Lec 3 Bones

Question 1

Bones originated during

Answer 1

late Cambrian and early Ordovician times, approximately 500 million years before present (MYBP) coincides with origin of vertebrates

Question 2

Early fish characteristic

Answer 2

they lacked jaws as well as paired fins, and all shared a thick exoskeleton; that is, their entire head and body was covered with plates of thick bone—heavy armor thought to have evolved to provide protection against predation. Their internal skeletal support was made up entirely of cartilage

Question 3

Eurypterida

Answer 3

largest and most fearsome marine predators of the Paleozoic. While the smallest were only about 10 cm long, others reached more than 2 m (8 feet) in length making them by far the largest arthropods that ever lived

Question 4

thick outer bony plates of these earliest kinds of fishes were multilayered, consisting

Answer 4

of a dense outer layer of dentine, a middle layer of cancellous vascular bone, and an inner or “basement” layer of lamellar bone

Question 5

Skeletal tissue :Cartilage

Answer 5

form of connective tissue that has an intercellular matrix composed of a complex, rubbery protein; throughout the matrix lies a complex network of connective tissue fibers as well as spaces that contain cells called “chondrocytes.” These cells secrete the surrounding matrix

Question 6

Skeletal tissue: Bone

Answer 6

similar to cartilage in that it consists of a matrix held together throughout by connective tissue fibers, within which cells are buried (in this case the cells are called “osteocytes”); but the matrix differs in having, in addition, deposits of a hard, complex mineral substance composed primarily of crystals of calcium phosphate and calcium hydroxide, a compound called “apatite

Question 7

TWO KINDS OF BONE: DERMAL AND ENDOCHONDRAL

Answer 7

1. Dermal bone, sometimes called “membrane bone”

2. Endochondral bone, sometimes called “cartilage bone

Question 8

Dermal bone

Answer 8

Dermal bone is laid down initially in a membranous connective tissue matrix and becomes ossified directly without passing through a cartilage stage; it originates evolutionarily from the multi-layered, external dermal armor of ancient jawless fishes. More primitive.

Question 9

Endochondral bone

Answer 9

is laid down initially within a cartilaginous matrix and is only later ossified; thus, it is really only a developmental extension of cartilage. Endochondral bone is phylogenetically younger than dermal bone. It is an extension of the cartilaginous internal skeletal support of the earliest vertebrates and thus tends to be associated with the internal parts of the body