Week 5. The chemical senses, the eye and the central visual system
This week we had a lot more reading than usual. However, even though we had to read three chapters, it turned out to be a little easier than reading one from earlier. The topic was more familiar from our previous studies. In addition, this week’s topic was quite real-life-based again. Despite the fact that the topic was not extremely complex for understanding, there were still parts that require a lot of attention and focus, for example, the one about chemical senses. Also, this week we had a virtual excursion to the Aalto Neuroimaging Infrastructure (ANI), the excursion showed how comprehensive and versatile the Aalto University equipment is, and inspired us to think about possible measurements we want to do with this equipment.
While reading and listening to the lecture we learned that there are three main chemical senses: taste or gestation, smell or olfaction, and trigeminal system. The taste system is responsible for the quality and safety of food (or something else) eaten. The smell system affects behavior in many animals and humans. The trigeminal system provides information about external sources, which could irritate skin, eyes, nose, or mouth. All three systems play a very important role in our everyday life and its quality by transmitting the action potential that comes from receptors to an appropriate region of the nerve system. Interestingly the olfactory pathway does not go through the thalamus: this raised the question if this structural detail has something to do with even very early memories and smells intertwined. The smells have a direct route to the limbic system where we have our brain regions related to memory and emotions. It would be interesting to know whether it is good/happy smells that we memorize best or also bad smells-for example in relation to a specific moment in our childhood. A study related to emotional responses connected to personally meaningful odors that we came across: https://pubmed.ncbi.nlm.nih.gov/14670575/ has a very small sample size but interesting results suggesting in addition that visual cues related to a specific object with a smell did not result in as strong activity (in hippocampus and amygdala) as the smell itself.
Interestingly, you could possibly even train your sense of smell as mentioned in this article. This makes sense as people can train to become connoisseurs of wines, teas etc. https://news.harvard.edu/gazette/story/2020/02/how-scent-emotion-and-memory-are-intertwined-and-exploited/
After getting familiar with the main chemical senses we dove deeper into the structure of the eye and central visual system. We got familiar with the structure of the human eye and the role of the central visual system, which processes and integrates the visual information coming to the brain along nerve fibers. The process that turns light into a neural impulse is called phototransduction cascade. This results in turning the rod cell off in the retina. Inside the rod there are lots of discs (hundreds), which are full of little proteins (multimeric protein, 7 subunits: rhodopsin; there is a molecule inside it : retinal). As some light hits the eye, it causes the the retinal to change conformation, this causes the rhodopsin to change shape. This again starts a cascade of events in the subunits: alpha, beta and gamma-transducin breaks away from rhodopsin and goes and binds to PDE, this takes cyclic GMP and turns it into regular GMP (this causes sodium channels to close) and the rod turns off (hyperpolarization of the photoreceptor).
Next week we have the excursion on brain anatomy finally, we are really looking forward to it.
Responses