Chapter 8/Lecture 12 notes
Chapter 8/Lecture 12 notes Zol 328
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This 7 page Class Notes was uploaded by Kelsey Bowe on Friday April 15, 2016. The Class Notes belongs to Zol 328 at Michigan State University taught by Dr. Pam Rasmussen in Spring 2016. Since its upload, it has received 16 views. For similar materials see Comparative Anatomy and Biology of the Vertebrates in Biology at Michigan State University.
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Date Created: 04/15/16
chapter 8 lecture 12 notes - axial skeleton axial skeleton/axis: notochord and vertebral column, supports body, prevent telescoping, sites for muscle attachment -earlist fossil evidenve of vertebrae were in Haikouella and Haikouichthys -ostracoderms primarily supported ny notochord only, as are extant hagfishes -lampreys have neural arches and spines, but lack main parts of vertebrae -it is likely that the vertebral column evolved independently more than once, many parts have been lost and gained throughout evolutionary history • vertebrae components - first components that evolved were the dorsal and ventral arches, resting on notochord dorsal arches= neural and interneural, protect neural tube ventral arches= hemal and interhemal , enclose blood vessels -scond parts of vertebral column to evolve were the two centra, intercentrum/hypocentrum and pleurocentrum, they anchor and support the arches -evetnually, the vertebrae became dominant strucutres and displaced the notochord as the main body axis regions/differentiations of the vertebral column • cervical neck • thoracic chest • lumbar between thorax and hips • sacral hip • caudal tail centrum structure -each centrum makes up the body of a vertebrae • aspondyly: no centrum present • monospondyly: single centrum present • diplospondyly: two centra present • polyspondyly: multiple centra present, Holocephali and Dipnoi can have five or six -may vary by vertebrate type within an individual -can be derived from intercentrum or pleurocentrum -in amniotes, the centra tend to be derived mostly from the pleurocentrum, and intervertebral disks originate from the intercentrum -tetrapods have distinct definitions to describe their vertebral elements: • aspidospondyly: the intercentrum, pleurocentrum, and neural arch all remain as separate ossified elements • holospondyly: vertebral elements fused into a single piece -types of centra • acoelous: flat ends • amphicoelous: concave at both ends • procoelous: anterior end concave, posterior end convex • opisthocoelous: anterior end convex, posterior end concave • heterocoelous: both ends are saddle shaped -apophyses: processes that project from centra and arches, several types: • diapophyses & parapophyses: articulate with ribs • basapophyses: paired processes, ventrolateral on centra, remnant of hemal arch base, may also articulate with ventral ribs • zygapophyses: interlocking processes between vertebrae • transverse process: general term for any process on centrum or neural arch intervertebral structures -intervertebral disk: used to describe many structures, technically only mammals have true intervertebral disks; composed of a pad of fibrocartilage with a gel-like core, this core is derived from the notochord and may also be called the nucleus pulposus, core contains proteoglycans -intervertebral cartilage: only a pad of fibrocartilage -intervertebral ligament: connects edges of centra together ribs -rib: struts that can fuse or articulate with vertebrae, develop as cartilage first within the myosepta provide sites for muscle attachment, protect organs, suspend body types of rib: • true rib articulates with sternum • false rib articulates with a true rib • floating rib has no ventral articulation • bicipital rib rib with 2 heads -capitulum head of bicipital rib that articulates with parapophysis on intercentrum -tuberculum head of bicipital rib that articulates with diapophysis on neural arch sternum -midventral skeletal structure, endochondral, arises from connective tissue and myoseptum -many be a single element or many -is not a deriviative of the ribs or pectoral girdle -not present in fish or early tetrapod fossils, present in modern ampibians and all other tetrapods, may have arisen several times independently rib and sternum structure of different taxa -Fish: most fishes have 2 sets of ribs (dorsal and ventral) dorsal ribs formed where myoseptum and horizontal septum meet ventral ribs form where the myoseptum meets the body wall, homologs of the hemal spine fish lack a sternum -Birds: reduced cervical ribs that are fused to vertebrae, first few ribs of the thoracic region are floating, and the rest are true ribs unicate process: projections found on some bird ribs, extend posteriorly, for muscle attachment birds (neognaths only) have a large keeled sternum, to allow attachment of flight muscles -Mammals: ribs present on all thoracic vertebrae, may some some floating and false ribs pleurapophyses: a remnant of ribs found on cervical and lumbar vertebrae of mammals, fused with the transverse process sternum consists of several elements, as chain of ossified sternebra and cartilagenous elements may have a modified 1ts sternebrae: manubrium and a modified last sternebrae: xiphisternum Gastralia -often called abdominal ribs, gastralia are an independent skeletal element, of dermal origin -located on sides of body wall, do not articulate with the vertebrae -found in crocodilians and tuataras, while remnants of gastralia may contribute to the plastron of turtles -may have evolved from ventral scales of rhipidistians • Embrylogy of Axial Column vertebrate form from embryonic mesenchyme, cells diferentiate after somite formation -Basal Fishes: cells from sclerotomes differentiate into cartilage, up to four pairs of cartlage per segement/arcualia -Teleost fishes: 3 steps of axial development 1 notochord sheath becomes chain of chordal centers middle portions of notochord become intervertebral ligaments 2 mesenchyme condenses to form arch centers/cartilaginous analgen these arch centers give rise to dorsal and ventral arches 3 sclerotome cells condense on surface of notochord, forming an ossified perichordal tube perichordal tube and notochord sheath become the centra of vertebrae -Terapods: 1 somites subdivide into cell layers (dermatome, myotome, sclerotome) 2 mesenchymal cells come from sclerotome and cluster along the notochord form pericardial rings along notochord and eventually become disks other mesenchymal cells connect the rings to form perichordal tube 3neural spines and arches form upward from the neural cord 4 intervertebral bodies or disks define boundaries of each vertebrae 5 ossification of cartilaginous vertebral column cells forming the perichordal tube, cells from the primary and secondary sclerotome become separated and then regroup before forming the complete tube. This allows the the sclerotome and myotome to become staggered as they form the vertebrae and musculature • Phyogeny to Know for axial column -Agnathans ostracoderms, lamprey, hagfish all have the notochord as prominent axis lampreys have vertebral elements on top of nerve cord and notochord some fossil agnathans had small unossified vertebral elements, but notochord most prominent feature -primitive gnathostome fishes (placoderms, acanthodians, early chondrichthyans, palaeoniscoids) notochord still prominent arches usually present, no centra -modern sharks notochord is enclosed within centra, arches present vertebra is main body axis -primitive bony fish(sturgeons, paddlefish) vertebral column unossified, may be secondarily lost -derived bony fish (bowfins, teleosts) vertebral column ossified centra much more prominent than notochord neural spines and ribs more developed how do fish swim? lateral flexing of vertebral column intervertebral ligaments keep coulmn stiff so vertebrae cannot buckle under movement some fishes, especially those with asymmetrical tails, will twist or wring the axial column to withstand these forces, neural spines must be long and join together fish tails (caudal fins) asymmetrical: no swim bladder -heterocercal -hypocercal symmetrical: swim bladder -diphycercal -homocercal -living sarcopterygian fish notochord major axial support some rudiemntary vertebral column structures, tend to be cartilaginous -rhipidistians (extinct taxa of sarcopts) vertebral elements ossified, aspidospondyly (separate elements/unfused) elements were; neural arch, intercentrum, and paired pleuricentra -early tetrapods (labyrinthodonts: two taxa) -Temnospondyls, intercentrum dominant (gave rise to lissamphibia) -Anthracosaurs, pleurocentrum dominant (gave rise to amniotes) from swimming to walking on land, body suspended by vetrebral column and supported by limbs ealry tetrapods, amphibians, some reptiles still use lateral flexing as major body motion similar to the swimming motion of fish tetrapods have less flexibility of the vertebral column, but it is also more stable due to fewer centra -amniotes pleurocentrum dominant has modified cervical vertebrae for movement of head • atlas 1st cervical vertebrae • axis 2nd cervical vertebrae provides 2 joints for head movement while maintaining strength of neck -turtles carapace: dorsal shell, convex plastron: ventral shell, flat or concave shell includes bone of dermal and endochondral origin appendicular skeleton (limbs) lie within the rib cage, a trait unique to this taxa only evolution of this anatomy debated, many gaps in fossil record for turtles -snakes have extra zygapophyses to reduce torsion (twisting force) of vertebrae • zygosphene anterior • zygantrum posterior do not significantly reduce ability to bend lateraly -birds cervical vertebrae are very mobile (owls can turn their heads a lot) heterocoelous cervical vertebrae the synsacrum is a structure many fused vertebrae (thoracic, lumbar, sacral, and caudal) fuses to pelvic bones and innomiate bone (fused iliac, ischium, and pubic) pygostyle end of caudal vertebrae -mammals usually only have 7 cervical vertebrae (except sloths and sirenians) fused in some mammals (armadillos) thorax, lumbar, and caudal vertebrae number is variable 2-5 sacral vertebrae vform and function of axial column: water vs land aquatic organisms do not need as strong of body support as land animals in water, the main force acting in aniamsl is friction, so bodies tend to be streamlined fins are used to stabilize position in the three dimensional fluid on land, animals must fight gravity nodal: point on axial coulmn between legs where a tetrapod's weight transfers neural spines reverse orientation at nodal height of a neural spine is proportional to the leverage muscles exert to move and stabilize vertebral column basal tetrapods have average neural spines, while very large mammals have tall, specialized neural spines to support the weight Fish only have two types of vertebrae: trunk and caudal Aquatic tetrapods have vertebrae very similar to fish, secondarily became less specialized Early tetrapods had caudal, trunk, sacral, and cervical vertebrae were still very similar to fish vertebrae Early amniotes had a thoracolumnar (trunk) region, retained from the ancestral condition, they also had a stronger sacral region to support life that was completely terrestrial -human vertebral column vertebral column curves, and upper pelvis is tilted back to support bipedalism birth canal is expanded due to sacral region being shifted further back
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