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5: The Axial Skeleton

  • Page ID
    12525
  • Information

    The bones of the human body can be divided into two broad groups, the axial skeleton and the appendicular skeleton. The axial skeleton comprises the bones found along the central axis traveling down the center of the body. The appendicular skeleton comprises the bones appended to the central axis.

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    Figure 5-1 The axial skeleton highlighted in blue.

    The axial skeleton consists of the bones of the skull, the bones of the inner ear (known as ossicles), the hyoid bone in the throat, and the bones of the vertebral column, including the sacrum and coccyx bones in the center of the pelvic girdle.

    LICENSES AND ATTRIBUTIONS

    CC LICENSED CONTENT, ORIGINAL

    A&P Labs. Authored by: Ross Whitwam. Provided by: Mississippi University for Women. Located at: http://www.muw.edu. License: CC BY- SA: Attribution-ShareAlike

    PUBLIC DOMAIN CONTENT

    Figure 5-1 The axial skeleton highlighted in blue.. Authored by: Axial_skeleton_diagram.svg: LadyofHats Mariana Ruiz Villarreal. Located at: https://commons.wikimedia.org/wiki/F...gram_blank.svg. License: Public Domain: No Known Copyright

    The Bones of the Skull

    Information

    There is only one movable joint in the skull. That is the joint connecting the lower jaw, or mandible, to the rest of the skull. All the other bones in the skull are firmly attached to one another by sutures.

    Sutures are rigid immovable connections holding bones tightly to one another. Some of the sutures in the skull take a few months-to-years after birth to completely form.

    The brain is encased in the cranium of the skull. The bones that make up the cranium are called the cranial bones. The remainder of the bones in the skull are the facial bones.

    image

    Temporal

    Figure 5.2 and Figure 5.3 show all the bones of the skull, as they appear from the outside. In Figure 5.4, some of the bones of the hard palate forming the roof of the mouth are visible because the mandible is not present. Figure 5.9 also shows the foramen magnum, the large hole at the base of the skull that allows the spinal cord to attach to the brain

    Zygomatic

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    Figure 5.3. The bones of the skull, anterior view.

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    Figure 5.5 The interior of the cranial cavity, viewed from above and behind, with the parietal bones removed.

    The sphenoid bone, from the outside, appears to contribute to only a small portion of the cranium, but when the parietal bones are removed and the interior of the cranial cavity (where the brain would be housed) is viewed, you can see the butterfly-like shape of the sphenoid bone makes a large contribution to the floor of the cranial cavity. The ethmoid bone, which from the outside is only visible in the eye sockets and as the upper conchae (internal bumps) of the nasal cavity, also contributes to the floor of the cranial cavity. The contributions of these two bones to the floor of the cranial cavity are shown in Figure 5.5.

    What is commonly referred to as the “cheekbone” is really the processes of two bones connected together: the zygomatic process of the temporal bone is sutured to the temporal process of the zygomatic bone to produce the zygomatic arch.

    There are three prominent bone markings on the temporal bones. The external acoustic meatus is the opening that leads to the organs of the inner ear. The styloid process is a thin, pen-like projection where muscles and ligaments of the neck are attached. The mastoid process is a wide and rough projection that serves as another attachment point for neck muscles.

    While all the bones of the skull, other than the mandible, are sutured to one another, the flat bones of the cranium are visibly sutured where they articulate to another. There are four different cranial sutures.

    The coronal suture is the articulation point of the frontal bone with the two parietal bones. The sagittal suture is the articulation point between the two parietal bones.

    The squamous sutures are the articulation points between the each temporal bone and the parietal bone superior to it.

    The lambdoid suture is the articulation point between the occipital bone and the two parietal bones.

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    Figure 5.6 The cranial sutures.

    LAB 5 EXERCISE 5-1

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    1. Models of human skulls may be found in the cabinets. On the models identify all of the following and on the diagrams below be able to label and/or color in all the following bones, processes, and foramina:

    Bones

    Sutures

    Foramina

    Processes

    B1 – frontal

    S1 – coronal

    F1 – supraorbital

    P1 – mastoid

    B2 – parietal

    S2 – squamous

    F2 – infraorbital

    P2 – styloid

    B3 – occipital

    S3 – lambdoid

    F3 – mental

    P3 – zygomatic

    B4 – temporal

       

    P4 temporal

    B5 – sphenoid

     

    B6 – ethmoid

    B7 – lacrimal

    B8 – nasal

    B9 – maxilla

    B10 – zygomatic

    B11 – mandible

    B12 – vomer

    B13 – palatine (not visible here)

    LICENSES AND ATTRIBUTIONS

    CC LICENSED CONTENT, ORIGINAL

    image

    The Vertebral Column

    Information

    The vertebral column is more colloquially called the backbone or the spine. It consists of

    24 vertebrae bones, and two bones from the axial section of the pelvic girdle, the sacrum and the coccyx.

    The vertebrae are divided into three groups. There are seven cervical vertebrae (names C1 through C7), twelve thoracic vertebrae (named T1 through T12), and five lumbar vertebrae (named L1 through L5).

    You can use a meal-related mnemonic to remember them – imagine a crunchy breakfast at 7 am (7 cervical vertebrae), a tasty lunch at 12 noon (12 thoracic vertebrae), and a light dinner at 5 pm (5 lumbar vertebrae).

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    Figure 5.8 The bones of the vertebral column.

    The first two cervical vertebrae have alternate names to C1 and C2. C1 is also called the atlas. In Greek mythology, Atlas was a titan who held the entire world on his shoulders. As the first vertebra in the column, Atlas in a sense holds up the skull. C2 is also called the axis. The axis allows both the skull and the atlas to rotate, so the head can be turned from side to side by neck muscles.

    All three types of vertebrae have some structural features in common and some features that should allow you to readily distinguish vertebrae in one category from another.

    All vertebrae, except C1 and C2, the atlas and axis, have a solid round portion on their anterior side called the body of the vertebra. The body is what allows the vertebrae in the vertebral column to be stacked upon one another, separated by pads of fibrocartilage called the intervertebral discs. The lower you go in the vertebral column, the larger the vertebrae’s bodies become.

    The axis, or C2 vertebra, also has a bulbous vertical process not found in any of the other vertebrae. This is called the dens and it is what allows the axis vertebra above it to rotate.

    Posterior to the vertebral body is a large opening in each vertebra called the vertebral foramen. This is the hole through which the spinal cord passes.

    Posterior to the vertebral foramen there is a central process jutting out of each vertebra. This is the spinous process. It points more or less downwards when the vertebrae are correctly stacked into their column.

    Surrounding the central spinous processes, there are other processes whose position and number vary depending on whether a vertebra is cervical, thoracic, or lumbar. Some of these processes allow a vertebra to articulate with the vertebrae superior and inferior to it, others, found only on thoracic vertebrae, allow a pair of ribs to articulate with the vertebra.

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    Figure 5.9 The three types of vertebrae. All are being viewed from behind. Note that C1 and C2 vertebrae, the atlas and axis, do

    not have vertebral bodies.

    The sacrum is part of both the vertebral column and the pelvic girdle. It articulates with the intervertebral disc under the L5 vertebra above it, and with two coxal bones lateral to it.

    The sacrum starts out as five vertebrae that fuse to form the one structure. This fusion is not complete until somewhere between the 18th and 30th year.

    The coccyx is a vestigial tailbone. It is the evolutionary remnant of an ancestral species to humans that did have tails. It no longer serves as a functional tail, but some muscles, tendons, and ligaments do attach to it, making it useful. It forms from the fusion of usually three vertebrae, but a small proportion of the population have four or even five vertebrae in their coccyx.

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    Figure 5.10 The sacrum and coccyx.

    LAB 5 EXERCISE 5-2

    1. Real or replica vertebrae bones may be found in the cabinets and on the back counters. Identify which in your group are the atlas, axis, cervical vertebrae, thoracic vertebrae, and lumbar vertebrae.

    2. Stack your vertebrae in the correct order and in the correct orientation.

    LICENSES AND ATTRIBUTIONS

    CC LICENSED CONTENT, ORIGINAL

    • A&P Labs. Authored by: Ross Whitwam. Provided by: Mississippi University for Women. Located at: http://www.muw.edu/. License: CC BY-SA: Attribution-ShareAlike

      CC LICENSED CONTENT, SHARED PREVIOUSLY

    • Figure 5-9. The three types of vertebrae. All are being viewed from behind. Note that C1 and C2 vertebrae, the atlas and axis, do not have vertebral bodies. . Authored by: Anatomist90. Located at: https://commons.wikimedia.org/wiki/F..._vertebrae.jpg. License: CC BY- SA: Attribution-ShareAlike

    • Figure 5-9. The three types of vertebrae. All are being viewed from behind. Note that C1 and C2 vertebrae, the atlas and axis, do not have vertebral bodies. . Authored by: Anatomist90. Located at: https://commons.wikimedia.org/wiki/F..._vertebrae.jpg. License: CC BY- SA: Attribution-ShareAlike

    • Figure 5-9. The three types of vertebrae. All are being viewed from behind. Note that C1 and C2 vertebrae, the atlas and axis, do not have vertebral bodies. . Authored by: Anatomist90. Located at: https://commons.wikimedia.org/wiki/F...l_vertebra.jpg. License: CC BY-SA: Attribution-ShareAlike

    • Figure 5-9. The three types of vertebrae. All are being viewed from behind. Note that C1 and C2 vertebrae, the atlas and axis, do not have vertebral bodies. Authored by: Anatomist90. Located at: https://bs.wikipedia.org/wiki/Datote..._vertebrae.jpg. License: CC BY- SA: Attribution-ShareAlike

    • Figure 5-9. The three types of vertebrae. All are being viewed from behind. Note that C1 and C2 vertebrae, the atlas and axis, do not have vertebral bodies. Authored by: Anatomist90. Located at: https://commons.wikimedia.org/wiki/F..._vertebrae.jpg. License: CC BY-SA: Attribution-ShareAlike

    • Figure 5-10. The sacrum and coccyx. Authored by: OpenStax College. Located

      at: http://cnx.org/resources/e394fc66a09810ea99d0165de1078c8af2d4dc46/720_Sacrum_and_Coccyx.jpg. License: CC BY-SA: Attribution-ShareAlike

      PUBLIC DOMAIN CONTENT

    • Figure 5-8. The bones of the vertebral column. Authored by: Henry Grey, Henry Vandyke Carter. Located

      at: https://upload.wikimedia.org/wikiped...red_Ro_mod.JPG. Project: Anatomy of the Human Body, 20th Edition (1918). License: Public Domain: No Known Copyright

      The Thoracic Cage – ribs and sternum

      Information

      There is one last component of the axial skeleton we did not cover last lab: the thoracic cage, also called the rib cage. The thoracic cage surrounds and protects the heart and lungs in the thoracic cavity. It consists of the ribs, the sternum, and the thoracic vertebrae, to which the ribs articulate.

      We examined the thoracic vertebrae last lab, so here we will only examine the ribs and sternum.

      There are twelve pairs of ribs. The number is the same in both males and females. Each pair articulates with a different thoracic vertebra on the posterior side of the body. The most superior rib is designated rib 1 and it articulates with the T1 thoracic vertebrae. The rib below that is rib 2, and it connects to the T2 thoracic vertebra, and so on. Ten of the twelve ribs connect to strips of hyaline cartilage on the anterior side of the body. The cartilage strips are called costal cartilage (“costal” is the anatomical adjective that refers to the rib) and connect on their other end to the sternum.

      On an individual rib, one end has various processes, facets, and bumps. This is the end that articulates with the vertebra. The other end is blunt and smooth. This is the end that connects to costal cartilage (unless it is a floating rib. See below.)

      Ribs 1-7 are called the true ribs. Each true rib connects to its own strip of costal cartilage, which in turn connects to the sternum. Ribs 8-12 are called the false ribs. Ribs 8, 9, and 10 do connect to the sternum, but the costal cartilage of each of these ribs connects to the costal cartilage of the rib above it, rather than directly to the sternum. Ribs 11 and 12 do not have any costal cartilage connected to

      them at all, and in addition to being grouped in the false ribs, these two are also called floating ribs, to reflect that fact.

      The sternum has three parts. The manubrium, at the superior end of the sternum, and wider than the rest of the bone, provides articulation points for the clavicles and for the costal cartilage extending from rib 1. The central, thin body provides articulation points for costal cartilage from ribs 2 through 7. The xiphoid process which hangs down at the inferior end of the process (“xiphoid” is from the Greek for sword), starts out as cartilage, and does not typically ossify into bone until an individual is about 40 years old.

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      Figure 5.11. Ribs and sternum.

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      Figure 5.12. True, false, and floating ribs.

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      Figure 5.13. The parts of a rib.

      LAB 5 EXERCISE 5-3

      1. Ribs may be found in the cabinets. On an individual rib, identify which end is the head and which is the anterior end.

      2. On one of the intact skeletons in the lab, identify all the following components of the thoracic cage:

        the true ribs the false ribs the floating ribs

        costal cartilage sternum xiphoid process

        manubrium sternal body

        LICENSES AND ATTRIBUTIONS

        CC LICENSED CONTENT, ORIGINAL

    • A&P Labs. Authored by: Ross Whitwam. Provided by: Mississippi University for Women. Located at: http://www.muw.edu. License: CC BY- SA: Attribution-ShareAlike

      CC LICENSED CONTENT, SPECIFIC ATTRIBUTION

    • Figure 5-1. Ribs and sternum.. Authored by: OpenStax College. Provided by: Anatomy & Physiology, Connexions Web site. https://cnx.org/contents/FPtK1zmh@8....-Thoracic-Cage. Located

      at: https://cnx.org/resources/e1cbee95a6...1_Rib_Cage.jpg. License: CC BY-SA: Attribution- ShareAlike

      PUBLIC DOMAIN CONTENT

    • Figure 7-2. True, false, and floating ribs.. Authored by: Cristobal carrasco. Located

      at: https://commons.wikimedia.org/wiki/File:Costillas.png. License: CC BY-SA: Attribution-ShareAlike

    • Figure 7-3. The parts of a rib.. Authored by: Henry Vandyke Carter. Located

    at: https://commons.wikimedia.org/wiki/File:Image122.gif. License: CC BY-SA: Attribution-ShareAlike

    10

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    Identify the bones

    LAB 5 EXERCISE 5-4

       

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    LAB 5 EXERCISE 5-5

    Label the following:

    Zygomatic bones * Lacrimal bones * Coronal suture * Sagittal suture * Superior orbital notch/foramen * Inferior orbital foramen * Glabella * Superior orbital fissure * Inferior orbital fissure.

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    Note: for all slides, you may wish to color, outline or otherwise

    enhance these images to make your job of labelling easier

    Sutural bones.

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    image

    LAB 5 EXERCISE 5-6

    Label the following:

    Occipital bone * Temporal bone * Sphenoid bone * Maxilla * Mandible * External acoustic meatus * Mastoid process * Styloid process * Lambdoid suture * Zygomatic process of the temporal bone * Temporal process of the zygomatic bone *

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    LAB 5 EXERCISE 5-7

    Label the following:

    Zygomatic arch * Foramen ovale * Foramen spinosum * Foramen lacerum * Jugular foramen * Carotid canal * Foramen magnum * Internal acoustic meatus * Occipital condyle * Mandibular fossa * Ethmoid bone * Optic canal * Anterior cranial fossa * Middle cranial fossa * Posterior cranial fossa.

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    LAB 5 EXERCISE 5-8

    Label the following:

    Ethmoid bone * Perpendicular plate * Crista galli * Lateral masses.

    Sphenoid bone * Lesser wing * Greater wing * Sella turcica * Pterygoid plates * Hypophyseal fossa.

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    LAB 5 EXERCISE 5-9

    Label the following:

    Maxilla * Palatine bone * Pterygoid plates * Vomer * Greater palatine foramen * Incisive foramen Mandible * Condylar process * Coronoid process * Mental foramen * Body of mandible * Ramus of mandible * Mandibular notch

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    ns Attribution-Sh

    & Physiology La

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    License: Anatomy b Homework by Laird C. Sheldahl, under a Creative Commo areAlike License 4.0 International

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    LAB 5 EXERCISE 5-10

    Label the following:

    Cervical vertebrae * Cervical curvature * Thoracic vertebrae * Thoracic curvature * Lumbar vertebrae * Lumbar curvature * 7 * 12 * 5.

    Atlas * Axis * Dens * C1 * C2.

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    7

    2#

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    LAB 5 EXERCISE 5-11

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    Label the following:

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    Cervical vertebrae * Thoracic vertebrae * Lumbar vertebrae * Transverse foramen * Superior articular process * Inferior articular process * Costal demi-facet * Vertebral foramen * Body * Spine * Arch * Transverse process * Transverse facet

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    Label the following:

    Sacrum * Sacral foramen * Ala (of the sacrum).

    Coccyx

    Sternum * Manubrium * Body * Xiphoid process * Jugular notch * Sternal angle. True ribs * False ribs * Floating ribs * Costal cartilages.

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    In the photomicrograph below of compact bone tissue, find and label the indicated structures

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      1. Obtain a slide of ground compact bone connective tissue from the slide box.

      2. View the slide on an appropriate objective.

      3. Fill out the blanks next to your drawing.

      4. In the circle below, draw a representative sample of key features you identified, taking care to correctly and clearly draw their true shapes and directions. Draw your structures proportionately to their size in your microscope’s field of view.

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        Easy difficulty

        Medium difficulty

        Hard difficulty

        Occipital, Frontal

        (sphenoid and ethmoid)

         
             
             

        my pet zebra laugh)

           
        • Bones:

        • Identify from external views:

        • Parietal, Ethmoid, Sphenoid, Temporal,

        • Vomer, Inferior nasal concha, Nasal, Maxilla, Mandible, Palatine, Zygomatic, Lacrimal

        • Bones:

        • identify bones than can be seen from the internal view (occipital, temporal, ethmoid, sphenoid, frontal)

        • Identify disarticulated skull bones

        • Bones :

        • Landmarks:

        • Mastoid Process, Mandibular Fossa,

        • Sphenoid: Greater & lesser wings

        • Sutures: sagittal, coronal, squamous, lambdoid.

        • Landmarks:

        • Cranium: Glabella. Occipital condyles. Styloid process.

        • Face: Alveolar processes of maxilla & mandible. lacrimal fossa

        • Understand the difference between the zygomatic bone, zygomatic arch & zygomatic process (of the temporal bone).

        • Temporal process of zygomatic bone

        • Sphenoid: sella turcica, pterygoid plates.

        • Mandible: ramus, condyle, body, coronoid process.

        • Landmarks:

        • Sinuses: frontal, sphenoid, maxillary.

        • Petrous & squamous part of temporal bone

        • Palatine process of maxilla

        • orbital margins

        • Sphenoid: Hypophyseal fossa

        • Ethmoid: lateral masses, superior & middle nasal conchae, crista galli, perpendicular plate, cribiform plates.

        • Foramen

        • Foramen magnum

        • External acoustic meatus

        • Foramen:

        • mental, optic canal, superior orbital notch/foramen, infraorbital , olfactory foramina, carotid canal, jugular, ovale, lacerum, spinosum.

        • Foramen:

        • stylomastoid, internal acoustic meatus, rotundum, hypoglossal, condylar canal, incisive, greater palatine.

        • Areas:

        • Cranium (mnemonic: Pest of 6)

        • Face (mnemonic: Virgil cannot make

        • Areas:

        • Cranial fossa: anterior, middle, posterior.

        TABLE 5.1: SKULL

        Easy difficulty

        Medium difficulty

        Hard difficulty

         

        atlas/axis/cervical/thoracic or lumbar

         

        foramenl, Vertebral foramen,

           
             
         

        surface

         
             
        • Bones:

        • 7 cervical, 12 thoracic, 5 lumbar vertebrae

        • Atlas & axis

        • Sacrum & coccyx

        • Sternum

        • Hyoid

        • Bones:

        • Identify disarticulated vertebrae as

        • Vertebrae landmarks:

        • Body

        • Transverse process, spinous process

        • Transverse foramen, Intervertebra

        • Superior & inferior articular processes

        • Vertebrae landmarks:

        • Costal facets

        • Costal demifacets: inferior & superior.

        • Dens of axis

        • Vertebrae landmarks:

        • Pedicles, Arch, Lamina, Superior & inferior notch

        • Sternum landmarks

        • manubrium, body, xiphoid process

        • Sternum landmarks

        • Jugular notch, sternal angle.

        • Sacrum landmarks

        • Sacral foramen, Ala, Body, Auricular

        • Misc:

        • Identify true/false/floating ribs on articulated spine.

        • Know number of ribs.

        • List 1 identifying characteristic of the 3 different types of vertebrae

        • Misc:

        • Misc:

        • Spinal curves: cervical, thoracic, lumbar, sacral

        TABLE 5.2: SPINE / AXIAL SKELETON