Tri-2, Wk11, Day 113 - Friday

It was a light day at school and about 20 people were missing from our Biochem class. We all had a pretty tough week. The big test next week is Neuroanatomy and I've got to score well on this upcoming test. It's got me debating about whether to go on Saturday's BACA (Bikers Against Child Abuse) Run. It's a great time but maybe too much time that could be better spent studying. So far, I think we've only got three test scheduled for next week which is a little bit scary because we only have about 4 weeks left and we'll be getting hit hard in the following weeks.

Today's picture is of different afferent nerve fibers. Afferent fibers are those which travel from various parts of the body back to the spinal cord. Unbenownst to me - they come in different varieties just like the different kinds of wires that can bring an Internet connection into your house to your computer. We have three different types of A fibers and one C type fiber.

Here's a pretty decent analogy pertaining to the speed of each fiber.

Fiber Type Analogous Speed

C Dial Up

A-delta DSL

A-beta Cable

A-alpha Fiber Optic

I guess that analogy will make the most sense to people who know a thing or two about the different ways of getting the internet to your computer. Hopefully, everyone knows that dial up is the slowest and a Fiber Optic light connection is the fastest.

C fibers are used for chronic (slow) pain and warmth and travel about 2.2 mph. A-delta nerve fibers conduct impulses are a little faster (maybe 20 mph) and are used to help detect acute pain and cold. A-beta fibers are faster and used in transmission of touch, pressure and vibration.

The fastest are A-alpha fibers and are used for limb position and motion - these nerves are capable of sending nerve impulses up to about 260 mph.

Of intersting note is that impulses from being touched travel faster than either kinds of pain (acute or chronic) impulses. This may be one reason why touch inhibits pain (or nociception) I'll have to take a closer look at the neural pathways of pain and touch to see if there is any neurological routing reason why touch inhibits pain. I think part of pain inhibition via touch may also have to do with different chemical releases in the body. GABA (gamma-aminobutyric acid) seems to come up a lot in various classes.

For inhibitors, at least in the basal ganglion portion of the brain, we learned about GABA and D2 (a type of dopamine). For excitatory chemicals we learned about Glutamate and D1 (another type dopamine).

There is also a concept known as DisInhibition which has the opposite effect on a target cell. Thing of it this way. To go faster in your car you can press down on the gas pedal (excitatory) or you can inhibit the acceleration by pressing on the break but you can also get the same effects by lightening up on the accelerator or by pressing harder or softer on the brake pedal.

Those previously mentioned inhibitory and excitory chemicals are the basis for grave diseases such as Parkinsons disease in which there is a dopamine deficiency which causes a decreased activation of the neurons of the cerebral cortex.