Skeletal System

Skeletal System Study Guide

Overview of the Skeletal System

  • The human skeletal system is composed of 206 bones.

I. Major Divisions of the Skeletal System
A. Axial Skeleton

  • Comprises the upright, central supporting axis of the body.

  • Components:

    1. Skull

    2. Rib Cage

    3. Vertebral Column

  • Notable bones found in the axial skeleton (refer to page 117).

B. Appendicular Skeleton

  • Consists of the bones of the limbs and the pelvic and shoulder areas.

  • Notable bones found in the appendicular skeleton (refer to page 117).

C. The Adult Skeleton

  • Reference to content on page 117.

The Skull

  • The skull is made up of 22 flat-shaped bones.

A. Cranium

  • Important bones include:

    1. Parietal Bones

      • Location: Sides and roof of the skull.

    2. Occipital Bones

      • Location: Back and base of the skull.

    3. Frontal Bone

      • Location: Forehead and anterior portion of the skull.

    4. Temporal Bones

      • Location: Sides of the skull, near the ears.

    5. Sphenoid Bone

      • Location: Base of the skull; forms part of the floor of the cranium.

    6. Ethmoid Bone

      • Location: Between the eyes; forms part of the nasal cavity and eye orbits.

B. Suture Lines

  • Coronal Suture: Between the parietal and occipital bones and frontal bone.

  • Lamboid Suture: Between parietal and occipital bones.

  • Squamous Suture: Between the parietal and temporal bones.

  • Sagittal Suture: Between the two parietal bones.

C. Bones Associated with the Skull

  1. Hyoid Bone

    • Characteristics: V-shaped bone that does not articulate with other bones.

    • Location: In neck, between the chin and larynx.

    • Function: Supports the tongue and assists with swallowing and speech.

D. The Infant Skull

  1. Differences Between Infant and Adult Skull:

    • Suture lines in the skull have not yet fused.

    • Purpose for Unfused Suture Lines: Allows for flexibility during birth and growth.

    • Age When Skull Bones Begin to Fuse: Typically begins at about 2 months of age.

  2. Fontanels (Soft Spots)

    • Definition: Areas on an infant's skull where the bones have not yet fused, allowing for brain growth.

    • Posterior Fontanel: Closes first, usually by 2 months of age.

    • Anterior Fontanel: Closes by about 18 months of age.

Vertebral Column

A. Five Sections of the Vertebral Column

  1. Cervical Vertebrae: 7 (neck)

  2. Thoracic Vertebrae: 12 (chest)

  3. Lumbar Vertebrae: 5 (lower back)

  4. Sacrum: 5 fused vertebrae

  5. Coccyx: fused vertebrae.

B. Vertebrae Characteristics

  1. Vertebral Foramen: Opening through which the spinal cord passes.

  2. Body: Weight-bearing portion of the vertebra.

  3. Spinous Process: Posterior projection for muscle attachment.

  4. Transverse Process: Lateral projection for muscle attachment.

  5. Intervertebral Disc:

    • Herniated Disc: Condition where the disc protrudes and presses on spinal cord nerves.

C. Specialty Vertebrae

  1. Atlas: First cervical vertebra; supports the skull and allows for head rotation.

  2. Axis: Second cervical vertebra; enables head rotation.

Thoracic Cage

A. Components

  1. Sternum

  2. Ribs

    • Manubrium: Superior portion of sternum

    • Body: Middle portion of sternum

    • Xiphoid Process: Inferior tip of the sternum

  3. Types of Ribs:

    • True Ribs: 1-7

    • False Ribs: 8-10

    • Floating Ribs: 11-12

B. Costal Margin

  • The lower edge of the rib cage formed by costal cartilage.

C. Conditions and Diseases

  • Conditions such as COPD (Chronic Obstructive Pulmonary Disease) may increase the angle of the costal margin.

Pectoral Girdle

  1. Clavicle: Collarbone.

  2. Scapula: Shoulder blade.

Upper Limb

  1. Humerus: Upper arm bone.

  2. Ulna: Medial forearm bone (pinky side).

  3. Radius: Lateral forearm bone (thumb side).

A. Hand Composition

  1. Wrist: Composed of carpal bones.

  2. Palm: Composed of metacarpal bones.

  3. Fingers: Composed of phalanges.

Pelvic Girdle

  1. Os Coxae: Each hip bone consists of three parts:

    • Ilium: Superior, flared portion of hip bone.

    • Ischium: Inferior, posterior portion of hip (sit bones).

    • Pubis: Anterior portion of hip bone.

    • Symphysis Pubis: Fibrocartilaginous joint between left and right pubic bones.

B. Features as Landmarks

  • Specific landmarks visible in a lateral view (refer to page 130).

Lower Limb

  1. Bones of the Lower Limb:

    • Femur: Thigh bone; longest and strongest in the body.

    • Patella: Kneecap.

    • Fibula: Lateral lower leg bone.

    • Tibia: Medial lower leg bone.

A. Foot and Ankle Composition

  1. Phalanges: Toe bones

    • Distal: Farthest from the body

    • Middle: Between proximal and distal (toes 2-5)

    • Proximal: Closest to the body

  2. Metatarsals: Bones in the midfoot (arch).

  3. Tarsal Bones: Comprising the ankle, include Talus, Calcaneus, Navicular, Cuboid, and Cuneiforms.