Bones of the Body - Comprehensive Notes

Types of Bones

Approximately 206 bones in the adult skeleton are categorized as follows:

• Long bones: These are tubular and include bones of the arms, legs, clavicle, metacarpals, metatarsals, and phalanges.
• Flat bones: Examples include the sternum, ribs, scapulae, and bones of the cranium.
• Short bones: These are boxy in shape and include the carpals and tarsals.
• Irregular bones: Vertebrae and os coxae fall into this category.
• Sesamoid bones: These are found within tendons and change the direction of pull. The patellae and other miscellaneous sesamoid bones are examples.

Skeletal Divisions

The skeleton is divided into two main divisions:

• Axial skeleton: This includes the skull, sternum, ribs, and vertebrae (including the sacrum). Its primary functions are to protect, support, and carry body structures.
• Appendicular skeleton: This includes the bones of the pectoral and pelvic girdles and the bones of the arms, legs, wrists, hands, ankles, and feet. These bones are primarily involved with the limbs.

Skeletal Features

Definitions of terms used to describe features located on bones can be found on page 178, Table 6.1.

• Fossa: A shallow depression.
• Tuberosity: A small, rough projection.

Skull Bones and Sutures

The skull consists of several bones, including the parietal bone, sphenoid bone, frontal bone, nasal bone, zygomatic bone, maxilla, mandible, temporal bone, and occipital bone. The bones are connected by sutures, such as the coronal suture, squamosal suture, sagittal suture, and lambdoidal suture.

Wormian bones, also known as ossicles, are extra bone pieces that can occur within a suture in the skull. The external occipital protuberance is a bony projection located on the occipital bone.

The nasal cavity includes the perpendicular plate of the ethmoid bone, nasal bones, zygomatic bone, maxilla, mandible, and vomer.

Temporal Bone Features

The temporal bone includes the external auditory meatus, zygomatic process (forming the zygomatic arch), mandibular fossa, styloid process, and mastoid process.

Temporomandibular Joint (TMJ)

The temporomandibular joint is formed by the mandibular condyle and the mandibular fossa of the temporal bone.

• TMJ disorder: Inflammation of the TMJ can cause pain and stiffness.

Ethmoid Bone

The ethmoid bone features the cribriform plate, crista galli, and ethmoid sinuses. The perpendicular plate is also part of the ethmoid bone.

Sphenoid Bone

The sphenoid bone includes the sella turcica, which houses the pituitary gland, and the sphenoid sinus.

Nasal Cavity

The medial view of the nasal cavity shows the sella turcica, sphenoid sinus, ethmoid bone, nasal bone, nasal cartilage (septum), vomer bone, palatine bone, and maxilla. The lateral wall of the nasal cavity includes the sella turcica, sphenoid sinus, ethmoid bone, nasal bone, nasal conchae, palatine bone, and maxilla.

Sella Turcica

The sella turcica, located on the sphenoid bone, contains the pituitary gland.

Paranasal Sinuses

The paranasal sinuses include the frontal sinus, ethmoid sinus, sphenoid sinus, and maxillary sinus. These sinuses are air-filled spaces within the skull bones.

Vertebral Column

The vertebral column consists of the following regions:

• Cervical vertebrae: C1-C7
• Thoracic vertebrae: T1-T12
• Lumbar vertebrae: L1-L5
• Sacrum: 5 fused vertebrae
• Coccyx: 3 to 5 fused vertebrae

Spinal Curvature Abnormalities

• Kyphosis: Exaggerated thoracic curvature.
• Lordosis: Exaggerated lumbar curvature.
• Scoliosis: Exaggerated lateral curvature.

Vertebral Anatomy

A typical vertebra consists of the following structures:

• Body (centrum): The main, weight-bearing portion of the vertebra.
• Vertebral arch: Formed by the pedicles and laminae.
• Vertebral foramen: The opening through which the spinal cord passes.
• Spinous process: A posterior projection.
• Transverse processes: Lateral projections.
• Superior articular processes: Articulate with the vertebra above.
• Pedicle: Connects the body to the transverse process.
• Lamina: Connects the transverse process to the spinous process.

Regional Characteristics of Vertebrae

• Cervical vertebrae: Have superior articular processes and facets.
• Thoracic vertebrae: Have superior costal facets for the head of the rib and transverse costal facets for the tubercle of the rib.
• Lumbar vertebrae: Have superior articular processes.

Range of Motion in Thoracic and Lumbar Regions

The approximate ranges of motion for the thoracic and lumbar regions are:

• Flexion: $0-80^{\circ}$
• Extension: $0-25^{\circ}$
• Lateral flexion: $0-35^{\circ}$
• Rotation: $0-45^{\circ}$

Atlas (C1) and Axis (C2)

• Atlas (C1): Articulates with the occipital condyles.
• Axis (C2): Features the dens (odontoid process).

Range of Motion in Cervical Region

Approximate Ranges of Motion (degrees):

• Occipitoatlantal Joint:
  • Flexion: $10^{\circ}$
  • Extension: $15^{\circ}$
  • Lateral Flexion: $7^{\circ}$
  • Rotation: $3^{\circ}$
• Atlantoaxial Joint:
  • Flexion: $11^{\circ}$
  • Extension: $1^{\circ}$
  • Lateral Flexion: $2^{\circ}$
  • Rotation: $45^{\circ}$
• Averages for Other Cervical Vertebrae:
  • Flexion: $8-19^{\circ}$
  • Extension: $7-16^{\circ}$
  • Lateral Flexion: $4-10^{\circ}$
  • Rotation: $8-14^{\circ}$

Spinal Ligaments and Intervertebral Discs

• Anterior longitudinal ligament: Runs along the anterior surface of the vertebral bodies.
• Posterior longitudinal ligament: Runs along the posterior surface of the vertebral bodies, inside the vertebral canal.
• Supraspinous ligament: Connects the tips of the spinous processes.
• Interspinous ligament: Located between the spinous processes.
• Ligamentum flavum: Connects the laminae of adjacent vertebrae.
• Intervertebral disc: Located between vertebral bodies, consisting of:
  • Annulus fibrosus: The outer, fibrous ring.
  • Nucleus pulposus: The inner, gelatinous core.

Herniated Disc

A herniated disc occurs when the nucleus pulposus protrudes through the annulus fibrosus, potentially compressing the spinal nerve root.

Sacrum and Coccyx

• Sacrum: Formed by five fused vertebrae, featuring:
  • Sacral canal
  • Superior articular process
  • Ala
  • Median sacral crest
  • Dorsal sacral foramina
  • Lateral sacral crest
  • Sacroiliac joint location
  • Sacral hiatus
• Coccyx: Formed by three to five fused vertebrae.

Rib Cage and Sternum

• True ribs (1-7): Attach directly to the sternum via costal cartilage.
• False ribs (8-12): Attach indirectly to the sternum or not at all.
• Floating ribs (11, 12): Do not attach to the sternum.
• Sternum: Consists of:
  • Manubrium: Includes the jugular notch and clavicular notch.
  • Body
  • Xiphoid process
    *Relevant Anatomical landmarks
  • Sternal angle
  • Xiphisternal joint
  • Costal margin

Limb Bones

• Upper Limb: Includes the humerus, radius (lateral, by the thumb), and ulna.
• Lower Limb: Includes the femur, patella, tibia, and fibula.

Shoulder Girdle

The shoulder girdle consists of the clavicle and scapula. Features of these bones include:

• Clavicle
• Scapula:
  • Acromion process
  • Coracoid process
  • Glenoid fossa
  • Supraspinous fossa
  • Infraspinous fossa
  • Subscapular fossa
    *Humerus
  • Head of humerus
  • Greater tubercle
  • Intertubercular groove
  • Lesser tubercle

Os Coxa (Hip Bone)

The os coxa consists of three bones:

• Ilium
• Pubis
• Ischium *Relevant Landmarks
  • Greater sciatic notch
  • Ala
  • Auricular Surface
  • Body

Pelvic Girdle

The pelvic girdle is formed by two os coxae and the sacrum. It includes the sacroiliac joint and the pubic symphysis, which contains fibrocartilage. Other landmarks include the iliac fossa, acetabulum, and pubic arch.

Femur and Acetabulum

The femur articulates with the acetabulum (acetabular fossa) of the os coxa. The ilium, pubis, and ischium contribute to the formation of the acetabulum.

Hand and Foot Bones

• Hand:
  • Carpals (8)
  • Metacarpals (5)
  • Phalanges
• Foot:
  • Tarsals (7)
  • Metatarsals (5)
  • Phalanges