The sleep-wake cycle shifts in which of the following ways with the removal of external cues?
When external cues are removed sleep wake cycle usually lengthens to 25 or 26 hours. The entrainment process in most cases is dependent on the suprachiasmatic nuclei (SCN) located bilaterally above the optic chiasma. These nuclei receive information about the light-dark cycle a special neural pathway, the retinohypothalamic fibers. Efferents from the SCN initiate neural and humoral signals that entrain a wide variety of well-known circadian rhythms including the sleep-wake cycle and the secretion of the pineal hormone melatonin.
Unchanged
Greater than 24 hrs
Less than 24 hrs
Greater than 36 hrs