Lecture 11- Integration of synaptic information

Question 1

what is synaptic integration?

Answer 1

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

Question 2

what factors play important roles in how the synaptic information will add up? (4)

Answer 2

AP frequency
divergence and convergence
temporal and spatial summation
location of synapses on postsynaptic cell

Question 3

what determines action potential frequency?

Answer 3

the strength of a stimulus

Question 4

what is a divergent pathway?

Answer 4

one presynaptic neuron branches to affect a larger number of postsynaptic neurons

Question 5

what is a convergent pathway?

Answer 5

many presynaptic neurons provide input to influence a smaller number of postsynaptic neurons (one neuron receives many signals)

Question 6

when does temporal summation occur?

Answer 6

occurs when two graded potentials from one presynaptic neuron occur close together in time

Question 7

what is no summation? what happens?

Answer 7

two subthreshold graded potentials will not initiate an action potential if they are far apart in time

Question 8

what occurs in a summation causing action potential?

Answer 8

if two subthreshold potentials arrive at the trigger zone within a short period of time, they may sum and initiate an action potential

Question 9

what is spatial summation?

Answer 9

when the currents from nearly simultaneous graded potentials combine

Question 10

what occurs in summation of several subthreshold signals? (3 steps)

Answer 10

1. three excitatory neurons fire, their graded potentials separately are all below threshold
2. graded potentials arrive at trigger zone together and sum to create a suprathreshold signal
3. an action potential is generated

Question 11

what occurs in postsynaptic inhibition?

Answer 11

1. one inhibitory (-) and two excitatory neurons fire
2. the summed potentials are below threshold so no action potential is generated

Question 12

what are the locations of synapses on post synaptic cells?

Answer 12

axodendritic
axosomatic
axoaxonic

Question 13

where is the axodendritic synapses?

Answer 13

dendrites

Question 14

where is the axosomatic synapses?

Answer 14

soma/ cell body of cell

Question 15

where is the axoaxonic synapses?

Answer 15

trigger zone
axon
synaptic terminal

Question 16

out of the 3 locations of synapses which one is the most powerful? which is the least?

Answer 16

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

Question 17

what is synaptic plasticity?

Answer 17

ability of neurons to change synaptic strength through long term potentiation (LTP) or long term depression (LTD)

Question 18

what does long- term potentiation study?

Answer 18

underlies the process of learning and memory and happens in many types of neurons

Question 19

what are the best studied neurons that exhibit LTP in mammalian brain?

Answer 19

hippocampus (critical for long term memories)

Question 20

what did Brenda Milner discover?

Answer 20

discovered that the hippocampus was critical for storage of memories

Question 21

what would happen if a part of your hippocampus was removed

Answer 21

cant remember new long term memories

Question 22

what is long term potentiation(LTP)?

Answer 22

long lasting increase in amplitude of depolarization caused by single presynaptic action potentials

Question 23

what does LTP require? 2

Answer 23

NMDA & AMPA receptors in the post synaptic membrane
metabotropic glutamate receptors

Question 24

what are the 3 types of glutamate receptors that play a key role in LTP?

Answer 24

metabotropic
AMPA (carries mostly Na+)
NMDA (carries Na+ and Ca++)

Question 25

recall: what must happen to NMDA receptors for them to open?

Answer 25

cell must be depolarized

Question 26

what are the 5 steps to induce LTP?

Answer 26

1. high frequency stimulation of presynaptic neuron, release of glutamate
2. activation of AMPA receptors leads to depolarization of the post- synaptic neuron via EPSPs
3. continued synaptic activity also activates metabotropic glutamate receptors which release intracellular stores of Ca++ ions
4. postsynaptic terminal experiences large increase in intracellular Ca++ concentration
5. increased Ca++ leads to activation of several kinases