Body rhythms and circadian Practice Questions
20 free Body rhythms and circadian practice questions for the Physiology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which structure serves as the primary biological clock regulating circadian rhythms in humans?
- A Pineal gland
- B Suprachiasmatic nucleus
- C Reticular formation
- D Hypothalamic arcuate nucleus
Correct answer: Suprachiasmatic nucleus
The suprachiasmatic nucleus (SCN) of the hypothalamus acts as the master circadian clock. It synchronizes physiological rhythms with the light–dark cycle.
The normal duration of the human circadian rhythm under constant environmental conditions is closest to:
- A 20 hours
- B 22 hours
- C 24 hours
- D 28 hours
Correct answer: 24 hours
Under constant conditions, the intrinsic human circadian rhythm is slightly longer than 24 hours but close to it. Environmental cues reset it to exactly 24 hours.
Light influences circadian rhythm primarily through which pathway?
- A Retina projecting to the lateral geniculate body
- B Retina projecting to the superior colliculus
- C Retina to suprachiasmatic nucleus
- D Optic nerve directly to the pineal gland
Correct answer: Retina to suprachiasmatic nucleus
Light information from the retina is transmitted directly to the suprachiasmatic nucleus. This pathway allows light to reset the circadian clock.
Melatonin secretion from the pineal gland is highest during:
- A Early morning
- B Midday
- C Evening twilight
- D Night
Correct answer: Night
Melatonin secretion increases in darkness and peaks at night. It plays a key role in promoting sleep and regulating circadian timing.
Which hormone shows a pronounced circadian rhythm with peak levels in the early morning?
- A Insulin
- B Cortisol
- C Thyroxine
- D Aldosterone
Correct answer: Cortisol
Cortisol levels rise in the early morning hours and peak shortly after waking. This rhythm supports alertness and energy mobilization.
The term 'zeitgeber' refers to:
- A An endogenous, self-sustaining biological rhythm
- B A sleep-promoting hormone released at night
- C An external cue that synchronizes rhythms
- D A core genetic clock protein oscillator
Correct answer: An external cue that synchronizes rhythms
Zeitgebers are external environmental cues, such as light, that entrain circadian rhythms. They align internal clocks with the external world.
Which physiological variable normally shows a circadian rhythm with a peak in the late afternoon?
- A Body temperature
- B Melatonin level
- C Growth hormone secretion
- D Prolactin secretion
Correct answer: Body temperature
Core body temperature typically reaches its maximum in the late afternoon or early evening. It is lowest during the early morning hours.
Jet lag occurs primarily due to:
- A Sleep deprivation occurring entirely on its own
- B Mismatch between internal clock and local time
- C Reduced production of the hormone melatonin
- D Increased sympathetic nervous system activity
Correct answer: Mismatch between internal clock and local time
Jet lag results from desynchronization between the internal circadian clock and the new time zone. Symptoms persist until re-entrainment occurs.
Which gene family plays a crucial role in generating molecular circadian rhythms?
- A Hox genes
- B Clock genes
- C p53 genes
- D Homeobox genes
Correct answer: Clock genes
Clock genes regulate transcription–translation feedback loops that generate circadian rhythms. These molecular oscillations drive rhythmic physiology.
Growth hormone secretion is most closely associated with which sleep stage?
- A Rapid eye movement (REM) sleep
- B Light non-REM stage two sleep
- C Deep slow-wave sleep
- D Only the moment of sleep onset
Correct answer: Deep slow-wave sleep
Growth hormone is predominantly secreted during deep slow-wave sleep. This links circadian and sleep-dependent regulation.
Which circadian rhythm disturbance is commonly seen in night-shift workers?
- A Advanced sleep phase syndrome
- B Delayed sleep phase syndrome
- C Free-running rhythm
- D Shift work sleep disorder
Correct answer: Shift work sleep disorder
Shift work sleep disorder occurs due to misalignment between work schedules and the circadian clock. It leads to insomnia and excessive sleepiness.
The pineal gland receives neural signals related to light exposure primarily from the:
- A Thalamus
- B Hypothalamus
- C Brainstem
- D Cerebellum
Correct answer: Hypothalamus
The pineal gland is regulated via hypothalamic pathways originating from the suprachiasmatic nucleus. These pathways convey information about light exposure.
Which physiological rhythm has a period shorter than 24 hours?
- A Circadian rhythm
- B Ultradian rhythm
- C Infradian rhythm
- D Seasonal rhythm
Correct answer: Ultradian rhythm
Ultradian rhythms have periods shorter than 24 hours, such as the sleep cycle stages. They occur multiple times within a day.
The sleep–wake cycle is best classified as a:
- A Ultradian rhythm
- B Infradian rhythm
- C Circadian rhythm
- D Seasonal rhythm
Correct answer: Circadian rhythm
The sleep–wake cycle follows an approximately 24-hour pattern. This makes it a classic example of a circadian rhythm.
Which factor is most effective in resetting the circadian clock?
- A Physical exercise
- B Meal timing
- C Ambient temperature
- D Light exposure
Correct answer: Light exposure
Light exposure is the most powerful zeitgeber for the circadian system. It directly influences the suprachiasmatic nucleus.
A free-running circadian rhythm is most likely to occur in:
- A Normal light–dark cycles
- B Constant darkness
- C Bright daylight exposure
- D Shifted meal timing
Correct answer: Constant darkness
In constant darkness, external cues are absent and the circadian rhythm runs at its intrinsic period. This is known as a free-running rhythm.
Which neurotransmitter is involved in transmitting light signals from the retina to the circadian clock?
- A Dopamine
- B Serotonin
- C Glutamate
- D GABA
Correct answer: Glutamate
Glutamate is released by retinal ganglion cells projecting to the suprachiasmatic nucleus. It mediates light-induced phase shifts.
Which circadian change contributes to increased alertness during daytime?
- A Rising melatonin levels
- B Falling core body temperature
- C Rising cortisol levels
- D Increased growth hormone secretion
Correct answer: Rising cortisol levels
Cortisol levels rise in the morning and support alertness and energy availability. This change aligns with daytime activity.
Seasonal affective disorder is primarily associated with alterations in:
- A Short ultradian rhythms of the body
- B Circadian melatonin secretion
- C Pulsatile growth hormone cycles
- D Sleep spindle rhythmic activity
Correct answer: Circadian melatonin secretion
Seasonal affective disorder is linked to altered melatonin secretion due to reduced light exposure. This disrupts circadian regulation of mood.
Which statement best describes circadian rhythms?
- A They depend entirely on external environmental cues
- B They arise from random, disorganized neural activity
- C They persist without external cues
- D They occur strictly during sleep
Correct answer: They persist without external cues
Circadian rhythms are endogenously generated and persist without external cues. Environmental signals mainly serve to synchronize them.