והנה על המשכת כל התרי״ג מיני כוחות וחיות מהעלם הנשמה אל הגוף להחיותו

Now, concerning the flow of all the 613 kinds of functional powers and vital forces which are drawn from the concealment of the soul, where they are previously hidden, and from where they are now drawn to the body to animate it, —

עליה אמרו שעיקר משכנה והשראתה של המשכה זו וגילוי זה, הוא כולו במוחין שבראש

concerning this flow [the Sages] have said that the principal dwelling-place and abode of this flow and revelation of the previously concealed powers and forces is entirely situated in the brains of the head.

ולכן הם מקבלים תחלה הכח והחיות הראוי להם, לפי מזגם ותכונתם, שהן חב״ד, וכח המחשבה, וכל השייך למוחין

Therefore it is they, the brains, which first receive the power and life-force appropriate to them according to their composition and character — namely, intellect which is divided into the three intellectual faculties called ChaBaD (Chochmah, Binah, Daat), and the faculty of thought, and whatever pertains to the brain. All these receive their life-force from the soul before the other parts of the body.

ולא זו בלבד, אלא כללות כל המשכת החיות לשאר האברים גם כן כלולה ומלובשת במוחין שבראש

And not only this — that the brains receive their own life-force before the other organs — but also the overall flow of all the individual streams of vitality to the other organs, is also first included and enclothed in the brains of the head, before it becomes revealed in the individual organs,

ושם הוא עיקרה ושרשה של המשכה זו בבחינת גילוי האור והחיות של כל הנשמה כולה

and it is there, in the brain, that the core and source of the said flow exist in a form in which the light and vitality of the entire soul are revealed. In other words, when the general flow of vitality reaches the brain, then the “light” and vitality of the entire body begin to be revealed.

ומשם מתפשטת הארה לשאר כל האברים ומקבל כל אחד כח וחיות הראוי לו כפי מזגו ותכונתו: כח הראיה מתגלה בעין, וכח השמיעה באוזן, וכו׳

From there, the brain, radiance flows to all the other organs, each of which then receives the functional power and vital force appropriate to it according to its composition and character: the power of sight is revealed in the eye, the power of hearing in the ear, and so on.

In other words: At which point does a power of sight come into existence, ready to be revealed in the eye, and a power of hearing in the ear? Only after the overall life-force of the whole body is drawn into the brain in a general manner, then a “radiance” is drawn from there to each organ, a radiance which is already constituted in accordance with the particular character of the individual organ.

וכל הכוחות מתפשטים מהמוח, כנודע, כי שם הוא עיקר משכן הנשמה כולה בבחינת גילוי

But all functional powers flow from the brain, as is known,1 for there, in the brain, is located the principal dwelling-place of the entire soul, in a revealed form,

Although the soul actually exists all over the body equally, with no difference between one organ and another, yet the principal place in which the soul is revealed is in the brain.

שנגלית שם כללות החיות המתפשט ממנה. רק כוחותיה של כללות החיות מאירים ומתפשטים משם לכל אברי הגוף, כדמיון האור המתפשט ומאיר מהשמש לחדרי חדרים

since there, in the brain, the overall life-force which flows from the soul is revealed. It is only the individual faculties of the overall life-force which shine forth and radiate from there, the brain, to all the organs of the body, just as light radiates and shines from the sun into the innermost of rooms.

ואפילו הלב מקבל מהמוח, ולכן המוח שליט עליו בתולדתו, כנ״ל

(2Even the heart, which is a central organ from which all other organs receive vitality — “The heart diffuses to all organs” — receives its own vital force from the brain, which is why the brain naturally dominates the heart, as explained above.)

In ch. 12 it was explained that man is created with a natural supremacy of the brain over the heart, and the reason is explained here — because the heart, despite its centrality, must in turn receive its own vital force from the soul through the medium of the brain.