KJ

Skeleton Vocabulary: Axial and Appendicular Terms from the Lecture

Axial Skeleton: Rib Cage and Sternum

  • Axial skeleton includes skull bones, facial bones, vertebrae, and the rib cage; the sternum sits at the center of the rib cage.
  • Sternum anatomy:
    • Manubrium: trapezoidal shape at the top of the sternum.
    • Body: the main central portion; this is the area used for chest compressions during CPR.
    • Xiphoid process: the small inferior projection; note: spelled with an x, not a z.
    • Practical CPR point: you locate the xiphoid process and go above it to stay on the body during compressions, because pushing into the lung cavity can cause injury.
  • Ribs: 12 pairs total.
    • True ribs: 1–7. They attach directly to the sternum via costal cartilage.
    • False ribs: 8–10. They attach to the sternum via shared cartilage linked to rib 7.
    • Floating ribs: 11–12. They do not connect to the sternum anteriorly; they attach to the thoracic vertebrae posteriorly only.
  • This completes the description of the axial skeleton in this lecture.

Appendicular Skeleton: Overview and Girdles

  • Appendicular skeleton supports movement of the limbs and connects to the axial skeleton via two girdles:
    • Pectoral (shoulder) girdle: clavicle (collarbone) and scapula (shoulder blade).
    • Pelvic (hip) girdle: os coxae (hip bone), consisting of three fused components.
  • Closer look at the upper limb girdle:
    • Clavicle: S-shaped bone with a thick, sternal end that articulates with the sternum; this end is called the sternal end.
    • The clavicle participates in the SC (sternoclavicular) joint and the AC (acromioclavicular) joint.
    • Acromion process: the bony tip at the distal end of the scapula, forming the AC joint with the clavicle.
    • Acromial end: the lateral end of the clavicle that articulates at the AC joint.
  • The scapula (shoulder blade): a triangular-shaped flat bone that sits on the posterior rib cage.
    • Spine of the scapula: prominent ridge on the posterior surface; leads to the acromion process at the top of the shoulder.
    • Glenoid fossa (glenoid cavity): shallow depression on the lateral aspect of the scapula that articulates with the humeral head; orientation to be lateral for proper arm articulation.
    • Coracoid process: a hook-like projection anteriorly that serves as a muscle/ligament attachment site.
    • Fossa terminology:
    • Subscapular fossa: anterior surface, where subscapularis muscle sits.
    • Supraspinous fossa: posterior surface above the spine.
    • Infraspinous fossa: posterior surface below the spine.
    • Borders and angles:
    • Inferior angle: bottom angle of the triangle.
    • Superior angle: top angle of the triangle.
    • Medial (vertebral) border: border closest to the vertebral column.
    • Lateral (axillary) border: border closest to the armpit.
    • Scapular notch: indentation near the superior border; path for blood vessels and nerves.
  • The shoulder joints (three primary joints):
    • SC joint: sternoclavicular joint between the clavicle and sternum.
    • AC joint: acromioclavicular joint between the clavicle and acromion.
    • GH joint: glenohumeral joint (shoulder joint) between the humeral head and the glenoid cavity; described as a ball-and-socket joint due to the humeral head fitting into the shallow glenoid cavity.
  • Orientation and left/right considerations:
    • The glenoid fossa must face laterally to articulate properly with the humerus; this helps distinguish left vs. right scapula.

Upper Extremity: Humerus to Hand

  • Humerus (upper arm bone):
    • Humeral head (proximal, rounded surface) articulates with the glenoid fossa.
    • Neck regions:
    • Anatomical neck: right below the head.
    • Surgical neck: the narrow region just distal to the anatomical neck; common site for humeral fracture repairs.
    • Tubercle landmarks:
    • Greater tubercle: large lateral projection.
    • Lesser tubercle: smaller anterior projection.
    • Intertubercular groove (bicipital groove): a groove between the tubercles where the tendon of the biceps brachii sits.
    • Also known as the bicipital groove.
    • The groove can snap or pop if the tendon slides out of its pulley, which is a common teaching analogy.
    • Shaft (diaphysis): the main midportion of the humerus.
    • Distal features for elbow articulation:
    • Medial epicondyle and lateral epicondyle: bony bumps for muscle attachments.
    • Medial condyle (trochlea) and lateral condyle (capitulum): smooth articular surfaces that form the elbow hinge joint.
    • Trochlea: articulates with the ulna.
    • Capitulum: articulates with the radius.
    • Anterior humerus landmarks:
    • Coronoid fossa: small anterior depression where the coronoid process of the ulna fits when the elbow bends.
    • Posterior humerus landmarks:
    • Olecranon fossa: large posterior depression where the olecranon process of the ulna fits when the elbow is extended.
  • Radius and ulna (forearm bones):
    • Radius: lateral bone in the forearm; radial head is rounded and articulates with the humerus.
    • Ulna: medial bone; medial border is closer to the body.
    • Styloid processes:
    • Styloid process of the radius: distal lateral projection near the wrist.
    • Styloid process of the ulna: distal medial projection near the wrist.
    • The radius and ulna work together to allow forearm rotation (pronation/supination).
  • The wrist and hand:
    • Carpal bones (eight small bones of the wrist): Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, Hamate.
    • Mnemonics for carpal bones (as used in lecture):
    • "Lovers try positions that they can't handle" to memorize Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, Hamate.
    • The instructor encouraged students to create their own silly mnemonic as extra credit.
    • The carpal tunnel:
    • Median nerve runs through the carpal tunnel; this canal can become compressed leading to symptoms of carpal tunnel syndrome.
    • A caution from the lecture: true carpal tunnel involvement was described as affecting only three fingers; in clinical terms, median nerve compression typically affects the lateral three and a half digits (thumb through half of the ring finger), but the speaker noted three fingers for teaching purposes; numbness in the ring finger alone is not carpal tunnel according to the teacher.
    • Metacarpals (hand bones): numbering 1–5 starting with the pinky (as stated in lecture; note that standard anatomical texts typically number 1–5 starting with the thumb).
    • Phalanges (finger bones): each finger has proximal, middle, and distal phalanges; the thumb has only a proximal and distal phalanx.
  • Practical notes for study and lab prep:
    • The wrist bones form the carpal region, which is a common focus in wrist identification labs.
    • Orientation and left/right identification are emphasized for accurate placement on models.

Lower Extremity: Pelvis to Foot

  • Pelvic girdle (os coxae): three bones that come together to form the hip socket (acetabulum) and support the trunk.
    • Ilium: forms the upper portion of the hip bone; features include the anterior superior iliac spine (ASIS) and anterior inferior iliac spine (AIIS) on the front; posterior superior iliac spine (PSIS) and posterior inferior iliac spine (PIIS) on the back.
    • Ischium: forms the inferior posterior part of the pelvis; contains the ischial tuberosity (the sit-down part) and the ischial spine.
    • Pubis: the anterior portion; the pubic bone points forward and meets at the pubic symphysis.
    • Iliac crest: the top border of the ilium, spanning from ASIS to posterior elements.
    • Acetabulum: the deep socket where the femur articulates with the pelvis; formed by all three bones: ilium, ischium, and pubis.
    • Sacroiliac (SI) joint: articulation between the ilium and the sacrum; stability is important for weight transfer.
    • The