Chapter 8 - Skeletal System (cranium and facial bones vertebrae, thoracic cage and ribs)

Skeletal System

Composed of bones, cartilages, joints, ligaments

Two major parts of Skeletal System

Axial and Appendicular

Axial

• skull — cranium and facial bones

• vertebral column — cervical, thoracic, lumbar, sacrum, and coccyx

• thoracic cage

Eight cranial bones

• Parietal (2)

• Ethmoid

• Sphenoid

• Temporal (2)

• Occipital

• Frontal

• 6

Frontal bone (forehead)

• Anterior portion of cranium

• most of anterior cranial fossa

• superior wall of orbits

• contains air filled frontal sinus

• articulates with parietal bones by coronal suture

Parietal Bones and Major Associated Sutures (walls)

• Superior and lateral aspects of cranial vault

• Coronal suture

• Sagittal suture

• Lambdoid suture

• Squamous (squamosal) sutures

Location of coronal suture

Between parietal bones and frontal bone

Location of Sagittal suture

Between right and left parietal bones

Location of Lambdoid suture

Between parietal bones and occipital bone

Location of Squamous sutures

Between parietal and temporal bones on each side of skull

Mnemonic

Class

Occipital Bone

• Most of skulls posterior wall and posterior cranial fossa

• Articulates with 1st vertebra

• Sites of attachment for ligamentum nuchae and many neck and back muscles

Temporal Bones

• Inferolateral aspects of skull and parts of cranial floor

• squamous - zygomatic

• tympanic - outer ear

• mastoid - anchor for neck MM

• petrous - inner/middle ear

Sphenoid Bone

• complex, bat shaped bone

• embedded in skull

• keystone bone

• three pairs of processes

Keystone bone

Articulated with all other cranial bones

Three pairs of processes in Sphenoid Bone

• greater wings

• lesser wings

• pterygoid processes

Ethmoid Bone (delicate bone)

• deepest skull bone

• superior part of nasal septum, roof of nasal cavities

• contributes to medial wall of orbits

• crista galli for dural attachment, secures brain in cranial activity

Fourteen Facial Bones

• Mandible

• Maxillary bones (maxillae) (2)

• Zygomatic bones (2)

• nasal bones (2)

• lacrimal bones (2)

• palatine bones (2)

• vomer

• inferior nasal conchae (2)

• Zoro Likes Punching my Vertebrae

Mandible

• lower jaw, U-shaped

• largest, strongest bone of face

• body and 2 rami

• temporomandibular joint (TMJ) — only freely movable joint in skull

Maxillary Bones

• keystone bones — articulate with all other facial bones except mandible

• contain maxillary sinuses — largest paranasal sinuses

Zygomatic bones

• cheekbones

• inferolateral margins of orbits

Nasal Bones

Form bridge of nose

Lacrimal Bones

• in medial walls of orbits

• lacrimal fossa houses lacrimal sac

Palatine Bones

• posterior one third of hard palate

• posterolateral walls of the nasal cavity

• small part of the orbits

Vomer

• plow shaped

• inferior part of nasal septum

Orbits

• cavities that encase eyes and lacrimal glands

• sites of attachment for eye muscles

• formed by parts of seven bones

  • frontal, sphenoid, zygomatic, maxilla, palatine, lacrimal, and ethmoid

Nasal cavity

• formed by parts of four bones

  • ethmoid

  • palatine bones

  • maxillary bones

  • inferior nasal conchae

• nasal septum of bone and hyaline cartilage

  • perpendicular plate of ethmoid

  • vomer

  • anterior septal cartilage

Ethmoid

sup/middle conchae

Palatine bones

perpendicular plates

Paranasal Sinuses

• frontal sinus

• ethmoid air cells (sinus)

• sphenoidal sinus

• maxillary sinus

Function of Paranasal Sinuses

• mucosa-lined, air filled spaces

• lighten skull

• enhance resonance of voice

• warm and humidify air

Hyoid bone

• not bone of skull

• does not articulate directly with another bone, attached by ligaments to styloid process

• movable base for tongue

• site of attachment for muscles of swallowing and speech

Vertebral column

• transmits weight of trunk to lower limbs

• surrounds and protects spinal cord

• flexible curved structure containing 26 irregular bones (vertebrae) in five major regions

  • cervical vertebrae

  • thoracic vertebrae

  • lumbar vertebrae

  • sacrum

  • coccyx

Cervical vertebrae (7)

Vertebrae of neck

Thoracic vertebrae (12)

vertebrae of thoracic cage

Lumbar vertebrae (5)

vertebrae of lower back

Sacrum

Bone inferior to lumbar vertebrae

Coccyx

terminus of vertebral column

Vertebral Column: curvatures

• increase resilience and flexibility of spine

  • cervical and lumbar curvatures

    • concave posteriorly

  • thoracic and sacral curvatures

    • convex posteriorly

• abnormal spine curvatures

  • scoliosis

  • kyphosis

  • lordosis

Scoliosis

Abnormal lateral curve

Kyphosis (hunchback)

exaggerated thoracic curvature

Lordosis (sawyback)

accentuated lumbar curvature

Intervertebral Discs

• cushion like pad composed of two parts

  • nucleus pulposus

  • anulus fibrosus

Nucelus pulposus

• inner gelatinous nucleus

• gives disc its elasticity and compressibility

Annulus fibrosus

• outer collar composed of collagen and fibrocartilage

• limits expansion of nucleus pulposus

General structure of vertebrae

• body or centrum

• vertebral arch

• vertebral foramina

• intevertebral foramina

Body or centrum of vertebrae

anterior weight bearing region

Vertebral arch of vertebrae

composed of pedicles and laminae that, along with centrum, enclose vertebral foramen

Vertebral foramina or vertebrae

Together make up vertebral canal for spinal cord

Intevertebral foramina in vertebrae

lateral openings between adjacent vertebrae for spinal nerves

Cervical (C1-C7) Vertebrae

• short spinous process (bifid)

• transverse foramen in transverse processes

• C1 (atlas), C2 (axis)

Thoracic (T1-T2) vertebrae

• long, down-ward pointing spinous processes

• articulate with ribs in posterior

Lumbar (L1-L5) Vertebrae

• short, hatchet-shaped spinous processes

• very large bodies

Cervical Vertebrae Atlas C1

• no body or spinous process

• consists of anterior and posterior arches

• articulate with occipital condyles

• movement for “yes”

• carries the skull

Cervical Vertebrae Axis (C2)

• dens projects superiorly into anterior arch of atlas

  • is missing body of atlas

• dens is a pivot for rotation of atlas

• movement for “no”

• no intervertebral disc between atlas and axis

Thoracic Vertebrae T1 to T12

Cricular vertebral foramen, long spinous process, facet for rib attachment

Lumbar Vertebrae L1-5 function

Receives the most stress, hatchet-like spinous process

Lumbar Laminectomy

Decompression for Spinal stenosis

Sacrum

• 5 fused vertebrae (S1-S5)

• forms posterior wall of pelvis, completes the ring

• articulates with L5 superiorly, and with auricular surfaces of hip bones, forming sacroiliac joints

Coccyx

• tailbone

• 3-5 fused vertebrae

• articulates superiorly with sacrum

Ribs and their attachments

• all attach posteriorly to bodies and transverse processes of thoracic vertebrae

• pairs 1-7

  • true ribs

• pairs 8-12

  • false ribs

• pairs 11-12

  • floating ribs

True ribs (pairs 1-7)

Attach directly to sternum via costal cartilage

False ribs (pairs 8-10)

attach indirectly by joining cartilage of rib above

Floating ribs (pairs 11-12)

no attachment to sternum