By combining all previous lectures, we will today see how and why eventually our brain learns and changes. So neurons are also considered to be plastic & changing devices. The plasticity of the brain makes us learn, this is what makes us actually learning machines. So, what exactly changes in your brain while you learn?... (click on Read More to continue).
Sirs Hodgkin and Huxley
A spike is an "all-or-none" phenomenon, a digital one, a 0/1. Along with synaptic potential, spikes (action potentials) form the 2 types of potential in the nervous system: the action potential, located at the axon of the pre-synaptic cell and the synaptic, at the dendritic spine of the post-synaptic cell (a reminder: synaptic potential is either EPSP or IPSP). We say spikes "overshoot" when momentarily they go above zero voltage (remember, resting potenital is -70mV) and they "undershoot" when momentarily the dive even below their resting potential, upon attenuation phase. This is also called "after-hyperpolarization) (lesson 4, video 1, 09:30-).
In the middle of 20th century people started to record brain activity, so they did a very simple thing: they injected positive current through an electrode inside a brain cell. What they saw was that there was a voltage change but not analogous to the injected positive current. It was rather growing with time while a constant current was inserted. When the current injection stopped, the voltage gradually attenuated with time to zero. So a cell can't be represented as a mere resistance because if the cell behavior would have been like a resistor then the Voltage should have been equal to V=I.R (Ohm's law, here) and looking something like this: