Demyelination The loss of the protective myelin sheath around an axon, usually due to damage to the Schwann and oligodendroglia cells. Dendrites Sensory processes of a neuron that are specialized to receive incoming information and send it to the neuron cell body. Deoxyribonucleic Acid (DNA) A nucleic acid known as the molecule of life that makes up the chromosomes.  It is composed of a chain of nucleotides containing the sugar deoxyribose and the nitrogen bases, adenine, guanine, cytosine, and thymine wound in a double helix and held together by weak bonds between complementary nitrogen base pairs. Depression A clinical psychiatric condition in which a person has a dejected mood, psychomotor retardation, insomnia and weight loss, sometimes associated with guilt feelings and often with delusional preoccupations. Diencephalon A portion of the brain that contains the thalamus, hypothalamus, and pituitary gland.  It relays and processes sensory information; control of emotions, autonomic functions, and hormone production. Digestive System The organ system that functions to process foods that are ingested, absorb nutrients into body, and provide metabolized nutrients to the body cells.  Consists of the mouth, salivary glands, esophagus, stomach, intestinal tract, liver, and pancreas, Disease A malfunction of any component of the body that can result in an abnormal and undesirable physiological or anatomical change. DNA (Deoxyribonucleic acid) A nucleic acid known as the molecule of life that makes up the chromosomes.  It is composed of a chain of nucleotides containing the sugar deoxyribose and the nitrogen bases, adenine, guanine, cytosine, and thymine wound in a double helix and held together by weak bonds between complementary nitrogen base pairs. Dying-back Neuropathy A neurological condition in which axons begin to die at the very distal end of the axon with necrosis slowly progressing toward the cell body. Dysplasia A condition of abnormal cell change or deranged cell growth in which the cells are structurally changed in size, shape, and appearance from the original cell type.