The Human Cerebral Cortex

The human cerebrum accounts for roughly 80% of total brain mass and is essential for language, cognition, memory, consciousness, and awareness of surrounding. In this article, our main focus is the cortex, the outer layer of the cerebrum, which is responsible for voluntary movements and cognitive functions. Generally, you can establish the idea that the cortex has three functioning areas- sensory, association, and motor areas, and is characterized into four regions, or lobes- frontal, temporal, occipital, and parietal lobes.

Before I confuse you with the different lobes of the cerebral cortex, let’s first talk about how the cerebral cortex receives and processes sensory information. Since we are still not familiar with the processing of memory and all that, scientists can only focus on the study of sensory information, which they developed through a method called functional imaging, brain scanning that assists the  observation of active brain regions in response to a certain stimulus. Hence, let’s only deal with sensory information for now.

The human cerebral cortex receives sensory information from two sources. The first is somatosensory receptors (soma=body). Somatosensory receptors are “body” receptors that provide information about touch, pain, pressure, temperature, and the position of muscles and limbs. The other is sensory organs such as the eyes and nose, which clusters of receptor neurons are organized. Most sensory information coming into the cortex is directed via the thalamus to primary sensory areas within the brain lobes, which is then passed along to nearby association areas where processes of sensory input take place. 

Now that we’ve talked about how and where sensory information is received, let’s take a brief view on the lobes of the cerebral cortex. Generally, the parietal, temporal, and occipital lobes are regions that deal with specific sensory information (auditory, touch, visual, odor, etc.), whereas the frontal lobe carries out processed information into action (movement). When constructing this concept in your brain, be sure to realize that every lobe consists of two parts, left and right, and the left and right side may have different functions that are not illustrated in the figure. For instance, the temporal lobe is responsible for the processing of both auditory, odor, etc., so don’t let the figure below limit your understanding. In addition, the parietal, temporal, and occipital lobes have what we characterized as “primary sensory areas” and “association areas,” which correlates with what we’ve mentioned about the receiving and processing of information in the prior paragraph. Keep in mind that these “areas” are defined through functional imaging (brain scanning); in other words, these areas are active when information is received and processed. And that’s all we know. In summary, what we’ve discussed is only the broad, general view regarding the functions of the lobes. The frontal lobe, for instance, plays other roles, such as managing memory; however, this subject, as well as many others, are still too blur for us to fully grasp. As a result, the idea above is pretty much what you should know, unless you are interested in pursuing neuroscience. It would be useful if you can draw and organize the above information yourself, so it is integrated into your mind.

Reference:

Campbell, et al. Biology: A Global Approach. 11th ed., Pearson, 2017.

An Update on the Coronavirus

As all kinds of news and information are being exposed to people, a clear comprehension must be made, particularly about what the coronavirus (COVID-19) really is, its pervasiveness and effects on the worldwide population, as well as potential post-infectious diseases.

To make it easy for all to understand, the virus is often being commonly referred to as the “coronavirus” or “COVID-19.” However, that is not the case. COVID-19 is the abbreviation for the term “coronavirus disease 2019”. The virus that causes all this chaos, meanwhile, is coined the name “severe acute respiratory syndrome coronavirus 2” (SARS-CoV-2). This virus, which is similar to the SARS-CoV in many aspects, differs in some major structures. Anyway, both of them are types of coronaviruses, and in this article, let’s still refer to the SARS-CoV-2 as the coronavirus, for the sake of concision. 

Typical coronavirus symptoms include coughing, fever, and shortness of breath. Since such symptoms are not indicative of lung infection, or pneumonia, people who are infected with the coronavirus very often do not have pneumonia. The majority of COVID-19 cases, in fact, are mild and only a small percentage of patients will require hospitalization. It is true, however, that COVID-19 can lead to pneumonia for some patients, especially those over the age of 60 and those with pre-existing lung diseases, such as asthma, emphysema, or any form of fibrosis, which make them prone to the development of pneumonia. This explains why the number of deaths in Italy soar above that of many other countries (Italy has an elderly population of roughly 23%).

According to the statistics provided by the World Health Organization (WHO), currently over 99,027 patients have recovered from the COVID-19 infection. However, multiple sources, such as doctors from Taiwan and Hong Kong, suggest that there are roughly 3%-5% of chances for patients who recovered from the coronavirus infection to be found with post-infectious diseases, most likely pulmonary fibrosis. Pulmonary fibrosis is a condition in which the lungs become scarred and tissues around and between the alveoli thickens over time, in this case, due to the repairing of the lungs after the coronavirus infection. Fibroblasts, which are responsible for the repairing of the lungs, tend to synthesize abundant amounts of extracellular matrix (this phenomenon is also called exaggerated ECM production), thus induces scarring and organ failure. This makes it more difficult for oxygen to pass into bloodstreams in the lungs, and the thickened alveoli results in a weakened lung capacity.

While it's too early to establish long-term effects of the disease, several scans released by a Hong Kong hospital have revealed "patterns similar to frosted glass [in the patients’ lungs], suggesting there was organ damage” (Fig.1). What appears in these patients’ CT scans are "ground glass," a phenomenon in which fluid builds up in lungs and presents itself as white patches. 

The coronavirus pandemic is still in its heights, and frankly, there are not much that we can do about. However, it is no longer something that we can underestimate or underrate. Despite no evidence in proving its effects against the prevention of the coronavirus, masks can prevent droplet transmissions and therefore should be wore, at least in crowded and confined spaces. Wash hands and use alcohol disinfectants after handling public objects and before eating. Most importantly, keep yourself healthy no matter what. 

Fig.1 CT scans of patients reveal the accumulation of fluids in lungs after the SARS-CoV-2 infection

Reference:

“False Claim: Doctors Offer Advice for Preventing COVID-19, Symptoms like Coughing and Fever Indicate Pulmonary Fibrosis, Fibrosis Is Detectable by Holding Your Breath for 10 Seconds, Drinking Water Every 15 Minutes Repels Coronavirus.” Reuters, Thomson Reuters, 17 Mar. 2020, www.reuters.com/article/uk-factcheck-covid-advice-self-test-drin/false-claim-doctors-offer-advice-for-preventing-covid-19-symptoms-like-coughing-and-fever-indicate-pulmonary-fibrosis-fibrosis-is-detectable-by-holding-your-breath-for-10-seconds-drinking-water-every-15-minutes-repels-coronavirus-idUSKBN2142B6.

Bostock, Bill. “Those Who Recover From Coronavirus Can Be Left With Reduced Lung Function, Say Doctors.” ScienceAlert, 14 Mar. 2020, www.sciencealert.com/even-those-who-recover-from-corona-can-be-left-gasping-for-breath-afterwards.

G M-K Tse, K-F To, et al. Pulmonary pathological features in coronavirus associated severe acute respiratory syndrome (SARS). NCBI, 2004.

Ryan T. Kendall, Carol A. Feghali-Bostwick. Fibroblasts in fibrosis: novel roles and mediators. NCBI, 2014.

Motor Proteins: Cytoskeleton Filament Motor Proteins

Motor proteins are proteins that transform chemical energy into mechanical work. They are divided into three categories: cytoskeleton filaments motor proteins, nucleic acid motor proteins, and rotary motor proteins. In this article, we will talk in-depth about cytoskeleton filament motor proteins.

Cytoskeleton filament motor protein

Cytoskeleton filament motor proteins are motor proteins that associate and move along cytoskeleton filaments. This includes myosins, kinesins, and dyneins.

Myosin

Myosins are motor proteins that move along microfilaments; thus, they are also called actin motor proteins (because they interact with the actin of microfilaments). Myosins hydrolyze ATP as the source of energy and use it to propel their movements toward the plus end of an actin filament.

There are as many as 18 types of myosins that are known. Myosin II, for instance, is responsible for generating muscle contraction and dividing a cell during cytokinesis. Myosin V is involved in vesicle and organelle transport. Myosin XI is involved in cytoplasmic streaming, wherein movement along  microfilament networks in the cell allows organelles and cytoplasm to stream in a particular direction.

The movement of myosin is characterized by a release of actin during every cycle. What does this mean? Take muscle-contracting myosin II as an example. Myosin attaches to an actin component, moves once, and then dissociates from the actin. It then attaches again onto actin. This is the cycle of myosin movement.

Kinesin

Kinesins associate and move along microtubules, involving in the anterograde movement [1], which directs the transport of cargoes toward the plus end of microtubules. However, kinesins can also travel toward the minus-end, depending on whether the kinesin has an N-terminal or a C-terminal cargo-binding region. Anyway, just keep in mind the relationship between kinesin and anterograde transport.

Kinesins are primarily involved in the separation of chromosomes during cell division and also the shuttling of mitochondria, Golgi bodies, and vesicles within eukaryotic cells.

Unlike the movements of myosins, kinesins are rather highly processive. This means that kinesins move a great deal of “steps” before dissociating their carriages. Recall the shape of a kinesin [click]. The two heavy chains that attach to the microtubule function like legs, “walking” on the microtubule for a cycle of as much as hundreds of steps, while the two light chains attach to vesicles or organelles like hands.

Dynein

Dyneins move along microtubules through the retrograde movement. Dyneins are larger and more complex than kinesin and myosin motors, composing of two or three heavy chains and a large and variable number of associated light chains. Dyneins move toward the minus end of microtubules, where the nucleus locates.

There are mainly two types of dyneins. Axonemal dyneins facilitate the beating of cilia and flagella by sliding microtubules. Cytoplasmic dyneins facilitate the transport of intracellular cargos. 15 types of axonemal dynein are presently discovered, but only two cytoplasmic forms are known.

Summary

Myosin – microfilament - muscle contraction - cytokinesis (microfilament)

Kinesin – microtubule - anterograde - separation of chromosome - transport

Dynein – microtubule – retrograde - beating of flagella and cilia - transport

Reference:

Lodish H, Berk A, Zipursky SL, et al. Molecular Cell Biology, 4th edition. W. H. Freeman, 2000.

Berg JM, Tymoczko JL, Stryer L. Biochemistry, 5th edition. W. H. Freeman, 2002.

Anatoly B. Kolomeisky. Motor Proteins and Molecular Motors: How to Operate Machines at Nanoscale. NCBI, 2013.