External environmental acquaintance with the living body is executed by five sense organs namely netra (eye), karna (ear), nasa (nose), jivha (taste buds), and twak (skin)- S.Sh.1-15.
All dnyanendriyas i.e. sense organs are panchbhautic in composition. In spite of this fact, every indriya or sense organ perceives object/tanmatra of that mahabhuta from which it is originated or one which is predominant. For example, the eye is originated from teja mahabhuta and hence perceives the object of teja mahabhuta only i.e. it is capable of performing ‘rupagrahana’, i.e. visual perception only. An eye is not capable of perceiving senses like audio, tactile etc. Virtual dnyanendriyas or sense organs or centers of perception are minute and are located in brain and organs perceiving them like the eye, ear etc. are the instrumental sense organs or ‘adhishthana’ (Charaka Sh.1-138).
Charaka in Sutrasthana Ch. 8 has explained the functioning of Dnyanendriya. He has laid down panch-panchaka concept for this. It includes pancha dnyanendriya, predominant mahabhoota originating them, adhishthana, artha i.e. sense objects and buddhi i.e. interpreting brain center of that sense organ. It is as follows in case of Netra.
|Dnyanendriya adhishthana||Netra (Eye)|
|Artha/ sense object||Roopa tanmatra/sight i.e. perception of size, shape, colour etc. of an object.|
|Indriya buddhi / Visual centres.||It is created by togetherness of Chakshurindriya buddhi i.e. visual centres in occipital cortex, mann (mind) and atma (soul)|
Perception of an image is the function of drushti which is the location of Alochaka pitta. This sensation is conveyed through dhamanis to mann and atma through pranavayu and the sequence is responsible for the perception of an object. In this way the external object is perceived when atma unites/linked with mann; Mann unites with indriyabuddhi; Indriyabuddhi unites with tanmatra; Tanmatra unites with adhishthana; Adhishthana unites with mahabhuta; and Mahabhuta unites with minute virtual dnyanendriya located in the brain. In this process of perception of an object by eye, pranavayu and kapha located in shira play an important role. Healthy status of all sense organs depends upon homeostatic i.e. physiological conditions especially of pranavayu and tarpaka kapha. Once the above sequence is completed, then the image of a particular object is interpreted and perceived.
Role of Dosha-Dhatu-Mala
The living body is sustained by 3 dosha, 7 dhatu, and 3 mala. All body functions are controlled by dnyanendriya, karmendriya, mann, and atma (S.Su 15-3). Dosha-dhatu-mala has to stay in equilibrium, their deviation either from physiology or towards pathology; triggers genesis of diseases. Following passages will explain how homeostatic conditions of dosha-dhatu-mala become responsible for normal functioning of dnyanendriya like Netra.