Cell communication (biology)
In cells, DNA is housed in the nucleus and it never leaves. The DNA within the nucleus is transcribed by tRNA, and the transcriptions of the DNA become RNA. The RNA (ribonucleic acid) leaves the nucleus to float freely around the cytoplasm, and it contains the instructions of the DNA that are vital to the coding, decoding, regulation and expression of genes. The ribosomes then take the RNA messages and turn them into proteins that build cells. When a virus enters a cell and inserts its DNA code into the nucleus, it gets transcribed and released into the cell for the ribosome to make it into a protein. This is how viral infections occur. The cell then explodes with the overproduction of the virus, releasing it into the body to infect any and all other cells it finds. It is theorized that through evolution, cells developed a defense system called RNAi (RNA interference) to stop the production of the proteins that have suspicious mirror image messages of the RNA. They don’t just destroy the suspicious messages, but the correct messages as well to stop all production of that message. This is a cell’s self-destruct mechanism and every cell, plant and animal, have RNAi: a way to turn off the production of a certain gene inside the protein.
Cochlear nucleus
The major input to the cochlear nucleus is from the auditory nerve, a part of cranial nerve VIII (the vestibulocochlear nerve). The auditory nerve fibers form a highly organized system of connections according to their peripheral innervation of the cochlea. Axons from the spiral ganglion cells of the lower frequencies innervate the ventrolateral portions of the ventral cochlear nucleus and lateral-ventral portions of the dorsal cochlear nucleus. The axons from the higher frequency organ of corti hair cells project to the dorsal portion of the ventral cochlear nucleus and the dorsal-medial portions of the dorsal cochlear nucleus. The mid frequency projections end up in between the two extremes; in this way the tonotopic organization that is established in the cochlea is preserved in the cochlear nuclei. This tonotopic organization is preserved because only a few inner hair cells synapse on the dendrites of a nerve cell in the spiral ganglion, and the axon from that nerve cell synapses on only a very few dendrites in the cochlear nucleus. In contrast with the VCN that receives all acoustic input from the auditory nerve, the DCN receives input not only from the auditory nerve but it also receives acoustic input from neurons in the VCN (T stellate cells). The DCN is therefore in a sense a second order sensory nucleus.