Why you can find your way in the dark

source
Recently, I came across a very intriguing puzzle, this puzzle really got my attention because as a Nigerian, I knew this situation is feasible in our society. The puzzle says:

A black man was wearing black cloths and was walking on the road in the dark, the street lights were not functional, as a result of this, and the road was lonely and dark but at the end of this was a car without audible sound. Also the car’s headlamp was no functional and the car was also painted black. The man was able to dodge the speedily approaching black car without a headlamp and the question was, how did he detect the car?

Finding our way in the dark is a general experience because sometimes we find ourselves in the dark without emergency light, personally, I feel burdened carrying the emergency lights, though the flashlight application in our smartphones has been instrumental as regards emergency illumination, we still fall into few situations where we have to walk our way through dark paths. We find ourselves moving efficiently with a little restriction, many could also read considerably well with dim light, though for many, it is impossible to read or walk without sufficient light, this is due to the biological differences in the human system.

In the normal human, there’s a relative vision in the dark, though this vision might not be explicit, it provides the individual the ability to at least detect the presence of objects in his path, maybe this was the answer to the puzzle, this observation is not wrong as the auditory system will be less functional in this scenario due to lack of sound in the approaching vehicle, so if the man detected the car, he must have used his intuition, this intuition must have been influenced by our body’s mechanism of sight in darkness.

credit: Canadian cancer society

The optical system controls our sight, our ability to see and appreciate things in our environment. This system is integrated with the nervous system and it enables us to differentiate and accord to each object its peculiar feature and as a result, we do not describe most things we see as being the same, these variations might be in color, shape, hence, inscriptions on these objects helps in differentiating these objects. Also the texture of these object helps us to differentiate them but this is controlled by a different system.

Integration with the central nervous system enables the optical system to store these nervous reaction, thus we have a memory of things we see and they don’t appear completely foreign the next time we see them, frequent contact with these objects also increases our familiarity with them and in some cases, we can even draw these objects without seeing them recently.

Our optical system is made up of the eye and its anatomical and physiological relationships. The eye is situated in its orbit, the orbit is designed by the union of the bones of the skull in a way to create a pit in which the eye ball fits, the orbit also have perforations which allows for bodies like vessels, nerves, muscles, etc. to pass through. The eye however has no lymphatics and thus, no lymphocytes, this accounts for the success of eye grafts. The eyeball itself is made up of projections, tissues and fluids which enables it to integrate light rays and also protective mechanisms to keep it safe from dangerous environmental factors.

The iris diaphragm also helps to regulate the amount of light rays entering the eye, the lens articulates these rays in an inverse manner, the final transfer of visual signals to the brain occurs in the retina which is the principal nervous aspect of the eye.

Of great importance is the optical mechanics which enables us to integrate bright and dim light or even darkness, the activities of the eyes at these situations vary as it tries to maintain a constant internal conditions despite the varying external state. This is also a natural homeostatic process. This activity also forms the basics of the inter-relationship between our optical system and our nutrition as vitamins (vitamin A, i.e. retinol) are very useful in this process.

The retina as already stated relays visual impulses to the brain, this enables the brain to articulate the image created, its shape, form and the intensity of light producing this image. On the intensity of the light producing the image, the retina is made up of two cells, the Rods, and the Cones; these cells acts at different state to enable visions.

The cone cells detects colors but are less sensitive to light. The rod cells on the other hand are less sensitive to colors but very sensitive to low light intensity. It is of importance to understand that the action of these cells are initiated by the retinol, a derivative of vitamin A which can be obtained via diets. This necessitates the consumption of food items with a good vitamin values as the deficiency of this vitamin presents some eye problems which includes night blindness.

Night blindness is the inability to see at night or to detect objects in a dim light, this is due to impairment of the activity of the rod cells

Rod cells are the most important cells in finding your way in the dark. The rod cells consist of an outer segment of stacks of membranous disks, this membranous disks contains a photoreceptor know as Rhodopsin and an inner portion which contains cell organelles, including mitochondria which produces energy in the form of ATP to power the Na ions on sodium and potassium (ATPase) which pumps out 3 ions of sodium (Na+) for every 2 ions of potassium (K+) it pumps in to create a transmembrane electrical potential, an ion channel which permits the passage of sodium or calcium which also contributes to their membrane potential, this ion channel is gated by cGMP.

credit:bionumbers

The cGMP gates acts in the dark to keep this channel open, the keeping of this gate open depends on the interaction of the Na+ and K+ ATPase located internally and Na+ gate located outside (controlled by cGMP). When in the dark, the rod cells contains enough cGMP to keep this gate open as it allows Na+ complex to depolarize the membrane and overpower the internal Na+ K+ ATPase channel (which pumps out Na+ and tends to polarize the membrane). Thus keeping the gate open. This action increases the rod cells’ sensitivity to light, so as to concentrate even the smallest ray of light.

This enables you to see objects in the dark. Increased exposure to darkness or dim light potentiates the actions of the rod cells. This is why your ability to see in darkness increases with time and you are able to see more in darkness after some period of time.

This process however halts when we come across bright light as rhodopsin, the photoreceptor absorbs bright light and undergoes series of conformational changes to form metarhodopsin II, this interacts with the protein Transducin to catalyze the transformation of cGMP to 5GMP, this closes the Na+ gate and the membrane is hyperpolarized and light vision continues, this process cycles as we also cycle through bright and dim lights or dark places.

Conclusion

With the aid of the cGMP influenced Na+ gate and the photoreceptor rhodopsin, our eyes are able to balance visions in light and darkness. This action of regulating vision in darkness and bright light is of importance and so is also our consumption of vitamin A right foods which includes vegetable, egg yolk and liver. This will enable the eyes to perform these actions efficiently and effectively.

---

Reference

1. photoreceptor cell -Wikipedia
2. rhodopsin and the eye
3. eye anatomy-medicinenet
4. Rod -wikipedia
5. ATPase -wikipedia

---

---

^{If you write STEM (Science, Technology, Engineering, and Mathematics) related posts, consider joining #steemSTEM on steemit chat or discord here. If you are from Nigeria, you may want to include the #stemng tag in your post. You can visit this blog by @stemng for more details. You can also check this blog post by @steemstem here and this guidelines here for help on how to be a member of @steemstem.}