Manas (मनः) also called as Satvam (सत्वम्) is popularly known as Mind. However, Manas in Vedas is something distinct from the physical body on one hand and consciousness or adhyatmik self on the other hand. Manas in vedas is the object of knowledge while Atman is believed to be the knower. Mind is not the faculty of consciousness but it is the tool for obtaining the knowledge of the external world in union with the Indriyas (इन्द्रियाणि । Senses).
According to Ayurveda, Manas along with Sharira (शरीरम्। physical body) and Atman (आत्मन् । consciousness) form the 3 pillars of individual’s life. Thus, Manas is neither a part of physical body nor a part of consciousness but equally important as the other 2 components. Also, it is distinct from Buddhi (बुद्धिः। intellect) and Ahankara (अहङ्कारः। Ego). A great emphasis has been given on understanding the nature, function, properties and development of Manas in Ayurveda because, along with the Sharira (Physical body) it is considered to be the site of diseases. Diseases affecting Manas are known as Manas rogas (मानस रोगाः।).
वैशेषिक दर्शने वर्णिता मनसः संकल्पना॥ Manas as in Vaisheshika Darshana
Ayurveda accepts philosophical foundations from Darshana Shastras (दर्शन शास्त्राणि।) to large extent but within its scope and area of application. Vaisheshika darshanam (वैशेषिक दर्शनम्।) has described Manas as one of the 9 dravyas (नवद्रव्याणि।). Dravyas are the eternal substances and seat for the gunas (गुणाः। qualities), the presence of which can be appraised by various means of knowledge. Thus Manas is considered as Dravya (द्रव्यम्।) by Darshanas. Further Vaisheshikas describe Manas as Nityam (नित्यम्। eternal), Anu (अणुः। atomic) and partless (एकम्।) i.e. unlike other substances it does not give rise to more complex substances.
आयुर्वेदे मनः ॥ Manas as in Ayurveda
अतीन्द्रियं पुनर्मनः सत्त्वसञ्ज्ञकं, ‘चेतः’ इत्याहुरेके, तदर्थात्मसम्पदायत्तचेष्टं चेष्टाप्रत्ययभूतमिन्द्रियाणाम्|| (Char Samh 8. 4)
atīndriyaṁ punarmanaḥ sattvasañjñakaṁ, ‘cetaḥ’ ityāhureke, tadarthātmasampadāyattaceṣṭaṁ ceṣṭāpratyayabhūtamindriyāṇām||
Meaning : Mind transcends the sense organs. It is also termed as satva, while some others call it as chetas. Its action is dependent on its objects and accomplishments of the Self i.e. atman. It is responsible for the actions of the sense organs.
According to Acharya Charaka, Manas is known as “Satva” or “Chetah” (bearer of capability of thinking). Its action is determined by its contact with its objects (like happiness, miseries) and the soul; this acts as a driving force for all the sense faculties.
मनसः अधिदैवतम्॥ Adhidaivatam of Manas
Chandrama (चन्द्रमा।) is regarded as Adhidaivatam (अधिदैवतम्। Controlling diety) of the Manas. (Sush. Samh 1.7)
मनसः लक्षणम् ॥ Characteristic of Manas
Manas cannot be perceived by any sense organ i.e by any direct method. As it is directing and mediating for inference of the objects. Gati (speed) of Manas is derived from Atma. A state of special relation between Atma and Manas aids to understand Atma, which is dependent on Manas. Main function of Manas is to act as a mediator in attaining knowledge
मनसः विषय़ाः अर्थाः च॥ Object of Manas and Function of Manas
Manas performs exclusive actions. It also has critical role in the process of gaining knowledge of all types. In close association with Indriyas, Buddhi and Atman it is responsible for gaining knowledge obtained by Jnanendriyas by generating a stimulus. Acharya Charaka has described the artha (Object) and function of Manas as follows,
चिन्त्यं विचार्यमूह्यं च ध्येयं सङ्कल्प्यमेव च| यत्किञ्चिन्मनसो ज्ञेयं तत् सर्वं ह्यर्थसञ्ज्ञकम्||
इन्द्रियाभिग्रहः कर्म मनसः स्वस्य निग्रहः| ऊहो विचारश्च|| (Char. Samh. 1.20-21) 
cintyaṁ vicāryamūhyaṁ ca dhyeyaṁ saṅkalpyameva ca| yatkiñcinmanaso jñeyaṁ tat sarvaṁ hyarthasañjñakam||
indriyābhigrahaḥ karma manasaḥ svasya nigrahaḥ| ūho vicāraśca||
Meaning: Things requiring thought, consideration, hypothesis, attention, determination or whatever can be perceived by the mind, are regarded as its objects. Control of sense organs, self restraint, analysis and initializing thought process represent the action of the mind. Beyond that flourishes the domain of intellect.
मनः आत्मा च॥ Manas and Atman
Contact of Manas with Atma is essential for all types of knowledge acquired through sense organs and also for performing actions in response to these stimuli. Once this contact is disturbed, one may not gain and kind of knowledge. One may say that contact of Manas with Atma is the essential link for acquiring knowledge. In the cause of perception, Satva should have contact with both the soul and the concerned sense faculty.
Manas is known as Chetah (चेतः) because though Manas is very active, but it is Achetana (अचेतन), and Atma is Chetana (चेतन), but it is action less. Manas gets Chetana from Atma and in turn provide Chetana to the whole body.
मनः इन्द्रियाणि च॥ Manas and Indriyas
The sense organs are capable of perceiving objects only when they are associated with the mind. (TBE)Manas is grouped under Indriya due to its super natural properties than other Indriyas, further qualifications and designation are attributed to Manas as Athindriya. According to Acharya Chakrapani mind is also to be regarded as a sense faculty as much as it is responsible for experiencing happiness etc. Mind is still above the other sense faculties, and controller of all the other sense faculties. Acharya Chakrapani stated that mind is much more subtle than the other sense faculties
महागुणानां सह मनसः सम्बन्ध॥ Mahagunas and Manas
(TBE)Manas as a Dravya is under influence of three Mahaguna, out of which generally all three are necessary for normal physiology being responsible for knowledge, action and control or rest respectively. But specially Rajas and Tamas are considered as cause of morbidity, hence called as Manas Dosha, remaining Sattva Guna becomes synonyms for Manas being cause of benefit i.e. well-being which means knowledge applying normality of intellectual faculty.
The important qualities of Manas are the ability to perceive, think, remember, imagine. In western philosophy mind is considered immaterial substance, it is conscious and is characterized by thinking. Since it is substance it cannot be destroyed.
मनोविकृतिहेतवः॥ Causes of abnormalities of mind
Manas can function independently and generate give rise to Buddhi (intellect) or together with Senses it can engage in the perception of objects of 5 sensory perception viz touch, taste, smell, sound and vision. Skewed association of mind and senses by their deficient, excess or inappropriate engagement in perceiving their respective objects leads to development of abnormalities in mind, sensory organs and the intellect developed due to their union. This results in various abnormalities of Manas and Indriyas.
मानसास्तु क्रोधशोकभयहर्षविषादेर्ष्याभ्यसूयादैन्यमात्सर्यकामलोभप्रभृतय इच्छाद्वेषभेदैर्भवन्ति | (Su su 1.25) http://niimh.nic.in/ebooks/esushruta/?mod=read
Commentary by Dalhana- मानसान् प्रतिपादयन्नाह- मानसास्त्वित्यादि| क्रोधः पराभिद्रोहलक्षणः, शोकः पुत्रादिवियोगे चित्तोद्वेगः, भयं परस्मात्त्रासः, हर्ष उत्सेकः, निर्निमित्तमन्यस्य दोषोत्पादनेनात्मनः प्रीतिजननं वा हर्षः, असिद्धिभयाद्विविधेषु कर्मसु सादोऽप्रवृत्तिः विषादः, ईर्ष्या परसम्पत्तावसहिष्णुता, छिद्रान्वेषितया परगुणेषु दोषारोपणमसूया, दैन्यं क्लिष्टचित्तता, मात्सर्यं परगुणेष्वमाध्यस्थ्यं क्रौर्यं वा, काम इन्द्रियार्थेष्वभिकाङ्क्षा, लोभः परस्वग्रहणाभिलाषः, आदिग्रहणान्मानमददम्भादयः| इच्छाद्वेषभेदैर्भवन्तीति इच्छा सातिशयोऽर्थाभिलाषः, सा च नानावस्त्ववलम्बिनी नानाकामतश्च भिन्ना भवति; तत्र हर्षशोकदैन्यकामलोभादय इच्छाभेदेन; द्वेषः अप्रीतिः,सोऽपि नानावस्त्ववलम्बी नानारूपो भवति, क्रोधभयविषादेर्ष्यासूयामात्सर्याणि द्वेषभेदेन| अन्ये तु ‘मानसाः क्रोधशोकभयदैन्येर्ष्यासूयामात्सर्यकामादयः’ इति पठन्ति||२५(३)||
मनसः तथा इन्द्रियाणां अनुपतापाय उपायाः॥ Measures to prevent abnormalities of Manas and Indriyas
Ayurveda is unique in its nature of providing curative as well as preventive measures to alleviate suffering from diseases affecting body, mind and senses. We are well aware of the preventive measures to stay physically fit and methods to achieve this can be found in multiple medical systems. But in its unique and extraordinary thinking, Ayurveda acharyas were also able to enumerate the methods to promote the health and prevent the diseases of mind and senses. For this reason, Ayurveda stresses on the practice of Sadvrtta on daily basis, which when observed religiously possess the capability to balance the mind and senses along with the physical body.
तत्रेन्द्रियाणां समनस्कानामनुपतप्तानामनुपतापाय प्रकृतिभावे प्रयतितव्यमेभिर्हेतुभिः; तद्यथा सात्म्येन्द्रियार्थसंयोगेनबुद्ध्या सम्यगवेक्ष्यावेक्ष्य कर्मणां सम्यक् प्रतिपादनेन, देशकालात्मगुणविपरीतोपासनेन चेति| तस्मादात्महितं चिकीर्षता सर्वेण सर्वं सर्वदा स्मृतिमास्थाय सद्वृत्तमनुष्ठेयम्|| (Char Samh 8.17)
Tatrēndriyāṇāṁ samanaskānāmanupataptānāmanupatāpāya prakr̥tibhāvē prayatitavyamēbhirhētubhiḥ;tadyathā- sātmyēndriyārthasaṁyōgēna buddhyā samyagavēkṣyāvēkṣya karmaṇāṁ samyakpratipādanēna, dēśakālātmaguṇaviparītōpāsanēna cēti| tasmādātmahitaṁ cikīrṣatā sarvēṇa sarvaṁ sarvadā smr̥timāsthāya sadvr̥ttamanuṣṭhēyam||
Meaning: One should always make efforts to maintain normalcy of sense organs with mind and protect them from any kind of trauma. This can be achieved by proper association of sense organs and their objects, performance of duties after duly considering their pros and cons with the help of the intellect together with the sense faculties and by following (preventive) measures opposite to the qualities of place, season and one’s own constitution. So all, who are desirous of their own well-being, should always remember and abide by all the codes of conduct.