Synaptic Transmission Flashcards
Some of these may be docked already without needed calcium to make them
Vesicles
These are procured by the spontaneous release of the contents of one vesicle
Mini postsynaptic potentials
This depends on internal resistance (ri) and membrane resistance (rm)
Length constant
These are easier to study than CNS synapses
NMJ
SLIDE 27
SLIDE 27
These synapses allow for the coordinate firing of cells or neurons
Electrical synapses
These are similar to CNS synapses
NMJ
There are thousands of these on every neuron
Channels
Synapses that are evolutionarily old and present in many organisms
Electrical synapses
Faster response, ionotropic receptors
Ligand gated
Summation that occurs when many signals come down the same axon quickly
Temporal summation
Synapses between dendrites and dendrites
Dendrodendritic
How can glia enhance presynaptic function?
Create more NT release due to cholesterol from glial cells
These synapses are usually inhibitory
Grays type 2
What types of things can G-proteins activate?
G-protein activated ion channels and second messengers
These can regulate synaptic development by creating silent but structurally normal synapses, enhanced presynaptic functions, and being postsynaptically active (functions)
Glia
What happens to voltage over a distance that can be shown in a formula?
It will dissipate over a distance
What does connexin make up and what does that make up?
Connexin makes up a connexon which makes up a gap junction (a connexon of two cells coming together to form one pore)
These are fast, large, reliable synapses. They release a lot of vesicles (lots of NTs)
NMJ
Usually dendrites cant fire these
APs
What can happen to the downstream steps for some time after the G protein has been inactivated?
They can proceed for some time
What happens after the G protein has activated or inhibited downstream effectors?
It eventually hydrolyzes the GTP and returns to the inactive form, terminating the signaling. It goes back to inactive to wait for the next signal
Comparing miniature and evoked potentials can be used to decide how many of these are released
Vesicles (NTs)
These are not released at the active zone and have a lower time course (50 msec), they generally are released in response to higher Ca levels (granules are parked further back)
Peptide NTs
There are present in all cells as basic amino acids used in protein synthesis, but are loaded into synaptic vesicles by specific vesicular transporters
Glycine and glutamate
When a neuron has two NTs and releases them at the same time, they are in the same vesicle
Co-release
Eventhough activation of GPCRs doesn’t immediately depolarize or hyperpolarize the cell, they can do this by acting through second messenger systems
Modulate signaling
What does ACh cause at negative membrane potentials (voltages)?
Inward current
This depends on diameter and electrical properties of cytoplasm and is constant in a mature neuron
Internal resistance
These are slower acting and are seen with amino acid, amine, and peptide NTs
GPCRs
What do axons often do at NMJs?
Spread out to create lots of surface area
This depends on synaptic activity and how many ion channels are open
Membrane resistance
These activate receptors and mimic the actions of NTs. Examples include nicotine
Agonists
These synapses are common in mammalian CNS, glia, cardiac muscle cells, smooth muscle, epithelial cells, liver cells
Electrical synapses
What are enzymes markers for in cells?
Markers for what NT the cell makes
Is the synapse empty and is it organized?
It is not empty and it is highly organized
Synapses between axons and axons
Axoaxonic
What is contained in a secretory granule (dense-core vesicle)
Protein NTs (they show up darker on EM views of a synapse)
Synaptic vesicles contain a large number of these specific vesicle SNARES
v-SNARES
These are between motor neurons and muscle
Neuromuscular junction (NMJ)
These block receptor activation. Examples are curare and cobra venom
Antagonists
What happens to many NTs in the synapse to terminate signaling (happens to the vast majority of NTs)?
Taken up into the neuron or nearby glial cells (astrocytes)
These types of synapses occur due to symmetrical membrane thickness at synapse
Grays type 2, usually inhibitory
This toxin inc ACh release
Black widow venom
What are synaptic vesicles bound to in the presynaptic cell?
Docking proteins
We want this to be high for a longer length constant
Membrane resistance
These produce opening of VG Ca channels producing large influx of Ca
APs
When a neuron has two NTs and releases them at the same time, they are in two different vesicles
Co-transmission
Only small molecules and ions can move through these
Gap junctions
Why can dendrites with Na, Ca, and K channels synapse further from the axon hillock?
They can generate APs because the depolarizing input is transmitted further. It doesn’t just diffuse, it gets replenished
What does the I/V (current/voltage) curve of a non-voltage dependent channel look like?
It is a straight line (SLIDE 48)
What is the equilibrium potential of Cl?
-65 mV
This is not empty and it contains extracellular matrix proteins which help organize the synapse and enzymes which can break down NTs
Synaptic cleft
Dendrites cant fire APs but they can do this
Add current
This part of the transmitter gated channel is usually closed until ligand binds, or is stabilized in the open state by an agonist
Pore (channel)
these are recycled by endocytosis in multiple ways
Vesicle membranes
Most of these are treated as electrically passive cables
Dendrites
If inhibitory synapses are present between the site of input (on soma or most likely dendrites) and the axon hillock, opening of Cl channels can do this to the depolarization
Shunt or short circuit the depolarization
What do various NTs have that is distinct for them?
Distinct synthetic pathways
These form a continuous channel pore that is open always and connects two cells
Gap junction channels
Discovered chemical synapses in 1921 and the first NT, vagusstoff (ACh)
Loewi
These can vary in structure seen as differences in membrane thickness
Pre and postsynaptic sides