Short science posts | Cubozoa (most advanced cnidarian nerve system)

Cubozoa, or box jellyfish, are another cnidarian class. Their name stems from their distinct cube-like shape. Cubozoa are also distinct from other cnidarian because their venom can be fatal to humans. As with all cnidarians, box jellyfish have two nerve nets and, like Scyphozoa, rophalia. However, box jellyfish also have a distinct nerve ring, as well as more developed eyes that consist of a lens, cornea, pupil, and a layer of retinal cells. Altogether, Cubozoa have 24 eyes, which makes them the most advanced cnidarian class in the sensory aspect.

Rophalia are mutually connected via the mentioned nerve ring. This ring is believed to be an integration center for the swimming, visual, and tentacle systems; it is comprised of oversized neurons, as well as some smaller neurites.
The communication between the nerve net and jellyfish muscles is regulated by chemical synapses.

Most of the information relating to Cubozoa, I already mentioned in the previous post about Scyphozoa, so I only wanted to relay the main differences between the two. These two classes are so similar that, until recently, they were actually considered one class.

Literature & more information:
Habdija et al: Protista-Protozoa, Metazoa-Invertebrata, Alfa, 2011, Zagreb
The ring nerve of the box jellyfish Tripedalia cystophora
Do jellyfish have central nervous systems?
Jellyfish nervous systems

Biology in popular culture – movies&TV (part 1)

I already wrote couple of posts on this topic, and today I’m focusing on several examples from movies and TV shows I’ve recently watched. The movies I’m going to write about are Lara Croft: Tomb Raider – The Cradle of Life, The Good Liar, Charlie’s Angels (2019 version), and Paranoid TV show. So, if you are planning to watch those, just a warning that there will probably be spoilers below!

Let’s start with the obvious and amusing misportrayal: in Lara Croft: Tomb Raider – The Cradle of Life (2003 movie), Lara is riding sharks in the opening sequence. I think no one would believe this is actually possible, but shark petting videos recently became very popular. However, many researches are strongly discouraging this type of behaviour.

The Good Liar (2019 movie) is an interesting thriller with really good cast that I actually enjoyed. Without giving out too much of the plot, I’ll just mention one scene where Helen Mirren’s character gives the haircut to the character played by Ian McKellen. She uses cut hair for the DNA analysis, factually linking McKellen’s character for the past crimes.
Of course, we all know that without the root, there is no DNA to analyze, right? Not quite.
Most companies that do DNA analysis require hair with follicles in order to extract DNA for analysis; however, they mostly deal with paternities, so they need the nuclear DNA. Mitochondrial DNA, on the other hand, apparently can be extracted from the hair itself. For the movie’s purposes, I think nuclear DNA was needed, so this seems like a movie mistake. But, recently scientists did manage to successfully extract nuclear DNA from rootless hair, but that DNA is often fragmented and complicated to extract.
I would also just like to mention that I believe this movie explains trauma and coping surprisingly well for a Hollywoood movie.

In Charlie’s Angels (2019 movie), which I hoped would be more enjoyable than it was, a very interesting premise was introduced; in order to effortlessly communicate, members of the team get a certain tattoo (at least I think it’s a tattoo, but don’t 100% quote me on that) and they can hear thanks to it. So, my first thought was, wow, they really went sci-fi on this one, but it sounded too out there. And then I remembered bone conduction. Simply, bone conduction allows you to hear the transmission, without blocking the outside sounds. And yes, only you can hear it. There are headphones already in use for this type of thing, and they can be also used to help with some kinds of hearing impairments. These headphones are placed on the skull, and I haven’t seen it implemented in a tattoo yet, but it’s actually a neat idea.

Paranoid (2016 TV show) is, in my opinion, really bad, despite only tangential connection to Biology. This show feel anti-medication and anti-psychiatrists, portrays them in a very bad light, and chooses not to mention how much medications and psychotherapy are actually helping people. The premise is also built on one of the cliche “anti-big pharma” representations. I was honestly insulted, despite not working in any of these fields. There is a also a subplot concerning a female character who had provocative photos of her taken 15 years ago, and she is not longer in possession of said photos; she is blackmailed with the possibility of leaking those. Her love interest immediately accuses her of things I won’t write here, but you get the main idea. I mean, am I the only one who sees this as highly problematic
This TV show is doing some serious damage to the health care, it is insulting to physicians, it is insulting to patients, and I honestly can’t believe that no one during the whole production didn’t say anything.


I hope you like these kind of posts, because I already have enough material for another one (there are a lot of Biology & science mistakes on the big screen). What is your favourite movie mistake related to Biology?

Short science posts | What is a nerve net?

A nerve net is a type of nervous system that consists of many neurons but there is no brain or cephalization. Nerve nets are found in animals with radial symmetry (Cnidaria) and biradial symmetry (Ctenophora). Despite being called a net, there sometimes exist some groupings of neural cells in some Cnidaria classes, which I will write more about during the next couple of weeks.
Cnidaria are specific due to their specialized organelles, cnidocytes, which they utilize to hunt for food or use for securing itself to a surface. Some cnidocytes contain toxins that can paralyze their prey (the burning sensation you may have felt when touching a sea anemone 😉).
As a rule, Cnidaria have two diffuse nerve nets, one in the epidermal layer and a second one in the gastrodermal layer. In between these two layers is the mesoglea, a layer that functions as sort of a skeleton. The epidermal net consists of bipolar and multipolar nerve cells, while the gastrodermal net is made up of only multipolar cells.

Cerianthus membranaecus (known as cylinder anemone or coloured tube anemone)

Cnidarian nerve systems are fascinating but also quite unexplored. What is known is that nerve cells consist of two types of neurons, sensory neurons that respond to stimuli and motor neurons which ultimately trigger a response. Chemical synapses exist and provide the communication between the neurons. Hormones have also been reported in some cnidarians (steroids, neuropeptides) but it is still not known how exactly these signalling molecules work.


In the next couple of weeks, I will write a post about every cnidarian class and also ctenophores, focusing on their nervous and sensory systems. If you have any questions or would like me to focus on something, please let me know!

Literature & more information:
Habdija et al: Protista-Protozoa, Metazoa-Invertebrata, Alfa, 2011, Zagreb
Endocrine-like Signaling in Cnidarians: Current Understanding and Implications for Ecophysiology
Evolution of sensory structures in basal metazoa

Short science posts | Do sponges have a nervous system?

Sponges (phylum Porifera) are sessile multicellular organisms that live predominantly in seas and oceans. They don’t have tissues or organs, and therefore, they don’t actually have a nervous system. However, they do have bipolar and multipolar cells that resemble nerve cells, which are found in the middle, “jelly-like”, layer.
Sequencing of some sponge species showed the presence of many genes associated with neural cells, such as genes that code enzymes for neurotransmitter synthesis and synaptic transmission. It is important to note that these genes have other functions in the organism. It has also been observed that some sponge larvae can respond to outer stimuli and show various “taxis” behaviour – phototaxis (response to light), geotaxis (response to gravity), rheotaxis (response to water current). Phototaxis has been closely studied in species Amphimedon queenslandica (class Demospongiae), a sponge native to Coral Sea.

Aplysina aerophoba, also of class Demospongiae, which can be found in Adriatic Sea.

Potassium channels have been observed in that same species, as well as glutamate, GABA, and NO systems, which have been investigated in Ephydatia muelleri, another species of class Demospongiae. Electrical signalling has been noted in glass sponges (class Hexactinellida). These sponges have bodies comprised of a syncitial tissue and their skeleton is made of silicon dioxide. The scientists were able to measure the action potential (5s long, with 29s refractory period) and deduce this signal relies on potassium and calcium ions.
Some scientists even suggest that sponges used to have a nervous system, but lost it during evolution – they introduced several hypothetical scenarios for this event, proposing that sponges lost their nervous system in order to focus on filtering.

Literature & more information:
Habdija et al: Protista-Protozoa, Metazoa-Invertebrata, Alfa, 2011, Zagreb
Evidence for Glutamate, GABA and NO in Coordinating Behaviour in the Sponge, Ephydatia Muelleri (Demospongiae, Spongillidae)

The GABAergic-like System in the Marine Demosponge Chondrilla Nucula
Where is my mind? How sponges and placozoans may have lost neural cell types
Elements of a ‘nervous system’ in sponges

Short science posts | Nervous system evolution

For the next couple of weeks, I would like to write a bit about the evolution of the nervous system, from early nerve cells to the human nervous system and brain evolution. Alongside nervous I will also focus, to a lesser extent, on sensory systems. These posts will be published on my Instagram account, but I decided to publish them on the blog as well.

Mostly, these posts will be about various animals and the nerve systems they have – nerve nets, nerve cords, complete systems. The main process behind this is called cephalization, and it starts with the groupings of nerve cells and ganglia at one end of the body. After some (long) time, this process led to us having a head with sensory organs and a brain inside it.

But when did all of it start? It is kind of hard to say, for even single-celled organisms, such as bacteria, have voltage-gated channels and genes that support the theory of possible synaptic transmission. These channels are potassium (the oldest), calcium, and, rarely, sodium channels as well. Action potentials have been detected in some algae and diatoms, although their function is mostly unclear. In Chlamydomonas (unicellular green algae) on the other hand, potentials were detected in flagellums, which clearly suggest they play the part in the movement of the algae. Action potentials were also recorded in the cilia of some protists, such as Parmecium.

Of course, the exact evolutionary processes are unknown, and there is a possibility that these organisms acquired the mentioned features later than scientists now assume. It is also possible that some more evolved organisms, such as sponges, subsequently lost some of the features discussed here (more about this in the next week’s post).

Literature & more information:
Habdija et al: Protista-Protozoa, Metazoa-Invertebrata, Alfa, 2011, Zagreb
Bacterial voltage-gated sodium channels (BacNaVs) from the soil, sea, and salt lakes enlighten molecular mechanisms of electrical signaling and pharmacology in the brain and heart
Early evolution of neurons
Deep evolutionary origins of neurobiology
From damage response to action potentials: early evolution of neural and contractile modules in stem eukaryotes

Studying | My top 5 tips & tricks

This week, I would like to write about studying. My studying to be precise, and since I’m at the near of earning my Master’s degree, you would probably guess I know how to study. Well, wrong. Well, maybe a bit wrong. My studying, of literally anything, is greatly affected by my health – without getting into more detail, I have problems with concentration and sometimes memory, which is directly mirrored in my grades and ability to study. However, despite often feeling isolated and defeated, I try my hardest.

I was on my first year of Bachelor’s, when I realized things are not quite right. At first, I thought that it’s just stress and the fact I would rather study neuroscience then General Chemistry, so I casually started couple of courses on Coursera. To my shock and frustration, I soon realized that things are just not working out. Since then, I switched up and changed up my study styles numerous times; places where I study, times when I study, and how I study. One of the first things I did was try the famous pomodoro technique, but I modified it for longer intervals – I found that studying 45 -60 minutes with a break works better for me. This, of course, depends on the subject I’m studying. Have you tried this technique? What did you think about it?

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Another thing that I always do, is having my headphones on – I simply focus better than when I have music blasting through normal speakers. Now, many people don’t recommend listening to music, or having a TV working in the background when studying, but to me, it has been proven to be most helpful. I usually like to put some Dick Wolf produced series in the background, no matter how many times I’ve already watched it, and start reading literature or writing notes. However, when I actively learn the material, I only like random noise, for which I use Noisli, a web site where you can make your own mixes of sounds (like fire, wind, thunder, train, rain…). This site saved me many times from my lack of attention. So, here are my top 5 tips for studying:

  1. Writing things down
    One of my high school teachers was a big fan of this method, claiming that if  we write things down, we tend to remember them better. Whether is simply writing down main phrases & keywords, or making a mental maps, this type of studying and revising proved to be really helpful. Another thing I sometimes do is, instead of writing things down physically, is writing them on the PC, as shorten versions of book chapters, or upgraded versions of PowerPoint lectures (my professors love their PowerPoints). However, sometimes I don’t feel comfortable doing this when I have a large amount of material to study.
  2. Mementos, short notes, and studying out loud
    Instead of lengthily texts, I also like to write down phrases or draw illustrations on post-it notes; I use this as a revision method, where I shuffle them and explain the word or process out loud. I prefer this type of studying when I don’t have enough time, or have a lot of things to study. My trick is to use different colored papers for different subjects 🙂
  3. Writing reminders or spelling out first letters for longer definitions and lists
    I think this is an old trick, but I wanted to include it nevertheless. Instead of definitions and long lists, it’s a good idea to write down first letters or syllables, in order to remember them easier.
  4. Watching videos
    Watching YouTube videos has helped me more than once when struggling with the study materials. Sometimes I just don’t quite comprehend the wording (strictly technically speaking, English is my 3rd language) or I need a reminder of basics, without going through my dusty books from the first year. Videos are here to help and they often include very useful graphics that can help to visualize the material. My go-to channels are JJ Medicine, Crash Course, and Neuroscientifically Challenged. What are your favourite channels? 🙂
  5. Explaining things to a friend/sibling/partner
    This is very similar to the second point, studying out loud, but sometimes I require more practice. Studying groups are a good idea but sometimes, I just can’t make myself to get out of the apartment. In those cases, I try to explain the material to someone in my household (and who usually doesn’t listen to me, but that’s okay :)) – I try to do this by myself as well, when I’m preparing for an oral exam.

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With time I realized that, before I even start studying, I always have a feeling like everything has to be perfect – I have to clean the room first, finish other assignments, eat lunch… My partner doesn’t. And that’s fine. We all study at different paces & places, and sometimes unforeseen circumstances can affect are studying and also grades. Many people struggle with illness, visible or otherwise, which can affect our performance – anxiety, headaches, insomnia… But the most important thing is to just keep going, give yourself enough breaks, and take care of your health. And since I’m publishing this in the midst of the pandemic, know that it’s perfectly okay if you don’t have any motivation or means to study right now! I know it’s easier said than done, but try not to stress too much and relax, if it’s possible.

I would also very much loved to hear about your studying tips & tricks – share them in the comments below! 🙂

*UPDATE: I was notified by a friend that, recently, Noisli put a daily limit for streaming. Also, I forgot to mention another useful app I use for studying, Forest – it functions in a way that you set a timer, and “grow” your virtual trees. I find it useful because the only way to leave the app is to stop the timer (and stop your tree from growing). It might sound trivial, but it helps me stay focused and not check my social media pages every other second.