Chapter 7: The Skeleton
Occipital condyles - Occipital Bone
- rockerlike. - articulate with the first vertebra of the spinal column in a way that permits a nodding motion of the head.
how many bones make up the axial skeleton?
80
The skull also has about (blank) named openings
85. - provide passageways for the spinal cord, major blood vessels serving the brain and the 12 pairs of cranial nerves which transmit information to and from the brain.
Check Your Understanding - What is the major shortcoming of the flexibility allowed by the shoulder joint?
A consequence of its flexibility is that it is easily dislocated.
Posterior sacral foramina of sacrum
- flank the median sacral crest laterally. - transmit the posterior rami of the sacral spinal nerves.
Most skull bones are (blank) bones
- flat. - except for the mandible, which is connected to the rest of the skull by freely movable joints, all bones of the adult skull are firmly united by interlocking joints called sutures. - the suture lines have a saw-toothed or serrated appearance.
Anterior sacral foramina of sacrum
- lie at the lateral ends of these ridges and transmit blood vessels and anterior rami of the sacral spinal nerves.
Inferior orbital fissure of maxilla
- located deep within the orbit at the junction of the maxilla with the greater wing of the sphenoid. - permits the zygomatic nerve, the maxillary nerve and blood vessels to pass to the face.
Facial Bones
- made up of 14 bones. - mandible and vomer: unpaired. - maxillae, zygomatics, nasals, lacrimals, palatines, inferior nasal conchae: paired. - facial skeleton of men is more elongated than that of women.
The body of sternum
- midportion. - forms the bulk of the sternum. - sides of the body are notched where it articulates with the costal cartilages of the 2nd-7th ribs.
What are thin and remarkably strong for their weight?
cranial bones
The roof of the nasal cavity is formed by the
cribriform plates of ethmoid bone
What is formed by the cranium and facial bones?
skull
Wht is the body's most complex bony structure?
skull
Check Your Understanding - Women with prominent (high) cheekbones are often considered beautiful by the modeling industry. What bones are the "cheekbones"?
zygomatic bones
How many cranial and facial bones are there?
22
Each scapula has three borders
1. Superior- the shortest, sharpest border. 2. Medial/Vertebral - parallels the vertebral column. 3. Thick lateral, or axillary, border - abuts the armpit. This cavity articulates with the humerus of the arm, forming the shoulder joint.
Like all triangles, the scapula has three corners or angles.
1. The superior scapular border meets the medial border at the superior angle the lateral border at the lateral angle. 2. The medial and lateral borders join at the inferior angle. The inferior angle moves extensively as the arm is raised and lowered, and is an important landmark for studying scapular movements.
Check Your Understanding - What two bones construct each pectoral girdle?
Each pectoral girdle is formed by a scapula and a clavicle.
Nuchal lines - Occipital Bone
- including the bony ridges between them, anchor many neck and back muscles. - superior nuchal line marks the upper limit of the neck.
The sternum has three important anatomical landmarks
1. Jugular notch, 2. Sternal angle, 3. Xiphisternal joint.
Infraspinous and supraspinous fossae of scapula
Inferior and superior to the spine.
Check Your Understanding - The perpendicular plates of the palatine bones and the superior and middle conchae of the ethmoid bone form a substantial part of the nasal cavity walls. Which bone forms the roof of that cavity?
The cribriform plates of the ethmoid bone.
Check Your Understanding - Besides the ribs and sternum, there is a third group of bones making up the thoracic cage. What is it?
The thoracic vertebrae also contribute to the thoracic cage.
Check Your Understanding - What is the normal number of cervical vertebrae? Of thoracic vertebrae?
There are 7 cervical and 12 thoracic vertebrae.
Palatine Bones
- L-shaped and is fashioned from 2 bony plates: horizontal and perpendicular. - has 3 important articular processes: pyramidal, sphenoidal, orbital.
Anterior nasal spine of maxilla
- formed at the junction that is inferior to the nose where the maxillae meet medially.
Small openings connect the sinuses to the nasal cavity and act as "two-way streets":
Air enters the sinuses from the nasal cavity, and mucus formed by the sinus mucosae drains into the nasal cavity. The mucosa of the sinuses helps to warm and humidify inspired air.
Major skull sutures
Attach cranial bones: 1. Coronal. 2. Sagittal. 3. Squamous. 4. Lambdoid. - most other skull sutures connect facial bones and are named according to the specific bones they connect.
Sacral canal of sacrum
Continuation of vertebral canal, lodges sacral nerves
Table 7.2 Regional Characteristics of Cervical, Thoracic, and Lumbar Vertebrae
Table
Check Your Understanding - Look at Figure 7.4. Which of the skull bones illustrated in view (a) are cranial bones?
The frontal, parietal, temporal, sphenoid, and ethmoid bones are all cranial bones.
Check Your Understanding - What are the five major regions of the vertebral column?
cervical, thoracic, lumbar, sacral, and coccygeal regions
The nasal cavity is divided into right and left parts by the
nasal septum. - bony portion of the septum is formed by the vomer inferiorly and the perpendicular plate of the ethmoid bone superiorly. - a sheet of cartilage called the septal cartilage completes the septum anteriorly.
Costal cartilages of rib
provides secure but flexible rib attachments to the sternum.
Check Your Understanding - Which skull bones house the external ear canals?
temporal bones
The floor of the nasal cavity is formed by
the palatine processes of the maxillae and palatine bones.
How many regions is the axial skeleton broken into?
three
Sagittal Suture.
where the parietal bones meet superiorly at the cranial midline
What forms the skull?
cranium and facial bones
Ribs
- 12 pairs. - form the flaring sides of the thoracic cage. - all ribs attach posteriorly to the thoracic vertebrae via bodies and transverse processes and curve inferiorly toward the anterior body surface. - increase in length from pair 1-7, then decrease in length from 8-12.
The axis (C2)
- has a body and the other typical vertebral processes. - not as specialized as the atlas. - only unusal feature is the knoblike dens projecting superiorly from its body. - dens: missing body of the atlas, which fuses with the axis during embryonic development. - dens: cradled in the anterior arch of the atlas by the transverse ligament. - dens: act as a pivot for the rotation of the atlas. - this joint allows you to rotate your head from side to side to indicate no.
The Orbits
-cone shaped. - bony cavities in which the eyes are firmly encased and cushioned by fatty tissue. - muscles that move the eyes ad the tear-producing lacrimal glands are also housed in the orbits. ] - also has superior and inferior orbital fissures and the optic canals.
Each lacrimal bone contains a deep groove that helps form a (blank)
lacrimal fossa. - the lacrimal fossa house the lacrimal sac, which is the part of the passageway that allows tears to drain from the eye surface into the nasal cavity.
Each clavicle is flattened at its (blank), which articulates with the (blank)
lateral acromial end, scapula
Flanking the perpendicular plate on each side is a (blank) riddled with sinuses called (blank)
lateral mass, ethmoidal air cells for which the bone itself is named.
Laterally, the maxillae articulate with the zygomatic bones via their
zygomatic processes
Cranial Vault/Calvaria
"bald part of the skull" - forms the superior, lateral and posterior aspects of the skull as well as the forehead.
The Nasal Cavity
- constructed of bone and hyaline cartilage.
External occipital crest - Occipital Bone
- secures the ligamentum nuchae.
3 major parts of temporal bone
squamous, tympanic and petrous parts.
Manubrium of sternum
"knife handle" - the superior portion and is shaped like the knot in a necktie. - articulate via its clavicular notches with the clavicles, collarbones, laterally and just below this, articulates with the first 2 pairs of ribs.
Clavicles (pectoral girdle)
"little keys" or collarbones. - slender, S-shaped and can be felt along their entire course as they extend horizontally across the superior thorax. - medial 2/3 of the clavicle is convex anteriorly. - lateral third is concave anteriorly. -superior surface is fairly smooth, but the inferior surface is ridged and grooved by ligaments and by the action of the muscles that attach to it. . - trapezoid line and the conoid tubercle are anchoring points for a ligament that connects the clavicle to the scapula.
Anulus fibrosus of the intervertebral discs
"ring of fibers. - surrounds the nucleus pulposus. - strong collar composed of collagen fibers superficially and fibrocartilage internally. - limits the expansion of the nucleus pulposus when the spine is compressed. - act like a woven strap to bind successive vertebrae together, withstands twisting forces and resists tension in the spine.
Xiphoid process of sternum
"sword-like" - forms the inferior end of the sternum. - small, variably shaped process. - a plate of hyaline cartilage in youth, but it is usually ossified in adults over the age of 40. - articulates only with the sternal body and serves as an attachment point for some abdominal muscles. - projects posteriorly is some people. Blows to the chest can push the xiphoid into the underlying heart or liver, causing massive hemorrhage.
Scoliosis
"twisted disease" - abnormal lateral curvature that occurs most often in the thoracic region. - quite common in late childhood, particularly in girls, for some unknown reason. - more severe cases result from abnormal vertebral structure, lower limbs of unequal length or muscle paralysis. - if muscles on one side of the body are non-functional, those of the opposite side exert an unopposed pull on the spine and force it out of alignment. - treated with body braces or surgically before growth ends to prevent permanent deformity and breathing difficulties to to compressed lung.
Thoracic Vertebrae
- 12, T1-T12. - all articulate with the ribs. - increase in size from the first to the last. Characteristics: ■ Body is heart shaped. It bears 2 small facets, called demifacets (half-facets), on each side, one at the superior edge, the superior costal facet, and the other at the inferior edge, the inferior costal facet. The demifacets receive the heads of the ribs. The bodies of T10-T12 vary from this pattern by having only a single facet to receive their respective ribs. ■ Vertebral foramen is circular. ■ Spinous process is long and points sharply downward. ■ With the exception of T11 and T12, the transverse processes have facets, the transverse costal facets, that articulate with the tubercles of the ribs. ■ The superior and inferior articular facets lie in the frontal plane, a situation that prevents flexion and extension, but which allows this region of the spine to rotate. Lateral flexion, though possible, is restricted by the ribs.
Regions and curvatures of vertebral column
- 70 cm/28 inches long in an average adult. - has 5 major regions. - when it is viewed from the side, it has an S or sinusoid shape. - vertebrae becomes progressively larger from the cervical to the lumbar region, as they must support greater and greater weight. - all of us have the same number of cervical vertebrae; variations in 5% of people.
Cervical Vertebrae
- C1-C7. - smallest, lightest vertebrae. - C1 and C2: unusual. C3-C7: ■ The body is oval—wider from side to side than in the anteroposterior dimension. ■ Except in C7, the spinous process is short, projects directly back, and is bifid, or split at its tip. ■ The vertebral foramen is large and generally triangular. ■ Each transverse process contains a transverse foramen through which the vertebral arteries pass to service the brain.
Mandible
- U-shaped bone of the lower jaw. - largest, strongest bone of the face. - has a body which forms the chin, and two upright rami.
Spinous Process of vertebral arch (1)
- a median posterior projection arising at the junction of the 2 laminae. - attachment sites for muscles that move the vertebral column and for ligaments that stabilize it.
Ligamentum nuchae - Occipital Bone
- a sheetlike elastic ligament that connects the vertebrae of the neck to the skull.
Inner gelatinous nucleus pulposus of the intervertebral discs
- acts like a rubber ball, giving the disc its elasticity and compressibility.
Sacral hiatus of sacrum
- an enlarged external opening that occurs since the laminae of the 5th and sometimes 4th vertebrae fail to fuse medially.
Lacrimal Bones
- delicate, finger-nail shaped. - contribute to the medial walls of each orbit. - articulate with the frontal bone superiorly. - articulate with the ethmoid bone posteriorly. - articulate with the maxillae anteriorly.
Functions of the clavicle
- anchoring muscles. - act as braces: they hold the scapulae and arms out laterally, away from the narrower superior part of the thorax. - transmit compression forces from the upper limbs to the axial skeleton. - are not very strong and likely to fracture. - curves in the clavicle ensure that it usually fractures anteriorly or outward. - sensitive to muscle pull and become noticeably larger and stronger in those who perform manual labor or athletics involving the shoulder and arm muscles.
Mandibular body
- anchors lower teeth.
Anterior Coronoid process of mandible
- anterior and is an insertion point for the large temporalis muscles that elevates the lower jaw during chewing.
Surface of Scapulae
- anterior, or costal, surface of the scapula is concave and featureless. - posterior surface bears a prominent spine that is easily felt through the skin.
Posterior condylar process of mandible
- articulates with the mandibular fossa of the temporal bone, forming the temporomandibular joint on the same side.
Jugular foramen - Temporal Bone
- at the junction of the occipital and temporal bones. - allows passage of the internal jugular vein and 3 cranial nerves.
Mandibular notch of mandible
- at the superior margin of each ramus are two processes separated by the mandibular notch.
Sphenoid Bone
- bat-shaped. - spans the width of the middle cranial fossa. - considered the keystone to the cranium because it forms a central wedge that articulate with all other cranial bones. - consists of central body and 3 pairs of processes: the greater wings, lesser wings, and pterygoid processes.
Intercostal spaces
- between the ribs and are occupied by intercostal muscles. - life and then depress the thorax during breathing.
Stylomastoid foramen - Temporal Bone
- between the styloid and mastoid processes. - allows cranial never VII (the facial nerve) to leave the skull.
Part 2 - The Appendicular Skeleton
- bones of limbs and their girdles. - they are appended to the axial skeleton that forms the longitudinal axis of the body. - allows us to carry out the movements typical of our freewheeling and manipulative lifestyle. - pectoral girdles: attach the upper limbs to the body trunk. - pelvic girdle: secures the lower limbs. - the bones of the upper and lower limbs differ in their functions and mobility, but have the same fundamental plan: Each limb is composed of three major segments connected by movable joints.
What is the skeleton/skeletal system composed of?
- bones, cartilages, joints, ligaments. - accounts for about 20% of body mass.
Suprascapular notch of scapula
- bounds the coracoid process medially and the glenid cavity laterally. - it is a nerve passage.
Sternum
- breastbone/dagger. - lies in the anterior midline of the thorax. - a flatbone 15 cm/6 inches long, resulting from the fusion of 2 bones: manubrium, the body and the xiphoid process.
Curvatures of vertebral column
- cervical and lumbar curvatures: concave posteriorly. - thoracic and sacral curvatures: convex posteriorly. - curvatures increase the resilience and flexibility of the spine, allowing it to function like a spring rather than a rigid rod.
Vertebral arch
- composite structure formed by 2 pedicles and 2 laminae. - pedicles: short bony pillars projecting posteriorly from the vertebral body and forms the sides of the arch. - laminae: flattened plates that fuse in the median plane and complete the arch posteriorly.
Ligamentum flavum of vertebral column
- connects adjacent vertebrae. - contains elastic connective tissue and is strong. - stretches as we bend forward and recoils when we resume an erect posture.
Vertebral Column in fetus and infants
- consist of 33 separate bones or vertebrae. - inferiorly, 9 of these eventually fuse to form 2 composite bones, the sacrum and tiny coccyx. - the remaining 24 persist as individual vertebrae separated by intervertebral discs.
Spine/Vertebral or Spinal Column
- consists of 26 irregular bones connected in such a way that a flexible, curved structure results. - serving as the axial support of the trunk, the spine extends from the skull to the pelvis, where it transmits the weight of the trunk to the lower limbs. - surrounds and protects the delicate spinal cord. - provide attachment points for the ribs and the muscles of the back and neck.
The Pectoral (Shoulder) Girdle
- consists of the clavicle anteriorly and the scapula posteriorly. - the paired pectoral girdles and their associated muscles form the shoulders. - anteriorly, the medial end of each clavicle joins the sternum; the distal ends of the clavicles meet the scapulae laterally. - the scapulae are attached to the thorax and vertebral column only by the muscles that clothe their surfaces. - pectoral girdles attach the upper limbs to the axial skeleton and provide attachment points for many of the muscles that move the upper limbs.
Mastoid process - Temporal Bone
- conspicuous feature of the petrous part of the temporal bone. - acts as an anchoring site for some neck muscles. - can be felt as a lump just posterior to the ear.
Middle cranial fossa - Temporal Bone
- constructed by the sphenoid bone and the petrous portions of the temporal bones . - supports the temporal lobes of the brain.
Maxillary sinuses
- contained in the regions that flank the nasal cavity. - the largest of the paranasal sinuses. - extend from the orbits to the roots of the upper teeth.
Transverse ridges of sacrum - 4
- cross its concave anterior aspect, marking the lines of fusion of the sacral vertebrae.
Ethmoid Bone
- delicate and has a complex shape like temporal and sphenoid bones. - lying between the sphenoid and nasal bones of the face. - forms most of the bony area between the nasal cavity and orbits.
Meatuses of the nasal cavity
- depressions under cover of the conchae on the lateral walls. - superior, middle and inferior meatuses.
Intervertebral discs
- each is a cushionlike pad composed of 2 parts: inner gelatinous nucleus pulposus and anulus fibrosus. - thickest in the lumbar and cervical region, which enhances the flexibility of these regions. - collectively, account for 25% of the height of the vertebral column. - flatten during the course of the day, so we are always a few millimeters shorter at night than when we wake up during the morning.
General Structure of Vertebrae
- each vertebra consists of a body or centrum anteriorly and a vertebral arch posteriorly. - the disc-shaped body is the weight bearing region.
Jugular (suprasternal) notch of the sternum
- easily palpated. - central indentation in the superior border of the manubrium. - in line with the disc between the 2nd and 3rd thoracic vertebrae. - the point where the left common carotid artery issues from the aorta.
Function of the cranial bones or cranium
- enclose and protect the fragile brain. - furnish attachment sites for head and neck muscles.
Vertebral foramen
- enclosed by the body and vertebral arch.
Superior and middle nasal conchae - ethmoid bone
- extend medially from the lateral masses. - delicately coiled. - named after the conch shells found on warm ocean beaches. - protrude into the nasal cavity.
Frontal processes of Maxilla
- extend superiorly to the frontal bone. - form part of the lateral aspects of the bridge of the nose.
Transverse Process of vertebral arch (2)
- extends laterally from each side of the vertebral arch. - attachment sites for muscles that move the vertebral column and for ligaments that stabilize it.
Sternal angle of the sternum
- felt as a horizontal ridge across the front of the sternum, where the manubrium joins the sternal body. - a cartilaginous joint that acts like a hinge, allowing the sternal body to swing anteriorly when we inhale. - in like with the disc between the 4th and 5th thoracic vertebrae and at the level of the 2nd pair of ribs. - handy reference for finding the 2nd rib, for counting ribs, for listening to sounds made by specific heart valves.
Squamous part of the temporal bone
- flaring and abuts the squamous suture. - has a barlike zygomatic process that meets the zygomatic bone of the face anteriorly. - these two bony structure form the zygomatic arch, which you can feel as the projection of your cheek or cheekbone. - mandibular fossa: small, oval and on the inferior surface of the zygomatic process receives the condylar process of the mandible (lower jawbone) forming the freely movable temporomandibular joint.
Lesser Wings of Sphenoid Bone
- form part of the floor of the anterior cranial fossa and part of the medial walls of the orbits. - the trough-shaped pterygoid processes project inferiorly from the junction of the body and greater wings. They anchor the pterygoid muscles, which are important in chewing.
Function of the facial bones
- form the framework of the face. - contain cavities for the special sense organs of sight, taste and smell. - provide openings for air and food passages. - secure the teeth. - anchor the facial muscles of expression, which is use to show our feelings.
Vertebral canal
- formed by successive vertebral foramina of the articulated vertebrae. - spinal cord passes through this canal.
Posterior cranial fossa - Occipital Bone
- formed by the occipital bone. - supports the cerebellum of the brain.
Functions of the Bony Thorax
- forms a protective cage around the vital organs of the thoracic cavity: heart, lungs and great blood vessels. - supports the shoulder girdles and upper limbs. - provides attachment points for many muscles of the neck, back, chest and shoulders.
Occipital Bone
- forms most of the skull's posterior wall and base. - articulate anteriorly with the paired parietal and temporal bones via the lambdoid and occipitomastoid sutures. - the basilar part of the occipital bone also joins with the sphenoid bone in the cranial base.
Cranial Base
- forms the skull's inferior aspect. - divided into the anterior, middle and posterior cranial fossae. - brain sit in the cranial fossae, enclosed by the cranial vault.
Maxillary Bones
- fused medially. - form the upper jaw and the central portion of the facial skeleton. - all facial bones except the mandible articulate with the maxillae. - are considered keystone bones of the facial skeleton.
Median sacral crest of sacrum
- fused spinous processes of the sacral vertebrae. - roughed the posterior midline of the sacral surface.
The atlas (C1)
- has no body and no spinous process. - it is a ring of bone consisting of anterior and posterior arches and a lateral mass on each side. - each lateral mass has articular facets on both its superior and inferior surfaces. - superior articular facets: receive the occipital condyles of the skull; they carry the skull. - these joints allow you to nod yes. - inferior articular facets: form joins with the axis below, C2
Hypoglossal canal - Occipital Bone
- hidden medially and superiorly to each occipital condyle. - through which a cranial nerve pass.
Petrous Part of the Temporal Bone
- houses the middle and internal ear cavities, which contain sensory receptors for hearing and balance. - extends from the occipital bone posteriorly to the sphenoid bone anteriorly and contributes to the cranial base.
Kyphosis
- hunchback. - a dorsally exaggerated thoracic curvature. - common in elderly people because of osteoporosis. - may also reflect tuberculosis of the spine, rickets or osteomalacia.
Foramen magnum - Occipital Bone
- in the base of the occipital bone. - through which the inferior part of the brain connects with the spinal cord. - flanked laterally by 2 occipital condyles.
Mandibular symphysis
- in the midline of the mandibular body. - slight ridge indicating where the two mandibular bones fused during infancy.
Scroll-shaped conchae of the nasal cavity
- increase the turbulence of air flowing through the nasal cavity. - this swirling forces more of the inhaled air into contact with the warm, damp mucosa and encourage trapping of airborne particles such as dust, pollen and bacteria in the sticky mucus.
Costal margin of ribs
- inferior margin of the rib cage. - formed by the costal cartilages of ribs 7-10.
Nasal Bone
- inferior to the frontal bones. - at the frontonasal suture.
Herniated/Prolapsed disc - slipped disc
- involves rupture of the anulus fibrosus followed by protrusion of the spongy nucleus pulposus through the anulus. - if the protrusion presses on the spinal cord or spinal nerves exiting from the cord, numbness or excruciating pain may result.
Zygomatic Bones
- irregularly shaped. - commonly called the cheekbones. - articulate with the zygomatic processes of the temporal bones posteriorly. - articulate with the zygomatic processes of the frontal bones superiorly. - articulate with the zygomatic processes of the maxillae anteriorly - zygomatic bones form the prominences of the cheeks and part of the inferolateral margins of the orbits.
Foramen lacerum - Temporal Bone
- jagged opening between the petrous temporal bone and the sphenoid bone. - almost completely closed by cartilage in a living person.
Horizontal plates of palatine bones
- joined at the median palatine suture. - complete the posterior portion of the hard plate.
Carotid canal - Temporal Bone
- just anterior to the jugular foramen. - transmits the internal carotid artery into the cranial cavity. - the two internal carotid arteries supply blood to over 80% of the cerebral hemispheres of the brain; - their closeness to the internal ear cavities explains why, during excitement or exertion, we sometimes hear our rapid pulse as a thundering sound in the head.
Infraorbital foramen of maxilla
- just below the eye socket on each side. - allows the infraorbital nerve, a continuation of the maxillary nerve, and artery to reach the face.
Alae of sacrum
- lateral to the anterior sacral foramina. - winglike and expand superiorly.
Frontal Sinuses
- lateral to the glabella.
Optical Canals - opening of sphenoid bone
- lie anterior to the sella turcica. - allow the optic nerves (cranial nerves II) to pass to the eyes.
Treatment of Herniated/Prolapsed disc
- moderate exercise, massage, heat therapy and painkillers. - the protruding discs may be removed surgically and a bone graft done to fuse the adjoining vertebrae. - no general anesthesia: part of the disc can be vaporized with a laser disc decompression that takes only 30-40 minutes. - tears in the anulus can be sealed by electrothermal means at the same time.
Styloid process - Temporal Bone
- needlelike. - attachment point for a ligament that secures the hyoid bone of the neck to the skull.
The Hyoid Bone
- not really part of the skull. - lies inferior to the mandible in the anterior neck and looks like a miniature version of it. - unique because it is the only bone in the bone that does not articulate directly with any other bone. - anchored by the narrow stylohyoid ligaments to the styloid processes of the temporal bones. - horse-shaped with a body and 2 pairs of cornua (horns). - act as a movable base for the tongue. - its body and greater horns are attachment points for neck muscles that rise and lower the larynx during swallowing and speech.
Intervertebral foramina
- notches on the superior and inferior borders of pedicles. - provide lateral openings between adjacent vertebrae. - the spinal nerves issuing from the spinal cord pass through here.
Superior orbital fissure - opening of sphenoid bone
- on each side of the sphenoid body is a crescent-shaped row of four openings. - anteriormost of these. - a long slit between the greater and lesser wings. - allows cranial nerves that control eye movements (III, IV, VI) to enter the orbit.
Squamous suture.
- one on each side. - where a parietal and temporal bone meet on the lateral aspect of the skull.
Mandibular foramina
- one on the medial surface of each ramus. - permits the nerves responsible for tooth sensation to pass to the teeth in the lower jaw. - dentists inject lidocaine into these foramina to prevent pain while working on the lower teeth.
Mental foramina of Mandible
- openings on the lateral aspects of the mandibular body. - allow blood vessels and nerves to pass to the skin on the chin and lower lip.
Body of Sphenoid Bone
- paired sphenoidal sinuses. - the superior surface of the body bears a saddle-shaped prominence, the sella turcica, meaning "Turk's saddle." - the seat of this saddle, called hypophyseal fossa, forms a snug enclosure for the pituitary gland (hypophysis).
Inferior Nasal Conchae
- paired. - thin, curved bones in the nasal cavity. - project medially from the lateral walls of the nasal cavity, just inferior to the middle nasal conchae of the ethmoid bone. - largest of the 3 pairs of conchae. - form part of the lateral walls of the nasal cavity.
Supraorbital foramen (notch)
- pierce the supraorbital margin. - allow the supraorbital artery and nerve to pass to the forehead.
Internal acoustic meatus - Temporal Bone
- positioned superolateral to the jugular foramen. - transmits cranial nerves VII and VIII.
Incisive fossa of maxilla
- posterior to the teeth and is a midline foramen. - serves as a passageway for blood vessels and nerves.
Foramen spinosum - sphenoid bone
- posterolateral to the foramen ovale. - transmits the middle meningeal artery, which serves the internal faces of some cranial bones.
Greater Wings of Sphenoid Bone
- project laterally from the sphenoid body, forming parts of: (1) the middle cranial fossa. (2) the posterior walls of the orbits. (3) the external wall of the skull, where they are seen as flagshaped, bony areas medial to the zygomatic arc.
Palatine processes of maxilla
- project posteriorly from the alveolar processes and fuse medially at the intermaxillary suture. - form the anterior 2/3 of the hard palate or bony roof of the mouth.
Coracoid process of scapula
- projecting anteriorly from the superior scapular border. - looks like a bent finger. - helps anchor the biceps muscles of the arm.
Perpendicular plate of the ethmoid bone
- projects inferiorly in the median plane and form the superior part of the nasal septum, which divides the nasal cavity into right and left halves.
Paired superior & inferior articular processes of vertebral arch (4)
- protrude superiorly and inferiorly from the pedicle-lamina junctions. - smooth joint surfaces of the articular processes, called facets, are covered with hyaline cartilage. - inferior articular processes of each vertebra form movable joints with the superior articular processes of the vertebra below. - vertebrae join both at their bodies and at their articular processes.
Foramen rotundum and foramen ovale - sphenoid bone
- provide passageways for branches of cranial nerve V (the maxillary and mandibular nerves, respectively) to reach the face. - foramen rotundum is in the medial part of the greater wing and is usually oval, despite its name meaning "round opening". - formanen ovale: a large oval foramen posterior to the foramen rotundum, is also visible in an inferior view of the skull.
False ribs or vertebrochondral ribs
- remaining 5 pairs of ribs. - false because they either attach indirectly to the sternum or entirely lack a sternal attachment. - ribs 8-10 attach to the sternum indirectly, each joining the costal cartilage immediately above it.
Lateral sacral crests of sacrum
- remnants of the transverse processes of S1-S5
Posterior ligament of vertebral column
- resists hyperflexion of the spine, which is bending too sharply forward. - narrow and relatively weak. - attaches only to discs.
Special Characteristics of the Orbits and Nasal Cavity
- restricted skull regions.
Vertebral ribs or floating ribs
- ribs 11-12. - they have no anterior attachments. - their costal cartilages lie embedded in the muscles of the lateral body wall.
Function of Intervertebral discs
- sandwiched between the bodies of neighboring vertebrae and act as shock absorbers during walking, jumping and running. - allow the spine to flex and extend and to bend laterally. - at points of compression, the discs flatten and bulge out a bit between the vertebrae.
Subscapular fossa
- shallow concavity formed by the entire anterior scapular surface. - lying within these fossae are muscles with similar names
Frontal Bone
- shell shaped. - forms the anterior cranium. - articulates posteriorly with the paired parietal bones via the prominent coronal suture. - the most anterior part is the vertical squamous part called the forehead.
Scapulae (pectoral girdle)
- shoulder blades. - thin, triangular flat bones. - lie on the dorsal surface of the rib cage, between ribs 2 and 7.
Vomer
- slender, plow-shaped. - lies in the nasal cavity, where it forms part of the nasal septum.
Glabella
- smooth portion of the frontal bone between the orbits.
Abnormal spinal curvatures
- some are congenital, which means present at birth; others result from disease, poor posture or unequal muscle pull on the spine.
7 processes project from the vertebral arch
- spinous process. - 2 transverse processes. - 4 articular processes.
Ligaments
- straplike and holds up the vertebral column. - major supporting ligaments are the anterior and posterior longitudinal ligaments. - they run as continuous bands down the front and back surfaces of the vertebrae from the neck to the sacrum. - short ligaments connect each vertebra to those immediately above and below.
Broad anterior ligament of vertebral column
- strongly attached to both the bony vertebrae and the discs. - along with its supporting role, it prevents hyperextension of the spine, which is bending too far backward.
Alveolar process of mandible
- superior border of body; - contains the sockets, dental alveoli, in which teeth are embedded.
External occipital protuberance - Occipital Bone
- superior to the foramen magnum. - median protrusion. - can be felt just below the most bulging part of the posterior skull.
Perpendicular (vertical) plates of palatine bones
- superiorly projecting. - form part of the posterolateral walls of the nasal cavity and a small part of the orbits.
Tympanic part of temporal bone
- surrounds the external acoustic meatus or external ear canal, through which sound enters the ear. - external acoustic meatus and the eardrum at its deep end are part of the external ear.
Lordosis
- swayback. - an accentuated lumbar curvature. - can result from spinal tuberculosis or osteomalacia. - temporary lordosis is common in those carrying a large load up front, such as men with potbellies and pregnant women. - in an attempt to preserve their center of gravity, these individuals automatically throw back their shoulders, accentuating their lumbar curvature.
Coccyx
- tailbone, small triangular bone. - consists of 4, 3 or 5 vertebrae fused together. - articulate superiorly with the sacrum. - offers slight support to pelvic organs, but is useless.
Parietal Bones and the Major Sutures
- the 2 large parietal bones are curved, rectangular bones that form most of the superior and lateral aspects of the skull. - they form the bulk of the cranial vault.
Sacral promontory of sacrum
- the anterosuperior margin of the first sacral vertebra. - bulges anteriorly into the pelvic cavity. - body's center of gravity lies about 1 cm posterior to this.
C1 and C2
- the atlas and the axis. - more robust that the typical cervical vertebra. - have no intervertebral discs between them. - they are highly modified, reflecting their special functions.
Shaft of rib
- the bulk of the rib. - its superior border is smooth. - its inferior border is sharp and thin and has a costal groove on its inner face that lodges the intercostal nerves and blood vessels. - beyond the tubercle, the shaft angles sharply forward and then extends to attach to its costal cartilage anteriorly.
Neck of rib
- the constricted portion of the rib just beyond the head. - lateral to this, the knoblike tubercle articulates with the coastal facet of the transverse process of the same-numbered thoracic vertebra.
Anterior cranial fossa
- the frontal bone extends posteriorly, forming the superior wall of the orbits and most of the anterior cranial fossa. - supports the frontal lobes of the brain.
Acromion of scapula
- the lateral end of the spine of the scapula that articulates with the clavicle to form the acromioclavicular joint. - roughened triangular projection.
Orbital plates - ethmoid bone
- the lateral surfaces of the ethmoid's lateral masses. - they contribute to the medial walls of the orbits.
The superior surface of the ethmoid is formed by
- the paired horizontal cribriform plates, which help form the roof of the nasal cavities and the floor of the anterior cranial fossa. - the cribriform plates are punctured by tiny holes called cribriform foramina that allow the filaments of the olfactory nerves to pass from the smell receptors in the nasal cavities to the brain.
Xiphisternal joint of sternum
- the point where the sternal body and xiphoid process fuse. - it lies at the level of the 9th thoracic cavity. - the heart lies on the diaphragm just deep to this joint.
Lumbar Vertebrae
- the small of the back. - receives the most stress. - enhanced weight bearing of L1-L5 is reflected in their sturdier structure. - bodies are massive and kidney shaped in a superior view. Characteristics: ■ Pedicles and laminae are shorter and thicker. ■ Spinous processes are short, flat, and hatchet shaped and easily seen when a person bends forward. These processes are robust and project directly backward, adaptations for the attachment of the large back muscles. ■ Vertebral foramen is triangular. ■ Orientation of the facets of the articular processes of the differs substantially from the other vertebra types. These modifications lock the lumbar vertebrae together and provide stability by preventing rotation of the lumbar spine. Flexion and extension are possible,, as when you do sit-ups, as is lateral flexion.
C7
- the spinous process is not bifid and is much larger than those of the other cervical vertebrae. - because its spinous process is palpable through the skin, C7 can be used as a landmark for counting the vertebrae and is called the vertebra prominens.
True or vertebrosternal ribs
- the superior 7 rib pairs that attach directly to the sternum by individual costal cartilages.
Temporal Bones
- there are 2. - lie inferior to the parietal bones and meet them at the squamous sutures. - form the inferolateral aspects of the skull and parts of the cranial base. - each temporal bone has a complicated shape.
Why are the first pair of ribs atypical?
- they are flattened superiorly to inferiorly and are quite broad, forming a horizontal table that supports the subclavian blood vessels that serve the upper limbs. - rib 1 and ribs 10-12 articulate with only one vertebral body. - ribs 11 and 12 do not articulate with a vertebral transverse process.
Nasal Bones
- thin, rectangular. - fused medially, forming the bridge of the nose. - articulate with the frontal bone superiorly. - articulate with the maxillary bones laterally. - articulate with the perpendicular plate of the ethmoid bone posteriorly. - inferiorly, they attach to the cartilages that form most of the skeleton of the external nose.
The Thoracic Cage
- thorax is the chest and its bony underpinnings are called the thoracic cage or bony thorax. Elements of the thoracic cage: - the thoracic vertebrae posteriorly, - the ribs laterally, - the sternum and coastal cartilages anteriorly. The coastal cartilages secure the ribs to the sternum. - cone-shaped with its broad dimension positioned inferiorly.
Sutural Bones
- tiny irregularly shaped bones or bone clusters that occur within sutures, most often in the lambdoid suture. - structurally unimportant, their number varies, and not all skulls exhibit them.
Crista galli - ethmoid bone
- triangular process projecting superiorly from the cribriform plate. - the dura matter, the outermost covering of the brain, attaches to the crista galli and helps secure the brain to the cranial cavity.
Sacrum
- triangular. - shapes the posterior walls of the pelvis and is formed by 5 fused vertebrae S1-S5 in adults. - articulate superiorly via its superior articular processes with L5 and inferiorly with the coccyx. - laterally, the sacrum articulates, via its auricular surfaces, with the two hip bones to form the sacroiliac joints of the pelvis.
Regional Vertebral Characteristics
- vertebrae exhibit variations that allow different regions of the spine to perform slightly different functions and movements. Movement that can occur between vertebrae are: (1) flexion and extension - anterior bending and posterior straightening of the spine, (2) lateral flexion - bending the upper body to the right or left, (3) rotation - in which vertebrae rotate on one another in the longitudinal axis of the spine.
Head of rib
- wedged shaped. - posterior end. - articulates with the vertebral bodies by 2 facets: one joins the body of the same-numbered thoracic vertebra, the other articulates with the body of the vertebra immediately superior.
Supraorbital margins
- where the frontal squamous region ends inferiorly. - the thickened superior margins of the orbits that lie under the eyebrows.
Alveolar Processes of the maxillae
- where the upper teeth is carried.
The lateral walls of the nasal cavity is largely shaped by
-the superior and middle conchae of the ethmoid bone, - the perpendicular plates of the palatine bones, - the inferior nasal conchae.
5 major regions of vertebral column
1- Cervical 7 vertebrae, 2- Thoracic 12 vertebrae, 3- Lumbar 5 vertebrae, 4- Sacrum 5 fused - articulates with hip bones of the pelvis. 5- Coccyx 4 fused
The four largest sutures occur where the parietal bones articulate (form a joint) with other cranial bones:
1. Coronal Suture. 2. Sagittal Suture. 3. Lambdoid suture. 4. Squamous suture.
Function of the axial skeleton
1. Form longitudinal axis of body. 2. Support head, neck, and trunk. 3. Protects brain, spinal cord, and thoracic organs
7 pairs of bones that form the walls of orbit
1. Frontal, 2. Sphenoid, 3. Zygomatic, 4. Maxilla, 5. Palatine, 6. Lacrimal, 7. Ethmoid.
What are the 8 cranial bones?
2 parietal, 2 temporal, frontal, occipital, sphenoid, and ethmoid. - together, they construct the brain's "helmet". - because its superior aspect is curved, the cranium is self bracing. - this allows the bones to be thin and the cranium is extremely strong for its weight.
How many cranial bones are there?
8
Check Your Understanding - How can you distinguish a lumbar vertebra from a thoracic vertebra?
A lumbar vertebra is heavier and its massive body is kidney shaped. Its spinous processes are short and project directly back. A thoracic vertebral body is generally heart shaped, its spinous process is long, sharp, and points downward, and its transverse processes have facets for articulating with the ribs.
Check Your Understanding - How does a true rib differ from a false rib?
A true rib connects to the sternum by its own costal cartilage. A false rib connects to the sternum via costal cartilages of other ribs or not at all.
Check Your Understanding - Johnny was vigorously exercising the only joints in the skull that are freely movable. What would you guess he was doing?
Eating or talking, because the only freely movable joints of the skull are the temporomandibular joints of the jaw.
Smaller Cavities of the skull
Includes: - middle and inner ear cavities—carved into the lateral side of its base. - nasal cavity—lies in and posterior to the nose. - orbits—house the eyeballs. - air-filled sinuses—occur in several bones of the skull and contain air-filled sinuses which lighten the skull.
Check Your Understanding - In which two of these regions is the vertebral column concave posteriorly?
The cervical and lumbar regions are concave posteriorly.
Check Your Understanding -How would a complete fracture of the dens affect the mobility of the vertebral column?
The dens is the axis on which the atlas rotates. If it's broken, movements of the atlas would be less controllable.
Check Your Understanding - What bones are the keystone bones of the facial skeleton?
The maxillae
Check Your Understanding - What bone forms the bulk of the orbit floor and what sense organ is found in the orbit of a living person?
The maxillae form the bulk of the orbit floor. The eye is housed in the orbit.
Check Your Understanding - What bones abut one another at the sagittal suture? At the lambdoid suture?
The parietal bones abut each other at the sagittal suture. The occipital bone abuts the parietal bones at the lambdoid suture.
Check Your Understanding - Where is the single point of attachment of the pectoral girdle to the axial skeleton?
The pectoral girdle attaches to the sternal manubrium of the axial skeleton via the medial end of its clavicle.
Check Your Understanding - What bones contain the paranasal sinuses?
The sphenoid, ethmoid, frontal, and maxillary bones contain paranasal sinuses.
Check Your Understanding - What is the sternal angle and what is its clinical importance?
The sternal angle is a ridge across the front of the sternum where the manubrium joins the sternal body. Acts as a hinge allowing the sternum to swing anteriorly when we inhale. Because it is aligned with the 2nd rib, it is a handy cue for finding that rib and then counting the ribs during a physical exam.
What cause mobility in pectoral girdles?
These girdles are very light and allow the upper limbs a degree of mobility not seen anywhere else in the body. This mobility is due to the following factors: ■ Because only the clavicle attaches to the axial skeleton, the scapula can move quite freely across the thorax, allowing the arm to move with it. ■ The socket of the shoulder joint, the scapula's glenoid cavity, is shallow and poorly reinforced, so it does not restrict the movement of the humerus (arm bone). Although this arrangement is good for flexibility, it is bad for stability: Shoulder dislocations are fairly common.
In the floor of the cranial cavity, the petrous part of the temporal bone looks like
a miniature mountain ridge. - the posterior slope of this ridge lies in the posterior cranial fossa. - the anterior slope is in the middle cranial fossa.
Check Your Understanding - Which part of the skeleton—axial or appendicular—is important in protecting internal organs?
axial skeleton
A typical rib is a
bowed flat bone.
Check Your Understanding - Which bone forms the crista galli?
ethmoid bone
A number of inconspicuous ridges, the (blank) and the (blank), mark the occipital bone near the foramen magnum.
external occipital crest, superior and inferior nuchal lines
Check Your Understanding - Besides the spinal curvatures, which skeletal elements help to make the vertebral column flexible?
fibrocartilage discs
Paranasal Sinuses
five skull bones: frontal, sphenoid, ethmoid, paired maxillary bones contain mucosa-lined, air-filled sinuses that give them a rather moth-eaten appearance in an X-ray image. - are called paranasal sinuses because they cluster around the nasal cavity. - lighten the skull and enhance the resonance of the voice.
Each ramus meets the body posteriorly at a (blank)
mandibular angle.
The mastoid process is full of air cavities (sinuses) called
mastoid air cells. - their position adjacent to the middle ear cavity (a high-risk area for infections spreading from the throat) puts them at risk for infection themselves. - a mastoid sinus infection, or mastoiditis, is notoriously difficult to treat. - because the mastoid air cells are separated from the brain by only a very thin bony plate, mastoid infections may spread to the brain as well. - surgical removal of the mastoid process was once the best way to prevent life-threatening brain inflammations in people susceptible to repeated bouts of mastoiditis. - - today, antibiotic therapy is the treatment of choice.
Each clavicle is cone shaped at its (blank), which attaches to the sternal (blank),
medial sternal end, manubrium
The nasal septum and conchae are covered with a
mucus secreting mucosa that moistens and warms the entering air and helps cleanse it of debris.
What three regions is the axial skeleton broken into?
skull, vertebral column, and bony thorax
Check Your Understanding - What are the three main parts of the axial skeleton?
skull, vertebral column, and thoracic cage
Coronal Suture.
where the parietal bones meet the frontal bone anteriorly
Lambdoid suture.
where the parietal bones meet the occipital bone posteriorly
