Somnolence

Key takeaways

Somnolence belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Somnolence to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Somnolence from memory before moving on to harder problems.

Reference excerpt

Somnolence (alternatively sleepiness or drowsiness) is a state of strong desire for sleep, or sleeping for unusually long periods (compare hypersomnia). It has distinct meanings and causes. It can refer to the usual state preceding falling asleep, the condition of being in a drowsy state due to circadian rhythm disorders, or a symptom of other health problems. It can be accompanied by lethargy, weakness and lack of mental agility. Somnolence is often viewed as a symptom rather than a disorder by itself. However, the concept of somnolence recurring at certain times for certain reasons constitutes various disorders, such as excessive daytime sleepiness, shift work sleep disorder, and others; and there are medical codes for somnolence as viewed as a disorder. Sleepiness can be dangerous when performing tasks that require constant concentration, such as driving a vehicle. When a person is sufficiently fatigued, microsleeps may be experienced. In individuals deprived of sleep, somnolence may spontaneously dissipate for short periods of time; this phenomenon is the second wind, and results from the normal cycling of the circadian rhythm interfering with the processes the body carries out to prepare itself to rest. The word "somnolence" is derived from the Latin "somnus" meaning "sleep".

Causes

Circadian rhythm disorders

Circadian rhythm ("biological clock") disorders are a common cause of drowsiness as are a number of other conditions such as sleep apnea, insomnia and narcolepsy. The body clock disorders are classified as extrinsic (externally caused) or intrinsic. The former type is, for example, shift work sleep disorder, which affects people who work nights or rotating shifts. The intrinsic types include:

Advanced sleep phase disorder (ASPD) – A condition in which patients feel very sleepy and go to bed early in the evening and wake up very early in the morning Delayed sleep phase disorder (DSPD) – Faulty timing of sleep, peak period of alertness, the core body temperature rhythm, hormonal and other daily cycles such that they occur a number of hours late compared to the norm, often misdiagnosed as insomnia Non-24-hour sleep–wake disorder – A faulty body clock and sleep-wake cycle that usually is longer than (rarely shorter than) the normal 24-hour period causing complaints of insomnia and excessive sleepiness Irregular sleep–wake rhythm – Numerous naps throughout the 24-hour period, no main nighttime sleep episode and irregularity from day to day

Physical illness Sleepiness can also be a response to infection. Such somnolence is one of several sickness behaviors or reactions to infection that some theorize evolved to promote recovery by conserving energy while the body fights the infection using fever and other means. Other causes include:

Anxiety Brain tumor Chronic pains Concussion – a mild traumatic brain injury Diabetes Fibromyalgia Head injury Hypercalcemia – too much calcium in the blood Hypermagnesemia Hyponatremia – low blood sodium Hypothyroidism – the body doesn't produce enough hormones that control how cells use energy Meningitis Mood disorders – depression Multiple sclerosis Narcolepsy – disorder of the nervous system Skull fractures Sleeping sickness – caused by a specific parasite Stress

Medicine

Analgesics – mostly prescribed or illicit opiates such as OxyContin or heroin Anticonvulsants / antiepileptics – such as phenytoin (Dilantin), carbamazepine (Tegretol), Pregabalin (Lyrica) and Gabapentin (Neurontin) Antidepressants – for instance, sedating tricyclic antidepressants amitriptyline and mirtazapine. Somnolence is less common with SSRIs and SNRIs as well as MAOIs. Antihistamines – for instance, diphenhydramine (Benadryl, Nytol), doxylamine (Unisom-2), hydroxyzine (Atarax) and promethazine (Phenergan) Typical antipsychotics - for example levomepromazine, chlorpromazine Antipsychotics – for example, thioridazine, quetiapine (Seroquel), olanzapine (Zyprexa), risperidone and ziprasidone (Geodon) but not haloperidol Dopamine agonists used in the treatment of Parkinson's disease – e.g. pergolide, ropinirole and pramipexole. HIV medications – such as efavirenz Hypertension medications – such as amlodipine Hypnotics, or soporific drugs, commonly known as sleeping pills. Tranquilizers – such as zopiclone (Zimovane), or the benzodiazepines such as diazepam (Valium) or nitrazepam (Mogadon) and the barbiturates, such as amobarbital (Amytal) or secobarbital (Seconal) Other agents impacting the central nervous system in sufficient or toxic doses

Assessment Quantifying sleepiness requires a careful assessment. The diagnosis depends on two factors, namely chronicity and reversibility. Chronicity signifies that the patient, unlike healthy people, experiences persistent sleepiness which does not pass. Reversibility stands for the fact that, even if the individual goes to sleep, the sleepiness may not be completely gone after waking up. The problem with the assessment is that patients may only report the consequences of sleepiness: loss of energy, fatigue, weariness, difficulty remembering or concentrating, etc. It is crucial to aim for objective measures to quantify the sleepiness. Measurement scales of sleepiness include:

Multiple sleep latency test (MSLT). It assesses the sleep onset latency during the course of one day—often from 8:00 to 16:00. An average sleep onset latency of less than 5 minutes is an indication of pathological sleepiness. Karolinska Sleepiness Scale

Severity A number of diagnostic tests, including the Epworth Sleepiness Scale, are available to help ascertain the seriousness and likely causes of abnormal somnolence.

Worked examples

Example 1 — a first encounter with Somnolence

Start with the simplest possible case. Write down what Somnolence claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Somnolence before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Somnolence ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Somnolence

In research: Somnolence appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Somnolence in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Somnolence is common in secondary-school and first-year university syllabi. It links to neighbouring topics Mental processes, Sleep, Symptoms and signs of mental disorders, so understanding it makes those chapters shorter.
In everyday life: Look for Somnolence outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Somnolence in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Somnolence means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Somnolence out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Somnolence in simple terms?

Somnolence (alternatively sleepiness or drowsiness) is a state of strong desire for sleep, or sleeping for unusually long periods (compare hypersomnia). It has distinct meanings and causes.

Why does Somnolence matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Somnolence?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Somnolence.