Skeletal System Organization

General Organization of the Skeletal System

The skeletal system provides the structural framework for the human body, supporting movement, protecting organs, and storing minerals. It is divided into two main parts: the axial skeleton and the appendicular skeleton.

• Axial Skeleton: Consists of the skull, vertebral column, and thoracic cage (ribs and sternum). It supports and protects the brain, spinal cord, and thoracic organs.

• Appendicular Skeleton: Includes the bones of the limbs and girdles (pectoral and pelvic), facilitating movement and interaction with the environment.

Key Terms: Axial skeleton, appendicular skeleton, girdles, thoracic cage.

Example: The femur is part of the appendicular skeleton, while the vertebrae are part of the axial skeleton.

Axial Skeleton: Skull and Vertebral Column

Skull Anatomy

The skull is composed of cranial and facial bones, protecting the brain and forming the structure of the face.

• Cranial Bones: Frontal, parietal, temporal, occipital, sphenoid, ethmoid.

• Facial Bones: Mandible, maxilla, zygomatic, nasal, lacrimal, palatine, vomer, inferior nasal concha.

• Key Landmarks: Foramen magnum, occipital condyles, external acoustic meatus, mastoid process.

Example: The occipital bone contains the foramen magnum, through which the spinal cord passes.

Vertebral Column

The vertebral column supports the body and protects the spinal cord. It is divided into regions based on vertebrae type and location.

• Cervical (7): Smallest vertebrae, support the head, allow for rotation (e.g., atlas and axis).

• Thoracic (12): Articulate with ribs, have long spinous processes.

• Lumbar (5): Largest vertebrae, support most body weight.

• Sacral (5, fused): Form the sacrum, connect spine to pelvis.

• Coccygeal (4, fused): Form the coccyx (tailbone).

Key Terms: Intervertebral discs, vertebral foramen, spinous process, transverse process.

Example: The atlas (C1) allows the head to nod, while the axis (C2) allows rotation.

Thoracic Cage and Sternum

Thoracic Cage

The thoracic cage protects vital organs and supports breathing. It consists of the ribs, sternum, and thoracic vertebrae.

• Ribs: 12 pairs; true ribs (1-7), false ribs (8-12), floating ribs (11-12).

• Sternum: Manubrium, body, xiphoid process.

• Functions: Protection, support, respiration.

Example: The manubrium articulates with the clavicles and first pair of ribs.

Appendicular Skeleton: Upper and Lower Limbs

Pectoral Girdle and Upper Limb

The pectoral girdle connects the upper limb to the axial skeleton and consists of the clavicle and scapula.

• Clavicle: S-shaped bone, articulates with sternum and scapula.

• Scapula: Flat bone, features include acromion, coracoid process, glenoid cavity.

• Upper Limb Bones: Humerus, radius, ulna, carpals, metacarpals, phalanges.

Key Landmarks: Deltoid tuberosity (humerus), olecranon process (ulna), styloid process (radius).

Example: The glenoid cavity of the scapula articulates with the head of the humerus.

Pelvic Girdle and Lower Limb

The pelvic girdle supports the lower limb and consists of the hip bones (ilium, ischium, pubis).

• Pelvic Bones: Ilium (superior), ischium (posterior/inferior), pubis (anterior/inferior).

• Lower Limb Bones: Femur, patella, tibia, fibula, tarsals, metatarsals, phalanges.

• Key Landmarks: Greater trochanter (femur), medial malleolus (tibia), lateral malleolus (fibula).

Example: The acetabulum of the pelvis articulates with the head of the femur.

Bone Structure and Landmarks

General Bone Structure

Bones are composed of compact and spongy tissue, providing strength and flexibility. Key features include:

• Diaphysis: Shaft of a long bone, composed of compact bone.

• Epiphysis: Ends of a long bone, contain spongy bone and red marrow.

• Articular Cartilage: Covers joint surfaces, reduces friction.

• Periosteum: Dense connective tissue covering bone surface.

Example: The femur's diaphysis is the main weight-bearing region.

Bone Markings and Landmarks

Bones have specific markings for muscle attachment, articulation, and passage of nerves and blood vessels.

• Foramen: Opening for nerves/vessels (e.g., foramen magnum).

• Process: Projection for muscle/ligament attachment (e.g., mastoid process).

• Fossa: Depression for articulation (e.g., olecranon fossa).

• Crest: Prominent ridge (e.g., iliac crest).

Example: The greater trochanter of the femur is a major site for muscle attachment.

Special Bones and Structures

Hyoid Bone

The hyoid bone is a unique U-shaped bone in the neck that supports the tongue and is not directly articulated with other bones.

• Location: Anterior neck, between mandible and larynx.

• Function: Supports tongue, aids in swallowing and speech.

Example: The hyoid bone is fractured in some cases of strangulation.

Articulations and Joints

Types of Articulations

Articulations (joints) are connections between bones that allow for movement and flexibility.

• Fibrous Joints: Immovable, bones joined by dense connective tissue (e.g., sutures of the skull).

• Cartilaginous Joints: Slightly movable, bones joined by cartilage (e.g., intervertebral discs).

• Synovial Joints: Freely movable, contain synovial fluid (e.g., shoulder, knee).

Example: The shoulder joint is a synovial ball-and-socket joint.

Selected Bone Landmarks: Table

The following table summarizes key bone landmarks and their anatomical significance.

Additional info:

• Some anatomical terms and examples have been inferred for completeness and clarity.

• Clinical significance of bone landmarks includes their use in physical examination and diagnosis of fractures or dislocations.