What do the sensitive and insensitive laminae do in the horse's hoof?

The insensitive laminae and the sensitive laminae intermesh together to hold the hoof wall to the coffin bone. The sensitive laminae are filled with nerves and blood vessels that help support the horse’s lower leg and hoof.

Laminitis, an inflammation of the laminae, results from the disruption of blood flow to the sensitive and insensitive laminae within the foot. When this occurs, the union between the hoof and the laminae can separate, and in severe cases the coffin bone can rotate and begin to penetrate the sole or sink within the hoof capsule, causing intense pain. Here are some additional resources you might find useful:

Equine Laminitis or Founder : http://www.extension.org/pages/10304/equine-laminitis-or-founder

Sensitive Structures of the Hoof: http://www.extension.org/pages/13024/sensitive-structures-of-the-hoof