Skeleton

Main Divisions of the Human Skeleton

The human skeleton is divided into two major parts: the axial skeleton and the appendicular skeleton. Each division has distinct components and functions in supporting and protecting the body.

• Axial Skeleton: Includes the skull, vertebral column, and thoracic cage (ribs and sternum). It forms the central axis of the body and protects vital organs such as the brain, spinal cord, and heart.

• Appendicular Skeleton: Comprises the limbs and girdles (pectoral and pelvic), facilitating movement and interaction with the environment.

Example: The axial skeleton includes the cranium and vertebrae, while the appendicular skeleton includes the femur and humerus.

Axial Skeleton

Skull

The skull is a complex structure composed of cranial and facial bones. It protects the brain and forms the structure of the face.

• Cranium: Encloses and protects the brain.

• Facial Bones: Form the structure of the face and support sensory organs.

Cranium

The cranium consists of several bones joined by immovable joints called sutures.

• Frontal bone: Forms the forehead and part of the eye sockets.

• Parietal bone: Forms the sides and roof of the cranial cavity.

• Temporal bone: Located at the sides and base of the skull.

• Occipital bone: Forms the back and base of the skull.

• Sphenoid bone: Forms part of the base of the skull and the sides of the orbits.

• Ethmoid bone: Located between the eyes, forms part of the nasal cavity and orbits.

Sutures: Fibrous joints connecting cranial bones.

• Coronal suture: Between frontal and parietal bones.

• Sagittal suture: Between the two parietal bones.

• Lambdoid suture: Between parietal and occipital bones.

• Squamous suture: Between parietal and temporal bones.

Example: The coronal suture separates the frontal bone from the parietal bones.

Facial Bones

Facial bones provide the framework for the face and house the openings for the respiratory and digestive tracts.

• Mandible: Lower jawbone, the only movable bone of the skull.

• Maxillae: Upper jawbones, form the central part of the face.

• Zygomatic: Cheekbones.

• Nasal: Bridge of the nose.

• Lacrimal: Small bones forming part of the medial wall of each orbit.

• Palatine: Form the posterior part of the hard palate.

• Vomer: Forms part of the nasal septum.

• Inferior Nasal Conchae: Thin, curved bones in the nasal cavity.

Example: The mandible articulates with the temporal bone at the temporomandibular joint.

Paranasal Sinuses

Paranasal sinuses are air-filled cavities within certain skull bones. They lighten the skull, produce mucus, and enhance voice resonance.

• Frontal sinus: Located in the frontal bone above the eyes.

• Ethmoid sinus: Located between the nose and eyes.

• Sphenoid sinus: Located in the sphenoid bone behind the eyes.

• Maxillary sinus: Located in the maxillae, largest of the sinuses.

Example: Sinus infections often affect the maxillary or frontal sinuses, causing facial pain and pressure.

Appendicular Skeleton

Main Components

The appendicular skeleton consists of the bones of the limbs and the girdles that attach them to the axial skeleton.

• Pectoral (Shoulder) Girdle: Clavicle and scapula, attach the upper limbs to the trunk.

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

• Pelvic (Hip) Girdle: Ilium, ischium, pubis, attach the lower limbs to the trunk.

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

Example: The femur is the longest bone in the body and forms the thigh.

Summary Table: Major Bones of the Human Skeleton

Additional info: The notes and diagrams provided are foundational for understanding the structure and function of the human skeleton, which is essential for further study in anatomy and physiology.