The Axial and Appendicular Skeleton
The skeletal system comprises two divisions: the Axial and Appendicular Skeleton. The distinction between the axial and appendicular can be elucidated by understanding axial as the center-line or pivot-line through an object, while appendicular refers to something "hung on" to this central element. This description aptly fits the human skeleton.
Axial Skeleton: Comprising the bones of the skull, vertebral column, and ribcage of the chest, the axial skeleton forms the central axis of the body.
Appendicular Skeleton: Consisting of bones that attach to the axial skeleton, the appendicular skeleton includes the bones of the pectoral girdle (shoulders, arms, hands) and pelvic girdle (pelvis, legs, feet). Essentially, the bones of the appendicular skeleton are attached or "hung off" the axial skeleton.
The term "appendicular" is derived from "appendicula," the diminutive of "appendix," both meaning a "small appendage." This terminology finds parallels in other structures like the vermiform appendix, hanging onto the colon, and the appendix in a textbook, an attachment added to the end of a book. In anatomy, terms and functions from everyday life are often utilized, as seen in the appendicular skeleton's attachment to the axial skeleton by girdles.
Understanding the vocabulary for bony landmarks aids in locating other markings. Particularly in the skull, processes are named for the bone they extend toward rather than the bone they are part of. These notes aim to provide fundamental information about bone structures.
The Axial Skeleton:
Starting with the axial skeleton, the focus begins with the skull:
Calvaria: Also known as the "skullcap," it comprises the superior portions of the frontal bone, occipital bone, and parietal bones. The calvaria is not a bone but an artificial section created by cutting off the top part of the skull.
Sutures: These are immovable joints of the skull, including the coronal, lambdoidal, sagittal, squamosal, and intermaxillary sutures.
Bones of the Skull:
1.Occipital Bone: Featuring landmarks such as the foramen magnum, occipital condyles, external occipital crest, and jugular foramen.
2.Parietal Bones: Including grooves for superior sagittal sinus.
3. Frontal Bone: With structures like the supraorbital margins, zygomatic process, and frontal sinus.
4. Temporal Bone: Featuring the squamous and petrous portions, mastoid process, and styloid process.
5. Sphenoid Bone: Comprising greater and lesser wings, sella turcica, and pterygoid processes.
6. Ethmoid Bone: Noteworthy structures include the crista galli, cribriform plate, and ethmoidal sinuses.
Bones of the Skull: Facial Bones:
1. Nasal, Maxillae, Mandible, Zygomatic, Palatine, Lacrimal, Vomer, and Inferior Nasal Conchae.
Hyoid Bone: The only bone not directly articulating with any other bone in the body.
Auditory Ossicles: The smallest bones in the human body, located in the middle ear.
Sinuses: Hollow cavities in bones lined with a mucous membrane, including the frontal, ethmoid, sphenoid, and maxillary sinuses.
Fetal Skull: Fontanels, or "soft spots," facilitate skull growth and development in infants, with four major fontanels identified.
Spinal Column: Comprising cervical, thoracic, lumbar, sacral, and coccygeal regions, featuring primary and secondary curvatures and various vertebral structures.
Ribs and Sternum: Twelve pairs of ribs, categorized into true, false, and floating ribs, along with the manubrium, body, and xiphoid process of the sternum.
The Appendicular Skeleton
Names play a crucial role in understanding bone structures, offering insights into their location, associations and functions.
Upper Limb: Pectoral Girdle:
1. Clavicle: Comprising sternal and acromial ends, along with the conoid tubercle.
2. Scapula: Featuring structures such as the acromion, coracoid process, and supraspinous fossa.
Arm: Humerus: With landmarks like the head, tubercles, anatomical and surgical necks and condyles.
Forearm: Ulna and Radius: Notable structures include the olecranon and coronoid processes of the ulna, and the radial head, neck, and styloid process of the radius.
Carpals, Metacarpals, and Phalanges: Comprising small wrist bones, hand bones, and finger bones, respectively, each with distinct anatomical features.
Lower Limb: Pelvic Girdle:
Pelvis: Comprising the false and true pelvis, with various landmarks such as the pelvic brim, inlet, outlet and arcuate line.
Os Coxae: Consisting of the ilium, ischium, and pubis, with their respective structures and articulations.
Bones of Lower Extremity: Including the femur, patella, tibia, fibula, tarsals, metatarsals, and phalanges, each with unique characteristics and functions.
