Human Anatomy: The Skeletal System

Comprehensive practice flashcards covering the human skeletal system, including bone classifications, histological types, cartilage varieties, axial and appendicular divisions, skeletal functions, skull landmarks, vertebral column curvatures, and pelvic girdle anatomy.

How many total bones are in the adult human skeleton, and how are they distributed among the main skeletal groups?

There are $206$ bones in total:

• Skull: $22$
• Middle ears (auditory ossicles): $6$
• Hyoid: $1$
• Vertebral column: $26$
• Thoracic cage: $25$
• Pectoral girdle: $4$
• Upper limbs: $60$
• Lower limbs: $60$
• Pelvic girdle: $2$

What is the structural difference between a ligament and a tendon?

A ligament connects bone to bone, whereas a tendon connects bone to muscle.

Which major parts of the skeleton belong to the axial skeleton versus the appendicular skeleton?

The axial skeleton consists of the skull, vertebrae, ribs, sternum, sacrum, hyoid, and auditory ossicles. The appendicular skeleton consists of the pectoral girdle, upper extremity, pelvic girdle, and lower extremity.

What are the four primary shape classifications of bones, along with an example of each?

1. Long bone (e.g., humerus of arm)
2. Short bone (e.g., carpals of wrist)
3. Flat bone (e.g., parietal bone of skull, sternum)
4. Irregular bone (e.g., vertebra)

What are the primary anatomical parts of a long bone shown in this diagram?

A long bone consists of a central shaft called the diaphysis, two expanded ends called epiphyses (proximal epiphysis and distal epiphysis), an epiphyseal line, a medullary cavity lined with compact bone and spongy bone, and an outer fibrous covering called the periosteum (covering all areas except articular surfaces).

How do compact bone and spongy bone differ in structure, arrangement, and function?

Compact bone forms the external layer, is arranged in structural units called osteons with concentric lamellae, and has central canals interconnected by perforating canals. Spongy bone lacks osteons, consists of a lattice of branching plates called trabeculae, is much lighter, forms the interior of short, flat, and irregular bones, and supports red bone marrow.

What defines a sesamoid bone, and what are two specific anatomical examples?

A sesamoid bone is a special type of short bone that forms within a tendon. Examples include the patella and the pisiform.

What are the key morphological features and examples of flat bones?

Flat bones are thin, flattened, and typically curved. Examples include the sternum, ribs, scapulae, and most bones of the cranial vault.

What is an irregular bone, and which bones fall into this category?

Irregular bones have complex, specialized shapes that do not fit into the long, short, or flat categories. Examples include the vertebrae, hip bones (os coxae), and certain cranial/facial bones such as the sphenoid and ethmoid bones.

What anatomical landmarks are present on the superior and posterior surfaces of the ethmoid bone shown in this figure?

Key landmarks include the crista galli, cribriform plate with olfactory foramina, perpendicular plate, lateral masses containing ethmoidal labyrinths (air cells), superior nasal concha, and middle nasal concha.

What are the vascular and neural characteristics of cartilage tissue, and what outer sheath encloses it?

Cartilage contains no blood vessels (avascular) and no nerves. It contains a high proportion of water for resilience and is surrounded by a dense irregular connective tissue membrane known as the perichondrium.

What are the three types of skeletal cartilage, their general functions, and where are they located?

1. Hyaline Cartilage: Provides smooth surfaces for gliding joints; located in articular cartilages of joints, costal cartilages, nasal cartilages, larynx, and trachea.
2. Elastic Cartilage: Highly flexible; forms the external ear and epiglottis.
3. Fibrocartilage: Highly compressible with high tensile strength; forms intervertebral discs, pubic symphysis, and menisci of the knee.

What are the six major functions of the skeletal system represented by the SPMABF mnemonic?

1. S - Support and structural framework
2. P - Protection of internal organs
3. M - Aid in movement (serving as levers for muscles)
4. A - Attachment sites for muscles, tendons, and ligaments
5. B - Blood cell formation (hematopoiesis in marrow cavities)
6. F - Fat/Triglyceride storage (chemical energy reserve in yellow bone marrow)

What role does bone tissue play in mineral homeostasis?

Bone acts as a mineral reservoir for calcium and phosphate ions, continually depositing and releasing them into the bloodstream to maintain physiological mineral levels.

What are the fibrous membrane regions of an infant skull shown here, and what is their functional importance?

The anterior fontanel, posterior fontanel, sagittal suture, and frontal suture; these soft membranous spaces allow the skull to compress slightly during birth and accommodate rapid brain growth during early development.

What prominent foramina and bony structures are visible from the superior view of the internal skull base?

Structures include the cribriform plate and crista galli of the ethmoid, the sphenoid with the sella turcica and foramen ovale, the petrous portion of the temporal bone with the internal acoustic meatus and jugular foramen, and the occipital bone with the foramen magnum.

What are the five regions and curvatures of the adult vertebral column, including vertebrae numbers?

1. Cervical curvature: concave, $7$ vertebrae ($C_1 - C_7$)
2. Thoracic curvature: convex, $12$ vertebrae ($T_1 - T_{12}$)
3. Lumbar curvature: concave, $5$ vertebrae ($L_1 - L_5$)
4. Sacrum: convex, $5$ fused vertebrae
5. Coccyx: $4$ fused vertebrae

Which three fused bones form each coxal bone (os coxae), and what key joint connects the pelvic girdle to the axial skeleton?

Each coxal bone is formed by the fusion of the ilium, ischium, and pubis. The pelvic girdle connects to the axial skeleton at the sacroiliac joint, where the ilium articulates with the sacrum.

How does spongy bone trabecular architecture differ between a healthy young adult and an individual with osteoporosis?

Normal spongy bone consists of thick, dense, interconnected trabecular bridges, whereas osteoporotic bone exhibits thinned, porous, and fractured trabeculae with markedly enlarged marrow spaces and reduced structural strength.