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Physiology of Nervous System
Śiras (Head) is the region where all ‘Prānas’ (most vital entities) are situated and all sensory and motor activities are controlled from. That is why ‘Head’ is called the ‘Most important organ’ among all parts of the body (Ca. Sū. 17/12). It is described that all sensory and motor organs along with their ‘Prāanavaha Srotāmsi’, are connected to the brain in a fashion that is similar to the connections between the sunrays and the Sun. (Ca. Si. 9/4). Bhela has explained that the mind is situated in between the head and palate. The efficiency of mind is beyond any other sensory or motor organ (Bh.Ci. 8/2-3).
Caraka has opined that one should not suppress the natural urges related to micturition, defecation, ejaculation, flatus, vomiting, sneezing, eructation, yawning, hunger, thirst, tears, sleep and also dyspnoea developed after exertion (Ca. Sū. 7/3-4). It should be noted that one or the other reflex is involved in all these activities. So, the term ‘Vega’ stands almost equivalent to reflex.
Concept of ‘Vāta’
All functions of nervous system in human body are represented through ‘Vāta’ in Ayurveda. In general, the functions ascribed to ‘Vāta’ are: Control and co-ordination of different parts of the body, initiation of all movements, regulation of psychological processes, initiation of all activities of sense organs, transmission of different sensations, production of speech, secreto- motor functions in the gut, expulsion of wastes from the body and control of respiration (Ca.Sū.12/8). ‘Vāta’ is divided into five sub types – ‘Prāna’, ‘Udāna’, ‘Vyāna’, ‘Samāna’ and ‘Apāna’.
This is situated in head and is responsible for the control over intellectual functions, cardiovascular functions, sense organs, psychological activities, respiration, and reflex activities like sneezing, belching and deglutition (A.H.Sū. 12/5). Based on this sub-type of ‘Vāta’, ‘Prānavaha Srotas’ has derived its name.
Its active site is chest region. It is basically responsible for production of speech. The effort and strength required for speech are also the functions of ‘Udāna’. It also helps in recall of vocabulary required for well-articulated speech (A.H.Sū. 12/5).
The active site of ‘Vyāna Vāta’ is Heart. It makes the circulation of blood possible by controlling the heart. Vyana makes ‘Rasa’ (the intravascular fluid including plasma and lymph) to get forcefully ejected out of the heart and makes it circulate throughout the body (Ca. Ci. 15/36). So, sympathetic and parasympathetic control of heart is indicated by ‘Vyāna Vāta’. Some authors have ascribed the functions of somatic nervous system also to ‘Vyāna Vāta’ as movements like flexion, extension, opening and closure of eyelids have been said to be under its control (Ca. Ci. 28/9).
Active site of ‘Samāna’ is adjacent to gastro intestinal tract. It performs the functions like reception of food, its digestion through the activation of ‘Agni’, its division into useful and waste parts and its onward propulsion (A.H. Sū. 12/8). All these functions are either those of parasympathetic nerves supplying the gut or those of enteric nervous system.
This is active in pelvic region. ‘Apāna’ governs physiological processes like micturition, defecation, ejaculation, menstruation and parturition (A.H.Sū.12/9). Autonomic nervous system has got a definite role in most of these activities. 
- The content Nervus system Physiology is borrowed from an article by Mr.Kishor Patwardhan