Neuroscience Exam 2

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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


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