The Axial Skeleton and Skull

• The lecture covers the skeletal system, specifically bones, with a focus on the axial skeleton.
• The axial skeleton forms the longitudinal part of the body.
• The axial skeleton is divided into the skull, vertebral column, and bony thorax.
• The axial skeleton supports and protects organs in the cranial, spinal, and ventral body cavities.
• It provides an extensive surface area for muscle attachment.
• The joints of the axial skeleton permit limited movement but are strong and strengthened with ligaments.

The Skull

• Consists of two sets of bones: cranium and facial bones.
• Bones are joined by sutures, except for the mandible, which is attached by a freely movable joint.
• Protects the brain and guards entrances to the digestive and respiratory systems.
• The skull contains 22 bones.

Cranium Bones

• Eight bones form the cranium (braincase).
• Occipital bone is located at the back.
• Parietal bones form the top and most of the sides.
• Frontal bone is located at the anterior.
• Temporal bones form the lower sides.
• Sphenoid and ethmoid bones form the floor.
• Six auditory ossicles are in the temporal bones.
• The hyoid bone is connected to the temporal bones by ligaments.

Face Bones

• Fourteen bones are associated with the face.
• Maxillary bones form the upper jawbone.
• Palatine bones form the anterior portion of the palate.
• Nasal bones fuse to form the bridge of the nose.
• The vomer is a thin bone that divides the nasal cavity.
• Inferior nasal conchae articulate with other bones.
• The zygomatic bone forms the prominence of the cheeks.
• Lacrimal bone is the smallest facial bone.
• The mandible forms the lower jaw bone.

Unique Features of the Skull

• Sutures are immovable joints between skull bones.
• Coronal, sagittal, lambdoid, and squamous are types of sutures.
• Paranasal sinuses are cavities located in bones near the nasal cavity.
• Fontanels are soft spots in the fetal skull.
• Fontanels allow deformation at birth and calcify to become sutures.
• Paranasal sinuses lighten the skull.
• The mucous membrane lining paranasal sinuses moistens and cleans the air.
• Paranasal sinuses give resonance and amplification to voice.
• Fontanelles are fibrous membranes connecting the cranial bones in fetuses.
• Fontanelles allow the brain to grow and convert to bone within 24 months after birth.

Hyoid Bone

• Supports the larynx.
• Serves as the attachment site for muscles of the larynx, pharynx, and tongue.
• The body of the hyoid is an attachment site for muscles of the larynx, tongue, and pharynx.
• Greater horns support the larynx and attach to muscles that move the tongue.
• Lesser horns attach to the stylohyoid ligaments.

The Orbits

• The orbits are cavities where the eyes are encased and cushioned by fatty tissue.
• Muscles that move the eyes and tear-producing lacrimal glands are housed in the orbits.
• The walls of the orbit are formed by seven bones.

The Vertebral Column

• Encloses the spinal cord. Supports the head and provides attachment points for muscles , ribs, and the pelvic girdle.
• Sections include 7 cervical, 12 thoracic, 5 lumbar, 1 sacrum, and 1 coccyx.
• The vertebral column averages 71 cm long in adults, with discs accounting for a quarter of the length.
• Individuals are about 1% shorter when in bed compared to upright.
• Compression during the day squeezes water from the intervertebral discs
• Discs reabsorb water when compression is removed during sleep.
• Functions include protecting the spinal cord, providing access for nerves and vessels, enabling movement, and supporting the skull.
• Discs act as shock absorbers and provide attachment for ribs, shoulder girdle, and limbs.

Features of the Vertebra

• The vertebral body is a disc-shaped anterior portion.
• The vertebral arch is posteriorly located and with the body, forms a hole (vertebral foramen).
• Every vertebra has seven processes.
• Transverse processes extend laterally.
• Spinous processes extend dorsally.
• Superior and inferior articular processes form joints with neighboring vertebrae.

Cervical Vertebrae

• Spinous processes are often bifid and have transverse foramina.
  • C1 (atlas) articulates with the head and lacks a body and spinous process.
  • C2 (axis) has a body and spinous process and the dens (tooth) creates a pivot for head rotation.

Thoracic Vertebrae

• Larger than cervical vertebrae and have facets for rib articulation.
• Lumbar vertebae are the largest and strongest with spinous processes that are short and thick.
• The sacrum consists of five fused vertebrae and the coccyx coccygeal consists of four vertebrae that fused into one .
• Cervical and lumbar curves are convex anteriorly.
• Thoracic and sacral curves are concave posteriorly.
• Curves increase strength, help with balance, and absorb shocks.
• Abnormal spinal curvatures include scoliosis (lateral curvature), kyphosis (exaggerated thoracic curvature), and lordosis (exaggerated lumbar curvature).

The Bony Thorax

• Sternum, costal cartilages, ribs and bodies of T1-T12 make up the bony thorax.
• Forming from 3 portions fused by age 25: manubrium, body, and xiphoid process the sternum
• Ribs consist of 12 pairs that include true ribs (1-7) which articulate with cartilages.
• False ribs (8-12) lack sternum articulation , floating ribs.
• Joints form between facets on the head of the rib and facets on the bodies of the two vertebrae.
• Intercostal nerves/blood vessels run along the inferior surface of the rib.