PSL-Week 1 Flashcards
What does permeability depend on?
molecular size, lipid solubility, and charge
What are characteristics of simple diffusion?
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
What differentiate facilitated diffusion from simple diffusion?
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
What does saturation mean in facilitated diffusion?
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.
What are differences and similarities between active transport and secondary active transport?
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
What makes channels different from pores?
channels are made from memebrane spanning proteins with pore loop that create selectivity and contain an S4 segment in teh 4th transmembrane protein
What are gated channels and their two types?
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
What are ligand gated channels
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
What are voltage gated channels?
memebrane channels which are sensitive to potential memebrane difference which causes conformation changes in channel to create a difffusion pore
Endocytosis vs Exocytosis
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
What are the two types of exocytosis and how do tehir mechanism differ?
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
What are the two conditions to generate memebrane potential?
1- create [ ] gradient by having ion pump actively transport certain ions
2- semipermeable membrane to allow one ion specie to diffuse more than others
Why are Na’K pump essential and found in all cells?
it creates that memebrane potential as it has Na/K dependent ATPase enzyme which moves 3 Na out for 2 K in
When does resting membrane potential occur?
when there is electrochemical equilibrium reached
What is electrochemical equilibirum?
when the electrial work that is repelling cation, K, out is equal to the chemical diffusion down [ ] gradient
What is nernest equation?
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.
Why is membrane potential -70 mV and not -90 mV as calculated from nernest equation?
even though membrane is most permeable to K at rest the other ions, Na and Cl, are still somewhat diffusing
What is the equation that can help us calculate the membrane potential by taking into consideration the relative permeability?
Goldman equation which is a form of exapnded Nernest equation
How is Cl- ions concentration distribution different from K and Na?
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
What is a characteristic for Na channnels that distinguish it from rest?
the channel has two gates: Activation gate and inactivation gate
How do the two gates open and close as membrane potential changes?
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.
When does the inactivation gate gets removed?
when the MP must go below threshold level
What does existance of Na channels in great amount in cell membrane tells us about that cell?
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
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?
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
What is meant by threshold?
it is the minimum depolarization necessary to induce regenerative mechanism for oprning of Na channels
What types of threshold do we have?
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
How is it that even though suprathreshold stimuli is strong, it doesn’t have an effect on magnetitude of AP?
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
If AP magnitide will be same no matter how strong the stimuli, why send a suprathreshold stimuli?
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
What is refractory period?
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
What are the two types of refractory periods?
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
How can depolarization block be achieved?
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
What does length constant in cable properties describe?
how quickly the potential difference disappear as function of distance as conduction of AP across axon depend on membrane length constant
What are the two ways to improve the conduction of AP in nervous system so it doens’t lose its strength along axon?
1- increasing diameter
2- increase memebrane resistance so less current of AP is leaked out and weakened
How can increasing membrane resistance be reached as it is most effective means of increasing conduction velocity?
by mylenation which is doen by glial cells
What are the glial cells that help with mylenation of axon?
Schwann cells in PNS and oligodendrocytes in CNS
Why is there a small gap left between portions of myelin sheaths?
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
What is a disease that person can suffer from when mylenation fo axon si lost?
multiple sclerosis which affect brain and spinal cord, and can slow or block signal btw braina nd body, etc
What is saltatory conduction?
it is the jumping mode which occur when AP is jumping from one node to next and in between
How do the unmylinated axons have their insulation?
by being engulfed by schwan cell or oligodendrites and make remak bundle
Why doesn’t action potential when it reaches the end of axon just reporpagate in direction it came from?
because of the refractory period where teh voltage gated channels are inactivated
What is electrical synapse characteristics?
uses gap junctions that are bridged by connexins which allow small ions to cross
Charactersitics of chemcial synapse?
transmitter get released into synaptic cleft to bing the specific receptores found on postsynaptic cell
What is axon terminal?
end of axons which has boutons with vesicles that contain neurotransmitter
What triggers vesicle release?
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
