Skeletal System

Major Functions of the Skeletal System

The skeletal system is essential for protecting organs, stabilizing the body, providing points of attachment for muscles, and maintaining posture.

• Protection: Shields vital organs such as the brain, heart, and lungs.

• Support: Maintains the body’s shape and structure.

• Movement: Provides attachment points for muscles, enabling movement.

• Storage: Stores minerals like calcium and phosphorus.

• Blood Cell Production: Houses bone marrow for hematopoiesis.

Axial and Appendicular Skeleton

The human skeleton is divided into two main parts: the axial and appendicular skeletons.

• Axial Skeleton: Includes the skull, thoracic cage (ribs and sternum), and vertebral column.

• Appendicular Skeleton: Comprises the limbs and girdles (shoulder and pelvic).

• Key Point: Anything attached to the axial skeleton is considered part of the appendicular skeleton.

Bone Types and Examples

Bones are classified by their shapes, which relate to their functions.

• Long Bones: e.g., femur

• Short Bones: e.g., carpals

• Flat Bones: e.g., sternum, skull

• Irregular Bones: e.g., vertebrae

• Sesamoid Bones: e.g., patella (knee cap)

Skull Bones

The skull consists of several bones, including the anterior cranium (frontal bone) and cheekbone (zygomatic bone).

• Frontal Bone: Forms the forehead.

• Zygomatic Bone: Forms the cheek.

• Foramen: Openings in bones for nerves and blood vessels (e.g., foramen magnum in the occipital bone).

Paranasal Sinuses

Paranasal sinuses are air-filled spaces within the skull bones that help lighten the skull and enhance voice resonance.

• Location: Found in the frontal, ethmoid, sphenoid, and maxillary bones.

• Function: Reduce skull weight and produce mucus.

Osteon Structure

The osteon (or Haversian system) is the fundamental unit of compact bone.

• Lamellae: Concentric rings of bone matrix.

• Lacunae: Small spaces housing osteocytes.

• Central Canal: Contains blood vessels and nerves.

Bone Cell Types

Bones contain several cell types, each with specific functions.

• Osteoblasts: Immature bone cells that build bone matrix.

• Osteoclasts: Break down bone matrix for remodeling.

• Osteocytes: Mature bone cells that maintain bone tissue.

Joints & Articulations

Classification of Joints

Joints are classified by their structure and function.

• Structurally:

  • Synovial Joints: Most movable (e.g., knee, shoulder).

  • Fibrocartilaginous Joints: Slightly movable (e.g., intervertebral discs).

  • Fibrous Joints: Immovable (e.g., sutures in the skull).

• Functionally:

  • Synarthrosis: Immovable joints.

  • Amphiarthrosis: Slightly movable joints.

  • Diarthrosis: Freely movable joints.

Joint Movement Types

Joints allow for various types of movement, including flexion, extension, abduction, and adduction.

• Flexion: Decreases the angle between bones.

• Extension: Increases the angle between bones.

• Abduction: Moves a limb away from the midline.

• Adduction: Moves a limb toward the midline.

Muscular System

Muscle Tissue Types

Muscle tissue is classified based on structure and function.

• Smooth Muscle: Uninucleated, involuntary, found in organs.

• Skeletal Muscle: Multinucleated, voluntary, attached to bones.

• Cardiac Muscle: Uninucleated, involuntary, found in the heart.

Muscle Anatomy

Muscle fibers (cells) are grouped into fascicles, which are surrounded by connective tissue layers.

• Muscle Fiber: Also known as a muscle cell.

• Fascicle: Group of muscle fibers.

• Perimysium: Connective tissue surrounding fascicles.

• Epimysium: Connective tissue surrounding the entire muscle.

Sarcomere Structure & Function

The sarcomere is the basic contractile unit of muscle fibers.

• Role: Responsible for muscle contraction.

• Components: Actin (thin filaments) and myosin (thick filaments).

• Sliding Filament Theory: Muscle contraction occurs as actin and myosin filaments slide past each other.

Muscle Contraction Mechanism

Muscle contraction is regulated by calcium ions and the role of T-tubules.

• T-tubules: Transmit action potentials into the muscle fiber.

• Calcium: Triggers contraction by binding to troponin.

• Neurotransmitters: Acetylcholine initiates muscle contraction at the neuromuscular junction.

Muscle Actions

Muscles work in groups to produce movement.

• Agonist: Prime mover of a movement.

• Antagonist: Opposes the prime mover.

• Synergist: Assists the prime mover.

• Fixator: Stabilizes the origin of the prime mover.

Muscle Naming Conventions

Muscles are named based on prefixes and anatomical features.

• Prefixes: "bi-" (two muscles), "tri-" (three muscles), "quad-" (four muscles).

• Example: Biceps brachii (two heads), triceps brachii (three heads), quadriceps femoris (four heads).

Bone Growth & Development

Bone Growth Terminology

Bones grow and develop through specific regions and processes.

• Epiphysis: Tips of long bones.

• Diaphysis: Shaft of long bones, contains yellow bone marrow.

• Epiphyseal Plate: Line of cartilage where bone growth occurs during childhood.

Significance of Epiphyseal Plate

The epiphyseal plate is crucial for longitudinal bone growth in children.

• Function: Allows bones to lengthen until adulthood.

• Remnants: Epiphyseal line in adults marks where growth has ceased.

Miscellaneous

Fibrocartilage Locations

Fibrocartilage is found in areas requiring strength and flexibility.

• Examples: Intervertebral discs, knee cap (meniscus), pubic symphysis.

Muscle Functions Beyond Movement

Muscles also contribute to functions such as thermoregulation (heat production).

• Example: Shivering increases body temperature.

Sex Differences in Skeletal Structure

Male and female skeletons differ in several ways, especially in the pelvic region.

Additional info: These differences are adaptations for childbirth in females.