Biology 336: Neurobiology II
greater
For a given concentration gradient, the ________ the membrane permeability to an ion species, the ________ the contribution that ion species will make the the membrane potential
C
Solutions A and B are separated by membrane permeable to K+ but not to Cl-. Solution A is 100mM KCl and solution B is 1mM KCl. Which of the following statements about solutions A and B is TRUE? A) K+ ions will diffuse from solution A to solution B until the [K+] of both solutions is 50.5 mM. B) K+ ions will diffuse from solution B to solution A until the [K+] of both solutions is 50.5 mM. C) K+ will diffuse from solution A to solution B until a negative charge develops that opposes the movement of K+. D) KCl will diffuse from solution A to solution B until the [KCl] of both solutions is 50.5 mM
false
T/F All cells can conduct action potentials
trigger zone
What part of a neuron is a region with a high density of voltage-gated sodium channels, at which action potentials initiate?
myelin sheath
What part of the myelinated axon creates a high resistance wall that prevents ion flow out of the cytoplasm?
closed
What state are the sodium and potassium channels at when the membrane is at a negative potential (ex: resting)?
inactivation
What state are the voltage gated sodium channels in when the voltage gated potassium channels open, allowing potassium to repolarize the membrane?
membrane depolarization
What triggers sodium and potassium channels to open?
repolarizing
When a depolarized membrane returns toward the resting value, it is ________.
disrupted
When a membrane potential difference is generated and a positive ion is moved out of the cell, the electrical equilibrium between extracellular fluid and intracellular fluid is ________
repolarization
When a neuronal membrane potential changes from a positive to a negative value, the cell membrane is undergoing:
intracellular fluid
Which body fluid compartment contains high levels of K+, large anions, and proteins?
overshoot
________ refers to a reversal of the membrane potential resulting in the inside of a cell becoming positive relative to the outside
synaptic cleft
a 10 to 20 nm extracellular space that separates the pre- and postsynaptic neurons which neurotransmitters must cross.
summation
if additional stimuli occur before the graded potential has died away, these can be added to the depolarization from the first stimulus
absolute scale
this form of measuring electrical gradients involves counting the numbers of ions on either side of the plasma membrane
relative scale
this form of measuring electrical gradients measures the difference in charge between the two points using a voltmeter
trigger zone
this is where an action potential is generated. It's generated in the cell body and the dendrites by the summation of depolarizing graded potentials.
61
this number in the Nernst equation is a constant that takes into account Faraday's constant for electrical forces; physiological temperature; and the universal gas constant
z
this variable in the Nernst equation represents the valence of the ion
graded potentials summate and depolarize the membrane potential to threshold membrane potential
How are voltage gated ion channels stimulated?
neurotransmitters
How do chemical synapses pass information from a presynaptic neuron to a postsynaptic cell?
C
A cell has a membrane potential of -100mV (more negative inside than outside) and has 1000 times more calcium ions outside the cell than inside. Which of the following describes the electrical and chemical gradients that influence the movement of calcium across the plasma membrane of this cell that is permeable to calcium? A) The chemical gradient favors and the electrical gradient opposes the entry of calcium into the cell. B) The electrical gradient favors and the chemical gradient opposes the entry of calcium into the cell. C) Both the chemical and the electrical gradients favor calcium entry into the cell. D) Both the chemical and the electrical gradients oppose calcium entry into the cell.
myelinated
Action potential propagation is faster in __________ axons
absolute refractory period
An action potential does not re-stimulate the adjacent membrane that was previously depolarized because the area of the plasma membrane is in _________.
depolarize
An action potential generates local currents that tend to ________ the membrane immediately adjacent to the action potential.
overshoot
As Na+ entry causes depolarization, which opens more voltage-gated Na+ channels. This positive feedback loop results in a large upstroke of the membrane potential, causing it to _______
decreases
As a result of permeability, the change in membrane potential ________ as the distance increases from the initial site of the potential change.
inactivation
As the membrane potential approaches its peak value, what occurs to the Na channels?
repolarization
As the potassium gated channels open, what occurs to the membrane?
Presynaptic membrane
At a chemical synapse, neurotransmitters are released when vesicles fuse with the:
chemical
At a(n) _________ synapse, a neurotransmitter is released into a synaptic cleft in order to affect a postsynaptic cell.
axon terminal
At what point on the axon does the flow of local current begin the conduction of the action potential?
3:2
At what ratio is sodium pumped out of the cell and potassium pumped into the cell, respectively?
hyperpolarization
Before the potassium channels close, what occurs to the membrane?
local current
how does positive charge from the depolarized trigger zone spread to adjacent sections of the membrane?
step 4 of neurotransmitter release
Calcium binds to synaptotagmin proteins associated with SNARE proteins. SNAREs anchor vesicles to the plasma membrane and undergo calcium dependent conformational changes to stimulate vesicle fusion with the plasma membrane.
electrical synapse
pass electrical signals directly from cell to cell through gap junctions
subthreshold potentials
Deolarizations less that threshold are _______.
-61
Given an extracellular Cl- concentration of 100 mM and an intracellular Cl- concentration of 10 mM, what is the equilibrium potential of a plasma membrane permeable only to Cl-? (Hint-you do not need a calculator to solve this question.)
no net direction
Given an extracellular Cl- concentration of 100 mM and an intracellular Cl- concentration of 10 mM, what is the net direction of movement of Cl- across a membrane permeable only to Cl- when the membrane is at the equilibrium potential? At the equilibrium potential:
+61
Given an extracellular Na+ concentration of 150 mM and an intracellular Na+ concentration of 15 mM, what is the equilibrium potential of a plasma membrane permeable only to Na+? (Hint-you do not need a calculator to solve this question.)
true
Graded potentials have no threshold or refractory period, unlike action potentials
gap junctions
How are individual cardiac muscle cells of the heart joined together?
recording
this electrode is inserted through the cell membrane into the cytoplasm
B
If a motor neuron was stimulated by a current-injection electrode to the threshold value about midway along the length of the axon: A) no action potential would be initiated. B) two action potentials would be initiated, one propagated toward the axon terminal and one propagated back toward the axon hillock. C) a single action potential would be initiated and be propagated back toward the axon hillock. D) a single action potential would be initiated but would die out before reaching the axon terminal. E) a single action potential would be initiated and be propagated toward the axon terminal.
chemical
In a(n) _______ synapse, there is a direct physical connection of the cytoplasm of pre- and postsynaptic cells.
hyperpolarized
In response to a stimulus, if the membrane potential becomes more negative than the resting potential, we say the membrane is _______
nodes of Ranvier
In what area of the myelinated axon does the extracellular fluid come in contact with the axon?
all or none
In what manner do action potentials occur?
CNS
In which neurons do electrical synapses occur mainly?
absolute refractory
In which period are the voltage gated sodium channels already open or have proceeded to the inactivated state? In this period the inactivation gate has blocked these channels and must be removed by membrane repolarization.
true
Is the following statement regarding graded potentials, True or False? "Graded potentials lose strength as they move through the cytoplasm because some positive ions leak out of the cell into the extracellular fluid through open leak channels in the neuronal plasma membrane."
decremental
Local current is ________, decreasing as the distance from the site of origin of the graded potential increases
slightly permeable to sodium
Neurons at rest are not at the equilibrium potential for K+ because the cell membrane is:
high
Nodes of Ranvier have _______ concentrations of voltage gated sodium channels
3 2 4 1
Put the following steps of synaptic transmission into the proper order: 1) neurotransmitter is released and binds receptors on the post-synaptic cell 2) voltage-gated Ca2+ channels open 3) an action potential travels down the axon 4) vesicles fuse with the plasma membrane
3:2 ratio of sodium to potassium
The Na+/K+ pump does not merely compensate for the "leakiness" of the cell membrane to these ions, but actively helps keep the intracellular fluid more negative than the extracellular fluid. This is primarily because:
B
The Nernst equation enables us to calculate the membrane voltage that exactly balances the diffusion of a particular ion down its concentration gradient. To use the equation, however, we must know all of the following, EXCEPT the: A) valence of the ion (for example, +1 for potassium; +2 for calcium) B) equilibrium potential of the ion in millivolts (mV) C) intracellular concentration of the ion B) extracellular concentration of the ion
55
The critical value of the membrane potential to which the cell must be depolarized to trigger an action potential is the threshold potential. In neuronal cells, threshold potential is at _______mV
Potassium out of the cell
The falling phase of the action potential is due primarily to:
sodium channels
The membrane depolarization at the trigger zones opens which voltage gated channels?
depolarized
The membrane is ________ when its potential becomes less negative (closer to 0)
sodium
The principle extracellular cation is:
B
The puffer fish, an expensive gourmet delicacy in Japanese cuisine, produces a potent neurotoxin called Tetrodotoxin (TTX). A chef must remove the tissues that produce TTX carefully before serving. TTX blocks the channel openings of voltage-gated Na+ channels. Which of the following is directly inhibited by TTX when ingested? A) the membrane hyperpolarization at the end of an action potential. B) the rapid membrane depolarization of an action potential caused by Na+ entry. C) the outward K+ current of an action potential repolarizing the membrane. D) the entry of Na+ through ligand-gated channels that generate excitatory graded potentials.
polarized
The resting membrane potential at -70 is ________ meaning that the outside and inside of the cell have a different net charge
sodium into the cell
The rising phase of the action potential is due to:
cocaine
This drug affects signaling in dopaminergic neurons by interfering with dopamine reuptake pumps
relative refractory
This period follows the absolute refractory period. It is an interval during which a second action potential may be produced, but only if the stimulus is stronger than usual and outlasts the absolute refractory period.
Sodium Potassium ATPase pump
This pump helps to directly establish the membrane potential by maintaining sodium and potassium concentrations at a stable levels of resting cell
Sodium channels respond quickly and have an inactivation gate
What are the two key differences between sodium and potassium channels?
potassium leak channels
What is the highest contributor to the resting membrane potential value?
rapid conduction
What is the primary advantage of electrical synapses? Cell to cell signals that synchronize activity within a network of cells.
sodium channels open and depolarize, becoming a positive feedback loop
What occurs once the membrane reaches threshold potential?
the net movement stops
What occurs when the electrical force attracting K+ into the cell becomes equal in magnitude to the chemical concentration gradient driving K+ out of the cell?
reference
this electrode is placed in the external bath and is given a value of 0 mV
A
Which is TRUE about neuronal membrane electrical and conentration gradients at the peak of the action potential? A) The electrical gradient is in a direction that tends to move K+ out of the cell. B) The concentration gradient for K+ is in a direction that tends to move K+ into the cell. C) The concentration gradient for K+ greatly increases compared to at rest. D) The concentration gradient for Na+ is in a direction that tends to move Na+ out of the cell. E) The electrical gradient for Na+ is in a direction that tends to move Na+ into the cell.
C
Which of the following is FALSE about the refractory period? A) Voltage-gated Na+ channel inactivation is responsible for the absolute refractory period. B) The refractory period is important in preventing the overlap of succeeding action potentials. C) The absolute refractory period refers to that time during which a stronger stimulus will lead to the generation of a new action potential. D) The relative refractory period refers to that time during which a stronger stimulus will lead to the generation of a new action potential. E) The relative refractory period coincides with the hyperpolarization phase of the action potential.
C
Which of the following is FALSE concerning an electrical synapse? Electrical synapses: A) are formed by gap junctions composed of protein complexes called Connexons. B) allow ions and small water-soluble molecules to move directly from the cytosol of one cell to another. C) allow for information to travel in only a single direction between neighboring cells. D) are the characteristic synapses of cardiac muscle cells of the heart.
B
Which of the following is NOT consistent with the function of voltage-gated Na+ channels? A) After becoming activated (opened) at the threshold voltage, these channels rapidly enter an inactivated state. B) Voltage-gated Na+ channels may go from the inactive state to the open state. C) Voltage-gated Na+ channels may go from the inactive state to the closed state. D) Voltage-gated Na+ channels may go from the open state to the inactive state. E) Voltage-gated Na+ channels cannot go from the open state to the closed state.
D
Which of the following statements concerning action potential propagation velocity is CORRECT? Action potential velocity is: A) fastest in unmyelinated axons. B) unaffected if the axon becomes demyelinated, as occurs in the pathophysiological state of multiple sclerosis (MS). C) increased by myelination that increases the ability of current to leak out of the axon. D) increased by concentrating voltage-gated ion channels at specific points along the axon, called nodes of Ranvier. E) increased by insulating the entire axonal surface with myelin.
E
Which of the following statements regarding graded potentials is FALSE? Graded potentials: A) diminish in strength over distance. B) can add up (summate) to produce greater depolarizations. C) can vary in strength and can even hyperpolarize a membrane. D) are generated in the dendrites and cell body of a neuronal cell. E) are always of equal magnitude and travel over long distances along axons.
C
Which of the following statements regarding the equilibrium potential for potassium is TRUE? When the plasma membrane of a cell reaches the potassium equilibrium potential, A) all diffusion of K+ stops. B) there are equal amounts of K+ ion on both sides of the cell membrane. C) K+ outward diffusion is balanced by electrical attraction inward. D) the membrane potential is about +60 mV.
chemical
Which type of synapse is most prevalent in the nervous system?
magnitude of the charge
Why are graded potentials called "graded"?
the entire axon membrane is in contact with the extracellular fluid
Why do unmyelinated axons propagate action potentials slower than myelinated axons?
absolute refractory period
Why does backward depolarization in the axon take no effect?
sodium leak channels
Why is the resting membrane potential not equal to the K+ equilibrium potential?
electrodes
________ are created from hollow glass tubes drawn to fine points. They are filled with a liquid that conducts electricity and then connected to a voltmeter.
post synaptic density (PSD)
a protein dense region in the postsynaptic membrane in close apposition to the presynaptic active zone ensuring that receptors are in close proximity to presynaptic neurotransmitter release sites.
synapse
a structure that permits a neuron to pass an electrical or chemical signal to another cell (neural or otherwise)
amplitude
action potentials can travel over long distances of a meter without losing __________.
hemichannels
all gap junction channels consist of a pair of ________, one in the presynaptic and the other in the post synaptic cell. The pore has a large diameter around 1.5 nm, it permits small intracellular metabolites to pass directly between the cytoplasm of the two cells
step 1 of neurotransmitter release
an action potential reaches the terminal of the presynaptic membrane
step 3 of neurotransmitter release
calcium activate processes that lead to the fusion of docked vesicles with the synaptic terminal membrane
Nernst equation
calculates the equilibrium potential to one ion. E(ion)= (61/z)log ([ion]out/[ion]in)
graded potential
changes in membrane potential from a relatively small region of the plasma membrane (depolarizations or hyperpolarizations that generally occur in the dendrites and cell body)
recorder
device that can record membrane potential over time. Neuronal and muscle cells have resting potentials between -40 and -90
connexon
each hemichanel is called a ________, made up of six identical protein subunits, called connexins
intracellular fluid
k+ is the major cation; phosphate ions and negatively charged proteins are the major anion; some protein anions do not have matching cations; slightly negative
voltmeter
measures the membrane potential when the recording electrode is placed in the cell. It measures the net electrical charge of the intracellular side to compared to the extracellular side (artificially set at 0)
extracellular fluid
na+ is the major cation; cl- is the major anion; some cations do not have matching anions; slightly positive
attract; repel
opposite charges _______; like charges _______
energy
separating positive charges from negative charges requires ________
step 2 of neurotransmitter release
terminals possess voltage gated calcium channels (in addition to potassium and sodium channels). Depolarization during an action potential opens calcium channels allowing calcium to flow into the axon terminal
saltatory conduction
the "jump" of the action potential as it passes from node to node
-70
the average value for a resting potential of a neuron is ________.
axon terminal
the axon of a presynaptic neuron ends in a slight swelling
electrical gradient
the difference in the net charge between two regions; the energy used to transport a cation across the membrane has created this.
electrical disequilibrium
the intracellular fluid and extracellular fluid exist in this state
electrical gradient
the loss of positive ions from the cell creates ________ ________
insulator
the material through which charges are unable to move (ex: phospholipid bilayer)
conductor
the material through which charges move when separated positive and negative charges can move freely toward each other (ex: water)
hyperpolarized
the membrane is ________ when the potential is more negative than the resting level
GHK equation (Goldman-Hodgkin-Katz)
the membrane potential can be calculated using this equation given the permeabilities of the ions for Na, K, and Cl
equilibrium potential
the membrane potential that exactly opposes the concentration gradient of the ion
law of conservation of electrical charges
the net amount of electrical charge produced in any process is zero
ions
the phospholipid bilayer of the cell is not permeable to ________
chemical synapse
the vast majority of synapses in the nervous system, use neurotransmitters to pass information to the target cell.
diffuse away; enzymatically transformed; reuptake
unbound neurotransmitters are removed from the synaptic cleft by: 1. ____________ from the receptor site 2. ____________ into inactive substances, some of which are transported back into the axon terminal for reuse 3. actively transported back into the presynaptic axon terminal, a process called ____________
negative
unequal transport of positive ions makes the inside of the cell more ________
kiss and run fusion
vesicles fuse only briefly to release contents and then withdraw into the terminal
negative
when a K+ leak channel is inserted into the membrane, the proteins build up a ________ charge inside the cell as more K+ diffuses out of the cell
no
will a second stimuli produce an action potential during the absolute refractory period?
synaptic vesicles
within the presynaptic active zone, where are neurotransmitters stored?
