Circadian Rhythms

An Independent Project by Monika Nemcova ’19

Part 4 of 4

Circadian Rhythms

This is the final blog post on my series about sleep. Last time, I wrote about the relationship between sleep and learning. Today, I would like to focus on why do we, as mammals, tend to become sleepy at roughly the same time every day. So, what makes us want to go to sleep? And what keeps us awake during the day?

The intricate system in charge of our sleep-and-wake patterns comprises of two so-called drives, homeostatic and circadian. The drives (sets of processes promoting an action) act in opposition [1], balancing each other – in the same way as the two conflicting forces, the gravitational and the centrifugal, balance the Earth on its orbit. However, unlike the forces affecting the Earth, the homeostatic and circadian drives change in size throughout the day – which allows us to transition between sleep and wakefulness.

Homeostatic drive

Homeostatic are any processes that organisms use to maintain stable conditions in their bodies. Homeostatic processes, for example, keep the blood levels of oxygen and sugar stable or maintain the optimal body temperature. Our bodies naturally strive to keep the inner conditions consistent and if an unusual spike in any chemical occurs, there are mechanisms that return said chemical on its normal level [2].

But how does that concern our sleep? Enter adenosine, the neurotransmitter I already wrote about in my second blog post (quick reminder: it makes us sleepy and caffeine functions by blocking it). Adenosine, alongside with other chemicals, builds up in the brain as we are awake – the longer we stay awake the more adenosine there is and, in turn, the sleepier we are. As you can see in Fig. 1, when adenosine levels reach a certain point, we feel sleepy enough to go to bed. During sleep (shown as the purple field), the adenosine levels get flushed out of the brain. That is why it is called the homeostatic drive – when there is too much adenosine, the body employs mechanisms to get rid of the chemical [1].

In addition, adenosine build-up explains how does sleep debt work. In the picture, you can see that after a night full of sleep, the adenosine levels are fairly low. But what happens when we do not allow ourselves enough time in the bed to get rid of all of the adenosine? Well, it just stays in the brain – and as the day progresses, the build-up starts at the levels left there from the previous night, not zero. That is the reason why we feel so horribly tired the day following insufficient sleep or even an all-nighter. Longer time in the bed effectively erases the sleep debt by decreasing the adenosine levels. Nevertheless, if we, once more, do not sleep enough, the morning baseline amount of adenosine increases again. That continues until the body cannot put up with the adenosine levels anymore. Then it just forces us to sleep [1] – and that is all the missed first periods and slept-through films, classed or ASM.

Fig. 1 Homeostatic and Circadian Drives (

Circadian drive

However, if sleep was determined only by the homeostatic drive, the time when we go to sleep and wake up would not matter. Yet very few of us thrive in a regime with a supposed activity peak around 4 a. m. and time for sleep around midday. Why do we naturally tend to sleep during the night and be awake during the day? And how does the brain regulate it?

The answer lies in the second cycle that drives sleep and wakefulness – the circadian rhythm. “Circadian” comes from the Latin words for “around” and “day”, so it won’t come as a big surprise that the circadian rhythm acts as an inner clock for many species, from plants and bacteria to animals. So while the homeostatic drive tells us that we are sleepy when we stayed up for late, the circadian rhythm tells that is is time to go to bed because it is past midnight [3]. The fact that we have inbuilt time makers that go beyond detecting the outward cues (such as the amount of sunlight outside) has been experimentally proven. A group of volunteers was left to live in total darkness for several weeks and their sleep-wake cycle still exhibited periodicity. However, without the outward visual clues, the average length of “one day” (period of wakefulness followed by a period of sleep) was about 25 hours. As a result of that, the volunteers went to sleep about one hour later every day – so after 6 days the difference between the time outside and their inner clock was the same as between the East Coast and Europe [1]. In normal conditions, the human inner clock synchronizes itself daily with environmental clues. This agility marks the second important characteristics of the circadian rhythm: it can adapt to various outward signal. That is what happens when we travel to a country in a different time zone – the inner clock slowly shifts so that the perceived clues match the intrinsic signals. Another peculiar thing our inner clock can do is to change the ratio of “night” and “day” – in the past, people in the Northern Hemisphere slept more during the long winter nights and less in summer. And last but not least, even the length of the circadian period can change. I already talked about the shift from the natural 25 hours period to the 24 hours period we exhibit normally, but, in fact, human beings can be entrained to accept anything between 23 to 25 hours as the length of a “day.” [1] Interestingly, a day on Mars lasts 25 hours [4], so at least our internal clock wouldn’t pose a barrier for possible future colonization of the red planet. I have never realized how important that is – it would be very inconvenient and unhealthy for the first colonists to cycle out of rhythm with the outward cues.

So, returning to the Fig. 1, circadian rhythm prompts our brain to go to sleep roughly around the same time every day. In mammals, the center for keeping track of the circadian rhythms is called the suprachiasmatic nucleus (SCN) [3]. But keeping track of time is not something impressive in the terms of our body – experiments showed that a wide array of cells are able to do that, from the cells of lungs and liver to the ones of skin. What is truly unique about SCN is its position next to the ending of the optical nerves. SCN’s timekeeping system is the only one in the body that can actively respond to visual cues and thus synchronize the inner time with the perceived outward time [3].

In addition, SCN helps to maintain a healthy sleep-wake cycle in other way: by initiating the circadian drive. I started talking about the circadian drive as the opposing force to the homeostatic drive but then went on about the circadian rhythm. It was necessary to understand the periodicity of the process but now I can finally explain how exactly does the circadian drive influence wakefulness. The circadian drive allows us to have a single period of consolidated wakefulness [1]. It is basically a signal from SCN to neurons that release wakefulness-promoting neurotransmitters, such as monoamines or acetylcholine [3]. If we did not have the circadian drive, we would be able to remain awake only for a few hours – after that the homeostatic drive would force us to go to sleep. After short rest, we would wake, be active for a while, and had a need to go to sleep again [1]. One can surely imagine that hunting, foraging or any other complicated activity would be severely hindered by that. So the circadian drive, which acts as the opposing force promoting wakefulness, is very important for the success of human or and many other bigger species. As you can see in Fig. 2, even though the upper arrows symbolizing adenosine levels increase as the day progresses, the wakefulness levels (the blue line) remains constant. That is because the circadian drive (lower arrows) gradually increases as well. In the evening, the circadian drive decreases but the homeostatic drive stays strong – as a result, we become tired and fall asleep. In the morning, the situation is reversed – the adenosine levels have decreased and the circadian drive, timed by the circadian rhythm in SCN, wakes us up [1].

Fig. 2 Intrinsic factors influencing the sleep-wake cycle
Fig. 2 Intrinsic factors influencing the sleep-wake cycle (

I hope that you have found the mechanism of the sleep-wake cycle as fascinating as I have.


[1] Lee, T. (n.d.). Sleep occurs as a circadian rhythm [Video file]. Retrieved from

[2] Rodolfo, K. (2000, January 3). What is homeostasis? Scientific American. Retrieved from

[3] Wright, K. P., Lowry, C. A., & LeBourgeois, M. K. (2012). Circadian and wakefulness-sleep modulation of cognition in humans. Frontiers in Molecular Neuroscience, 5(50).

[4] Mars Facts [Fact sheet]. (n.d.). Retrieved May 8, 2019, from Mars Exploration website:


Welcome Back!

Another Year, Another Great Set of Blog Posts!

Welcome back to Andover! I am sure for a lot of you, it has been a great summer, but it is time to get back into the swing of things!

We have a lot of great things planned for you this year! Be sure to check out one (or more!) of our amazing Science classes this year!

If you are enjoying your Science class or have a Science-related independent project and would like to write one (or more!) blog post – let Ms. Andersen know at! It can even count as your work duty… (!!!!!)

Have a great year!

Mornings with MAC – Retirement Edition

Get to know the retiring Science Faculty with this week’s Mornings with MAC!

Guest Post by Michael Codrington ’18

Mornings with MAC logoLadies and gentlemen, you must’ve had a lonely Wednesday morning last week without Mornings with MAC and I apologize for that. However, we have an exciting retiring faculty Morning with MAC. I was able to interview 3 Andover greats, Dr. Stern, Mr. Cone and Dr. Watt. With a combined 96 total years of teaching (16+51+29), it’s safe to say they’re veterans of PA. First up is Dr. Stern. Stern taught me for a total of 5.5 weeks when I thought that Chemistry 300 was the way to go. 300 had other plans… So, I eventually dropped down to 250. But, I will always remember Stern for his Charisma and willingness to help.

FA 3221764 Stern, DavidMC: What do you teach at Andover?
DS: Chemistry 250, 300, 550, and IPs. It’s been varied, but I enjoy it.

MC: How long have you been working at Andover?
DS: I’ve been here for 16 years. Day 1 was a very famous day – 9/11/2001.

MC: Really?
DS: Absolutely, it was my first day at Andover, ever teaching in a high school. I taught very briefly in a Bronx high school for a couple of months, but that was temporary. The all school meeting was on that first day of class. It was a beautiful Tuesday. The seniors were yelling 02, 02, 02!

MC: What brought you here?
DS: Before I was at Andover, I was selling high quality chemistry instruments, Spectrometers. It was about a 20,000 dollar instrument and I sold to Temba Macabela. He taught the organic chemistry class and organic chemists love this thing called Infrared Spectrometers.

MC: Where did you go to college? What did you study?
DS: I went to Lafayette College in Pennsylvania and got a bachelor of science degree. I could’ve gotten a bachelor of arts and taken different courses, more english and history courses. But the bachelor of science degree meant I had to take more physics and chemistry. It was very rigorous. Then I went to grad school and got a PhD in Analytical Chemistry.

MC: What is your favorite thing about Andover?
DS: The energy of the students. Every September, I would see new faces and new students and meeting them the first couple of weeks, slowly learning names and 9th grade boys soccer. Haha, That was a fun experience.

MC: If you weren’t studying/teaching chemistry, what other discipline would you be in?
DS: Probably math. I love math, I love plane geometry. I could teach you some algebra, not like these Phillips guys, but I know a decent amount. I loved how it was a puzzle. You figure it out with all your information. It’s great.

MC: What’s your favorite movie?
DS: I’ve got a lot of favorites, you wouldn’t know ’em though, so I love “Casablanca”. “Saturday Night Fever”, took place in Brooklyn about the New York scene. I love the James Bond movies of course. “12 Angry Men”, took place in the Bronx, about a big court case and really shows the prejudices from the time and that are still there in the Bronx. I don’t know I could watch a movie yesterday and forget the name.Cod and Stern

MC: Do you consider yourself an easy or hard teacher?
DS: Grade-wise I’m fair but hard. I could use a pun, I’m very stern…
MC: …
DS and MC: Hahahaha!
DS: But yeah, I grade a little difficult, but I understand that I’m teaching high school kids college chemistry and it blows my mind when I see one of them in a theater production or something like that.

MC: What’s one thing that a lot of people don’t know about you?
DS: They don’t know that I love to dance and rock and roll and that my favorite rock and roll band is The Stones.

Next on the roster is Mr. Cone. Cone boasts 51 total years of Andover teaching experience, having been able to both teach and teach alongside many Andover alums like Ms. Elliott ‘94, Mr. Ventre ‘71, and fellow science teacher Mr. Faulk ‘00.

FA 3046736 Cone, ThomasMC: How long have you been working at Andover and what do you teach?
TC: I’ve been here 51 years.

MC: Wow, that’s a really long time.
TC: Hahaha! I’ve taught first year Biology for many years, the name keeps changing. I’ve taught AP level Bio, I’ve taught Biology 500. I’ve taught term-contained courses. The last 20 plus years I’ve taught term contained courses for seniors, mostly. Animal Behavior in the fall, Microbiology in the winter and Ornithology in the spring.

MC: What brought you here?
TC: Well, I was overseas in the Peace Corps and my father was retiring from the Navy, he was a doctor at Harvard, and since I was coming back from the Corps, I wanted to live somewhere in New England and I applied to teach at a bunch of these New England Preparatory Schools.

MC: Where did you go to college? What did you study?
TC: I went to Trinity College in Hartford and I majored in Biology and minored in Education.

MC: What is your favorite thing about Andover?
TC: Wonderful student body. It’s always exciting, active, interesting students. Science faculty has always been superb. A beauty of a school like this is you have a number of teachers in the same department.

MC: If you weren’t studying/teaching biology, what other discipline would you be in?
TC: I enjoy history a lot, I think it would probably be the history department.

MC: What’s your favorite movie?
TC: Uh.. a recent movie or?

MC: It’s up to you I don’t really know, haha!
TC: My favorite movie when I was a kid growing up was “High Noon” with Gary Cooper – 1951. Also loved “African Queen” with Humphrey Bogart.

MC: Do you consider yourself an easy or hard teacher?
TC: I’d say somewhere in the middle. Students do what I ask them to do and they’ll do well. If they take good notes they should be fine. I want them to do well, that’s the point of a teacher. It’s like being a coach. When my students took APs, I wish I was in there with ’em, I mean I obviously couldn’t be, but I wish I could.cod-and-cone.jpg

MC: What’s one thing that a lot of people don’t know about you?
TC: Don’t know about me? When you say a lot of people you mean like you or like…

MC: Yeah, I mean uhh.. Like.. I don’t know… 
TC: Hahaha, it’s ok. Well in class, we joked about having animals and I had a black mamba as a pet. There was this long black snake in Liberia that was my favorite.

MC: That’s insane.
TC: It was a party, haha!

MC: Thank you, Mr. Cone it was great to meet you.
TC: You too, have a good one.

Last on the roster is Dr. Watt. I learn physics in the classroom next to Watt everyday during 4th period, but I have never really met him before. I immediately regretted that because he is hilarious. I sat down with Watt in his office at Gelb 222.

FA 3036992 Watt, J. PeterMC: How long have you been working at Andover and what do you teach?
DW: Physics and Geology. 29 years, which is nothing compared to Mr. Cone.

MC: Where did you go to college? What did you study? What brought you to Andover?
DW: I went to college in a place called Dalhousie in Canada, I got my bachelors and masters in Physics. I got my PhD at Harvard. Then I was a research fellow at the University of Colorado for a year then I was a research fellow at the seismological lab at CalTech for a year. I was trying to raise research funds for graduate students and it was hard for me to raise money and do science, so I decided why not come to some place with great teachers and great students.

MC: What is your favorite thing about Andover?
DW: The enthusiasm of the students.

MC: Favorite song?
DW: Nothing. Oh dear, I’ve got nothing, next one.

MC: If you weren’t studying/teaching biology, what other discipline would you be in?
DW: Likely Mathematics.cod-and-watt.jpg

MC: What’s your favorite movie?
DW: Harold and Maude

MC: Do you consider yourself an easy or hard teacher?
DW: Yes

MC: Hahaha! What?
DW: Haha! I try to cover the material, but I also try and be sympathetic of the students because I know they have a lot going on and it’s hard so I’d have to say I’m reasonable.

MC: What’s one thing that a lot of people don’t know about you?
DW: I’m from Canada.

That concludes Mornings with MAC for the 2016-2017 academic year. It’s been real and you can look out for a new edition coming in the fall of 2017. Have a great summer!

Mornings with MAC – Faulk Edition

Get to Know Your Science Faculty with your Weekly Installment of Mornings with MAC!


Mornings with MAC logoOn this week’s Mornings with MAC, we have former Andover student and Chemistry Department Chair, Mr. Faulk. Brian Faulk was Andover class of 2000, having shared parts of his Andover experience with many faculty including Natalie Wombwell ‘01 and Terrell Ivory ‘00.

Faulk taught my last term of Chemistry 250, and definitely offered a challenge. Gifting me the nickname MC3+, after one of the ions we worked with, it’s safe to say me and Mr. Faulk had a good relationship. I sat down with him during his morning coffee to ask him some questions.

FA 3075722 Faulk, BrianMC: What do you teach at Andover?
BF: Are you recording me?

MC: Yes I am – hahaha!
BF: I teach all levels of chemistry, primarily chem 250 and organic chemistry.

MC: How long have you been working at Andover?
BF: I’ve worked here for 10 years.

MC: What brought you here?
BF: As a student I was really inspired by my teachers not just my classroom teachers but my coaches and my academic advisor. I thought it’d be cool to come back and serve in those roles as a faculty member.

MC: Where did you go to college? What did you study?
BF: I went to Stanford to study chemistry and Harvard for grad school to study chemistry.

MC: What is your favorite thing about Andover?
BF: I think my favorite thing is the people – both students and faculty, it’s a really rich and vibrant community and that makes it fun to come to work everyday.

MC: If you weren’t studying/teaching chemistry, what other discipline would you be in?
BF: History. Probably history – I love history and I’d probably do something with the Civil War.

MC: What’s your favorite movie?
BF: What?

MC: What is your favorite movie?
BF: I really like Patton.

MC: Like the General?
BF: Yeah, they won an Academy Award. It was a great film.

MC: Do you consider yourself an easy or hard teacher?
BF: I’m sure the students would say I’m difficult. I have high expectations, but I always want to do what’s best for the students. I want to coach them along to learn as much as possible.

MC: What’s one thing that a lot of people don’t know about you?Snapchat-1945347321
BF: I think it’s probably that I love history, and it’s my passion. Sometimes I wish I was a history teacher. I read a lot of history magazines in my free time.

MC: I understand you went to Andover. How was that experience and who was your favorite teacher from when you were a student?
BF: It was tough at times, but I certainly learned a lot, how to work and manage my time, how to ask for help. It prepared me everything after. I think my favorite teacher was Henningsen, recently retired. He was just really good and brilliant. A great historian and a great teacher.

Non Sibi Day 2017

Students and Alumni help clean up Thompson Island on Earth Day

Astronaut Mae Jemison Visits Andover

The first African-American woman to travel to space speaks to the Andover Community

Guest Post by Isabelle Bicks ’18

Dr Mae Jemison Poster Final

Last Friday evening, Andover had the privilege to welcome Dr. Mae Jemison, first African-American woman to travel to space, accomplished physician, and lifelong dancer. Her vast knowledge and passion for science were palpable, but I was most interested by the connection Dr. Jemison made between the arts and sciences. As both a ballet dancer and biology student, I loved that she drew from both seemingly opposite experiences to illustrate how she was a pioneer in her career. Dancing has been such an integral part in my own life and has most certainly impacted how I work as a student at Andover. Dr. Jemison explained that the arts are the study of ourselves, while science is the study of the world around us. I had never before realized this connection. Although our world today tends to compartmentalize people and label them as either gifted math/science people or arts and humanities people, Dr. Jemison completely disrupted this tendency and explained how her own passion for the arts translated into the successful career she leads.  I think that these ideas about integrating arts and sciences can be utilized at Andover. Bridging the curriculum between the two disciplines seems necessary and beneficial.  At a school that strives to achieve “empathy and balance,” Dr. Jemison was the perfect speaker to embody these qualities.

The Science Faculty had an opportunity to attend a reception with Ms. Jemison and here is a bonus photo of her with Carol Artacho (physics), Sheena Hilton (chemistry), Caroline Odden (physics), and Fei Yao (physics).


Happy Spring (Term)!

Today’s Vernal Equinox also brings the start of the Spring Term at Phillips Academy

This morning, Monday, March 20th, at 6:29am marks the vernal equinox and the official arrival of Spring. Though, it does not look very spring-like outside the Gelb Science Center.


During the vernal equinox, “the sun’s most direct rays cross over from the southern hemisphere into the northern hemisphere. During this process, the sun is shining directly over the earth’s equator, bathing the earth’s northern and southern hemispheres in nearly an equal amount of sunlight.

Instead of a tilt away from or toward the sun, the Earth’s axis of rotation is perpendicular to the line connecting the centers of the Earth and the sun during an equinox. During the equinox, both day and night are balanced to nearly 12 hours each all over the world.

Good news for those [of us] in the northern hemisphere: Daylight continues to grow longer until the summer solstice, which occurs on Wednesday, June 21. The opposite occurs in the southern hemisphere, where daylight continues to grow shorter toward their winter solstice on the same day.”*

Blue Moon

An introduction to Andover’s new STEM-based Magazine


The Phillips Academy students have published a new STEM Magazine – Blue Moon – a magazine of student-written research papers and articles.

Blue Moon was created as a platform for STEM research, as a means by which students can exercise the final step of the scientific method: communication. It aims to foster curiosity and cooperation in both its writers and its readers. Bi-annual print publications are made possible by a grant from the Abbot Academy Association, continuing Abbot’s tradition of boldness, innovation, and caring. Issue I of Blue Moon spotlights the diversity of student interest within the sciences, topics ranging from immunotherapy to gender discrimination to prosthetics. (*from the inside cover of Issue I)

We spoke with Amanda Li, ’18 who pioneered this project, which has been about two years in the making, thus far. During her freshman spring, she began to look for a place on campus to share a paper she had written. When she could not find an outlet on campus, she began to formulate the idea of a student scientific publication. 

“Seeing as there wasn’t any such thing yet, I reached out to students from different grades and backgrounds to see if they were interested in a STEM journal. The overwhelming response was yes, so I decided to take some action and hopefully allow other students to share their research and ideas. It also allows new students to start exploring various STEM areas, by allowing them to read about the interests that their peers hold.” -Amanda Li, ’18

img_6869She applied for an Abbot Grant in her lower fall to fund the publication of bi-annual issues. She received full funding and got to work! She gathered editors, graphic designers, and potential writers during her lower spring and summer. They officially started Blue Moon last fall and they have received over 30 articles so far!

“I’m really grateful for the AAA’s support, otherwise I doubt this would be possible. I’m looking forward to start the process of making the next issue!”  -Amanda Li, ’18

If you are interested in learning more or reading the many articles submitted, visit They are always looking for submissions and feedback!

Welcome and Welcome Back!

On the first full day of classes, the Division of Natural Sciences would like to WELCOME all new students to PA and WELCOME BACK all returning students!

As you can see by the photos above, our Gelb Garden has flourished throughout the summer and we will continue to use these plots as a teaching tool in our Biology Classes. We are excited about the new year and new possibilities!

Chemistry Visits Addison Art Gallery

Chem 200 Visits the Addison Art Gallery to Learn About the Chemical History of Photography

Guest Post by Sofie Brown ’18

Our Chem 200 class was a little bit surprised when Mr. Robinson told us that we would be taking a class field trip to campus’ Addison Gallery of American Art. Chemistry is usually not something associated with art museums but Chem 200 was there to take the sometimes abstract and hard to understand equations and formulas and apply them to photography.

Before the trip, the class divided up into pairs to research the different types and chemical processes involved the history of the creation of photographs. We researched the Daguerreotype, Tin type, Ambrotype, Albumen Prints, and Gelatin Silver Prints. All of these photograph types uses a different chemical process to create the image and by looking at the chemical processes involved in the creation we could trace the history of photographs.


By looking at rare old photographs and sharing our research we discussed how chemical advances have made photography more accessible which has significantly altered the country’s memory and way of looking at history. Photography made memory visual and became the most democratic way of capturing the stories of all people, not just those who could afford to have their portraits painted. Chemical advances took photography from using large equipment in many steps with many poisonous chemicals to print a fragile easily faded photo to a small two step process on paper that is durable and cheap. Photographers would take large wagons of equipment and glass around with them to Civil War battlefields in order to photograph soldiers and the fields of dead when photography first came to prominence. Soldiers also often had Daguerreotypes taken (the classic framed black and white head shot). Gradually, Daguerreotypes evolved to be printed on tin and cheaper and more durable and then eventually became a two step process and printed on paper.


The digital photographs we have today would not be possible without the chemical advances in photography over many, many years. Learning about the chemistry of photographs offered our class real world applications and implications of the molecules and elements we struggle to fit into formulas and categories in the classroom.