Lecture 5: Chemical Synaptic Transmission; Synaptic Integration & Specialized Synapses Flashcards
where are acetylcholine receptors found in the NMJ
crests of the folds
synaptic cleft distance
30 nm
NMJ receptor density
10000 receptors/square micron
acetylcholinesterase function
getting acetylcholine out of the synapse after it is released, while still leaving enough Ach to cause a quick muscle twitch (effectively stops signaling process)
- density: 2600 molecules / square micron
safety factor
the ratio of excess NT release required for excitation of the muscle fiber under nominal conditions at the NMJ
what is the safety factor in mammals
3-5
purpose of safety factor
ensures reliable firing of the NMJ, maximizes the number of EPSPs
organophosphate pesticide function
prevents Ach esterse from catalyzing Ach
what happens when there is too much Ach in the NMJ
constant firing, prolonged muscle contraction
what do postganglionic axons terminate in
presynaptic varicosities
presynaptic varicosities characteristics
unmyelinated & metabotropic, signals quite small
- good for long-scale stuff like raises & decreases in heart rate
what is the probability of NT release following AP in central synapses
low probability
Granseth (2006) experiment significance
showed that individual traces show no change in fluorescence; only see change in fluorescence when a larger number of APs fire
- used pH-mediated changes in fluorescence as a measure for vesicle fusion
what causes reliability on a neuron
greater number of synapses
what other factors determine whether an input is excitatory or inhibitory
reversal potential of the neuron and of the ions
what happens if the reversal potential for an ion is above the membrane threshold for delivering an AP
activating that receptor/channel = excitatory
what happens if an ion’s reversal potential is below the neuron’s AP threshold
then it is inhibitory
what kind of inputs are excitatory
depolarizing inputs that make you more likely to fire an AP
what kind of inputs are inhibitory
depolarizing inputs that make you less likely to fire an AP, and hyperpolarizing inputs that make you less likely
EPSP
excitatory postsynaptic potential: bring neuron closer to firing
IPSP
inhibitory postsynaptic potential: reduce the likelihood that a neuron will fire
developing neurons’ chloride concentration
high [Cl-], due to high Na+/K+/Cl- cotransporter expression
Berglund (2006) and Obata (1978) experiments contribution
found that most neurons are under constant inhibitory control; dysregulation causes abnormal activation & circuits
how does distance from soma affect significance
synapses carry more weight if they are closer to the soma
spatial summation
simultaneous inputs from multiple synapses sum to generate a larger EPSP
temporal summation
one synapse fires 2+ times in rapid succession
- EPSPs sum to depolarize the neuron more than a single EPSP would
what did Stuart & Sakmann (1994) find about dendritic current
they found that initiating an AP by injecting current directly into a dendritic branch far from the soma was enough to deliver an AP
- usually, the AP initiated at the soma before back-propogating through the dendrites
what determines CA1 neuron postsynaptic potential
summing EPSP & IPSP
