Presentation 8: Axial Skeleton Flashcards
Axial Skeleton
Vertebral column, Skull, Thoracic Cage (chest)
Centrum
Notochord ossifies to form main body of vertebrae (centrum) with two main parts, intercentrum dominant and pleurocentrum dominant.
Intercentrum dominant
Anterior and slightly ventral structure surrounding the notochord, no longer in living amniotes but present in extinct amphibians
Pleurocentrum dominant
Posterior and slightly dorsal structure, in living amniotes, pleurocentrum is dominant in living amniotes
Neural Arches
2 Bars that connect dorsally (at the Neural Spine) to form the Neural Canal
Neural Canal
Canal above the notochord and centrum formed by the 2 neural arches. Protects the spinal chord.
Neural Spine
Where the 2 neural arches fuse dorsally
Hemal Arches
Present only in posterior vertebrae, 2 bars that extend ventrally under the notochord and centrum and connect ventrally together at the Hemal Spine forming the Hemal Canal
Hemal Spine
Connection of Hemal Arches present in posterior vertebrae that form the Hemal Canal (= chevron bones in amniota)
Hemal Canal
Created by the Hemal Arches connecting ventrally at the Hemal Spine
Processes of Centrum
Apophyses (include Parapophyses, Diapophyses, and Hypapophyses)
Parapophyses
One of the processes of centrum - Slightly ventral on vertebrae
Diapophyses
One of the processes of centrum - (aka transverse processes) extends to sides to articulate with the tuberculum of the rib (capitulum of rib connects to ventral side of centrum)
Hypapophyses
One of the processes of centrum - mostly found in fossils, not necessarily in living organisms today
Processes of Neural Arches
Zygapophyses (Include Prezygapophyses and Postzygapophyses)
Prezygapophyses
One of the processes of neural arches -(aka anterior processes) extends slightly forwards/dorsally - smooth surface faces each other)
Postzygapophyses
One of the processes of neural arches -(aka posterior processes) extends slightly backwards / ventrally - smooth surface faces away
Hypomere
Embryonic mesoderm section
differentiates somatic and splanchnic layers
somatic layer gives rise to outside muscles while
splanchinc layer gives rise to muscles around organs
Embryonic mesoderm sections
Epimere (dorsal somite)
Mesomere (gives rise to urogenital organs)
Hypomere (differentiates somatic and splanchnic layers - somatic layer gives rise to outside muscles while splanchinc layer gives rise to muscles around organs)
Mesomere
Embryonic mesoderm section
gives rise to urogenital organs
Epimere
Embryonic mesoderm section
(dorsal somite) divides into dermatome, myotome, and sclerotome which gives rise to dermis, muscle formation, and vertebrae respectively
Dermatome
Epimere section
Gives rise to the dermis
Myotome
Epimere section
Contributes to muscle formation
Sclerotome
Epimere section
gives rise to vertebrae (sheet around the notochord aka perichordial tube, posterior/caudal part of flanking sclerotome thickens, more cell density, & caudal half of one sclerotome attaches to cranial half of the next sclerotome)
Vertebral Column Development ( 5 steps)
- Embryonic mesoderm divides into epimere, mesomere, and hypomere
- Epimere divides into dermatome, myotome, and sclerotome
- Vertebrae are intersegmental in relation to the primary segmentation of the mytomes (neural and hemal arches associated w/ anterior part (caudal halves), spinal ganglia line up with posterial cranial part, blood vessels line up withe middle part.
- When it is all lined up, chondrification begins (formation of cartilage)
- Cartilage is continuous for a short period when spinal ganglia, notochord, and myotomes induce breaks before ossification begins and then individual vertebrae are established
Classification of Vertebrae ( 4 options)
Opistocoelous (anterior convexity + posterior concavity)
Procoelous (anterior concavity + posterior convexity)
Amphiocoelous (concavity both anteriorly and posteriorly)
Acoelous (no concaves, both sides flat)
Opistocoelous
Classification of Vertebrae
(anterior convexity + posterior concavity)
Procoelous
Classification of Vertebrae
(anterior concavity + posterior convexity)
Amphiocoelous
Classification of Vertebrae
(concavity both anteriorly and posteriorly)
Acoelous
Classification of Vertebrae
(not concave, both sides flat)
Specialization of Amphibia Vertebrae
1st vertebrae differentiates into atlas (specialized to articulate w/ occipital arch)
Trunk vertebrae
Single Sacral Vertebrae which articulates with the pelvic girdle and connects to Illium
Several caudal vertebrae remain in tail for salamanders
Caudal vertebrae of frogs fuse into urostyle
Specialization of Amniota Vertebrae
pleurocentrum makes up bulk of the vertebral column
Strong zygopophyses
1st cervical vertebrae - atlas
2nd cervical vertebrae - axis
(both 1st and 2nd cervical vertebrae support head)
Types of Vertebrae
1. Cervical (distinguished neck)
2. Thoracic (associated with ribs)
3. Lumbar (posterior section)
4. Sacral (at articulation w/ posterior limbs)
5. Caudal (all vertebrae in the tail)
Diversity of Vertebrae in Amniota - BIRDS
BIRDS:
Sternum = highly enlarged + durable to support breast muscles for flying
Last 4 caudal vertebrae fuse to form the pygostyle
Synsacrum present
Unicate process (enlarged sternum for flight) part of RIBS
Diversity of Vertebrae in Amniota - MAMMALS (2 main points)
MAMMALS:
1. 20 Trunk vertebrae that divide into thoracic vertebrae and lumbar vertebrae
2. 3 of sacral vertebrae fuse
Types of Vertebrae in Amniota (5 types)
Types of Vertebrae
1. Cervical (distinguished neck)
2. Thoracic (associated with ribs)
3. Lumbar (posterior section)
4. Sacral (at articulation w/ posterior limbs)
5. Caudal (all vertebrae in the tail)
Fish Ribs (2 types)
Dorsal Rib: intermuscular the junction of the myoseptum and the horizontal septum
Septa are made of connective tissue
Horizontal septum separates epaxial (dorsal) and hypaxial (ventral) muscles
Ventral Rib - Pleural (subperitoneal) at junction of the myoseptum and peritoneum
Tetrapod Ribs - ancestral and later condition
- Ancestrally bicapitate (Tuberculum articulates with diapophyses and Capitulum articulates with paraphophyses)
- Later unicapitate
Amniota Ribs (2 types) and function
Ribs: thorax: costal rib (ossified) and sternal rib (cartilaginous) - ribs participate in respiration by enabling expansion while protecting the lungs
Sternum
(amphibians, amniotes, lizards, turtles snakes and gymnophiona, mammals, and birds)
- amphibian sternum not homologous to amniote sternum
- Amniotes : ventral midline structure
- turtles snakes and gymnophiona : sternum absent
- lizards: either cartilaginous or bony
- mammals: composed of several elements
- birds: enlarged for attatchment of flight muscles
Mammalian Sternum Components
- Manubrium
- Body
- Xiphoid process
