Glossary of plant morphology others may form a tight spiral, or whorl, around the flower stem. First, at the base, are those non-reproductive structures involved in protecting the flower when it is still a bud, the sepals, then are those parts that play a role in attracting pollinators and are typically coloured, the petals, which together with the sepals make up the perianth (perigon, perigonium). If the perianth is differentiated, the outer whorl of sepals forms the calyx, and the inner whorl of petals, the corolla. If the perianth is not differentiated into sepals and petals, they are collectively known as tepals. In some
Calyx of Held calcium into the mitochondria, and providing energy for glutamate synthesis. Various glial cells are also associated with the calyx of Held. Two types of glial cells surround the calyx: astrocytes and NG glial cells. The astrocytes express glutamate transporters to remove glutamate from the synapse. This is the only known mechanism for removal of glutamate from the synapse. The NG glial cells express AMPA receptors. At postnatal day two (P2), the immature calyx of Held is formed, easily distinguished by its characteristic sealed-spoon morphology. The primary synaptic contacts that form the calyx are assembled between neurons of the MNTB (medial