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Proxima C has 22 Earth days between sunrises and human beings living underground; therefore, this suggests that most of the time, the people will be in dark conditions. On a human being on Earth, the alternation of day and night is essential to inducing rhythms that affect several physiological functions. Even in isolation, these rhythms related to the time of day are sustained from neuronal and neuroendocrine, providing information. For instance, the human cycle is equal to Earths 24-hour cycle. Consequentially, this means that the rhythms in Proxima C inhabitants will have to adjust to fit the 22 Earth days that occur between sunrises. It is essential to note that the circadian rhythm is affected by temperature. On Earth, the temperature is averagely 30ºC, while on the exoplanet, it is -40ºC.
Physiology of the Human Nervous System in Relation to the Circadian Rhythm
In mammals, light is sensed by the outer cones and rods, and inner ganglion cells. Via the visual pathway, rods are photoreceptors responsible for scoptic vision, also referred to as low light levels (VanPutte et al). On the other hand, cones are suitable for color vision at high light levels (photopic vision) (VanPutte et al). Based on the intensity and duration of exposure, light significantly impacts physiology and behavior. This is achieved by stimulating the hypothalamic suprachiasmatic nucleus (SCN), the biological master clock. Since human beings are organisms that are active during the day, most of their behavioral and physiological functions exhibit a diurnal rhythm that is generated by the bilateral SCN. Via the process of internal synchronization, the SCN connects to central and peripheral tissues that comprise cells with self-sustaining cycles that regulate the local time and tissue-specific processes (González et al.). These are called peripheral clocks.
Rhythm activation and deactivation are reset daily by zeitgebers, external time cues, that can regulate the circadian clock based on environmental changes. Out of all factors, the light-dark cycle is the zeitgeber having the most significant effect, which synchronizes endogenous cycles with the light and dark phase by the process of entrainment (González et al.). The SCN primarily entrains the rhythm present in the autonomic nervous system, the hypothalamic-pituitary-adrenal axis (HPA), and the neuronal system to the light-dark cycle. Furthermore, in diurnal mammals, the intrinsically photosensitive ganglion cells contain melanopsin that can transduce photic energy into electric signals. These influence cardiovascular and motor activity, endocrine secretion, metabolism, sleep, and wakefulness cycle; hence bringing about the efficiency of physiological processes, homeostatic constancy, and adaptation to external or internal changes
Moreover, the SN has two different oscillators, which include the ventrolateral (VL) and dorsomedial (DM) subdivisions. The VL SCN receives an impulse from the retina through the retinohypothalamic tract. On the other hand, DM SCN is not influenced by light and runs independently of the lighting conditions. It is essential to note that although the temperature has been established as one of the factors affecting the circadian rhythm, its ability to adjust the biological clock remains poorly understood (Yadlapalli et al.).
How the Environment of Proxima C Affects the Circadian Rhythm
The synchronization of behavior and physiology with the biological clock can only be attained by the entrainment of the VL and DM SCN oscillators to the lighting conditions on the solar LD cycle. Therefore, in the absence of light conditions, including other external time cues, the molecular clock will continue to produce ~24 hours of circadian rhythms. However, in the case of Proxima C inhabitants who live in caves in circumstances where the duration of SCN rhythms is shorter than the environmental LD cycle; the circadian rhythm begins to operate on a free-run mode (González et al.). This is slightly longer than 24 hours, thereby leading to the loss of rhythmicity. According to Gonzalez et al., the study findings illustrated that dark conditions would interrupt the synchronization between the SCN oscillators and dissociate the rhythmic output; therefore, resulting in depression after the dysregulation of the trans-synaptic efferent neuronal circuits that innervate the ANS.
Adaptation to the Human Nervous System the Proxima C Humanoid Would Have To Compensate For the Environment
Circadian rhythms must be repeatedly or continually reset to synchronize with natures cycle. To maintain this entrainment in Proxima C to 22 Earth days, the duration of light exposure plays a role. This is vital to their well-being and survival as the lack of synchrony to the external environment may result in pathophysiological mechanisms that might even bring about death. To survive such conditions, also considering that human beings a diurnal, the body will have to adapt. One would expect the relaxation and eventually, the loss of circadian rhythms, followed by the regressive evolution of the underlying biological clock. These anatomical changes will occur primarily in the eye since it is the only organ in the body capable of trapping light (Beale et al.). It will be characterized by enlarged pupils to increase the amount of light entering the eye, and increased concentration of rods to trap more of the low-intensity light (Beale et al.). Overall, these changes will attempt to enhance the amount of light being harnessed to sustain the biological clock.
Works Cited
Beale, Andrew, et al. Life in a Dark Biosphere: A Review of Circadian Physiology in Arrhythmic Environments. Journal of Comparative Physiology. B, Biochemical, Systemic, and Environmental Physiology, vol. 186, no. 8, 2016, pp. 947-968.
González, Mónica, et al. Dim Light at Night and Constant Darkness: Two Frequently Used Lighting Conditions That Jeopardize the Health and Well-being of Laboratory Rodents. Frontiers in Neurology, vol. 9, no. 609, 2018, pp. 1-17.
VanPutte, Cinnamon, et al. Seeleys Anatomy and Physiology. 12th ed., McGraw-Hill Education, 2019.
Yadlapalli, Swathi, et al. Circadian Clock Neurons Constantly Monitor Environmental Temperature to Set Sleep Timing. Nature, vol. 555, 2018, pp. 98102.
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