The Hindbrain

The brain is the most complex and mysterious part of the body. Despite the multiple research studies done, we are way far from completely understanding its functioning.
When we think about the brain, we usually think about the cerebral cortex. Few of us know that that, in fact, what most people believe is he brain (the cerebral cortex) is just a part of it. The brain is composed of many small parts that are very important.
First of all it is divided into three sections: the hindbrain, the midbrain, and the forebrain.

This time we are going to talk about the hindbrain.
The hindbrain is located in the posterior (towards the back of the head) part of the brain. It is composed of the medulla, pons, and cerebellum.

The medulla is like an extension of the spinal cord into the brain. the medulla controls some vital reflexes such as hearth rate, vomiting, sneezing, breathing, etc. As you may guess, damage to the medulla may be life threatening.

The pons is located anterior (towards the face) and ventral (towards the feet) to the medulla. This is very interesting because here is where the axons from the right side of the spinal cord cross to the left side of the brain and vice versa, making your left hemisphere able to control the right side of your body and your right hemisphere the left side of your body.

Last but not least we have the cerebellum. Before, we used to believe that the cerebellum's only function was for coordination and balance. However, our little friend is way more important. Research has proven that damage to the cerebellum affects the ability to alternate from visual to auditory stimuli. Besides, it also affects the sensory timing. Therefore, if your cerebellum has been injured/damaged/affected somehow, becoming a musician is probably not going to work for you.

Temporal Summation

Last semester I took a biology class. One day at the laboratory they had us doing some experiments on the reflexes (contraction of the pupil, etc.). I was then trying to perform the I’m sure very familiar procedure of the following picture to my partner.

 

 

It is a very easy procedure, so of course I was really pissed when I could not get it right. No matter how hard I hit her knee, it just would not lift. It was until few days ago that I realize what I was doing wrong.

When I was doing the experiment I was not told about temporal summation. Since I do not want you to make the same mistake whenever you find yourself in the necessity of performing the same procedure, I will explain the concept.

At the beginning of the 20^th century, the scientist Charles Scott Sherrington made an experiment with a dog. He would suspend the dog above the ground and pinch one of its feet. Then he observed its reactions which were to flex the pinched leg and extend the others. Seems easy and basic right? However, from this experiment, Sherrington discovered 3 things and won a novel prize.

He discovered (1)that reflexes are actually slower than conduction along an axon, (2)that few weak stimuli presented at short time intervals or slightly different locations produce a stronger reflex than a single stronger stimulus, and (3)that when a set of muscles becomes excited, another relaxes.

 

He observed that when he would pinch the dog’s foot several times really fast but not hard, he would cause a reflex. He assumed then that it was because the continuous stimuli must accumulate in a single axon causing it to reach its threshold and begin an action potential. He named this temporal summation. He also noticed that pinching in different spots close by in the dog’s foot would also cause a reflex, which means that stimuli in different spaces also accumulates. He named this spatial summation.

 

So, Why did my experiment not work? Because I was trying to produce the reflex in one single blow. I should have tried with a few continuous. Or maybe not. Maybe I am just very untalented for those kind of experiments. Try it yourself! Do the experiment and let me know what was easier: one strong blow, or few weaker hits.

The Purge And The Blood-Brain Barrier

The other day I was watching this movie called “The Purge.” In this movie, all kinds of crime are legal for one night a year. That night, either you go out to find a way to release your criminal instincts, or you install a very powerful security system to protect yourself and your family (since police and medical services are not available during that time).

 The following day, I was reading about the nervous system. In my reading, there was this one part about something called the blood-brain barrier and I thought “OMG this is just like the movie.”

In the movie, there is this one family perfectly locked up for the night, no one can get in. However, nobody knew that someone with no good intentions was inside the house before they locked up. Then this man appears on the street asking for help and the little boy decides to let him in without his parents’ permission. The situation here is that they cannot disable the security system again to get the strangers out because it could cause more bad people to come inside. Besides, there is also the problem that there is no police or anything to help them get through the night. That’s as far as the resemblance goes.

The blood-brain barrier has sort of the same situation. Since neurons are not very easy to replace once they have been damaged by a virus, they need to be particularly protected. That is why we have a barrier that separates the blood from brain cells. This barrier (as well as the security system in the movie) prevents many chemicals and bacteria from coming into the nervous system; however, it also keeps away may nutrients that cells need in order to function (which would be medical services, police, and fire fighters in the movie). The blood-barrier can only be trespassed by a few small, uncharged molecules such as O2 and CO2, in addition to certain fat-soluble molecules. Besides, active transport systems pump glucose and certain amino acids across the membrane. However, most large molecules and electrically charged molecules cannot cross from the blood to the brain.

 

Although the lack of nutrients is not a positive feature, our brain cells have adapted to it. The real problems is what happens once a virus does get pass the barrier. Just like in the movie, the virus will try (and possibly succeed) to kill you. If it can’t, at least it will stay inside your nervous system (your house) the rest of your life (the night). Besides, when the cells of the blood vessels that form your barrier shrink, harmful chemicals may get in and cause certain diseases such as Alzheimer’s.

 

The question here is: how can we treat Alzheimer’s or Parkinson’s disease, or some brain cancers if the chemicals used for the treatments are not able to cross the barrier? In the following video Devin Wiley explains his approach to this issue and his theory for overcoming the barrier.

http://www.youtube.com/watch?v=WLEPr3mz4qc