How Does a Neuron Work?

So I was playing with some more machine learning and trying to make a perceptron from scratch again, I have to admit the one that I made few months back was somewhat buggy so I wanted to make something that works without errors.

Perceptron is the basic unit of a neural network just like the neuron which is the building block of our nervous system. So before talking about artificial neural networks I thought of writing about some physiology that I learned at first year of medical college. The physiological mechanism of a real neuron.

The neuron is the building block of our nervous system, there are nearly hundred billion neurons inside the human brain, that is a lot of neurons. How does so many neurons fit inside our head? One reason is that our brain is not flat, it had bumps, and ridges which increase the surface area of the brain which will make room for many more neurons as opposed to the brain being a flat hemispherical object.

The Structure

 

Although the brain different kinds types of neurons specialized for different functions, the basic structure is the same. It has a cell body, which has the nucleus and from the cell body comes out dendrites which connects with adjacent neurons, these dendrites brings signals towards the neuron (cell body).

And from the cell body comes out a long process called the axon, this axon can be few centimeters in length, it end by splitting in to small processes called axon terminals, which connect to adjacent dendrites. So the axon carries signals away from the neuron coming from the cell body.

Each neuron connects with nearly a thousand adjacent neurons, that is nearly hundred billion multiplied by thousand connections inside our human brain.

 

The Function

The way neurons work is based on electricity, the neurons outside is positively charged and the inside is negatively charged, the voltage difference between them is called the resting potential. It is the neutral state of a neuron. The main reason that outside is more positive is due to more sodium on the outside of the cell than inside.

And along the membrane of the neuron we have sodium channels, and when a stimulation is received these channels which is closer to the stimulation are opened and sodium which is abounded on the outside comes inside the cell causing the voltage difference to rise (making the inside of the cell more positive than the outside) and as more and more sodium comes in the voltage difference become, this depends on the strength of the stimulus.

So if the voltage difference passes a certain threshold then the neuron fires, casing an impulse to be carried along the axon to the adjacent neurons stimulating the ones connected to them. If the stimulus is not strong enough then the threshold is not reached and the neuron doesn't fire. This goes on until a desired action occurs in the body.

So coming back to the neuron, once the voltage difference rise to a certain level then another type of channels open on the cell membrane, these are potassium channels which pumps potassium from inside of the cell to outside.

So as more and more potassium is pumped outside the voltage difference becomes less and less because potassium is also a positively charge ion. So the voltage difference comes to the level of resting potential and goes even beyond the resting potential and comes to a period called absolute refractory period. Which means during a small time period no matter how strong the new stimulation is, it is not going to fire, but after sometime the voltage difference comes back to the resting potential and the neuron is ready for a new stimulus. And this cycle repeats itself.

So like I said before there are nearly hundred billion to thousand connections in the human brain, so how does the brain recognize patterns? This depends on the pattern of which neurons get activated by reaching the threshold and which neurons do not. It's like binary 0,0,1,1,1,0,0....0 will represent one pattern and the next binary code will represent another. This these are the things that we learn since our childhood and gets hard-coded in to our brain.

This is just a simplified version of how brain works, the brain has different areas for different functions like a part for processing visual data, a different area for processing audio and different area for processing language etc. So the brain is a complex machine that we are yet to understand.