The spine has four natural curves that help with balance, flexibility, and shock absorption:
Cervical spine - The neck region has a slight inward curve, or lordotic curve, that resembles a backward C-shape.
Thoracic spine - The middle back region has a slight outward curve, or kyphotic curve, that resembles a forward C-shape
Lumbar spine - The lower back region has a slight inward curve, or lordotic curve, that resembles a backward C-shape.
Sacrum - The triangle-shaped bone that connects to the hips.