Chapter 7 Objectives

1. Define the components of the axial and appendicular skeleton.
2. Identify the sutures: coronal, sagittal, lambdoidal, squamosal.
3. Define fontanels, cranial vault, cranial floor.
4. Identify all the bones of the skull listed in your handout and any unique facts about them.
5. Identify the purpose and location of the following structures: foramen magnum, occipital condyles, external auditory meatus, sella turcica, crista galli, cribriform plate, mandibular condyles.
6. Identify the purpose and location of the hyoid bone.
7. Describe the bones of the pelvic girdle and lower limb and any unique facts about them.
8. Identify the purpose and location of the following structures: acetabulum, ala, obturator foramen, femoral condyles, lateral malleolus.
9. Describe the general characteristics of the vertebral column: number of vertebrae in each section, fibrocartilage discs, anterior and posterior ligaments (and what they do).
10. Label the general structure of a typical vertebra: body, arch, foramen, pedicles, laminae, processes (spinous, transverse, superior and inferior articular).
11. Identify the atlas and axis (also dens) and describe their functions.
12. Describe how ribs articulate with thoracic vertebrae.
13. Identify the sacrum and coccyx. Describe unique features and function of the sacrum.
14. Identify elements forming the bony thorax.
15. Identify sternum and its 3 regions. Describe how the sternum articulates with the clavicles.
16. Describe ribs: 12 pair, true ribs, false ribs, floating ribs, tubercle, head.
17. Distinguish between sternoclavicular and acromioclavicular joints.
18. Describe the bones of the pectoral girdle and upper limb and any unique facts about them.

SKELETAL SYSTEM

The skeletal structure is strong, yet light and is almost perfectly adapted for the protective, locomotor, and manipulative functions it performs. The skeleton is composed of bones, cartilage, joints, and ligaments and accounts for about 20% of body mass, weighing about 30 pounds in a 160 pound man. There are 206 bones in the human skeleton and they are divided into the axial and appendicular skeleton. The axial skeleton forms the long axis of the body and includes the bones of the skull, vertebral column, and rib cage. The appendicular skeleton consists of the bones of the upper and lower limbs and the girdles that attach the limbs to the axial skeleton.

Classification: Almost all the bones of the body may be classified into four principal types on the basis of shape: long bones, short bones, flat bones, and irregular bones

Surface Markings: The surface of bones reveal various structural features adapted to specific functions. Long bones have rounded ends for forming sturdy joints. They provide adequate surface area for ligaments and muscle attachment. Other bones have depressions that receive rounded ends.Rough areas serve as points for attachment of muscles, tendons, and ligaments. Grooves provide for passage of blood vessels.Openings occur where blood vessels and nerves pass through the bone.

Divisions of the Skeletal System:
Axial Division:
Skull: 22 bones. Rests on the superior end of the vertebral column.
Two sets of bones: cranial - 8 bones and facial - 14 bones
Cranial bones include: frontal parietal (2), temporal (2), occipital, sphenoid, ethmoid
Facial bones include: nasal (2), maxillae (2), zygomatic (2), mandible (2), lacrimal (2), palatine (2), inferior nasal conchae (2), vomer
Sutures: "seam" unmovable joint found only between skull bones. Four prominent sutures: coronal, sagittal, lambdoidal, squamosal
Fontanels: at birth, membrane filled spaces are found between the cranial bones. These "soft" spots are areas of dense connective tissue that will eventually be replaced by bone. They function to enable the fetal skull to compress during birth and permit the rapid growth of the brain.

Overview of the Skull:

With the lower jaw removed, the skull resemble a lopsided, hollow, bony sphere. Facial bones fond the anterior aspect; the cranium forms the rest. Cranium is divided into the cranial vault forming the top, sides, and back of the skull, and the cranial floor. Internally, prominent bony ridges divided the base into three distinct fossae: anterior, middle, and posterior. The brain sits snugly into these three fossae. The skull has about 85 named openings, the most important are: openings for the spinal cord, major blood vessels, and cranial nerves.

Cranium: 8 bones - strong, yet light weight. Protects the brain.

Frontal Bone: Anterior portion - forehead. Forms the roofs of the orbits. Anterior portion of the cranial floor.Attached to the parietal bones via the coronal suture.Thickened.Extends posteriorly forming the anterior cranial fossae which supports the frontal lobes of the brain.

Parietal Bones: Forms most of the top and superolateral sides of the skull.4 major sutures occur where the parietal bones join with the other cranial bones. Coronal suture - parietal meet frontal bones anteriorly Sagittal suture - 2 parietal bones meet at midline Lambdoidal suture - parietal meet occipital bones posteriorly Squamous suture - parietal and a temporal bone meet on the lateral aspect of the skull

Occipital Bone: Attaches anteriorly with the paired parietal and temporal bones. Joins with the sphenoid bone in the cranial floor.Forms most of the posterior wall and base of the skull externally. Internally forms the walls of the posterior cranial fossa. Base is the foremen magnum (large hole) passage way for the spinal cord. Foramen magnum is flanked laterally by 2 occipital condyles -articulates with the atlas (l st vertebra).

Temporal Bones:Lie inferior to the parietal.Meet at the squamous suture. Form the inferolateral aspects of the skull and part of the cranial floor. 4 regions: squamous - helps form zygomatic arch, tympanic - attaches to the mandible, mastoid - external auditory meatus, petrous - forms part of middle cranial fossa.

Sphenoid Bone: Spans the width of the cranial floor. Considered the keystone of the cranium. Central wedge - articulates with all other cranial bones. Consists of a central body and 3 pairs of processes: greater wings, lesser wings, paired pterygoid processes. Greater wings form part of middle cranial fossa. Sella Turcica - holds pituitary gland. Lesser wings forms part of anterior cranial fossa. Pterygoid processes form part of the lateral walls of nasopharynx.

Ethmoid Bone: Deeply hidden. Forms most of the bony area between nasal cavity & the orbits. Projection - "crista galli" - outer most covering of the brain attaches and helps secure the brain in cranial cavity. Cribriform plate forms part of the nasal septum.

Facial Bones: 14 bones. Mandible and vomer are the only bones unpaired. General rule - male facial bones are more elongated, female faces tend to be rounder, less angular.

Mandible: U-shaped. Lower jaw. Largest and strongest of the facial bones. Body forms the chin. 2 upright rami - each meets the body at the mandibular angle. Mandibular condyle - articulates with the mandibular fossa of the temporal bone.

Maxillary Bones: Fused medially. Form upper jaw and central portion of face. All facial bones except the mandible articulate with the maxillae - Keystone bone. Carry the upper teeth. Articulate with the zygomatic bones laterally via the zygomatic processes.

Zygomatic Bones: Cheekbones. Articulate with the zygomatic processes of the temporal bones posteriorly and with the zygomatic processes of the maxillae anteriorly.

Nasal Bones: Thin, rectangular bones fused medially forming the bridge of the nose. Articulate with the frontal bones.

Lacrimal Bones: Minor contribution to the medial wall of each orbit. Part of the passage way that permits tears to drain from the eye surface into the nasal cavity.

Hyoid Bone:Not really part of the skull. Only bone of the body that does not articulate directly with any other bone. Suspended in the midneck region. Horse-shoe shaped. Serves as a movable base for the tongue and attachment points for neck muscles that raise and lower the larynx during swallowing and speech.

Vertebral Column:

General Characteristics: Makes up about 215 of the total height of the body. Average adult male - column is 71 cm Average female - column is 61 cm. Strong flexible rod. Encloses the spinal cord, supports the skull, serves as point of attachment for the ribs and back muscles. 26 vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, 4 coccygeal. Between vertebrae are intervertebral discs composed of an outer fibrous ring of fibrocartilage and an inner soft pulpy elastic material. The discs form strong joints, permit various movements and absorbs vertical shock. Under compression they flatten, broaden and bulge. Accounts for 25% of the column length. Anterior and posterior ligaments run as continuous bands down the anterior and posterior surface of the spine from the neck to the sacrum. The anterior ligament is strongly attached to both the bony vertebrae and the discs. Very important in preventing hyperextension of the spine. Posterior ligament prevents hyperflexion. It is narrow and relatively weak. Attached only to the discs. Vertebral column as viewed from the side has 4 characteristic curvatures that give it its shape: cervical & lumbar - concave posteriorly, thoracic & sacral- convex posteriorly. Increases strength and flexibility. Makes the spine function like a spring.

General Structure: All vertebrae have a common structural pattern. Discoid weight-bearing body and vertebral arch. Body and arch together enclose the vertebral foramen. Vertebral arch - composite structure formed by 2 pedicles and 2 laminae.

7 processes project from the arch:

Cervical Vertebrae: C1 - C7 Smallest and lightest First two are atypical. Features: Body is broader from side to side. Except C7 the spinous process is short and projects directly back and is split at its tip (bifid). Vertebral foramen are large and generally triangular. C7 spinous process is not bifid, and larger. Used as a landmark for counting vertebra. "Vertebra Prominens"
Atlas: C1. Highly modified. Has no body or spinous process. Essentially a ring of bone consisting of anterior and posterior arches and a lateral mass on each side containing articular facets to receive the occipital condyles.
Axis: C2. Projecting superiorly from the body is a tooth-like process called the dens. Acts as a pivot for the rotation of the atlas

ThoracicVertebrae: T1 - T12. Articulate with the ribs. Increase in size from the first to the last. Body is roughly heart-shaped. 2 demifacets on each side articulate with the head of the rib. Vertebral foremen is circular. Spinous process - long and hooks sharply downward. Transverse processes (1-10) have facets mat articulate win the tubercles of the ribs.

Lumbar Vertebrae: L1 - L5. Largest and strongest. Enhanced weight bearing function. Bodies are massive and kidney shaped. Spinous processes are short, flat and hatchet shaped. Vertebral foremen is triangular. Articular processes lock the lumbar vertebrae together and provide stability by preventing rotation of the lumbar spine.

Sacrum: Triangular bone formed by fission of 5 sacral vertebrae. Shapes posterior wall of the pelvis. Strengthens and stabilizes the pelvis. Articulates superiorly with Ls and inferiorly with the coccyx. Two wing-like alae articulate with the 2 hip bones to form the sacroiliac joints.

Coccyx: 3-5 fused vertebrae. Forms a small triangular bone. Muscle attachment site.

Thorax:
General: Chest. Elements forming the bony thorax include: thoracic vertebrae dorsally, ribs laterally, sternum and costal cartilages anteriorly. Forms a protective cage around vital organs. Supports the shoulder girdles and upper limbs. Provides attachment for the muscles. Intercostal spaces occupied by intercostal muscles which elevate and depress the thorax during breathing.

Sternum: Breastbone. Midline of thorax. Consists of three regions: manubrium, body, xiphoid process. Manubrium articulates with the clavicles. Body forms the bulk of the sternum. Xiphoid serves as the attachment point for the diaphragm and some abdominal muscles.

Ribs: 12 pair. All attached posteriorly to the thoracic vertebrae, then curve down and forward toward the anterior. Upper 7 pair attach directly to the sternum (true ribs). Other 5 pair (false ribs) either attach indirectly to the sternum or lack a sternal attachment entirely. Ribs 11 and 12 are floating ribs. Ribs gradually increase in length from the first to 7th pair. Pairs 8-12 decrease in length. Typical rib is a bowed flat bone. Bulk of the rib is the shaft. Wedged shaped head has two facets. The neck of the rib is the constricted portion. Lateral to the head is the knoblike tubercle that articulates with the transverse process of the thoracic vertebrae.

Appendicular Skeleton:
General:

Bones hang suspended from bony girdles anchored to the axial skeleton. Appended to the longitudinal axis of the body Pectoral girdle attach the upper limbs. Pelvic girdle attach the lower limbs. Each 1imb is composed of 3 major segments connected together by freely movable joints. Appendicular skeleton functions in movement and manipulation.

Pectoral Girdle: Consists of two bones: clavicle (anterior side), scapula (posterior side). 2 girdles plus their muscles form the shoulders. Anteriorly the medial end of each clavicle joins the sternum -- the distal ends meet the scapulae laterally. Pectoral girdles provide insertion points for many muscles. Girdles are very light and allow the upper limb a high degree of flexibility and mobility. Only attachment point of the pectoral girdles to the axial skeleton is at the sternoclavicular joints anteriorly. The socket of the shoulder joint is small and shallow and poorly reinforced by ligaments. Good for flexibility but poor for stability.

Clavicles: Collar bones. Slender, doubly curved long bones. Extend horizontally across the upper thorax. Clavicles act as braces anteriorly. They hold out the scapulae and their limbs away from the upper, narrower portion of the thorax. Exceptionally sensitive to muscle pull and become noticeably larger and stronger in those performing manual labor.

Scapulae: Shoulder blades. Flattened triangular bones. 3 borders: superior border - shortest & sharpest border, Vertebral border - parallels vertebral column, Lateral border - abuts with armpit. Has shallow fossa (glenoid cavity) articulates with humerus of arm. The lateral aspect of the scapulae ends in the anterior projection - acromion - which articulates with the clavicle forming the acromioclavicular joint which is crucial in attaching the upper limb to the body.

Upper limb:
General: 30 separate bones. Comprises the arm, forearm and the hand.
Arm: Part of the upper limb between the shoulder and elbow.


Humerus - sole bone. Typical long bone. Articulates with the scapula at the shoulder & radius & ulna at elbow. Proximal end (head) fits into the glenoid cavity. Distal end has 2 condyles that articulate with the ulna arid radius respectively.


Forearm: Radius and ulna - 2 parallel bones. Proximally they articulate with the humerus.Distal end forms the joints with the bones of the wrist. Both articulate with each other at small radioulner joints.Connected lengthwise by an interosseous membrane.

Ulna: Slightly longer. Forms the elbow joint with the humerus. Shaft is triangular and ridged. Proximal end articulates with the humerus. Distal ulnar head is separated from the bones of the wrist by a fibrocartilage disc.

Radius: Triangular. Articulates with the humerus and ulna proximally. Distally it articulates with the carpal bones of the wrist. Major forearm bone contributing to the wrist joint. When the radius moves the hand moves with it.

Hand: Carpus - wrist. Metacarpals - palm. Phalanges - fingers

Pelvic Girdle: Hip girdle. Attaches the lower limbs to the axial skeleton. Transmits upper body weight to the lower limbs. Supports the visceral organs. Secured to the axial skeleton by some of the strongest ligaments in the body. Sockets are deep and cuplike and heavily reinforced by ligaments. Formed by a pair of coxal bones (ossa coxae) - hip bones. Each coaxal bone unites with its partner anteriorly and with the sacrum posteriorly. Deep basin structure formed - bony pelvis. Each large coaxal bone consist of 3 separate bones: ilium, ischium, pubis. Fused in adults forming a deep socket - acetabulum -which articulates with the head of the femur.

Ilium: Large flaring bone forming the major portion of the coxal bone. Winglike portion is called the ala. Thickened superior margin of the ala - iliac crest.

Ischium: Roughly L- or arc shaped. Upper thicker part attaches to the ilium. Lower thinner ramus joins the pubis.

Pubis: Pubic bone. Forms the anterior portion of the os coxa. Opening formed by the pubic rami and the ischial rami is the obturator foremen. Bodies of the 2 pubic bones are joined by fibrocartilage disc forming the pubic symphysis.

Thigh: Lower limbs carry entire weight of the erect body. Thicker and stronger bones. Bones specialized for stability and weight bearing.

Femur is the single thigh bone. Largest, longest and strongest. Clothed by bulky muscles. Length is about 1/4 of persons height. Proximally articulates with the hip bone - acetabulum. Articulates with the knee. Head is carried on a short neck that angles laterally to join the shaft. Neck is the weakest part of the femur. Distally the femur articulates with the tibia. Smooth patellar surface between the condyles (anterior) articulates with the patella.

Lower 2 parallel bones - tibia and fibula. Connected by interosseous membrane. Articulate with each other proximally and distally. Tibiofibular joints of the leg allows for essentially no movement. Bones are less flexible but stronger and more stable. Larger tibia articulates with the femur to form the hinge joint of the knee and distally with the talus bone of the foot.

Tibia: Shinbone. Receives weight of the body from the femur and transmits it to the foot. Except for the femur, tibia is the largest and strongest bone. Broad proximal end articulate with the femur condyles.

Fibula: Non-weight bearing bone. Sticklike with slightly expanded ends. Articulates proximally and distally with the tibia. Upper end is the head; lower end is the lateral malleolus -ankle bone.

Foot: Tarsals, Metatarsals, Phalanges. 2 important functions: supports body weight, acts as a lever to propel the body forward. Body weight is carried primarily by the 2 largest posterior tarsals: talus - articulates with tibia and fibula and the calcaneus - heel The enlarged part of the metatarsals (head) forms the ball of the foot.