Test 2 - Signaling Across Synapses Flashcards
Neurotransmitter
molecules released by presynaptic neurons that travel across a synaptic cleft and act ona postsynaptic target cell (muscle cell or another neuron)
Neuromuscular junctions
nerve to muscle cell communication
EPP
End plate potential - depolarization produced in postsynaptic muscle cell (muscle cell recdeving info from a neuron)
Active zone
binding site of neurotransmitter after crossing cleft
Postsynaptic density
grouping of receptors on membrane of cell receiving signal (i.e. muscle cells will have Ach receptors as p.s. density)
How does a vesicle fuse with the plasma membrane of the end of the axon?
- Axon potential of an axon reaches the axon terminal and the voltage change opens ion channels and releases calcium
- Synaptotagmin (in vesicle membrane) is a calcium sensor and binds to calcium
- When calcium ion channels open they change conformation and cause a complex of RIM, RIMBP and RAB3 (attached to vesicle), which when activated draws synaptic vesicle into close proximity of Ca channels tethering vesicle to cleft membrane
- The complex can also active a change to actin cytoskeleton which polymerized the leading edge and pushes vesicle closer to the plasma membrane.
- During this Complexin activates the SNARE complex (V-snare to T-SNARE binding catalyzed by SM proteins)
What are the interactions between the pre- and post- synaptic proteins during vesicle fusion?
- Cadherin (homophilic binding)
- Neurexin (pre-) & Neuroligin (post-) - heterophilic binding
What are the 3 ways of synaptic clearing?
- Diffusion (slow - product just leaves out sides)
- Enzymatic digestion/cleavage (fast - destruction of NT)
- Recycling (reuptake)
What is the most probable mechanism for synaptic vesicle and neurotransmitter recycling?
Synaptic vesicle recycling - specifically kiss and run mechanism that is mediated by Clathrin - which recycles vesicle & neurotransmitter at the same time - don’t need a mechanism for digestion if recycling
What is a facilitating synapse?
post-synaptic cell receives information and causes 2 cells to come together
What is a depressing synapse?
leads to a shut down on post-synaptic cells and they go farther away from each other
Kiss and run mechanism
vesicle comes back really quick and takes back whatever is left (almost doesn’t complete fusing) - most likely usually the correct mechanism saves the cell time and energy- clathrin-mediated
Examples of excitatory neurotransmitters
- acetylcholine
- glutamate
- neuropeptides
Examples of inhibitory neurotransmitters
- GABA
- glycine
- neuropeptides
Examples of modulatory neurotransmitters
- serotonin
- dopamine
- norepinephrine
- histamine
- neuropeptides
Neuropeptides
usually co-released from excitatory, inhibitory, or modulatory neurons; neurosecretory cells
- from hypothalamus for physiological needs
- ex. oxytocin
Location of Ach vs. glutamate
Ach - all over nervous system & muscle
Glutamate - brain & sensory
Where is glycine found?
brainstem & spinal cord (post-brain CNS)
Acetylcholine
depolarizes muscle membrane
How does acetylcholine lead to depolarization and contraction of muscle cells
- Ca release causes action potential which triggers ACH release from the motor axon terminal
- Ach diffuses across synaptic cleft, binds to Ach receptors
- Ach receptors conduct nonselective cation conductance (more Na in, and K out) 4. which produces depolarization
- If threshold is reached, muscle cell fires action potential
- This leads to muscle contraction
Ionotropic receptor
a neurotransmitter binds to a ligand-gated ion channel subfamily (quick)
What is the major difference between the two?
speed
Metabotropic receptor
binds to GPCR (slow)
What is an agonist for a receptor and how does it affect a cell to which it binds
a molecule that mimics another endogenous molecule (NT) - when bound it can increase or decrease the signal
What usually blocks the ion channel in and NMDAR and is released when glutamate binds to an NMDAR?
At rest it is blocked by magnesium (Na trickles in - minimal effect)
When glutamate binds magnesium comes off ca and an come in and there is a larger effect (depolarized)
What influxes into the cell when glutamate binds to an NMDAR?
Ca and Na
What is the role of calcium after it comes into the cell?
most common 2nd messenger in chemical signaling - facilitating synapse - gene expression
How does actin polymerization affect facilitating synapses?
CAMKII changes structure of actin - another way to grow cell closer together
GABA and glycine are both inhibitory, so what is the difference in ion type that influxes when you compare GABA or glycine?
ionotropic - glycine & GABAa receptors - selective for anions (e.g. Cl-)
metabotropic - GABAb receptors - intracellular signaling to open K+ channels
- both cause hyperpolarization which is not going to send action potential - therefore inhibitory
What is the difference in Ach receptor types in skeletal muscles vs. cardiac muscle and what is the outcome of the differences?
skeletal - ionotropic - Ach speed up/activates skeletal contraction
heart- metapotropic - Ach slows heart rate (here the K going out hyperpolarizes the reverse is true for the muscle cell)
How can presynaptic depression occur?
It occurs by stopping the pre-synaptic cell from releasing what it has been releasing overtime - usually reuptake of Ca and closing Ca channels is what stops NT release
What can be said about the placement of synapses/wiring during development?
axon will grow to find somewhere to receive its NT if its neighbor won’t receive it
