BSCI353 Exam 1 (Chapters 1-4)
T/F: The flow of ions across the membrane is solely due to ion channels.
False ~ active transporters like ion pumps are also involved in moving ions and maintaining the concentration gradients (e.g. Na/K pump).
electrophysiology
a very thin electrode is inserted into nervous system to record electrical signals inside neurons
Exp with voltage clamp method: membrane potential from -65mV to -130mV
- a quick capacitive current occurs, and the the membrane potential settles at -130 -then there was no current after that -shows the membrane isn't permeable to any ions at -130mV
process of ion channels during an AP
--100mV: Na+ closed, K+ closed -depol to -50mV: Na+ opens (Na+ flows in ), K+ closed -still at -50mV: Na+ inactivates with inactivation gate, K+ opens (K+ flows out) -drives membrane potential down -repol to -100mV: mem pot is hyperpolarized, Na+ and K+ closed
patch clamp method
-1970's (invented bc ion channel theory needed to be tested and we weren't able to in the 1950's) -Pipette tip can suction up a tiny piece of the neuronal membrane with a v tight seal (gigaohm seal) -the membrane has a channel in it -the current of the ion channel can be observed, indicating if the channel is open or closed -cell-attached recording, whole-cell recording, inside-out recording, outside-out recording
voltage gates Na+ ion channel structure
-4 subunits -additional separate protein domains for voltage sensing -voltage sensors -depol causes a paddle-like voltage sensor to move toward extracellular surface of the membrane bc inner membrane is positive -hyperpol causes paddle-like voltage sensor to more toward the intracellular surface bc of the more negative inner membrane
The resting membrane potential typically ranges from _______ to _______. 0 mV; 90 mV -90 mV; 90 mV 40 V; 90 V -40 mV; -90 mV 40 mV; 90 mV
-40 mV; -90 mV
how do neurons transmit AP"s?
-AP conductance requires both active and passive current flow 1) Na+ channels locally open in response to stimulus, generating an AP 2) some depolarizing current passively flows down axon 3) local depolarization causes neighboring Na+ channels to open and generates an AP here 4) upstream Na+ channels inactivate, while K+ channels open. Membrane potential repolarizes and axon is refractory here 5) the process is repeated, propagating the AP along the axon
equilibrium potentials generated from giant squid axons (K+, Na+, Cl-, Ca2+)
-EK: -75mV -ENa: +55mV -ECl: -50mV -ECa: +145mV
Debate between Golgi and Cajal
-Golgi: reticular theory: neurons are not distinct units, but are fused together, acting as a whole -Cajal: neural doctrine: each neuron is its own entity, isolated from neighboring neurons by a small space
how do Na+ and K+ conductance react to an increase in membrane potential
-Na+ and K+ conductance grows larger, however Na+ conductance drops instantly after it peaks
types of vg channels
-Na+, K+, Ca2+, Cl- -in our genome, at least 10 different genes specify Na+ channels --> so, there are many types of channels! -same for Ca2+, but much more for K+! -mRNA for a particular channel tht were injected into ion channels of xenopus oocytes would only show protein channels for that particular gene --> allowed us to study them individually
who discovered the structure of ion channels?
-Roderick MacKinnon -used x-ray crystallography to get a 3D model of the channels -found K+ channel structure 1st, Na+ channel structures found much later
Exp with voltage clamp method: membrane potential from -65mV to 0mV
-a quick capacitive current responds to the change to account foe charge redistribution -a transient inward current occurs (ions entering) -a delayed outward current occurs (ions exiting) -shows that when membrane potential is at 0mV, the membrane is permeable to 2 ions (which ones?)
capacitive current
-a quick current that responds to changes in membrane potential to account for charge redistribution
active transporters (general)
-a type of ion pump -actively move selected ions against concentration gradients -creates an ion concentration gradient -uses ATP to pump ions (like K+) against their concentration gradient
ion exchangers
-a type of ion pump -use electrochemical E -types: symporters and antiporters
different types of K+ channels
-all with different currents inactivations, delays, etc 1) K v2.1: like squid giant axon K+ channels (no inactivation) 2) Kv4.1: inactivating K+ channel 3) HERG: inactivating K+ channel, but inactivation happens much faster than opening 4) inward rectifier: inward rectifying , only open at hyperpolarized voltages
antiporters
-allow different ions to go through membrane in opposite directions
-symporters
-allow different ions to go through membrane in the same direction
ion channel characteristics
-allow ions to pass at high rates -selectively permeable: Na+ and K+ flow across membrane independently -voltage dependent: those channels are able to sense the voltage across the membrane and open only when the voltage reaches appropriate levels
voltage clamp method
-allowed researchers to hold membrane potential at a certain value to observe 1) dissect squid giant axon and place in dish with salt water 2) insert recording electrode on one end, connected to a voltmeter 3) voltmeter is also connected to a feedback circuit with a voltage generator that records the difference between the commanded membrane potential and the actual membrane potential, and inject a current to make up the difference to the commanded value
why do we have such a diversity of ion channels?
-allowing different neurons to: -react to different inputs in different ways -integrate different signals (neural computation)
ion channels (very general)
-allows ions (like K+) to diffuse down their concentration gradients -selectively permeable to certain ions
Golgi Staining (general)
-allows us to see a single neuron in great detail by impregnating it with silver salts -still used today -by Golgi and Cajal
types of glial cells
-astrocytes -oligodendrocytes -microglial cells
resting potential (general)
-at rest, the inside of a neuron has a negative charge, allowing a positive wave of electricity to occur through it -at rest, a neuron's potential can be from -40mV - -90mV (more commonly -60mV) -this negative potential is due to ion concentration inside and outside the neuron -K+ dominates the neuron resting potential (there is way more [K+] inside than outside the cell
2 types of signaling between neurons
-btw the axon and dendrite of 2 neighboring neruons is a synapse 1) electrical signaling 2) chemical signaling
Glial cells (general)
-cells in the brain that aren't neurons -don't use electrical signals, don't carry electricity, don't produce electrical impulses -methods discussed previously were used to identify types of glial cells
Exp: voltage clamping at different potentials
-currents responded differently at several different potentials -with increasingly depolarized mem pot: the later outward current gets larger, the early inward current increases in size and then decreases -at +52mV, there is no inward current! (no net movement of ions) so, this ion must have reached its equilibrium potential -Na+ equilibrium potential (calculated with nernst equation) is +55mV, so this ion must have reached its equilibrium potential
Exp: Na+ removal exp to prove Na+ creates the inward current
-dependence of the early current on sodium -Na+ was removed from outside the neuron --> inward current would disappear -Na+ was restored to outside the neuron --> inward current reappeared -proved Na+ was probably in charge of the inward current
how were electrical signals read?
-electrophysiology recordings -a tiny glass probe is filled with salt water (highly conductive), and it inserted into the brain to read electrical signaling (read by a voltmeter) -we can see the patterns and frequency of the electrical signaling -today, we can target/read specific neurons
Whirligig beetles
-example of use of golgi staining -mushroom bodies of neurons in the brain were observed with gogli staining to look at how the two pairs of eyes on the beetle interact -found that the olfactory learning and memory centers get input from the visual sensors
K+ ion channel structure
-found by x ray crystallography -4 subunits, each with 2 transmembrane spanning domains (made up of alpha helices) -loop (1 per subunit) that inserts into membrane to form pore -this pore does the selectivity stuff --> the selectivity filter only lets K+ in -in the center of the pore is a narrow channel that allows K+ to flow -this region is termed the SELECTIVITY FILTER -multiple K+ ions in channel repel each other --> pushes the ions out faster -negatively charged pore helices pull K+ ions into pore, other K+ ions push each other out
Answer to Golgi and Cajal debate
-found with electron microscopy (can focus down to a nm in resolution) -showed there was a gap between neighboring neurons (synaptic cleft) -Cajal was right
synaptic potential
-happens at the post-synaptic site of the dendrite of the next neuron -slight positive or negative charge in potential of dendrite of the next neuron
receptor potential
-happens on dendrites of receptor neurons -sensitive to change in the external environment (change in light, touch, etc)
Ohm's Law
-helped H & H wanted to observe this by calculating voltage-dependent ion permeability -at rest, the inside of the neuron is more negative than the outside voltage (V) = current (I) * resistance (R) V = I * R V = I / G (G: conductance, G = 1/R) I = G * V = G * (Vm - Eion)
Active signaling
-if a current is large enough to get above threshold, an all-or-none response creates and AP -larger signals create more AP's but all are the same size
how was the 1st single neuron electrical signal recorded?
-in a giant squid axon -squids use jet propulsion, which evolved to help them quickly escape predators in open water -squids have 2 large stellate ganglion behind the brain that branch into many giant axons (500x larger than human axons)
electrical potential (general)
-in action, a positive wave is pushed down the axon
conclusion drawn from Na+ and K+ patch clamp experiments
-individual Na+ and K+ channels are responsible for the generation of AP's -both channels are voltage sensitive (vg Na+ and K+ channels) -Na+ channels open immediately and close right away, while the K+ channels open late and have prolonged effect
which patch clamp methods of recording are beset for looking at single channel properties
-inside-out or outside-out
after a few SP's, how does a neuron maintain its ionic electrochemical gradients?
-ion pump (active transporters) aka ATPase pumps -many (10^5 - 10^7) on the surface of cells -hydrolyze ATP to move ions -up to 65% of brain's E is used to do this
In Situ Hybridization
-mRNA level of gene expression measured -30% of 20,000 human genes (so, 6,000) are expressed in the brain -complimentary molecular sequences can be designed to target a distinct mRNA gene that is expressed -the complementary strand can be tracked with fluorescence or radioactive material so that when it is applied to a brain region, any neuronal types that have the original mRNA expressed will show up in color bc of the complementary strand -a way to show expression of a specific gene in the nervous system
explain axon myelination
-myelin sheaths insulate axons -nodes of ranvier occur btw myelinated regions -Na+ channels are concentrated here, so this is where AP's are regenerated, and then jumps down myelin sheaths to the next node of ranvier -this is called saltatory conduction! (jumping)
what happens when you stimulate a neuron with a negative or positive current
-negative current: a negative, or hyperpolarized, response from the neuron -positive current: a positive response from the neuron -this is called PASSIVE SIGNALING
what is the resistance of a cell like if the channels are closed
-no ion flow --> very high resistance, very low conductance -conductance is very similar to permeability
axon terminal
-where nt's are packed into vesicles to be sent out across synapses
axon
-where the electrical signal is generated and sent to the terminal -major output region
describe the all-or-none response
-once even 1 AP is signaled (by a current that at least got to threshold), it will travel all the way down the axon -if an even larger stimulus is injected, the same size AP will be created, but more AP's can be generated -frequency of AP's will increase, but the size/amplitude of each AP is always the same)
Exp with patch clamp method: looking for Na+ channels in a patch of squid axon
-outside-out method used so that we can change the ions outside the channel (since there's more Na+ outside) -apply TEA (K+ channel blockers)to just focus on the Na+ current -results: with K+ currents blocked, depolarizing a path of membrane from giant squid axon causes tiny transient inward currents -as soon as the mem was depol, some inward currents occurred (microscopic) -events have unitary amplitude 10^-12 of an Ampere -a current of 2pA reflects the flow of 200 ions per millisecond -the inward currents summed up looked very similar to the H&H model of the Na+ inward current of the entire neuronal membrane (macroscopic) -both micro and macro currents blocked by TTX --> showed the micro is def a sodium channel
Past and present views of glial cells
-past: glia were thought to be just scaffolding that held neurons together ("glia" is greek for "glue") -present: -glia can release glutamate (a nt) -glia can integrate neuronal inputs -glia can modulate synaptic transmission by controlling uptake of nt's -some glia (oligodendrocytes) make myelin: a lipid used to insulate axons ***glia are very much a component of brain circuitry***
Antibody Labeling (Immunolabeling)
-protein level of gene expression measures -targets specific protein products -design antibodies that target the protein products of specific genes -fluorescence or radioactivity will show where these genes are expressed
Dendrites
-receive info and signals from other neurons -major input region
how do neurons generate electrical signals?
-resting potential -electrical potential
summary of ionic permeability underlying AP's
-resting potential: PK >> PNa -rising phase: increased PNa -AP peak: PNa >> PK -repolarizing phase: decreased PNa -back to resting potential: PK >> PNa
cell morphologies that have been defined by golgi staining
-retinal amacrine cells -retinal ganglion cells -retinal bipolar cells -neurons in mesencephalic trigeminal nucleus -cerebellar purkinje cells
Exp: pharmacological exp
-separating inward and outward currents into Na+ and K+ components a) TTX (tetradotoxin- puffer fish toxin) added --> Na+ current blocker b) tetraethyl-ammonium added: K+ current blocker
ligand gated ion channels
-share similar pore structure, but the pores are usually larger in size -open in response to chemicals rather than a voltage -types: neurotransmitter receptor, Ca2+-activated K+ channel, cyclic nucleotide gated channel
action potential
-strong stimulus allows membrane to form a v large response, sending electrical signals -we can stimulate neurons w/ one probe and observe their reactions with another
Brainbow
-target expression of genetically coded chemical tags -same idea as GFP, but now the same genes can be engineered with different colors -allows us to distinguish one cell from its neighbors in groups of the same cells
what makes an AP?
-the difference in inter- and extracellular ion concentrations -allows us to see which ions determine which parts of the AP -the Nernst equation can be used to look at different ion equilibrium potentials, allowing us to see which ones take control at different parts of the AP
conclusions from patch clamp experiment for sodium channel
-the microscopic inward currents are resulting from the opening of single Na+ channels -evidence: -the currents have a time course that matches the kinetics of macroscopic Na+ channels (mostly occur at the beginning of depol) -the currents are blocked by TTX
what regulates ion flow in neurons
-the rapid changes in permeability across insulating membrane is controlled by ion channels
explain what would happen to KCl ions in a non-permeable membrane
-the voltmeter reads 0mV -there is the same number of positive and negative charges on the left side, and the same number of positive and negative charges on the right side -this results in the 0mV charge on both sides, so a 0mV charge overall
explain what would happen to KCl ion in a membrane that is selectively permeable to K+
-there is a strong diffusion force of K+ from left to right because they travel through the membrane, down its concentration gradient -the electrical force then draws K+ back to even out the charges -this force gets larger as more K+ moves right -once the diffusion and electrical forces are equal, there is no net movement of K+ (equilibrium potential of the K+ ions)
what happens when you inject a current into a neuron that is larger than the threshold?
-threshold is at ~-50mV -a large response called an action potential is generated -this is how most neurons communicate
how do we prove that Na+ contributes the most to the rising phase of the AP
-tried removing different amount of Na+ from the extracellular environment, showing that the equilibrium (and AP size/peak) changes and that Na+ contributes the most to the rising phase
Fluorescent Dye Injections
-use needle inserted into cell body to measure electrical signal and then inject with fluorescent dye to visualize
Exp with patch clamp method: looking for K+ channels in a patch of giant squid axon
-used inside-out method of recording bc more K+ is on the inside of the mem -added TTX to block Na+ currents
calcium imaging
-uses transferred genes that produces a product that is very sensitive to changes in calcium concentration -shows that different neurons respond to different moving visual patterns by showing Ca2+ concentration changes
electrical signaling
-wave of electricity travels from dendrites tot he cell body and then is sent down the axon
chemical signaling
-when the electrical signal reaches the axon terminal, it changes to chemical signaling -nt's release from the axon terminal to the post synaptic dendrite, which then send this signal further by electrical signaling
Exp with patch clamp method to look for K+ channels- results
-with Na+ currents blocked, depolarizing a patch of membrane from squid giant axon causes tiny but very prolonged outward current (depol leads to delayed outward current) -events have a unitary amplitude at 2pA -summed up, this was very similar to H&H's macroscopic -close correlation btw summed/average micro outward currents and macro K+ currents -blocked by TEA
can neurons increase their AP speed? how?
-yes! (important for escape circuits) -we know neurons are bad conductors bc of all their ion channels (leaky hose) 1) axons could be larger in diameter --> less resistance 2) axons could be better insulated --> oligodendrocytes (glial cells) myelinate axons
Green Fluorescent Protein-Labelled Neuronal Line
-you can borrow a gene from other animals and transfer it to the brain of interest -ex: a green fluorescent protein (GFP) in jellyfish brains makes their brain glow -this GFP was injected into a mouse hippocampus -allowed us to see in green fluorescence where the same protein and thus genes were located and expressed in the mouse hippocampus
what makes the membrane negatively charged at rest?
1) Na+/K+ pumps (active transporters) produce and maintain a much greater K+ ion concentration inside the neuron than outside 2) neuronal membrane at rest is highly permeable to K+ ions (through K+ channels) 3) outflow of K+ ions down their concentration gradient leaves the inside of the neuron negatively charged
2 advantages of the voltage clamp method
1) ability to hold current at a certain membrane potential 2) circuits allowed to record the current as well as the voltage
Na+ / K+ shuffle with the Na+/K+ pump
1) conformation change allows K+ release and Na+ binding 2) Na+ bound but occluded 3) conformation change causes Na+ release and Na+ binding 4) K+ bound but occluded -steps 1 to 2: pump phosphorylation (P added) -steps 3 to 4: pump dephosphorylation (P removed) -3 Na+ removed per each 2 K+ entering cell
how to ion pumps work/discovery? (Na+ efflux path)
1) efflux of Na+ (radioactively labeled) 2) Na+ efflux reduced by removal of external K+ 3) recovery when K+ restored 4) efflux decreases by metabolic inhibitors, such as dinitrophenol, which blocks ATP synthesis (ao, ATP is clearly needed for the pump to work) 5) recovery when Na+ is restored
2 primary ways to study brain function
1) electrophysiology 2) calcium imaging
3 types of neuronal electrical signals
1) receptor potential 2) synaptic potential 3) action potential
3 major classes of ion channels
1) vg ion channels 2) ligand-gates ion channels 3) stretch and heat activated ion channels
Now that you have the theoretical resting potential of this Giant Neuron assuming calcium ions are the only contributors to the resting potential, how can you check if other types of ions, like sodium (Na+) or chloride (Cl- ), don't have an effect? What would you expect to see if other ion types also have an impact?
Adding Na+ or Cl- to either side of the membrane should not affect the resting membrane potential you measured if the neuronal membrane at rest is not permeable to either ions. If the membrane potential changes significantly, then the neuronal membrane is also permeable to those ions.
what experiment would you do to identify the glial cells near these neurons?
An experiment would be to apply GFAP antibodies that specifically bind to the protein in astrocytes, therefore revealing astrocytes in the brain area but not other cell types lacking the protein. Another possible experiment would be to insert a transgene tagged with green fluorescent protein (GFP) that is driven by GFAP expression. Where GFAP is normally expressed, GFP will be expressed also, allowing astrocytes to be identified if the glial cells in question are indeed astrocytes. The same process can be repeated with antibodies or similar genetic markers for microglia or oligodendrocytes.
In neurons, why is the concentration of ions (e.g. K+, Na+) on the two sides of the plasma membrane not equal?
Because active transporters, a group of transmembrane proteins and in neuronal membranes, the Na/K pumps in particular, use ATP to pump 3 Na+ ions out of the neurons and 2 K+ ions into the neurons. These ion pumps create and maintain the unequal concentration of ions on the two sides of the plasma membrane.
Now you want to examine whether a group neurons of a different type in a different region are connected via synapses to the original neuronal population you were initially studying. What experimental technique could you use to determine this?
By injecting a fluorescent dye to either group of neurons and seeing if it connects to the other group of neurons through axons labelled by the tracer.
In which part of a neuron would most of the endoplasmic reticulum be concentrated? Dendrite Presynaptic terminal Postsynaptic terminal Axon Cell body
Cell body
Cell body
Cell membrane with nucleus that hold DNA
What would occur if the ATPase pumps in a neuron stopped functioning? During the action potential, the voltage-gated ion channels would remain closed At rest, potassium would continuously depolarize the cell At rest, sodium would continuously depolarize the cell Concentration gradients would not be maintained across the membrane During the action potential, the sodium channel would not inactivate
Concentration gradients would not be maintained across the membrane
Passive Signaling
Current injected is matched in size by membrane potential response (+ or -)
Nernst equation
Eion = (58mV/z) * log ([ion]out/[ion]in) -allows us to calculate the equilibrium potential of any one ion
Which of the following was observed in studies measuring the efflux of radioactive sodium from the squid giant axon? Dramatic increase of efflux during a brief train of action potentials Decrease of efflux when ATP synthesis was increased Dependence of efflux upon the presence of ATP Sharp drop in efflux when intracellular potassium was removed No recovery when potassium or ATP was restored.
Dependence of efflux upon the presence of ATP
Which of Camillo Golgi's contributions enabled Santiago Ramón y Cajal to make observations that suggested that nerve cells are discrete entities? Articulation of the neuron doctrine Improving the understanding of the pathophysiology of malaria Identifying the organelle later called the Golgi apparatus Development of a staining method based on impregnation with silver salts Articulation of the reticular theory of nerve cell communication
Development of a staining method based on impregnation with silver salts
The classic voltage clamp technique would be suitable for which application? Indirect measurement of unidirectional current flowing through cell membrane Measurement of current flowing through a single ion channel Evaluation of effects of large intracellular molecules on the function of ion channels Direct measurement of current flowing through the cell membrane Study of the ionic composition of the intracellular environment
Direct measurement of current flowing through the cell membrane
Which technique first produced unequivocal support for the neuron doctrine of the nervous system (as opposed to the reticular theory)? Extracellular electrical recordings EEG (electroencephalogram) Acetylcholinesterase staining Calcium imaging Electron microscopy of nervous tissue
Electron microscopy of nervous tissue
Which statement regarding membrane potential and equilibrium potential is true? Both membrane and equilibrium potentials change during an action potential. Equilibrium potentials are affected by membrane permeability; membrane potentials are not. Equilibrium potentials are the same for all neurons; membrane potentials can be different depending on the neuron. Equilibrium potential is affected by the concentration and electrical gradients of one ion; membrane potential is affected by gradients of all ions. Membrane potential is affected by ion concentration in- and outside of the cell; equilibrium potential is affected only by ions inside the cell.
Equilibrium potential is affected by the concentration and electrical gradients of one ion; membrane potential is affected by gradients of all ions.
T/F: Myelinated neurons are found in most vertebrate, but not invertebrate, nervous systems.
False
T/F: Neurons transmit electrical signals well because they are naturally good conductors.
False ~ neurons and the biological material they are composed of are poor conductors, meaning that the passive flow of current is inefficient for our signaling needs in the nervous system (the current leaks out and cannot change membrane potential over longer distances). Next week, we will see how myelin and action potential help us overcome this signaling barrier.
T/F: The inside of the neuronal membrane is more positive relative to the outside.
False ~ the inside of the neuron is more negative than the outside, usually ranging from -40 to -90 mV.
A commonly used marker to identify one glial subtype is called GFAP. What does this stand for? Do some quick research into what type of marker it is and explain how markers like this work to specifically identify cells
GFAP stands for glial fibrillary acidic protein. It is a marker of astrocyte glial cells. By specifically labelling this biomolecule (intermediate filament), cells that are astrocytes can be identified.
Quickly list some reasons as to why glial cells are important for neuron and brain function (and why they are typically overlooked)
Glial cells in most cases outnumber neurons and help support the functions of neurons, namely regulating nutrient uptake from blood vessels, neurotransmitter level uptake/regulation, waste removal, neurotrophic signaling or mediating synaptic contacts, modulating the neuron environment (ion/pH levels), providing structural support for neuron development, and treating neural injury, etc. However, glia cells do not have typical neuronal structures (axons) and do not participate in electrical signaling as neurons do, making them easy to overlook considering the huge role of neuron's in brain signaling and function.
You are wondering how many of those blue-stained nuclei belonging to neurons and how many are glial cells. Name two potential techniques you could use to identify neurons and what you expect to see.
Golgi stain, fluorescent dye injections, antibody staining, genetic labelling/transgenic integration of neuronal markers Note: In situ hybridization wouldn't label neuronal processes (axons and dendrites).
Refer to the figure. Which method was used to visualize the retinal neurons shown? Cresyl violet staining Silver impregnation (the Golgi method) Nissl stain Intracellular injection of an enzyme Intracellular injection of a fluorescent dye
Intracellular injection of a fluorescent dye
Which statement best describes the function of a neuron with multiple, highly branched dendrites and one axon? It integrates information from many neurons. It receives information from only one other neuron. It cannot integrate information from multiple neurons. The information it receives will not be relayed. It passes information directly to multiple neurons.
It integrates information from many neurons.
Which statement about Na + permeability during an action potential is most accurate? It is responsible for the falling phase of the action potential. All of them It is responsible for the rising phase of the action potential. It restores the membrane potential to its usual level following the action potential. It is long lasting. None of them
It is responsible for the rising phase of the action potential.
Which statement best describes the Nernst equation? It relates the equilibrium potentials of multiple ions to their intra- and extracellular concentrations. It relates the equilibrium potential of an ion to its extracellular concentration. It relates the equilibrium potentials of multiple ions to their intracellular concentrations. It relates the equilibrium potential of an ion to its intracellular concentration. It relates the equilibrium potential of an ion to its intra- and extracellular concentrations.
It relates the equilibrium potential of an ion to its intra- and extracellular concentrations.
How will a neuron respond to an injection of negative current? It will reach the threshold potential. It will have a positive electrical response. It will become hyperpolarized. It will generate a single action potential. It will generate multiple action potentials.
It will become hyperpolarized.
Which statement accurately describes the difference between bacterial and mammalian channels that are selectively permeable to K +? Mammalian channels have four subunits. Bacterial K + channels do not have a selectivity filter. There is no difference between bacterial and mammalian K + channels. Bacterial K + channels have four pore loops. Mammalian K + channels have four additional structures that act as voltage sensors.
Mammalian K + channels have four additional structures that act as voltage sensors.
Which statement accurately describes the expression of genes in the nervous system? Most of the genes in the human genome are expressed in the CNS. The genes that are expressed in the CNS are expressed equally in all neurons. A small subset of the total human genome is expressed in the CNS. Every gene in the human genome is expressed in the CNS. Splice variants add diversity to brain function via beneficial mutations.
Most of the genes in the human genome are expressed in the CNS.
What features will you look for to confirm the labelling you did is specific to neurons? More generally, what distinguishes neurons from other cell types in terms of structure?
Neurons have distinct structure, with regions consisting of axon, dendrites, and cell bodies. If a labelled cell has these features, particularly the branching neurites, it can be identified as a neuron.
How do lesion-driven experiments compare to more modern technologies?
Non-invasive modern brain imaging technology such as EEG and fMRI can be used to observe brain activity at the sub-regional level of the brain (hundreds to thousands of neurons).
What is the major determinant of the permeability of a membrane to a specific ion? Concentration of the ion inside the cell Size of the ion Concentration of the ion outside the cell Number of open ion channels specific for that ion Electrical charge of the ion
Number of open ion channels specific for that ion
In which way do potassium channels in the squid giant axon differ from sodium channels? The potassium channels open in response to hyperpolarization of the membrane. Once the potassium channels open in response to a voltage step command, they tend to remain open. The potassium channels show little voltage dependence. The summing of the individual potassium channels does not reconstruct the macroscopic current. The potassium channels pass only a few ions per second.
Once the potassium channels open in response to a voltage step command, they tend to remain open.
What level of the brain can be better understood by lesion-driven experiments?
Only higher levels of the brain (entire regions) and their general function can be investigated through lesions. For Phineas Gage, the lesion he suffered affected him at a behavioral level. Early in the field of neuroscience, unfortunate accidents (that were rather serendipitous for science though) were required to draw tentative links between brain and structure function.
Which technique would you use to study the effects of the extracellular environment on ion channel activity? Outside-out patch clamp Whole-cell patch clamp Conventional voltage clamp Inside-out patch clamp Cell-attached patch clamp
Outside-out patch clamp
Practically speaking, how would you determine that Na + influx into a cell underlies the early current? Remove Na + from the extracellular compartment and assess the early current under new conditions. Replace intracellular Na + with its radioactive form and trace its movement across the membrane. Use the voltage clamp method to measure the current. Treat the cell with tetraethylammonium. Remove K + from the intracellular compartment and assess the early current under the new conditions.
Remove Na + from the extracellular compartment and assess the early current under new conditions.
Can you make an estimate of how many percentages of cells in the region are glia?
Since most cells in the brain are either neurons or glia, the cells not labelled by the neuron-specific marker in a certain region but are labelled by the ubiquitous nuclei marker DAPI are a good guess to be glia of some type. The image shows neuron-specific labeling (magenta) only around a small fraction of nuclei (blue), around 5% - 30%. Therefore, glia are likely around 70-95% in that region of the brain.
At what resolution would an experiment need to be conducted to resolve the past debate between Golgi's Reticular Theory and Cajal's Neuron Doctrine? What would you expect to see in order to support one side or the other?
Since the reticular theory and neuron doctrine differ in how they believe neurons are connected, this most direct, single experiment to resolve this debate would have to occur at the level of synapses, which wasn't able to be effectively resolved until the development of electron microscopy (and, much later, super resolution light microscopy)
Refer to the figure. What is the function structure C? Regeneration of action potential Speeds up conduction of an action potential Receives incoming signals from other neurons Location of protein synthesis and cellular machinery Regulates chemical environment for signaling
Speeds up conduction of an action potential
Refer to the figure. Where will voltage-gated Na + channels be most abundant? Structure A Structure B Structure D Structure C Structure E
Structure D
Refer to the figure. What would happen if the membrane became permeable to the Y + ions? The Y + ions would move into the top chamber, down their electrical gradient. The Y + ions would move into the bottom chamber, down their electrical gradient. The Y + ions would move into the bottom chamber, down their concentration gradient. The Y + ions would not move. The Y + ions would move into the top chamber, down their concentration gradient.
The Y + ions would move into the top chamber, down their concentration gradient.
Name a non-invasive strategy towards functional imaging that allowed us to understand brain behavior in living, even conscious, organisms without reliance on post-mortem analyses or random brain damage.
The ability to correlate blood flow/nutrient uptake with brain activity as in PET/fMRI. The ability to make sense of brain signals, like the general electrical activity of brainwaves in EEG, and field potentials in TMS
For genetic analyses (such as using Green Fluorescent Protein, GFP, to label neurons in this area), what other information you need to know beforehand to make this work?
The genetic sequence of the marker (i.e. the gene that codes for GFP) and the expression system of the target neuronal population.
Why is it that at equilibrium (no net movement of ions) the membrane potential is not 0?
The ionic concentration difference between the two sides of neuronal membrane produces a chemical force for those ions to flow down their concentration gradient. Ion channels, another group of transmembrane proteins, selectively allow certain types of ions to pass through, down their concentration gradient. Because ions are charged, when they move across the membrane through their ion channels they also create an electrical force on the opposite direction. This electrical force forms an electrical potential (separation of charge) across the membrane. Ions keep flowing down their concentration gradient until the chemical force and the electrical force are counterbalanced. This is the point where the net movement of ions between the two sides of membrane is zero and its electrochemical equilibrium is reached. The membrane is now polarized (not 0), with an electrical potential counterbalances the chemical concentration difference.
Which phenomenon explains the unidirectional propagation of action potentials? The voltage dependence of the potassium channels The voltage dependence of the sodium channels The polarized orientation of microtubules within the axon Sufficient "leakiness" of the axons, such that backward propagation of action potentials is prevented The presence of a refractory period at a location where an action potential has just passed
The presence of a refractory period at a location where an action potential has just passed
A student new to neuroscience research is practicing recording resting membrane potentials from giant squid axons. During one of the trials, the resting membrane potential, which is normally around -60 mV, measured -15 mV. Which statement best describes what might have occurred during the experiment? The student added too much sodium to the extracellular solution. The student did not add enough sodium to the extracellular solution. The student added too much potassium to the extracellular solution. The student did not add enough potassium to the extracellular solution. The student added too little potassium and too much sodium to the extracellular solution.
The student added too much potassium to the extracellular solution.
Which statement best describes most neurons? They are polarized. They receive information via axons. They transmit electrical signals via cytoplasmic continuity. They conduct signals bidirectionally. They transmit information to other cells via dendrites.
They are polarized
What do microscopic and macroscopic Na+ currents have in common? They flow through a large area of neuronal membrane They represent a flow of many ions They have a magnitude of 1-10 pA They flow through a single ion channel They flow through multiple ion channels
They represent a flow of many ions
Which function is a characteristic primarily of neurons only, and not glia? Prevents regeneration of the nervous system Transmits action potentials Supports electrical signals Repairs the nervous system Produces myelin
Transmits action potentials
T/F: Nerve cells use electrical potentials to transmit information and these potentials are generated by differences in ion concentrations between the inside and outside of the plasma membrane
True
T/F: The resting membrane potential arises both because many K+ selective channels are open in resting neurons and the action of the active transporter Na/K pump.
True
What would happen to the resting potential if you increase extracellular calcium to 50mM?
Vm = Eca = 58 / 2 * log10 (50/1000) = -38 (mV) The resting potential would depolarize to -38 mV
Outside the neuron you have 10 mM calcium. You also notice that the resting potential of this neuron at room temperature is -58 mV. Assuming the resting membrane potential is caused by calcium alone, how much calcium is in the neuron?
When resting membrane potential is caused by calcium ions alone, Resting Membrane Potential (Vm) = Calcium Equilibrium Potential (Eca) According to Nernst equation at room temp: -58 = 58/2 * log10 (10/[Ca]in) -2 = log10 (10/[Ca]in) --> 10^ -2 = (10/[Ca]in) --> [Ca]in = 1,000 mM
The resting potential of a cell is negative because at rest there is an excess of K + inside the cell, and the membrane is permeable chiefly to K +. there is an excess of Cl - ions outside of the cell at rest. at rest there is an excess of K + outside of the cell, and the membrane is permeable chiefly to K +. there is an excess of K + outside of the cell at rest. at rest there is an excess of K + inside the cell, but the membrane is permeable to all ions.
at rest there is an excess of K + inside the cell, and the membrane is permeable chiefly to K +.
The paddle-like, charged transmembrane domains of potassium channels may dehydrate the ions as they cross the membrane. be the primary voltage sensors. enable the aggregation of channel subunits into functional channels. serve as a plug or inactivation gate. confer ion selectivity to the channel.
be the primary voltage sensors.
An action potential occurs if current injected into a neuron _______ the neuron to reach _______ potential. hyperpolarizes; synaptic hyperpolarizes; resting depolarizes; synaptic hyperpolarizes; threshold depolarizes; threshold
depolarizes; threshold
Identify the technology and outline a simple experiment to see which brain region is activated by arm movement
fMRI is the answer here. While holding the subject's head still and recording through a fMRI cap, the subjects should voluntarily move their arm within the desired contexts/conditions. Control movements should also be recorded, such as moving fingers, turning wrists or moving legs. The region of the brain that lights up specifically for arm motion (adjusting for controls) is correlated with it and very likely involved in arm motion signaling.
Nodes of Ranvier represent areas of high synaptic density. segments of axon where only K + channels are located. gaps in myelin wrapping. segments of axon where passive current flows. points where two axons connect.
gaps in myelin wrapping.
Refer to the figure.In the phase labeled D, the voltage-gated sodium channels are ________ and the voltage-gated potassium channels are ________. closed; inactivated open; closed closed; open open; open inactivated; open
inactivated; open
The voltage clamp method controls the _______ at any desired level. membrane potential K + current amplitude of an action potential frequency of an action potential Na + current
membrane potential
In a two-compartment model of a cell with a K +-permeable membrane, at K + equilibrium potential, there is _______ flux of K + ions. no net a small outward a small inward a large inward a large outward
no net
Refer to the figure.In the phase labeled B, the voltage-gated sodium channels are ________ and the voltage-gated potassium channels are ________. closed; open closed; inactivated open; closed open; open inactivated; open
open; closed
Subthreshold current injected into an axon flows _______ along the axon and _______ with distance from the site of injection. passively; remains constant actively; decays actively; grows actively; remains constant passively; decays
passively; decays
The technique that first revealed the tremendous diversity of neuronal cell types, by revealing different cell bodies along with their processes, is: electron microscopy. cresyl violet staining. the Nissl stain. the Golgi technique (stain). fluorescence staining.
the Golgi technique (stain).
Hodgkin and Katz proposed that sodium was the predominant ion associated with the firing of an action potential because sodium ions are the only ions that can flow into the nerve cell body. the sodium gradient explains the rising phase, falling phase, and overshoot of the action potential. the membrane potential approaches the Na + Nernst potential during the falling phase. sodium ions can move more quickly than other ionic species. the membrane potential approaches the Na + Nernst potential during the rising phase.
the membrane potential approaches the Na + Nernst potential during the rising phase.
The in situ hybridization method is based on using nucleic acid probes to detect specific proteins. formation of an insoluble colored product within cell bodies. using nucleic acid probes to detect mRNAs that encode specific genes. injecting a fluorescent dye into a neuron. labeling specific neuronal components with antibodies.
using nucleic acid probes to detect mRNAs that encode specific genes.
Ion channels that are involved in generation of action potentials open or close in response to second messengers. mechanical stimulation. voltage. temperature. neurotransmitters.
voltage
