THE SKELETAL SYSTEM: AXIAL SKELETON
A.
DIVISIONS OF THE SKELETAL SYSTEM
What is the axial skeleton?
The axial skeleton consists of those bones that lie in the longitudinal axis
of the body, running through its center of gravity.
Name the axial bones.
The bones of the axial skeleton include the bones of the skull, the hyoid,
the ribs, sternum, and vertebrae,
What is the appendicular skeleton?
The appendicular skeleton contains the bones of the upper and lower
extremities, including the pectoral (shoulder) girdle and pelvic girdle.
Name the appendicular bones.
The bones of the appendicular skeleton include the:
clavicle, scapula, humerus, radius, ulna, carpals, metacarpals, and
the phalanges of the upper extremities
os coxa, femur, tibia, fibula, tarsals, metatarsals, and the phalanges
of the lower extremities
B.
SKULL
The skull contains 22 bones and rests on the superior end of the vertebral
column. It consists of two sets of bones.
Identify the cranial bones versus the facial bones.
The cranial bones are the: 1 frontal, 2 parietal, 2 temporal, 1occipital,
1 sphenoid, and 1 ethmoid.
The facial bones are the: 2 nasal, 2 maxillae, 2 zygomatics ( zygomas),
1 mandible, 2 lacrimal, 2 palatine, 2 inferior nasal conchae, and 1 vomer.
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1.
SUTURES
What is a suture of the skull?
A suture is an immovable fibrous joint in the skull where bone
surfaces are closely united by connective tissue.
Identify the following sutures:
Coronal -- The coronal suture is located between the frontal bone
and the 2 parietal bone.
Sagittal -- The sagittal suture is located between the 2 parietal
bone.
Lambdoidal -- The lambdoidal sutures are found between the right
and left parietal bones and the occipital bone
Squamosal -- The squamosal sutures are located between the
parietal bone and the temporal bone of each side
What are Wormian bones?
Wormian bones are small fragments of bones found in the sutures,
particularly in the sagittal and lambdoidal sutures.
2.
FONTANELS
What are the fontanels and what are their functions?
Fontanels are membrane-filled spaces between the bones of the
cranium seen at birth. These “soft spot” areas of dense fibrous
connective tissue bridge the incompletely formed cranial bones.
They close as the bones, and the brain, complete their development.
Fontanels have two functions:
(1)
allow head to change shape while passing through
the birth canal
(2)
allow for rapid growth of brain during the first two
years.
Identify the following fontanels:
Anterior -- The anterior (frontal) fontanel is found between the two
parietal bones and the two segments of the frontal bone;
closes between 18 - 24 months.
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Posterior -- The posterior (occipital) fontanel is found between the
two parietal bones and the occiput; closes at 2 months.
Sphenoidal -- The anterolateral (sphenoidal) fontanel is located at
the junction of the frontal, parietal, temporal, and sphenoid
bones; closes at 3 months.
Mastoidal -- The posterolateral (mastoidal) fontanel is found at the
junction of the parietal, occipital, and temporal bones; closes
at 12 months.
C.
HYOID BONE
Describe the hyoid bone. What are its functions?
The hyoid bone is unique in the body because it articulates with no other
bone. It is suspended by ligaments and tendons from the temporal bone
in the anterior neck, between the mandible and the larynx. It supports the
tongue and provides attachment for some of its muscles, as well as other
muscles of the neck and pharynx.
D.
VERTEBRAL COLUMN
1.
DIVISIONS
Name the bones of the thorax.
The vertebral column (spine), together with the ribs and the
sternum, forms the skeleton of the thorax.
Describe the vertebral column.
The vertebral column is composed of a series of individual bones
called vertebrae (a single one is called a vertebra). Together, the
vertebrae form a strong, flexible rod that bends anteriorly,
posteriorly, and laterally, and rotates.
What are the functions of the vertebral column?
Functions of the vertebral column:
1.
Enclose and protect the spinal cord.
2.
Support and allow for movement of the head.
3.
Give points of attachment for ribs and muscles of the back.
What are intervertebral foramina?
Between individual vertebrae are openings called intervertebral
foramina through which pass the spinal nerves.
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Identify the five different types of vertebrae.
The 26 vertebrae of the adult are distributed as:
7 cervical, 12 thoracic, 5 lumbar, 1 sacrum, 1 coccyx.
What are intervertebral discs?
Between each adjacent vertebra from level C-1 to the sacrum are
pads of connective tissue called intervertebral discs.
What are the two parts of a disc?
Each disc is composed of two parts. The outer portion, formed of
fibrocartilage, is the annulus fibrosus. The inner portion is a soft,
pulpy tissue rich in hyaluronic acid, elastin, and water. It is called
the nucleus pulposus.
How do the discs function?
The discs form strong, slightly movable joints between the adjacent
vertebrae, permitting the movements of the spine and absorbing
vertical shock. When they are compressed, the discs bulge
outward, particularly in the lumbar region where the weight of the
upper body is brought to bear on the pelvis.
2.
NORMAL CURVES
Describe the vertebral curves.
When viewed from the side the vertebral column shows four normal
curves. The cervical and lumbar curves are anteriorly convex. The
thoracic and sacral curves are anteriorly concave.
What are there functions?
These curves, like those in long bones, give the spine strength and
absorb vertical shock, acting like a spring.
What are the primary curves?
The thoracic and sacral curves are said to be primary curves
because they retain the original curvature of the embryo/fetus.
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What are the secondary curves?
The cervical and lumbar curves are said to be secondary curves
since they are modifications of the original curve related to
assuming and erect posture by holding up the head and walking.
E.
THORAX
Describe the bony thorax.
The term thorax refers to the entire chest. The skeletal portion of the
thorax is a bony cage formed by the sternum, ribs, costal cartilages, and
bodies of the thoracic vertebrae. The cage is cone-shaped with the
narrow end superior and the broad end posterior. It is flattened front-toback.
What are the functions of the bony thorax?
The bones give partial protection to thoracic organs, support and attach
the upper extremities to the axial skeleton, and give sites for muscle
attachment.
1.
STERNUM
Describe the sternum.
The sternum (breastbone) is a flat narrow bone lying in the midline
of the anterior thoracic wall.
The sternum is formed by fusion of three parts:
1.
Manubrium
2.
Body (gladiolus)
3.
Xiphoid process.
What is the sternoclavicular notch?
The superior- most portion of the sternum, where the two clavicles
join the sternum at the manubrium, forms the sternoclavicular
notch. This is an important clinical landmark.
2.
RIBS.
Describe the posterior articulation of the ribs.
Each rib articulates posteriorly with its corresponding thoracic
vertebra and the vertebra directly below it. Ex. Rib 1 articulates
with both thoracic vertebrae 1 and 2.
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What are the true ribs?
Ribs 1-7 have a direct attachment to the sternum via the costal
cartilages. Therefore, they are called true ribs.
What are the false ribs?
Ribs 8-10 have a single cartilaginous union with the sternum
because their costal cartilages fuse into one. Along with ribs 11-12,
these are the false ribs. Ribs 11-12 are also known as floating ribs
because they have only a posterior attachment. They have no
costal cartilages.
Describe an intercostal space.
Between the ribs are the intercostal spaces, each containing
intercostal muscles, blood vessels, and nerves.
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