1. Learning Outcomes: Define homeostasis and negative feedback
Predict how a sleepiness factor will fluctuate throughout a 24 hour period
Graph a sleepiness factor’s fluctuation throughout a 24 hour period under various conditions
Provide feedback to peers about their predictions and graphs

2. Think/Pair/Share: Define Homeostasis
How is it like driving a car on a highway?
Students should recognize that homeostasis is about maintaining/regulating internal conditions even when the environment fluctuates greatly.
Like driving a car on a highway, you maintain a constant speed even when your may be going up a hill or down a hill etc.

3. Think/Pair/Share:
Your body’s thermostat in the brain is set at 98.6F (unless you have a fever).
What does your body specifically do to maintain this constant body temperature if the ambient temperature is cold? What is your body’s effector mechanism? Will your body just get warmer and warmer and warmer?
What is your body’s effector mechanism for when you are too warm?
Students should discuss how the brain (hypothalamus) activates warming mechanisms in the cold: blood vessels in the skin constrict to prevent heat loss across the body surface and skeletal muscles contract; shivering produces heat (behaviorally, we’ll put on more clothes) body temp rises—if it rises too much the brain will activate cooling mechanisms. (NEGATIVE FEEDBACK shuts off warming mechanism)
The brain activates cooling mechanisms in warm temps: sweat glands secrete sweat for evaporative cooling across the body surface; blood vessels dilate to increase heat loss (behaviorally, we shed clothes) body temp lowers

4. Brainstorm: what else in the body is “maintained” through homeostatic mechanisms besides temperature?
Possibilities are numerous. This is a good way to introduce other systems you might cover….Water, solutes, blood glucose, hormones, pH, O2, CO2, etc…
SLEEP….

5. SLEEPINESS CAN BE DEADLY
Approximately 100,000 automobile crashes each year result from drivers who were “asleep at the wheel.”
In a survey of drivers in New York State, approximately 25 percent reported they had fallen asleep at the wheel at some time.
Crashes in which the driver falls asleep are especially common among young male drivers. One large study found that in over 50 percent of fall-asleep crashes, the driver was 25 years old or younger.
In addition to the high risk of automobile crashes, problem sleepiness can cause difficulties with learning, memory, thinking, and feelings, which may lead to poor school and work performance and difficulty with relationships

6. Consider that the longer an individual remains awake, the stronger the desire and need to sleep become. This pressure to sleep defines the homeostatic component of sleep.
The precise mechanism underlying the pressure that causes us to feel a need to sleep remains a mystery.
A sleepiness factor appears to “keep track” of lost sleep and may induce sleep. We usually sleep once daily because the homeostatic pressure to sleep is hard to resist after about 16 hours.
Copyright © 2003 by BSCS

7. What about sleep homeostasis?
Scientists are still looking for and learning about a possible “sleepiness factor” (SF).
SF levels rise
Sleep homeostasis
AWAKE
ASLEEP
SF levels decrease

8. Graphing a “sleepiness factor” (10 minutes)
Predict, by drawing a line graph, the relative concentration levels of the “sleepiness factor” throughout a normal 24 hr period.
Use paper. Put names on your graph; I will be collecting these.
Label the X axis and the Y axis and give your graph a title.
Make sure awake and asleep periods are obvious on your appropriate axis.
Draw the line that makes your prediction about the sleepiness factor in a normal 24 hour period.
Draw a second graph predicting what would happen to a student that stays up studying and only gets a very small amount of sleep. How is the line different?
SF levels rise
Sleep homeostasis
AWAKE
ASLEEP
SF levels decrease

9. Peer evaluation and feedback (10 minutes)
Swap papers with a partner.
Give written feedback on the graph about whether you agree or disagree with their graph.
Write any questions you have for them.
Discuss.

10. Which of these two graphs is a college student cramming late into the night?
Could

11. Which of these two graphs is a college student cramming late into the night?
Normal: Student won’t be tired until the entire day passes.
Sleep deprivation: student will be tired in a few hours.

12. The precise mechanism underlying the pressure that causes us to feel a need to sleep remains a mystery.
There is recent evidence that the molecule adenosine (composed of the base adenine linked to the five-carbon sugar ribose) is an important sleepiness factor: it appears to “keep track” of lost sleep and may induce sleep.
Interestingly, caffeine binds to and blocks the same cell receptors that recognize adenosine. This suggests that caffeine disrupts sleep by binding to adenosine receptors and preventing adenosine from delivering its fatigue signal. (COMPETITIVE INHIBITION).
This may link back to an idea covered with enzymes: competitive inhibition.
You may have students

13. Think/Pair/Share:
Caffeine would cover up the fatigue feeling, but would not affect the SF level. Thus, when caffeine wears off, sleep pressure will be even higher.
If this student cramming into the night and sleeping only a few hours drinks caffeine when waking, what will happen to the sleepiness factor?
It will decrease
It will increase
Nothing, it will not be affected by caffeine