Skeletal System: Gross Anatomy Study Guide

Skeletal System: Gross Anatomy

Overview of the Skeletal System

The human skeletal system provides structural support, protection for internal organs, and facilitates movement. An adult human typically has 206 bones, which are organized into two main divisions: the axial skeleton and the appendicular skeleton.

• Axial Skeleton: Consists of the skull, ossicles (middle ear bones), hyoid bone, vertebral column, and thoracic cage (ribs and sternum).

• Appendicular Skeleton: Includes the bones of the upper and lower limbs, as well as the pectoral (shoulder) and pelvic girdles.

Classification of Bones by Shape

Bones are classified according to their shapes, which relate to their functions and locations in the body.

• Long Bones: Longer than they are wide; primarily found in the limbs (e.g., femur, humerus).

• Short Bones: Approximately equal in length and width; found in the wrist (carpals) and ankle (tarsals).

• Flat Bones: Thin and often curved; provide protection and broad surfaces for muscle attachment (e.g., skull, ribs, sternum).

• Irregular Bones: Complex shapes that do not fit other categories (e.g., vertebrae, sphenoid bone).

Skeletal Terminology

Specific terms are used to describe the features of bones, which are important for understanding bone anatomy and for identifying attachment sites for muscles and ligaments.

Projections (Processes)

• Process: Prominent projection on a bone.

• Head: Enlarged, often rounded end of a bone.

• Neck: Constriction between head and body of a bone.

• Border or Margin: Edge of a bone.

• Angle: Bend in a bone.

• Ramus: Branch off the body of a bone.

• Crest: Prominent ridge.

• Line: Low ridge.

• Spine: Sharp, slender projection.

• Tubercle: Small, rounded projection.

• Tuberosity: Knob-like projection, usually larger than a tubercle.

• Trochanter: Large, tuberosity found only on the proximal femur.

• Epicondyle: Projection near or above a condyle.

• Lingula: Flat, tongue-shaped process.

• Hamulus: Hook-shaped process.

• Horn: Horn-shaped projection.

Depressions and Openings

• Fossa: General term for a depression in a bone.

• Notch: Depression in the margin of a bone.

• Fovea: Small pit or depression.

• Groove or Sulcus: Narrow depression or furrow.

• Foramen: Hole through a bone for passage of nerves or blood vessels.

• Canal or Meatus: Tunnel-like passageway.

• Fissure: Narrow, slit-like opening.

• Labyrinth: Complex cavity or series of cavities.

Axial Skeleton

The axial skeleton forms the central axis of the body and is essential for protecting the brain, spinal cord, and thoracic organs. It consists of the skull, vertebral column, and thoracic cage.

• Skull: Protects the brain and forms the structure of the face.

• Vertebral Column: Supports the body and protects the spinal cord.

• Thoracic Cage: Protects vital organs such as the heart and lungs.

Appendicular Skeleton

The appendicular skeleton is involved in movement and manipulation of the environment. It includes the bones of the limbs and the girdles that attach them to the axial skeleton.

• Pectoral Girdle: Clavicle and scapula, which attach the upper limbs to the trunk.

• Upper Limbs: Humerus, radius, ulna, carpals, metacarpals, and phalanges.

• Pelvic Girdle: Hip bones (ilium, ischium, pubis) and sacrum.

• Lower Limbs: Femur, tibia, fibula, tarsals, metatarsals, and phalanges.

Table: Classification of Bones by Shape

Bone Shape	Description	Example
Long	Longer than wide, mostly compact bone	Femur, humerus
Short	Cube-shaped, mostly spongy bone	Carpals, tarsals
Flat	Thin, flattened, often curved	Sternum, skull bones
Irregular	Complex shapes	Vertebrae, sphenoid

Example Application

• Clinical Relevance: Understanding bone terminology and classification is essential for interpreting radiographs, diagnosing fractures, and describing locations of injuries or surgical procedures.

Additional info: The provided notes and images are foundational for students beginning the study of the skeletal system in Anatomy & Physiology, focusing on gross anatomical features and terminology.