Mol and Cel Essay

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4. What are the potential advantages of having spines with high neck resistance?

What are spines?

The spine, also known as the vertebral column or spinal column, is a column of 26 bones in an adult body — 24 separate vertebrae interspaced with cartilage, and then additionally the sacrum and coccyx

Dendritic spines are small door knob shaped extension from the dendritic processes of neurons (Karch et al 2001). Dendrict spines contain post synaptic densities allowing them to receive signals form presynaptic neurotransmitter. The door knob shape of the spine is made of the spine head and neck which play pivotal roles in the function of the spine. The spine neck geometry is an important factor in spine ca2+ signalling.

What is High Neck Resistance?

What are the potential advantages of having spines with high neck resistance?

One possible scenario is that in spines with a neck resistance high enough to produce voltage deflections at the spine head that can remove Mg2+block from NMDA receptors and activate voltage-gated channels, quick changes in synaptic conductance (on the order of a few additional channels; Fig. 5 E and F) are a major contributor to the changes in synaptic strength in response to our pairing plasticity protocol. Such a mixed scenario—with a large voltage drop along the neck, amplification of spine head EPSPs, and activation of voltage-dependent conductances—could potentially interfere with a Hebbian mechanis

Localising Signlaing

the spine neck plays an electrical role in the transmission of membrane potentials, isolating synapses electrically.

As an alternative function, spines could be electrical compartments; i.e., their special morphology could enable synaptic inputs to generate and experience different membrane potential dynamics than if they were situated on the dendritic shaft.

Electrical compatilisation

http://www.annualreviews.org/doi/full/10.1146/annurev-neuro-062111-150455?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub%3Dpubmed&

spine neck resistance could be significant enough to partly isolate spine voltages from dendritic ones.

significant electrical reduction of synaptic potentials occurs at the spine neck

the diffusional isolation generated by the spine neck can be regulated by neuronal activity and becomes significant enough to isolate the spine electrically

bath application of the sodium-channel blocker TTX selectively blocks glutamate uncaging potentials generated on the spines but does not affect those in the neighboring dendritic shaft (Sodium channels amplify spine potentials http://www.pnas.org/content/104/30/12347.full)

Small number of ions cause big effects, High Neck resistance due to ohms law, V=IR explain this

Changes un potential within the spine is adv as it allows mg relieve allow nmda- ca infllux - induces ltp

Amplifying Epsp

The EPSP in the spine had is increased to allow for the release of Mg+ from the channels

Calcium efflux for LTP

What is biochemical compartilisation

‘compartmentalization’ is considered the basis of local modifications of dendritic properties, in particular to achieve input-specific changes of synaptic strength.

Research Articles

Spine Neck Plasticity Controls Postsynaptic Calcium Signals through Electrical Compartmentalization

http://www.jneurosci.org/content/28/50/13457.short