الهيكل العظمي المحوري: الجمجمة

• The axial skeleton forms the central axis of the body.
• It includes the bones of the skull, vertebral column, and thoracic cage.
• The axial skeleton protects the brain, spinal cord, and thoracic organs.
• It supports the body's weight and is involved in movements such as bending and twisting.

Skull

• The skull is composed of 22 bones, including cranial and facial bones.

Cranial Bones

• The cranial bones enclose and protect the brain.
• There are eight cranial bones: frontal, parietal (2), temporal (2), occipital, sphenoid, and ethmoid.
• The frontal bone forms the forehead and the superior part of the orbits.
• The parietal bones form the lateral and superior walls of the cranial cavity.
• The temporal bones form the lateral inferior walls of the cranial cavity and house the middle and inner ear structures.
• The occipital bone forms the posterior part of the skull and contains the foramen magnum through which the spinal cord passes.
• The sphenoid bone is a complex bone that articulates with all other cranial bones and contributes to the base of the skull, the orbits, and the nasal cavity.
• The ethmoid bone is located between the orbits and contributes to the nasal cavity and the orbits.

Facial Bones

• The facial bones form the face and provide attachments for muscles of facial expression.
• There are fourteen facial bones: nasal (2), maxillae (2), zygomatic (2), mandible, lacrimal (2), palatine (2), inferior nasal conchae (2), and vomer.
• The nasal bones form the bridge of the nose.
• The maxillae form the upper jaw and contribute to the floor of the orbits and the nasal cavity.
• The zygomatic bones form the cheekbones and contribute to the lateral wall of the orbits.
• The mandible forms the lower jaw and is the only movable bone of the skull.
• The lacrimal bones are small bones located in the medial wall of the orbits.
• The palatine bones contribute to the posterior part of the hard palate and the floor of the nasal cavity.
• The inferior nasal conchae are located in the nasal cavity and help to swirl and humidify incoming air.
• The vomer forms the inferior part of the nasal septum.

Sutures of the Skull

• Sutures are immovable joints that connect the bones of the skull.
• The major sutures of the skull include coronal, sagittal, lambdoid, and squamous.
• The coronal suture connects the frontal bone to the parietal bones.
• The sagittal suture connects the two parietal bones.
• The lambdoid suture connects the occipital bone to the parietal bones.
• The squamous sutures connect the temporal bones to the parietal bones.

Fontanelles

• Fontanelles are fibrous membranes that connect the cranial bones of infants.
• They allow for growth and deformation of the skull during birth.
• The major fontanelles include anterior, posterior, mastoid, and sphenoidal.
• The anterior fontanelle is located at the junction of the frontal and parietal bones.
• The posterior fontanelle is located at the junction of the parietal and occipital bones.
• The mastoid fontanelles are located at the junction of the temporal, parietal, and occipital bones.
• The sphenoidal fontanelles are located at the junction of the frontal, parietal, temporal, and sphenoid bones.

Vertebral Column

• The vertebral column, also known as the spine, provides support and flexibility to the body.
• It protects the spinal cord and allows for movement of the head and trunk.
• The vertebral column consists of 24 vertebrae, plus the sacrum and coccyx.
• The vertebrae are divided into cervical, thoracic, lumbar, sacral, and coccygeal regions.

Cervical Vertebrae

• There are seven cervical vertebrae (C1-C7) located in the neck.
• They are the smallest and most mobile vertebrae.
• C1 (atlas) articulates with the occipital bone of the skull and allows for nodding movements.
• C2 (axis) has a dens (odontoid process) that articulates with the atlas and allows for rotational movements.
• The cervical vertebrae have transverse foramina that transmit the vertebral arteries.

Thoracic Vertebrae

• There are twelve thoracic vertebrae (T1-T12) located in the upper back.
• They articulate with the ribs and provide attachment points for muscles of the back and chest.
• The thoracic vertebrae have costal facets for articulation with the ribs.
• Their spinous processes are long and point inferiorly.

Lumbar Vertebrae

• There are five lumbar vertebrae (L1-L5) located in the lower back.
• They are the largest and strongest vertebrae.
• The lumbar vertebrae support the weight of the upper body.
• Their spinous processes are short and thick.

Sacrum

• The sacrum is a triangular bone formed by the fusion of five sacral vertebrae.
• It articulates with the hip bones to form the sacroiliac joints.
• The sacrum provides stability to the pelvis and supports the vertebral column.

Coccyx

• The coccyx is a small bone formed by the fusion of three to five coccygeal vertebrae.
• It is located at the inferior end of the vertebral column and provides attachment points for ligaments and muscles of the pelvic floor.

Intervertebral Discs

• Intervertebral discs are fibrocartilaginous pads located between the vertebrae.
• They act as shock absorbers and allow for movement of the vertebral column.
• Each disc consists of a nucleus pulposus (inner gelatinous core) and an annulus fibrosus (outer fibrous ring).

Curvatures of the Vertebral Column

• The vertebral column has four normal curvatures: cervical, thoracic, lumbar, and sacral.
• The cervical and lumbar curvatures are concave posteriorly (lordosis).
• The thoracic and sacral curvatures are convex posteriorly (kyphosis).
• These curvatures increase the strength and flexibility of the vertebral column.

Thoracic Cage

• The thoracic cage protects the thoracic organs and provides attachment points for muscles of respiration and the upper limbs.
• It consists of the sternum, ribs, and thoracic vertebrae.

Sternum

• The sternum is a flat bone located in the anterior midline of the thorax.
• It consists of three parts: manubrium, body, and xiphoid process.
• The manubrium articulates with the clavicles and the first pair of ribs.
• The body articulates with the second through seventh pairs of ribs.
• The xiphoid process is a small cartilaginous projection that ossifies in adulthood.

Ribs

• There are twelve pairs of ribs that articulate with the thoracic vertebrae.
• The ribs are divided into true ribs (1-7), false ribs (8-10), and floating ribs (11-12).
• True ribs articulate directly with the sternum through costal cartilages.
• False ribs articulate indirectly with the sternum through the costal cartilage of the seventh rib.
• Floating ribs do not articulate with the sternum.