Chapter 7: The Skeleton

Overview and Learning Objectives

This chapter introduces the human skeletal system, focusing on the classification, structure, and function of bones. Key objectives include identifying bones by region and shape, describing major landmarks, understanding cranial sutures and sinuses, recognizing fontanelles, spinal curvatures, and comparing male and female pelvises, as well as describing the arches of the foot.

• Classification of Bones: Bones are classified by region (axial vs. appendicular) and by shape (long, short, flat, irregular).

• Landmarks: Important anatomical features on bones serve as attachment points and passageways for nerves and blood vessels.

• Cranial Sutures and Sinuses: Sutures are immovable joints between skull bones; sinuses are air-filled spaces that lighten the skull and enhance resonance.

• Fontanelles: Soft spots on a newborn's skull that allow for growth and flexibility during birth.

• Spinal Curvatures: Normal and abnormal curvatures affect posture and movement.

• Pelvic Comparison: Structural differences between male and female pelvises relate to function and childbirth.

• Foot Arches: Arches provide support and flexibility for movement and weight-bearing.

The Skeletal System

General Structure and Divisions

The skeletal system consists of bones, cartilages, joints, and ligaments, accounting for approximately 20% of body mass. It is divided into two major regions:

• Axial Skeleton: Forms the central axis of the body.

• Appendicular Skeleton: Includes the limbs and girdles that attach them to the axial skeleton.

Part 1: The Axial Skeleton

Regions and Functions

The axial skeleton is composed of 80 bones and is divided into three major regions:

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

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

• Thoracic Cage: Protects the heart and lungs.

Main functions of the axial skeleton:

• Forms the longitudinal axis of the body

• Supports the head, neck, and trunk

• Protects the brain, spinal cord, and thoracic organs

The Human Skeleton: Overview

The human skeleton is a framework of bones that provides structure, protection, and movement. It is typically illustrated in anatomical diagrams showing anterior and posterior views, with major bones labeled (e.g., cranium, mandible, clavicle, scapula, humerus, femur, tibia, fibula).

Bones of the Skull

The skull consists of several bones joined by immovable joints called sutures. Key bones include the frontal, parietal, occipital, temporal, sphenoid, and ethmoid bones. Each bone has distinct landmarks and functions.

Cranial Sutures

Sutures are immovable joints that connect the bones of the skull. Major cranial sutures include:

• Coronal Suture: Between parietal and frontal bones

• Sagittal Suture: Between right and left parietal bones

• Lambdoid Suture: Between parietal and occipital bones

• Squamous Suture: Between parietal and temporal bones

Paranasal Sinuses

Paranasal sinuses are air-filled spaces within certain skull bones (frontal, sphenoid, ethmoid, and maxillary). They are lined with mucosa and serve several functions:

• Warm and humidify inhaled air

• Lighten the weight of the skull

• Enhance resonance of the voice

Fontanelles

Fontanelles are soft, membranous gaps between the cranial bones of a newborn. They allow for flexibility during birth and rapid brain growth in infancy. The major fontanelles include the anterior, posterior, mastoid, and sphenoidal fontanelles.

Hyoid Bone

The hyoid bone is located in the anterior neck, inferior to the mandible. It is unique because it does not articulate directly with any other bone. It is anchored by ligaments and serves as a movable base for the tongue and as an attachment site for muscles involved in swallowing and speech.

Vertebral Column

The vertebral column (spine) consists of 26 vertebrae in adults, divided into cervical, thoracic, lumbar, sacral, and coccygeal regions. It supports the body, protects the spinal cord, and allows for flexible movement.

• Cervical (7): Neck region

• Thoracic (12): Upper back

• Lumbar (5): Lower back

• Sacrum (5 fused): Pelvic region

• Coccyx (4 fused): Tailbone

Spinal Curvatures

Normal spinal curvatures include cervical and lumbar lordosis (inward curve), and thoracic and sacral kyphosis (outward curve). Abnormal curvatures include:

• Scoliosis: Lateral curvature

• Kyphosis: Exaggerated thoracic curvature

• Lordosis: Exaggerated lumbar curvature

Thoracic Cage

The thoracic cage consists of the ribs, sternum, and thoracic vertebrae. It protects vital organs such as the heart and lungs and provides attachment points for muscles involved in respiration.

Part 2: The Appendicular Skeleton

Regions and Functions

The appendicular skeleton includes the bones of the limbs and the girdles that attach them to the axial skeleton:

• Pectoral Girdle: Attaches upper limbs to the trunk (clavicle and scapula)

• Pelvic Girdle: Attaches lower limbs to the trunk (hip bones)

Comparison of Male and Female Pelvis

The pelvis differs structurally and functionally between males and females, primarily to accommodate childbirth in females.

Bones of the Appendicular Skeleton

The appendicular skeleton includes the bones of the upper and lower limbs, as well as the pectoral and pelvic girdles. Major bones include:

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

• Lower Limb: Femur, tibia, fibula, tarsals, metatarsals, phalanges

Arches of the Foot

The foot contains three arches maintained by interlocking bones, ligaments, and tendons. These arches allow the foot to bear weight and provide flexibility for movement.

• Lateral Longitudinal Arch: Low curve elevating the lateral part of the foot

• Medial Longitudinal Arch: Higher curve elevating the medial part of the foot

• Transverse Arch: Runs obliquely from one side of the foot to the other

Key Equations and Terms

• Bone Mass Percentage:

• Number of Bones in Adult Skeleton: $206$

Additional info: The above notes expand on the brief points in the slides, providing definitions, examples, and comparisons for a comprehensive study guide suitable for Anatomy & Physiology students.