Item 5 Flashcards
Action potentials occur in the membranes of _ tissue (whether nerve or muscle)
excitable
During an action potential, a large, rapid _polarization occurs in which the polarity of the membrane potential actually reverses; that is, the membrane potential becomes positive for a brief time
de-polarization
The initial membrane potential changes very quickly (in about 1 msec) from a resting level of approximately -70mV to __ mV
+30 mV
Once initiated, an action potential, unlike a graded potential is capable of being propagated long distances along the length of _ _ without any decrease in strength
an axon
The generation of an action potential is based on…and the Na+ and K+ electrochemical gradients that exist across the membrane
the selective permeability of the plasma membrane
At rest, the plasma membrane is _ times more permeable to potassium than to sodium ions because of the presence of more K+ leak channels to sodium channels
25 times
Changes in the permeability of the plasma membrane in excitable cells resulting from the opening and closing of _ _ _ can produce action potentials
gated ion channels
An action potential in a neuron consistws of 3 distinct phases:
1. rapid depolarization
2. repolarization
3. _
after-hyperpolarization
depolarization leads to a mV reading of _ due to influx of sodium ions into the cell
+30 mV (note it is yet not the equivalent of the sodium equilibrium potential of +60 mV)
The repolarization of the membrane potential brings the membrane potential down to _ mV due to a reduction in sodium permeability, and increase of potassium permeability, with potassium moving DOWN its electrochemical gradient out of the cell, repolarizing the membrane potential to bring it back to resting levels
-70 mV
Potassium permeability at after-hyperpolarization remains elevated for a brief time (_ - _ msec) after the membrane potential reaches the resting membrane potential, resulting in an after-hyperpolarization
5 - 15 msec
During after-hyperpolarization, the membrane potential is even more _ than at rest as it approaches the potassium equilibrium potential
negative (close to -94 mV)
Voltage-gated sodium and potassium channels are mostly found in the plasma membrane of the __ and axon, as well as of some muscle cells
axon hillock
In _ axons, voltage-gated sodium and potassium channels are at a greater concentration at the nodes of Ranvier; in _ axons, these channels are evenly distributed along the entire axon
myelinated;
unmyelinated
Are the exact mechanisms of gating in the voltage-gated sodium and potassium channels known?
no, that’s why models are used
In/activation gates are responsible for the opening of sodium channels during the depolarization phase of an action potential
Activation
In/activation gates are responsible for the close of sodium channels during the repolarization phase of an action potential
Inactivation
For a sodium channel to be open, the activation gate has to be _, and the inactivation gate has to be _
both open!
A sodium channel can exist in _ conformations
3
The first confirmation for the sodium channel is closed…
but capable of opening
The first confirmation for the sodium channel is closed but capable of opening. At rest, the _ gate is open, but the _ gate is closed. In this state, the channel is closed, but it can be opened by a depolarizing stimulus that causes the activation gate to open.
the inactivation gate is open but the activation gate is closed, meaning the channel is closed but capable of opening
The activation gate is on the _ of the cell, whereas the inactivation gate is on the _ of the cell
exterior;
Interior
On depolarization, the _ gate opens and with both gates in their open position, the channel is open and sodium ions move through the channel into the cell
activation gate opens (inactivation gate is already open) - part of depolarization of an action potential
The 3rd sodium channel conformation is _ and in/capable of opening
closed and incapable of opening
The 3rd sodium channel conformation is closed and incapable of opening. Within 1 msec of initial stimulus opening the activation gate, the _ gate closes
inactivation gate closes
The closing of the inactivation gate in the 3rd sodium channel conformation is a delayed response initiation by…
the same depolarization that caused the activation gate to immediately open
The closing of the inactivation gate in the 3rd sodium channel conformation, with the inactivation gate closed and the activation gate open, the channel is closed. The inactivation gate remains closed until…
the membrane potential returns to near its resting value
Until the membrane potential returns to near its resting value, the channel cannot open in response to a second depolarizing stimulus because…
the inactivation would remain closed; it does not open in response to a depolarization
Once repolarization has occurred, the inactivation gate opens and the activation gate closes, returning the channel to its _ _
resting state
The opening of sodium activation gates is a _ mechanism; the opening of some sodium activation gates causes more sodium activation gates to open by _ing the stimulus to open the gates (depolarization)
regenerating
Sodium channel opening is part of a _ feedback loop that allows for the rapid depolarization of the cell
POSITIVE
What prevents the oversaturation of sodium ions in the cell is…
the sodium inactivation gates closure
Threshold occurs when the inward flux of sodium ions…
exceed the outward flux of potassium ions
Voltage-dependent potassium channels are part of a _ feedback loop during an action potential
negative
Voltage-dependent potassium channels are part of a negative feedback loop during an action potential because the effect of opening potassium channels (repolarization) is an action opposite to…
the initial stimulus that opened the potassium channels (depolarization)
As the cell repolarizes, the depolarizing stimulus _, and potassium channels slowly close
weakens
The _ principle suggests that whether a membrane is depolarized to threshold or greater, the amplitude of the resulting action potential is the same; if the membrane is not depolarized to threshold, no action potential occurs
all=or=none principle
The level of depolarization reached at the peak of an action potential depends not on the strength of the stimulus, but rather on the relative strengths of the electrochemical gradients for so- dium and potassium ions and …
the relative permeabilities of the membrane to these ions
During the depolarization phase, sodium permeability exceeds potassium permeability _ fold and the membrane potential approaches the sodium equilib- rium potential of +60 mV
several 100 fold
The 4 different phases of an action potential are:
_
depolarization
repolarization
after-hyperpolarization
resting
The membrane potential for a resting neuron is:
a. -70 mV
b. -70 mV to 30 mV
c. 30 mV to -70 mV
d. -70 mV to -85 mV
a. -70 mV
Voltage-gated sodium channels are _ during a neuron at rest.
closed
They can’t be open unless they are triggered by an action potential
Voltage-gated sodium channels are _ during depolarization
open
They have to be open, otherwise the sodium couldn’t enter the cell during an action potential
Voltage-gated sodium channels are _ during repolarization
closed
Repolarization is all about potassium leaving the cell, not about much sodium movement
Voltage-gated sodium channels are _ during after-hyperpolarization
closed
They have to be closed to enable the continued high outward flow of potassium through the voltage-gated channels
The inactivation gate of a voltage-gated sodium channel is only CLOSED during _
REPOLARIZATION
It can’t be during depolarization, since they’re all open at that time. It can’t be during resting and after-hyperpolarization the ACTIVATION gate is closed, and it would take extra energy to close both gates the rest of the time
the activation gate is open during depolarization and repolarization, but closed during rest and after-hyperpolarization
the inactivation gate is only CLOSED during repolarization
the voltage-gated sodium channel is only open during depolarization
The voltage-gated sodium channel is only open during _
depolarization
The activation gate of the voltage-gated sodium channel is closed during _ and _
resting and after-polarization
The depolarization of the membrane is met by _ feedback with sodium flow into the cell, creating a net positive change in the cell
positive feedback
The depolarization of the membrane is met by _ feedback with potassium flow into the cell, creating a net negative charge in the cell
negative feedback
T or F: the neuron can never meet or exceed the sodim equilibrium potential for the same reason that the resting membrane potential can never equal or exceedthe potassium equilibrium potential
true
Sodium movement into the cell is countered by potassium movement out of the cell, primar- ily through potassium leak channels and later through the opened voltage-gated potassium channels.
During the depolarization phase of an action potential, is the membrane more permeable to sodium or to potassium?
Sodium!
If a neuron had equal permeability to sodium and potassium ions, would the resting membrane potential of that cell be more negative or less negative than -70 mV?
less negative (i.e., closer to +60 mV)
What equation does this give regarding sodium, potassium and chloride ions?
Vm = 61log (PNa[Na+]o + PK[K+]o + PCl[Cl-]i) / (PNa[Na+]i + PK[K+]i + PCl[Cl-]o
the GHK equation to calculate the MEMBRANE POTENTIAL for a membrane that is somewhat permeable to sodium, potassium and chloride but IMPERMEABLE to other ions
TTX is a toxin that blocks voltage-gated sodium channels, and TEA is a toxin that blocks voltage-gated potassium channels. Predict what effect each of these toxins would have on (1) the resting membrane potential
TTX (tetrodotoxin) blocks the voltage-gated sodium channels responsible for the rapid depolarization phase of the action poten- tial and, therefore, blocks the generation of action potentials. Because some of these channels (albeit only a few) are open at rest, TTX would decrease sodium permeability, thereby causing a hyperpolarized resting membrane potential
TTX is a toxin that blocks voltage-gated sodium channels, and TEA is a toxin that blocks voltage-gated potassium channels. Predict what effect each of these toxins would have on the generation of action potentials
TEA (tetraethylammonium) blocks the voltage-gated potassium channels responsible for the repolarization phase of the action poten- tial. Thus, once an action potential occurs, the depolarization phase will be prolonged. Because some of these channels are open at rest, TEA would decrease potassium perme- ability, thereby causing a depolarized resting membrane potential
Multiple sclerosis is an autoimmune disease in which the immune system attacks myelin in the central nervous system. What effect does multiple sclerosis have on the conduction of action potentials in the nervous system?
By decreasing the amount of myelin, multiple sclerosis slows down the conduction of action potentials in the central nervous system. Eventually, the degree of demyelination causes the cessation of action potentials along some axons
The absolute refractory period does/not allow another action potential to take place, whereas the relative refractory period does/no
absolute RP doesn’t, relative RP does
Does a stimulus preclude the absolute refractory period?
yes
To generate a second action potential during the relative refractory period, a stimulus must be strong enough to open enough sodium channels such that sodium inflow overcomes the elevated potassium outflow that occurs during the relative refractory period, and the stimulus may have to overcome some sodium _ gates that are still closed
inactivation
Peripheral neuropathy, a disease of the peripheral nervous system, can affect the somatic or _ efferent or the afferent branch
autonomic
Peripheral neuropathy is correlated with issues with blood _ _
glucose regulation
Why does saltatory conduction occur in myelinated axons?
because very little current flows across the membrane where myeline insulates it, needing it to flow all the way to the next node of Ranvier
Does the amplitude in current diminish because some current leaks across the axon membrane, even in myelinated axons?
yes, but the stimuli that reaches the next node of Ranvier is typically sufficient to create another threshold for action potentials to continue along each node
Conduction velocity is greater in _-diameter axons
larger-diameter
We can think of speedy conduction velocity for myelinated axons as…
express trains that make fewer stops, getting to their destination in quicker time
Which of the nerve fibers do not have myelin present?
A alpha
A beta
A gamma
A delta
B
C
C - it’s the smallest fiber diameter at 0.3 - 1.3 um, and has the slowest conduction velocity at 0.7 - 2.3 m/sec
The largest nerve fiber diameter is A alpha, which is typical of…
stimulation of skeletal muscle contraction
Note the missing example of function in the following nerve fiber types (highest to lowest diameter):
A alpha - stimulation of skeletal muscle contraction
A beta - …
A gamma - stimulation of muscle spindle contractile fibers
A delta - pain, temperature sensation
B - visceral afferents, autonomic preganglionics
C - pain, temperature sensation, autonomic postganglionics
A beta - touch, pressure sensation
Depolarization of a neuron to threshold stimulates:
a) Opening of sodium channels.
b) Delayed closing of sodium channels.
c) Delayed opening of potassium channels.
d) Both a and c.
e) All of the above.
e) all of the above
Neurotransmitters are released most commonly from the
a) Cell body.
b) Dendrites.
c) Axon terminals.
d) Axon hillock
c) Axon terminals.
If a cation is equally distributed across the cell membrane (that is, its concentration inside the cell equals its concentration outside the cell), then which of the follow- ing statements is false?
a) At —70 mV, the chemical force on the ion is zero.
b) At —70 mV, the electrical force on the ion acts to move it into the cell
c) At +30 mV, the chemical force on the ion is zero.
d) The equilibrium potential for the ion is zero.
e) At —70 mV, the electrochemical force on the ion acts to move it out of the cell
e) At —70 mV, the electrochemical force on the ion acts to move it out of the cell
The depolarization phase of an action potential is caused by the
a) Opening of potassium channels.
b) Closing of potassium channels.
c) Opening of sodium channels.
d) Closing of sodium channels
c) Opening of sodium channels.
During the relative refractory period, a second action potential
a) Cannot be elicited.
b) Can be elicited by a threshold stimulus.
c) Can be elicited by a subthreshold stimulus.
d) Can be elicited by a suprathreshold stimulus
d) Can be elicited by a suprathreshold stimulus
Nerves are found
a) In the central nervous system.
b) In the peripheral nervous system
c) Both a and b.
d) Neither a nor b
b) In the peripheral nervous system
If the membrane potential of a neuron becomes more negative than it was at rest, then the neuron is _. In this
state, the neuron is _ excitable.
a) depolarized; more
b) hyperpolarized; more
c) depolarized; less
d) hyperpolarized; less
d) hyperpolarized; less
Oubain is a poison that blocks the Na+/K+ pump. If this pump is blocked, then the concentration of potassium inside the cell would
a) Increase.
b) Decrease.
c) Not change
b) Decrease.
read the question - the answer is specific to increasing inside the cell, not outside the cell, or elsewhere
If potassium concentrations in the extracellular fluid of the brain increased, activity in the brain would
a) Increase.
b) Decrease.
c) Not change
a) Increase
Which of the following neurons are part of the peripheral nervous system?
a) Motor neurons innervating skeletal muscles
b) Parasympathetic neurons
c) Sympathetic neurons
d) All of the above
d) All of the above
Which of the following axons exhibits the greatest conduction velocity?
a) An unmyelinated axon with diameter 5 fxm
b) A myelinated axon with diameter 5 fxm
c) An unmyelinated axon with diameter 20 luim
d) A myelinated axon with diameter 20 [xm
d) A myelinated axon with diameter 20 [xm
Which of the following best describes the status of sodium channels at the resting membrane potential?
a) Activation gates are open and inactiva- tion gates are closed.
b) Activation gates are closed and inacti- vation gates are open.
c) Activation gates and inactivation gates are closed.
d) Activation gates and inactivation gates are open
b) Activation gates are closed and inacti- vation gates are open.
inactivation gates are only closed during repolarization
Which of the following is not a part of the efferent division of the nervous system?
a) Parasympathetic nervous system
b) Sympathetic nervous system
c) Motor neurons
d) Sensory receptors
d) Sensory receptors
Of the following ions, which is (are) lo- cated in greater concentration inside the cell?
a) Sodium only
b) Potassium only
c) Chloride only
d) Sodium and potassium
e) Potassium and chloride
b) Potassium only
Which of the following statements about graded potentials is false?
a) The magnitude of a graded poten- tial varies with the strength of the stimulus.
b) Some graded potentials are hyperpo- larizations; others are depolarizations.
c) Graded potentials are produced at ligand-gated ion channels.
d) Graded potentials can sum over space and time.
e) Graded potentials are limited in dura- tion by the refractory period
e) Graded potentials are limited in dura- tion by the refractory period
What are the subdivisions of the periph- eral nervous system?
afferent and efferent ns
Information from the periphery is brought to the central nervous system by (afferent/ efferent) pathways
afferent pathways
Which cell type is more abundant in the nervous system — glial cells or neurons?
glial cells - workers behind the scenes outnumber the stars of the show
Voltage-gated calcium channels are lo- cated in which region(s) of a neuron?
axon terminal
(Schwann cells/Oligodendrocytes) form myelin in the peripheral nervous system, and (Schwann cells/oligodendrocytes) form myelin in the central nervous system
Schwann cells in PNS, oligodendrocytes in the CNS
Myelin (increases/decreases) conduction velocity in axons
increases
If an anion is present in greater concentration outside the cell compared to inside the cell, would the equilibrium potential for that anion be positive, negative, or zero?
negative
Which ion is closer to equilibrium at the resting membrane potential of -70 mV— sodium or potassium?
potassium
In the peripheral nervous system, cell bodies of afferent neurons are located in _
ganglion (as opposed to…?)
The electrochemical force for potassium ions when the membrane potential is at the peak of an action potential is (greater than/less than) the electrochemical force for potassium ions when the membrane potential is at rest
greater than
Both sodium and potassium channels have inactivation gates that close shortly after the activation gates open, (true/ false)
false
When sodium inactivation gates are closed, a second action potential is im- possible, (true/false)
true - this occurs during repolarization, which is the absolute refractory period
In myelinated axons, action potentials are propagated by _ conduction
saltatory
The Na+/K^ pump causes the repolariza- tion phase of an action potential, (true/ false)
false -
When a neuron is at the peak of an ac- tion potential (+30 mV), the direction of the electrical force for potassium ions is (into/out of) the cell
out of the cell
Electrical synapses operate by al- lowing electrical signals to be transmitted from one neuron to another or a neuron to a glial cell through _ _
gap junctions
Chemical synapses operate through the release of neurotransmitters that activate signal _ mechanisms (described in Chapter 5) in the target cell
transduction
When an elec trical signal is generated in one cell, it is directly transferred to the adjacent cell by means of … through the gap junctions
ions flowing through
Can second messenger molecules move through gap junctions, in addition to other ions flowing through them?
yes
Rapid communication between adjacent neurons that synchronizes the electrical activity in these cells can be _l
bidirectional
Electrical synapses are found in:
a. retina of the eye
b. certain areas of the cortex
c. the brainstem for regulating breathing
d. synchronizing the neurons responsible for inspiration
e. all of the above
e. all of the above
Hypothalamic neurons release tropic hormones by _ _ thereby synchronizing their activity and resulting in bursts of tropic hormone release
gap junctions - electrical activity
T or F: much is unknown about the function of electrical synapses
true
A synapse between a neuron and an effector cell is called a _ junction
neuroeffector
Synapses can occur at dendrites, cell bodies, or with other _s
axon
(axondendritic, axosomatic or axoaxonic)
Signaling across a chemical synapse is _directional
unidirection: pre to post-synaptic neuron
voltage-gated _ channels open when the axon terminal is depolarized, which occurs upon arrival of an action potential at the axon terminal
calcium
When the calcium channels open, they allow cal- cium to flow down its electrochemical gradient into the _ _, thereby increasing the concentration of cytosolic calcium in the axon terminal
axon terminal
Calcium then causes the membranes of synaptic vesicles to fuse with vesicle attachment sites on the inner surface of the axon terminal membrane and undergo _, which re- leases the neurotransmitters into the synaptic cleft
exocytosis
The amount of neurotransmitter released depends on the con- centration of calcium in the cytosol of the axon terminal, which depends on the …
frequency of action potentials in the presynaptic neuron
Following a single action potential, neurotransmitter re- lease stops within a few milliseconds because the voltage-gated calcium channels close soon after opening, and because calcium ions are _ively transported in/out of the axon terminal on a continual basis, bringing the cytosolic calcium concentration back to its rest- ing level
actively;
out
If neurotransmitter molecules were to remain indefinitely in the synaptic cleft following their release, they would bind to re- ceptors over and over again, inducing a …
continual response in the postsynaptic neuron
Ways to prevent neurotransmitter continually binding to receptors is its degradation by enzymes: -
on the postsynaptic neuron’s plasma membrane
- on the presynaptic neuron’s plasma membrane
- on the plasma membrane’s nearby glial cells
- in the interstitial fluid of the synaptic cleft
…
in the cytoplasm of the presynaptic neuron or glial cells
Reuptake involves neurotransmitter molecules actively being transported back…
into the presynaptic neuron that released them
what prevents neurotransmitter degradation by enzymes, etc.?
binding to receptorsin the post-synaptic neuron
Neurotransmitter is usually present in the synaptic cleft for a fair amount/only a few ms after its release from the presynaptic neuron
only a few ms; they are dealt with quickly to prevent over-stimulation of the post-synaptic neuron
Several pharnnaceutical agents work by decreasing the activity of specific neurotransnnitter reuptake proteins or enzynnes that degrade neurotransnnitters. Describe the effects of each type of inhibitor on the concentration of neurotransnnitter in the synaptic cleft and, therefore, on communication across specific synapses
Drugs that block the degradation or reuptake of neurotransmitter increase the concentra- tion of neurotransmitter in the synaptic cleft of active neurons, enhancing the communication. However, if a neuron is not releasing neurotrans- mitter, then these drugs will have no effect
The time it takes for an action potential arriving at the axon terminal before a response occurs in the postsynaptic cell is called _ _
synaptic delay
The time lag for an action potential arriving at the axon terminal before a response occurs in the postsynaptic cell is mostly due to the time required for…
calcium to trigger the exocytosis of neurotransmitter
A fast response whenever a neurotransmitter binds to a post-synaptic receptor is a _-gated channel, or a channel-linked receptor
ligand-gated channel
A slow response of a neurotransmitter absorbed by a postsynaptic neuron is through _ _-linked receptors called metabotropic receptors
G protein-linked
Fast responding signal transduction is associated with a change in the membrane potential, called a _ potential
postsynaptic potential (PSP)
PSPs occur _ and terminate _
rapidly; rapidly
Slow response neurotransmitter binds occur _ and terminate _
slowly (milliseconds to hours)
A slow response, direct coupling synaptic transmission involves more than one _, produced by activation or inhibition of an enzyme after the metabotropic receptor binds to a neurotransmitter to activate a G protein
messenger
the enzyme from the G protein activation can create a second messenger
In a slow response, direct coupling synaptic transmission, the… can produce a second messenger which can produce other cell responses as well as open or close ion channels
G protein, which activates or inhibits an enzyme that produces the second messenger
_ synapses depolarize the post- synaptic neuron
excitatory
ESPSs or _ postsynaptic potentials, can occur as either a fast response or a slow response
excitatory
T or F: EPSPs are action potentials
false - they’re graded potentials, with the amplitude of depolarization increasing as more neurotransmitter molecules bind to receptors
Fast EPSPs are generally caused by the binding of neurotrans- mitter molecules to their receptors on the postsynaptic cell, in the process opening channels that allow small _ to move through them
cations (sodium and potassium ions)
In EPSPs, the neurotransmitter binds to a receptor and activates a G protein, the G protein then activates the enzyme adenylate cyclase; which in turn catalyzes the reaction converting ATP to cAMP which activates the protein _ A which catalyzes the addition of a phosphate group to the potassium channel
kinase A
_s, a type of voltmeter, is used to measure electrical activity in the cell when measuring excitatory synapses
oscilloscopes
In fast EPSPs, the series of steps results in the phosphorylation and closure of the potassium channel, resulting in…
depolarization, decreasing potassium permeability and maintaining sodium permeability, the same effect as if sodium permeability increased
Slow EPSPs last seconds to _
hours
What takes slow EPSPs so long to return to resting level is waiting for the potassium channels to be _, which will not occur until enough cAMP has been degraded by phosphodiesterase to return the cAMP concentration to its resting level
phosphorylated
At inhibitory synapses, the binding of a neurotransmitter to its receptors opens channels for either potassium or _ ions
chloride
When a neurotransmitter causes potassium channels to open, potassium will move out of the cell, hyperpolarizing it, known as a _ postsynaptic potential
inhibitory postsynaptic potential (IPSP)
Both IPSPs and EPSPs are _ potentials
graded
Because the chloride ion has a negative charge (it is an anion), the membrane potential at rest is an electrical force that acts to move chloride … the cell
out of the cell
During an IPSP, if a neurotransmitter is present at an inhibitory synapse while a second neurotransmitter is present at an excitatory synapse, chloride will move … the cell at the same time that positive charges enter the channel opened by NT2, opposing any change in membrane potential
into
During an IPSP, depolarization of the membrane means that chloride is no longer at _. The more positive potential inside the cell pulls the negative chloride ions into the cell, stabilizing the membrane potential by countering the influence of positive charge moving into the cell. This effect is considered an inhibitory action because it decreases the likelihood that the neuron will reach threshold for an action potential
EQUILIBRIUM
During an IPSP, the more positive potential inside the cell pulls the negative chloride ions into the cell, stabilizing the membrane potential by countering the influence of positive charge moving into the cell. This effect is considered an inhibitory action because it decreases the likelihood that …
the neuron will reach threshold for an action potential
_l _n is the process that determines whether the particular combination of synaptic inputs arriving at a given time at a postsynaptic cell will produce an action potential
neural integration
The _ _ rule: an action potential is triggered if the membrane potential at the axon hillock is depo- larized to threshold; if the potential is below threshold; no action potential will occur
neural integration
In _e, a single neuron communicates to several other neurons, whereas In _e, a single neuron receives communication from several other neurons.
divergence; convergence
What is the degree of hyperpolarization from temporal IPSPs limited by?
the equilibrium potential for the ion causing the hyperpolarization
When, for example, the opening of potassium channels produces a hyperpolarization, the more potassium channels that are open, the greater the hyperpolarization will be, until the membrane potential approaches -94 mV (the potassium equilibrium po- tential). The membrane potential can never exceed this value; in fact, it will never reach —94 mV because even when all potassium channels in a membrane are open, sodium leak channels will al- low some sodium to leak into the cell, counteracting the move- ment of potassium
The synapse of neuron A with the postsynaptic cell is closer to the axon hillock than is the synapse of neuron B. If a single action potential in each presynaptic neuron results in an 8-mV depolarization at the axon hillock, which presynaptic neuron had to produce the larger depolarization at the site of the synapse?
synapse of neuron B because graded potentials diminish along the axon, resulting in less than the initial 8-mV depolarization
Temporal summation can occur because postsynaptic poten- tials … than action potentials
last considerably longer
T or F: when metabotropic receptors are involved in a spatial summation neural integration, a postsynaptic potential cannot persist, even after the neurotransmitter that initiated it has been cleared from the synaptic cleft
false - they are so slow to respond that the postsynaptic potential may persist
spatial summation occurs as postsynaptic potentials originat- ing at different synapses spread to the _ _, overlapping along the way.
axon hillock
once a depolarizing stimulus exceeds thresh- old, the degree of depolarization does not affect the size of action potentials, but rather their _
frequency
increases in the strength of supratheshold stimuli cause the frequency of action potentials to increase
increases in the strength of supratheshold stimuli cause the frequency of action potentials to increase in the postsynaptic neuron, an effected called frequency _
coding
EPSPs and IPSPs typically occur at axodendritic and axo_ synapses
axosomatic (to the body of the cell)
In axoaxonic synapses, neurotransmitter from the presynaptic neuron does/not generate electrical signals in the postsynaptic neuron
DOES NOT - it is about a change in the amount of calcium that enters the axon terminal in response to an action potential, rather than neurotransmitter to a postsynaptic neuron
By binding to receptors on the membrane of the axon terminal of the postsynaptic neuron [i.e., an axoaxonic synapse], the neurotransmitter induces a change in the amount of calcium that enters the axon terminal in response to an action potential, in turn altering the amount of neurotransmitter…
released from the post- synaptic neuron
In axoaxonic synapses, the enhancement of release of neurotransmitter based on increased amount of calcium that enters the axon terminal in response to an action potential is considered presynaptic _, whereas in cases the neurotransmitter is decreased, it is referred to as presynaptic _
facilitation; inhibition
In axoaxonic synapses, presynaptic modula- tion affects transmission to the postsynaptic neuron at …
one specific synapse, thereby altering the ability of that one synapse to excite or inhibit the postsynaptic neuron,
axodendritic and -somatic synapses don’t care which presynaptic neurons excite or inhibit, but that it happens
Enkephalins are morphinelike substances produced in the body. They presynaptically inhibit the release of neurotransmitter from neurons that convey signals from pain receptors (called nociceptors) in the skin to the spinal cord. Based on this information, explain what effect, if any, enkephalins would have on the perception of pain, which occurs at the level of the brain, and thereby acting as an _PSP
would reduce the effect of pain, perhaps when it is at its extreme because they inhibit those neurotransmitters (therefore acting as an IPSP)
For a person to perceive pain, information must be transmitted from the sensory receptor in the skin to the primary somatosensory cortex. Disruption of the communication at any level in between the skin and the cortex will decrease the perception. Thus, by decreasing commu- nication from the afferent to the second- order neuron in the spinal cord, less signal is trans- mitted to the cortex and the perception of pain is diminished
Neurotransmitters belong to a variety of chemical classes, includ- ing acetylcholine, biogenic amines, amino acids, purines, and neuropeptides. Most are small molecules, with the notable excep- tion of _
the neuropeptides
_ is released from neurons in both the central and peripheral nervous systems. The most abundant neurotrans- mitter in the peripheral nervous system, it is found in efferent neu- rons of both the somatic and autonomic branches
Acetylcholine (ACh)
Acetylcholine (ACh) is synthesized in the _ _ of neurons from two substrates, acetyl CoA and choline, and catalyzed by CAT (choline acetyl transferase)
axon terminal
Acetyl CoA is found in almost all cells of the body, including those neurons that synthesize and release acetylcoline (i.e., _ neurons)
cholinergic
T or F: choline (NOT acetylcholine) cannot be synthesized by neurons
true
although it can be synthesized in the liver, most is obtained from the diet and delivered by the bloodstream to cholinergic neurons
Acetyl CoA is a two-carbon molecule produced during the catabolism of lipids, carbohydrates and proteins, and is the initial substrate for the _ cycle
Krebs cycle - the citric acid cycle that is used by organisms to respire to generate energy through aerobic respiration. it is also a precursor of certain amino acids, and is integral to metabolism
What triggers the release of acetylcholine by exocytosis?
an action potential!
Acetylcholine can be degraded by an enzyme on the pre-, postsynaptic neuron, or either, is known as _
acetylcholinesterase (AChE)
The following are biogenic amines, including:
catecholamines (which include dopamine, epinephrine and norepinephrine)
serotonin
_
histamine
Amino acid class of neurotransmitters include:
glutamate
aspartate
glycine
_
GABA
The purine class of neurotransmitters includes:
ATP
ADP
_
adenosine
Neuropeptides are larger neurotransmitters that include:
TRH
_
Oxytocin
Substance P
Cholecystokinin
Endogenous opioids (enkephalins, endorphins)
Orexin
Vasopressin
Unique molecules that act as neurotransmitters are:
nitric oxide
_
endocannabinoids
Receptors for acetylcholine are of two types:
muscarinic cholinergic receptors and
_ cholinergic receptors
nicotinic
Nicotinic cholinergic receptors are _tropic, and have TWO binding sites for acetylcholine and trigger the opening of channels that allow both sodium and potassium to move through, causing an EPSP in the postsynaptic cell (mostly in the PNS, although some in the CNS)
ionotropic (meaning, they are fast responses of synaptic transmission, compared to slower metabotropic ones)
Muscarinic cholinergic receptors are _ receptors…Their binding with acetylcholine can open or close ion channels and activate enzymes,
slow receptors / metabotropic receptors that operate through the action of G protein
Muscarinic cholinergic receptors are found on some _ organs of the autonomic nervous system and are the dominant cholinergic receptor type in the CNS
effector
The action of any chemical messenger ultimately depends not on the nature of the messenger, but rather on the signal trans- duction mechanism activated by the _ once the messenger binds to it.
receptor
Biogenic amines are a class of neurotransmitters derived from _ _s
amino acids
The biogenic amines (neurotransmitters) are both released primarily by neurons in the _NS [including epinephrine, but it’s generally considered a hormone released from the adrenal medulla, i.e., the sympathetic nervous system], but neuroepinephrine is also released from neurons in the _NS
CNS; PNS
Epinephrine and norepinephrine are a_ receptors, with subclasses designated by numerical subscripts, such as alpha 1, alpha 2, beta 1, beta 2, and beta 3.
adrenergic (i.e., alpha adrenergic and beta adrenergic)
- think of them as adrenaline and noradrenaline, respectively
Adrenergic receptors (i.e., adrenaline and noradreline, i.e., epinephrine and norepinephrine) are found in the _NS and in the effector organs for the sympathetic branch of the _ nervous system
CNS; autonomic
Which cholinergic receptor type (nicotinic or muscarinic) produces the faster response?
nicotinic, since it’s an ionotropic receptor
Catecholamines generally produce fast/slow responses mediated through _ _ and changes in second messenger systems
slow; G proteins
_ function as autocrines, binding to receptors on the axon terminal of the cell that released them, enabling a neuron to modulate its own release of neurotransmitter mostly by altering the amount of calcium entered during an action potential
catecholamines
Catecholamines can be degraded by two enzymes:
_
catechol-O-methyltransferase (COMT)
monoamine oxidase (MAO)
MAO (monoamine oxidase), a type of enzyme that degrades catecholamines, is located in the:
synaptic cleft
_ of the axon terminal of the neurons that release the catecholamines
some glial cells
mitochondria
catechol-O-methyltransferase (COMT), a type of enzyme that degrades catecholamines, is located in the _ _
synaptic cleft
Serotonin and histamine are biogenic amines, but they are not _
catecholamines
Serotonin is found in the CNS, particularly in the _ _
brain stem
Serotonin, a biogenic amine, regulates sleep and _
emotions
Histamine, which is better known for its release from non-neuronal cells during allergic and other types of reactions, can also function as a neurotransmitter. It is found in the CNS, primarily in the _
hypothalamus
_ _ neurotransmitters are the most abundant class in the CNS, where they are widely distributed
amino acid
Aspartate and glutamate are amino acid neurotransmitters released at _ synapses, whereas glycine and gamma-aminobutryic acid (GABA), are released at _ synapses (also amino acid neurotransmitters)
excitatory; inhibitory
Glutamate is the most commonly released neurotransmitter at excitatory synapses in the _NS
CNS
Glutamate inspires a fast EPSP when it binds with receptors to move sodium into the cell, and when it binds with other receptors, _ channels open, which acts as a second messenger
calcium
_ is the neurotransmitter most commonly released at inhibitory synapses in the CNS
GABA
T or F: GABA is a type of ionotropic receptor
false - there are 2 ionotropic receptors and 1 metabotropic receptor found from GABA
GABAc receptors are located in the _ where they play a role in communication of visual information
retina - they inhibit certain impulses to the brain, enabling one to see (revisit perception chapter in cognitive psych)
GABAa receptors in the CNS can bind to sedatives such as _, thereby depressing neural activity
Valium
ATP, ADP, GTP and AMP are stored in synaptic vesicles and released by exocytosis. _, however, is generated from ATP released into the extracellular fluid by enzymes located there
adenosine
T or F: ATP can be in the form of an ionotropic receptor or a metabotropic receptor
true - P2X is an ionotropic receptor that allows cations to move through the cell membrane, excitatory; whereas P2Y is coupled to G proteins
Adenosine, ADP and ATP are all neurotransmitters that can bind to the P2Y receptor, the _ receptor of ATP
metabotropic receptor
Drugs that act on GABAergic systems include
_ (such as Valium)
sleeping aids (such as zolpidem)
alcohol
benzodiazepines
Benzodiazepines treat anxiety by deadening the fight-or-flight response from the sympathetic nervous system, a branch of the _ nervous system
autonomic
Monoamine oxidase inhibitors prevent the breakdown of biogenic amines, including _ and _ by inhibiting their degradation, acting as though these neurotransmitters are increased
norepinephrine and serotonin
selective serotonin reuptake inhibitors _ the amount of serotonin that remains in the synaptic cleft
increase
Nucleotidases break down _ and _ wherease adenosine deaminase breaks down adenosine
ADP and ATP
_s are short chains of amino acids that are synthesized in the same manner as proteins, and more than 50 of them are found in neurons which function as neurotransmitters
neuropeptides
Much like _ that are to be secreted from cells, neuropeptides are synthesized in the rough endoplasmic reticulum and packaged into secretory vesicles by the Golgi apparatus
proteins
Neuropeptides occur in the _
soma/cell body
Neuropeptides are more commonly known as _s
hormones
e.g., vasopressin, oxytocin, enkephalins, etc.
_n, a type of neuropeptide, regulates urine output by the kidney
vasopressin
_n, a type of neuropeptide, regulates contractions of the uterus and the flow of milk from the breasts
oxytocin
Endogenous _ are types of neuropeptides that exert effects similar to morphine, which include enkephalins and endorphins
Opioids
S_, a type of neuropeptide, decreases gastointestinal motility
substance P
c_n, a type of neuropeptide, regulates gallbladder contraction
cholecystokinin
_n, a type of neuropeptide, is a hypothalamic neurotransmitter that regulates the sleep-wake cycle, inducing arousal or wakefulness (potentially a treatment for narcolepsy)
orexin
Although neuropeptides are colocalized with other small neurotransmitters (i.e., released from the axon terminal as non-neuropeptides at the same time), neuropeptides are packaged in larger vesicles, called d_ c_ vesicles
dense core vesicles
Neuropeptides often act on _ receptors and modulate the response of the postsynaptic neuron to the colocalized small neurotransmitter
metabotropic receptors (the small neurotransmitter acting as the second messenger)
What makes gas nitric oxide and endocannabinoids unique as neurotransmitters?
they are not stores in synaptic vesicles or released by exocytosis
Nitric oxide (one nitrogen atom and one oxygen atom)is released as soon as it’s _, because it easily crosses the plasma membrane
synthesized
Controlling nitric oxide synthesization and release is the catalyzation by the enzyme nitric oxide _
synthetase
_ are a family of chemicals manufactured in neurons from membrane phospholipids; they include anandamide and 2-arachidonylglycerol, which are produced to increase cytosolic calcium levels
endocannabinoids
THC, a drug that targets CB1 _c receptors, which are the most common type of cannabinoid receptor in the brain
metabotropic
THC’s influence on cannabinoid receptors have led its widespread use for diseases such as:
Parkinson’s
anxiety disorders
- _ disorder
post-traumatic stress disorder
Suppose that the electrochemical force for anion X (X~) acts to move the anion out of the cell. If a neurotransmitter bind- ing to its receptor opened channels for X~ on the postsynaptic cell, then the response would
a) Be an EPSP.
b) Be an IPSE
c) Be stabilization of the membrane.
d) Not occur.
a) Be an EPSP.
Suppose that all the calcium could be removed from the extracellular fluid sur- rounding a neuron. Such removal would inhibit the ability of a neuron to
a) Produce action potentials.
b) Release neurotransmitter.
c) Respond to the binding of a neuro- transmitter to its receptor.
d) Degrade neurotransmitters
b) Release neurotransmitter.
Synaptic vesicles
a) Store calcium.
b) Release neurotransmitters by exocytosis.
c) Degrade neurotransmitters.
d) Form gap junctions.
e) Synthesize neurotransmitters
b) Release neurotransmitters by exocytosis.
If sodium channels closed in response to a stimulus, then
a) The neuron would be depolarized.
b) The neuron would be hyperpolarized.
c) The membrane potential would be stabilized.
d) A second messenger would be produced.
e) The neuron would remain at rest
b) The neuron would be hyperpolarized.
Assumes that potassium would rush in instead, creating a hyperpolarization
A fast EPSP is most commonly produced by
a) The opening of sodium-selective channels.
b) The opening of potassium-selective channels.
c) The opening of chloride channels.
d) The opening of channels selective for both sodium and potassium.
e) The opening of calcium-selective channels
d) The opening of channels selective for both sodium and potassium.
The enzyme that catalyzes the synthesis of acetylcholine is
a) Adenylate cyclase.
b) Choline acetyl transferase.
c) Monoamine oxidase.
d) Acetylcholinesterase.
e) Catechol- 0-methyltransferase.
b) Choline acetyl transferase.
Which of the following neurotrans- mitters is a biogenic amine but not a catecholamine?
a) Norepinephrine
b) Serotonin
c) Dopamine
d) Epinephrine
b) Serotonin
Which of the following is most likely to occur at an axoaxonic synapse?
a) An EPSP
b) AnIPSP
c) Stabilization of the membrane potential
d) Temporal summation
e) Presynaptic modulation
e) Presynaptic modulation
What happens to the concentration of neurotransmitter in the synaptic cleft when the frequency of action potentials increases in the presynaptic neuron?
a) It increases
b) It decreases
c) It remains constant
a) It increases
The EPSPs from two different synapses occur at the same time and cause a larger depolarization than either one alone can cause. This is an example of
a) Membrane stabilization.
b) Presynaptic inhibition.
c) Presynaptic facilitation.
d) Temporal summation.
e) Spatial summation
e) Spatial summation
At electrical synapses, which type of junc- tion exists between the two cells?
gap junction
When the opening of ion channels allows both sodium and potassium ions to move through, no change in membrane poten- tial occurs because sodium moves into the cell and potassium moves out of the cell, (true/false)
false - they flow at different rates
Neurotransmitter receptors are found at (chemical/electrical) synapses
chemical
Whether a synapse is excitatory or inhibi- tory is determined by the mechanism of coupling between the neurotransmitter receptor and ion channels in the postsyn- aptic cell, (true/false)
true
The synaptic delay includes the time it takes for an action potential to travel from the trigger zone of a presynaptic cell to the axon terminal, (true/false)
false - it’s from the axon terminal to the synaptic cleft (calcium levels)
A given neurotransmitter might be ex- citatory at one synapse and inhibitory at another synapse, (true/false)
true
Given that release of an inhibitory neu- rotransmitter is altered by presynaptic facilitation, the response in the postsyn- aptic cell will be a (larger/ smaller) degree of hyperpolarization.
larger
The response to a neurotransmitter is faster at (ionotropic/metabotropic) receptors
ionotropic
The enzymes that catalyze the degrada- tion of catecholamines are _ and _
monoamine oxidase (MAO), catechol- O- methyltransferase (COMT)
Adenylate cyclase catalyzes the formation of _
cAMP
The voltage-gated Na+ channel activation gate is voltage and/or time dependent
voltage dependent
The voltage-gated Na+ channel activation gate opens during…
threshold and depolarization
The voltage-gated Na+ channel activation gate is influenced by _ feedback
positive feedback -
The voltage-gated Na+ channel INactivation gate is voltage and/or time dependent
voltage and time dependent
The voltage-gated Na+ channel INactivation gate closes during _
repolarization
The voltage-gated K+ channel gate depends on voltage and/or time
voltage and time
Action potentials from threshold stimuli has a magnitude that is… supra-threshold stimuli
the same as
Relative refractory period finds that some of the sodium voltage-gated channel _ gates are closed, but some have opened
inactivation gates
The absolute refractory period includes the period of depolarization and…
most of repolarization
Action potential intensity is understood as…
a greater number of action potentials in a given time, rather than an action potential being greater than the next (i.e., frequency coding). This would defy the all-or-none principle
