Transcript Axial Skeleton

The Axial Skeletal System
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.
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)
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)
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
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
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.
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
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
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.
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
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.
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.
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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Number 1-12
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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.
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.
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.
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
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.
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.
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).
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
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
Pause and Practice Again!
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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).
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.
Maxillary Landmarks cont…
• Maxillary sinuses: a series of small spaces
within the maxillae.
– Empty into the nasal cavity.
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.
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.
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.
• 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.
• 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.
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.
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”.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
Lumbar Vertebrae
• The next 5 vertebrae (L1-L5).
• The largest and strongest of the bones of
the spine.
• Spinous processes are thick and broad.
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.
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.
Vertebrae Investigation
• Differentiate between cervical, thoracic and
lumbar
– Look at vertebral body size, vertebral foramen
size, transverse processes (presence/absence of
foramen) and articulation surfaces
• Identify C1-Atlas, C2-Axis and C7 Vertebra
Prominens
• T12
• Identify sacrum and coccyx
– Auricular surfaces of the sacrum
• Put the entire vertebral column together
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ACT-UP
What region of the vertebral
column might be most affected
by osteoporosis? Explain your
reasoning.