Skeletal System (HLTAAP002 Session 4)

Introduction to the Skeletal System

• The skeletal system, comprised of bones and cartilage, provides a strong supporting framework for the human body and offers essential protection for softer tissues.
• The skeleton serves as the attachment surfaces for muscles, tendons, and ligaments. These structures pull on individual bones to facilitate movement in conjunction with joints.
• Bones perform vital physiological functions, including:
  • The storage of critical minerals.
  • The production of Red Blood Cells (RBC) through the process of haematopoiesis.
• The adult human skeleton is composed of exactly $206$ bones.
• Division of the Skeleton:
  • The Axial Skeleton: The central core of the body.
  • The Appendicular Skeleton: The limbs and their respective girdles.

The Axial Skeleton

• The axial skeleton is composed of the bones comprising the skull, the thorax (thoracic cage), and the vertebral column.

The Human Skull

• The skull is made up of several bones that protect the brain and provide the base structure for the head and face.
• Total Bone Count: The skull contains $22$ bones in total.
  • Cranial Bones: $8$ bones that encase the brain.
  • Facial Bones: $14$ bones that form the front of the skull and shape the face.
• Cranial Bone Specifics:
  • Frontal bone: Forms the forehead and the upper portion of the eye sockets.
  • Parietal bones (left and right): Form the sides and top of the skull.
  • Temporal bones (left and right): Form the sides of the skull and contain ear structures.
  • Occipital bone: Forms the back and base of the skull.
• Facial Bone Specifics:
  • Nasal bones (left and right): Form the bridge of the nose.
  • Maxilla (upper jaw) bones (left and right): Form the upper jaw and part of the hard palate.
  • Zygomatic bones (left and right): Commonly referred to as the cheekbones.
  • Lacrimal bones (left and right): Located near the tear ducts, contributing to the eye socket.
  • Palatine bones (left and right): Form the back section of the hard palate.
  • Inferior nasal conchae (left and right): Thin, scroll-like bones located within the nasal cavity.
  • Vomer bone: Forms the lower portion of the nasal septum.
  • Mandible (lower jaw): Forms the lower jaw and houses the lower teeth.
• Structural Features of the Skull:
  • Sutures: These are joints that connect the skull bones. They allow flexibility during childbirth and during infancy as the skull grows.
  • Sinuses: Air-filled cavities that lighten the weight of the skull and modulate vocal sound. There are four types: Frontal, Ethmoidal, Sphenoidal, and Maxillary.
  • Foramen Magnum: A large opening at the base of the skull within the occipital bone. The term is Latin for ‐large hole‐ ($Foramen$ = hole/opening; $Magnum$ = large). It serves as the passage for the brainstem to connect the brain to the spinal cord.

Disorders of the Developing Skull

• Anencephaly: A severe and fatal congenital birth defect where the upper part of the brain and skull are largely absent.
• Microcephaly: A condition characterized by an abnormally small head and brain size, often associated with developmental issues and neurological deficits.

The Vertebral Column

• The vertebral column is divided into distinct sections:
  • Cervical: $7$ bones.
  • Thoracic: $12$ bones.
  • Lumbar: $5$ bones.
  • Sacral: Fused bones.
  • Coccyx: Fused bones.
• Specialized Vertebrae:
  • Atlas (C1): Responsible for the nodding motion signifying ‐yes.‐
  • Axis (C2): Responsible for the rotational motion signifying ‐no.‐
• Components of Vertebrae:
  • Vertebral foramen.
  • Body.
  • Lamina.
  • Spinous process.
  • Intervertebral discs: Provide padding between vertebrae.
• The Sacrum and Coccyx:
  • The sacrum involves sacral nerves ($S1$ through $S5$) and anterior sacral foramina.
  • The Cauda equina is associated with this region.
  • The Sacrococcygeal junction connects the sacrum and coccyx.

Disorders of the Vertebral Column

• Spinal Curvatures:
  • Scoliosis: A lateral (side-to-side) curve of the spine.
  • Kyphosis: Often called ‐hunchback‐; an exaggerated outward curvature.
  • Lordosis: Often called ‐swayback‐; an exaggerated inward curvature of the lower back.
• Spina Bifida: A birth defect occurring when the neural tube (the embryonic precursor to the brain and spinal cord) fails to close properly during early pregnancy, leading to incomplete development of the spinal cord and protective bones.

The Thoracic Cage

• The thoracic cage protects vital organs and consists of the sternum, ribs, and thoracic vertebrae.
• Sternum Components:
  • Manubrium (features the sternal notch and manubrial-sternal joint).
  • Body.
  • Xiphoid process (features the xiphisternal joint).
• Rib Structures: There are $12$ pairs of ribs in total.
  • True Ribs: The first $7$ pairs.
  • False Ribs: The remaining $5$ pairs, which include $2$ pairs of floating ribs.
• Costal cartilages connect the ribs to the sternum through costochondral joints, forming the costal arch and costal margin.

The Appendicular Skeleton

Pectoral Girdle and Upper Limbs

• Pectoral Girdle: Connects the upper limbs to the axial skeleton. It consists of two bones on each side:
  • Clavicle (collarbone).
  • Scapula (shoulder blade).
• Upper Limb Bones:
  • Humerus: Upper arm bone.
  • Radius and Ulna: Forearm bones.
  • Carpals: Wrist bones.
  • Metacarpals: Palm bones.
  • Phalanges: Finger bones.

Pelvic Girdle and Lower Limbs

• The Pelvis: Composed of the Sacrum, Coccyx, Ilium (Ilia), Ischium (Ischia), Pubis, Symphysis pubis, and the Acetabulum (the hip socket).
• Pelvic Functions:
  • Weight bearing for the upper body.
  • Providing an attachment point for lower limbs.
  • Protection of internal organs.
• Dimensions of the pelvis are critical for vaginal deliveries in females.
• Lower Limb Bones:
  • Femur: The thigh bone, including the neck and ball of the femur.
  • Patella: The kneecap.
  • Tibia: The shin bone.
  • Fibula: The calf bone.
• Bones of the Ankle and Foot:
  • Tarsal bones: Includes the Talus, Calcaneus (heel bone with calcaneus tuber), Navicular, Cuboid, and Cuneiforms (Medial, Intermediate, and Lateral).
  • Metatarsals: Mid-foot bones.
  • Phalanges (Phalanxes): Toe bones (Proximal, Middle, and Terminal/Distal phalanges).
• Foot Disorders:
  • Bunion: A misalignment of the big toe joint where the big toe leans toward the second toe, creating a painful bony protrusion at the base of the big toe.

Bone Classification, Structure, and Growth

• Bone Shapes and Sizes:
  • Long bones.
  • Short bones.
  • Flat bones.
  • Irregular bones.
• Bone Development:
  • Newborns possess ‐bones‐ primarily made of flexible cartilage.
  • Ossification: As the individual grows, cartilage hardens into bone.
• Types of Bone Tissue:
  • Compact Bone: The hard outer layer.
  • Spongy Bone: The soft, ‐honeycomb‐ like inner section.
• Growth Plates (Epiphyseal Plates):
  • Located at the ends of long bones rather than the center.
  • These plates remain soft during growth to allow bones to lengthen.
  • Ossification completes in the early $20s$ (earlier for females), leaving only an epiphyseal line, at which point height growth ceases.

Anatomy of the Bone

• Medullary cavity: The central inner cavity of the bone.
• Endosteum: A layer of bone cells lining the medullary cavity responsible for growth, repair, and remodeling.
• Periosteum: A double-layered outer covering containing blood and lymphatic vessels that nourish compact bone and cells for repair and remodeling.
• Chemical Composition: Classified as connective tissue, bone is composed mainly of collagen fibers and calcium phosphate salts.

Bone Cells

• Osteocytes: Mature bone cells.
• Osteoblasts: Bone-forming cells essential for growth and fracture repair; they replace old or damaged tissue.
• Osteoclasts: Bone-resorbing cells responsible for breaking down tissue to maintain calcium balance and remove weakened bone.

Red Bone Marrow

• Red bone marrow is responsible for haematopoiesis (blood cell production).
• Stem cells residing in the marrow create red blood cells, white blood cells, and platelets.

Bone and Cartilage Pathology

• Fractures:
  • Simple: A break that does not pierce the skin.
  • Compound: A break where the bone protrudes through the skin.
  • Greenstick: An incomplete fracture where the bone bends and cracks, common in children.
• Osteogenesis Imperfecta (Brittle Bone Disease): A genetic disorder caused by mutations in genes responsible for producing collagen. It results in abnormally fragile bones prone to breakage with minimal stress.

Cartilage

• Cartilage is a strong, flexible connective tissue that cushions joints and provides structure.
• Functions:
  • Shock Absorption: Reduces stress on bones during impact.
  • Friction Reduction: Lubricates joints to allow bones to slide smoothly.
  • Structural Support: Maintains joint shape and connects tissues (muscles, tendons, ligaments) to bones.
• Types of Cartilage:
  • Hyaline Cartilage: The most common type. Smooth and slippery. Found at the ends of bones in joints, between ribs, and in nasal passages.
  • Elastic Cartilage.
  • Fibrocartilage.
• Cartilage Issues:
  • Injuries: Torn meniscus or separated shoulder resulting from sports or trauma.
  • Osteoarthritis: The breakdown of cartilage due to age. Approximately $80\%$ of adults over the age of $55$ are affected. It leads to inflammation and pain due to reduced lubrication and cushioning.

Joints and Aging

• A joint (articulation) is a junction between two or more bones.
• Classification of Joints:
  • Immovable.
  • Slightly movable.
  • Freely movable (e.g., Ball-and-socket joints in shoulders/hips; Pivot joints like the Atlas-Axis joint).
• Rheumatoid Arthritis: A chronic inflammatory autoimmune condition where the immune system attacks the joint lining, causing swelling, bone erosion, and deformity.
• Effects of Aging on the Skeleton:
  • Loss of calcium and decreased ability to form the protein framework.
  • Slower cellular metabolism leads to weaker, less dense, fragile bones.
  • Thinned cartilage and loss of synovial fluid.
  • Loss of height due to vertebral column changes.
  • Reduced collagen in bones, tendons, and ligaments leading to loss of flexibility.
• Osteoporosis: A condition where bone resorption exceeds bone creation. Causes include aging, hormonal changes (menopause), and certain medications.

Multidisciplinary Care Team

• General Practitioner (GP).
• Orthopedists and Orthopedic surgeons.
• Rheumatologists.
• Chiropractors.
• Occupational therapists.
• Physical therapists.
• Podiatrists.
• Dieticians.
• Pain specialists.