Ch. 7 The Axial Skeleton

The bones, muscles, and joints together form an integrated system called the _____.
musculoskeletal system
There are two principal divisions in the adult skeleton:
the axial skeleton and the appendicular skeleton
Axial skeleton
lies around the longitudinal axis of the human body, an imaginary vertical line that runs through the body’s center of gravity from the head to the space between the feet. The axial skeleton consists of the skull bones, auditory ossicles, hyoid bone, ribs, sternum (breastbone), and bones of the vertebral column.
Appendicular skeleton
contains the bones of the upper and lower limbs, plus the bones forming the girdles that connect the limbs to the axial skeleton.

There are 206 bones in the body. ____ bones in the axial skeleton and ____ bones in the apendicular skeleton.
80 and 126
Bones of the axial skeleton:
*Skull*Cranium 8Face 14*Hyoid* 1*Auditory ossicles* 6*Vertebral column* 26*Thorax* Sternum 1Ribs 28——–*Number of bones = 80*
Bones of the appendicular skeleton:
*Pectoral (shoulder) girdles*Clavicle 2Scapula 2*Upper limbs*Humerus 2Ulna 2Radius 2Carpals 16Metacarpals 10Phalanges 28*Pelvic (hips) girdle*Hip, pelvic, or coxal bone 2*Lower limbs*Femur 2Patella 2Fibula 2Tibia 2Tarsals 14Metatarsals 10Phalanges 28———*Number of bones = 126*
surface markings
bones have characteristic surface markings, structural features adapted for specific functions. Most are not present at birth, but develop in response to certain forces and are most prominent in the adult skeleton. In response to tension on a bone surface results in raised or roughened areas. Compression on a bone surface results in a depression.
Two major types of surface markings:
(1) depressions and openings, which usually allow passage of blood vessels and nerves or help form joints, and (2) processes, which are projections or outgrowths that either help form joints or serve as attachment points for connective tissue (such as ligaments and tendons).

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Depressions and openings: Sites allowing the passage of soft tissue (nerves, blood vessels, ligaments, tendons) or formation of joints:
1. fissure, 2. foramen, 3.

fossa, 4. sulcus, 5. meatus.

1. Fissure
A narrow slit between adjacent parts of bones through which blood vessels or nerves pass. Example: superior orbital fissure of the sphenoid bone.


Opening (foramen = hole) through which blood vessels, nerves, or ligaments pass. Example: Optic foamen of the sphenoid bone.


Shallow depression (fossa = trench). Example: Coronoid fossa of the humerus.
4. Sulcus
Furrow along a bone surface that accomodates a blood vessel, nerve, or tendon. Example: Intertubercular sulcus of the humerus.


Tubelike opening (meatus = passageway). Example: External auditory meatus of the temporal bone.
Processes: Projecting or outgrowths on bone that form joints or attachment points for connective tissue, such as ligaments and tendons.
1. condyle, 2. facet, 3.


1. Condyle
Large, round protuberance (condylus = knuckle) at the end of a bone. Example: Lateral condyle of the femur.

2. Facet
Smooth flat articular surface. Example: Superior articular facet of a vertebra.
3. Head
Rounded articular projection supported on the neck (constricted portion) of a bone. Example: Head of the femur.

Processes that form attachment points for connective tissue
1. crest, 2. epicondyle, 3. line, 4. spinous process, 5.

trochanter, 6. tubercle, 7. tuberosity

1. Crest
Prominent ridge or elongated projection. Example: Median sacral crest of the sacrum.
2. Epicondyle
Projection above (epi = above) a condyle.

Example: Medial epicondyle of the femur.

3. Line
Long, narrow ridge or border (less prominent than a crest). Example: Linea aspera of the femur.

4. Spinous process
Sharp, slender projection. Example: Spinous process of a vertebra.
5. Trochanter
Very large projection. Example: Greater trochanter of the femur.


Small, rounded projection (tuber = knob). Example: Greater tubercle of the humerus.
7. Tuberosity
Large, rounded, usually roughened projection. Example: Ischial tuberosity of the hip bone.
The skull
contains 22 bones and rests on the superior end of the vertebral column.

The bones of the skull are grouped into two categories:
cranial bones and facial bones.
The cranial bones or cranium
form the cranial cavity which encloses and protects the brain.
The eight cranial bones are the
frontal bone, two parietal bones, two temporal bones, the occipital bone, the sphenoid bone, and the ethmoid bone.

Fourteen facial bones form the face:
two nasal bones, two maxillae (or maxillas; singular is maxilla), two zygomatic bones, the mandible, two lacrimal bones, two palatine bones, two inferior nasal conchae, and the vomer.
Besides forming the large cranial cavity, the skull also forms several smaller cavities, including
the nasal cavity and orbits (eye sockets), which both open to the exterior. Certain skull bones also contain cavities called paranasal sinuses that are lined with mucous membranes and open into the nasal cavity. Also within the skull are small middle and inner ear cavities that house the structures involved in hearing and equilibrium (balance).
Other than the auditory ossicles, the ____ is the only movable bone in the skull.
The frontal bone
forms the forehead, the roofs of the orbits (eye sockets), and most of the anterior part of the cranial floor.

Most of the skull bones are held together by immovable joints called
The skull also has many surface markings such as ____ and ____.
foramina (rounded passageways; singular is foramen) and fissures (slit-like openings) through which blood vessels, nerves, and ligaments pass.
Soon after birth the left and right sides of the frontal bone are united by the ____, which usually disappears between the ages of 6 and 8.
metopic suture
Supraorbital margin
superior to the orbits the frontal bone thicken, forming this.
Supraorbital foramen
Within the supraorbital margin is this which is a passageway for nerves of the eyebrow and eyelid.
Frontal sinuses
lie deep to the frontal bone.
Temporal bones
Both form the inferior lateral sides of the cranium and part of the cranial floor.
Occipital bone
forms the posterior part and most of the base of the skull.

Foramen magnum
is in the inferior part of the bone. Within this foramen, the medulla oblongata (inferior part of the brain) connects with the spinal cord. The vertebral and spinal arteries also pass through this foramen.
Sphenoid bone
lies at the middle of the base of the skull. This bone is the keystone of the cranial floor because it articulates with all the other cranial bones, holding them together.
Optic foramen
through which impulses of vision are carried to the brain.
Internal auditory meatus
is the opening in the petrous portion through which impulses for hearing and equilibrium are carried to the brain.
Ethmoid bone
is spongelike in appearance and is located in the anterior part of the cranial floor medial to the orbits.

It is anterior to the sphenoid and posterior to the nasal bones. The ethmoid forms (1) part of the anterior cranial floor; (2) the medial wall of the orbits; (3) the superior portions of the nasal septum, which divides the nasal cavity into right and left sides; and (4) most of the superior sidewalls of the nasal cavity.

Olfactory foramina
through which smell senstations are transmitted to the brain.
The ethmoid bone contains
3 to 18 air spaces, or “cells.” The ethmoidal cells together form the ethmoidal sinuses.

The nasal conchae (superior nasal concha, middle nasal concha, and the inferior nasal conchae)
increase the vascular and mucous membrane surface area in the nasal cavity, which warms and mositens inhaled air to swirl, and the result is that many inhaled particles become trapped in the mucus that lines the nasal cavity. This action of the conchae helps cleanse inhaled air before it passes into the rest of the respiratory passageways.
The shape of the face changes dramatically during the first ____ years after birth.

Growth of the face ceases at about ____ years of age.
The 14 facial bones include:
two nasal bones, two maxillae, two zygomatic bones, the mandible, two lacrimal bones, two palatine bones, two inferior nasal conchae, and the vomer.
The paired *nasal bones*
are small, flattened, rectangular-shaped bones that form the bridge of the nose. These small bones protect the upper entry to the nasal cavity and provide attachment for a couple of thin muscles of facial expression.
For those who wear glasses, the ____ bones form the resting place for the bridge of the glasses. The major structural portion of the nose consists of cartilage.
The paired *maxillae*
unite to form the upper jawbone. They articulate with every bone of the face except the mandible, or lower jawbone.

Hard palate
the bone roof of the mouth, separates the nasal cavity from the oral cavity.
The two *zygomatic bones*
commonly called cheekbones, form the prominences of the cheeks and part of the lateral wall and floor of each orbit.
The paired *lacrimal bones*
(lacrim = teardrops) roughly resemble a fingernail in size and shape. These bones, the smallest bones of the face, are posterior and lateral to the nasal bones and form a part of the medial wall of each orbit.
The two *palatine bones*
(are L-shaped) form the posterior portion of the hard palate, part of the floor and lateral wall of the nasal cavity, and a small portion of the floors of the orbits.

The two *inferior nasal conchae*
are inferior to the middle nasal conchae of the ethmoid bone and are separate bones that are not part of the ethmoid bone. These scroll-like bones form a part of the inferior lateral wall of the nasal cavity and project into the nasal cavity. All three pairs of nasal conchae (superior, middle, and inferior) increase the surface area of the nasal cavity and help swirl and filter air before it passes into the lungs.
The *vomer*
is a roughly triangular bone on the floor of the nasal cavity that articulates superiorly with the perpendicular plate of the ethmoid bone and sphenoid bone and inferiorly with both maxillae and palatine bones.

It forms the inferior portion of the bony nasal septum.

The *mandible*
or lower jawbone, is the largest, strongest facial bone. It is the only freely movable skull bone (other than the auditory ossicles, the small bones of the ear).
Nasal septum
The inside of the nose, called the nasal cavity, is divided into right and left sides by a vertical partition called this.
The three components of the nasal septum are the
vomer, septal cartilage, and perpendicular plate of the ethmoid bone.

The term broken nose
in most cases, refers to damage to the septal cartilage rather than the nasal bones themselves.
Seven bones of the skull join to form each ____ which contains the eyeball and associated structures.
orbit (eye socket)
Associated with each orbit are five openings:
1. supraorbital foramen, 2. optic foramen, 3.

superior orbital fissure, 4. inferior orbital fissure, 5. lacrimal fossa

1. Supraorbital foramen
is found on the supraorbital margin of the frontal bone.
2. Optic foramen
is in the sphenoid bone.

3. Superior orbital fissure
is in the sphenoid bone.
4. Inferior orbital fissure
is located between the sphenoid bone, zygomatic bone, and maxilla.

5. Lacrimal fossa
is in the lacrimal bone.
Paranasal sinuses
are mucous membrane-lined cavities near the nasal cavity and are found within the frontal, sphenoid, ethmoid, and maxillary bones. The paranasal sinuses are lined with mucous membranes that are continous with the lining of the nasal cavity. Secretions produced by the mucous membranes of the paranasal sinuses drain into the nasal cavity. The paranasal sinuses lighten the mass of the skull and increase the surface area of the nasal mucosa to help moisten and cleanse inhaled air. In addition, paranasal sinuses serve as resonating (echo) chambers that intensify and prolong sounds, thereby enhancing the quality of the voice. The influence of the paranasal sinuses on your voice becomes obvious when you have a cold.

found only between skull bones, hold most skull bones together.
Coronal suture
unites the frontal bone and both parietal bones.
Sagittal suture
unites the two parietal bones on the superior midline of the skull. The sagittal suture is so named because in the infant, before the bones of the skull are firmly united, the suture and the fontanels (soft spots) associated with it resemble an arrow.

Lamboid suture
unites the two parietal bones to the occipital bone. This suture is so named because of its resemblance to the Greek letter lambda.
The two *squamous sutures*
unite the parietal and temporal bones on the lateral sides of the skull.
The paired *anterolateral fontanels*
located laterally between the frontal, parietal, temporal, and sphenoid bones, are small. Normally, they close about 3 months after birth.

The paired *posterolateral fontanels*
are located laterally between the parietal, occipital, and temporal bones. They begin to close 1 to 2 months after birth, but closure is generally not complete until 12 months.
Hyoid bone
is a unique component of the axial skeleton because it does not articulate with any other bone.

Rather, it is suspended from the styloid processes of the temporal bones by ligaments and muscles. The hyoid bone supports the tongue and provides attachment sites for some tongue muscles and for muscles of the pharynx and larynx. The hyoid bone consists of a body and paired projections called the lesser horns and the greater horns.

Vertebral column
also called the spine, makes up about two-fifths of your total height and is composed of a series of bones called *vertebrae* and connective tissue.

The ____, ____, and ____ form the skeleton of the trunk of the body.
vertebral column, sternum, and ribs
The ____ functions as a strong, flexible rod with elements that can rotate and move forward, backward,and sideways.
vertebral column
In addition to enclosing and protecting the spinal cord, the ____ supports the head, and serves as a point of attachments for the ribs, pelvic girdle, and muscles of the back and upper limbs.
vertebral column
The vertebral column is divided into five regions, superiorly to inferiorly:
cervical, thoracic, lumbar, sacral, and coccygeal.

As a child, you have 33 total ____, but as you grow, several ____ in the sacral and coccygeal regions fuse. As a result, the adult vertebral column typically contains 26 ____.
vertebrae, vertebrae, and vertebrae
7 cervical vertebrae
in the neck region (cervical means neck).
12 thoracic vertebrae
are posterior to the thoracic cavity.
5 lumbar vertebrae
support the lower back.
1 sacrum
consists of the five fused *sacral vertebrae*.

1 coccyx
consists of four fused *coccygeal vertebrae*.
The cervical, thoracic, and lumbar vertebrae are ____, but the sacrum and coccyx are not.
When viewed from the side, the adult vertebral column shows four slight bends called
normal curves.
The curves of the ____ column increase its strength, help maintain balance in the upright position, absorb shocks during walking, and help protect the vertebrae from fracture.

Intervertebral discs
are found between the bodies of adjacent vertebrae from the second cervical vertebra to the sacrum.
Each disc has an outer fibrous ring consisting of fibrocartilage called the ____ and an inner soft, pulpy, highly elastic substance called the ____.
annulus fibrosus and nucleus pulposus
The discs form strong joints, permit various movements of the ____ column, and absorb vertical shock. Under compression, they flatten and broaden. During the course of the day the discs compress so that we are a bit shorter at night. While we are sleeping there is less compression so that we are taller when we awaken in the morning. As we age, the nucleus pulposus hardens and becomes less elastic.

Decrease in vertebral height with age results from bone loss in the vertebral bodies and not a decrease in thickness of the intervertebral discs.

Intervertebral discs are ____.
avascular and rely on blood vessels from the bodies of vertebrae to obtain oxygen and nutrients and remove wastes.
The adult vertebral column typically contains ____ vertebrae.
____ typically consist of a vertebral body, a vertebral arch, and several processes.
The vertebral body
is the thick, disc-shaped anterior portion that is the weight-bearing part of a vertebra. Its superior and inferior surfaces are roughened for the attachment of intervertebral discs.

The anterior and lateral surfaces contain nutrient foramina through which blood vessels supply the osseous tissue.

Vertebral arch
Two short, thick processes, the *pedicles* (little feet), project posteriorly from the vertebral body and then unite with the flat *laminae* (thin layers) to from this.
Together, the vertebral body and the vertebral arch surround the spinal cord by forming the:
vertebral foramen
The vertebral foramen contains
the spinal cord, adipose tissue, areolar connective tissue, and blood vessels.
Collectively, the vertebral foramina of all vertebrae form the
vertebral canal
When the vertebrae are stacked on top of one another, they form an opening between adjoining vertebrae on both sides of the column that permits the passage of a single spinal nerve carrying information to and from the spinal cord. Each opening is called an ____.

intervertebral foramen
Seven ____ arise from the vertebral arch.
*processes* (a projection or outgrowth of tissue)
The five regions of the vertebral column, from superior to inferior are:
cervical, thoracic, lumbar, sacral, and coccygeal
The bodies of ____ vertebrae (C1 – C7) are smaller than all other vertebrae except those that form the coccyx.
All cervical vertebrae have three foramina:
one vertebral foramen and two transverse foramina.
The *atlas* (C1)
named after the mythological Atlas who supported the world on his shoulders, is the first cervical vertebra and supports the head. The atlas lacks a body and a spinous process. Instead, it consists of a ring of bone with anterior and posterior arches. The superior, lateral surfaces contain superior articular facets that articulate with the occipital condyles of the occipital bone.

These articulations permit you to move your head to signify “yes.”

The *axis* (C2)
the second cervical vertebra does have a body. A peglike process on the body, the dens (tooth), projects superiorly through the anterior portion of the vertebral foramen of the atlas. The dens makes a pivot on which the atlas and head rotate. This arrangement permits side-to-side movement of the head, as when you move your head to signify “no.”
The seventh cervical vertebra (C7)
called *vertebra prominens* has a single large spinous process that may be seen and felt at the base of the posterior neck.

Thoracic vertebrae
are considerably larger and stronger than cervical vertebrae. In addition, the spinous processes on T1 through T10 are long, laterally flattened, and directed inferiorly. In contrast, the spinous processes on T11 and T12 are shorter, broader, and directed more posteriorly. Compared to cervical vertebrae, thoracic vertebrae have longer transverse processes.

The most distinguishing feature of ____ vertebrae is that they articulate with the ribs.
The bodies of thoracic vertebrae have either ____ or ____ (half facets) that articulate with the heads of the ribs, and their transverse processes have facets that articulate with the tubercles of the ribs..
facets or demifacets.

Movements of the ____ region are limited by the attachment of the ribs to the sternum.
The *lumbar vertebrae*
are the largest and strongest of the unfused bones in the vertebral column because the amount of body weight supported by the vertebrae increases toward the inferior end of the spine. Their various projections are short and thick. The spinous processes are well adapted for the attachment of the large back muscles.
is a triangular bone formed by the union of the five sacral vertebrae. The sacral vertebrae begin to fuse between ages 16 and 18; this process is usually completed by age 30. The sacrum serves as a strong foundation for the pelvic girdle. The accommodate pregnancy and childbirth, the female sacrum is shorter, wider, and more curved than the male sacrum.

like the sacrum, is triangular in shape. It is formed by the fusion of four coccygeal vertebrae as Co1-Co4. The coccygeal vertebrae fuse between the ages of 20 and 30. In females, the coccyx points inferiorly to allow the passage of a baby during birth; in males, it points anteriorly.
refers to the entire chest region.
Thoracic cage
is the skeletal part of the thorax. It is a bony enclosure formed by the sternum, ribs, and their costal ccartilages, and the bodies of the thoracic vertebrae. The thoracic cage is narrower at its superior end and broader at its inferior end.

The thoracic cage encloses and protects the organs in the thoracic and superior abdominal cavities, provides support for the bones of the upper limbs and plays a role in breathing.

or breastbone, is a flat, narrow bone located in the center of the anterior thoracic wall that measures about 15 cm (6 inches) in length and consists of three parts.
The three parts of the sternum:
1. Manubrium, 2. Body, 3.

Xiphoid process

1. Manubrium
(handlelike.) The superior part
2. Body
The middle and largest part.

3. Xiphoid process
the inferior and smallest part.
The parts of the ____ typically fuse by age 25, and the points of fusion are marked by transverse ridges.
There are twelve pairs, numbered 1 – 12 from superior to inferior.

They give structural support to the side of the thoracic cavity. The ribs increase in length from the first through the seventh, and then decrease in length to the twelfth rib.

The first through seventh pairs of ribs have a direct anterior attachment to the sternum by a strip of hyaline cartilage called ____ cartilage.
costal. The costal cartilages contribute to the elasticity of the thoracic cage to allow breathing and to prevent various blows to the chest from fracturing the sternum and/or ribs.

The ribs that have costal cartilages and attach directly to the sternum are called ____ ribs.
The remaining five pairs of ribs are termed ____ ribs because their costal cartilages either attach indirectly to the sternum or do not attach to the sternum at all. The cartilages of the eighth, ninth, and tenth pairs of false ribs attach to one another and then to the cartilages of the seventh pair of ribs.
The eleventh and twelfth false ribs are also known as ____ ribs because the costal cartilage at their anterior ends does not attach to the sternum at all. ____ ribs attach only posteriorly to the thoracic vertebrae.

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