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Human Anatomy, First Edition

McKinley & O'Loughlin

Chapter 7 Lecture Outline:

Axial Skeleton

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Skeletal System

The bones of the skeleton form an internal framework to support soft tissues, protect vital organs, bear the body’s weight, and help us move.

Typically, there are 206 bones in an adult skeleton, although this number varies in some individuals.

A larger number of bones are present at birth, but the total number decreases with growth and maturity as some separate bones fuse.

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Skeletal System

The axial skeleton is composed of the bones along the central axis of the body,

1. the skull

2. the vertebral column

3. the thoracic cage

4. Hyoid

The appendicular skeleton consists of the bones of the appendages

1. upper and lower limbs

2. the bones that hold the limbs to the trunk of the body.

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The Skull

1. Cranial bones form the

rounded cranium, which

completely surrounds

and encloses the brain.

2. Facial bones form the

bones of the face. They

also

• protect the entrances

to the digestive and

respiratory systems as

well as

• provide attachment

sites for facial muscles

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The Mandible

The lower jaw is formed by the mandible.

The prominent “chin” of the mandible is called the mental protuberance.

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Cavities of

The Skull – The largest cavity

is the cranial

cavity, which

encloses,

cushions, and

supports the brain.

– The skull also has

several smaller

cavities, including

the orbits (eye

sockets), the oral

cavity (mouth), the

nasal cavity, and

the paranasal sinuses.

Cavity (space) in bone.

F= Frontal sinuses;

E=Ethmoid sinuses;

M=Maxillary sinuses

• the maxillary sinuses, are

under the eyes, in the

maxillary bones.

• the ethmoidal sinuses,

between the nose and the

eyes.

• the sphenoidal sinuses, in

the sphenoid bone.

behind the ethmoids

(sphenoidal sinuses

• the frontal sinuses,

superior to the eyes, in

the frontal bone.

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Markings of the Skull

Numerous bone markings

canals

fissures

foramina

passageways for blood vessels and nerves

Foramen – Opening or Cavity that provides a passageway for nerves or blood vessels.

Foramen transversarium in the cervical vertebrae

Foramen obturator in the Os Coxa (hip)

Skull Base Anatomical Landmarks:

Foramen magnum

Fissure – Narrow slit.

The slits you see are the Superior Orbital Fissures in the Eye Socket

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Fontanels • The regions between the

cranial bones are thickened,

fibrous membrane remnants

that are not yet ossified.

• Sometimes referred to as

the “soft spots” on a baby’s

head.

• They close by 15 months of

age.

• When a baby travels

through the birth canal, the

cranial bones overlap at

these fontanels, in order to ease the baby’s passage.

• Newborns frequently have a

“cone-shaped” head due to this temporary deformation.

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(craniosynostosis) of the lambdoid suture. Notice the swelling on the right side of the head

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Sutures of the Skull

• Sutures are immovable fibrous joints that form the boundaries between the cranial bones.

• Dense regular connective tissue seals cranial bones firmly together at a suture.

• Allow the cranium to grow and expand during childhood.

• In adulthood, when cranial growth has stopped, the sutures fuse and are obliterated(destroyed)

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The sphenoid bone is an unpaired cranial bone situated at the front middle of the skull in front of the temporal bone and basilar part of the occipital bone.

The sphenoid bone is one of the seven bones that articulate to form the orbit.

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Insert Fig. 7.9 superior view of skull

The sphenoid bone has median portion, known as the body of sphenoid bone, containing the sella turcica, which houses the pituitary gland as well as the paired paranasal sinuses, the sphenoidal sinuses two greater wings and two lesser wings.

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The sphenoid bone shape somewhat resembles that of a butterfly or bat with its wings extended

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The ethmoid bone from Greek ethmos, "sieve") is a bone in the skull that separates the nasal cavity from the brain. It is located at the roof of the nose, between the two orbits.

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The ethmoid has three parts: the cribriform plate, the ethmoidal labyrinth, and the perpendicular plate

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the zygomatic bone (cheekbone, malar bone) is a paired bone which articulates with the maxilla, the temporal bone, the sphenoid bone and the frontal bone.

part of the lateral wall and floor of the orbit

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The vomer is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones. The vomer forms the posterior part of the nasal septum.

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Palatine bone

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upper palate of mouth or maxilla:two halves that are fused at the intermaxillary suture to form the upper jaw.

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the mandible, lower jaw or jawbone

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Sinuses

Have a mucous lining that helps to humidify and warm inhaled air.

Cause these skull bones to be lighter.

Provide resonance to the voice.

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The following bones Superior margin: frontal bone Inferior margin: maxilla, palatine and zygomatic Medial margin: frontal, lacrimal and ethmoid Lateral margin: zygomatic and sphenoi

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Auditory Ossicles

Three tiny ear bones called auditory ossicles are housed within the temporal bone.

the malleus

the incus

the stapes

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Hyoid Bone

Slender, curved bone located inferior to the skull between the mandible and the larynx (voice box).

Does not articulate with any other bone in the skeleton.

Serves as sites for attachment for tongue and larynx muscles and ligaments.

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The Vertebral Column

• Composed of 26 bones, including

– 24 individual vertebrae and the

– fused vertebrae that form both the sacrum and the coccyx

C- Vertebral column.

• Vertebral column

consists of vertebrae

• Cervical vertebrae,

they are 7 in number,

• Thoracic vertebrae,

they are 12

• Lumber vertebrae,

they are 5 in number

• Sacral vertebrae

(sacrum), 5 fused

• Coccygeal vertebrae

3 or 4 united

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The vertebral column has several functions:

1. Providing vertical support for the body

2. Supporting the weight of the head

3. Helping to maintain upright body position

4. Helping to transfer axial skeletal weight to the appendicular skeleton of the lower limbs

5. Housing and protecting the delicate spinal cord and providing a passageway for spinal nerves connecting to the spinal cord

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Between each vertebra is an intervertebral disk, which acts as a shock absorber.

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Atlas: the 1st cervical vertebra has no body, and this is due to the fact that the body of the atlas has fused with that of the next vertebra

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The movement of shaking or rotating the head left and right happens almost entirely at the joint between the atlas and the axis, the atlanto-axial joint.

The movement of nodding the head takes place predominantly through flexion and extension at the joint between the atlas and the occipital bone, the atlanto-occipital joint.

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(sacrum 5 fused bodies united by four intervertebral disk;

Coccygeal vertebrae (coccyx), triangular tail bone united with sacrum by intervertebral disk (embryonic tail).

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Three Main Spinal Curvature

Deformities

Kyphosis is an exaggerated thoracic curvature that is directed posteriorly, producing a “hunchback” look.

Lordosis is an exaggerated lumbar curvature, often called “swayback,” that is observed as a protrusion of the abdomen and buttocks.

Scoliosis is an abnormal lateral curvature that sometimes results during development when both the vertebral arch and body fail to form, or form incompletely, on one side of a vertebra.

scoliosis is the most common spinal curvature deformity.

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B- Thorax / (bony thorax).

The rib cage or consists of:

A. 12 thoracic vertebral bodies posteriorly,

B. 12 pairs of ribs laterally

C. sternum (1) anteriorly.

Posterior View Of Ribs & Articulating Vertebrae

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Thoracic Cage

Acts as a protective cage around vital organs, such as the heart, lungs, trachea, and esophagus.

Provides attachment points for many muscles supporting the pectoral girdles, the chest, the neck, the shoulders, the back, and the muscles involved in respiration.

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Ribs

• Both males and females 12

pairs

– Ribs 1–7 are called true ribs.

At the anterior body wall, the

true ribs connect individually

to the sternum by separate

cartilaginous extensions

called costal cartilages.

– Ribs 8–12 are called false ribs

because their costal cartilages

do not attach directly to the

sternum. The costal cartilages

of ribs 8–10 fuse to the costal

cartilage of rib 7 and thus

indirectly articulate with the sternum.

– The last two pairs of false ribs

(ribs 11 and 12) are called

floating ribs because they

have no connection with the sternum.

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