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488 APPENDIX ASubstance P A neuropeptide and neurotransmitter that is widely distributed inthe brain, spinal cord, and peripheral nervous system that acts across nerve synapsesto produce prolonged postsynaptic excitation. In the CNS, substance P isimportant in regulating mood disorders, anxiety, stress, reinforcement, neurogenesis,neurotoxicity, emesis, and pain.Subunit A single protein molecule that assembles with other protein moleculesto form a multimeric (formed with many different subunits) or oligomeric (composedof many identical subunits) protein. A subunit is made up of one polypeptidechain, the sequence specifics of which are stored in the code of genes.SulcusA groove between two gyri in the cerebral cortex.Sympathetic adrenal medullary (SAM) The adrenal medulla, the principal siteof catecholamine synthesis, is actually a ganglion, a tissue mass that contains thedendrites and cell bodies of neurons, of the sympathetic nervous system.SynaptogenesisThe formation of nerve synapses.Telencephalon The anterior-most embryological region of the brain that givesrise to the cerebral hemispheres and other, smaller structures within the brain.Thalamus Located in the center of the brain, serves as a relay station for nerveimpulses carrying sensory information into the central nervous system and processesmost of the information reaching the cerebral cortex. For localization, seeFigures B1 and B2.Transcription The process of using a DNA molecule as a template to enzymaticallyconstruct a complementary messenger RNA molecule, thereby transferringgenetic information.Transcription factors Any of various proteins that bind to DNA at specific promoteror enhancer regions to regulate gene expression by enhancing transcription.Transporter A protein that mediates the active transport of ions, nutrients, andother molecules into a cell against their electrochemical gradient by using energyfrom ATP hydrolysis, a reaction in which chemical energy stored in the form ofphosphate bonds in ATP (adenosine triphosphate) is released.Trinucleotide repeat sequences Stretches of DNA in a gene that contain thesame trinucleotide sequence repeated many times and occur throughout all genomicsequences. However, if the repeat is present in a gene, an expansion of therepeats may result in a defective gene product that can often lead to disease states.