Axial and Appendicular Skeletons

Overview of the Human Skeleton

• Axial skeleton: Forms the central axis of the body and includes the skull, vertebral column, and thoracic cage.

• Appendicular skeleton: Comprises the limbs and girdles (pectoral and pelvic) that attach them to the axial skeleton.

Functions of the axial skeleton:

• Supports and protects the brain, spinal cord, and thoracic organs.

• Provides attachment points for muscles involved in head, neck, and trunk movements.

• Facilitates respiratory movements.

Major Divisions of the Axial Skeleton

• Skull: Protects the brain and forms the structure of the face.

• Vertebral column: Supports the body and protects the spinal cord.

• Thoracic cage: Protects the heart and lungs; supports the shoulder girdles and upper limbs.

The Skull

Cranial Bones

• Frontal bone: Forms the forehead and the superior part of the orbits.

• Parietal bones (2): Form the superior and lateral aspects of the skull.

• Occipital bone: Forms the posterior part and base of the skull.

• Temporal bones (2): Form the inferolateral aspects of the skull and part of the cranial floor.

• Sphenoid bone: Spans the width of the cranial floor; acts as a keystone bone.

• Ethmoid bone: Forms part of the nasal cavity and the orbits.

Major Skull Sutures

• Coronal suture: Between frontal and parietal bones.

• Sagittal suture: Between right and left parietal bones.

• Lambdoid suture: Between parietal and occipital bones.

• Squamous suture: Between parietal and temporal bones.

Special Features of the Skull

• Fontanelles: Soft spots in the fetal and infant skull where ossification is incomplete; allow for brain growth and skull compression during birth.

• Auditory ossicles: Three small bones (malleus, incus, stapes) in the middle ear that transmit sound vibrations.

• Occipital condyles: Articulate with the first cervical vertebra (atlas) to allow nodding motion of the head.

• Foramen magnum: Large opening in the occipital bone for passage of the spinal cord.

• Sella turcica: Saddle-shaped depression in the sphenoid bone that houses the pituitary gland.

Other Skull Features and Terms

• Mastoiditis: Inflammation of the mastoid process of the temporal bone; can lead to serious infections spreading to the brain.

• Sutural bones: Small, irregular bones found within sutures, especially in the lambdoid suture; formed from additional ossification centers.

Facial Bones

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

• Maxillary bones (2): Form the upper jaw and central part of the facial skeleton.

• Zygomatic bones (2): Cheekbones; form part of the orbit.

• Nasal bones (2): Form the bridge of the nose.

• Lacrimal bones (2): Small bones in the medial wall of each orbit.

• Palatine bones (2): Form the posterior part of the hard palate.

• Vomer: Forms the inferior part of the nasal septum.

• Inferior nasal conchae (2): Form part of the lateral walls of the nasal cavity.

Key Features of Facial Bones

• Alveolar process: Ridge containing tooth sockets in the maxilla and mandible.

• Mandibular fossa: Depression in the temporal bone that articulates with the mandible.

• Lacrimal fossa: Depression in the lacrimal bone for the lacrimal sac (tear duct).

Other Axial Bones

• Hyoid bone: Located in the neck between the mandible and larynx; does not articulate with other bones; supports the tongue and serves as an attachment for muscles of swallowing and speech.

Orbits and Nasal Cavity

• Orbits: Bony cavities that house the eyes; formed by parts of the frontal, sphenoid, zygomatic, maxillary, palatine, lacrimal, and ethmoid bones.

• Zygomatic arch: Formed by the zygomatic process of the temporal bone and the temporal process of the zygomatic bone.

• Nasal septum: Formed by the perpendicular plate of the ethmoid, vomer, and septal cartilage.

• Lateral walls, floor, and roof of the nasal cavity: Formed by the ethmoid, maxilla, palatine, and inferior nasal conchae.

Paranasal Sinuses

• Air-filled spaces in the frontal, sphenoid, ethmoid, and maxillary bones.

• Lighten the skull, enhance voice resonance, and produce mucus.

Vertebral Column

Divisions and Curvatures

• Cervical (7 vertebrae): Neck region.

• Thoracic (12 vertebrae): Upper back; each articulates with a pair of ribs.

• Lumbar (5 vertebrae): Lower back; largest vertebrae for weight-bearing.

• Sacrum (5 fused vertebrae): Forms posterior wall of pelvis.

• Coccyx (4 fused vertebrae): Tailbone.

Normal curves: Cervical, thoracic, lumbar, and sacral curves provide resilience and flexibility.

Abnormal curves: Scoliosis (lateral), kyphosis (excessive thoracic), lordosis (excessive lumbar).

General Structure of a Vertebra

• Body (centrum): Weight-bearing region.

• Vertebral arch: Encloses the vertebral foramen.

• Vertebral foramen: Passage for the spinal cord.

• Processes: Spinous, transverse, and articular processes serve as attachment points for muscles and ligaments.

Special Vertebrae

• Atlas (C1): Supports the skull; allows nodding motion; lacks a body.

• Axis (C2): Has the dens (odontoid process) for rotation of the head.

• Transverse foramina: Found in cervical vertebrae; transmit vertebral arteries.

• Thoracic vertebrae: Articulate with ribs; spinous processes point downward (resemble giraffe heads in lateral view).

• Lumbar vertebrae: Large, robust; spinous processes are short and thick (resemble moose heads in lateral view).

Intervertebral Discs and Foramina

• Intervertebral discs: Pads of fibrocartilage between vertebrae; absorb shock and allow movement.

• Structure: Annulus fibrosus (outer ring) and nucleus pulposus (gel-like center).

• Herniated disc: Nucleus pulposus protrudes through annulus fibrosus, compressing nerves and causing pain.

• Intervertebral foramina: Openings for spinal nerves to exit the vertebral column.

Clinical Considerations

• Spina bifida: Congenital defect where vertebral arches fail to fuse, exposing the spinal cord.

• Aging and osteoporosis: Lead to decreased bone density and increased risk of vertebral fractures.

Thoracic Cage (Bony Thorax)

Components and Functions

• Sternum: Flat bone at the anterior midline of the thorax; consists of manubrium, body, and xiphoid process.

• Ribs: 12 pairs in both males and females.

• Thoracic vertebrae: Posterior attachment for ribs.

Functions: Protects thoracic organs, supports shoulder girdles and upper limbs, provides attachment for muscles of respiration.

Sternum Features

• Manubrium: Superior portion; articulates with clavicles and first two ribs.

• Body: Main part; articulates with costal cartilages of ribs 2-7.

• Xiphoid process: Inferior tip; attachment for abdominal muscles.

• Clavicular notches: Articulation points for clavicles.

• Jugular notch: Central indentation at the superior border of the manubrium.

• Sternal angle: Junction of manubrium and body; landmark for rib counting.

CPR Note: Correct hand position is crucial to avoid breaking the xiphoid process and damaging underlying organs.

Classification of Ribs

Foramina of the Skull

Major Openings and Their Functions

Laboratory Identification: Key Bones and Features

Skull Bones and Features

• Students should be able to identify all cranial and facial bones, as well as the major features listed above, on both intact and disarticulated skulls.

• Key features include foramina, processes, fossae, and sinuses as described in the lecture and lab objectives.

Other Axial Bones

• Hyoid bone: Unique, does not articulate with other bones; supports tongue and larynx.

• Auditory ossicles: Malleus, incus, stapes; transmit sound in the middle ear.

Summary Table: Major Bones of the Axial Skeleton

Key Terms and Definitions

• Foramen: Opening in a bone for nerves and blood vessels.

• Process: Projection or outgrowth of bone for muscle or ligament attachment.

• Fossa: Depression or hollow in a bone.

• Sinus: Air-filled cavity within a bone.

• Suture: Immovable joint between skull bones.

Example Application

During CPR, correct hand placement on the sternum is essential to avoid fracturing the xiphoid process, which could puncture the liver or other abdominal organs.

Additional info: The above notes expand on the provided outline by including definitions, clinical relevance, and anatomical context for each structure. Tables have been inferred and constructed for clarity and exam preparation.