Week 5. Chemical control of the brain and behavior

The chemical control of behavior is a very fragile and fundamental function of the brain. The main systems responsible of it are: the hypothalamus, the Autonomic Nervous system (ANS) and the diffuse modulatory systems.

The hypothalamus is in charge of the maintaining of homeostasis, regulating the function of glands through the liberation of the neurohormones (oxytocin and vasopressin) and the control of pituitary. These systems form a closed loop system when receiving the feedback from other glands in order to maintain the chemical equilibrium. It is very interesting to study the complete loop and to know all the subsystems and processes involved in everyday tasks as the hydration of the body.

The ANS is also a very complicated system that controls several hormonal and visceral processes through its main divisions the sympathetic and parasympathetic systems. These two divisions work together for the functioning of all the autonomous systems. So, in a broad sense, it is also a closed loop system, but this time with two different effector elements. Both divisions work sometimes with the same transmitters, but one of them would generate excitatory activity and the other one inhibitory. The main idea of equilibrium is also present in this case.

Finally, there are the diffuse modulatory systems of the brain, normally called since their main neurotransmitter. The noradrenergic system in locus coeruleus, the serotonergic system in Raphe nuclei, the dopaminergic substantia nigra and ventral tegmental area, and the cholinergic basal forebrain and brain stem are some of the most studied pathways in the brain. All of them related in the control of processes as emotions, learning or memory. Some elements in the functioning of those pathways are of special interest are they could be related to some illnesses as Parkinson’s disease or Alzheimer’s syndrome. But there is also a lot that remains unknown, the use of chemical drugs to study the interaction of those systems is useful but also difficult; when the equilibrium is broken, a cascade of effects is started and the track of those effects is not evident task.

The maintenance of the equilibrium in the body is a very good example of the high complexity of the brain’s work. And it also reveals the fragility of it, if one of the elements in the chemical processes chain is missing or deficient, the consequences could be unexpected and could affect any other element in very different ways. The track of all those interactions will be useful in the treatment of several illnesses and conditions.

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Week 4. Neurotransmitter Systems

This week was focused in more detail in the mechanisms of neurotransmitter systems. There are several kinds of neurotransmitters, typically classified in amino acids, amines and peptides. The research in this field is constantly characterizing new transmitters and trying to track their receptors, both agonists and antagonists. This task is particularly challenging, as the tracking of molecules in body systems is not evident, and the recognition of a substance as a neurotransmitter has several constraints: the molecule should be synthesized and stored in the neuron, it should be released when the neuron is stimulated, and it should produce the same response when introduced artificially.

There are also three main kinds of channels opening mechanisms linked to neurotransmitters. These channels could be transmitter-gated; this means that they bind directly with the transmitter. They could also be G-protein coupled, and in this case they will bind to a second messenger liberated by an effector stimulated by the neurotransmitter. This process could be done in a shortcut pathway, in which the there is only one second messenger. Or the process can involve several stages, originating very elaborate series of biochemical reactions. In this later case, the mechanism is known as a second messenger cascade. These cascades work as an amplifier if the signal, as one potential that stimulates the activation of one receptor, can lead to the activation of several ion channels at the end of the cascade.

All these processes related to neurotransmitters are fundamental for the correct brain functioning. The research associated to the comprehension of neurotransmitter systems has been able to explain some conditions as epilepsy or illnesses as Alzheimer. The development of psychiatric medications, as well as the study of addictions is also dependent of the research in this field. It is highly probable that a lot of other illnesses and conditions could be explained and tackled trhough the neurotransmitter systems.

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Week 3. Chemical Senses and Visual System

This week we were been learning about the somatic system, particularly the chemical senses and the sight. I think perception is one of the most important brain functions, as it allows us to get information from the world, and from our own systems, to make decisions and act accordingly. This means that perception is necessary for our survival, our creativity and creation ability and for our social way of living.

 Chemical Senses

Olfaction and Taste are the most studied and known chemical senses, even if there are some others. These senses are possible because of the chemoreceptors: specialized receptor cells that are sensitive to some chemical substances; once the concentration of those substances reaches threshold, neurotransmitters are released. In taste, there are also electrical synapses when tasting saltiness and sourness.

The other common mechanism between olfaction and taste is the “processing” of the sensed data. Even if all the chemoreceptors are more sensitive to a particular molecule (taste or odorant), they will respond in some way to any substance. So, there is not a direct relation between sensor type and molecule sensed, but a population coding. This mean, that a certain pattern of several responses from different receptor cells to the same molecule will form the stimulus to be processed by the brain. This population coding mechanism has been difficult to “decode” in order to get a deeper understanding of the chemical senses functioning.

The Central Visual System

The sight is probably the most studied human sense, as there is some hegemony of visual information in our way of living and in consequence, the disabilities and illnesses related to visual perception have been deeply addressed. It is also very interesting to know that even if it is the most studied sense, we still know very little about it. There is this general understanding that sight is the perception of images, so, if we understand an image as the reconstruction of light reflected in objects, then we know enough about the phenomenon. But in reality the visual system is not a photo camera, and the reconstruction of images is just the beginning of the brain processing of visual information. There are specialized neurons to process color, shapes, movement, directions, even faces. The quantity of information we get from one glance is enormous, and we only know that all that information is being processed in different brain areas, we have an idea of the specialization of those areas but we are completely unaware of how is the brain capable to process and give meaning to the very complex visual world.

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Week 2. Action Potential

The Action Potential

Studying the physiological, chemical and electrical mechanisms that make the action potential possible is very interesting as it allows me to understand in greater depth how it impacts the functioning of many body systems, as well as the principle of many imaging methods that detect and then interpret the electrical and magnetic activity that is initially generated with the action potential.

The detailed description of how the sodium, potassium and other ion channels work is also fascinating. It is almost incredible to be able to describe mechanically how a molecule changes its shape to allow or not the passage of ions through it. I believe that the use of high technology for the simulation and observation of this phenomenon could greatly benefit learning, but also research, since it would accelerate the process of understanding a phenomenon so unique and far from our human scale.

Synaptic Transmission

There are two types of synapses, electrical and chemical. While electrical synapses are very fast and simple, chemical synapses require a slightly more complicated processes and are therefore slower. One of the mechanisms, that I find the most interesting, is how a neuron can self-regulate its activity through autoreceptors; that is, when the neuron receives the neurotransmitters it releases.

Finally, the integration of the excitatory and inhibitory postsynaptic potentials is one of the most important tasks of the neuron, since it is precisely through this integration process that the neuron “makes decisions”. The number of operations carried out by a neuron is so extensive that until now there is no method that allows us to trace in detail how this process is carried out, if we could understand in greater depth the circumstances that favor a certain frequency and magnitude of postsynaptic action potentials, it would be possible to design some tools able to simulate neuronal functioning.

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Week 1. Introduction

During this first week of lecture we began a reveal the deep secrets, at least, those that are known, of the Nervous System. The brain is probably the most complex organ in the human body, in order to understand how we (humans) function, how we create, how we have built such a complicated and technologized society, it is necessary to address this complexity and try to understand the mechanisms that allow our existence, and the consciousness that we have of it.

Neurons and Glia

It is necessary to begin the learning process with the anatomical and physiological description of the organ: lobes, different types of tissues, gray matter, white matter; the tasks it performs such as interpreting sensory information, storing information, processing information, or controlling the body.

And of course, it is necessary to describe the main actors, the nerve cells that are mostly neurons and glial cells. Neurons are by far the leading characters since, apparently, the main task of interpreting, processing and storing information falls on them. However, glial cells are essential to maintain proper neuronal function.

The Neuronal Membrane at Rest

The understanding of how the electrochemical equilibrium is maintained in the neuronal membrane at rest is essential to understand the mechanisms that allow the generation of the action potential. Until now, I believed I understood the basics of ion channels and sodium and potassium pumps. However, by having a deeper reflection on the role they play in the ionic equilibrium maintenance, they become much more important and then I understand how fundamental is their existence. This reflection also reveals to me the enormous fragility of our biological systems; a small error in the RNA coding, a misfolded or wrong structured protein and the complete system can stop working or function erratically (of course the error must be persistent). A former professor of anatomy asked us to imagine the most unlikely situation that we could think of, some error in the functioning of the human body that would lead to some erratic behavior, surely that disease or condition would be real and would have a name. Thinking about the many diseases derived from errors in the functioning of ionic channels makes me wonder how far we are from properly characterize and treat those diseases, since we would very accurately know the composition and operation of each type of channel at the molecular level, a definitely challenging task.

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