Week 3: Synaptic Transmission Flashcards
Compare and contrast the structure of electrical and chemical synapses.
Electrical synapses occur at gap junctions (3nm gap between cells, bridged by a pore formed by connexins). Ions can pass directly from one cytoplasm to the next.
Chemical synapses occur at synaptic cleft (20 - 50nm wide, filled with matrix of fibrous extracellular protein).
What are the three major groups of neurotransmitters?
amino acids,
amines
peptides
List the three major amino acids used as neurotransmitters.
Gamma-aminobutyric acid (GABA)
Glutamate (Glu)
Glycine (Gly)
Describe the general methods of synthesis and storage of neurotransmitters
Small neurotransmitters (amino acids and amines) are synthesized in the synaptic terminal from a precursor molecule. They are stored in synaptic vesicles.
Neuropeptides are transported from the soma and are stored in secretory granules.
Which of the following are an amino acid? (select all that apply)
a. Dopamine (DA)
b. Gamma-aminobutyric acid (GABA)
c. Epinephrine
d. Dynorphin
e. Somatostatin
f. Glycine (Gly)
b. Gamma-aminobutyric acid (GABA)
f. Glycine (Gly)
Which of the following are an amine? (select all that apply)
a. Dopamine (DA)
b. Gamma-aminobutyric acid (GABA)
c. Epinephrine
d. Dynorphin
e. Somatostatin
f. Glycine (Gly)
a. Dopamine (DA)
c. Epinephrine
What are SNARE proteins?
SNARE proteins allow one membrane to snare another. Each SNARE protein has a lipid-loving end that embeds itself within a membrane, and a longer end that projects into the cytosol.
The SNARE (SNAP receptor) are thought to be
involved in the fusion of vesicles to the plasma
membrane
What is synaptotagmin?
Synaptotagmin is the Ca2+ sensor. It rapidly triggers vesicle fusion and thus transmitter release.
What is a connexon?
A connexon is a pore formed by six connexins. Two connexons (one from each cell) form a gap junction.
They allow for the flow of ions. The pore’s diameter is relatively large (1-2nm).
Cells connected by gap junctions are said to be…?
a. Invertebrate cells
b. Electrically coupled
c. Postsynaptic
b. electrically coupled
List the six major amines used as neurotransmitters.
Acetylcholine (ACh) Dopamine (DA) Epinephrine Histamine Norepinephrine (NE) Serotonin (5-HT)
List the five CNS chemical synapses, as distinguished by which part of the neuron is postsynaptic.
- Axodendritic: axon to dendrite
- Axosomatic: axon to cell body
- Axoaxonic: axon to axon
- Axospinous: axon to dendritic spine
- Dendrodendritic: dendrite to dendrite
Which of the following is NOT a peptide?
a. Cholecystokinin (CCK)
b. Dynorphin
c. Enkephalins (Enk)
d. N-acetlyaspartylglutamate (NAAG)
e. Histamine
f. Somatostatin
g. Substance P
e. Histamine
Which of the following is NOT a peptide?
a. Cholecystokinin (CCK)
b. Dynorphin
c. Enkephalins (Enk)
d. N-acetlyaspartylglutamate (NAAG)
e. Histamine
f. Somatostatin
g. Substance P
e. Histamine
What are asymmetrical synapses?
Chemical synapses
Gray’s Type I synapse
Memrane differentiation is thicker on the postsynaptic side than the presynaptic side (aka more proteins within membrane on the postsynaptic side)
Usually excitatory
What’s the difference between synaptic vesicles and synaptic granules.
Synaptic vesicles hold amino acids and amines.
Synaptic granules hold neuropeptides, and are transported from the soma.
What are the five major mechanisms of neurotransmitter release?
- Process of exocytosis stimulated by intracellular calcium [Ca2+]
- Proteins alter conformation—activated
- Vesicle membrane incorporated into presynaptic membrane
- Neurotransmitter released into cleft
- Vesicle membrane recovered by endocytosis
A CNS synapse that connects axon to dendrite is called…?
a. Axodendritic
b. Axosomatic
c. Dendrodendritic
d. A gap junction
a. Axodendritic
What is EPSP?
transient postsynaptic membrane depolarization
caused by presynaptic release of neurotransmitter
What is the difference between Gray’s Type I and Gray’s Type II synapses?
Gray’s type I: asymmetrical, usually excitatory
Gray’s type II: symmetrical, usually inhibitory
A dendrodendritic synapse connects ____ to ____?
a. axon to dendrite
b. axon to axon
c. dendrite to dendrite
d. axon to dendritic spine
c. dendrite to dendrite
What is IPSP?
transient hyperpolarization of postsynaptic
membrane potential caused by presynaptic release of
neurotransmitter
Which of the following is true regarding membrane differentiations? Select all that apply.
a. Presynaptic membrane differentiations are called “active density”
b, They are proteins within the membrane on either side of the synaptic cleft
c. Postsynaptic membrane differentiations are called “postsynaptic zones”
d. They are usually symmetrical (of a similar thickness) in inhibitory synapses
b, d
Corrections:
a. Presynaptic membrane differentiations are called “active ZONES”
c. Postsynaptic membrane differentiations are called “postsynaptic DENSITY”
Comparing electrical synapses with chemical synapses, which of the following statements is CORRECT?
a. Both types of synapses can operate equally well in either direction
b. In general chemical synapses have shorter transmission delays than electrical synapses.
c. Electrical synapses usually amplify signals as they pass from the presynaptic to the postsynaptic neuron
d. Chemical synapses are always strong enough to to trigger an action potential in the postsynaptic cell, but electrical synapses are usually too weak to trigger action potentials
e. If neuron 1 and neuron 2 are connected by an electrical synapse and a strong IPSP is triggered in neuron 1 by a GABAergic synapse, then an IPSP would also be generated in neuron 2 even if it does not have any GABAergic inhibitory synapses on it
e. If neuron 1 and neuron 2 are connected by an electrical synapse and a strong IPSP is triggered in neuron 1 by a GABAergic synapse, then an IPSP would also be generated in neuron 2 even if it does not have any GABAergic inhibitory synapses on it
Which of the following statements regarding neuropeptide synaptic transmission is CORRECT?
Select one:
a. Unlike the release of small neurotransmitters such as glutamate, neuropeptide release is not dependent on Ca++ entry at the presynaptic terminal
b. Neuropeptide release usually occurs at the same action potential frequency as that required for release of small neurotransmitters such as amino acids
c. Neuropeptides are contained within the same synaptic vesicles as small neurotransmitter molecules, such as glutamate
d. In response to an action potential in the nerve terminal, the release of neuropeptide transmitters is much faster than that of small neurotransmitters, such as amino acids
e. The release of neuropeptide transmitters usually requires a higher Ca++ concentration in the presynaptic terminal than is required for release of small neurotransmitters, such as glutamate
e. The release of neuropeptide transmitters usually requires a higher Ca++ concentration in the presynaptic terminal than is required for release of small neurotransmitters, such as glutamate
AMPA and NMDA receptors are:
Select one:
a. both G-protein coupled receptors
b. both highly permeable to Ca++ ions
c. both receptors for glutamate
d. never present at the same synapse
e. both voltage-gated as well as ligand-gated
c. both receptors for glutamate
Vesicular neurotransmitter transporters:
Select one:
a. transport the neurotransmitter from the presynaptic to the postsynaptic membrane
b. transport the neurotransmitter from the cell body to the axon terminal
c. transport the neurotransmitter from the cytoplasm and concentrate it in synaptic vesicles
d. are blocked by botulinum toxin
e. transport the neurotransmitter back to the cell body for recycling
c. transport the neurotransmitter from the cytoplasm and concentrate it in synaptic vesicles
SNARE proteins are synaptic proteins that:
Select one:
a. are located in postsynaptic thickenings
b. are involved with the docking of synaptic vesicles at the active zones
c. coat the vesicle membrane with protein so that it can be recycled
d. act as a Ca++ detector to trigger vesicle exocytosis
e. pump neurotransmitter molecules back into the nerve terminal
b. are involved with the docking of synaptic vesicles at the active zones
What is a connexon?
- Pore formed by six connexins
- Gap junction channel formed by two connexon
- Between electrically coupled cells
If cells a and b were electrically coupled, what would be expected if cell a experienced an action potential?
Cell b would experience a simultaneous action potential.
When an action potential reaches the axon terminal, voltage-gated Ca++ channels open and allow Ca++ ions to enter the terminal. Which of the following statements most accurately describes the function of these Ca++ ions?
a. The Ca++ ions cause synaptic vesicles to enter the synaptic cleft and release their neurotransmitter molecules
b. The Ca++ ions only cause synaptic vesicles to move towards the active zones of the presynaptic membrane
c. The Ca++ ions cause synaptic vesicles to dock at the active zones of the presynaptic membrane
d. The Ca++ ions bind to the postsynaptic membrane, triggering an action potential in the postsynaptic neuron
e. The Ca++ ions cause the membrane of synaptic vesicles to fuse with the presynaptic membrane, forming a pore though which neurotransmitter molecules
can enter the synaptic cleft
e. The Ca++ ions cause the membrane of synaptic vesicles to fuse with the presynaptic membrane, forming a pore though which neurotransmitter molecules
can enter the synaptic cleft
Which of the following is CORRECT regarding peptides?
a. They are synthesized in the cytosol of the terminal
b. They are embedded into vesicles by vesicle neurotransmitter transporters
c. They are carried to the axon terminal by axoplasmic transport
d. They cause rapid changes in the membrane potential of the postsynaptic cell
c. They are carried to the axon terminal by axoplasmic transport
a, b and c apply to amines and amino acids
Which of the following regarding electrical synapses is NOT true?
a. They occur in interneurons within the cerebral cortex
b. They occur where synchronization is important, such as in the inferior olive in the brainstem nucleus
c. They are formed by a single connexon
d. Ions flow directly from the cytoplasm of one cell to the cytoplasm of another cell
c. They are formed by two connexon
a may link to the binding problem
Summarise the events occurring in chemical synaptic transmission.
Transmitter synthesised ->
transmitter stored in vesicles ->
AP generated in presynaptic neuron ->
AP reaches terminal ->
AP opens voltage-gated Ca2+ channels ->
Ca2+ causes vesicle to fuse with membrane ->
Exocytosis ->
Transmitter diffuses across cleft ->
transmitter binds to receptors on postsynaptic membrane ->
Transmitter alters function of the receptor protein ->
Transmitter may be degraded in cleft; reuptaken to be broken down; vesicles recycled
List the nine “true” or “classic” neurotransmitters, which cause rapid change in the postsynaptic potential.
GABA Glutamate Glycine Acetylcholine Dopamine Adrenaline (epinephrine) Noradenaline (norepinephrine) Histamine Serotonin
Arrange the following steps of exocytosis in order:
a. Vesicle fuses to membrane and releases contents
b. Vesicle is eventually recycled by endocytosis
c. A synaptic vesicle loaded with neurotransmitter is docked and primed
d. Influx of Ca2+ through voltage-gated Ca2+ channels
c, d, a, b
- A synaptic vesicle loaded with neurotransmitter is docked and primed
- Influx of Ca2+ through voltage-gated Ca2+ channels
- Vesicle fuses to membrane and releases contents
- Vesicle is eventually recycled by endocytosis
Which of the following is CORRECT regarding Ca2+?
a. It binds to synapotagmin, catalyzing membrane fussion
b. Unlike the release of small neurotransmitters such as glutamate, neuropeptide release is not dependent on Ca++ entry at the presynaptic terminal
c. It regulates gap junctions and synaptic clefts through different mechanisms
d. It affects only the presynaptic neuron
a. It binds to synapotagmin, catalyzing membrane fussion
List the three steps of G-protein-coupled receptors
- Neurotransmitter binds to receptor protein embedded in the postsynaptic membrane
- Receptor proteins activate small proteins: G-proteins, which are free to move along the intracellular face of the postsynaptic membrane
- Activated G-proteins activate effector proteins
How do Botulinum toxin and tetanus toxin prevent the release of neurotransmitters?
Botulinum toxin and tetanus toxin block vesicle
release by cleaving the SNARE protein
If a channel is permeable to only a single ion the reversal potential is equal to…?
a. a negative value of
membrane potential
b. the equilibrium potential for that ion
c. a positive value of
membrane potential
d. A steady outward current causing a depolarisation
b. the equilibrium potential for that ion
Describe the mechanisms of neurotransmitter release.
Process of exocytosis stimulated by intracellular calcium
• Proteins alter conformation—activated
• Vesicle membrane incorporated into presynaptic membrane
• Neurotransmitter released into cleft
• Vesicle membrane recovered by endocytosis
A transient postsynaptic membrane depolarization
caused by presynaptic release of neurotransmitter is known as…?
EPSP
If an ACh ionotropic receptor
channel is permeable
to Na+ and K+, and the membrane potential was -40mV before ACh is applied, in which direction will net current flow?
Net current will glow inward, causing a depolarisation.
What is an IPSP?
transient hyperpolarization of postsynaptic membrane potential caused by presynaptic release of
neurotransmitter
What do receptor agonists do?
Bind to receptors and mimic actions of a neurotransmitter
How are IPSPs caused?
AP arrives at presynapitc terminal -> Neurotransmitter released -> Transmitter binds to Cl- permeable transmitter-gated ion channels in postsynaptic membrane -> Cl- enters the postsynaptic cell -> Cell becomes hyperpolarised
Which of the following is CORRECT regarding autoreceptors?
a. They are presynaptic receptors sensitive to the neurotransmitter released by the postsynaptic cell.
b. They are usually ionotropic
c. Consequences of activating autoreceptors vary; common effect is inhibition of neurotransmitter release.
d. They are found on the membrane of the postsynaptic terminal
e. They are mostly activated by Ca2+
c. Consequences of activating autoreceptors vary;
common effect is inhibition of neurotransmitter release.
AChE cleaves ACh when ACh is in high concentrations at neuromuscular junctions. This is an example of:
a. Desensitization prevention
b. Reuptake
c. Autoreceptor feedback
d. Diffusion
e. Receptor antagonists
a. Desensitization prevention
Which of the following is CORRECT regarding the quantum?
a. It is dependent on the number of postsynaptic receptors available
b. It is an integer
c. It is the number of neurotransmitter molecules in a single vesicle
d. It is a divisible unit
c. It is the number of neurotransmitter molecules in a single vesicle
Which of the following is NOT true regarding EPPs.
a. They are end plate potentials
b. They are recorded in the postsynaptic membrane
c. EPP is a large depolarizing synaptic potential that normally always exceeds
threshold for an action potential
d. EPP is a small spontaneous depolarizing
potentials (< 1 mV) that can be recorded at many CNS synapses
d. EPP is a small spontaneous depolarizing
potentials (< 1 mV) that can be recorded at many CNS synapses
Which of the following is CORRECT regarding temporal summation?
a. EPSPs generated simultaneously at different sites
b. Allows organism to differentiate intensity of a stimulus
c. was taken as evidence for
quantal release of neurotransmitter
d. Take membrane
potential away from action potential threshold
b. Allows organism to differentiate intensity of a stimulus
What is shunting inhibition?
Action of inhibitory synapses—Take membrane
potential away from action potential threshold.
Inhibitory synapses exert powerful control over
neuron output.
Inhibitory synapses do not need to hyperpolarize the postsynaptic neuron to produce inhibition
Inhibitory synapses are much more effective when they are located close to the trigger zone
Why don’t GABA inhibitory synapses have to hyperpolarize the
postsynaptic neuron
to produce inhibition?
a. They are located close to the trigger zone
b. They use Cl- channels
c. They are axodendritic
d. They are antagonists that block the effects of excitatory neurotransmitters
b. They use Cl- channels: ECl- is close to -65mV, so no flow at resting; but Cl- flows into the cell if ESPS happens, counteracting it
