Lecture 11- Integration of synaptic information Flashcards
what is synaptic integration?
the idea that whether or not the postsynaptic neuron fires an action potential depends on the grand sum of synaptic activity acting on the cell
what factors play important roles in how the synaptic information will add up? (4)
AP frequency
divergence and convergence
temporal and spatial summation
location of synapses on postsynaptic cell
what determines action potential frequency?
the strength of a stimulus
what is a divergent pathway?
one presynaptic neuron branches to affect a larger number of postsynaptic neurons
what is a convergent pathway?
many presynaptic neurons provide input to influence a smaller number of postsynaptic neurons (one neuron receives many signals)
when does temporal summation occur?
occurs when two graded potentials from one presynaptic neuron occur close together in time
what is no summation? what happens?
two subthreshold graded potentials will not initiate an action potential if they are far apart in time
what occurs in a summation causing action potential?
if two subthreshold potentials arrive at the trigger zone within a short period of time, they may sum and initiate an action potential
what is spatial summation?
when the currents from nearly simultaneous graded potentials combine
what occurs in summation of several subthreshold signals? (3 steps)
- three excitatory neurons fire, their graded potentials separately are all below threshold
- graded potentials arrive at trigger zone together and sum to create a suprathreshold signal
- an action potential is generated
what occurs in postsynaptic inhibition?
- one inhibitory (-) and two excitatory neurons fire
- the summed potentials are below threshold so no action potential is generated
what are the locations of synapses on post synaptic cells?
axodendritic
axosomatic
axoaxonic
where is the axodendritic synapses?
dendrites
where is the axosomatic synapses?
soma/ cell body of cell
where is the axoaxonic synapses?
trigger zone
axon
synaptic terminal
out of the 3 locations of synapses which one is the most powerful? which is the least?
axoaxonic on trigger zone
axodendritic is the least powerful because its furthest away from the trigger zone so it would be very disintegrated by the time it gets to the trigger zone
what is synaptic plasticity?
ability of neurons to change synaptic strength through long term potentiation (LTP) or long term depression (LTD)
what does long- term potentiation study?
underlies the process of learning and memory and happens in many types of neurons
what are the best studied neurons that exhibit LTP in mammalian brain?
hippocampus (critical for long term memories)
what did Brenda Milner discover?
discovered that the hippocampus was critical for storage of memories
what would happen if a part of your hippocampus was removed
cant remember new long term memories
what is long term potentiation(LTP)?
long lasting increase in amplitude of depolarization caused by single presynaptic action potentials
what does LTP require? 2
NMDA & AMPA receptors in the post synaptic membrane
metabotropic glutamate receptors
what are the 3 types of glutamate receptors that play a key role in LTP?
metabotropic
AMPA (carries mostly Na+)
NMDA (carries Na+ and Ca++)
recall: what must happen to NMDA receptors for them to open?
cell must be depolarized
what are the 5 steps to induce LTP?
- high frequency stimulation of presynaptic neuron, release of glutamate
- activation of AMPA receptors leads to depolarization of the post- synaptic neuron via EPSPs
- continued synaptic activity also activates metabotropic glutamate receptors which release intracellular stores of Ca++ ions
- postsynaptic terminal experiences large increase in intracellular Ca++ concentration
- increased Ca++ leads to activation of several kinases
