V. INTRODUCTION TO SKELETAL SYSTEM
A. Function/Fossils
B. Mineralized connective tissue from mesenchyme
C. Bone constituents
1. Collagen
2. Hydroxyapatite Crystals CaPO4OH
3. Water and Mucopolysaccharides
4. Usually osteocytes
D. Bone Types
1. Compact
a. Osteon –Basic cylindrical unit of compact bone
b. Haversian Canal –Central canal containing blood vessels
c. Lamellae [lamellar bone] –Concentric rings of osteon
d. Osteocytes in lacunae (pools)
2. Spongy = Cancellous –Locations include facial bones, ribs, scapula
a. Trabeculae –Spicules of bone
b. Red marrow
3. Acellular –Cells die & space fills with bone; e.g. fish scales
4. Membrane –Dermal bone
5. Replacement –Endochondral
E. Cartilage –Connective tissue consisting of collagen, matrix & chondrocytes
1. Hyaline
2. Fibrous
3. Elastic
4. Calcified –Found in sharks; can’t remodel as bone can
F. Axial vs Appendicular Skeleton
VI. AXIAL SKELETON – VERTEBRAE, RIBS, STERNUM
A. VERTEBRAE
1. General function –Locomotion, protects spinal cord, suspend trunk
2. Structure of typical vertebra
a. Centrum– Body of vertebra; surrounds/restricts notochord
1. Amphicelous = Amphicoelous [fish, tailed amphibians, caecilians, primitive lizards] –“Both hollow cavity”; limited motion allowed
2. Opisthocelous = Opisthocoelous [terrestrial salamanders, some fish such as gar] –“Behind hollow”
3. Acelous = Acoelous [mammals] –“No hollow” , can withstand compression
4. Procelous = Procoelous [reptiles, frogs] –“Front hollow”
b. Neural = Vertebral arch– Archway lateral & dorsal to spinal cord
1. Neural spine= Spinous process – Dorsal projection
2. Neural [vertebral] canal
c. Hemal arch= chevron bone in amniotes – Ventral archway around caudal blood vessels
– Hemal spine – Ventral projection
d. Transverse process = diapophyses
e. Zygapophyses(tetrapod feature) (zyg = union; physes = growth)
1. Prezygapophyses – Cranial
2. Postzygapophyses – Caudal
3. Development– Ancient structure
a. Mesenchyme from sclerotomes around notochord
b. Intersegmental– from somites
c. Chondrification of notochord –In fish and amphibians, cartilage surrounds & invades notochord
d. Bone replacement of notochord in some –Replacement bone; Anurans and higher classes
4. ADVANCED FISH
a. Centra
b. Notochord –Invaded by cartilage
c. Diplospondyly –2 centra per vertebral segment; found in tail for increased mobility
d. Regional differentiation
1. Dorsal = Trunk
2. Caudal = Tail
e. Craniovertebral joint –No movement
5. AMPHIBIANS
a. Terrestrial life –Spine must support body, resist bending, yet provide mobility.
b. Intercentrum (=hypocentrum) and Pleurocentrum– Which ancient centrum segment becomes the modern centrum?
c. Zygapophyses –Limits dorsal/ventral bending
d. Regional differentiation
1. Cervical –Usually one
2. Trunk = dorsal –Ribs present
3. Sacral [1]
4. Caudal/tail –No zygapophyses
5. Urostyle –Order Anura
e. Craniovertebral joint [1-2 occipital condyles]
6. REPTILES
a. Centrum/ Notochord
1. Procelous
2. Pleurocentrum
b. Zygapophyses –Not in tail
c. Regions
1. Cervical [8 – including atlas, axis]
2. Dorsals = Trunk [Thoracic & Lumbar]
3. Sacral [2] –Stronger support
4. Caudal –No zygapophyses, hemal arches present
a. Hemal arch = chevron bone
b. Autotomy
d. Craniovertebral joint –Ball & socket type
1. Single occipital condyle
2. Atlas
3. Axis – odontoid process –Allows for rotation
4. Proatlas
7. BIRDS
a. Centrum – Heterocelous –Saddle shaped
b. Cervical vertebrae, Single Occipital Condyle
c. Trunk vertebrae [4-6] –Tend to fuse
d. Synsacrum –Fusion of last thoracic vertebrae, all of lumbar, 2 sacral, and a few caudal vertebrae; allows for streamline shape and rigid brace.
e. Caudal vertebrae, Pygostyle (last few caudal vertebrae fused)
8. MAMMALS
a. Centrum – Acelous
b. Cervical (7), thoracic
c. Lumbar, sacrum [3-5]
d. Caudal – chevron, coccyx
e. Intervertebral disc
1. Fibrocartilage
2. Pulpy nucleus
f. Craniovertebral joint
1. Two Occipital condyles
2. Atlas
3. Axis
4. Movements
9. Evolutionary Trends of Vertebrae
-Regional differentiation – Head/neck evolution – Sacral stability – Zygapophyses – Loss of notochord
B. RIBS
1. Function –Protection, Respiration
2. Phylogeny –New structure
3. Endochondral
4. Dorsal vs Ventral Ribs
5. Bicipital vs Monocipital
a. Dorsal head = tuberculum
b. Ventral head = capitulum
6. Costal = Vertebral ribs vs. Sternal ribs/Costal Cartilage in amniotes
7. FISH
Agnathans & Placoderms , skates, sea horses have no ribs; Most are ventral ribs; sharks are dorsal ribs.
8. AMPHIBIANS
Short in Anurans and Urodeles; long in Apodans.
9. REPTILES
Short in neck, long in trunk
a. Turtles –None in cervical region; trunk ribs fused to carapace, 2 sacral ribs fused to pelvis
b. Snakes –Long and curved.
c, Crocodiles –Have “abdominal ribs” or gastralia which are integumentary structures
10. BIRDS
a. Costal & Sternal ribs
b. Uncinate processes –For muscle attachment
11. MAMMALS
a. Thorax
b. True(own costal cartilage to sternum), false(do not have own costal cartilage to sternum), floating ribs (no costal cartilage)
C. STERNUM
1. Tetrapods
2. Function –Protection, strengthens ventral body wall, attaches pectoral muscles
3. Endochondral
4. AMPHIBIANS
a. Toads –Poor but ossified
b. Urodeles –Flimsy when present
c. Caecilians –None
5. REPTILES
a. Lizards –Large; cartilaginous or bony
b. Crocodiles –Cartilaginous plate
c. Snakes –None
d. Turtles –None; not needed
6. BIRDS
a. Keel = Carina –For flight muscle attachment
7. MAMMALS
a. Segments
b. Xiphoid process –Caudal-most segment