Most input comes from collaterals of fibers passing through the thalamic reticular nucleus. They receive input from the reticular formation of the pons in the brainstem. The pons first evolved as an offshoot of the medullary reticular formation. The DLF ascending tract has its origins in nuclei of the reticular formation. Modern scientists usually refer to the individual nuclei that compose the reticular formation. It is lined by reticular cells, fibroblasts and fixed macrophages. Medullary sinuses contain histiocytes (immobile macrophages) and reticular cells. Adipose tissue is held together by reticular fibers. The pedunculopontine nucleus is one of the main components of the reticular activating system. Several nuclei, tracts, and the reticular formation are contained here. The ascending reticular activating system is an important enabling factor for the state of consciousness. There are more than 20 types of reticular fibers. They are generally geophytes, but with linear leaves, and a lack of fine reticular venation. It is a part of the reticular activating system. Damage to the reticular formation can produce a permanent state of coma.