PSL-Week 1

Question 1

What does permeability depend on?

Answer 1

molecular size, lipid solubility, and charge

Question 2

What are characteristics of simple diffusion?

Answer 2

allow movement of small, lipid soluble molecules and gases through phospholipid bilayer or pores
movement is down its concentration gradient
passive as no energy is required

Question 3

What differentiate facilitated diffusion from simple diffusion?

Answer 3

in this type of diffusion, the molecules pass through with assistance from carrier protein
however, it is similar to simpel diffusion as movement is down its concentration gradient and no energy is required

Question 4

What does saturation mean in facilitated diffusion?

Answer 4

since the substances require assistance of carrier proteins, the amount of molecules to transport can exceed than amount of available transporters which means that the transporters are saturated and adding more molecules won’t increase transport.

Question 5

What are differences and similarities between active transport and secondary active transport?

Answer 5

similarities: both move substances against their concentration gradient, both require energy
differences: energy for primary transport comes from ATP hydrolysis while secondary active transport is powered by chemical energy in substance diffsuing down its [ ] gradient to push other substance agiant its [ ] gradient

Question 6

What makes channels different from pores?

Answer 6

channels are made from memebrane spanning proteins with pore loop that create selectivity and contain an S4 segment in teh 4th transmembrane protein

Question 7

What are gated channels and their two types?

Answer 7

are channels which are closed off by branch of protein structure that act as gate and when it opens it has selectivity on what it allows through
There are 2 types: ligand and voltage gated

Question 8

What are ligand gated channels

Answer 8

also known as cell membrane receptores which are important in synaptic transmission and once they get bound by ligand, they trigger events like activation of enzyme

Question 9

What are voltage gated channels?

Answer 9

memebrane channels which are sensitive to potential memebrane difference which causes conformation changes in channel to create a difffusion pore

Question 10

Endocytosis vs Exocytosis

Answer 10

endo- is the inward pinching of memebrane to create vesicle which is usually receptor mediated to capture proteins from out to in

exo- partial or complete fusion of vesicles with cell memebrane for bulk trans memebrane transport of specific molecules from in to out

Question 11

What are the two types of exocytosis and how do tehir mechanism differ?

Answer 11

Exo 1- more rapid mechanism which is known as kiss and run
Exo 2- full exocytosis
in Exo 1- the vesicle will dock and fuse with membrane at locations called fusion pores and will connect and disconnect several times until it empties the vesicle completly
in Exo 2- complete fusion of vesicle with membrane and release of contents at once

Question 12

What are the two conditions to generate memebrane potential?

Answer 12

1- create [ ] gradient by having ion pump actively transport certain ions
2- semipermeable membrane to allow one ion specie to diffuse more than others

Question 13

Why are Na’K pump essential and found in all cells?

Answer 13

it creates that memebrane potential as it has Na/K dependent ATPase enzyme which moves 3 Na out for 2 K in

Question 14

When does resting membrane potential occur?

Answer 14

when there is electrochemical equilibrium reached

Question 15

What is electrochemical equilibirum?

Answer 15

when the electrial work that is repelling cation, K, out is equal to the chemical diffusion down [ ] gradient

Question 16

What is nernest equation?

Answer 16

in ideal situation, it describes the balance between chemical work of diffusion with electrical repulsion to give potential difference across memebrane and only valid when and only for when there is one ion specie diffusing across memebrane.

Question 17

Why is membrane potential -70 mV and not -90 mV as calculated from nernest equation?

Answer 17

even though membrane is most permeable to K at rest the other ions, Na and Cl, are still somewhat diffusing

Question 18

What is the equation that can help us calculate the membrane potential by taking into consideration the relative permeability?

Answer 18

Goldman equation which is a form of exapnded Nernest equation

Question 19

How is Cl- ions concentration distribution different from K and Na?

Answer 19

Cl ions is more concentrated outside than inside due to existance of anions inside the cell that are impermeable and only leave by exocytosis so the negative inside repel the chlorine and not the active pumps like Na/K pumps

Question 20

What is a characteristic for Na channnels that distinguish it from rest?

Answer 20

the channel has two gates: Activation gate and inactivation gate

Question 21

How do the two gates open and close as membrane potential changes?

Answer 21

at rest, when the MP is -70, the activation gate is closed while the inactivation gate is swinging freely and no Na is allowed through, as the MP changes and reaches the threshold of -55, the activation gate opens and allows Na in while the inactivation gate waits 0.5 ms to start closing. The period in which the inactivation gate is waiting, this will allow Na to enter and reach +30 MP before the inactivation gate starts closing up.

Question 22

When does the inactivation gate gets removed?

Answer 22

when the MP must go below threshold level

Question 23

What does existance of Na channels in great amount in cell membrane tells us about that cell?

Answer 23

that the cell has an exciatble membrane and when the Na channel opens, MP urges to reach +60 mV but the existance of inactivation prevents that and by Na channels inactivated, the only main current is K leakage

Question 24

How come the opening of voltage gated channels of both Na and K when teh threshold of -55 have been reached only has Na entering more than K leaving and depolarizing the cell?

Answer 24

that’s because the opening of Na channels occur faster than K so by the time K voltage gated channels open, the Na channels have allowed enough Na in to depolarize cell to +30

Question 25

What is meant by threshold?

Answer 25

it is the minimum depolarization necessary to induce regenerative mechanism for oprning of Na channels

Question 26

What types of threshold do we have?

Answer 26

1- subthreshold stimuli- opens some channels but not enough to generate AP
2- threshold stimuli- opens just teh right anount of channels
3- suprathreshold- causes more than enough opening of Na channels to generate AP

Question 27

How is it that even though suprathreshold stimuli is strong, it doesn’t have an effect on magnetitude of AP?

Answer 27

that’s because of the all-or-none principle which means that as long as there is enough depolarization to generate AP, the magnitude of AP will be same

Question 27

If AP magnitide will be same no matter how strong the stimuli, why send a suprathreshold stimuli?

Answer 27

That’s because even if the magnitude of AP is same, the stron ger the stimuli the longer is last which means more AP can be stimulated

Question 28

What is refractory period?

Answer 28

time after AP have been geenrated where the Na channels haven’t reconfigured yet to their original state and are still in inactivation state so no AP can be generated during this period even if there is stimuli send

Question 29

What are the two types of refractory periods?

Answer 29

Absolute RP: none of channels are reconfigured so no respond from membrane to any stimuli
Relative RP- some Na channels have reconfigured and will be able to generate AP if stimuli send by then but will be weak

Question 30

How can depolarization block be achieved?

Answer 30

destroying the concnetration gradient for K by introducing more K into ECF which result in permenanet Na inactivation and membrane remains in absolute refractory state so inexitable and won’t generate AP

Question 31

What does length constant in cable properties describe?

Answer 31

how quickly the potential difference disappear as function of distance as conduction of AP across axon depend on membrane length constant

Question 32

What are the two ways to improve the conduction of AP in nervous system so it doens’t lose its strength along axon?

Answer 32

1- increasing diameter
2- increase memebrane resistance so less current of AP is leaked out and weakened

Question 33

How can increasing membrane resistance be reached as it is most effective means of increasing conduction velocity?

Answer 33

by mylenation which is doen by glial cells

Question 34

What are the glial cells that help with mylenation of axon?

Answer 34

Schwann cells in PNS and oligodendrocytes in CNS

Question 35

Why is there a small gap left between portions of myelin sheaths?

Answer 35

these gaps get left because each glial cell wrap one section and another cell does next section, and they leave these gaps called Nodes of ranvier which is where AP is generated as current can depolarize that area

Question 36

What is a disease that person can suffer from when mylenation fo axon si lost?

Answer 36

multiple sclerosis which affect brain and spinal cord, and can slow or block signal btw braina nd body, etc

Question 37

What is saltatory conduction?

Answer 37

it is the jumping mode which occur when AP is jumping from one node to next and in between

Question 38

How do the unmylinated axons have their insulation?

Answer 38

by being engulfed by schwan cell or oligodendrites and make remak bundle

Question 39

Why doesn’t action potential when it reaches the end of axon just reporpagate in direction it came from?

Answer 39

because of the refractory period where teh voltage gated channels are inactivated

Question 40

What is electrical synapse characteristics?

Answer 40

uses gap junctions that are bridged by connexins which allow small ions to cross

Question 41

Charactersitics of chemcial synapse?

Answer 41

transmitter get released into synaptic cleft to bing the specific receptores found on postsynaptic cell

Question 42

What is axon terminal?

Answer 42

end of axons which has boutons with vesicles that contain neurotransmitter

Question 43

What triggers vesicle release?

Answer 43

the diffusion of Ca ions into bouton triggers cascades of reactions that result in vesicle exocytosis and Ca enters the cell when membrane of bouton gets depolarized and the voltage gated Ca channels on the membrane will open at -55mV