Skeletal System I

Skeletal System I

• The skeleton consists of bones, cartilage, joints, and ligaments
• It's composed of 206 named bones divided into two sections: Axial and Appendicular
• Axial Skeleton: includes the skull, vertebral column, and thoracic cage (80 bones)
• Appendicular Skeleton: includes the bones of the upper and lower limbs (126 bones)

Skull

• Formed from cranial and facial bones
• Cranium: encloses the brain
  • Composed of 8 bones: 1 frontal, 2 parietal, 2 temporal, 1 occipital, 1 ethmoid, 1 sphenoid bones
• Facial Bones: form the face; 14 bones (12 paired & 2 single bones):
  • 2 nasal bones, 2 maxillary bones, 2 zygomatic bones, 2 lacrimal bones, 2 palatine bones, 2 inferior nasal conchae, 1 vomer, 1 mandible

Skull Cavities

• Middle and inner ear cavities (lateral aspect of cranial base)
• Nasal cavities
• Orbits (house the eyeballs)
• Air-filled sinuses (occur near nasal cavity: four paranasal air sinuses)

Cranial Foramina

• Approximately 85 openings (foramina, canals, and fissures) in the skull
• Provide passageways for: spinal cord, blood vessels serving the brain, and 12 pairs of cranial nerves

Cranial Bone Sutures

• Three main sutures:
  • Coronal suture: parietal/frontal bones meet
  • Sagittal suture: right/left parietal bones meet
  • Lambdoid suture: parietal/occipital bones meet

Bones of the Face, Including the Nose

• Includes the bones forming the face, including the nose.
• Frontal, temporal, nasal, zygomatic, maxilla, mandible

Paranasal Sinuses

• Air-filled spaces in the skull bones
• Types: frontal, ethmoidal, sphenoidal, maxillary (largest)

Neonatal Skull

• Cranial bones are incompletely fused in infants.
• Soft spots (fontanelles) are found on the skull.

Hyoid Bone

• Lies inferior to the mandible and superior to the larynx.
• The only bone with no direct articulation with any other bone.
• It serves as a base for the tongue, offering attachment points for swallowing muscles.

Vertebral Column

• Formed from 26 separate bones in adults
• Transmits trunk weight to lower limbs.
• Surrounds and protects spinal cord, provides attachments for neck/back muscles.
• Sections include: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral fused vertebrae, and 3-4 coccyx fused vertebrae.
• Supported by ligaments (anterior & posterior longitudinal ligaments, ligamentum flavum) and synovial joints

Intervertebral Discs

• Cushion-like pads between vertebrae
• Act as shock absorbers
• Composed of nucleus pulposus (inner gelatinous material) and annulus fibrosis (outer ring of cartilage)
• Note: A remnant of the notochord becomes part of the nucleus pulposus.*

Normal Vertebral Curvatures

• Four characteristic curves in the vertebral column (S shape)
• Cervical and lumbar curvatures are concave posteriorly
• Thoracic and sacral curvatures are convex posteriorly
• These curvatures increase the resilience of the spine
• A fetus initially has only thoracic and sacral curvatures.

Abnormal Vertebral Curvatures

• Scoliosis, kyphosis, lordosis are examples of abnormal curvatures

Thoracic Cage

• Composed of thoracic vertebrae, ribs, and rib cartilages, and the sternum
• Protects the heart and lungs
• Sternum's shape is like a dagger; constructed of manubrium, body, and xiphoid process

Ribs

• 12 pairs (true and false).
• First 10 pairs attach to the sternum via hyaline cartilage; the lower two (floating ribs) do not attach to the sternum.