Neurotransmission 1 - Kenyon Flashcards
What allows ions to move between cells to create electrical transmission?
gap junctions
Cells connected by gap junctions are (blank) coupled
electricaly
Do electrically coupled cells have the same membrane potential?
Yes
Can action potentials travel in both directions across a synapse?
Yes!
Can subthreshold activity be conducted bidirectionally?
Yes!
In what tissues is electrical coupling of significant importance?
- CNS neurons
- Cardiac muscle
- smooth muscle
Can a synaptic vesicle contain more than one type of neurotransmitter?
yes!
When an action potential is fired presynaptically, what are the three possible changes to the postsynaptic membrane potential?
- Hyperpolarization
- Depolarization
- No change
Depolarization of presynaptic terminals causes opening of voltage gated (blank) ion channels
Ca
Does calcium flow in or out after activation of voltage gated channels?
IN
what does Ca do to the presynaptic terminal?
it causes vesicle fusion with the membrane
By what process are neurotransmitters released from membrane fused vesicles?
Exocytosis
What are the two general processes of removal of neurotransmitter from the cleft?
Glial uptake or enzymatic degradation
Postsynaptic current causes (blank) or (blank) postsynaptic potential that changes the excitability of the postsynaptic cell
excitatory or inhibitory
Is calcium necessary AND sufficient to cause neurotransmission?
YES
Na channel inhibitors block what step in neurotransmission? (lidocaine)
action potential
Lambert-Eaton and conotoxin block the influx of what ion?
Ca
botulinum and tetanus block what step of neurotransmission?
Vesicle release
Curare, benzo’s, and myasthenia gravis do what to receptors?
Activate OR inactivate them
What two drugs block the inactivation or uptake of neurotransmitters?
Prozac and physotigmine
Name the five general groups of small neurotransmitters
- ACh
- Glutamate
- GABA and glycine
- Biogenic amines (Nepi, ,Epi, dopamine, serotonin, histamine)
- ATP, ADP, AMP, adenosine
What are the three unconventional neurotransmitters?
- Nitric oxide
- Carbon monoxide
- Endocannabinoids
during, synthesis of small molecule neurotransmitters, where are enzymes synthesized in the neuron?
Cell body
Where are small molecule neurotransmitters synthesized and packaged in the neuron?
terminal
Transport of enzymes and NEUROPEPTIDES from the cell body to the terminal are moved down (blank) tracks
microtubule
Where are neuropeptide precursors modified to produce active neuropeptides?
Terminal
Are small molecules or neuropeptides transported “slowly” down the axon?
small molecule
Once small molecules are broken down in the cleft, what happens with their components?
They are reabsorbed by the presynaptic neuron and recycled
What happens to the neuropeptides in the cleft after they do their job?
They diffuse out of the cleft or are degraded by proteolytic enzymes
What unconventional neurotransmitter has a Ca dependent enzyme in its synth?
Nitric oxide
What enzyme is Ca dependent for nitric oxide?
NO synthase
NO acts on what membrane bound effector protein?
guanylyl cyclase
Are unconventional neurotransmitters highly permeable?
yes!
What is the precursor to NO?
ARRRRRRginine
What is the “old school” criteria to define a neurotransmitter? (3)
- substance must be present presynaptically in vesicles
- Substance release must be triggered by increase in presynpatic Ca concentration
- Specific receptors for the substance must be present postsynaptically
What is the “new school” criteria to define a neurotransmitter?
- The substance can be synthesized “on demand” (unconventional neurotransmitters).
- The substance can be synthesized “on demand” by Ca2+-activated enzymes and diffuse out of the presynaptic cell
- Specific receptors for the substance can be present in the cytoplasm of the postsynaptic cell
Is ALL nuerotransmitter release Ca dependent?
YES YES YES
Vesicle membranes recycling is mediated by what type of endocytosis?
Clathrin-mediated endocytosis?
What are the three proteins needed in vesicle recycling?
- Synaptotagmin
- SNAREs
- Ca channel
Explain “kiss and run” vesicle fusion
Only a small pore opens up between the membrane and vesicle, instead of the whole vesicle fusing, allowing for rapid vesicle recyling
What is quantal release of a neurotransmitter?
Vesicle fuses and dumps all its contents into the cleft
What effect will removal of extracellular Ca or blockage or lowering Ca entry presynaptically have on neurotransmitter release?
it will be reduced
Is the role of Ca in skeletal muscle the same as it is in cardiac or smooth muscle?
NO
Agatoxin and conotoxin act on Ca channels in what cells?
Nerve terminals and dendrites and neuroendocrine cells
What is the idea of co-transmission?
One neuron can release more than one type of neurotransmitter
What are the two factors necessary to release a neuropeptide instead of a small molecule?
- Higher frequency of presynaptic APs
2. Higher elevation of intracellular Ca
Will the release of neuropeptides also stimulate the release of small molecules simultaneously?
Yes!
Where are small molecules ejected?
Into the synaptic cleft
Where are neuropeptides ejected?
They’re squirted out all over the damn place
Ca binds at what protein during vesicle fusion?
Synaptotagmin
What SNARE is found on the vesicle?
synaptobrevin
What SNARE is found in the plasma membrane?
syntaxin
Is synaptotagmin on the vesicle or the plasma membrane?
Vesicle, strangely enough
does postsynaptic membrane PERMEABILITY change DURING synaptic transmission?
yes
In the Nernst equation ion concentration gradient is essentially equal to (blank)
voltage
the (blank) of a cell membrane to a given ion determines the contribution of that ion to the membrane potential
permeability
If Pk (permeability to K) is large, Em (membrane conductance) is close to (blank)
Ek (conductance of K)
if PNa (permeability to Na) is large, Em (membrane conductance) is close to (blank)
ENa (conductance of Na)
does the Nernst equation work with divalent ions?
NOOOOOPE, just monovalent (K, Na, Cl, NOT CALCIUM)
What physical change in the plasma membrane sets permeability to an ion?
Opening or closing of ion channels
Is there such a thing as gradual opening of ion channels?
No, they are either fully open or fully closed
Describe the steps in ion passage through an ionotropic receptor?
- Neurotransmitter binds TO THE CHANNEL
- Channel opesn
- Ions flow into cell
Describe the steps in ion passage through a metabotropic receptor?
- Neurotransmitter binds to a G PROTEIN
- G protein is activated
- G protein subunits move to an effector protein
- Intracellular messengers from effector proteins activate the ion channel
- Ions flow into the cell
If channels highly selective for Na open, what happens to PNa?
it increases!
Does PNa move to EQUAL ENa?
NO, it just moves TOWARD ENa
The larger the increase in PNa, the (blank) it becomes to ENa
closer
Nonselective channels move membrane potential to what value?
0 mM!!!
What potential is halfway between ENa and Ek?
0!!
the reversal potential is the (blank) potential associated with opening a particular channel
target
For a highly selective channel Erev is the (blank) potential of the chosen ion.
Nernst equilibrium
For a poorly or non-selective channel Erev will be (greater than, less, than, betwen) the Nernst equilibrium potentials of the ions that pass through the channel.
between
Opening a channel will shift the membrane potential towards the (blank) potential.
reversal
The more channels you open the closer the membrane potential will move to (blank)
Erev
What happens to the membrane potential of -65mV when you open nonselective channels?
It becomes less negative
What happens to the membrane potential of +65mV when you open nonselective channels?
It becomes more negative
If the membrane potential is already 0mV, what happens if you open a nonselective channel?
it stays the same!!
The action of a neurotransmitter drives the postsynaptic potential towad (blank) for the particular ion channels being activated
Erev (target potential)
The value of (blank) is determined by the relative permeability of the channels to Na+, K+, Ca2+, Cl-,
Erev
The main channels activated by neurotransmitters to generate receptor potentials are (blank) for monovalent cations, or (blank) for divalent ions
nonselective, selective
If the target potential is positive, the action potential is a (blank)
EPSP
If the target potential is negative, the action potential is a (blank)
IPSP
An EPSP makes the postsynaptic neuron (more/less) likely to fire an AP
more
What neurotransmitter is used for EPSPs?
glutamate! Think MSG and chinese restaurant syndrome and getting super wired!
What neurotransmitter is used for IPSPs?
GABA. That’s why its in OTC sleep meds!
An IPSP makes the postsynaptic neuron (more/less) likely to fire an AP
less
Can an IPSP still cause a depolarization of membrane potential?
Yes, as long as the Erev remains below the threshold.
Ion channels nonselective for cations or selective for Ca ions mediate (blank)
EPSPs
Ion channels selective for K mediate (blank)
IPSPs
Ion channels selective for Cl mediate (blank) if Ecl is negative to threshold or (blank) if ECl is positive to threshold
- IPSPs
2. EPSPs
Erev>threshold= (blank)
excitatory
Erev<threshold= (blank)
inhibitory
Can a neuron sum input from thousands of inputs?
YES
Will one AP at one synapse cause an EPSP to reach threshold
Hellllll no!
Will one AP at one synapse cause an end plate potential at a nueromuscular junction to reach threshold?
Good god yes!
It takes (multiple/single) APs at (multiple/single) synapses for an EPSP to reach threshold
multiple, multiple
Can APs arrive at different times and still be summed to generate an EPSP?
NO, they have to arrive at nearly the same time
What is the effect of the summation of suprathreshold EPSPs and an IPSP?
the IPSP will drag the summed EPSPs down towards the target potential of the inhibitory signal
Is the summation of EPSPs and IPSPs linear?
NO
Can postsynaptic neurons signal back to the presynaptic neuron?
YES
What are the retrograde transmitters? (4)
- Nitric Oxide
- Carbon monoxide
- Endocannabinoids
- Prostaglandins
In retrograde signaling, glutamate causes an increase in (blank) influx leading to a retrograde signal
postsynaptic calcium
Can a neurotransmitter inhibit its own release?
YES
Where are the receptors located for neurotransmitter self-regulation?
on the presynaptic terminal
Are glia important in neurotransmission?
Yes, they are involved in clearing the synaptic cleft
What current type are the calcium channels used for neurotransmitter release?
PQ or N
What inhibits PQ calcium channels?
agotaxon
What inhibits N calcium channels?
conotoxin
