Transmission electron micrograph (TEM) of human bone showing an osteocyte. An osteocyte is an osteoblast (bone- producing cell) that has become trapped within a bone cavity (lacuna). Osteocytes are responsible for bone formation, but eventually become embedded in the bone matrix. A number of long tunnels called canaliculi can be seen. Osteocytes uses these tunnels to interconnect and exchange gases and nutrients within the bone.