Skeletal System Overview

• Course: Anatomy and Physiology I (BS 121)
• Instructor: Dr. Nancy Brandt
• Chapters Covered: 11-14

Divisions of the Skeleton

• Axial Skeleton
  • Composed of 80 bones including head, neck, and torso.
  • Consists of:
  • 74 bones forming the upright axis of the body
  • 6 tiny middle ear bones
• Appendicular Skeleton
  • Composed of 126 bones forming appendages to the axial skeleton.
  • Formed by the upper and lower extremities.

Major Bones of the Skeleton

• Axial Skeleton Structures:

  • Frontal bone
  • Nasal bone
  • Zygomatic bone
  • Maxilla
  • Mandible
  • Sternum
  • Ribs
  • Vertebral column
  • Cervical vertebrae (7)
  • Thoracic vertebrae (12)
  • Lumbar vertebrae (5)
  • Sacrum
  • Coccyx
  • Coxal (hip) bones
  • Ilium
  • Ischium
  • Pubis
  • Clavicle
  • Scapula

• Appendicular Skeleton Structures:

  • Humerus
  • Radius
  • Ulna
  • Femur
  • Patella
  • Tibia
  • Fibula
  • Carpal bones
  • Metacarpal bones
  • Phalanges
  • Tarsal bones
  • Metatarsal bones

Axial Skeleton Details

Skull

• Composed of 28 bones divided into cranial bones and facial bones.

Cranial Bones

1. Frontal Bone:

   • Forms the forehead and anterior part of the top of the cranium.
   • Contains frontal sinuses.
   • Forms the upper portion of the orbits.
   • Forms the coronal suture with the two parietal bones.

2. Parietal Bones:

   • Form the bulging top of the cranium.
   • Form several sutures:
     • Lambdoid suture with the occipital bone.
     • Squamous suture with the temporal bone and part of the sphenoid.
     • Coronal suture with the frontal bone.

3. Temporal Bones:

   • Form several sutures, including:
     • Lambdoid
     • Squamous
     • Coronal

4. Occipital Bone:

   • Forms the lower, posterior part of the skull.
   • Forms immovable joints with three other cranial bones and a movable joint with the first cervical vertebra.

5. Sphenoid Bone:

   • Bat-shaped bone located in the central portion of the cranial floor.
   • Anchors the frontal, parietal, occipital, and ethmoid bones and forms part of the lateral wall of the cranium and part of the floor of each orbit.
   • Contains sphenoid sinuses.

6. Ethmoid Bone:

   • Irregular bone that lies anterior to the sphenoid and posterior to the nasal bones.
   • Forms the anterior cranial floor, medial orbit walls, upper parts of the nasal septum, and sidewalls of the nasal cavity.
   • Contains the cribriform plate.

Facial Bones

1. Maxilla (Upper Jaw):

   • Two maxillae form the keystone of the face.
   • Articulate with nasal, zygomatic, inferior concha, and palatine bones.
   • Form parts of the orbital floors, roof of the mouth, and floor and sidewalls of the nose.
   • Contains maxillary sinuses.

2. Mandible (Lower Jaw):

   • Largest and strongest bone of the face.
   • Forms the only movable joint of the skull with the temporal bone.

3. Zygomatic Bone:

   • Shapes the cheek and forms the outer margin of the orbit.
   • Forms the zygomatic arch with the zygomatic process of the temporal bones.

4. Nasal Bone:

   • Both nasal bones form the upper part of the bridge of the nose; the lower part is made of cartilage.
   • Articulates with the ethmoid, nasal septum, frontal bone, maxilla, and the other nasal bone.

5. Lacrimal Bone:

   • Thin bone that lies just posterior and lateral to each nasal bone.
   • Forms the nasal cavity and medial wall of the orbit; contains a groove for the nasolacrimal duct.
   • Articulates with maxilla, frontal, and ethmoid bones.

6. Palatine Bone:

   • Two bones that form the posterior part of the hard palate.
   • The vertical portion forms the lateral wall of the posterior part of each nasal cavity.
   • Articulates with the maxillae and sphenoid bone.

7. Inferior Nasal Concha:

   • Forms the lower edge projecting into the nasal cavity and forms the nasal meatus.
   • Articulates with ethmoid, lacrimal, maxillary, and palatine bones.

8. Vomer Bone:

   • Forms the posterior portion of the nasal septum.
   • Articulates with the sphenoid, ethmoid, palatine, and maxillae.

Fetal Skull

• Characterized by unique anatomical features not seen in adult skulls.
• Fontanels (soft spots) allow the skull to mold during birth and allow for rapid growth of the brain.

Hyoid Bone

• U-shaped bone located just above the larynx and below the mandible.
• Suspended from the styloid processes of the temporal bone.
• Notable for being the only bone in the human body that articulates with no other bones.

Vertebral Column

• Composed of 24 vertebrae, plus the sacrum and coccyx.
• Vertebrae articulate with each other and with the ribs, forming the vertebral column as a flexible longitudinal axis of the skeleton.
• Notable features of vertebrae:
  • The cervical vertebrae have distinct characteristics compared to the thoracic and lumbar vertebrae, including unique attachment points for muscles and the skull.

Sternum

• Dagger-shaped bone in the anterior chest wall composed of three parts:
  • Manubrium (upper handle part)
  • Body (middle blade part)
  • Xiphoid Process (blunt cartilaginous lower tip, ossifies with age)

Ribs

• Twelve pairs of ribs articulate with the vertebral column and sternum, forming the thoracic cage.
• Ribs attach directly to the sternum in various ways (true ribs vs. false ribs) and articulate with vertebrae in specific patterns depending on the rib.

Review Questions

1. Name the eight bones of the cranium and describe how they fit together.
2. Name the fourteen bones of the face and describe their articulation.
3. Which bone is unique in not forming a joint with any other bones in the skeleton?

Conclusion

• Understanding the skeletal system is crucial for grasping the anatomy and physiology of the human body, forming the foundational structure for all other anatomical study.