Axial and Appendicular Skeleton: Structure and Function Study Guide

Axial Skeleton

Overview of the Axial Skeleton

The axial skeleton forms the central axis of the human body and provides support and protection for vital organs. It consists of several major bone groups.

• Skull, vertebral column, thoracic cage: These structures protect the brain, spinal cord, and thoracic organs.

• Shoulder and hip girdles: Additional info: These are technically part of the appendicular skeleton, but sometimes included for context.

• Clavicle, scapula, and ribs: Ribs form the thoracic cage; clavicle and scapula are part of the pectoral girdle.

Main Functions of the Axial Skeleton

The axial skeleton serves several essential functions in the body:

• Produce movement: Provides attachment points for muscles that facilitate movement.

• Protect and support vital organs: Shields the brain, heart, lungs, and spinal cord.

• Store fat: Some bones contain marrow that stores fat.

• Anchor muscles for the limbs: Serves as a foundation for limb movement.

Connections Between Skull Bones

Skull bones are joined by specialized structures:

• Sutures: Immovable joints that fuse skull bones together.

• Cartilage plates, tendons, ligaments: Additional info: Sutures are the primary connection in the adult skull; cartilage and ligaments are more relevant in other joints.

Key Foramina and Bone Landmarks

Openings and depressions in bones serve as passageways and attachment points:

• Foramen magnum: Located in the occipital bone; allows passage of the spinal cord.

• Sella turcica: A depression in the sphenoid bone that houses the pituitary gland.

Bone Articulations and Isolated Bones

• Mandible: The only skull bone that does not articulate directly with another bone; forms the lower jaw.

• Vomer, hyoid, maxilla: Additional info: The hyoid bone is unique in that it does not articulate with any other bone, but is suspended by ligaments.

Movements and Features of the Spine

The vertebral column allows for various movements and contains specialized vertebrae:

• Nodding "yes": Movement at the atlanto-occipital joint.

• Flexion of the spine: Bending forward.

• Axis (C2) vertebra: Contains the odontoid process (dens), which allows rotation of the head.

Distinguishing Cervical Vertebrae

• Transverse foramina: Openings in cervical vertebrae for vertebral arteries.

• Large, heart-shaped bodies; long spinous processes: Additional info: These features are more typical of thoracic and lumbar vertebrae.

Thoracic Cage and Rib Classification

The thoracic cage protects vital organs and is composed of ribs and the sternum.

• Protects: Heart, lungs, major blood vessels.

• True ribs: Ribs 1–7, which attach directly to the sternum.

• Floating ribs: Ribs 11–12, which do not attach to the sternum.

Sternum Structure

• Three parts: Manubrium, body, xiphoid process.

• Additional info: The sternum does not include the clavicle or scapula as structural parts.

Appendicular Skeleton

Overview of the Appendicular Skeleton

The appendicular skeleton consists of the bones of the limbs and girdles, which facilitate movement and interaction with the environment.

• Limbs and girdles: Includes arms, legs, pectoral and pelvic girdles.

• Head and trunk, thoracic cage, vertebral column: Additional info: These are part of the axial skeleton.

Pectoral Girdle Structure

• Clavicle and scapula: Form the shoulder girdle.

• Scapula and sternum, humerus and clavicle, sternum and ribs: Additional info: Only the clavicle and scapula form the pectoral girdle.

Glenoid Cavity and Articulations

• Glenoid cavity: Located on the scapula; articulates with the head of the humerus to form the shoulder joint.

• Clavicle's medial end: Articulates with the sternum.

Humerus Landmarks

• Surgical neck: Common site of fractures.

• Olecranon process: Located on the ulna; forms the point of the elbow.

Wrist and Hand Bones

• Carpus (wrist): Contains 8 bones.

• Phalanges: The hallux (big toe) has 2 phalanges.

Pelvic Girdle and Lower Limb

• Acetabulum: Deep socket in the pelvis that articulates with the femur.

• Fibula: Does not bear weight but stabilizes the ankle; is shorter and lateral to the tibia.

• Calcaneus: Heel bone; largest tarsal bone.

Summary Table: Rib Classification

The following table summarizes the classification of ribs:

Type of Rib	Numbers	Attachment
True Ribs	1–7	Directly to sternum
False Ribs	8–10	Indirectly to sternum via cartilage
Floating Ribs	11–12	No anterior attachment

Summary Table: Sternum Parts

Part	Description
Manubrium	Upper portion; articulates with clavicles and first ribs
Body	Main central portion
Xiphoid Process	Small, cartilaginous lower tip

Key Terms and Definitions

• Foramen magnum: Large opening in the occipital bone for the spinal cord.

• Sella turcica: Depression in the sphenoid bone for the pituitary gland.

• Glenoid cavity: Socket in the scapula for the humerus.

• Acetabulum: Socket in the pelvis for the femur.

• Olecranon process: Projection of the ulna forming the elbow.

Equations and Formulas

• Number of bones in the wrist:

$\text{Number of carpal bones} = 8$

• Number of phalanges in the hallux (big toe):

$\text{Phalanges in hallux} = 2$

Examples and Applications

• Clinical relevance: Fractures of the surgical neck of the humerus are common in elderly patients.

• Movement: The axis (C2) allows rotation of the head, as in shaking "no".

• Protection: The thoracic cage shields the heart and lungs from external injury.

Additional info: Some answer choices and details were inferred based on standard anatomy and physiology curriculum.