Question

• How does driving force factor into dendritic integration? And so then why is integration sublinear?

• What is dendritic attenuation? Why does it occur? Why does it matter?

• What is "shunting inhibition"? What properties could this provide neurons with for processing information?

• In the context of the simulations from NIA, what is meant by “deliberation time” for an AP?

• Describe the oscillations in mechanoreceptors simulation in detail based on the plots of voltage, current, and conductance.

• Is action potential size fixed over a range of inputs? Present evidence one way or the other from the third simulation in NIA.

Answer 1

Answer: To describe the solution first we need to understand the dendritic integration, which is as follows:

Dendritic integration:- Dendrites are basically the acceptor elements of neurons. These elements basically collect the information through presynaptic inputs. Further moving to dendritic integration, the study of this field enables us to understand primary anatomical methods such as the architecture of dendritic trees, electron microscopic analysis etc. Therefore, it describes anatomy taking thousands of presynaptic inputs.

· How does driving force factor into dendritic integration? And so then why is integration sub linear?

As per cable theory definition, in dendritic integration electrically isolated inputs adds up linearly, nevertheless, the inputs which are nearly located generate attenuated response owing to the decrease in the ionic driving force or due to the fall in dendritic input resistance leading to shunting of synaptic currents. Further, to explain why this integration is sublinear we should know that there are numerous types of neurons in the brain which are termed as granule cells. Each granule cell receives on average only four excitatory inputs, each made onto a very short dendrite. Because of small size dendrites does not affect much on synaptic integration, which in turn beneficial to understand synaptic physiology. Such studies and glutamatergic synapses suggest that each activated synapse results in an excitatory postsynaptic current (EPSC), which is basically sublinear. This sublinear summation is a consequence of the effect of membrane potential on current flow at the synapse, which is further ruled by the driving force for synaptic current. This driving force is basically the difference between the membrane potential and the synaptic reversal potential. Owing to the depolarization of the membrane by EPSC, the driving force automatically reduced. As a consequence, the charge entering the synapse is also reduced. As an example, a 7 mV EPSP would decrease the driving force by 10%. This is the basis for sublinear EPSP summation in a passive system.

· What is dendritic attenuation? Why does it occur? Why does it matter?

Dendritic attenuation defines the process of decreasing the strength of Excitatory Post-Synaptic Potentials (EPSPs) and Inhibitory Post-Synaptic Potentials (IPSPs) as they move down the dendrites.

Various factors promote dendritic attenuation of signals, such as the size and diameter of a dendrite. Larger dendrites are responsible for weakening the signals. Further, there is a generation of large resistance due to the small diameter of dendrites. Furthermore, the individual features of a dendrite's membrane also contribute the dendritic attenuation. Some neurons have leakier ion channels than others.

This process is significant because it defines the differentiate role of different neurons to EPSPs and IPSPs. As an example, the size of dendrites is comparatively larger for pyramidal cells, which leads to the reduction of voltage from EPSPs quite quickly. On the other hand, the short sized dendrites of granule cells do not let the loss of charge. This implies that pyramidal neurons require a large number of EPSPs to produce an action potential in comparison to a granule cell.

What is "shunting inhibition"? What properties could this provide neurons with for processing information?

The mechanism, due to which multiplicative nonlinearities appear to be possible is called shunting inhibition