Chapter 7: The Skeleton – Structure and Function

Chapter 7: The Skeleton

The Axial Skeleton

The axial skeleton forms the longitudinal axis of the body and is essential for protecting vital organs and supporting the head, neck, and trunk. It consists of the skull, vertebral column, and thoracic cage.

• Components: Skull, vertebral column, thoracic cage (rib cage)

• Functions: Protects brain, spinal cord, thoracic organs; supports head, neck, trunk

The Skull

The skull is composed of cranial and facial bones, most of which are flat and joined by immovable sutures. It houses 85 openings for nerves, arteries, and veins.

• Cranial Vault: Forms the superior, lateral, and posterior portions of the skull and forehead

• Cranial Base: Forms the inferior aspect of the skull

• Sutures: Joints between skull bones; include coronal, sagittal, lambdoid, and squamous sutures

Cranium Bones

• Frontal Bone: Forms the anterior portion of the cranium; ends at supraorbital margins; contains supraorbital foramen for artery and nerve passage

• Parietal Bones: Paired bones; connected by coronal, sagittal, lambdoid, and squamous sutures

• Occipital Bone: Forms the posterior wall; contains foramen magnum for spinal cord passage; external occipital protuberance above foramen magnum

• Temporal Bone: Includes zygomatic process and arch (cheek bones), tympanic region (external acoustic canal), and petrous region (middle and internal ear cavities)

• Sphenoid Bone: Bat-shaped bone with several foramina

• Ethmoid Bone: Deepest skull bone; forms roof of nasal cavity and floor of anterior cranial fossa

Facial Bones

• Mandible: Largest and strongest bone; forms jaw; includes mandibular angle, alveolar process, mental foramen

• Maxillary Bone: Upper jaw; holds upper teeth in alveolar processes; includes zygomatic, palatine, frontal, and infraorbital processes

• Zygomatic Bones: Form cheekbones

• Nasal Bones: Form bridge of nose

• Lacrimal Bones: Allow for tears

• Palatine Bones: Form hard palate and part of nasal cavity

• Inferior Nasal Conchae: Form part of lateral nasal cavity

• Hyoid Bone: Not a skull bone; movable base for tongue; attaches muscles for swallowing and speech

Vertebral Column

The vertebral column extends from the skull to the pelvis and is divided into five regions. It provides structural support and protects the spinal cord.

• Regions:

  1. Cervical (7 vertebrae)

  2. Thoracic (12 vertebrae; 12 ribs: 6 true, 4 false, 2 floating)

  3. Lumbar (5 vertebrae)

  4. Sacrum (1 vertebra)

  5. Coccyx (4 vertebrae)

• Curvatures: Cervical & lumbar (concave); thoracic & sacral (convex)

• Ligaments: Anterior & posterior longitudinal ligaments prevent hyperflexion & hyperextension

• Intervertebral Discs: Cushion pads between vertebrae; act as shock absorbers

  • Nucleus Pulposus: Central, gelatinous region; provides elasticity

  • Anulus Fibrosus: Collagen and fibrocartilage; limits expansion

• Homeostatic Imbalance: Herniated (prolapsed) disc can press on spinal cord/nerves, causing numbness/pain; treatments include exercise, massage, heat, surgery

• Abnormal Curvatures:

  • Scoliosis: Lateral rotation (S curve); can cause breathing difficulty

  • Kyphosis: Dorsal thoracic curve (hunchback); seen in osteoporosis, rickets, tuberculosis

  • Lordosis: Lumbar curvature (swayback); seen in disease, pregnancy, obesity

Vertebrae Structure

• Body (Centrum): Main weight-bearing region

• Vertebral Arch: Formed by pedicles (sides) and laminae (posterior plates)

• Vertebral Foramen: Central hole for spinal cord

• Vertebral Canal: Series of vertebral foramina

• Intervertebral Foramina: Lateral openings for nerve passage

• Processes: Spinous (posterior), transverse (lateral), superior/inferior articular (up/down)

Unique Cervical Vertebrae

• C1 (Atlas): No body/spinous process; articulates with occipital condyles; allows nodding "yes"

• C2 (Axis): Has body and dens; allows rotation "no"

Thoracic Vertebrae

• Body: Heart-shaped

• Spinous Process: Long and sharp

• T1-T12: Articulate with ribs

Pectoral Girdle and Upper Limb

The pectoral girdle consists of the clavicle and scapula, connecting the upper limbs to the axial skeleton. The upper limb includes the arm, forearm, and hand.

• Clavicle: Attaches upper limbs to axial skeleton

• Acromioclavicular Joint: Connects clavicle and scapula

• Scapula: Glenoid cavity is unstable, making shoulder dislocations common

• Upper Limb: Arm, forearm, hand