Lec 13 Flashcards
If you were to decrease the temperature at a neuromuscular junction, what would happen to the synaptic delay?
the synaptic delay would increase
in Amperometry, What happens to the serotonin molecules near the surface of the carbon fiber?
they are oxidized - losing electrons to carbon fiber.
neurotransmitter transport protein that exchanges ACh for H+ ions?
ACh-H+ exchanger
By increasing external Ca2+ concentrations at a NMJ, (at subthreshold) the endplate potential will..
increase with the increase of Ca concentrations
mast cell secretory vesicles can “flicker” this means…
they can open and close several times.
If you were to increase the temperature at a neuromuscular junction, what would happen to the synaptic delay?
the synaptic delay would decrease
In amperometry, what is a stand alone flicker?
the opening and closing of secretory vesicles diffusing a small amount of NT (low level release) , where a full fusion event does not follow.
which type of neurotransmitter vessel is transported already full of its contents?
dense core secretory granules are prefilled.
The filling of synaptic vesicles depends on what 2 types of pumps?
1.vacuolar-type H+ proton pump 2. ACh-H+ exchanger
What multisubunit complex of proteins uses energy from the hydrolysis of ATP to drive H+ ions into the vesicle ?
vacuolar-type H+ pump
EPP is inhibited by increasing ____ levels.
Mg2+ (Ca2+ blocker)
what is the experimental detection of neurotransmitter release using a carbon fiber microelectrode?
Amperometry
How can Exocytotic fusion be measured?
by measuring rapid changes in cell capacitance.
What is an active zone?
an active zone is the multilinear arrangement of vesicles near the presynaptic membrane that align with the postjunctional folds that contain AChR.
What is the name of the cells that closely adhere to the motor endplate or neuromuscular junction?
Schwann cells
As the Presynaptic potential in a presynaptic terminal of a motor endplate becomes more positive, the synaptic delay will…
decrease. as presynaptic potential gets more positive the current reverses
EGTA wont work if Voltage gated Ca channels are within _____ of the site at which calcium triggers neurotransmitter release.
100 nm
What type of solution would be needed to observe MEPP’s?
a solution that is either low in extracellular Ca or high is Mg (Ca blocker).
The delay between Ca influx and the postsynaptic response in a neuromuscular transmission is due to..
1.ACh release 2.diffusion, and activation of postsynaptic 3. receptors.
What are 2 ways to prevent neurotransmitter release?
- prevent Ca2+ influx by using a Ca Channel blocker: Cd (cadmium) 2. prevent increase in Ca2+ levels by using a fast Ca2+ chelator: BAPTA or EGTA (slower)
Which type of neurotransmitter vessel contains peptide neurotransmitters?
dense core secretory granules contain peptides or precursors of peptides.
Where is the cell body of a motor neuron?
ventral horn of the spinal cord
The depletion of presynaptic vesicles is a _________ (reversible/nonreversible) reaction.
reversible
Where is Choline Acetyltransferase located?
Presynaptic membrane
What would happen if you added Cd to a presynaptic neuromuscular junction?
The Ca voltage gated channels would be blocked and without an increase in intracellular Ca the vesicles couldn’t fuse to the membrane and release Neurotransmitters.
What drug is used to measure quantal release by increasing transmitter release by prolonging the action potential?
4-aminopyridine
exocytotic and endocytotic fusion can accounted for by measuring a cell’s..
size or capacitance.
How large are dense core secretory granules?
100-200nm in diameter
Which type of neurotransmitter vessel is “dark” ?
dense core secretory granules
As the Presynaptic potential in a presynaptic terminal of a motor endplate depolarizes but remain negative, the post synaptic potential will..
increase as the pre synaptic potential remains negative.
in Amperometry, In order to measure Quantal release what would need to be done?
a low extracellular Ca concentration in order to see the two distinct types quantal release spikes small and large.
A motor neuron axon contacts a muscle fiber at one spot in the center of the fiber, and is called the …
neuromuscular junction or motor end plate
exocytosis of mast cells can be triggered by the binding of what substance?
Antigen complexed to an immunoglobin (IgE)
What is important when microinjecting BAPTA?
Speed of injection
If a NMJ presynaptic terminal is treated with curare, the responses become…
subthreshold … are unable to reach threshold levels
Depolarization of the presynaptic membrane leads to what?
neurotransmitter release
a small vesicle (synapse) contains how many neurotransmitters?
5000 molecules
What type of cell contains histamine?
mast cells
Antigen complexed to an immoglobin (IgE) when bound to a mast cell will cause…?
exocytosis of histamine filled dense core vesicles.
EPP is the strongest near what structure?
the endplate
EPP is stimulated by increasing ____ levels.
Ca2+
What happens to the total surface area of the cell after the fusion and exocytotic release of dense core secretory granules?
increase in total cell surface area.
What are MEPP’s?
Miniature end plate potentials , NMJ spontaneous EPPs that have a depolarization of ~0.4 mV. Equal to 1 quanta
ACh transmission is terminated by what enzyme?
Acetylcholinesterase
A single quanta of ACh released is equal to..
~0.4 mV depolarization
What is the rapid exocytotic fusion of thousands of dense core vesicles that contain histamine called?
massive “degranulation”
What subunit of Acetylcholine is reabsorbed by the presynaptic terminal of a Neuromuscular junction?
Choline
What structures assist in the transport of vesicles and dense core secretory granules?
transferred down microtubules to the nerve terminal.
Exocytosis of presynaptic membrane will cause the capacitance of the presynaptic terminal to increase or decrease?
increase in a stepwise fashion.
Endocytosis of presynaptic membrane will cause the capacitance of the presynaptic terminal to increase or decrease?
decrease in a stepwise fashion
a large vesicle (dense core) contains how many neurotransmitters?
15000- 300000 molecules
What is located in the Basal lamina?
AChE - acetylcholinesterase
How is EGTA a good determination of distance between Ca channels and the vesicles?
Because EGTA is a slow chelator, if the Calcium enters the cell at a location that is close to the site at which calcium triggers neurotransmitter release, the Ca will bind to the receptors before EGTA can bind to the Ca and inactivate it.
which type of neurotransmitter vessel is transported empty and filled at the nerve terminal?
secretory vesicles
the production of a “foot” during Amperometry is a result of…
the opening and closing of secretory vesicles diffusing a small amount of NT (low level release) that is prior to a large full fusion event. A full fusion event does not always follow.
What are the 2 types of neurotransmitter vessels that are present in neurons ?
Synaptic vesicles and dense core secretory granules
Under experimental conditions, how can massive exocytosis of mast cells be triggered?
by inclusion of nonhydrolyzable analog of GTP in an intracellular recording electrode.
What would happen if you added a nonhydrolyzable analog of GTP to a mast cell?
massive exocytosis
Studies of MEPP (miniature end plate potentials) demonstrated what phenomenon ?
Quantal release or that ACh is released in a Quantal fashion.
Will the step increases during exocytotic fusion of vesicles be equal with each similar type of vesicle?
No , they are unequal no matter what because of the variability in diameter of a cell.
How large are synaptic vesicles?
40-50nm in diameter
the motor end plate is the arborization of the motor nerve into many presynaptic terminals also known as …
boutons
in Amperometry, if there is a high concentration of extracellular Ca what happens to the amount of serotonin oxidation by the carbon fiber?
an increase in Ca will increase the amount of NT (serotonin) released.
BAPTA and EGTA are examples of ….
Fast(BAPTA) and Slow(EGTA) chelators for the buffering of Ca2+ ions.
Where are synaptic vesicles and dense core secretory granules initially formed?
They are formed in the golgi within the cell body of the nerve.
If the amplitude of the presynaptic potential decreases, what will happen in the post synaptic terminal?
the amplitude will decrease in the postsynaptic terminal as well.
By increasing external Mg2+ concentrations at a NMJ, (at subthreshold) the endplate potential will..
decrease with an increase in Mg concentration because it will block Ca2+ channels and prevent neurotransmitter release.
What protein is used to fill vesicles with ACh?
ACh-H+ exchanger
the fusing of vesicles in the presynaptic membrane of a NMJ causes a temporary . .
increase in presynatpic cell membrane size.
Which type of neurotransmitter vessel is “clear” ?
secretory vesicle
The axon of a motor neuron innervates several muscle fibers and is known as a ..
motor unit.
in Amperometry the current carried by the carbon fiber is increased with …
the amount of serotonin that is released.
If a NMJ is treated with curare, you realize that the delay between presynaptic action potential and postsynaptic EPSP increases with response to …
a decrease in distance from the motor endplate.
Why is the synaptic delay in motor endplates not caused by simple diffusion?
- Synaptic delay in motor endplates is much longer than would be caused by simple diffusion. (50nm in 50usec) 2. The process is temperature dependent which suggesting the delay is in the neurotransmitter release mechanism.
What is released as a result of Ca2+ influx into the presynaptic terminal?
release of neurotransmitters
What Enzyme synthesizes Acetylcholine?
Choline Acetyltransferase
The release of secretory vesicles and dense core secretory granules is triggered by what?
the increase in Ca concentration
What is a Mast cell?
secretory cells of the immune system that contain large dense core vesicles filled with histamine.
If tetrodotoxin is applied to a presynaptic terminal, what will happen to the current amplitudes in the presynaptic and post synaptic terminals over time?
Both signals current amplitudes will decrease over time with the post synaptic terminal falling faster.
What is the concentration of ACh within a presynaptic vesicle?
150 mM ACh
During a “flicker” what happens to the cells capacitance?
increases and decreases repeatedly
Quantum are fixed in amplitude but variable in…
number of quantum
Whats the width of the Basal lamina?
50nm
As the potential for presynaptic terminal in a neuromuscular junction is increased to more positive potentials, what happens to the post synaptic potential?
post synaptic potential will decrease and with a reduced amplitude as the potential becomes more positive the current reverses.
EPP decays when far from what structure?
the endplate
If a NMJ is treated with curare, you realize that the delay between presynaptic action potential and postsynaptic EPSP decreases with response to …
an increase in distance from the motor endplate.
What would hpapen if you added BAPTA (buffer chelator) to a presynaptic neuromuscular junction?
The influx of Ca within the presynaptic terminal will be buffered or bound by BAPTA before it can reach the Ca receptors at the vesicles. This will prevent release of Neurotransmitters.
When ACh is broken down, what are its subunits?
Acetyl Coenzyme A + choline
What USUALLY happens to the EPSP when adding BAPTA OR EGTA?
EPSP will decrease
What happens to the total surface area of the cell after endocytosis ?
decrease in total cell surface area.
During a complete fusion event what happens to the cells capacitance?
increases by a standard amount.
Which type of neurotransmitter vessel contains non-peptide neurotransmitters?
secretory vesicles
What is the result of ACh binding to the post synaptic membrane of a NMJ?
causes an EPSP (excitatory postsynaptic potential) or an action potential if the stimulus surpasses the threshold.
