The Nervous System:

Hey period 8 and 9, this is what Tuesday's lecture was on:

Ok so The Nervous System! Err, Umm, What To Say.......Yea

So why do animals need a nervous system and what characterisitcs are needed in a nervous system. A Nervous system needs to be -Fast!, -Accurate! and needs to -Reset Quickly!.

Ok, so the nervous system has cells called neurons. They happen to be the most specialized cells in animals. They can be extremely large, for example like the Blue Whale and Giraffe (10-30 Meters and 5 Meters) or Small, for example like in humans (1-2 meters depending on the size of the person). Ok so in the Neuron, which is a nerve cell and it has many parts to it. There are Dendrites, which are branch like structures that receive signals. Then there is the cell body which leads to the axon. The axon furthers the signal to the synapse where it leaves the neuron and keeps traveling. Ok, so the neuron fits its function well, as their are many possible entries for the signal to travel to, so theres a possibility that more information can be gathered. But, theres only one path out out neuron.





So, a neuron has many protein channels. Once one opens, the rest open with succession, an "all or nothing response". So the cell is surrounded by a "sea" of charged ions. There are anions, which a concentrated on the inside of the cell and are negative, for example Chlorine and Amino Acids, and there are Cations, which are concentrated in the extracellular fluid and are positive, for example Potassium and Sodium. The potassium channel happens to leak some potassium, which is normal, but this is an extremely slow process. Cells actually have voltage and this could be measured. An unstimultated neuron at its resting potential has a voltage of -70mV or mini-volts. So their happen to be opposite charges on the opposite sides of the cell membrance which is polarized. The inside is negative while the outside is positive. This means there is a Charge Gradient! Energy

So how does a nerve impulse travel? Ok, first the nerve is stimulated. Once the threshold potential is rached, the Sodium channels in the membrane open up and the Sodium ions diffuse into the cell. At this point the charges on the neuron are reversed. It becomes positive on the inside and negative on the outside. This means the cell becomes Depolarized. So how does the signal keep traveling down? Well remember how I said if one Sodium channel opens up, the rest open up in succession, yea so that happens in a line. The Sodium ions continue to diffuse into the cell. Finally the wave that mmoves down the neuron is called the action potential or basically a nerve impulse. (The rest of the Dominoes fall! Yay!)

Ok, hopefully you got that. Now how does that 2nd wave travel down the neuron. Well it has to re-set itself. So basically the Potassium channels open up, but much slower than the Sodium channels. Then the Potassium ions diffuse out of the cell. Therefore the charges reverse back to the original state, negative on the inside and positive on the outside. (Setting up the dominoes! Quickly!) So the signal moves down one and in one direction only. The flow of Potassium out of the cell stops the activation of Sodium channels in the wrong direction. (Ready Again!)

Ok so thats basically it! Allright thats it, Thanks guys, Umm the Sherpa for Wednesday is "I Dont Know" Ok then, Night



-Liver