Chapter 7: The Skeletal System: The Axial Skeleton

Chapter 7:The Skeletal System: The

Axial Skeleton

Copyright 2009, John Wiley & Sons, Inc.

The Skeletal System: The Axial SkeletonChapter 7n Divisions of the Skeletal Systemn Types of Bonesn Bone Surface Markingsn Skulln Hyoid Bonen Vertebral Columnn Thorax


Divisions of the Skeletal Systemn The human skeleton consists of 206 named bonesn Bones of the skeleton are grouped into two principal

divisions:q Axial skeleton

n Consists of the bones that lie around the longitudinal axis of the human body

n Skull bones, auditory ossicles (ear bones), hyoid bone, ribs, sternum (breastbone), and bones of the vertebral column

q Appendicular skeletonn Consists of the bones of the upper and lower limbs

(extremities), plus the bones forming the girdles that connect the limbs to the axial skeleton

Divisions of the Skeletal System

Divisions of the Skeletal System


n Bones can be classified into five types based on shape:

n Longn Shortn Flatn Irregularn Sesamoid

Types of Bones


Types of Bones

n Long Bonesq Greater length than width and are slightly curved for strengthq Femur, tibia, fibula, humerus, ulna, radius, phalanges

n Short bonesq Cube-shaped and are nearly equal in length and widthq Carpal, tarsal

n Flat bonesq Thin and composed of two nearly parallel plates of compact

bone tissue enclosing a layer of spongy bone tissueq Cranial, sternum, ribs, scapulae

n Irregular bonesq Complex shapes and cannot be grouped into any of the

previous categoriesq Vertebrae, hip bones, some facial bones, calcaneus

n Sesamoid bonesq Protect tendons from excessive wear and tearq Patellae, foot, hand

n Sutural bonesq Small bones located in sutures of cranial bones



Bone Surface Markingsn Bones have characteristic surface markings

q Structural features adapted for specific functions

n There are two major types of surface markings:q 1) Depressions and openings

n Allow the passage of blood vessels and nerves or form joints

q 2) Processesn Projections or outgrowths that form joints or serve as

attachment points for ligaments and tendons


Skulln Skull (cranium)n Consists of 22 bonesn Bones of the skull are grouped into two

categories:q Cranial bones

n Eight cranial bones form the cranial cavityq Frontal bone, two parietal bones, two temporal bones, the

occipital bone, the sphenoid bone, ethmoid boneq Facial bones

n Fourteen facial bones form the faceq Two nasal bones, two maxillae, two zygomatic bones, the

mandible, two lacrimal bones, two palatine bones, two inferior nasal conchae, vomer


Skull

Skulln The cranial and facial bones protect and support

special sense organs and the brainn Besides forming the large cranial cavity, the skull

also forms several smaller cavitiesq Nasal cavityq Orbits (eye sockets)q Paranasal sinuses q Small cavities which house organs involved in hearing

and equilibrium


Skulln Immovable joints called sutures fuse most of the

skull bones togethern The skull provides large areas of attachment for

muscles that move various parts of the headn Skull and facial bones provide attachment for

muscles that produce facial expressionsn The facial bones form the framework of the face

and provide support for the entrances to the digestive and respiratory systems

Skull (Cranial Bones)n Frontal Bone

q Forms the foreheadn Parietal Bones

q Form the sides and roof of the cranial cavityn Temporal Bones

q Form the lateral aspects and floor of the craniumn Occipital Bone

q Forms the posterior part and most of the base of the craniumn Sphenoid Bone

q Lies at the middle part of the base of the skulln Ethmoid Bone

q Located on the midline in the anterior part of the cranial floor medial to the orbits

q A major superior supporting structure of the nasal cavityq Contain thin projections called conchae which are lined by

mucous membranesq Increased surface area in the nasal cavity helps to humidify

inhaled air trapping inhaled particles

Skull

Skull

Skull

Skull (Facial Bones)n Nasal Bones

q Form the bridge of the nosen Maxillae

q Form the upper jawboneq Form most of the hard palate

n Separates the nasal cavity from the oral cavityn Zygomatic Bones

q commonly called cheekbones, form the prominences of the cheeks

n Lacrimal Bonesq Form a part of the medial wall of each orbit

n Palatine Bonesq Form the posterior portion of the hard palate

n Inferior Nasal Conchaeq Form a part of the inferior lateral wall of the nasal cavity

Skull (Facial Bones)n Vomer

q Forms the inferior portion of the nasal septumn Mandible

q Lower jawboneq The largest, strongest facial boneq The only movable skull bone

n Nasal Septumq Divides the interior of the nasal cavity into right and left sidesq “Broken nose,” in most cases, refers to septal damage rather

than the nasal bones themselvesn Orbits

q Eye socketn Foramina

q Openings for blood vessels , nerves , or ligaments of the skull

Skull

Skull


Skull

Skull


Skull


Skulln Unique Features of the Skull

q Sutures, Paranasal sinuses, Fontanelsn Sutures

q an immovable joint that holds most skull bones togethern Paranasal Sinuses

q Cavities within cranial and facial bones near the nasal cavityq Secretions produced by the mucous membranes which line the

sinuses, drain into the nasal cavityq Serve as resonating chambers that intensify and prolong sounds

n Fontanelsq Areas of unossified tissueq At birth, unossified tissue spaces, commonly called “soft spots”

link the cranial bonesq Eventually, they are replaced with bone to become suturesq Provide flexibility to the fetal skull, allowing the skull to change

shape as it passes through the birth canal


Skull


Skull

Hyoid Bonen Does not articulate

with any other bonen Supports the tongue,

providing attachment sites for some tongue muscles and for muscles of the neck and pharynx

n The hyoid bone also helps to keep the larynx (voice box) open at all times


Vertebral Columnn Also called the spine, backbone, or spinal

columnn Functions to:

q Protect the spinal cordq Support the headq Serve as a point of attachment for the ribs, pelvic

girdle, and musclesn The vertebral column is curved to varying

degrees in different locationsq Curves increase the column strengthq Help maintain balance in the upright positionq Absorb shocks during walking, and help protect the

vertebrae from fracture


Vertebral Column


Vertebral Columnn Various conditions may exaggerate the normal

curves of the vertebral columnq Kyphosisq Lordosisq Scoliosis

n Composed of a series of bones called vertebrae (Adult=26)q 7 cervical are in the neck regionq 12 thoracic are posterior to the thoracic cavityq 5 lumbar support the lower backq 1 sacrum consists of five fused sacral vertebraeq 1 coccyx consists of four fused coccygeal vertebrae

Vertebral Column


Vertebral Column (Intervertebral Discs)n Found between the bodies of adjacent

vertebraen Functions to:

q Form strong jointsq Permit various movements of the vertebral

columnq Absorb vertical shock

n Vertebrae typically consist of:q A Body (weight bearing)q A vertebral arch (surrounds the spinal cord)q Several processes (points of attachment for

muscles)

Vertebral Column

Vertebral Column (Regions)n Cervical Region

q Cervical vertebrae (C1–C7)q The atlas (C1) is the first cervical vertebraq The axis (C2) is the second cervical vertebra

n Thoracic Regionq Thoracic vertebrae (T1–T12)q Articulate with the ribs

n Lumbar Regionq Lumbar vertebrae (L1–L5)q Provide for the attachment of the large back muscles

n Sacrumq The sacrum is a triangular bone formed by the union of five sacral

vertebrae (S1–S5)q Serves as a strong foundation for the pelvic girdle

n Coccyxq The coccyx, like the sacrum, is triangular in shapeq It is formed by the fusion of usually four coccygeal vertebrae

Vertebral Column

Vertebral Column

Vertebral Column

Vertebral Column

Vertebral Column


Thoraxn Thoracic cage is formed by the:

q Sternumq Ribsq Costal cartilagesq Thoracic vertebrae

n Functions to:q Enclose and protect the organs in the thoracic

and abdominal cavitiesq Provide support for the bones of the upper

limbsq Play a role in breathing


Thoraxn Sternum

q “Breastbone” located in the center of the thoracic wall

q Consists of the manubrium, body, xiphoid process

n Ribsq Twelve pairs of ribs give structural support to

the sides of the thoracic cavityn Costal cartilages

q Costal cartilages contribute to the elasticity of the thoracic cage

Vertebral Column

Vertebral Column

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Chapter 7: The Skeletal System: The Axial Skeleton