Comprehensive Study Guide: Human Skeletal Anatomy and Fracture First Aid

Composition and Classification of the Human Skull

The human head is a complex structure composed of a total of $22$ bones. This total is subdivided into two primary groups: the $8$ bones comprising the neuro-cranium (cranium) and the $14$ bones comprising the viscero-cranium (facial bones). Additionally, the anatomy of the head includes $6$ small ossicles located within the middle ear. The cranial bones, which protect the brain, are categorized using the mnemonic "FOPEET" and consist of: $1$ Frontal bone, $2$ Parietal bones, $1$ Sphenoid bone, $2$ Temporal bones, $1$ Occipital bone, and $1$ Ethmoid bone.

The facial bones, known as the facial skeleton, are remembered by the mnemonic "MaMa Mala y Un PaVo Con Nariz." These $14$ bones include: $2$ Nasal bones, $2$ Lacrimal (also called Unguiz) bones, $2$ Malar (or Zygomatic) bones, $2$ Inferior Nasal Conchae (Cornetes), $1$ Vomer bone, $2$ Superior Maxillary bones, $2$ Palatine bones (located behind the superior maxilla), and $1$ Inferior Maxillary bone, more commonly known as the Mandible.

Detailed Anatomy of Cranial Bones

The Frontal bone is an odd, medium, and symmetrical flat bone that forms the forehead. It is situated in the anterosuperior part of the cranium and articulates with several bones: the parietals, ethmoid, sphenoid, nasals, zygomatics (malares), lacrimals (unguis), and superior maxillae. It features three distinct faces—anterior, inferior, and posterior—and three borders—anterior, posterior, and superior. Key landmarks include the supraorbital notch, the supraorbital border, and the frontal squama.

The Ethmoid bone is an irregular, odd, medium, and symmetrical bone shaped like a scale or balance. It is located between the frontal and sphenoid bones. Its articulations include the frontal, sphenoid, palatines, nasals, superior maxillae, lacrimals, vomer, and inferior nasal conchae. It consists of three principal parts: a vertical plate (lamina), a horizontal plate, and two lateral masses. Structural highlights include the Crista Galli and the perpendicular plate.

The Sphenoid bone is a medium, odd, irregular bone famously described as being shaped like a bat with extended wings. It sits in the middle part of the skull base, posterior to the ethmoid and anterior to the occipital. It holds the distinction of being the only bone that articulates with every other cranial bone, as well as the vomer and palatines. It possesses three main parts: any central body, two lesser wings, two greater wings, and two pterygoid processes. Specific features include the sella turcica, the superior orbital fissure, and the pterygoid fossa.

The Occipital bone is a flat, odd, medium, and symmetrical bone with a rhomboid shape located in the postero-inferior and medial part of the cranium. It rests upon the first cervical vertebra, the atlas. It articulates with the parietals, temporals, sphenoid, and the atlas. Its anatomy includes the foramen magnum (Agujero occipital), the basilar process, lateral masses, and the occipital squama. It presents two faces (exocranial and endocranial) and four borders (two superior and two inferior). Landmarks include the external occipital protuberance and the nuchal lines.

The Parietal bone is a paired flat bone of quadrilateral shape that forms the major part of the skull's roof. Positioned on both sides of the midline, it articulates with the frontal, occipital, and temporal bones. It has two faces (exocranial and endocranial) and four borders (superior, inferior, anterior, and posterior). It is noted for reflecting vascular grooves from the middle meningeal artery on its internal surface.

The Temporal bone is a paired irregular bone located on the lateral and inferior sides of the cranium. It is vital because it encloses the essential organs for hearing and equilibrium. It articulates with the occipital, parietal, sphenoid, mandible, and zygomatic bones. It consists of three portions: the squamous portion (with two faces and one border), the mastoid portion (with two faces and one border), and the petrous portion (also called the peñasco, containing one base, one vertex, four faces, and four borders). Landmarks include the external auditory meatus, the zygomatic process, and the styloid process.

Detailed Anatomy of Facial Bones and Middle Ear

The Inferior Maxillary (Mandible) is an irregular, odd, and medium bone located in the lower part of the face. It is unique as the only movable bone in the head. It articulates with the temporal bone and is composed of a body (with two faces and two borders) and two ascending rami (each with two faces and two borders). Key features include the coronoid process, the condylar process, and the mental foramen.

The Vomer is a flat, thin, odd, and medium bone with a quadrilateral shape, located in the posterior and inferior part of the nasal fossae. It articulates with the ethmoid, sphenoid, superior maxillae, and palatines, possessing two faces and four borders.

The Inferior Nasal Concha (Cornete inferior) is a thin, paired, irregular bone shaped like a horn or curved plate. Located in the lower portion of each nasal fossa, it articulates superiorly with the ethmoid and superior maxillae, anteriorly with the lacrimal, and posteriorly with the palatines. It has two faces (internal and external), two borders (superior and inferior), and two extremities (anterior and posterior).

The Superior Maxilla is a paired, irregular, quadrilateral bone at the center of the face, below the orbits and above the buccal cavity. It articulates with the frontal, ethmoid, zygomatics, lacrimals, nasal bones, vomer, inferior conchae, and palatines. It features two faces (internal and external) and four borders (superior, anterior, posterior, and inferior). Major landmarks include the infraorbital foramen, the canine fossa, and the alveolar process.

The Palatine bone is a paired, irregular bone shaped like the capital letter "L," located behind the superior maxilla. It articulates with the opposite palatine, the superior maxillae, ethmoid, sphenoid, inferior conchae, and vomer. It consists of two main parts: a vertical (perpendicular) plate and a horizontal plate.

The Nasal bones (Huesos propios de la nariz) are paired flat bones of quadrilateral shape located on either side of the midline between the ascending processes of the superior maxillae and the frontal bone. They form a large part of the nasal bridge and articulate with each other, the maxillae, the frontal bone, and the nasal cartilage.

The Lacrimal bone (Unguis) is a paired flat bone shaped like a fingernail, located in the anterior part of the medial wall of the orbit. It articulates superiorly with the frontal, anteriorly with the maxilla, posteriorly with the ethmoid, and inferiorly with the inferior nasal concha.

The Malar bone (Zygomatic or Pómulo) is a paired irregular bone forming the prominence of the cheeks. It articulates with the frontal bone (superiorly), the superior maxilla (inferiorly and anteriorly), and the temporal and sphenoid bones (posteriorly). It consists of two faces, four borders, and four angles (superior, posterior, anterior, and inferior).

Additionally, the middle ear contains three ossicles: the Malleus (Martillo), the Incus (Yunque), and the Stapes (Estribo). The Stapes is recognized as the smallest bone in the human body. Furthermore, the Hyoid bone is an odd, medium, and symmetrical "U"-shaped bone located in the anterior neck, below the tongue and above the thyroid cartilage. It is the only bone in the body that does not articulate with any other bone.

Anatomy of the Vertebral Column

The vertebral column, also known as the "raquis" or dorsal spine, supports the human skeleton and body weight while protecting the spinal cord (medula espinal). There is a numerical difference between children and adults regarding vertebrae count: children possess a total of $33$ vertebrae, while adults have $26$ due to fusion. The distribution is as follows: $7$ Cervical, $12$ Thoracic (or Dorsal), $5$ Lumbar, $5$ Sacral (which fuse into one Sacrum in adults), and $3$ to $4$ Coccygeal (which fuse into one Coccyx in adults).

Each vertebra consists of a vertebral body, which is a voluminous cylindrical part that increases in size as one descends the column. Adjacent bodies are separated by intervertebral discs. The vertebral arch consists of two pedicles and two laminae. The pedicles have vertebral notches that form the intervertebral foramen, allowing for the passage of spinal nerves. The superposition of vertebral foramina creates the vertebral canal for the spinal cord. Seven processes arise from the vertebral arch: one spinous process (postero-inferior), two transverse processes (posterolaterally), and four articular processes containing articular facets. These processes serve as attachment points for muscles and ligaments.

Cervical vertebrae ($7$ bones) have the smallest discs but the greatest range of movement. The first two, Atlas ($C1$) and Axis ($C2$), facilitate head rotation. Thoracic vertebrae ($12$ bones) form the upper back and assist in forming the thoracic cavity. Lumbar vertebrae ($5$ bones) form the lower back and have the largest bodies to support weight. The Sacrum ($5$ fused bones) transmits weight from the upper body to the pelvis. The Coccyx ($3 - 4$ fused bones) constitutes the final segment of the spine.

The Thoracic Cage: Ribs and Sternum

The thoracic cavity is defined by the ribs, the vertebral column, and the sternum, housing the heart and lungs. Ribs are flat, curved bones that are lightweight yet resilient. A standard human has $12$ pairs of ribs ($24$ total): $7$ pairs of true (sternal) ribs ($I - VII$), $3$ pairs of false ribs ($VIII - X$), and $2$ pairs of floating ribs ($XI$ and $XII$). A typical rib structure includes a head (articulating with thoracic vertebrae), a neck, and a body (where the iliocostalis muscle inserts). The body also contains a costal groove.

The Sternum is an odd, long, and flat bone in the center-front of the thoracic wall. It is divided into three parts: the Manubrium (upper part articulating with the clavicle and first ribs), the Body (the central part), and the Xiphoid Process (the lower tip). It is connected to the first seven pairs of ribs via costal cartilages.

Skeletal Anatomy of the Upper Extremities

The scapular girdle is an incomplete bony ring connecting the upper limb to the thorax, consisting of the Scapula (Omóplato) and the Clavicle. The Scapula is a triangular bone forming the shoulder; its anterior costal face is smooth and concave (subscapular fossa), while its posterior face is convex and irregular, featuring the acromion and coracoid process. The Clavicle is an "S"-shaped elongated flat bone situated horizontally above the thorax, articulating medially with the sternum and laterally with the scapula.

The arm consists of a single long bone, the Humerus, which articulates proximally with the shoulder (humeral head) and distally with the radius and ulna at the elbow. The forearm contains the Radius (lateral and shorter) and the Ulna (medial, longer, and parallel to the radius). Both forearm bones consist of two epiphyses and one diaphysis.

The hand comprises $27$ bones divided into three types. The Carpus (wrist) consists of $8$ bones: Scaphoid, Lunate (Semilunar), Triquetrum (Piramidal), Pisiform, Trapezium, Trapezoid, Capitate (Grande), and Hamate (Ganchoso). The Metacarpus consists of $5$ bones forming the palm. The Phalanges are $14$ bones in the fingers; each finger has three (distal, middle, proximal), except the thumb, which has only two.

Skeletal Anatomy of the Lower Extremities

The pelvic region consists of the Sacrum, Coccyx, and two Hip bones (Iliacos or Coxales). The pelvic girdle itself is formed by the hip bones. Each hip bone is developed through the fusion of three originally separate bones: the Ilium (the largest part), the Pubis, and the Ischium. In females, these bones are wider to allow for gestation.

The thigh is composed of the Femur, the largest bone in the human skeleton. It consists of a body (diaphysis) with three faces (anterior, internal, external) and three borders, a superior epiphysis (articulating with the hip), and an inferior epiphysis (articulating with the tibia). The leg consists of the Tibia and the Fibula (Peroné). The Tibia is the weight-bearing "shin bone" located anteromedially. The Fibula is a slender, cylindrical bone on the posterior-lateral side. It features a head (superior part) and a lateral malleolus (external malleolus) at the inferior part.

The foot contains $26$ bones. The Tarsus (posterior foot) includes $7$ bones: Calcaneus, Astragalus (Talus), Navicular (Escafoides), Cuneiforms (medial, intermediate, lateral), and Cuboid. The Metatarsus consists of $5$ long bones with triangular prismatic bodies. Like the hand, the foot has $14$ Phalanges (three per toe, two for the big toe).

First Aid and Fracture Prevention

A fracture is defined as a total or partial interruption of a bone. Basic first aid requires keeping the victim immobile; they should not be moved unless there is immediate danger, particularly in cases of suspected fractures of the skull, spine, ribs, pelvis, or femur. Bleeding wounds must be treated first by applying firm pressure with a clean dressing. If a bone protrudes, pressure should be applied around the edges rather than directly on the bone. One should never attempt to straighten broken bones. For limb fractures, support should be provided using pillows or makeshift splints (like wooden planks or folded magazines), ensuring the limb is immobilized above and below the site. Slings are used for arm or clavicle breaks. Raising the area and applying cold compresses can reduce swelling. Professional medical attention must be sought, and recovery with a cast typically lasts between $1$ and $3$ months. Common fracture sites include the wrist, hand, fingers, ankle, and hip.

Fracture prevention involves maintaining strong bones through exercise (running and jumping) and a proper diet. Proteins like collagen form the bone's scaffold; fish is a vital source providing calcium, Omega-3, and Vitamin D. Omega-3 provides mineralization and prevents osteoporosis. Zinc, the most abundant trace element in bones, is crucial for cell division and healing (found in legumes, liver, almonds, dairy). Vitamin D (from sun, fish, avocado) is required for magnesium and calcium absorption. Vitamin C (from oranges, tomatoes) is essential for collagen synthesis. Calcium must be consumed with other nutrients to be fixed to the bone; sources include algae, sesame, green leafy vegetables, and soy. Additionally, protective gear like helmets and pads should be used. While children have a higher risk due to developing bones, they recover faster than adults. Conversely, older adults are more prone to fractures due to age-related weakening, and habits like smoking or alcohol consumption significantly decrease bone density.