Final answer:
Depressions running across the width of the nail plate are known as Beau's lines, which occur when nail growth is disrupted. The nail plate, nail bed, and nail matrix are part of the complex structure of the nail that can reflect overall health issues.
Step-by-step explanation:
Depressions running across the width of the nail plate are known as Beau's lines. These indentations may appear when growth at the area under the cuticle, known as the nail matrix, is interrupted by injury or severe illness. The nail plate is the hard part of the nail that is most visible, the nail bed is the skin beneath the nail plate, and the cuticle, or eponychium, is the tissue that overlaps the nail plate at the base. Beau's lines are an important clue to health issues that may affect nail growth, and they could be a sign of systemic diseases, zinc deficiency, or exposure to cold temperatures. The nail bed provides a pinkish color to the nail plate due to its rich blood supply, and the nail matrix at the base of the nail is where the growth of the nail begins, supported by a framework of keratin cells.