PSY 3740 Module 4 Consciousness and Homeostasis Paper: Arousal Systems, Why We Sleep and Sleep Loss and Appetite Example

Awake, Asleep and Hungry: How the Brain Regulates Arousal and Appetite on Night Shift

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Bachelor of Arts in Psychology, Thomas Edison State University

PSY-3740: Physiological Psychology

Mentor Name

Month Day, Year

Awake, Asleep and Hungry: How the Brain Regulates Arousal and Appetite on Night Shift

Introduction

I work rotating night shifts at a sleep lab, ironically, and on weeks when I sleep only five hours I feel foggy, irritable and constantly hungry, especially for sweets. This module examines how the brain regulates states of consciousness, such as waking and sleep, and homeostasis, the maintenance of stable internal conditions such as body temperature and energy balance. This paper explains what keeps us awake, why we sleep and how sleep and appetite are connected.

Homeostasis

Homeostasis is the process by which the body keeps internal variables, such as temperature, fluid balance and energy, within a stable range. The hypothalamus plays a central role, detecting changes and triggering responses such as shivering, thirst or hunger. Sleep is regulated in a similar way: a homeostatic sleep pressure builds the longer we are awake and dissipates during sleep, while a circadian clock in the hypothalamus's suprachiasmatic nucleus times sleepiness and alertness across the 24-hour day.

What Keeps Us Awake

Moruzzi and Magoun (1949) stimulated regions of the brain stem in anesthetized cats while recording the EEG. Stimulation of the reticular formation, a network of neurons running through the core of the brain stem, changed the EEG from the slow, synchronized waves of sleep or drowsiness to the fast, low-amplitude pattern of alert wakefulness. They proposed that ascending pathways from the reticular formation activate the cortex and maintain wakefulness, a system later called the ascending reticular activating system. Damage to this system can produce coma, and modern research has identified the specific neurotransmitter systems involved, including acetylcholine, norepinephrine, serotonin, histamine and orexin.

Stages of Sleep

In the sleep lab, I watch patients pass through sleep stages. Non-REM sleep includes light stages and deep slow-wave sleep, marked by large, slow EEG waves. REM sleep shows fast, desynchronized EEG similar to waking, rapid eye movements, vivid dreams and near-paralysis of the body's muscles. A night cycles through these stages about every 90 minutes, with more deep sleep early in the night and more REM sleep toward morning.

Why We Sleep

Many theories propose functions for sleep, including energy conservation, memory consolidation and restoration. Xie et al. (2013) investigated one restorative function in mice. Using imaging and tracer techniques, they found that during natural sleep and anesthesia, the space between brain cells expanded by about 60 percent compared with waking. This expansion increased the flow of fluid through the brain and sped the clearance of waste products, including beta-amyloid, a protein that accumulates in Alzheimer's disease. The authors suggested that one function of sleep is to clear waste that builds up in the brain during waking activity.

Sleep Loss and Appetite

Spiegel et al. (2004) tested 12 healthy young men twice, in random order: two nights of restricted sleep, four hours in bed, and two nights of extended sleep, ten hours in bed. After sleep restriction, levels of leptin, a hormone that signals satiety, fell, and levels of ghrelin, a hormone that stimulates hunger, rose. Participants reported greater hunger and greater appetite, most of all for sweet and starchy, energy-rich foods. The changes in hormones were related to the changes in reported hunger.

Shift Work and Health

Shift workers like me sleep at times when the circadian clock promotes wakefulness, so daytime sleep is often shorter and lighter. Research links long-term shift work to higher risks of obesity, metabolic problems and accidents, and the hormonal changes Spiegel and colleagues found offer one pathway.

Practical Steps

The research suggests several strategies: keeping a regular sleep schedule even on days off when possible, sleeping in a dark, quiet room with blackout curtains, limiting caffeine in the hours before sleep, using bright light during night shifts and avoiding it on the drive home and planning healthy snacks to resist the cravings that follow short sleep.

The Circadian Clock in Detail

The suprachiasmatic nucleus receives light information directly from special cells in the retina and uses it to align the body's internal day with the outside world. It controls the release of melatonin from the pineal gland, which rises in darkness and signals night to the body. Bright light at night suppresses melatonin, which is why morning light on the commute home from a night shift can make daytime sleep harder.

Sleep Disorders

In the sleep lab, I see disorders that show what happens when regulation fails. Obstructive sleep apnea repeatedly interrupts breathing and fragments sleep. Narcolepsy, linked to loss of orexin-producing neurons in the hypothalamus, causes sudden sleep attacks and intrusions of REM sleep into waking. Insomnia, the most common complaint, often involves heightened arousal that keeps the brain from switching off.

Hunger Signals

Leptin, released by fat cells, signals to the hypothalamus that energy stores are adequate, while ghrelin, made in the stomach, climbs before mealtimes and sharpens appetite. The balance between these signals helps keep body weight within a range, and anything that shifts it, including short sleep, can tip the balance toward eating more.

Caffeine

Caffeine keeps people alert by blocking receptors for adenosine, which accumulates the longer we stay awake and adds to sleep pressure.

Limits

Moruzzi and Magoun's work used anesthetized animals. Xie and colleagues studied mice, and whether the same clearance process works the same way in humans is still being studied. Spiegel and colleagues' study was short and involved only young men.

Conclusion

Moruzzi and Magoun showed that brain stem systems activate the cortex and sustain wakefulness, Xie and colleagues showed that sleep expands the brain's spaces to clear waste and Spiegel and colleagues showed that short sleep shifts appetite hormones toward hunger. My 4 a.m. vending machine trips are not a lack of willpower but a predictable result of the brain's regulation of arousal, sleep and energy balance.

References

Moruzzi, G., & Magoun, H. W. (1949). Brain stem reticular formation and activation of the EEG. Electroencephalography and Clinical Neurophysiology, 1(1-4), 455-473. https://doi.org/10.1016/0013-4694(49)90219-9

Spiegel, K., Tasali, E., Penev, P., & Van Cauter, E. (2004). Brief communication: Sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite. Annals of Internal Medicine, 141(11), 846-850. https://doi.org/10.7326/0003-4819-141-11-200412070-00008

Xie, L., Kang, H., Xu, Q., Chen, M. J., Liao, Y., Thiyagarajan, M., O'Donnell, J., Christensen, D. J., Nicholson, C., Iliff, J. J., Takano, T., Deane, R., & Nedergaard, M. (2013). Sleep drives metabolite clearance from the adult brain. Science, 342(6156), 373-377. https://doi.org/10.1126/science.1241224