Anatomy Quiz: Axial Skeleton and Cartilage

Human Anatomy & Physiology: Bones and Skeletal Tissues

• The human skeleton has 206 named bones.
• Bones are classified into two groups: axial and appendicular.
• The axial skeleton includes the skull, vertebral column, and rib cage.
• The appendicular skeleton includes the bones of the upper and lower limbs and the girdles attaching them to the axial skeleton.

Skull Geography

• The skull has cranial sutures, cranial fossae, and a cranial cavity.
• Also includes middle and internal ear cavities, nasal cavity, and orbits.
• There are 85 named openings (foramina, canals, fissures).

Major Cavities of the Skull

• The skull contains various cavities, including the cranial cavity, orbits, and nasal cavity.
• The frontal sinus, ethmoidal air cells, maxillary sinus, and sphenoidal sinus are parts of the paranasal sinuses.

Anatomy of the Anterior and Posterior Aspects of the Skull

• Diagrams show many specific bones like frontal, parietal, sphenoid, temporal, maxilla, mandible, etc. and sutures like sagittal and lambdoid
• There are named openings like the supraorbital foramen (notch), optic canal, mental foramen, and others.

Bones of the Lateral Aspect of the Skull

• Sagittal suture, coronal suture, lambdoid suture show the relationships of various bones.
• Other details like squamous suture, zygomatic process, mastoid process, external acoustic meatus are indicated.

Inferior Aspect of the Skull (Mandible Removed)

• The illustration shows the hard palate, palatine bone, zygomatic bone, temporal bone (zygomatic process), vomer and other bones in the lower skeletal structure.
• Structures like foramen ovale, foramen spinosum, foramen lacerum, carotid canal, etc. are present.
• Inferior view of the skull, with mandible removed. This shows the relationships of various bones in the bottom of the cranium

Paranasal Sinuses

• The paranasal sinuses are air-filled spaces within the bones of the skull, including the frontal sinus, ethmoidal air cells, sphenoidal sinus, and maxillary sinus.

Developmental Aspects: Fetal Skull

• Infant skulls have more bones than adult skulls.
• Skull bones are unfused, connected by fontanelles (unossified remnants of fibrous membranes).
• Fontanelles (anterior, posterior, mastoid, and sphenoidal) ease birth and allow brain growth.

Skull of a Newborn

• The figure displays the four fontanelles in the newborn skull.
• Illustrates the positions and relations of the frontal, parietal, and occipital bones.

Developmental Aspects: Growth Rates

• At birth, the cranium is large relative to the face.
• By 9 months, the cranium is about half its adult size.
• Mandible and maxilla shorten at birth but lengthen with age.
• Arms and legs grow faster than the head and trunk, establishing adult proportions.

Vertebral Column

• The vertebral column transmits the weight of the trunk to the lower limbs.
• It surrounds and protects the spinal cord.
• It has 26 irregular bones (vertebrae) in five major regions.
• Cervical (neck), Thoracic (Thoracic cage), Lumbar (Lower back), Sacrum, Coccyx.

Vertebral Column: Curvatures

• The spine's curvatures increase its resilience and flexibility.
• The cervical and lumbar curvatures are concave posteriorly.
• The thoracic and sacral curvatures are convex posteriorly.
• Abnormal curvatures include scoliosis (lateral curve), kyphosis (exaggerated thoracic curvature), and lordosis (accentuated lumbar curvature).

Types of Bones

• There are long (limb, hand, and foot), short, flat (sternum, scapula, ribs, skull), and irregular bones (vertebrae, coxal bones).

Physiology of Bones

• Bones have seven important functions: support, protection, movement, mineral and growth factor storage, blood cell formation, triglyceride storage, and hormone production.
• Calcium is required for many processes (including nerve impulse transmission, muscle contraction, blood clotting)

Skeletal Cartilages

• Three major types of skeletal cartilage: hyaline, elastic, and fibrocartilage.
• Location varies and shows specific types in different regions of the body.

Membranes: Periosteum & Endosteum

• Periosteum is a double-layered membrane covering the external bone surfaces.
• Endosteum is a delicate membrane covering the internal bone surfaces, and trabeculae of spongy bone which lines canals in compact bones.

Hematopoietic Tissue in Bones

• Red bone marrow is found within trabecular cavities of spongy bone and diploë in flat bones.
• In newborns, red marrow is present in the medullary cavities and spongy bones.
• In adults, red marrow is mostly found in the diploë of flat bones and some irregular bones.
• Yellow marrow can convert to red marrow if needed.

Microscopic Anatomy of Bone

• Compact bone is also called lamellar bone.
• Osteons (or Haversian systems) are the structural units of compact bone.
• The osteon contains lamellae, central canals, perforating canals, and canaliculi.

Spongy Bone

• The trabeculae align along lines of stress, supporting the bone.
• Spongy bone lacks osteons and contains irregular lamellae.
• Osteocytes are interconnected by canaliculi, and capillaries supply nutrients.

Chemical Composition of Bone

• Bones are composed of inorganic hydroxyapatite mineral and organic collagen fibers.
• This composition makes bone strong and resists compression.

Endochondral Ossification

• Endochondral ossification forms most bones except clavicles.
• It begins in the second month of fetal development.
• It uses hyaline cartilage models.

Intramembranous Ossification

• Intramembranous ossification forms flat bones of the skull and clavicles.
• Mesenchymal cells condense to form an ossification center.
• Osteoid is secreted, then calcified, forming woven bone.

Interstitial Growth

• In long bones, chondroblasts in the epiphyseal plate divide.
• New cartilage is added at the epiphysis.
• This leads to bone lengthening before the epiphyseal plates close.

Bone Remodeling

• Bone is constantly being remodeled.
• Cartilage growth and bone replacement mechanisms occur during growth.
• Bone growth occurs where cartilage grows occurs.

Results of Mechanical Stressors: Wolff's Law

• Bones adapt to stresses and demands placed upon them.
• Handedness leads to thicker, stronger bones in the dominant upper limb.
• Curved bones are thickest where they are most prone to buckling.
• Trabeculae of bony tissue form trusses along stress lines.
• Large projections occur where heavy, active muscles are attached.
• Bones of fetuses and bedridden individuals have less defined structure.

Fracture Classification

• Fractures are classified by the position of bone ends (displaced/nondisplaced), completeness of the break (complete/incomplete), and whether skin is penetrated (open/closed).

Common Types of Fractures

• Includes comminuted (shattered fracture), compression, spiral, epiphyseal, depressed, and greenstick types.

Healing of a Bone Fracture

• Fracture healing involves a sequence of steps, including hematoma formation, fibrocartilaginous callus formation, bony callus formation, and bone remodeling.

Homeostatic Imbalances: Osteomalacia & Rickets

• Osteomalacia involves poorly mineralized bones, causing soft, weak bones.
• Rickets is osteomalacia in children, leading to bowed legs and bone deformities.

Osteoporosis

• Osteoporosis is a group of diseases where bone resorption exceeds deposition.
• Spongy bone in the spine and neck of femur is affected.
• Vertebral and hip fractures are common.

Risk Factors for Osteoporosis

• Risk factors for osteoporosis, include increasing age, being a postmenopausal woman, petite body form, insufficient exercise, poor diet, smoking and certain hormone-related conditions.

Developmental Aspects of Bones

• Embryonic skeleton ossifies, so fetal age can be estimated from X-rays or sonograms.
• Most long bones begin ossifying by 8 weeks, with primary centers apparent by 12 weeks in development.
• By age 25, most bones are completely ossified, and skeletal growth ceases.