Information Processing in Dendrites

What is the role of dendrites?

-Reach out to connect to relevant inputs ← collect inputs in different layers or spatial locations

-Integrate the subthreshold synaptic input ← spatial and temporal summation

Why do signals decrement in dendrites over distance?

-Axial resistance (high)

-Membrane resistance (low)

-Capacitance (charge is absorbed by membrane)

-Adverse effects of impedence mitchmatch

What are some non resistance/capacitance ways to weaken an EPSP?

-Adjacent synapses sum sublinearly← the whole is less than the sum of its parts ← why? ← opening the channels allows some charge to escape

How does a cell even the playing field between distal and proximal synapses?

-distal synapses are usually made intrinsically stronger to even things out← There conductances are higher than proximal synapses

-At the end of the day with this alteration proximal and distal will end up being equal in weight.

Dendritic geometry

-Isolating inputs ← prevents short circuiting that can occur in sublinearization and occlusion.

-Well seperate dendritici branches ^^

Why don’t inhibitory neurons usually have a stronger conductance at distal synapses (Scaling)

-Its to keep the effects of inhibition local and controlled

What is the limit of the EPSP of the strongest synapse?

-The reversal potential (0 mv)

What kinds of channels do dendrites have?

-Voltage gates calcium and sodium ← can help to make an EPSP bigger

5 properties that allow dendrites to overcome signal attentuation

1) Input resistance

2) Branch separation

3) Conductance modulation

4) Active Properites (VG NA/CA channels)

5) Spine effects

How can co-activation be allowed?

-Synchronously active synapses can be dispersed or clustered

How should each dendrite be viewed?

-Like its own separate computing unit/segment

-Each spine is biochemically isolated

-Spine neck is full of intermediate filaments, mitochrondia, ER

bAP

-backpropagating action potential

-spreads into distal dendrites

-The bAP depdens on the V-G Ca/Na channels to spread effectively ←this channel distribution varies a lot across cell type

What is the role of STDP

-Sets the timing for LTD/LTP

-Link activated synapses w/ action potential ← co-incident synapses

What are main adaptive advantages of having dendritic spines?

-Increases surface area

-Spine has a high input resistance and is not very leaky

-Also has a low capacitance which makes them fast/leads to very little charge loss.

-Spines are also very dynamic → Actively grow and shrink to catch passing axons. Can also change very frequently in adults

What are some example spine shapes?

-Stub

-Lollipop

-Mushroom

-Filipodia

What are the benefits of isolated synapses?

-Hard for single synapse to depolarize

-Prevents sub-linear occulsion

-Each single head can have different VG channels and properties

-Independent thresholding functions within spine or branch

Why is the biochemical content of the dendritic spine important?

-The large amount of material makes it hard for molecules like calcium, 2nd messengers, kinases, and mRNA to diffuse in

-This keeps plasticity specific and the molecular response distinct

What is the computational unit of the brain?

-Information is modified at EVERY LEVEL