensitisation”

Question 27

Tetrodotoxin (from Japanese puffer fish)

1. Functions similar to []
2. blocks the action of voltage-gated [] channels
   
   1. Does not allow for []
3. Interupts [] activity

Answer 27

1. Lidocaine
2. Na+
   
   1. Depolarization
3. Neuronal

Question 28

A [] stimulus can result in the genration of multiple action potentials

Answer 28

Suprathreshold

Question 29

Since all action potentials are all-or-nothing how does the body differntiate between strong and weak stimuli?

Answer 29

• The body will differentiate the strength of stimuli based on the frequency of stimuli
  
  • Ex: if the stimuli is strong, there will be many action potentials, in quick succession, to signal this stimuli.

Question 30

• Absolute Refractory Period -
• Relative Refractory Period -

Answer 30

• period during which another action potential cannot be generated
• Period during which another action potential cna be generated, but only by a suprathreshold stimulus

Question 31

What three states can the voltage gated Na+ channels exist in?

What is the conductance during each of these states?

Answer 31

• Open
  
  • Na+ channels open after threshold has been reach and Na+ influxes.
• Closed
  
  • Na+ voltage-gated channel is closed while the membrane potential is below -55mV
• Inactive
  
  • State that follows the open configutation, for Na+ voltage gated channels. The channel is in this state for a certain amount of time before it reverts to the “closed” state.
  • Na+ is not allowed through at this point and this helps contribute to the absolute refractory period

Question 32

Oligodendrocytes are the insulation in the []

Schwann Cells are the insulation in the []

Answer 32

1. CNS
2. PNS

Question 33

Where does the neuron first get depolarized to threshold to then begin the flow of an action potential down the axon?

Answer 33

Axon Hillock

Question 34

Where does the actual action potential start in a neuron?

Answer 34

The initial segment

Question 35

Breakdown the Action Potential into 4 basic steps as it reaches the presynaptic bulb and as it transfers its stimuli to the post synaptic membrane…

Answer 35

1. Action Potential reaches Presynaptic bulb and depolarizes the buoton
2. Depolarization causes voltage-gated Ca2+ channels to open, allowing for Ca2+ influx
3. Ca2+ influx signals vesicles to fuse with presynaptic plasma membrane and dump its contents (neurotransmitter) into the synaptic cleft
4. Neurotransmitter binds to ligand-gated channels on post-synaptic membrane causing ion channels to open and therefore generate electrical signals int eh postsynaptic cell.

Question 36

After the action potential has caused the neurotransmitter to be released into the synaptic cleft, what are the possible fates of neurotransmitters stuck in the cleft?

Answer 36

1. Reuptake to the presynaptic cell for further use
2. Broken down by enzymes
   
   1. Acetylcholinesterase breaks down acetylcholine
   2. Mainly the Acetyl part, allowing choline to go back into the presynaptic cell via a specific choline transporters.

Question 37

What are examples of excitatory neurotransmitters?

Answer 37

Acetylcholine, norepinephrine, epinephrine, dopamine, gluamate, serotonin

Question 38

What are examples of inhibitory neurotransmitters?

Answer 38

GABA and glycine

Question 39

1. Excitatory neurotransmitters open [] and [] channels
   
   1. why can excitatory neurotransmitters lead to an action potential?
2. Inhibitory neurotransmitters open [] channels
   
   1. Why does this inhibit action potentials?

Answer 39

• Na+ and K+ channels are opened
  
  • Na+ influx is greater than K+ eflux…leading to a normal action potential
• Cl- channels
  
  • This causes an influx of Cl-, causing the membrane potential to become even more negative, making it harder to reach threshold….thus inhibiting action potentials

Question 40

Excitatory and Inhibitory neurotransmitters bind to “what” kind of channels on the post-synaptic cell?

Answer 40

LIGAND-gated channels

Question 41

What is a graded potential?

Answer 41

If the change in membrane potential is below threshold

Question 42

Where are EPSPs and IPSPs received?

Can these directly cause/inhibit action potential?

Answer 42

• They are received on the dendrites and soma of a neuron
• Most likely, 1 EPSP or IPSP cannot illicit an action potential. There must be multiple stimuli from an EPSP to reach the axon hillock and cause a depolarization –> action potential

Question 43

What is the difference between Temporal Summation and Spatial Summation, in regards to action potentials?

Answer 43

1. Temporal - several stimuli are sent from the presynaptic cell at once - possibly causing an action potential in the post synaptic cell
2. Spatial - 1 stimuli is sent from MULTIPLE pre-synaptic cells and converge on the post synaptic cell at the same time - also possibly causing an action potential in the post synaptic cell.

Question 44

Can inputs from presynaptic cells be both excitatory or inhibitory?

Answer 44

Yes