Structure and Operation of the Human Brain – Week 5

This week the topic of last week was continued: Neurotransmitter systems.

I found good that the lecture was started with a revision of what had been done in the previous lecture. We then started with acethylcolinergic pathways as one of the diffuse brain systems. This pathway is thought to be linked to Alzheimer’s disease as the death of ACh cells was found together with early signs of the disease. Alzheimer’s disease is therefore characterized as a neurodegenerative disease and also as a form of dementia because it is linked to memory loss and cognitive impairment. To decelerate the progress of the disease the patients can take drugs which inhibit acethylcholinesterase to raise the acethylcholin levels in the brain. However, these drugs can neither cure the disease nor stop the progress completely.

ACh in the nucleus basalis of Meynert is also believed to play a role in learning progress by interpreting sensory stimuli.

Another diffuse brain system are the norepinephrine pathways. These pathways that ascend from the Locus Coeruleus widely innervate the brain as there are around twelve thousand neurons in the LC, each with around 250 thousand synapses. Each neuron can innervate both cortex and cerebellum. The NE pathways were found to react to salient environmental stimuli, leading to increased alertness, the enhancement of formation and retrieval of memory, and more focused attention, but they are also connected to mood, particularly to clinical depression, as norepineohrine increases restlessness and anxiety.

We went on to the dopamine pathways of the brain, the nigrostriatal pathway and the mesocortical and -limbic pathways. The dopamine pathways might be connected to Parkinson’s disease, as patients suffering from this disease were found to have low levels of dopamine in their basal ganglia. These low levels are a result of the death of dopamine neurons in the substantia nigra. There is no cure for the disease yet, but it is possible to improve movement related problems by giving the patients the drug L-Dopa which increases the dopamine levels in the basal ganglia.

The third diffuse brain system is the serotonin system. These pathways ascending from the Raphe nuclei in the brainstem innervate almost the whole brain. The serotonin system regulates wakefulness and arousal but was also found to play a role in mood. Together with the norepinephrine pathways it forms the reticular activation system of the brain.

After that we discussed the roles of hypothalamus and pituitary in controlling hormones and talked about the autonomic nervous system. The lecture was ended with an overall principle of neurotransmitter system functions, including that “everything influences everything” and that the change in the activity of one neurotransmitter system, for example through drugs, can widely influence other neurotransmitter systems, often in unpredictable ways, followed by a summary of what had been done in this lecture.

I really liked the references to current research status in some diseases and hope that the next weeks will include that as well and feature summaries of what has been done so far too.

Posted by Franziska Schrank

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Structure and Operation of the Human Brain – Week 4

This fourth week started, as usual, with a quiz. The quiz reviewed last week’s topics, the synaptic transmission. At the start of the course I was a little annoyed by having one type of examination each week; however I’ve come to like these quizzes, since they provide feedback as to how much you understood the previous topic and whether you should study more on some concepts so you don’t get left behind and can follow the following topics easily, since the topics build upon each other.

Things got a little fresh since we had some changes in the structure and approach to the lectures and exercise sessions. The lecture was prepared and given by Iiro instead of Risto like the last few lectures. The topic for this week was neurotransmitters and neurotransmitter system, things were a little bit more varied as we started with some background experiments between the link in alcoholism and opioid receptors and before going into the topic we also were presented with some videos to exemplify with some animations the ligand gated channels and the second messengers (cAMP).

Afterwards we boarded the lecture’s topic with some basic concepts, like what exactly is a neurotransmitter, their classification and what do they do; whether they are inhibitory or excitatory. We delved into each type of neurotransmitter and looked into the most prominent and common ones like Acethylcholine, GABA and glutamate, their receptors and what kind of reactions ensue when they’re recognized by said receptors; the principles of cholinergic synapses and the role of some neurotransmitters like GABA in the inhibition in the brain.

After this we returned to the second messengers cascades and then the relation between opioids and social bonding was discussed further.

Regarding the experiment session, although I wasn’t able to attend it I managed to do it later by running the program in my computer. We were presented with an experiment; to react to aural and visual stimuli and how different environments changed the reaction times.

I was pleasantly surprised to see some variety in how the lectures and exercises are presented and explained as this allows for a better understanding of them. I hope we can expect different approaches to the following topics.

Posted by Salvador Gutierrez Medina

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Structure and Operation of the Human Brain – Week 3

The third week started with a quiz again. One question of the quiz was about the cause of Alzheimer’s disease which is that the neurons fill up with neurofilaments and eventually die. As this had not been discussed in the lecture and wasn’t mentioned in the course book it was a tough question but also very interesting. In the exercise session, we discussed the different answering possibilities that were offered to the question and to which diseases they belonged, e.g. the degeneration of myelin sheaths in the central nervous system as a cause for multiple sclerosis. I hope that there will be more about diseases caused by defects in the neurons in one of the next lectures.

In the lecture, we first studied the different phases of the action potential and what happens in each of them with the concentration levels of potassium and sodium. This was terminated with a brief introduction to the patch-clamp-method which allows the study of single or multiple ion channels in a membrane. We went on to the different factors for the conduction velocity of the action potentials which are myelination and the thickness of the axon. The purpose of myelin-sheaths around the axons of neurons is mainly electrical insulation but it also decreases the capacitance in the axon so that it is easier for the action potential to travel. If the myelin-sheath isn’t intact anymore, signals that travel along the axon are slowed or stopped completely. Apart from the earlier mentioned multiple sclerosis there are several other diseases affecting the myelin-sheath, e.g. the Guillain-Barre syndrome.

Apart from characterizing neurons through their structure, for example pyramidical cells or stellate cells, which was discussed last week, neurons can also be classified by their behaviour in respect of the frequency of their action potentials. There are for example neurons with consistent action potentials that might have the function to transport a signal continuously over a certain time span while there are other neurons that only transmit a few action potentials at a high frequency which might be to transmit only the strength of a signal.

From there we went on to synapses between neurons. Synapses can exist between an axon and a dendrite, an axon and a soma or between two axons and one axon can also have multiple synapses. For chemical synapses, a neurotransmitter has to be synthesized, converted and stored in transporter proteins in the pre-synaptic neuron and then be released into the synaptic cleft, in response to an influx of calcium ions through voltage-gated calcium channels in the pre-synaptic membrane. I wonder, if this process could be interrupted in any way, for example using drugs and what consequences that would have.

Posted by Franziska Schrank

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Structure and Operation of the Brain – Week 2

After going through a general overview of both the course and the brain itself. This week we had the first quiz before the second lecture. Some of the gripes I’ve listened my classmates had was that it wasn’t really clear which topics would be covered for this quiz and that most questions only covered one part of the reading material. However, this week we got an announcement that clarified the topics that will be evaluated in next week’s quiz, showing us that the feedback has been heard.

In the lecture itself we covered some general topics from a biological standpoint, from neurons and glial cells, their types, classification, their organelles and their respective functions to the cellular membrane and finally we delved into proteins, amino acids, the ion channels and the Na/K pump. Even though the explanation dragged on for a bit, it’s understandable the detail of explanation that was given seeing as some people may not have previous knowledge about these topics if they don’t have a biological background and even for us who do, it was useful as well since we can remember things we may have forgotten.

In the exercise session we followed the topics in the first lecture, the brain itself and its different areas, with the twist that we dropped pen and paper and got our hands dirty!-so to speak. As we went with a hands-on approach and were tasked to build a model of the brain using modeling clay while we studied the different structures that make up the brain.

Even as a person who learns better just by reading I enjoyed the exercise session and I also understand that it may have been structured this way to aid people who learn better with visual cues.

I’m looking forward to the next lectures as we delve into the action potential and I wonder if we’ll go into detail with the Nernst equation and the Goldman-Hodgkin-Katz equation to end up studying the Hodgkin-Huxley model.

Posted by Salvador Gutierrez Medina

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Structure and Operation of the Human Brain – Week 1

The first lecture gave an overview of the human brain. Its functions are for example to receive and interpret sensory data and to produce knowledge. Receiving data is something we do all the time – we hear, we smell, we see etc. But only the brain can work with this data and develop something new out of it, for example why we can see a colour. The brain does all this to keep us alive and to satisfy our needs. We can study the brain for example by looking at its anatomy in an x-ray image or by observing it via magnetic resonance imaging. By analysing the brains anatomy, one can see that the brain consists of different areas which have different tasks for example one area to exploit what we see with our eyes. One can also examine the brains electrical signals which are processed through neurons.

Most of these things I already knew from a former lecture about the human body, for example how the brain is assembled with its different areas and how signal processing through neurons works. I am looking forward to learning more about certain brain diseases, how they develop and how you can cure them, in the following weeks of the course.

Posted by Franziska Schrank

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Posted by Franziska Schrank

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