Topic 7: The Axial Skeleton Topic 7: The Axial Skeleton What makes up the axial skeleton? Ribs and...

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Transcript of Topic 7: The Axial Skeleton Topic 7: The Axial Skeleton What makes up the axial skeleton? Ribs and...

  • 1/9/2013

    1

    Topic 7: The Axial Skeleton

    � What makes up the axial skeleton?

    � Ribs and Sternum

    � What is the morphology of these structures?

    � What sorts of specializations have evolved?

    � Vertebrae

    � How do they develop?

    � What are their forms and how have they evolved?

    � Vertebral column

    � What are the evolutionary trends in the regionalization

    and complexity of the vertebral column?

    � What are the functions of the vertebral column?

    � What specializations have evolved?

    Divisions of the Skeleton:

    Liem et al. Fig. 8-15, 8-18; Dean 1895

    � Endochondral

    � _____________

    � Sternum

    � _____________

    � Unpaired fins

    � Dermal

    � Gastralia

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    � What are the functions of

    a rib cage?

    Sternum & Ribs

    T ru e R ib s

    F a ls e R ib s

    Floating Ribs

    Liem et al. Fig. 8-7

    � Ribs reduced to absent in

    amphibians

    � Lack a rib cage

    � ______________ single element

    � Associated with pectoral girdle

    � Well-developed in amniotes

    � Full rib cage

    � Differentiate ___________ &

    _______________

    � Sternum articulates with ribs

    � ________________ protect

    abdomen in some

    Sternum & Ribs

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    Gastralia

    © ucmp.berkeley.edu; plesiosauria.com

    � Crocodylia

    � Plesiosauria

    � Protection of abdomen

    Turtle Shell

    Liem et al. Fig. 8-15; © Nova Scotia Museum

    � _________ – top

    � _________ – bottom

    � Overlaid by

    keratinized scutes

    � Primarily dermal

    � Ribs & vertebrae fuse to overlying plates

    � What might be the

    costs and benefits of

    such a shell?

    Turtle Shell - Development

    Liem et al. Fig. 8-16

    � Rib cage is external to the ________________

    � Costal scerotomal cells move laterally, not ventrally

    � Myotomal cells and

    girdle sclerotome

    move ventrally

    Bird _______________

    � Bony posterior

    projection of ribs

    � Overlaps one rib caudally

    � Locks ribs together to

    increase ___________

    efficiency

    � Some crocs have cartilaginous uncinate

    processes

    Liem et al. Fig. 8-17; © www.livescience.org

    Vertebrae

    � ______________

    � Variable in morphology

    � Form a vertebral column

    © KA Stevens

    � What kind of homology

    do they demonstrate?

    Vertebral Development

    See Liem et al. Table 4-1

    Paraxial Mesoderm

    Dermatomes

    Myotomes

    Sclerotomes

    Somites

    Dermis

    of Skin

    Trunk

    Muscles

    Vertebrae

    Segmentation

    © R Anderson

    Wolpert, 1998

    Paraxial mesoderm

    Somite

    Dissociation

    Resegmentation

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    Vertebral Development:

    Determination of Vertebral Number

    ________________________ Model

    � Opposing Retinoic Acid and FGF/Wnt gradients set up a

    posteriorly-moving determination front

    � Expression of Lunatic Fringe is cyclic and anterior to posterior

    � Each time Lunatic Fringe expression hits the determination

    front a new somite boundary is formed

    Gomez & Pourquie 2009; Gomez et al. 2008

    Vertebral Development:

    Determination of _________________

    _____________ Evolution

    � One Hox gene duplicated

    � Cluster of 13 paralogues

    � Hox cluster was duplicated

    twice

    � 4 paralogous clusters, or

    52 Hox genes

    � Some Hox genes have

    been lost by mutation

    � Fishes have 44 Hox genes

    � Amniotes have 39 Hox

    genes

    Liem et al. 2001, Fig 4-41

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    Vertebral Development:

    Determination of Vertebral Identity

    � Hox gene expression is ______

    � Combination of Hox genes expressed determines vertebral identity

    � e.g., Chicken HoxC expression

    Modified from Burke et al. 1995

    HoxC4

    HoxC11

    HoxC9

    HoxC8

    HoxC6

    HoxC5

    HoxC10

    Vertebral Development

    � Somite _____________

    � Sclerotome condensation

    � _________________

    Chal & Pourquie 2009, Fig 3-6; © PJB

    A n te

    rio r

    P o s te

    ri o r

    Vertebral Morphology

    � Categorize where they

    are concave � _______________

    � Amphicoelous

    � _______________

    � Opisthocoelous

    � _______________

    � Who has acoelous vertebrae?

    � How about

    amphicoelous?

    Kardong Fig. 8-4

    Vertebral Morphology

    � Petromyzontiformes

    � _____________

    � “Exposed” notochord

    � Chondrichthyes

    � _____________

    � Encapsulated notochord

    � Neural arch & canal

    � Hemal arch & canal

    Liem et al. Fig. 7-5A, 8-1A

    Vertebral Morphology

    � _______________

    � Bone, amphicoelous vertebrae

    � Undifferentiated

    vertebrae

    � Enclosed, continuous

    notochord

    Liem et al. Fig. 8-2A , 8-8B; A Morton

    Salmon

    Vertebral Morphology

    � ____________ vertebrae

    � Increased robustness

    � Closer articulation

    � Increased elaboration

    Photo: M Taylor

    • Opisthocoelous – many amphibians, some ‘reptiles’

    • Procoelous – many ‘reptiles’ • Zygapophyses

    • Transverse processes • Neural & hemal spines

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    Vertebral Morphology

    � Bird vertebrae are more

    differentiated

    � Cervical

    � Heterocoelous

    � Saddle-shaped articulation

    � _________________ along two axes, twisting

    � Lumbar

    � Fused to pelvis and sacral

    vertebrae

    � ____________________

    � Eliminate ____________

    © R Jayasena; Liem et al. Fig. 8-17B

    Vertebral Morphology

    � Mammals

    � _____________ & differentiated

    � Intervertebral disks

    � Many processes –

    What are they for?

    © indyspinemed.com, Univ. Maryland; De Iullis & Pulera Fig. 7.8

    Vertebral Morphology

    � What is meant by vertebral

    regionalization?

    � What trends have we seen in complexity of vertebrae?

    � What are the (competing)

    functions of the vertebral column?

    � ______________________

    � ______________________

    © indyspinemed.com

    Vertebral Regionalization & Complexity

    � Fish vertebrae are relatively undifferentiated

    � Other vertebrates have

    increasingly differentiated vertebrae

    � Fish: Trunk, ___________

    � Amphibians & “Reptiles”:

    � ___________, trunk, sacral, caudal

    � Mammals:

    � Cervical, _____________,

    lumbar, sacral, caudal

    Kardong, Fig. 8-39

    Vertebral Column Function

    � Stability & Support � Control torsion

    � Control bending

    � Reduction in number of vertebrae

    � What are some examples of this?

    � ___________________________

    � ___________________________

    � ___________________________

    Kardong, Fig. 8-34, 8-38; KA Stevens

    Vertebral Column Function

    � Movement & flexibility

    � Bounding locomotion in mammals

    � Lateral undulation in sprawlers

    � Movement allowed in some planes, not others

    � How might flexibility be increased?

    Vertebrate Life 24-2; © KP Bergmann

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    Human ___________________

    � Humans have greater

    lordosis than other apes

    � Spinal loading

    � Balanced COM

    � Pregnancy shifts COM

    _______________

    � Lordosis is increased in response

    Whitcome et al. 2007

    Human spinal lordosis

    � Females have greater lordosis than males

    � What does this tell us?

    Whitcome et al. 2007

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