In-Depth Notes on the Skeletal System

Axial and Appendicular Skeleton

• Definitions:

• Axial Skeleton: Comprises the bones of the skull, vertebral column, and rib cage. Its primary function is to support and protect the brain, spinal cord, and thoracic organs.

• Appendicular Skeleton: Includes the bones of the arms, legs, and the girdles that attach them to the axial skeleton. Its main role is to facilitate movement and locomotion.

• Comparison:

• Bones: Axial skeleton has 80 bones; the appendicular skeleton has 126 bones.

• Functions: Axial supports and protects while appendicular aids in movement.

Cranial and Facial Bones

• Cranial Bones: 8 bones (e.g., frontal, parietal, occipital).

• Function: Protects the brain and supports facial structure.

• Facial Bones: 14 bones (e.g., maxilla, mandible, nasal bones).

• Function: Forms the face and supports teeth.

• Unique Bones:

• Mandible: Only movable bone of the skull, involved in chewing.

• Hyoid: Supports the tongue, unique as it does not articulate with other bones.

Sutures

• Definition: A suture is an interlocking line of union between bones.
• Key Sutures:
  • Coronal Suture: Separates the frontal from the parietal bones.
  • Sagittal Suture: Separates the two parietal bones.
  • Lambdoid Suture: Separates the parietal bones from the occipital bone.

Auditory Ossicles

• Function: These small bones (malleus, incus, stapes) transmit sound vibrations from the outer ear to the inner ear.
• Location: Found in the middle ear; vital for hearing.

Fontanelles

• Function: Allow for flexibility during childbirth and brain growth in infants.
• Two Largest Fontanelles: Anterior and posterior fontanelles; typically disappear by 18-24 months as the bones fuse.

Vertebral Column

• Regions (Superior to Inferior):
• Cervical, Thoracic, Lumbar, Sacral, Coccygeal.
• Comparison of Regions:
• Cervical: 7 vertebrae, supports the head.
• Thoracic: 12 vertebrae, attachment for ribs.
• Lumbar: 5 vertebrae, supports lower back weight.
• Sacral: 5 fused vertebrae, forms the pelvis.
• Coccygeal: 4 fused vertebrae, tailbone.

Curvatures

• Primary Curvatures: Present at birth; thoracic and sacral curves.

• Secondary Curvatures: Develop after birth; cervical (around 3 months) and lumbar (around 12 months).

• Conditions:

• Hyperkyphosis: Excessive outward curvature of the thoracic region.

• Hyperlordosis: Excessive inward curvature of the lumbar region.

Thoracic Cage

• Components: Ribs, sternum, thoracic vertebrae.

• Function: Protects the organs in the thorax (heart and lungs).

• Rib Types:

• True Ribs: 1-7, attach directly to the sternum.

• False Ribs: 8-10, attach indirectly to the sternum.

• Floating Ribs: 11-12, do not attach to the sternum.

Limbs and Mobility

• Upper Limb vs. Lower Limb:
• Upper Limb: Designed for mobility and manipulation.
• Lower Limb: Built for weight-bearing and stability.

Pectoral Girdle

• Bones: Clavicle and scapula.

• Function: Connects the upper limb to the trunk and allows for a wide range of motion.

• Winged Scapula: Occurs due to weakness in the serratus anterior muscle, causing the scapula to protrude.

Upper Limb and Hand Bones

• Bones: Humerus, radius, ulna, carpals, metacarpals, phalanges.
• Forearm Position:
• Pronation: Radius crosses over ulna.
• Supination: Radius and ulna are parallel.

Fractures

• Colles’s Fracture: Distal radius fracture, often from falling on an extended wrist.
• Smith’s Fracture: Reverse of Colles’s, fracture of the distal radius due to falling on a flexed wrist.

Pelvic Girdle and Pelvis

• Bones: Ilium, ischium, pubis.

• Function: Supports weight of the upper body and protects pelvic organs.

• True vs. False Pelvis:

• True Pelvis: Lower part of the pelvis, contains the pelvic cavity.

• False Pelvis: Upper part, does not enclose pelvic organs.

• Pelvic Inlet: The space defined by the boundaries of the true pelvis; important in childbirth.

Male vs. Female Pelvis

• Comparison: Female pelvis is generally wider and has a larger pelvic inlet for childbirth.

Lower Limb and Foot Bones

• Bones: Femur, patella, tibia, fibula, tarsals, metatarsals, phalanges.
• Stress Fractures: Common in metatarsals due to repetitive stress or overuse.