Chapter 7: The Skeletal System

Vocabulary practice flashcards covering the cranial and facial bones, vertebral column, thoracic cage, appendicular skeleton, pelvis comparisons, and developmental aspects of the skeletal system.

Skeletal System

The organ system composed of bones, cartilages, joints, and ligaments; it accounts for approximately $20\%$ of body mass and is divided into the axial and appendicular skeletons.

Axial Skeleton

The skeletal division consisting of $80$ bones distributed across three major regions: the skull, vertebral column, and thoracic cage.

Appendicular Skeleton

The division of the skeleton comprising the bones of the upper and lower limbs and the pectoral and pelvic girdles that anchor them to the body trunk.

Cranial Bones

A group of $8$ skull bones (frontal, $2$ parietal, occipital, $2$ temporal, sphenoid, ethmoid) that enclose the brain within the cranial cavity and form the cranial vault and base.

Facial Bones

A group of $14$ bones forming the framework of the face, housing special sense organs, providing air/food passages, and anchoring facial muscles and teeth.

Coronal Suture

The cranial articulation line located between the frontal bone and the parietal bones.

Sagittal Suture

The midline cranial suture located between the right and left parietal bones.

Lambdoid Suture

The cranial suture separating the parietal bones from the occipital bone on the posterior aspect of the skull.

Squamous Sutures

The cranial sutures located laterally on each side of the skull between a parietal bone and a temporal bone.

Sutural Bones

Tiny, irregularly shaped bones that occasionally develop within the suture lines of the skull.

Frontal Bone

Cranial bone forming the anterior portion of the cranium, the superior wall of each orbit, most of the anterior cranial fossa, and housing the frontal sinus.

Occipital Bone

Bone forming the posterior skull wall and posterior cranial fossa; articulates with the first vertebra and provides attachment sites for the ligamentum nuchae.

Temporal Bones

Bones forming the inferolateral aspects of the skull and parts of the cranial floor; divided into squamous, tympanic, mastoid, and petrous regions.

Sphenoid Bone

A complex, bat-shaped keystone bone of the cranium that articulates with all other cranial bones and contains greater wings, lesser wings, and pterygoid processes.

Ethmoid Bone

The deepest bone of the skull, forming the superior portion of the nasal septum, the roof of the nasal cavity, and the medial orbital walls.

Crista Galli

A superior projection on the cribriform plate of the ethmoid bone that anchors the dura mater of the brain.

Mandible

The lower jawbone; the largest and strongest bone of the face, forming the temporomandibular joint, which is the only freely movable joint in the skull.

Maxillary Bones

Medially fused keystone facial bones forming the upper jaw and central face; articulate with all other facial bones except the mandible and contain the largest paranasal sinuses.

Zygomatic Bones

The cheekbones; paired facial bones that form the inferolateral margins of the orbits.

Lacrimal Bones

Delicate, paired facial bones situated in the medial orbital walls containing the lacrimal fossa that houses the lacrimal sac.

Palatine Bones

L-shaped bones forming the posterior one-third of the hard palate, part of the posterolateral nasal cavity walls, and a small portion of the orbits.

Vomer

A slender, plow-shaped facial bone that forms the inferior part of the nasal septum.

Inferior Nasal Conchae

The largest of the three pairs of nasal conchae, forming part of the lateral walls of the nasal cavity.

Paranasal Sinuses

Mucosa-lined, air-filled cavities located within the frontal, sphenoid, ethmoid, and maxillary bones that warm/humidify air, enhance vocal resonance, and lighten the skull.

Hyoid Bone

A U-shaped bone in the anterior neck that does not articulate directly with any other bone; serves as a movable base for the tongue and anchors swallowing and speech muscles.

Vertebral Column

A flexible curved structure composed of $26$ irregular bones organized into $5$ regions (cervical, thoracic, lumbar, sacrum, and coccyx) that shields the spinal cord and bears trunk weight.

Scoliosis

An abnormal lateral curvature of the vertebral column.

Kyphosis

An exaggerated thoracic curvature of the vertebral column, commonly referred to as hunchback.

Lordosis

An accentuated lumbar curvature of the vertebral column, commonly referred to as swayback.

Nucleus Pulposus

The gelatinous central core of an intervertebral disc that provides elasticity and compressibility.

Anulus Fibrosus

The outer ring of an intervertebral disc composed of fibrocartilage and collagen fibers that confines the nucleus pulposus.

Atlas

The first cervical vertebra ($C_1$), lacking a body and spinous process; its lateral masses articulate with the occipital condyles to permit the 'yes' nodding motion.

Axis

The second cervical vertebra ($C_2$); contains the dens (odontoid process) which acts as a pivot around which the atlas rotates to allow the 'no' head rotation.

Dens

A tooth-like superior process projecting from the body of the axis ($C_2$) into the anterior arch of the atlas ($C_1$).

Vertebra Prominens

The seventh cervical vertebra ($C_7$), distinguished by a long, non-bifid spinous process that is easily palpated through the skin.

Thoracic Vertebrae

Twelve vertebrae ($T_1\text{–}T_{12}$) characterized by costal facets and demifacets for rib articulation, circular vertebral foramina, and long, inferiorly directed spinous processes.

Lumbar Vertebrae

Five heavily built vertebrae ($L_1\text{–}L_5$) with thick pedicles/laminae, hatchet-shaped spinous processes, and articular facet orientations that prevent rotation.

Sacrum

A curved triangular bone formed by the fusion of $5$ vertebrae ($S_1\text{–}S_5$) that forms the posterior wall of the pelvis and articulates laterally at the sacroiliac joints.

Coccyx

The tailbone, composed of $3\text{ to }5$ fused vertebrae that articulate superiorly with the apex of the sacrum.

Sternum

The flat breastbone formed by the fusion of three bones: the superior manubrium, the midportion body, and the inferior xiphoid process.

Sternal Angle

A palpable horizontal ridge across the front of the sternum where the manubrium fuses with the sternal body.

True Ribs

Vertebrosternal rib pairs $1$ through $7$ that attach directly to the sternum via individual costal cartilages.

False Ribs

Rib pairs $8$ through $12$; pairs $8\text{–}10$ connect indirectly to the sternum via the cartilage of the rib above, and pairs $11\text{–}12$ have no sternal attachment.

Floating Ribs

Vertebral rib pairs $11$ and $12$ that completely lack an anterior attachment to the sternum.

Pectoral Girdle

The shoulder girdle, composed of the clavicles and scapulae, which attaches the upper limbs to the axial skeleton and provides muscle attachment sites.

Clavicle

The collarbone, featuring a medial sternal end articulating with the sternum and a lateral acromial end articulating with the scapula.

Scapula

The shoulder blade; a flat, triangular bone located on the dorsal surface of the rib cage between ribs $2$ and $7$, bearing the spine, acromion, and glenoid cavity.

Humerus

The largest and longest bone of the upper limb; articulates proximally with the glenoid cavity of the scapula and distally with the radius and ulna.

Ulna

The medial bone of the forearm; forms the primary hinge of the elbow joint with the trochlea of the humerus via the olecranon and trochlear notch.

Radius

The lateral bone of the forearm; articulates proximally with the capitulum of the humerus and the radial notch of the ulna, and distally with the carpal bones.

Carpus

The wrist; consists of $8$ short bones in two rows: proximal (scaphoid, lunate, triquetrum, pisiform) and distal (trapezium, trapezoid, capitate, hamate).

Pollex

Digit $1$ of the hand (the thumb), containing only $2$ phalanges (proximal and distal) without a middle phalanx.

Pelvic Girdle

A heavy, weight-bearing basin formed by two coxal bones and the sacrum that attaches the lower limbs to the axial skeleton.

Coxal Bone

The hip bone (os coxae), formed by the developmental fusion of the ilium, ischium, and pubis at the acetabulum.

Pubic Symphysis

The fibrocartilage joint along the midline of the body where the anterior surfaces of the right and left pubic bones meet.

Female Pelvis

A pelvis modified for childbearing, featuring lighter/thinner bones, a broader pubic arch ($80^\circ\text{ to }90^\circ$), and a wider, shallower true pelvis.

Male Pelvis

A pelvis adapted for greater weight support, characterized by thicker/heavier bones, a narrower and deeper true pelvis, and an acute pubic arch ($50^\circ\text{ to }60^\circ$).

Femur

The thigh bone; the largest and strongest bone in the body, measuring roughly $\frac{1}{4}$ of an individual's height, articulating with the acetabulum proximally and the tibia/patella distally.

Patella

A triangular sesamoid bone enclosed within the quadriceps tendon that shields the anterior knee joint.

Tibia

The medial and larger bone of the leg; receives body weight from the femur and conveys it to the foot.

Fibula

The non-weight-bearing lateral bone of the leg that articulates proximally and distally with the tibia and provides attachment points for muscles.

Tarsus

The posterior half of the foot, composed of $7$ tarsal bones: talus, calcaneus, cuboid, navicular, and three cuneiforms.

Hallux

Digit $1$ of the foot (the great toe), possessing only $2$ phalanges (proximal and distal) and lacking a middle phalanx.

Fontanelles

Unossified fibrous membrane spaces in the fetal and infant skull (anterior, posterior, mastoid, and sphenoidal) that allow cranial deformation during birth and facilitate rapid brain growth.

Cleft Palate

A congenital condition of the skull characterized by failure of the right and left halves of the palate to fuse medially during development.

Primary Spinal Curvatures

The thoracic and sacral curvatures present at birth that are convex posteriorly, giving the infant vertebral column a C shape.

Secondary Spinal Curvatures

The cervical and lumbar curvatures that develop postnatally (convex anteriorly) as the infant learns to lift its head and walk.