7 The Skeleton: Part A.

7 The Skeleton: Part A

The Axial Skeleton Consists of 80 bones Three major regions Skull
Vertebral column Thoracic cage

Cranium Skull Facial bones Clavicle Thoracic cage Scapula (ribs and
sternum) Scapula Sternum Rib Humerus Vertebra Vertebral column Radius Ulna Sacrum Carpals Phalanges Metacarpals Femur Patella Tibia Fibula Tarsals Metatarsals (a) Anterior view Phalanges Figure 7.1a

The Skull Contains 22 cranial and facial bones
Forms the framework of the face Contain cavities for special sense organs Provide openings for air and food passage Secures the teeth Anchor muscles of facial expression Most skull bones are flat bones joined by interlocking joints called sutures (exception: mandible: movable joint)

The Skull Anterior aspect: facial bones Remainder: cranium
Skull cavities: Cranial cavity- houses the brain Ear cavities Nasal cavity Orbits- house the eyeballs 85 named openings providing passageways for the spinal cord, major blood vessels, and the cranial nerves.

The Skull Two sets of bones Cranial bones
Eight strong, superiorly curved bones Enclose the brain in the cranial cavity Cranial vault (calvaria) Cranial base: anterior, middle, and posterior cranial fossae Provide sites of attachment for head and neck muscles

The Skull Facial bones Framework of face
Cavities for special sense organs for sight, taste, and smell Openings for air and food passage Sties of attachment for teeth and muscles of facial expression

Bones of cranium (cranial vault)
Coronal suture Squamous suture Lambdoid suture Facial bones (a) Cranial and facial divisions of the skull Figure 7.2a

(b) Superior view of the cranial fossae
Anterior cranial fossa Middle cranial fossa Posterior cranial fossa (b) Superior view of the cranial fossae Figure 7.2b

Cranial Bones Frontal bone Parietal bones (2) Occipital bone
Temporal bones (2) Sphenoid bone Ethmoid bone

Frontal Bone Articulates posteriorly with the parietal bones via the coronal suture Anterior portion of cranium (cranial fossa) Most of anterior cranial fossa Superior wall of orbits (supraorbital margins) Contains air-filled frontal sinus

Frontal bone Glabella Parietal bone Frontonasal suture
Supraorbital foramen (notch) Squamous part of frontal bone Supraorbital margin Nasal bone Superior orbital fissure Sphenoid bone (greater wing) Optic canal Temporal bone Inferior orbital fissure Ethmoid bone Lacrimal bone Middle nasal concha Zygomatic bone Ethmoid bone Infraorbital foramen Perpendicular plate Maxilla Inferior nasal concha Mandible Vomer Mental foramen (a) Anterior view Mandibular symphysis Figure 7.4a

Parietal Bones and Major Associated Sutures
2 large, rectangular bones on superior and lateral aspects of cranial vault (majority of cranial vault) Four largest sutures mark the articulations of parietal bones with frontal, occipital, and temporal bones: Coronal suture—between parietal bones and frontal bone Sagittal suture—between right and left parietal bones Lambdoid suture—between parietal bones and occipital bone Squamous (squamosal) sutures—between parietal and temporal bones on each side of skull

(a) External anatomy of the right side of the skull
Coronal suture Frontal bone Sphenoid bone (greater wing) Parietal bone Ethmoid bone Temporal bone Lacrimal bone Lambdoid suture Lacrimal fossa Squamous suture Nasal bone Occipital bone Zygomatic bone Zygomatic process Maxilla Occipitomastoid suture External acoustic meatus Mastoid process Alveolar margins Styloid process Mandibular condyle Mandible Mandibular notch Mental foramen Mandibular ramus Mandibular angle Coronoid process (a) External anatomy of the right side of the skull Figure 7.5a

Occipital Bone Most of skull’s posterior wall and posterior cranial fossa (base of skull) Articulates with 1st vertebra, parietal, temporal, & sphenoid bones Sites of attachment for the ligamentum nuchae and many neck and back muscles Foramen magnum- large opening connects brain to the spinal cord (in the base of the occipital bone)

Sagittal suture Parietal bone Sutural bone Lambdoid suture
Occipital bone Superior nuchal line External occipital protuberance Mastoid process Inferior nuchal line Occipitomastoid suture External occipital crest Occipital condyle (b) Posterior view Figure 7.4b

Intermaxillary suture Hard palate Palatine bone (horizontal plate)
(palatine process) Incisive fossa Intermaxillary suture Hard palate Palatine bone (horizontal plate) Median palatine suture Infraorbital foramen Maxilla Zygomatic bone Sphenoid bone (greater wing) Temporal bone (zygomatic process) Foramen ovale Vomer Foramen spinosum Foramen lacerum Mandibular fossa Carotid canal External acoustic meatus Styloid process Stylomastoid foramen Mastoid process Temporal bone (petrous part) Jugular foramen Occipital condyle Pharyngeal tubercle of basilar region of the occipital bone Inferior nuchal line Parietal bone Superior nuchal line External occipital crest External occipital protuberance Foramen magnum (a) Inferior view of the skull (mandible removed) Figure 7.6a

Temporal Bones Articulate with the parietal bones
Inferolateral aspects of skull and parts of cranial floor Mandibular fossa: forms part of the temporomandibular joint external auditory meatus & petrous: house the ear Four major regions Squamous Tympanic Mastoid Petrous

Squamous region External acoustic meatus Mastoid region
Zygomatic process Mandibular fossa Mastoid process Tympanic region Styloid process Figure 7.8

Anterior cranial fossa Optic canal Lesser wing Sphenoid
Cribriform plate Frontal bone Ethmoid bone Crista galli Olfactory foramina Anterior cranial fossa Optic canal Lesser wing Sphenoid Foramen rotundum Greater wing Foramen ovale Hypophyseal fossa of sella turcica Foramen spinosum Foramen lacerum Middle cranial fossa Internal acoustic meatus Temporal bone (petrous part) Jugular foramen Hypoglossal canal Posterior cranial fossa Foramen magnum View Parietal bone Occipital bone (a) Superior view of the skull, calvaria removed Figure 7.7a

Sphenoid Bone Spans the width of the middle cranial fossa
Complex, bat-shaped bone Keystone bone Articulates with all other cranial bones Three pairs of processes Greater wings Lesser wings Pterygoid processes

Lesser wing Optic canal Superior orbital fissure Foramen Greater
rotundum Greater wing Foramen ovale Hypophyseal fossa of sella turcica Foramen spinosum Body of sphenoid (a) Superior view Figure 7.9a

Body of sphenoid Lesser wing Superior orbital fissure Greater wing
Pterygoid process (b) Posterior view Figure 7.9b

Ethmoid Bone Lies between the sphenoid and nasal bones
forms most of the bony area between the nasal cavity and the orbits. Deepest skull bone Superior part of nasal septum, roof of nasal cavities Contributes to medial wall of orbits

Crista galli Olfactory foramina Cribriform plate Orbital plate
Left lateral mass Ethmoidal air cells Perpendicular plate Middle nasal concha Figure 7.10

Anterior cranial fossa Optic canal Lesser wing Sphenoid
Cribriform plate Frontal bone Ethmoid bone Crista galli Olfactory foramina Anterior cranial fossa Optic canal Lesser wing Sphenoid Foramen rotundum Greater wing Foramen ovale Hypophyseal fossa of sella turcica Foramen spinosum Foramen lacerum Middle cranial fossa Internal acoustic meatus Temporal bone (petrous part) Jugular foramen Hypoglossal canal Posterior cranial fossa Foramen magnum View Parietal bone Occipital bone (a) Superior view of the skull, calvaria removed Figure 7.7a

Sutural Bones Groups of tiny irregularly shaped bones that appear within sutures A.k.a. Wormian bones vary in number not present on all skulls

Sagittal suture Parietal bone Sutural bone Lambdoid suture
Occipital bone Superior nuchal line External occipital protuberance Mastoid process Inferior nuchal line Occipitomastoid suture External occipital crest Occipital condyle (b) Posterior view Figure 7.4b

Facial Bones Mandible Maxillary bones (maxillae) (2)
Zygomatic bones (2) Nasal bones (2) Lacrimal bones (2) Palatine bones (2) Vomer Inferior nasal conchae (2)

Mandible Lower jaw Largest, strongest bone of face
Articulates with the mandibular fossae of the temporal bones via the mandibular condyles to form the temporomandibular joint Temporomandibular joint: only freely movable joint in skull

(a) Mandible, right lateral view
Mandibular fossa of temporal bone Temporomandibular joint Mandibular notch Coronoid process Mandibular condyle Mandibular foramen Alveolar margin Ramus of mandible Mental foramen Mandibular angle Body of mandible (a) Mandible, right lateral view Figure 7.11a

Maxillary Bones Medially fused to form upper jaw and central portion of facial skeleton Keystone bones Articulate with all other facial bones except mandible

(b) Maxilla, right lateral view
Articulates with frontal bone Frontal process Orbital surface Infraorbital foramen Zygomatic process (cut) Anterior nasal spine Alveolar margin (b) Maxilla, right lateral view Figure 7.11b

Zygomatic Bones Cheekbones Inferolateral margins of orbits
Articulate with temporal, frontal, and maxillary bones

Nasal Bones and Lacrimal Bones
Form bridge of nose Articulate with the frontal, maxillary, and ethmoid bones, along with the cartilages that form most of the skeleton of the external nose Lacrimal bones In medial walls of orbits Lacrimal fossa houses lacrimal sac Articulate with the frontal, ethmoid, and maxillary bones

(a) External anatomy of the right side of the skull
Coronal suture Frontal bone Sphenoid bone (greater wing) Parietal bone Ethmoid bone Temporal bone Lacrimal bone Lambdoid suture Lacrimal fossa Squamous suture Nasal bone Occipital bone Zygomatic bone Zygomatic process Maxilla Occipitomastoid suture External acoustic meatus Mastoid process Alveolar margins Styloid process Mandibular condyle Mandible Mandibular notch Mental foramen Mandibular ramus Mandibular angle Coronoid process (a) External anatomy of the right side of the skull Figure 7.5a

Palatine Bones and Vomer
Posterior one-third of hard palate Posterolateral walls of the nasal cavity Small part of the orbits Vomer Plow shaped Lower part of nasal septum Lies in the nasal cavity

Inferior Nasal Conchae
Form part of lateral walls of nasal cavity Thin, curved bones in the nasal cavity project medially from the lateral walls of the nasal cavity

(perpendicular plate) Palatine bone (horizontal plate)
Frontal sinus Superior, middle, and inferior meatus Superior nasal concha Ethmoid bone Middle nasal concha Inferior nasal concha Nasal bone Anterior nasal spine Sphenoid sinus Maxillary bone (palatine process) Sphenoid bone Pterygoid process Palatine bone (perpendicular plate) Palatine bone (horizontal plate) (a) Bones forming the left lateral wall of the nasal cavity (nasal septum removed) Figure 7.14a

Orbits Bony cavity that encases eyes and lacrimal glands (tear-producing) Sites of attachment for eye muscles Formed by parts of seven bones (next slide) consist of the frontal, sphenoid, zygomatic, maxilla, palatine, lacrimal, and ethmoid bones

• Lesser wing of sphenoid bone
Superior orbital fissure Roof of orbit Supraorbital notch Optic canal • Lesser wing of sphenoid bone • Orbital plate of frontal bone Medial wall • Sphenoid body Lateral wall of orbit • Orbital plate of ethmoid bone • Zygomatic process of frontal bone • Frontal process of maxilla • Greater wing of sphenoid bone • Lacrimal bone • Orbital surface of zygomatic bone Nasal bone Floor of orbit Inferior orbital fissure Infraorbital groove • Orbital process of palatine bone Zygomatic bone • Orbital surface of maxillary bone Infraorbital foramen • Zygomatic bone (b) Contribution of each of the seven bones forming the right orbit Figure 7.13a

Nasal Cavity Roof, lateral walls, and floor formed by parts of four bones Ethmoid Palatine bones Maxillary bones Inferior nasal conchae Nasal septum of bone and hyaline cartilage Vomer Anterior septal cartilage Divides nasal cavity into right and left halves

(perpendicular plate) Palatine bone (horizontal plate)
Frontal sinus Superior, middle, and inferior meatus Superior nasal concha Ethmoid bone Middle nasal concha Inferior nasal concha Nasal bone Anterior nasal spine Sphenoid sinus Maxillary bone (palatine process) Sphenoid bone Pterygoid process Palatine bone (perpendicular plate) Palatine bone (horizontal plate) (a) Bones forming the left lateral wall of the nasal cavity (nasal septum removed) Figure 7.14a

Crista galli Ethmoid bone Cribriform plate Frontal sinus Sella turcica
Nasal bone Perpendicular plate of ethmoid bone Sphenoid sinus Septal cartilage Palatine bone Vomer Alveolar margin of maxilla Hard palate Palatine process of maxilla (b) Nasal cavity with septum in place showing the contributions of the ethmoid bone, the vomer, and septal cartilage Figure 7.14b

Paranasal Sinuses Mucosa-lined, air-filled spaces Lighten the skull
Enhance resonance of voice Found in frontal, sphenoid, ethmoid, and maxillary bones

Frontal sinus Frontal sinus Ethmoidal air cells (sinus) Ethmoidal
Sphenoid sinus Sphenoid sinus Maxillary sinus Maxillary sinus (a) Anterior aspect (b) Medial aspect Figure 7.15

Hyoid Bone Not a bone of the skull
Does not articulate directly with another bone Site of attachment for muscles of swallowing and speech lies inferior to the mandible in the anterior neck

Greater horn Lesser horn Body Figure 7.12

Vertebral Column Transmits weight of trunk to lower limbs
Surrounds and protects spinal cord extending from the skull to the pelvis provides attachment for ribs and muscles of the neck and back Flexible curved structure containing 26 irregular bones (vertebrae) Cervical vertebrae (7)—vertebrae of the neck Thoracic vertebrae (12)—vertebrae of the thoracic cage Lumbar vertebrae (5)—vertebra of the lower back Sacrum—bone inferior to the lumbar vertebrae Coccyx—terminus of vertebral column

Vertebral Column: Curvatures
Increase the resilience and flexibility of the spine Two posteriorly concave curvatures Cervical and lumbar Two posteriorly convex curvatures Thoracic and sacral Abnormal spine curvatures Scoliosis (abnormal lateral curve) Kyphosis (hunchback) Lordosis (swayback)

Figure 7.16 C1 Cervical curvature (concave) 7 vertebrae, C1–C7 Spinous
process Transverse processes Thoracic curvature (convex) 12 vertebrae, T1–T12 Intervertebral discs Intervertebral foramen Lumbar curvature (concave) 5 vertebrae, L1–L5 Sacral curvature (convex) 5 fused vertebrae sacrum Coccyx 4 fused vertebrae Anterior view Right lateral view Figure 7.16

Ligaments Anterior and posterior longitudinal ligaments
From neck to sacrum major supporting ligaments of the spine run as continuous bands down the front and back surfaces of the spine support the spine and prevent hyperflexion and hyperextension Ligamentum flavum Connects adjacent vertebrae Short ligaments Connect each vertebra to those above and below

Intervertebral Discs act as shock absorbers
allow the spine to flex, extend, and bend laterally Cushionlike pad composed of two parts Nucleus pulposus Inner gelatinous nucleus that gives the disc its elasticity and compressibility Anulus fibrosus Outer collar composed of collagen and fibrocartilage

Supraspinous ligament
Intervertebral disc Supraspinous ligament Transverse process Anterior longitudinal ligament Sectioned spinous process Intervertebral foramen Ligamentum flavum Posterior longitudinal ligament Interspinous ligament Anulus fibrosus Nucleus pulposus Inferior articular process Sectioned body of vertebra Median section of three vertebrae, illustrating the composition of the discs and the ligaments Figure 7.17a

Vertebral spinous process (posterior aspect of vertebra)
Spinal cord Spinal nerve root Transverse process Herniated portion of disc Anulus fibrosus of disc Nucleus pulposus of disc (c) Superior view of a herniated intervertebral disc Figure 7.17c

General Structure of Vertebrae
Body or centrum Anterior weight-bearing region Vertebral arch (posterior) Composed of 2 pedicles and 2 laminae that, along with centrum, enclose vertebral foramen Vertebral foramina Together make up vertebral canal for spinal cord Intervertebral foramina Lateral openings between adjacent vertebrae for spinal nerves notches on the superior and inferior borders of pedicles

General Structure of Vertebrae
Seven processes per vertebra: Spinous process—projects posteriorly (median) Transverse processes (2)—project laterally Superior articular processes (2)—protrude superiorly inferiorly Inferior articular processes (2)—protrude inferiorly PLAY Animation: Rotatable Spine (horizontal) PLAY Animation: Rotatable Spine (vertical)

Posterior Vertebral Lamina arch Spinous Transverse process process
Superior articular process and facet Vertebral foramen Pedicle Body (centrum) Anterior Figure 7.18

Cervical Vertebrae C1 to C7: smallest, lightest vertebrae
C3 to C7 share the following features Oval body Short spinous processes are bifid (except C7) Large, triangular vertebral foramen Transverse foramen in each transverse process

Table 7.2

(a) Cervical vertebrae
Dens of axis Transverse ligament of atlas C1 (atlas) C2 (axis) C3 Inferior articular process Bifid spinous process Transverse processes C7 (vertebra prominens) (a) Cervical vertebrae Figure 7.20a

Cervical Vertebrae C1 (atlas) and C2 (axis) have unique features
Atlas (C1) No body or spinous process Consists of anterior and posterior arches, and two lateral masses Articular facets on the superior surfaces of lateral masses articulate with the occipital condyles of the skull superiorly articular facets on the inferior surface that articulate with the second cervical vertebra, the axis, inferiorly.

(a) Superior view of atlas (C1) (b) Inferior view of atlas (C1)
Posterior Posterior Posterior tubercle Posterior tubercle Posterior arch Posterior arch Inferior articular facet Lateral masses Transverse process Lateral masses Transverse foramen Superior articular facet Transverse foramen Anterior arch Anterior tubercle Anterior arch Facet for dens Anterior tubercle (a) Superior view of atlas (C1) (b) Inferior view of atlas (C1) Figure 7.19a-b

Cervical Vertebrae Axis (C2)
has a body, spine, and other typical vertebral processes Knoblike Dens (odontoid process) projects superiorly from the body into the anterior arch of the atlas Dens is a pivot for the rotation of the atlas

(c) Superior view of axis (C2)
Posterior C2 Spinous process Lamina Inferior articular process Pedicle Superior articular facet Transverse process Dens Body (c) Superior view of axis (C2) Figure 7.19c

Thoracic Vertebrae T1 to T12
All articulate with ribs at facets and demifacets gradually transition between cervical structure at the top, and lumbar structure toward the bottom have a roughly heart-shaped body, which bear two facets on each side for rib articulation circular vertebral foramen and superior and inferior articular processes Long spinous process Location of articular facets allows rotation of this area of spine

Table 7.2

(b) Thoracic vertebrae
Superior articular process Transverse process Transverse costal facet (for tubercle of rib) Intervertebral disc Body Inferior costal facet (for head of rib) Spinous process Inferior articular process (b) Thoracic vertebrae Figure 7.20b

Lumbar Vertebrae L1 to L5 large vertebrae that have kidney-shaped bodies Short, thick pedicles and laminae triangular vertebral foramen Short, flat hatchet-shaped spinous processes Orientation of articular facets locks lumbar vertebrae together so as to prevent rotation

Table 7.2

Superior articular process Transverse Body process Intervertebral disc
Inferior articular process Spinous process (c) Lumbar vertebrae Figure 7.20c

Sacrum and Coccyx Sacrum Coccyx 5 fused vertebrae (S1–S5)
Forms posterior wall of pelvis Articulates with L5 superiorly Articulates with the coccyx inferiorly and the hip bones laterally via the sacroiliac joint Vertebral canal continues through the sacrum, often ending at a large external opening, the sacral hiatus Coccyx Tailbone Small bone 3–5 fused vertebrae Articulates superiorly with sacrum

Sacral promontory Ala Body of first sacral vertebra Transverse
ridges (sites of vertebral fusion) Anterior sacral foramina Apex Coccyx (a) Anterior view Figure 7.21a

Sacral Facet of Body canal superior Ala articular process Auricular
surface Median sacral crest Lateral sacral crest Posterior sacral foramina Sacral hiatus Coccyx (b) Posterior view Figure 7.21b

Thoracic Cage Composed of Functions Thoracic vertebrae dorsally
Sternum anteriorly Ribs (laterally) and their costal cartilages (anteriorly) Functions Protects vital organs of thoracic cavity Supports shoulder girdle and upper limbs Provides attachment sites for many muscles, including intercostal muscles used during breathing

Sternum (Breastbone) Anterior midline of the thorax
flat bone resulting from the fusion of three bones: the manubrium, body, and xiphoid process Three fused bones Manubrium Articulates with clavicles and ribs 1 and 2 Body Articulates with costal cartilages of ribs 2 through 7 Xiphoid process Inferior end Articulates only with the body Site of muscle attachment Not ossified until ~ age 40

Ribs and Their Attachments
Form sides of the thoracic cage 12 pairs All attach posteriorly to thoracic vertebrae and curve inferiorly toward the anterior body surface Pairs 1 through 7 True (vertebrosternal) ribs Attach directly to the sternum by individual costal cartilages

Ribs and Their Attachments
Pairs 8 through12 False ribs Pairs 8–10 also called vertebrochondral ribs Attach indirectly to sternum by joining costal cartilage of rib above Pairs 11–12 also called vertebral (floating) ribs No attachment to sternum

(a) Skeleton of the thoracic cage, anterior view
Jugular notch Clavicular notch Manubrium Sternal angle Body Sternum True ribs (1–7) Xiphisternal joint Xiphoid process False ribs (8–12) Intercostal spaces Costal cartilage Costal margin L1 Vertebra Floating ribs (11, 12) (a) Skeleton of the thoracic cage, anterior view Figure 7.22a

Structure of a Typical Rib
Main parts: Head Articulates posteriorly with facets (demifacets) on bodies of two adjacent vertebrae Neck Tubercle Articulates posteriorly with transverse costal facet of same-numbered thoracic vertebra Shaft

Transverse costal facet (for tubercle of rib) Superior costal facet
(for head of rib) Angle of rib Body of vertebra Head of rib Intervertebral disc Neck of rib Tubercle of rib Shaft Sternum Cross- section of rib Costal groove Costal cartilage (a) Vertebral and sternal articulations of a typical true rib Figure 7.23a

Articular facet on tubercle of rib Spinous process Shaft Transverse
costal facet (for tubercle of rib) Ligaments Neck of rib Body of thoracic vertebra Head of rib Superior costal facet (for head of rib) (b) Superior view of the articulation between a rib and a thoracic vertebra Figure 7.23b

7 The Skeleton: Part A.

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7 The Skeleton: Part A.

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