Voltage Propagation along the dendrite

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Aims of this Lecture

- Revise the electrical properties of the membrane

• Describe shape and electrical properties of spines

• Examine the role of the dendrite in the propagation of excitatory post-synaptic potentials (EPSP)

• Discuss the role of voltage-gated channels in potential propagation

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Legnth constant is how far changes in voltage can propagate along an axon

The shape of a spine affects its electrical properties

Impact of morphology on signal conduction

Neck resistance effects voltage propagation, low neck resistance allows voltage spread from the spine to the dendrite and subsequently to the soma.

Spines with high neck resistance aare compartements (almost) electrically isolated from the dendrite.

How we measure neck resistance. Action Potentials propagate backwards (mostly passively). Somatodendritic propagation of action potentials can be used to study neck resistance of individual spines.

What is the advantage of compartmentalising?

Fewer ions lead to large changes in potential Relief of Mg++ block of NMDA receptors Calcium entrance Synaptic plasticity

Dendrites in pyramidal neurons.

Dendritic democracy doesnt matter when the denderite signal is generated, the signal is amplified by a mechanism

Synaptic scaling and homeostatic scaling are not the same.

Proposed Mechanisms for Synaptic Scaling Higher AMPA density at distal synapses Sub-threshold boost (no experimental evidence) Local Dendritic Spike (thin dendrites) Global Dendritic Spike (thick dendrites)

Proposed Mechanisms for Synaptic Scaling Higher AMPA density at distal synapses Sub-threshold boost (no experimental evidence) Local Dendritic Spike (thin dendrites) Global Dendritic Spike (thick dendrites)