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The Axial Skeletal System

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Title: The Axial Skeletal System


1
The Axial Skeletal System
2
Divisions of the Skeletal System
  • Humans are born with approximately 300 bones
    which fuse to 206 bones as adults.
  • There are 2 main divisions of the skeletal
    system axial skeleton and appendicular skeleton.

3
Divisions of the Skeletal System
  • Axial skeleton forms the vertical axis of the
    body.
  • 80 bones skull (22), vertebral column (26),
    ribcage (25), auditory ossicles (6), and hyoid
    (1)
  • Appendicular skeleton forms the arms, legs and
    the girdles
  • Girdles attach the arms and legs to the axial
    skeleton
  • 126 bones pectoral girdle (4), arms (60), legs
    (60) and pelvic girdle (2)

4
Skull
  • Superior end of the vertebral column
  • Composed of flat and irregular shaped bones
  • Large hollow space within the skull is called the
    cranial vault or cranial cavity.
  • Functions to
  • Surround and protect the brain
  • Be points of attachment for the facial muscles
    (landmarks)

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Divisions of the Skull
  • Cranial division consists of 8 flat bones that
    form a protective box around the brain.
  • Help to form the cranial vault (cavity)
  • Frontal (1) forms the anterior portion of the
    cranial cavity
  • Forms the superior orbits of the eyes and forms
    the forehead

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Frontal Bone Landmarks
  • Supraorbital margin a thickened ridge of bone
    found superior to the orbit of the eye.
  • Just deep to the eyebrow and more prominent on
    the lateral portion
  • Point for muscle attachment (PFMA)
  • Supraorbital foramen a small opening found on
    the medial aspect of the supraorbital margin.
  • Can feel it best inferior to the margin
  • Allows blood vessels and nerves to enter the
    frontal bone

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Frontal Bone Landmarks
  • Frontal sinus A hollow space found within the
    frontal bone, superior and medial to the
    supraorbital margin.
  • Can only be seen with a sagittal cut
  • ¼ inch superior to the eyebrows
  • House mucus and macrophages for trapping and
    destroying foreign particles.

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Frontal Bone Landmarks
  • Frontal sinus A hollow space found within the
    frontal bone, superior and medial to the
    supraorbital margin.
  • Can only be seen with a sagittal cut
  • ¼ inch superior to the eyebrows
  • House mucus and macrophages for trapping and
    destroying foreign particles.

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Parietal Bones (2)
  • Form the lateral walls and the superior portion
    of the cranium.
  • Landmarks
  • Temporal fossa A large, shallow depression that
    begins on the parietal bone and extends to the
    frontal bone.
  • PFMA

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Temporal Bones (2)
  • Form the inferior lateral walls and a portion of
    the floor of the cranium.
  • Articulate with the mandible (lower jaw) to form
    the temporomandibular joint (TMJ)
  • Temporal bone landmarks
  • Mastoid process A large, blunt projection found
    posterior to the external auditory meatus.
  • Bump behind the ear
  • PFMA

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Temporal Bone Landmarks cont..
  • Styloid process A thin, sharp projection found
    inferior and medial to the external auditory
    meatus.
  • Covered with muscle so it is more difficult to
    identify
  • PFMA
  • Zygomatic process A thin, flat projection found
    anterior to the external auditory meatus.
  • PFMA
  • External auditory meatus The external ear canal
  • Opening through which the auditory nerve runs.

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Temporal Bone Landmarks cont..
  • Mandibular fossa A shallow depression found
    inferior and slightly anterior to the external
    auditory meatus
  • This forms an articulation with the mandible
  • Easy to see inferiorly if the mandible is removed

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Occipital Bone (1)
  • Forms the posterior wall and the floor of the
    cranium.
  • The spinal cord passes through this as it exits
    the cranial vault.
  • Occipital bone landmarks
  • External occipital protuberance A prominent
    midline projection found on the superior surface.
  • Where the occipital bone turns to form the
    horizontal part.

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Occipital Bone Landmarks cont..
  • Superior nuchal line Two curved ridges that
    extend laterally from the external occipital
    protuberance.
  • PFMA
  • Inferior nuchal line Two curved ridges that
    extend laterally from the external occipital
    protuberance, inferior to the superior nuchal
    line.
  • PFMA
  • Foramen magnum A large opening in the inferior
    surface of the occipital bone that allows the
    spinal cord to exit the cranial cavity.
  • Largest foramen in the body.

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Occipital Bone Landmarks cont..
  • Occipital condyles Paired oval-shaped
    projections found lateral to the foramen magnum.
  • Form an articulation with the 1st bone of the
    spine (atlas)

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Sphenoid Bone (1)
  • Forms the anterior floor of the cranial cavity.
  • Also forms a portion of the lateral walls of the
    cranial cavity.
  • Forms the posterior wall of the orbits of the
    eyes.
  • The keystone bone for the cranium because it
    articulates with all other cranial bones.
  • Shape resembles a bat with outstretched wings
    when viewed superiorly.

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Sphenoid Bone Landmarks
  • Greater wing The larger, inferior projection of
    the sphenoid that forms a portion of the floor
    and the lateral walls of the cranium.
  • Also forms the posterior wall of the orbits of
    the eyes.
  • Lesser wing The smaller, superior projection of
    the sphenoid bone located posterior to the
    frontal bone.

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Sphenoid Bone Landmarks cont..
  • Sella turcica A small, saddle-like depression
    found between the greater and lesser wings that
    surrounds and protects the pituitary gland.
  • Pituitary is an important endocrine gland
  • 3 parts to the sella turcica
  • Tuberculum sellae The anterior portion of the
    sella turcica.
  • Closest to the lesser wing.

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Sphenoid Bone Landmarks cont..
  • 3 parts to the sella turcica continued
  • Hypophyseal fossa The seat of the saddle.
  • Where the pituitary gland resides
  • Dorsum sellae The posterior portion of the sella
    turcica.
  • Closer to the greater wing

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Ethmoid Bone (1)
  • The small bone located anterior to the sphenoid
    bone in the middle of the frontal bone.
  • Forms a small portion of the anterior floor of
    the cranium.
  • Also forms a small portion of the medial wall of
    the eye orbits.
  • Also forms the superior portion of the nasal
    septum.

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Ethmoid Bone Landmarks
  • Cribriform plate Paired projections found
    lateral to the crista galli.
  • Has small openings called the olfactory foramina.
  • Olfactory foramina A series of small openings
    found within the cribriform plate that allow
    nerves from the olfactory epithelium to pass
    directly into the brain.
  • These nerves give us our sense of smell.

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Ethmoid Bone Landmarks cont..
  • Crista galli A small triangular projection found
    in the center of the ethmoid bone.
  • Near the front of the cranial cavity.
  • Point of attachment for the meninges (protective
    coverings of the brain).
  • Perpendicular plate A small vertical projection
    arising from the inferior surface of the ethmoid
    bone.
  • Forms the superior portion of the nasal septum.
  • Articulates with the vomer (facial bone).

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Ethmoid Bone Landmarks cont..
  • Superior and middle nasal conchae Two thin,
    scroll-shaped projections found lateral to the
    perpendicular plate
  • The middle nasal conchae is inferior to the
    superior nasal conchae.
  • These increase surface area of the nasal
    passageways
  • Ethmoidal cells Air spaces found within the
    lateral masses of the ethmoid bone.
  • Small sinuses

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Sutures
  • Fibrous joints found between the bones of the
    cranium.
  • There are 4 major sutures
  • Coronal unites the frontal bone and both
    parietal bones
  • Sagittal unites the two parietal bones on the
    superior midline of the skull
  • Lambdoid unites the two parietal bones to the
    occipital bone.
  • Squamous (2) unite the parietal and temporal
    bones on the lateral sides of the skull

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The Facial Division
  • A group of 14 irregular bones that serves as
    points of attachment for muscles of the face.
  • Nasal (2) form the bridge of the nose.
  • Rectangular shaped bones
  • PFMA
  • Maxillae (2) Form the upper jaw.
  • Articulate with every face bone except the lower
    jaw.
  • Form part of the floors of the orbits, lateral
    walls and floor of the nasal cavity, and most of
    the hard palate (bony roof of the mouth).

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Maxillary Landmarks
  • Infraorbital foramen Small openings found
    inferior to the orbits of the eyes.
  • Allows passage of blood vessels and nerves.
  • Palatine process a lateral projection that forms
    one half of the anterior portion of the hard
    palate.
  • Typically the 2 processes unite during weeks
    10-12 of embryo development. If not, cleft
    palate will result. This negatively impacts
    speech and swallowing.

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Maxillary Landmarks cont
  • Maxillary sinuses a series of small spaces
    within the maxillae.
  • Empty into the nasal cavity.

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Zygomatic Bone (2)
  • Form the prominence of the cheeks.
  • Also form part of the lateral wall and floor of
    each orbit.
  • Articulate with the frontal, maxilla, sphenoid
    and temporal bones.
  • Zygomatic bone landmarks
  • Temporal process a thin, flat projection arising
    from the lateral, posterior surface of the
    zygomatic bone.
  • Articulates with the zygomatic process of the
    temporal bone.

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Zygomatic Bone Landmarks cont..
  • Zygomatic arch created by the articulation of
    the temporal process of the zygomatic bone and
    the zygomatic process of the temporal bone.

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Lacrimal Bones (2)
  • The smallest bones of the facial division.
  • Resemble the shape and size of a fingernail
  • Posterior and lateral to the nasal bones and form
    part of the medial wall of each orbit.
  • Lacrimal bone landmark
  • Lacrimal fossa a small vertical groove formed
    with the maxilla, that helps drain fluid away
    from the eye.
  • Houses a lacrimal sac that gathers tears and
    passes them into the nasal cavity.

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  • Palatine Bones (2) L shaped bones that form
    the posterior portion of the hard palate.
  • The parts that make-up the hard palate are called
    horizontal plates.
  • Inferior Nasal Conchae (2) scroll shaped bones
    that form a portion of the inferior, lateral
    walls of the nasal cavity.
  • Increase surface area and help filter air along
    with the superior and middle nasal conchae of the
    ethmoid bone.

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  • Vomer (1) a triangular bone that forms a portion
    of the posterior floor of the nasal cavity.
  • Articulates with the perpendicular plate of the
    ethmoid bone to form the inferior portion of the
    bony nasal septum.
  • Mandible (1) the largest bone of the facial
    division.
  • Except for the ossicles, it is the only moveable
    skull bone.

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Mandibular Landmarks
  • Mandibular body a triangular bone that forms a
    portion of the posterior floor of the nasal
    cavity.
  • Ramus the short, vertical portion of the
    mandible.
  • Angle the area where the ramus and the body of
    the mandible meet.
  • Coronoid process a small triangular projection
    found on the superior anterior portion of the
    ramus.

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Mandibular Landmarks cont
  • Condylar process a small rounded projection
    found on the superior posterior portion of the
    ramus.
  • Articulates with the mandibular fossa to create
    the temporomandibular joint (TMJ).
  • Mental foramen small openings found in the
    anterior surface of the body of the mandible that
    allow blood vessels and nerves to enter the
    mandible.
  • Alveoli sockets for teeth

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Auditory Ossicles
  • The 6 smallest bones in the human body.
  • Located medial to the eardrum.
  • Connected by synovial joints.
  • Function to transfer sound waves from the eardrum
    to the inner ear.
  • The bones are as follows
  • Malleus- attaches to the eardrum and is commonly
    called the hammer.
  • Incus- middle bone that is commonly called the
    anvil.
  • Stapes- Smallest bone and is commonly called the
    stirrup.

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Hyoid Bone
  • Located superior to the larynx (voice box).
  • U shaped
  • The only bone that does not articulate with
    another bone.
  • Suspends from the styloid processes by ligaments
    and muscles.
  • Often fractured during strangulation.
  • Functions to support the tongue.

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The Vertebral Column
  • Also called the spine, backbone or spinal column.
  • Consists of 33 (children) or 26 (adults) bones
    called vertebrae.
  • Functions to protect the spinal cord, support the
    head, and serve as attachment points for the
    ribs, pelvis, back muscles and arm muscles.

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Vertebrae
  • Vary in size, shape and detail but have many
    similarities.
  • Consist of 3 main parts vertebral body,
    vertebral arch and several processes.
  • Vertebral body the thickened anterior portion of
    a vertebra.
  • Holds the intervertebral disc and contains
    foramina for the entrance of blood vessels.
  • Intervertebral discs pads of fibrocartilage that
    help hold the vertebrae in place.
  • Compress throughout the day due to weight and
    water loss. This compression does not change
    height as we age.

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Vertebrae continued
  • Vertebral arch located posterior to the
    vertebral body.
  • Forms the vertebral foramen with the vertebral
    body.
  • The vertebral arch consists of the pedicles and
    the laminae.
  • Pedicles the shorter anterior portions of the
    vertebral arch.
  • Laminae the longer posterior portions of the
    vertebral arch.

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Vertebrae continued
  • Vertebral foramen the opening formed by the
    vertebral body and the vertebral arch.
  • Contains the spinal cord, adipose tissue, areolar
    connective tissue and blood vessels.
  • Processes bony projections that arise from the
    vertebral arch.
  • Transverse processes paired lateral projections
    that arise from the vertebral arch.
  • Spinous process the single posterior projection
    that arises from the vertebral arch.
  • Both of these are PFMA

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Cervical Vertebrae
  • The first 7 vertebrae (C1-C7).
  • Smaller bones than other vertebrae but larger
    vertebral foramen.
  • Also have 2 transverse foramen through which the
    vertebral artery, vein and nerve fibers pass.
  • C2-C6 have a branching spinous process.
  • C1 is called the atlas.
  • Supports the skull.
  • It lacks a body and a spinous process.

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Cervical Vertebrae cont
  • C2 is called the axis.
  • Has a body and a peglike process called the dens
    or the odontoid process.
  • The dens makes a pivot on which the atlas and
    head rotate.
  • C7 is called the vertebra prominens.
  • Has a large spinous process that is not branched
    and can be felt at the back of the neck.

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Thoracic Vertebrae
  • The next 12 vertebrae (T1-T12).
  • Have facets (flat surfaces) where they articulate
    with the 12 rib pairs.
  • Movement of these vertebrae are most limited
    because the ribs attach to the sternum anteriorly.

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Lumbar Vertebrae
  • The next 5 vertebrae (L1-L5).
  • The largest and strongest of the bones of the
    spine.
  • Spinous processes are thick and broad.

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Sacrum
  • The next vertebra in the adult vertebral column.
  • A triangular shaped bone formed from the fusion
    of 5 bones. This starts around age 16 and is
    usually completed by age 30.
  • Auricular surfaces large, ear-shaped roughened
    surfaces found on the lateral aspect of the
    sacrum.
  • This articulates with the hip bones of the pelvis.

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Coccyx
  • The last vertebra in the adult vertebral column.
  • The tailbone that is formed by the fusion of 4
    vertebrae that occurs between the age of 20-30.
  • In males, it points anteriorly and in females it
    points inferiorly.

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ACT-UP
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ACT-UP
  1. What region of the vertebral column might be most
    affected by osteoporosis?
  2. Why?
  3. What would we expect to see (on the outside) when
    looking at a person suffering from osteoporosis?

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Thorax
  • Includes the sternum, ribs and the bodies of the
    thoracic vertebrae.
  • Sternum located along the anterior midline of
    the thorax.
  • Also known as the breastbone
  • Consists of 3 parts that fuse by age 25 and the
    points of fusion can be seen as transverse
    ridges.
  • If thoracic surgery is necessary, the sternum may
    be cut along the midline.

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Regions of the Sternum
  • Manubrium the superior portion of the sternum
  • Articulates with the clavicles (collarbones) and
    the costal cartilages of the 1st-2nd rib pairs.
  • Sternal body the intermediate portion of the
    sternum.
  • Articulates directly or indirectly with the
    costal cartilages of the 2nd-10th rib pairs.
  • Xiphoid process the inferior portion of the
    sternum.
  • Where some abdominal muscles attach.

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Ribs
  • 12 pairs of flat bones that form a protective
    cage around the heart and the lungs.
  • Increase in length from 1-7 and then decrease
    from 7-12.
  • Each rib pair articulates posteriorly with its
    corresponding thoracic vertebra.
  • Costal cartilage elongated pads of hyaline
    cartilage used to attach the ribs to the sternum.
  • Allows the ribcage to be more elastic and limits
    fracturing from blows to the chest.

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Types of Ribs
  • True ribs Rib pairs 1-7
  • Their costal cartilages attach directly to the
    sternum.
  • False ribs Rib pairs 8-12
  • Their costal cartilages do not attach directly to
    the sternum. Rib pairs 8-10 have cartilages that
    attach to the cartilage of 7 (which attaches to
    the sternum.
  • Floating ribs Rib pairs 11-12
  • The costal cartilages do not attach to the
    sternum at all.

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