Essentials of Anatomy and Physiology

as colds, or with allergies such as hay fever. These
sinuses, however, do have functions: They make the
skull lighter in weight, because air is lighter than bone,
and they provide resonance for the voice, meaning
more air to vibrate and thus deepen the pitch of the
voice.
The mastoid sinusesare air cavities in the mastoid
process of each temporal bone; they open into the
middle ear. Before the availability of antibiotics, mid-
dle ear infections often caused mastoiditis, infection of
these sinuses.
Within each middle ear cavity are three auditory
bones: the malleus, incus, and stapes. As part of the
hearing process (discussed in Chapter 9), these bones
transmit vibrations from the eardrum to the receptors
in the inner ear (see Fig. 9–7).

VERTEBRAL COLUMN

The vertebral column(spinal column or backbone) is
made of individual bones called vertebrae. The names

of vertebrae indicate their location along the length of

the spinal column. There are 7 cervical vertebrae, 12

thoracic, 5 lumbar, 5 sacral fused into 1 sacrum, and

4 to 5 small coccygeal vertebrae fused into 1 coccyx

(Fig. 6–10).

The seven cervical vertebraeare those within the

neck. The first vertebra is called the atlas, which artic-

ulates with the occipital bone to support the skull and

forms a pivot jointwith the odontoid process of the

axis, the second cervical vertebra. This pivot joint

allows us to turn our heads from side to side. The

remaining five cervical vertebrae do not have individ-

ual names.

The thoracic vertebraearticulate (form joints)

with the ribs on the posterior side of the trunk. The

lumbar vertebrae, the largest and strongest bones of

the spine, are found in the small of the back. The

sacrumpermits the articulation of the two hip bones:

the sacroiliac joints. The coccyxis the remnant of

tail vertebrae, and some muscles of the perineum

(pelvic floor) are anchored to it.

The Skeletal System 119

Frontal sinus

Ethmoid sinus Maxillary sinus

Sphenoid sinus

Ethmoid sinus

A B

Figure 6–9. Paranasal sinuses. (A) Anterior view of the skull. (B) Left lateral view of skull.

QUESTION:Which of these sinuses often cause the pain of a sinus headache?