Sushumna is the symbolic passage through which kundalini rises through the chakras. It is generally regarded as starting at mooladhara chakra and ascending in turn through the other higher chakras to sahasrara. However, some scriptures give apparently contradictory information. For example, in the Nigam Tattvasara, a tantric text, it says categorically: “The bony rod (sushumna) goes from the feet to the brahma randhra (entrance to the sahasrara); it is known as the merudanda (literally spine, but meaning sushumna) of the fourteen spheres of being (the fourteen chakras from the patala to the ajna).”
This verse states that sushumna does not start at the mooladhara, but the lowest of the lower chakras, the patala. And this is acceptable for the same reason that the kundalini can abide in patala, mooladhara, manipura or in any other chakra. It depends on definition. The sushumna starts wherever the kundalini is regarded as having its seat. In the Buddhist system, therefore, sushumna can be considered to begin at manipura chakra. In the case of a piece of rock, the sushumna, in a wide sense, can be regarded as beginning at the patala chakra. For the purposes of man in relation to yoga-tantra practices, however, sushumna is considered as starting at the mooladhara chakra.
This is the centre where people are almost entirely self-centred, where the predominant drives, thoughts and actions are directed towards attaining some measure of security in the world. Even children are produced often with a strong motive of ensuring security by continuing one’s family line in the future. People surround themselves with material objects, money, friends, etc. in order to feel secure. All things and all people are regarded as a means to obtaining the desperately sought after security.
There are many other aspects, but this is sufficient to indicate the general trends associated with mooladhara chakra.