Chapter 8: Axial Skeleton

Question 1

Centrum

Answer 1

connects one part of vertebra to another; middle circular piece of spine
- includes pleuocentrum and intercentrum

Question 2

Spinal Canal

Answer 2

houses spinal cord

Question 3

Neural Arch/spine

Answer 3

o Neural spine forms neural arch
o Neural arch holds dorsal hollow nerve cord

Question 4

Hemal arch/spine

Answer 4

o Skeletal structure pieces of vertebrae
o Arch holds blood vessel
o Spine outer edges/tips of vertebrae pieces

Question 5

Tranverse processes

Answer 5

• Processes: for attachment of axial muscles
• On the outer edge of the skeletal vertebrae structure

Question 6

Regions of the vertebral column

Answer 6

o Cervical
o Thoracic
o Lumbar
o Sacral
o Caudal
o (3-4 bones) of coccyx

Question 7

Describe each and the relationship between the Prezygapophyses and postzygapophyses

Answer 7

• Articular processes: joints between vertebrae
• Both these parts are attached to opposite sides of the neural arch along the vertebral column
• They are a pair between junctions; their structures are formed in specific shapes to fit around each other like a puzzle

Question 8

Which embryonic germ layer is the primary contributor to vertebrae?

Answer 8

vertebrae develop from sclerotome

Question 9

What are arcualia in cartilaginous and “primitive” bony fish?

Answer 9

• Arcualia: cells from the sclerotome gather around the notochord, form discrete blocks of cartilage (up to four pairs per segment)
• Each arcualium develops into part of the adult vertebra
• four blocks of cartilage included

Question 10

Four blocks of cartilage

Answer 10

o Basidorsal, forms neural arch
o Interdorsal, forms internueral
o Interventral, forms pleurocentrum
o Basiventral, forms intercentrum

Question 11

Describe the chordal center in teleosts and which parts of adult vertebrae they make:

Answer 11

o Chordal center (chordacentrum) forms within the notochordal sheath
o Becomes center of centrum, remains or sits more rigid

Question 12

Describe the intervertebral ligament in teleosts and which parts of adult vertebrae they make:

Answer 12

• the intervertebral ligaments play a key role in supporting the spine and enabling flexibility
• intervertebral ligaments contribute to the formation of specific parts of adult vertebrae, namely the neural arches and centra. The neural arches protect the spinal cord, while the centra bear the main structural load of the vertebral column

Question 13

Describe the dorsal and ventral arch centers in teleosts and which parts of adult vertebrae they make:

Answer 13

o Paired cartilaginous rudiments of dorsal and ventral arches form at myosepta
- dorsal arch center responsible for forming neural arches, encase spinal cord
- central arche center gives rise to hemal arches, protecting blood vessels

Question 14

Describe the Perichordal center in teleosts and which parts of adult vertebrae they make:

Answer 14

Within the perichordal tube (formed from sclerotomal cells – black) perichordal centers of ossification appear

Question 15

Describe the relationship amongst the chordal center, the perichordal center, and arches

Answer 15

• Chordal center becomes incorporated within the ossified perichordal center, forming the centrum
• Arches may or may not fuse with the centrum to ossify along with it

Question 16

How can the notochord persist in teleost organisms?

Answer 16

• intervertebral cartilaginous pads, intervertebral ligaments, or a constricted notochord running through the centers of the centra

Question 17

What are primary sclerotomes in tetrapods?

Answer 17

The primary sclerotome forms from cells on the medial side of the somite that depart and stream downward toward the notochord (solid arrows)

Question 18

What are secondary sclerotomes in tetrapods?

Answer 18

Migrating cells form secondary sclerotomes - half derived from one somite, and the other half from the next adjacent somite

Secondary sclerotomes form repeating perichordal rings that fuse to form a more or less continuous perichordal tube

Question 19

Resegmentation

Answer 19

the secondary sclerotomes come to lie between adjacent myotomes

Question 20

What is the perichordal tube/ring in tetrapods?

Answer 20

• The perichordal tube grow upward around the nerve cord forming neural arches and spines
• Chondrification, followed usually by ossification, produces the adult bony vertebrae

Question 21

Why do vertebrae develop intersegmentally in tetrapods?

Answer 21

o The intervertebral disks differentiate between vertebrae within the former perichordal rings
o Axial muscles that form from myotomes cross the intervertebral joint, instead of attaching to the same vertebra, thereby giving the muscles useful actions