Chronobiology and Circadian Rhythms — MCQs

Chronobiology and Circadian Rhythms Indian Medical PG Practice Questions and MCQs

Question 11: The blood levels of hormones are elevated during exercise and sleep as shown. Which hormone would exhibit this diurnal pattern?

A. Growth hormone (Correct Answer)
B. Insulin
C. Cortisol
D. Thyroid hormones

Explanation: ***Growth hormone*** - **Growth hormone (GH)** secretion is known to increase significantly during both **strenuous exercise** and **sleep**, particularly during deep sleep stages. - The elevated levels during exercise promote **lipolysis** and **glucose production**, while during sleep, it facilitates **tissue repair** and **growth**. *Insulin* - **Insulin** levels typically **decrease during exercise** to promote the utilization of fat as fuel and increase during sleep in response to reduced metabolic demand and preparation for morning. - Its primary role is to regulate blood glucose, and its secretion is mainly stimulated by **high blood glucose** rather than exercise or sleep directly in this pattern. *Cortisol* - **Cortisol** secretion follows a **circadian rhythm**, peaking in the early morning and gradually decreasing throughout the day, reaching its lowest point at night. - While exercise can acutely increase cortisol, its **sleep-related pattern** is the opposite of what is shown, typically decreasing during early sleep. *Thyroid* - **Thyroid hormones (T3 and T4)** maintain a relatively **stable level** throughout the day and night, with minor diurnal fluctuations. - Their primary function is to regulate **metabolism** and they do not exhibit sharp, distinct peaks in response to exercise or sleep in the manner depicted.

Question 12: A polysomnography is performed on a patient. Based on the provided EEG, EOG, and EMG findings, which stage of sleep is indicated? (Image: img-182.jpeg)

A. NREM 1
B. NREM 2 (Correct Answer)
C. NREM 3
D. REM

Explanation: ***NREM 2*** - This stage is characterized by the presence of **sleep spindles** (bursts of brain activity) and **K-complexes** (large, slow waves) on the EEG. - The EOG typically shows **no significant eye movement**, and the EMG registers **lower muscle tension** compared to wakefulness or NREM 1. *NREM 1* - This initial stage of sleep is marked by the appearance of **theta waves** on the EEG and a reduction in alpha wave activity. - The EOG often shows **slow, rolling eye movements**, and the EMG indicates slightly **reduced muscle tone** compared to the wake state. *NREM 3* - Often referred to as **deep sleep** or slow-wave sleep, this stage is characterized by a significant presence of **delta waves** (high amplitude, low frequency) on the EEG, comprising 20-50% of the epoch. - Eye movements are **minimal or absent** on EOG, and muscle tension on EMG is **lower** than in NREM 2 but still present. *REM* - This stage is distinguished by **rapid eye movements** (REMs) observed on the EOG and a characteristic **sawtooth pattern** or low-voltage, mixed-frequency activity on the EEG. - A key feature of REM sleep is **atonia** (paralysis of skeletal muscles), resulting in the **lowest muscle tone** on the EMG, often appearing as a flat line.

Question 13: During polysomnography, which stage of sleep is represented by the marked areas when observing the following wave patterns? EOG (Electrooculography) EEG (Electroencephalography) EMG (Electromyography)

A. REM sleep
B. NREM I sleep (Correct Answer)
C. NREM II sleep
D. NREM III sleep

Explanation: ***NREM I sleep*** - This stage is characterized by a transition from wakefulness to sleep, identifiable by the appearance of **slow eye movements** in the EOG and a reduction in EEG frequency with the presence of **theta waves**. - The EMG shows a decrease in muscle tone but without the complete atonia seen in REM sleep. *REM sleep* - **Rapid eye movements** are characteristic in the EOG, and the EEG shows **low-amplitude, mixed-frequency waves** similar to wakefulness. - The EMG would display profound muscle atonia, which is not evident in the provided tracing. *NREM II sleep* - This stage is marked by the presence of **sleep spindles** and **K-complexes** in the EEG, which are absent in the marked area. - Eye movements are generally absent, and muscle activity continues to be low. *NREM III sleep* - This is the deepest stage of sleep, characterized by **high-amplitude, slow-delta waves** (20-50% of the epoch) in the EEG. - Eye movements are typically absent, and muscle tone is very low but not completely absent.

Question 14: All of the following factors are involved in altered patterns of hormone release except

A. Day time duties (Correct Answer)
B. Travel across time zones
C. Aging
D. Lights on throughout 24 hours of the day

Explanation: **Day time duties** - **Daytime duties** are part of normal diurnal rhythms and do not inherently alter the **circadian clock** or hormone release patterns. - While they coincide with certain hormone fluctuations, they are not a disruptive factor like the other options. *Travel across time zones* - **Travel across time zones** causes **jet lag**, disrupting the body's internal clock and desynchronizing **circadian rhythms**. - This desynchronization directly affects the timing and amount of various hormones released, such as **cortisol** and **melatonin**. *Aging* - **Aging** brings about natural changes in hormone production and release patterns, including decreases in **growth hormone**, **sex hormones**, and alterations in **cortisol** rhythms. - These changes are a physiological consequence of the aging process, leading to altered hormonal profiles. *Lights on throughout 24 hours of the day* - Prolonged exposure to **light at night** disrupts the natural **sleep-wake cycle** and suppresses **melatonin** production, a key hormone for regulating circadian rhythms. - This constant light exposure can significantly alter the release of numerous other hormones that follow a **diurnal pattern**.

Question 15: Hormonal secretions are tightly controlled by the time of day due to an inbuilt biological clock in human body. This rhythmic secretion is controlled by:

A. Ventrolateral nucleus
B. Supraoptic nucleus
C. Suprachiasmatic nucleus (Correct Answer)
D. Posterolateral nucleus

Explanation: ***Suprachiasmatic nucleus*** - The **suprachiasmatic nucleus (SCN)**, located in the hypothalamus, is the primary pacemaker of the body's **circadian rhythms**, controlling the timing of hormonal secretions, sleep-wake cycles, and other daily oscillations. - It receives direct input from the **retina** about light-dark cycles, allowing it to synchronize the body's internal clock with the external environment. *Ventrolateral nucleus* - The **ventrolateral preoptic nucleus (VLPO)** is involved in **sleep regulation** and promoting non-REM sleep, but it does not act as the primary circadian pacemaker. - It receives input from the SCN and collaborates in regulating sleep, but its role is primarily inhibitory to wakefulness. *Supraoptic nucleus* - The **supraoptic nucleus** is primarily involved in the production and secretion of **vasopressin (ADH)** and **oxytocin**, which are neurohormones regulating fluid balance and social bonding, respectively. - It does not directly control the rhythmic aspect of general hormonal secretions or act as the central circadian clock. *Posterolateral nucleus* - This term is less commonly used in the context of circadian rhythm control; however, if referring to a thalamic nucleus, the **posterolateral nucleus** is generally associated with sensory processing, particularly somatosensory information. - It has no known role as a central pacemaker for hormonal secretions or circadian rhythms.

Question 16: Melatonin is secreted by

A. Melanocytes
B. Pineal gland (Correct Answer)
C. Hypothalamus
D. Adrenal cortex

Explanation: ***Pineal gland*** - The **pineal gland** is a small endocrine gland located in the brain that primarily produces **melatonin**. - Its main function is to regulate **sleep-wake cycles** (circadian rhythms), with melatonin secretion increasing in darkness. *Melanocytes* - **Melanocytes** are cells found in the skin and eyes that produce **melanin**, a pigment responsible for skin, hair, and eye color. - They are not involved in the production of melatonin. *Hypothalamus* - The **hypothalamus** is a crucial part of the brain that links the nervous system to the endocrine system via the pituitary gland. - It produces various **releasing and inhibiting hormones** that control other glands, but it does not secrete melatonin. *Adrenal cortex* - The **adrenal cortex** is the outer part of the adrenal gland, responsible for producing **steroid hormones** like glucocorticoids (e.g., cortisol) and mineralocorticoids (e.g., aldosterone). - It does not produce melatonin; melatonin production is distinctly associated with the pineal gland.

Question 17: Which of the following statements is MOST accurate regarding REM sleep?

A. Slow waves on EEG
B. Low muscle tone (Correct Answer)
C. Decrease in BP
D. Dreams

Explanation: ***Low muscle tone*** - **Muscle atonia** (near-complete loss of skeletal muscle tone) is one of the **defining physiological characteristics** of **REM sleep**. - This **muscle paralysis** prevents individuals from acting out their dreams and is a consistent, measurable feature of REM sleep. - Along with rapid eye movements and desynchronized EEG, **muscle atonia** is one of the three hallmark features that define REM sleep. *Dreams* - While **vivid dreams** are commonly associated with **REM sleep** and dream recall is highest during this stage, not all REM periods result in recalled dreams. - Dream recall varies significantly between individuals and circumstances. - Dreams can also occur during **NREM sleep**, though they are typically less vivid and less frequently recalled. *Slow waves on EEG* - **Slow waves** are characteristic of **deep non-REM sleep (N3 stage)**, not REM sleep. - During REM sleep, the **EEG** shows a **low-voltage, mixed-frequency pattern** resembling wakefulness (desynchronized EEG). *Decrease in BP* - During **REM sleep**, blood pressure often **fluctuates** and can even **increase** due to autonomic instability, rather than consistently decreasing. - The cardiovascular system exhibits **irregularities** in both heart rate and blood pressure during REM sleep.

Question 18: Delta waves are seen in which stage of sleep?

A. Awake with mental activity
B. Awake while resting
C. Deep sleep (Correct Answer)
D. Sleeping

Explanation: ***Deep sleep*** - **Delta waves** are characteristic of **Stage N3 sleep**, also known as **deep sleep** or **slow-wave sleep**. - This stage is crucial for **physical restoration** and is the deepest stage of non-REM sleep, exhibiting the slowest brain activity. *Awake with mental activity* - This state is typically associated with **beta waves**, which are high-frequency, low-amplitude waves indicative of an **alert and active mind**. - Mental activity such as problem-solving or focused attention does not involve the prominent slow waves seen in deep sleep. *Awake while resting* - When awake but resting with eyes closed, the brain typically produces **alpha waves**, characterized by a relaxed and calm state. - While alpha waves are slower than beta waves, they are still distinct from the very slow delta waves of deep sleep. *Sleeping* - This option is too general, as "sleeping" encompasses multiple stages, including light sleep (N1, N2), deep sleep (N3), and REM sleep. - While deep sleep is a stage of sleeping, the term itself doesn't specify the unique **EEG pattern** of delta waves.

Question 19: Melatonin is produced in all of the following, except?

A. Gut
B. Pineal gland
C. Retina
D. Suprachiasmatic nucleus (Correct Answer)

Explanation: ***Suprachiasmatic nucleus*** - The **suprachiasmatic nucleus (SCN)** is the master circadian clock in the brain but does not produce melatonin itself. Instead, it plays a crucial role in **regulating the pineal gland's synthesis and secretion of melatonin**. - It receives light input from the retina and then sends signals to the pineal gland, inhibiting melatonin production during the day and promoting it during the night, thereby **controlling circadian rhythms**. *Gut* - The gastrointestinal tract is a significant extra-pineal source of melatonin, with concentrations often **hundreds of times higher than in the pineal gland**. - Gut melatonin plays various roles, including **regulating motility**, mucosal protection, and modulating local immune responses. *Pineal gland* - The **pineal gland** is the primary and most well-known source of melatonin in the body, releasing it directly into the bloodstream as a **neuroendocrine hormone**. - It synthesizes melatonin from **serotonin** in a light-dependent manner, with production peaking during periods of darkness to regulate the sleep-wake cycle. *Retina* - The **retina** contains photoreceptor cells and neurons that can synthesize melatonin endogenously. - This locally produced melatonin in the retina helps in **light adaptation**, modulation of retinal neurotransmission, and acts as an antioxidant within the eye.

Question 20: Which of the following is true about NREM sleep?

A. Narcolepsy
B. Teeth grinding (Correct Answer)
C. Nightmares
D. Sleep paralysis

Explanation: ***Teeth grinding*** - **Bruxism** (teeth grinding) commonly occurs during **NREM sleep stages**, particularly stage N2. - It is an **involuntary motor activity** that can lead to dental issues and jaw pain. *Narcolepsy* - Narcolepsy is a neurological condition characterized by overwhelming daytime sleepiness and involves dysregulation of **REM sleep**. - Patients often experience **sudden REM sleep onset** during waking hours, not typically an NREM sleep phenomenon. *Nightmares* - Nightmares are generally vivid, disturbing dreams that occur during **REM sleep**. - While other sleep disturbances can occur in NREM, classic nightmares are a **REM-related parasomnia**. *Sleep paralysis* - Sleep paralysis is a temporary inability to move or speak that occurs when waking up or falling asleep, often associated with **REM sleep**. - It involves the persistence of **REM atonia** into the waking state.

Practice by Chapter

Biological Clock Mechanisms

Practice Questions

Suprachiasmatic Nucleus

Practice Questions

Circadian Rhythm Generation

Practice Questions

Light Entrainment Pathways

Practice Questions

Melatonin and Sleep Regulation

Practice Questions

Circadian Control of Metabolism

Practice Questions

Temperature and Activity Rhythms

Practice Questions

Shift Work and Jet Lag Physiology

Practice Questions

Circadian Rhythm Disorders

Practice Questions

Chronopharmacology

Practice Questions

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