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Selected Topics in The Bone Chapter

The identification of bones and bone markings will be done almost entirely
in the laboratory.

Axial  Skeleton

SKULL - see pg. 203.

Black Eye - a sharp blow to the ridge above the eye sockets will lacerate tissues that
then bleed downward to the "bags" below the eye.

Ethmoid - The ethmoid forms the upper roof of the nasal cavities. Its roof, the
cribriform plate, is penetrated by small olfactory foramena which contain sensory
nerves for the sense of smell (olfaction). There is a disease, amoebic encephalitis, in
which amoebae (found in muddy pond water) travel through these passages to the
brain where they destroy it if antibiotics are not used. If the cribriform plate is
fractured, a loss of the sense of smell may result whether you have taken a shower lately or not.
 
 

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Occipital bone - the large opening through which the spinal cord passes is the
foramen magnum. In contusions of the brain, blood pooling in the skull can force the
brain partially out through this foramen. Death results when the brain stem is
compressed because breathing is inhibited.

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Label the foramena.
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Sinuses and Sinusitis -  The sinuses are cavities in the frontal,
ethmoidal and sphenoidal bones which are lined with a mucous membrane. They
lighten the skull and add mucous membrane area for filtration and moisturization
of inhaled air. If these membranes are swollen by allergies or infection and therefore
plugged up, a sinus headache may result.

Mandible - The condylar process of the mandible fits into a groove formed in  the
temporal bone, the mandibular fossa. If the ligaments holding the joint together
loosen or there is an imbalance in muscle strength and pull on the mandible, the jaw
may pop out of joint and soreness result. Eventually arthritis (joint inflammation)
may result. One non surgical remedy is to wear an appliance which keeps the jaw in
line. This is called temporal-mandibular joint syndrome (TMJ).  See p. 271.

The "soft spots" on the baby's head are connective tissue sheets called fontanels.

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1. Frontal fontanel - the largest, most prolonged (up to 2 years) fontanel, is found
between the two developing  parietal bones and the frontal bones. See p. 247 and the
Marieb lab manual p. 117.

2. Posterior - found between the parietals and the occipitals.

3. Anterolateral  (sphenoid) - located at the junction of the frontal, parietal, temporal and
sphenoid bones in the temporal area just posterior to the eye socket.

4. Posterolateral (mastoid) - located on each side on the skull just superior to the mastoid process.
 

Hyoid bone -. This bone sits on the top of the larynx and serves as a point of
attachment for pharyngeal muscles and the tongue. It is frequently broken during
strangulation. See pg. 218.

Cervical Vertebrae- cervical means neck, these seven vertebrae, C1 to C7, have
transverse foramena which conduct the vertebral arteries to the brain. Because
spinal nerves come off the spinal cord between vertebrae, the numbering of all
vertebrae is important in the diagnosis of neurological symptoms resulting from
nerve impingement and the the administering of spinal anesthesia.
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What passes through the transverse foramina?
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The vertebra at top left is _______?
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Atlas - the first vertebra supports the skull by articulating with the occipital
condyles.

Axis - notice the odontoid (tooth or dens) process. This protrudes upward into the
vertebral foramen of the atlas. In execution by hanging, this process tilts forward as the
laminae fracture anteriorly and is driven into the spinal cord. In general, compression of
the spinal cord by the cord by broken or dislocated bones and processes, or severing
the spinal cord causes paralysis and perhaps death. I'll say more about this in the
Nervous System chapters. The atlas and axis, the atlantoaxial joint, forms a pivot joint
functionally, because the head can be rotated on the neck.

Thoracic Vertebrae - there are twelve thoracic vertebrae, T1 to T12. They form the
postero-medial portion of the thoracic cavity. Ribs form movable joints with the thoracic
vertebrae because the rib cage must move upward and outward during inhalation and vice-
versa during exhalation. Notice where the head and tubercle of the rib articulates with
the thoracic vertebrae. The thoracic curve is called a kyphosis.  A posteriorly directed
curvature of the thoracic spine occurs, a exagerated kyphosis or "hunch back" results.
A laterally directed curvature is called a scoliosis.
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Sacral Vertebrae - S1 to S5 are fused together to make the larger sacrum. The sacrum
forms an immovable joint with the ilium of the hip girdle, the sacroiliac. Inferiorly, is the hiatal
canal; epidural anesthesia may be injected there.
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Coccyx - strangely enough we have a short tail of 3-5 vertebrae attached to the sacrum by ligaments.

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Identify: the curves of the spine.

Spina Bifida - in fetal development, if the vertebral laminae fail to unite at the
spinous process, the meninges (covers) of the spinal cord may protrude, sometimes
forming a protruding, round cyst (spinal bifida cystica). Sometimes the defect cannot
be seen at the surface, but may be marked by a round patch of hair, then its called
spina bifida occulta. Partial paralysis and poor bladder and bowel control may result.
Recently, it has been shown that supplements of the vitamin folic acid reduce the
occurrence of this and other neural tube defects.
 

THORAX

The ribs form immovable joints with the sternum. What will happen to the thoracic
cavity if muscles like the sternocleidomastoids pull the sternum up?

STERNUM - See pg. 226.

1. Xiphoid process- this is a piece of cartilage that projects caudally from the body
of the sternum. In the chest compressions of CPR, care must be taken not to break the
xiphoid process off and drive it into the soft liver. Profuse bleeding will result.
2. Body - ribs #2-10 articulate with the body. Ribs that have a direct cartilagenous
connection to the sternum (1-7) are called "true ribs." Ribs #8-10 share a cartilagenous
connection and therefore are included as "false ribs," along with ribs #11-12 that are
also called "floating ribs." Ribs are brittle; when fractured, shards may puncture the
lungs or other organs.
3. Manubrium - this articulates with ribs #1-2 and the clavicle.

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 Email:jaliff @ gpc.edu