Exam 1 Flashcards
Who developed the neuron staining method
Golgi
what theory did Golgi refute as a result of his staining method?
the reticular theory
Cajal used the golgi stain to do what?
study the development and anatomical diversity of neurons
what are the four tenets of the neuron doctrine?
- The neuron is the structural and functional unit of the nervous system
- Neurons are individual cells, which are not anatomically continuous to other neurons
- The neuron has three parts: dendrites, soma (cell body) and axon. The axon has several terminal arborizations, which make close contact to dendrites or the soma of other neurons
- Conduction takes place in the direction from dendrites to soma, to the end arborizations of the axon (Law of Dynamic Polarization)
amacrine means:
no axon
what cellular structural units run down the length of the axon?
microtubules
Name the 5 functions of glial cells:
- help maintain ionic environments
- regulate synaptic transmission
- involved in neurotransmitter reuptake
- scaffold indevelopment
- promote and inhibit recovery from injury
______ cells are phagocytic (type of nerve cell)
microglial
Is the stimulus related to the signal amplitude in a passive response (receptor potential or synaptic potential)?
What about an active response (action potential)?
No
Yes
Electrochemical voltages are dependent on two factors:
Ionic concentration gradients
Selective permeability
Ion ____ create concentration gradients, while ion _____ cause selective permeability
transporters
channels
equilibrium potential for a particular ion is the voltage at which _________
net flux of the ion across the membrane is zero
nernst equation can calculate:
the equilibrium potential for a single permeant ion
what is the nernst equation?
Eion = 58log[ion]2/[ion]1
remember, if the charge on the ion is anything besides +1 then you need to take that into account
Goldman Equation:
can estimate the membrane potential by considering the relative permeability of all permeant ions.
the value of a cell membrane potential will be closest to:
the equilibrium potential of the most permeant ion
ganglion-
primarily a collection of cell bodies
why is the squid giant axon so big?
increased axon diameter leads to faster conduction velocity.
Hodgkin and Katz ran an experiment in which they plotted the change in membrane potential with increasing extracellular K concentration. What did they find?
the relationship was not linear, implying that K was not the only ion that contributed to resting membrane potential.
Hodgkin and Katz also experimented with Na and found 2 things:
Changing Na concentration did not really have an effect on membrane potential.
Lowering the extracellular Na concentration lead to smaller amplitude action potentials.
Hodgkin and Huxley hypothesized and subsequently proved what hypothesis?
Sodium and Potassium permeability was necessary and sufficient for action potential production
Voltage Clamp –
allows experimenter to control voltage, and records the current moving across the plasma membrane
In the voltage clamp method, a recording electrode and reference electrode register the axon membrane potential and send that information to the ________, which compares that potential to the ________ potential. If the potentials are different, the ________ injects current into the axon to make the membrane potential the same as the _______. The current flowing back into the axon can then be measured.
In the voltage clamp method, a recording electrode and reference electrode register the axon membrane potential and send that information to the voltage clamp amplifier, which compares that potential to the command potential. If the potentials are different, the clamp amplifier injects current into the axon to make the membrane potential the same as the command potential. The current flowing back into the axon can then be measured.
When membrane potential becomes more positive than Ena, which direction does sodium flow?
out of the cell
what toxin blocks Na+ channels? what is the result?
- tetrodotoxin
- early inward current blocked
what toxin blocks K+ channels? what is the result?
- tetraethylammonium
- the late outward current is blocked
membrane conductance changes underlying the action potential are _____ and _____ dependent.
- time
- voltage
the more appropriate functional term for the axon hillock is the ________
spike initiation zone
During relative refractory period the membrane can be stimulated to produce an action potential, but the stimulus must be:
stronger than during resting membrane potential
what are the gating parameters for the Na+ gate?
m^3h
what are the gating parameters for the K+ gate?
n^4
In reference to gating parameters:
m stands for-
h stands for-
n stands for-
activation (Na+)
inactivation (Na+)
activation (K+)
Hodgkin and Huxley theorized 4 things about ionic channels for action potentials:
- Large ionic currents/High ionic flux rates
- Currents dependent on E-C gradients for ions
- Conductance pathways of sodium and potassium were independent of each other
- Gates were Voltage-dependent
How are ionic channels voltage dependent?
they contain mobile gating charges whose movement can open and close channels
__________________, in 1976 described a method called patch clamping (learn these names!)
Won Nobel prize in 1991
Bert Sakmann and Erwin Neher
how many charges must move in an Na+ and K+ channel to open them
3 and 4 respectively
what is the resistance of the seal made between the glass patch pipet and membrane?
Why so high?
1 giga-ohm
so current doesn’t leak out
what are the three recording methods of patch clamp?
whole cell recording, inside out recording, and outside out recording.
whole cell recording allows you to measure:
electric potentials and currents from the entire cell
inside out recording allows you to study:
the cytosolic factors that affect channel function
outside out recording allows you to study:
the effect external signals have on channel activity
when you depolarize a cell you do not instantly open all the voltage gated channels, you increase:
increase the probability of channels opening.
how do you get xenopus oocytes to translate ion channels during development?
inject the eggs with mRNA for said ion channels
What species is transfected with ion channel mRNA for study?
What is this process called?
- Xenopus laevis
- site directed mutagenesis
variations in action potentials and electrical properties between cells is due to:
variations in their channel composition
dysfunctional channels due to mutation is called:
channelopathy
the variability in the severity of symptoms of diseases due to channelopathies is based on:
the number and place of channel mutations
alpha subunits are the main subunits of a given channel. Auxiliary subunits are sometimes necessary, sometimes not. They provide ________
functional diversity through kinetics or voltage sensitivity
how many genes encode a voltage gated sodium channel?
1
describe the sodium channel:
it is one large alpha subunit that is subdivided into 4 roughly equivalent domains that each contains one transmembrane voltage sensor and 5 other transmembrane segments. there is also a beta subunit on each side of the channel.
what/where is the inactivation gate of the sodium channel?
it is the loop between domains 3 and 4.
how did researchers figure out that the inactivation gate was in the cytosol?
they injected a squid axon cytosol with protease and there was subsequently no inactivation of sodium channels.
each domain of the sodium channel has a pore loop, which sticks partially into the membrane and contributes to:
ion selectivity
what are the 4 families of K+ channels?
- Kv and HERG
- Inward rectifier
- Ca++ activated
- 2-pore
how many subunits make up these K+ Channels?
- Kv and HERG
- Inward rectifier
- Ca++ activated
- 2-pore
4
4
4
2
variations in action potentials and electrical properties between cells is due to:
variations in their channel composition
dysfunctional channels due to mutation is called:
channelopathy
the variability in the severity of symptoms of diseases due to channelopathies is based on:
the number and place of channel mutations
alpha subunits are the main subunits of a given channel. Auxiliary subunits are sometimes necessary, sometimes not. They provide ________
functional diversity
how many genes encode a voltage gated sodium channel?
1
describe the sodium channel:
it is one large alpha subunit that is subdivided into 4 roughly equivalent domains that each contains one transmembrane voltage sensor and 5 other transmembrane segments. there is also a beta subunit on each side of the channel.
what/where is the inactivation gate of the sodium channel?
it is the loop between domains 3 and 4.
the task of Kv4.1 is to:
space out action potentials
each domain of the sodium channel has a pore loop, which sticks partially into the membrane and contributes to:
ion selectivity
Without a voltage sensor, how is the inward rectifier voltage dependent?
it is typically clogged with Mg++ and cytosolic components, but when membrane potential is less than Ek, K+ moves inward and pushes this shit out to let K+ flow in.
which K+ channel classes have S4 voltage sensors?
Kv, HERG, and Ca++ activated
what kind of channel is a 2-pore K+ channel
leak channel
which voltage gated K+ channel does not have an S4?
inward rectifier
How many transmembrane segments are there in each subunit of:
- Kv and HERG
- Inward rectifier
- Ca++ activated
- 2-pore
- 6
- 2
- 7
- 4
some K+ channels actually have inactivation, which is mediated by ________
beta subunits
Kv K+ channels are also known as ______ channels
delayed rectifier
The task of Kv2.1 is to:
bring an action potential to an end
the task of Kv4.1 is to:
space out action potentials
Ion selectivity in channels was discovered using __________.
What was the difficulty with this method?
- x-ray crystallography
- Ion channels are difficult to crystallize because large parts of them prefer to be in a lipid environment
Without a voltage sensor, how is the inward rectifier voltage dependent?
it is typically clogged with Mg++ and cytosolic components, but when membrane potential is less than Ek, K+ moves inward and pushes this shit out to let K+ flow in.
Why is there not a current flowing through HERG channels after a stimulus?
they open and close so rapidly that no current flows until the end of a depolarization when inactivation is rapidly removed.
increasing intracellular Ca++ concentrations means what for Ca++ dependent K+ channels?
a smaller depolarization will cause the channels to open.
the 2 pore K+ channel is _____ sensitive
pH
Beta subunits are required for ________ channels to function
Ca++ dependent K+ channels
Ca++ dependent K+ channels have inactivation gates. (just know this) these channels also serve a dual function:
They open from depolarization, which will lead to more cell depolarization in the cell, but they also allow Ca++ into the cell, which can regulate the activity of other ion channels and many many other functions in the cell (think muscle function and gene expression). So there is a voltage importance and a cytosolic regulation importance.
Calcium channels are divided into groups by their activation levels.
HVA (high voltage activated) requires ______ depolarization to activate, and typically regulate _____, _____, ______
LVA (low voltage activated) requires ________ depolarization to activate, and are common during __________
- large
- exocytosis, secretion, enzyme function
- small
- early development
what do Cl- channels resemble?
Why is this?
they resemble transporters
the current consensus is that they probably evolved from transporters.
how many alpha helix transmembrane domains does a Cl- channel have?
17-18
Ion selectivity in channels was discovered using __________.
What was the difficulty with this method?
- x-ray crystallography
- Ion channels are difficult to crystallize because large parts of them prefer to be in a lipid environment
how does the pore helix contribute to ion selectivity?
negatively charged carbonyl oxygens on the helix face the water filled cavity, which draws K+ ions into the cavity and dehydrates them so they can continue on their journey.
what is the selectivity filter and how does it select for K+?
it is the narrow part of the channel lined with oxygen atoms attached to amino acids. The oxygens interact with the dehydrated K+. The charge of more incoming K+ ions forces K+ to move through the pore.
What is the exchange ratio of Ca++ to protons in the Ca++ pump?
2 Ca++ out for every 4 H+ in
The voltage sensor of K+ channels is contained within “______” that rest on the ______ of the cell when keeping the channel closed.
paddles; inside
Depolarization of the membrane will stimulate the paddles of the K+ channel to:
flip to the outside of the membrane and open the channel
________ mediate the majority of the flux of water across cell membranes
aquaporins
P class pumps get their name because:
when ATP is hydrolyzed, that phosphate is used to activate the pump itself
V-class pumps get their name for:
vacuolar membrane- ??????
Gradients are _______ by ATPase pumps
maintained and fine tuned
Two ATPase pumps of importance are:
Na+/K+ pump and the Ca++ pump
Describe briefly the process of the Na+/K+ pump
3 Na+ bind inside the cell–> the pump hydrolyzes ATP–> the pump changes its conformation to release Na+ outside the cell and pick up 2 K+ –> the pump is dephosphorylated and returns to its original conformation, releasing the 2 K+ inside the cell.
Why would Na+ bind to the ATPase on the inside of the cell if it is in such a low concentration?
the pump’s affinity for Na+ is way higher for Na+ when it is open to the inside of the cell. Vice versa for outside facing conformation.
What is the exchange ratio of Ca++ to protons in the Ca++ pump?
2 Ca++ out for every 4 H+ in
The inequality of charge movement in the Na+/K+ ATPase means it is _____
electrogenic
Does the sodium/potassium pump contribute to membrane potential?
Yes, but only slightly. it adds 2.3 mV of charge separation
what compound blocks the Na/K pump?
Ouabain
Why are the Ca++ pumps so vital to cells?
If they were not present, Ca++ would slowly leak into the cell and overstimulate certain functions/eventually kill the cell. The Ca++ gradient necessary for other functions would also disappear.
What are the 2 types of P-class Ca++ pumps?
PMCA and SERCA
PMCA is very sensitive to _______ binding so that it can maintain low cytosolic Ca++ levels
calcium-calmodulin
SERCA recovers calcium released from _______ and moves it out of the cell
ER or SR
PMCA stands for
Plasma Membrane Calcium ATP-ase
SERCA stands for
Sarcoplasmic and Endoplasmic Reticulum Calcium ATP-ase
Are PMCA and SERCA electrogenic?
No. They do a 2 for 2 switch
Describe briefly the cycle of the SERCA pump
2 Ca++ and 1 ATP bind to their binding sites on the pump –> ATP hydrolysis phosphorylates an aspartate on the pump which leads to a conformational change that ejects calcium out of the cell –> dephospho rylation of aspartate changes the pump back to the original conformation
Secondary active transport can move substrates against their concentration gradient by:
cotransporting them with ions (like Na+) down the ion’s concentration gradient.
The Na+/Ca++ exchanger is high capacity, meaning:
it can function just with the binding of these ions, not requiring ATP phosphorylation.
The Na+/Ca++ exchanger exchanges __ Na+ for ___ Ca++
3; 1
Is the affinity of The Na+/Ca++ exchanger for Ca++ relatively low or high?
low
