Skeletal System

8.1 Components of the Skeleton

8.1a The Two Divisions of the Skeletal System

  • Axial Skeleton

    • Composed of 80 bones.

    • Includes the bones of the skull, vertebral column, and rib cage.

  • Appendicular Skeleton

    • Composed of 126 bones.

    • Includes the bones of the upper and lower limbs, and the girdles that attach them to the axial skeleton.

8.1b Cranial Bones

  • There are eight cranial bones:

    1. Frontal Bone - forms the forehead.

    2. Parietal Bones (2) - located on the sides and roof of the skull.

    3. Temporal Bones (2) - located beneath the parietal bones, involved in hearing and balance.

    4. Occipital Bone - forms the back and base of the skull, contains the foramen magnum.

    5. Sphenoid Bone - resembles a butterfly; articulates with all other cranial bones.

    6. Ethmoid Bone - located between the nasal cavity and the orbits, contributes to the nasal septum and the medial wall of the orbits.

8.5 Bones of the Vertebral Column

8.5a Types of Vertebrae

  • The vertebral column is composed of 33 vertebrae divided into five regions:

    1. Cervical Region - 7 vertebrae (C1-C7).

    2. Thoracic Region - 12 vertebrae (T1-T12).

    3. Lumbar Region - 5 vertebrae (L1-L5).

    4. Sacral Region - 5 fused vertebrae forming the sacrum.

    5. Coccygeal Region - 4 fused vertebrae forming the coccyx.

8.5b Spinal Curvatures

  • Primary Curvatures:

    • Thoracic Curvature - accommodates the thoracic organs.

    • Sacral Curvature - accommodates the pelvic organs.

  • Three Main Spinal Curvature Deformities:

    1. Kyphosis - excessive outward curvature of the spine, typically in the thoracic region.

    2. Lordosis - excessive inward curvature of the lumbar region, often referred to as swayback.

    3. Scoliosis - lateral curvature of the spine.

8.5c Vertebral Anatomy

  • All vertebrae share common structural features:

    • Vertebral Body - bears weight.

    • Vertebral Arch - forms the posterior part of the vertebra.

    • Vertebral Foramen - the hole through which the spinal cord passes.

    • Transverse Processes - lateral projections for muscle attachment.

    • Spinous Process - posterior projection for muscle and ligament attachment.

8.7 The Upper and Lower Limbs: A Comparison

  • Pectoral Girdle vs Pelvic Girdle:

    • Pectoral Girdle:

    • Composed of the clavicle and scapula.

    • Provides a high degree of mobility.

    • Less stable than the pelvic girdle.

    • Pelvic Girdle:

    • Composed of the os coxae (hip bones).

    • More stable and supports weight during bipedal locomotion.

8.8 The Pectoral Girdle and Its Functions

Bones of the Pectoral Girdle

  • Clavicle:

    • Acts as a strut to keep the shoulder in place.

  • Scapula:

    • Provides attachment points for muscles that move the upper limb.

8.9 Bones of the Upper Limb

Number of Bones in the Upper Limb

  • There are 30 bones in the upper limb:

    • Humerus (1)

    • Radius (1)

    • Ulna (1)

    • Carpals (8)

    • Metacarpals (5)

    • Phalanges (14)

8.9a Humerus

  • Difference between the Surgical and Anatomical Neck:

    • Anatomical Neck: located just below the head of the humerus.

    • Surgical Neck: located further down the humerus; common fracture site.

8.9b Radius and Ulna

  • The Radius:

    • Located on the lateral side of the forearm, primarily involved in wrist movement.

  • The Ulna:

    • Located on the medial side of the forearm, primarily aligns with the pinky finger.

8.9c Carpals, Metacarpals, and Phalanges

  • Carpals:

    • Eight small bones forming the wrist.

  • Metacarpals:

    • Five bones forming the middle part of the hand.

  • Phalanges:

    • Fourteen bones forming the fingers and thumb.

8.10 The Pelvic Girdle and Its Functions

Description of the Pelvis

  • The pelvis supports the weight of the upper body and protects pelvic organs.

8.10a Os Coxae

  • Os Coxae:

    • Each os coxae is formed by the fusion of three bones: ilium, ischium, and pubis.

8.11 Bones of the Lower Limb

8.11a Femur and Patella

  • Basic Characteristics of the Femur:

    • The longest and strongest bone in the body, articulates with the acetabulum of the pelvic girdle.

    • Patella (kneecap) protects the knee joint.

8.11b Tibia and Fibula

  • Crura:

    • The tibia is the larger, weight-bearing bone of the leg.

    • The fibula is a slender bone that stabilizes the ankle.

8.11c Tarsals, Metatarsals, and Phalanges

  • Bones of the Ankle and Foot:

    • Tarsals:

      • Seven bones that comprise the ankle.

    • Metatarsals:

      • Five bones that form the middle part of the foot.

    • Phalanges:

      • Fourteen bones that form the toes.