Correct option is A
Correct Answer: (a)
Explanation: The suprachiasmatic nucleus (SCN) of the hypothalamus functions as the master circadian clock in higher vertebrates. It receives direct photic input from the retina and synchronizes physiological and behavioral rhythms to the light–dark cycle. Signals from the SCN coordinate daily rhythms such as sleep–wake cycles, hormone secretion, and body temperature. Hence, regulation of circadian rhythm primarily resides in the SCN.
Information Booster
· The SCN is located in the anterior hypothalamus above the optic chiasm.
· Retinohypothalamic tract conveys light information directly to the SCN.
· SCN neurons exhibit endogenous rhythmic activity with ~24-hour periodicity.
· It controls peripheral clocks present in other tissues and organs.
· Melatonin secretion by the pineal gland is regulated indirectly by the SCN.
Additional Knowledge
The cerebral cortex is involved in higher cognitive functions and does not act as a circadian pacemaker. The pituitary gland responds to hormonal signals but does not independently regulate circadian timing. The thymus is primarily associated with immune system development. Thus, among the given options, only the suprachiasmatic nucleus serves as the central regulator of circadian rhythms in higher vertebrates.
