Plant reproductive morphology is asexual, producing only spores. Similarly, flowers produced by the sporophyte may be described as "unisexual" or "bisexual", meaning that they give rise to either one sex of gametophyte or both sexes of gametophyte. The flower is the characteristic structure concerned with sexual reproduction in flowering plants (angiosperms). Flowers vary enormously in their construction (morphology). A "complete" flower, like that of "Ranunculus glaberrimus" shown in the figure, has a calyx of outer sepals and a corolla of inner petals. The sepals and petals together form the perianth. Next inwards there are numerous stamens, which produce pollen grains, each containing a
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