Anatomy: The Skeletal System

The Skeletal System

• The body's structural framework is composed of bones, cartilage, ligaments, and tendons.
• Serves as the foundation of the body, providing support, protection, and movement.
• Divided into axial and appendicular skeletons.

Axial Skeleton

• Includes the skull, vertebral column, and bony thorax.
• Forms the central axis of the body and protects vital organs.

Appendicular Skeleton

• Includes the limbs and girdles (shoulder and pelvic).
• Facilitates movement and interaction with the environment.

Parts of the Skeletal System

• Bones (skeleton)
• Joints
• Cartilages
• Ligaments (bone to bone)
• Tendon (bone to muscle)

Importance of the Skeletal System

• Provides the structural framework that maintains the body's shape and posture.
• Without the skeleton, the body would collapse under its own weight.
• The vertebral column supports the head and trunk.
• Lower limbs support the body's weight during standing and walking.

Protection

• Bones protect vital organs from injury.
• The skull protects the brain.
• The rib cage protects the heart and lungs.
• The vertebral column protects the spinal cord.

Movement

• Bones act as levers.
• Joints act as pivots.
• Enables movement when skeletal muscles contract.
• Example, the femur (thigh bone) and hip joint work together to allow walking, running, and jumping.

Storage

• Bones store essential minerals, such as calcium and phosphorus.
• These are released into the bloodstream as needed.
• Bones also store fat in the yellow marrow, which can be used as an energy reserve.

Blood Cell Formation

• Hematopoiesis (the production of blood cells) occurs in the red marrow of certain bones.
• Red blood cells, white blood cells, and platelets are produced in the marrow of the femur, pelvis, and sternum.

Connection to Other Systems

• Interacts with other body systems to maintain homeostasis.

Muscular System

• Bones and muscles work together to produce movement.

Circulatory System

• Bones store calcium, which is essential for muscle contraction and blood clotting.

Nervous System

• The skeleton protects the brain and spinal cord.
• These control movement and sensation.

Endocrine System

• Bones release hormones (e.g., osteocalcin).
• These regulate energy metabolism and insulin secretion.

Function of Bones

• Support of the body.
• Protection of soft organs.
• Movement due to attached skeletal muscles.
• Storage of minerals and fats.
• Blood cell formation.

Bones of the Human Body

• The skeleton has 206 bones.
• Two basic types of bone tissue.

Compact Bone

• Homogeneous.

Spongy Bone

• Small needle-like pieces of bone.
• Many open spaces.

Flat Bones

• Thin and flattened.
• Usually curved.
• Thin layers of compact bone around a layer of spongy bone.
• Examples: Skull, ribs, sternum.

Irregular Bones

• Irregular shape.
• Do not fit into other bone classification categories.
• Example: Vertebrae and hip.

Long Bones

• Typically longer than wide.
• Have a shaft with heads at both ends.
• Contain mostly compact bone.
• Examples: Femur, humerus.

Short Bones

• Generally cube-shape.
• Contain mostly spongy bone.
• Examples: Carpals, tarsals.

Bone Growth

• Epiphyseal plates allow for growth of long bone during childhood.
• New cartilage is continuously formed.
• Older cartilage becomes ossified.
• Cartilage is broken down and replaced by bone.
• Bones are remodeled and lengthened until growth stops.
• Bones change shape somewhat and grow in width.

Type of Bone Cells

• Osteocytes: mature bone cells.
• Osteoblast: bone-forming cells.
• Osteoclasts: bone destroying cells.
• Osteoclasts break down matrix also for the remodeling and release of calcium.

Bone Remodeling

• A process by both osteoblasts and osteoclasts.

Repair of Bone Fractures

• Hematoma (blood-filled swelling) forms.
• The break is splinted by fibrocartilage to form a callus.
• Fibrocartilage callus is replaced by a bony callus.
• Bony callus is remodeled to form a permanent patch.

Bone Fracture

• A break in a bone.

Types of Bone Fractures

• Closed (simple) fracture is a break that does not penetrate the skin.
• Open (compound) fracture is a broken bone penetrates through the skin.
• Bone fractures are treated by reduction and immobilization.
• Realignment of the bone.

The Axial Skeleton

• Forms the central axis of the body and includes the skull, vertebral column, and bony thorax.

Cranium

• Encloses and protects the brain.
• Made up of eight bones: frontal, parietal (2), temporal (2), occipital, sphenoid, and ethmoid.
• Bones of the cranium are joined by sutures, which are immovable joints that provide stability.
• The coronal suture connects the frontal and parietal bones.
• The sagittal suture connects the two parietal bones.

The Skull

• Consists of the cranium and facial bones.
• Bones are joined by sutures.
• Mandible is attached by a freely movable joint.

Functions of the Skull

• Protects the brain and sensory organs (e.g., eyes, ears).
• Provides attachment sites for muscles involved in facial expression, chewing, and head movement.
• Houses the paranasal sinuses, which lighten the skull and enhance voice resonance.

Paranasal Sinuses

• Hollow portions of bones surrounding the nasal cavity.

Functions of Paranasal Sinuses

• Lighten the skull.
• Give resonance and amplification to voice.

The Hyoid Bone

• A U-shaped bone located in the neck, just above the larynx.
• Unique because it does not articulate with any other bone.
• Suspended by ligaments and muscles.

Functions of the Hyoid Bone

• Supports the tongue.
• Serves as an attachment point for muscles involved in swallowing and speech.
• The only bone that does not articulate with another bone.
• Serves as a moveable base for the tongue

The Vertebral Column

• Vertebrae separated by intervertebral discs.
• The spine has a normal curvature.
• Each vertebrae is given a name according to its location
• Composed of 33 vertebrae, divided into five regions.

Functions of the Vertebral Column

• Protects the spinal cord.
• Supports the head and trunk.
• Allows for movement (e.g., bending, twisting).

Bone Markings

• Specific features on bones that serve as attachment sites for muscles, ligaments, and tendons, or as passageways for nerves and blood vessels.

Common Bone Markings

• Processes - projections or outgrowths of bone.
• Foramina - openings or holes in bones that allow for the passage of nerves and blood vessels.
• Fossae - depressions or hollows in bones.

Cervical Vertebrae

• Located in the neck.
• Support the head and allow for neck movement.
• The first cervical vertebra (atlas) supports the skull.
• The second (axis) allows for rotation of the head.

Thoracic Vertebrae

• Located in the upper back.
• Articulate with the ribs, forming the posterior part of the thoracic cage.
• Provide attachment sites for muscles involved in respiration.

Lumbar Vertebrae

• Located in the lower back.
• Bear the most weight and provide stability.
• Allow for bending and twisting movements.

Sacrum

• Located at the base of the spine.
• Connects the spine to the pelvic girdle.
• Provides strength and stability to the pelvis.

Coccyx

• Commonly referred to as the tailbone.
• Provides attachment sites for muscles and ligaments.

Intervertebral Discs

• Located between the vertebrae.
• Act as shock absorbers, cushioning the spine during movement.
• Allow for flexibility and movement of the spine.

The Bony Thorax

• Forms a protective cage around the heart, lungs, and major blood vessels.

It is composed of three parts

• Sternum
• Ribs
• Thoracic vertebrae.

True Ribs (1-7)

• Attach directly to the sternum via costal cartilage.

False Ribs (8-10)

• Attach indirectly to the sternum or not at all.

Floating Ribs (11-12)

• Do not attach to the sternum.
• The ribs protect the thoracic organs and assist in respiration by expanding and contracting during breathing.

Thoracic Vertebrae

• The 12 thoracic vertebrae articulate with the ribs, forming the posterior part of the thoracic cage.

Development of the Axial Skeleton

• The axial skeleton develops through ossification, where cartilage is replaced by bone.

Skull Development

• The bones of the skull are initially separated by fontanelles (soft spots) in infants.
• Fontanelles allow for brain growth and flexibility during birth.

Vertebral Column Development

• The vertebrae develop from cartilage models, which gradually ossify during childhood and adolescence.

Kyphosis (Kyphotic Curve)

• An excessive outward curvature of the thoracic spine (upper back).
• Leads to a hunched or rounded posture.

Lordosis (Lordotic Curve)

• An excessive inward curvature of the lumbar spine (lower back).
• Causes a swayback appearance.

Scoliosis (Scoliotic Curve)

• A lateral (sideways) curvature of the spine, often accompanied by rotation of the vertebrae
• Can form an "S" or "C" shape.

Genu Varum (Bowlegs)

• A condition where the legs curve outward at the knees.
• Creates a gap between the knees when the feet are together.
• Can be normal in infants, but may indicate an issue if it persists or develops later.

Bone Cancer

• Refers to malignant tumors that originate in the bone (primary bone cancer) or spread to the bone from other organs (metastatic bone cancer).