Mahabharat Episode Discussion Thread #12 - Page 24

Now Lord Krishna speaks of the characteristics and nature of theksetra or field of activity beginning with the words maha-bhutanimeaning the five fundamental elements being earth, water, fire, air and ether. These are the elements comprising material existence and these are the elements that constitute the physical body.Ahankarah is the false ego, buddhi is the intellect,avyaktam is the unmanifest nature known as prakriti the material substratum pervading all physical existence. The five organs of perception for the senses being the five senses: eye, ears, nose, tongue and skin. The five objects of the senses being sight, sound, smell, taste and touch and the five organs of action being the hands, the legs, the voice, the genitals for procreation and the anus for evacuation. These 24 elements have already been iterated by Lord Krishna millenniums before in His lilaavatar or pastime incarnation as Kapila deva; but here He also names the modifications such as desire and aversion as well. Desire is attachment to that which gives happiness and repugnance is aversion to that which gives misery. Both are mental tendencies formed from a conditioned perception of what is favourable and unfavourable relegated by the karma or reactions to one's meritorious and unmeritorious actions and as they are caused by the actions of the physical body they are experienced by the jiva or embodied being through contact of the physical body as it is the receptacle of feeling for all jivas. The word cetana meaning awareness is apparent in all forms and species of life relative to their individual consciousness. This starts with being conscious of food only to being conscious of life with its six transformations of birth, infancy, youth, maturity, old age and death; to being conscious of the atma or the immortal soul, to being conscious of a Supreme Lord to being conscious of loving devotion to the Supreme Lord Krishna. All these things have been explained in brief as being part of the ksetra along with the mind, the senses, the objects of the senses and the modifications of dsire and aversion which causes the sensations of pleasure and pain for the jivas.

Reference: http://www.bhagavad-gita.org/Gita/verse-13-05.html