I was in a lecture about how a single neuron functions.

The lecturer talked about how the dentrites get excited and how the message gets passed on and all that. I have some questions about this.

He said that half the energy that a neuron spends is spent on altering the concentrations of the ions in and around it. So, the ionic concentrations are all that acts as a factor in deciding whether the neuron is in rest or "excited" right?

So, the analog ionic waves of excitation travel from the dentrites and hit the Axon Hillock. Then the Axon Hillock sees whether the ionic waves meet the threshold level and decides whether the action potentioal must be released. My questions is:

How does the Axon Hillock detect the magnitude of the incoming ionic wave/concentration? I, being a physics student, am very interested in the mechanism it uses.

Regards

through a high concentration of voltage-gated ion channels

I beleive that at the axon hillock has what is referred to as a critical density of voltage gated sodium channels. Basically, along dendrites the number of VGSC are sparse (relatively) and so depolarization remains localized. Once a certain number of voltage gated sodium channels are opened, the cytosol (or neuron soma equivalent) is depolarized enough that its spreads to the hillock region. Once this occurs, a vast number open. So its not that the hillock detects the maginitude at all; its that a certain magnitude is needed for the graded potential to reach the hillock.

Also the the mechanism for adjusting the ionic concentration is called the Na+/K+ ATPase pump. It uses one ATP molecule to move 1 Na+ ion out and 2 K+ ions in. Interesting stuff!

Great. On second glance, my reply was a long winded ver. of what was already stated.

The barriers also play a major roll for threshold ..just like a semiconductor ,,eg: Zener diode is a classic one .. brake down voltage..

Sory I add one pricese name .. just adding that Raghave please refer about "Inhibitory Postsynaptic Potentials" better to say "membrane voltage "