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Axial Skeleton
| Question | Answer |
|---|---|
| Axial Skeleton | skull, vertebrae, ribs, sternum |
| Appendicular skeleton | Limbs and girdles |
| Embryological origins of the axial skeleton | Sclerotome |
| Evolutionary Trends of Vertebral Components | 1.) Some vertebral elements enlarge while others regress 2.) The vertebral elements displace the notochord as the primary mechanical axis 3.) The vertebral segments become regionally differentiated |
| Aspondyly | No centra Ex:// Lamprey |
| Monospondyly | 1 centrum Most vertebrate |
| Diplospondyly | 2 centra Most vertebrates |
| Polyspondyly | Multiple centra Ex:// Holocephali and some sarcopterygians |
| Amphicoelous | Both ends concave Limited motion in most directions Ex://Fish |
| Procoelous | Anterior end concave, posterior end convex Extensive motion in most directions Ex:// Snakes |
| Opisthocoelous | Anterior end convex, posterior end concave Extensive motion in most directions Ex:// Hoofed mammals |
| Acoelous | Both ends flat Limited motion in most directions but suited to receive and distribute compressive forces Ex:// Most mammals |
| Heterocoelous | Both ends saddle shaped Allow for lateral and vertical flexion but prevent rotation Ex:// birds |
| Zygopophyseal joint | Articulation between vertebrae )prezygopophysis-postzygopophysis) |
| Prezygopophyses | -Project from the anterior edge of neural arch -Articular surface faces dorsally |
| Postzygopophyses | -Project from the posterior edge of neural arch -Articular surface faces ventrally |
| Diapophysis | Rib attachment on neural arch for tuberculum of dorsal rib |
| Parapophysis | Rib attachment on centrum for capitulum of dorsal rib |
| Basapophysis | Attachment for ventral rib (if present) |
| Transverse process | General term for process extending laterally from a centrum or neural arch |
| Cervical vertebrae | Neck region (most anterior)-- Ribs short or absent Amphibians- only 1 Aves- 12 (most)-25 Reptiles and mammals: 6-9 Allows for head movement independent of body |
| C1 and C2 | C1- atlas Prezygopophytes articulate with occipital. C1 centrum attached to C2 as the dens C2- Axis Articulates with C1 via zygopophyses and specialized atlanto-axial joint at dens |
| Thoracic vertebrae | Anterior trunk vertebrae with ribs Attachment site for ribs |
| Lumbar vertebrae | Posterior trunk vertebrae without ribs Loss of ribs allowed hindlimbs to swing forward to increase stride length during rapid locomotion |
| Sacral vertebrae | Vertebrae attached to pelvic girdle Attachment site for hindlimbs, increasing hindlimb stability and force distribution |
| Synsacrum | Complex of fused posterior thoracic, lumbar, sacral, and anterior caudal vertebrae found in birds |
| Caudal vertebrae | Tail region posterior to the sacrum *can be fused in some vertebrates Frog- urostyle Bird- Pygostyle Human- Coccyx Tail region (variable function) |
| Function of ribs | -Provide sites for muscle attachment -Form a protective case around organs -Aid in respiration in tetrapods |
| Development of ribs | Sclerotome within myosepta |
| Fish ribs | Dorsal ribs: seperate hypaxial and epaxial muscles Ventral ribs: develop where myosepta meet the wall of the coelom |
| Tetrapod ribs | -Only have dorsal ribs -Ribs are bicipital Capitulum- articulates with parapophysis Tuberculus- articulates with the diapophysis |
| Amniote ribs | Ribs become increasingly important in respiration |
| True ribs | Connect directly to sternum. Have two jointed segments that accommodate changes in chest shape during respiration: vertebral rib (dorsal)- articulates with vertebrae sternal rib (ventral)- articulates with sternum *amniotes |
| False ribs | Either connect to sternum indirectly or do not connect at all Floating ribs- do not connect to sternum |
| Sternum | Found only in tetrapods (evolved independently multiple times Anatomy directly rleated to use of forelimbs in locomotion Attachment for ribs Mammals have three parts: Manubrium (anterior) Sternebrae (body) Xiphisternum (posterior) |