Neuroscience Exam 2
why does capacitive current occur?
because step from one potential to another alters charge separation/electro-potential difference across membrane
phosphoanhydride bond
bond that connects phosphates in an ATP molecule; most important in respect to energy storage
inactivation gate
bottom portion of the voltage-gated sodium or potassium channel that closes the channel (open in resting state)
much of energy from ATP is consumed by the __________ to keep the ___________ working
brain;Na+/K+ pump
At rest Vm/ K+ equilibrium potential are
in a "tug of war"; higher conductance of K+ than Na+ ions flowing in/out (returns to negative K+ voltage)
absolute refractory period
includes times of depolarization + repolarization; Na/K gates in configuration where they can't cause an AP (ensures AP travels in one direction and keeps it separate on axon)
ATP is an RNA nucleotide with three ______________ bound to it (_____________ in center attaching phosphates to _______________ base adenine
phopshates; ribose-5 C sugar; nitrogenous
what do the four domains in plasma membrane create
pore
If Na+ equilibrium potential is reached,
positive Na+ ion channels close, but K+ channels remain open; Vm will go in direction of Ek since membrane is permeable
electrical forces
produced by K+ ions toward negative interior; generates a gradient to pull K+ back in
voltage-gated sodium channels can't __________ until ___________ returns
reopen; potential
how is ATP metabolized?
through glycolysis, Lrebs Cycle, and ETC/ocidative phopshorylation
relative refractory period
time of hyperpolarization; enough Na+ gates have reset, so they can cause another AP (much higher EPSP required to reach threshold since Vm is much lower)
activation gate
top part of the voltage-gated Na+ channel that opens when the membrane voltage reaches threshold (closed in resting state)
passive conduction is traveling of a ___________ potential along __________
graded; membrane
resting potential is usually between...
-40 to -90 mV
_________ ADP is _________________ to ___________
34; dehydrated; 34 ATP
what is the maximum yield of ATP per glucose?
38 (2 lost)
inactivation gate is formed between ___________ and folds over, ____________
3rd/4th domain; blocking pore
Chemiosmosis
A process for synthesizing ATP using the energy of an electrochemical gradient and the ATP synthase enzyme.
electron transport chain
A sequence of electron carrier molecules (membrane proteins) that shuttle electrons during the redox reactions that release energy used to make ATP.
receptor potential
A slow, graded electrical potential produced by a receptor cell in response to a physical stimulus
protons must travel through ____________
ATP synthase (won't move to area of lower concentration)
what is pyruvic acid oxidized to prior to entering Krebs?
Acetyl-CoA
AP: Resting state
All gated Na/K channels are closed (Na+ activation gates closed; inactivation gates open); will remain in configuration until EPSP is reached
NADH dehydrogenase
An enzyme located on the inner mitochondrial membrane that catalyzes the oxidation by NAD+ of pyruvate to Acetyl-CoA. This reaction links glycolysis and the Krebs cycle.
what is produced when pyruvic acid loses a carbon during converison?
CO2
what needs to be eliminated from body through cardiovascular/pulmonary systems and why?
CO2; acidic so buildup leads to enzyme denaturation
if chemically gated channel is permeable to Cl- ions and opened by a neurotransmitter,.....
Cl- ions may cause an IPSP, inhibiting firing of an AP
what produces the bulk of ATP?
ETC/oxidative phosphorylation (from NADH + FADH2 production in Krebs)
FADH2 is oxidized to ________, transferring electron to ___________________, passing it to ___________________
FAD; succinate dehydrogenase; coenzyme Q
True/False: In patch clamp, if resting membrane potential is -64 mV and Vc is set to 64 mV then no current will be injected.
False; A current will be injected such that the membrane potential of -64 mV is brought up to 64 mV.
True/False: Once generated, an action potential's amplitude may vary as a function of the size of the preceding stimulus.
False; Action potentials are either all or none. Their magnitude does not vary down the same axon.
True/False: At reverse potential (equilibrium potential) there is no net movement of ions across the neuronal membrane. If membrane potential goes lower then ions will move in one direction, if membrane potential goes higher then ions will move in the opposite direction. If any type of ion moves, then all types of ions will move in the same direction.
False; Each ion has its own unique equilibrium potential. Thus, different types of ions can move in opposite directions simultaneously.
True/False: If resting membrane potential is -80 mV, then a change to -82 mV is considered depolarization.
False; If membrane potential becomes less negative it is called hyperpolarization. Here it gets more negative.
True/False: In a neuron, diffusional force and electrical force are always equal.
False; If that were the case then the net flow of ions would always be 0. Graded and action potentials would not be possible.
True/False: If EK = -87mV and ENa = 53mV, ECl = -45mV, membrane potential is -62mV, and gNa is not 0, then an EPSP is likely occurring, but it is not likely that an action potential is occurring.
False; If there is a Na conductance then you know that Na will cross the neuronal plasma membrane inward under these conditions.
True/False: If EK = -87mV and ENa = 53mV and resting potential is -66mV, then the highest membrane potential achievable during depolarization is 119mV
False; It can't be any value higher than 53 mV, the reverse potential for Na.
True/False: If you add potassium chloride (KCl) to pure water in a beaker, it will break apart into potassium and chloride ions. Since the chloride ions have a negative charge, the solution will become very negative.
False; K has a positive change and Cl has a negative charge. Together (KCl) their charges are perfectly in balance. If KCl is dissolved in water, then there will be an equal number of positive charges balances to the negative charges when K dissociates from Cl. Thus, the water will not become very negative, it will say the same.
True/False: There is a strong INa during the relative refractory period.
False; Only K channels are open during the relative refractory period.
True/False: Receptor potentials may be generated when a neurotransmitter binds to its receptor and causes some ion channel to open.
False; Receptor potentials are not generated by neurotransmitters. They can be generated by several stimuli with the exception of neurotransmitters. Receptor potentials are associated with the lack of a synapse. No synapse = no neurotransmitter.
True/False: The Nernst equation is used to solve for the total length of an axon (excluding the axon hillock and the axon terminal.
False; The Nernst equation is used to determine equilibrium potential for some particular ion.
True/False: There is a very high gNa associated with depolarization and a very high gK associated with repolarization associated with every graded potential.
False; This statement is true for an action potential, not a graded potential.
synaptic potential
Graded potentials produced in the post-synaptic cell in response to neurotransmitters binding to receptors
If membrane potential=electrochemical force (K+)
K+ remains permeable since channels remain open (travel in both directions); conductance= + and ionic current= 0
outward current is carried by _____________ ions; voltage-gated channels activated more ___________ and do not show inactivation in _________
K+, slowly, axons
ATP synthase
Large protein that uses energy from H+ ions to bind ADP and a phosphate group together to produce ATP
during conversion of pyruvic acid, another molecule of __________ is reduced to _____________ with a leftover proton
NAD+; NADH
what sources energy providing electrons of ETC?
NADH and FADH2 (Glycolysis/Krebs and Krebs)
solution devoid of Na+?
Na+ current can be eliminated by removing all external sodium; recorded current similar to that of TTX (Na+ still inside; can flow down concentration gradient)
AP: Depolarization Phase
Na+ ion channels open when threshold (ie -55 mv) is reached; moves into channel down electrochemical gradient (permeability increases; potential reversal and timing mechanism started to cause inactivation gate to close soon)
inward current is carried by___________ and is ____________gated; activates rapidly in response to a _____________ stimulus
Na+ ions; voltage; depolarization
what is the final electron acceptor?
O2
If Ca 2+ has a reverse potential of ECa+= 40 mV, then net ion flow for 58 mV is in or out?
OUT; more positive
oxidative phosphorylation
Part of the electron transport chain. A process occurring in the mitochondria that results in the formation of ATP from the flow of electrons across the inner membrane to bind with oxygen.
AP: Repolarization Phase
Timing mechanism causes Na+ inactivation gates to close (no longer permeable to ions); voltage-sensitive K+ gates open, moving out of cell with positive charge (causes repolarization/decrease of Vm to resting value/internal negativity)
True/False: During the depolarization phase of an action potential, a very high gNa is established when the Na action gate opens. There is also a very high INa associated with this event (assuming resting potential is -60 mV and ENa = 67mV).
True
True/False: Tetraethylammonium interferes with gK.
True
True/False: The voltage sensor, associated with the voltage gated potassium ion channel, is located on the alpha subunit.
True
True/False: There is always at least a slight K conductance across a neuron's plasma membrane (a neuron removed from an animal).
True
True/False: When solutes such as ions are placed in a solution without physical barriers, they become evenly distributed throughout the solution by the random movement of particles toward a state of equilibrium
True
True/False: There are several recording electrodes inserted into a dendrite; A, B, C and D. There is also a stimulating electrode inserted into the same dendrite, and a current is injected. For this neuron, resting membrane potential is -70mV. At the same moment in time the recorded membrane potentials are: A, -70mV; B, -68mV; C, -65mC; and D, -66mV. Based only on these data, recording electrode C is the recording electrode that is likely positioned closest to the stimulating electrode.
True: Graded potentials lose magnitude as they travel away from the site of stimulus. Recording electrode C has the highest change in membrane potential from the resting state. Thus, based on these data, it is most likely the one closest to the recording electrode.
True/False: If antidromic action potential conduction is occurring then the action potential was not started at the axon hillock.
True; If it started at the axon hillock, it can only travel in the orthodromic direction.
True/False: There are four recording electrodes inserted into a neuron; A, B, C and D. A reads -66mV, B reads -60mV, C reads -40mV and D reads -66mV. The only interpretation of these data are that an action potential is in the process of moving in the direction of A towards D.
True; The potentials associated with B and C are different. Thus, it is much more likely that this is a graded potential, not an action potential.
AP: Hyperpolarization Phase
Vm goes below resting potential since K+ gates remain open (eventually close when -90 mv is reached); excessive efflux of K+ causing undershoot
AP: After-hyperpolarization
Vm will return to resting potential through diffusion and Na/K pump after K+ gates close; Na+ channel starts resetting by closing activation gate (neuron insensitive to stimulus + depolarization)
If all K+ channels are open,
Vm=Ek since all K+ ions can freely move across membrane (in absence of leaky channels; always open, so K+ is primary contributor to resting potential)
ADP
a lower-energy molecule that can be converted into ATP by the addition of a phosphate group (hydrolyzed form)
all-or-none response
a neuron's reaction of either firing (with a full-strength response) or not firing.
coenzyme
a non protein compound that is necessary for the functioning of an enzyme
if an injected current drives potential higher than threshold, a ______________will propogate, traveling both _________ and __________ away from injected site since in axon not ________________
action potential; left/right; hillock
diffusion force
acts to pull K+ ions down concentration gradient; depletion in positive internal charges
voltage-gated sodium channel is made up of a single _________________ with ___________ distinct domains, made up of ________________ helicies
amino acid strand; four, sigma-alpha
unlike in passive conduction, when axon potential is propagated, ______________________ does not _____________
amplitude; decrease
GABA binding to a Cl- channel is
an IPSP (hyperpolarization) due to it being Cl-
what happens if magnitude of depolarization doesn't reach threshold?
an action potential won't fire
Nernst equation
an equation predicting the voltage needed to just counterbalance the diffusion force pushing an ion across a semipermeable membrane from the side with a high concentration to the side with a low concentration
where is the greatest flow of ions?
at site of stimulus; where open ion channel is located
ohm's law
can be used to predict the relationship between potential difference, current, and resistance (I=gv); calculate Na+/K+ during AP
neuron functions as a ________________; stores electrical energy in an electric field (will store some of energy at first and release after peak)
capacitor
what is the primary generator of ATP?
consumption of glucose
voltage clamp
controls voltage across membrane to a desired value so changes in Na/K conductance can be studied
passive responses
currents that do not cause an action potential (graded); only EPSPs cause Vm towards AP (IPSPs inhibit firing)
where does glycolysis occur?
cytoplasm
graded potentials are generated on __________ making up _____________ receptors; greater touch, causes a greater ______________ contributing to EPSP
dendrite; touch(mechano); flow of ions
action potential speed is affected by axons' ______________ and ___________________
diameter; presence of myelin sheath
If membrane voltage (Vm) does not equal command voltage (Vc), comparator generates a ____________________ signal
different
different axons can yield ___________ speeds/___________ of action potentials
different; shapes
Action potentials are different than graded potentials since they ___________ different _____________ when traveling down same axon
do not; magnitudes
an __________________ potential is generated when K+ concentrations are not ____________
electrical; equal
O2 functions to accept ____________ from ____________
electrons; cytochrome C oxidase
ATP (adenosine triphosphate)
energy storage molecule that stores chemical energy from consumed food
what is the driving force in all of the conversions in Krebs Cycle?
enzymes
_______________ keeps membrane voltage as close to command voltage as possible
feedback circuit
energy-consuming phase
first phase of glycolysis, in which two molecules of ATP are necessary to start the reaction; G3P produced
tetrodoxin
found in pufferfish, blocks INa (current)
voltage-gated potassium channel is made up of __________ subunits; _______ and ________
four; 2 alpha/2 beta
what determines stimulus intensity in action potentials and why?
frequency (EPSPs causing an AP must have a magnitude if occurring frequently; high stimulus must overlap with refractory periods)
EPSP magnitude effects ___________
frequency of action potentials
myelin sheath requires many ________ cells, thus maintenance cost (nutrients/___________ much higher; found in circuit where speed is critical)
glial; ATP
stimulating electrode
injects a current to artificially stimulate neuron (mimic opening of ion channel)
Krebs cycle
inside mitochondria and is series of reactions where Acetyl-CoA is oxidized to form ATP
when an EPSP crosses threshold,....
it fires an action potential; enough magnitude
If Na+ channel open,
it has a higher conductance since more are open, so there is more movement of Na+ in than K+ leaving; inward flux of Na brings positive charge with them so Vm toward ENa
tetraethylammonium (TEA)
large organic cation; specifically blocks K+ channels (except leaky)
What happens in presence of leaky K+ channels?
low permeability to ions; cause resting potential to be immediately leak out after flowing in for Na/K pump
recording electrode
measures changes in voltage (membrane potential)
each molecule of NADH produced in the_______________ provides the energy for ___________ molecules.
mitochondria; 2 ATP
If membrane is permeable to K+
more K+ inside so cross out to lower concentration (down gradient); conductance and ionic current = +
graded potential either make membrane more __________ or _________. This is either a ____________ or ___________
negative/positive; hyperpolarization (IPSP)/depolarization (EPSP)
as a positive current is injected, there is an area of ______________ electrons in all directions around it
negatively charged (keep moving right. downward from membrane)
if there is no net driving force, there is _____________
no movement (in balance; equilibrium)
If K+ permeability=0
no open channels for K+ ion; conductance and ionic current= 0
hyperpolarization
occurs when starting at rest, but traveling towards more negative (recovery)
with __________ revolutions of Krebs Cycle, two molecules of _________ are produced, one molecule of _____________, one molecule of ____________, and three molecules of ____________
one; CO2, ATP; FADH2, NADH
If membrane potential goes lower than equilibrium potential, ions will move in ________________ direction. If higher, they will move in ___________ direction (unique to each ion)
one; opposite
voltage gated potassium channels does not ______________; delay rectifier
open immediately
The electrical gradient for 4 mV should be_______, given ENa= 57 mV
out
Graded potentials travel _________ in ___________
outward; all directions
when enough ____________ is available, ___________ acid will transport to mitochondria and enter into Krebs Cycle
oxygen; pyruvic
repolarization
return to resting potential after depolarization
Multiple action potentials fire at __________
same magnitude (same height of depolarization/hyperpolarization); ALL OR NONE RESPONSE
energy-producing phase
second stage in glycolysis where 4 ATP are produced (net increase of two; used in cellular processes)
O2 is ________, yielding two oxygens that rapidly combine with ____________ to form ___________
split; 2 H+ ions, H2O
when membrane potential reaches -50 mV, it
steadily depolarizes and rapidly repolarizes, followed by hyperpolarization + recovery
conductance
the degree to which an object conducts electricity, calculated as the ratio of the current that flows to the potential difference present.
saltatory conduction
the propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials.
What happens if both + and - are entering the cell at the same time?
they cancel each other out; equal distances apart when graphed
change in Vm causes sensors to ____________, causing _______ loops to move; establishes a ______________
twist; pore; selectivity filter
4 H+ are produced and carried by __________ to be transferred to ___________
ubiquinone (coenzyme Q); cytochrome bc1 complex
S4 helix serves as a ____________, causing a change in _____
voltage sensor; membrane voltage
_____________ sensing part of K+ voltage channel is _________ helix; serves also as a __________ (does not open immediately in response to voltage)
voltage; 4th alpha; delay rectifier
metabolic water
water generated in the tissues during the chemical breakdown of the energy-yielding nutrients in foods
