Chapter 5 (exam 2) Flashcards
What is a synapse?
Functional contacts between neurons.
What are the types of synapses?
Electrical synapses and chemical synapses.
What characterizes electrical synapses?
Gap junctions allow cytoplasmic continuity between neurons.
What are connexons?
Hemichannels formed by connexins that allow communication between neurons.
How long do connexons typically remain stable?
Stable for a couple of hours.
What can pass through large pores of connexons?
ATP, nutrients, and second messengers.
What is the speed and directionality of electrical synapses?
Fast and bidirectional flow
What is often the configuration of electrical synapses?
Often dendrodendritic with no set presynaptic and postsynaptic roles.
What is the typical function of electrical synapses?
Typically excitatory, but can also be inhibitory.
Where are electrical synapses commonly found?
In breathing and interneurons, such as in the hippocampus.
What was observed in mice without brain connexons?
Slight delay in temporal motor precision and inability to distinguish novel from previously seen objects.
What characterizes chemical synapses?
Presynaptic neuron releases neurotransmitter into the synaptic cleft.
Where are neurotransmitters typically stored?
In vesicles.
What is the active zone in chemical synapses?
A specialized area where small molecule neurotransmitters are released.
What is the synaptic cleft?
The area of interstitial fluid between presynaptic and postsynaptic neurons
What role do filaments in the synaptic cleft play?
They help maintain alignment of presynaptic and postsynaptic neurons.
What do postsynaptic neurons contain?
Receptors for neurotransmitters.
What is found in excitatory synapses?
Intracellular scaffolding known as postsynaptic density.
What are the typical events in a chemical synapse?
AP → VGCC open → neurotransmitter exocytosed in response to elevated Ca2+ → diffuse across cleft → bind to receptor → changes status of ion channel in postsynaptic cell → current generated → neurotransmitter removed → vesicular membrane recovered.
What did Loewi’s experiment demonstrate?
Chemical signaling by neurons using frog hearts, vagus nerve, and fluid while monitoring heart beat
What were the conclusions from Katz’s experiments?
A specific amount (a quanta) of ACh is spontaneously released, neurotransmitters must be packaged, and calcium plays a role in neurotransmitter release.
depolarization -> End plate potential -> current generated -> action potential (EPP smaller).
What did Boyd and Martin find in their experiments?
Distribution of MEPP amplitudes clustered around a single value, confirming neurotransmitters are released in vesicles.
What is the role of calcium in neurotransmitter release?
Calcium influx is necessary for neurotransmitter release and postsynaptic depolarization.
Katz used TTX, but an action potential in muscle fiber was still produced
What is the conclusion from studies visualizing Ca2+?
Calcium ions are necessary and sufficient for neurotransmitter release.
How are neurotransmitter vesicles released?
Via exocytosis.
What did electron microscopy work confirm?
The existence of vesicles and the presence of ACh in them.
What is the ‘kiss-and-run’ method?
An alternative method of neurotransmitter release that doesn’t involve complete fusion of the vesicle membrane with the axon terminal membrane.
What is the recycling process of synaptic vesicles?
A complete cycle includes reserve pool, mobilization, docking, priming, fusion, coating, budding, uncoating, endosome, and loading.
What proteins are involved in vesicle docking and fusion?
Synapsin, SNAREs (v-SNAREs and t-SNAREs), and synaptotagmin.
What is the role of clathrin in endocytosis?
It is the most important protein that attaches to the vesicular membrane.
What are the types of neurotransmitter receptors?
Ionotropic receptors and metabotropic receptors.
What distinguishes ionotropic receptors?
Ligand binding site is integral to the receptor molecule and opens an ion channel.
What characterizes metabotropic receptors?
Ligand binds to G protein coupled receptor, activating intracellular signaling cascades.
Cascade can open pore in protein that is NOT receptor
What is an EPSP?
Excitatory postsynaptic potential with a reversal potential more positive than threshold.
What is an IPSP?
Inhibitory postsynaptic potential with a reversal potential more negative than threshold.
What factors influence synaptic potentials?
Temporal and spatial summation, and glial cell influence.
How do glial cells influence synaptic transmission?
By stimulating secretion of signaling molecules that bind to receptors on neurons.
Where are neuropeptide neurotransmitters released from?
More distant locations, not in active zone
How can a neurotransmitter be removed (at a chemical synapse)?
Glial uptake or enzyme degredation
Compare neurons and muscle fibers
Muscle fibers need generation of only one end plate potential for contraction, while neurons need multiple stimuli
Explain how miniature end plate potentials were discovered by Katz
the channels were blocked by drugs that blocked ACh receptors, which shows that MEPPs are stimulated by ACh spontaneously
What did Llinas study?
- used volatage clamp of presynaptic and postsynaptic terminal
- blocking Na+ and K+ channels still had depolarization
If you inject Ca2+ into the presynaptic cell, what happens?
Depolarization in the post synaptic cell
What did biochemical staining show?
ACh in vesicles.
Math used to determine number of ACh molecules in vesicle and number needed for MEPP, and they matched
True or False: All neurotransmitters are packaged in vesicles
False
Nitric oxide and some ATP are not packaged in vesicles
True or False: all neurotransmitters packaged in vesicles released through exocytosis
False
Heuser & Reese experiment
used horseradish peroxidase to trace vesicle contents (and that they were being recycled)
Horseradish peroxidase enzyme which can break down substrate to yield a color
What are all the steps in recycling synaptic vesicles?
- reservepool
- mobilization
- docking
- priming
- fusion
- coating
- budding
8.uncoating
9.endosome - budding
- loading
- tethered, forming reserve pool
Synapsin function
tethers loaded vesicles to reserve pool
Phosphorylation of synapsin releases vesicles
SNAREs
- receptors for SNAPs
- Involved in docking, priming, and fusion
v-SNAREs
attached to vesicle
ex: Synaptobrevin
t-SNAREs
attached to axon terminal membrane
ex: Syntaxin and SNAP-25 (NOT a “soluble NSF attachment protein/SNAP”)
NSF-ATPase
regulates SNAREs by binding to SNAPs
SNAPS
soluble NSF attachment protein
Synaptotagmin
Binds calcium, leading to conformational changes causing fusion of vesicle and axon terminal membranes
attached to vesicle membrane
Munc 13 and munc 18
necessary for vesicle exocytosis (facilitate SNARE entwining)
Important components endocytosis
- Clathirin: most important protein
- three-pronged “triskelia” attach to vesicular membrane
- adaptor proteins (AP-2, AP-180)
dynamin
GTPase; pinches of clatharin-coated vesicle
uncoating of clatharin
- phosphatase (Synaptojanin)
- chaperones (HSC70 and auxilin)
acetylcholine receptor at NMJ experiment
- outside out patch clamp
- end plate current produced (microscopic inward currents)
Voltage clamp with ACh application
Macroscopic inward current
Voltage clamp myofiber (muscle cell) with electrical stimulation experiment
reversal potential not equal to equilibrium of any single ion (determined these experimentally)
What happens to reversal potential of you decrease extracellular Na+?
shifts left; more negative reversal potential for the channel
What happens to reversal potential when you increase extracellular K+?
shift right; reversal potential becomes more positive
EPSP: Reversal potential (equilibrium potential) more ___ than threshold
postive
IPSP: Reversal potential (equilibrium potential) more ___ than threshold
negative
Temporal Summation
high frequency stimulation at the same synapse
Spatial summation
simultaneous stimulation at multiple locations
How can glial cells influence synaptic transmission?
- Modulate neurotransmitter release
- Modulate signaling in postsynaptic neuron
- Role in plasticity
- Prune synapses
