Anatomy and Physiology: Skeletal System, Arthrology, and Muscular System

Comprehensive practice flashcards covering bone biology, ossification, cranial and axial skeleton anatomy, joint classifications and movements, and axial and appendicular musculature.

What are the three major functional roles of cartilage in the human body?

Cartilage functions to support soft tissues (such as airways and rib-to-sternum attachments), provide smooth gliding surfaces at joint articulations (modified hyaline cartilage), and act as a model for embryonic long bone formation.

What is the difference between interstitial growth and appositional growth of cartilage?

Interstitial growth is growth from within (internal expansion) where embedded chondroblasts divide and secrete matrix. Appositional growth occurs along the outer surface from stem cells in the perichondrium adding new layers.

What four-step process of cartilage development is illustrated in this diagram?

Interstitial growth of cartilage: (1) A chondrocyte in a lacuna undergoes mitosis; (2) Two chondroblasts occupy a single lacuna; (3) Each cell secretes new matrix and separates into its own lacuna as an inactive chondrocyte; (4) The cartilage mass continues expanding from within.

What proportion of the adult human skeleton is composed of compact bone versus spongy bone?

Compact (dense) bone forms the outer shell and comprises approximately $75\%$ of the skeleton, whereas spongy (cancellous or trabecular) bone occupies the inner sections and comprises approximately $25\%$.

How are bones classified according to shape, and what constitutes a sesamoid bone?

Bones are classified into long bones, short bones, flat bones, and irregular bones. A sesamoid bone is a small, seed- or bean-shaped bone that develops embedded within a tendon (e.g., the patella).

What are the primary anatomical regions and structural coverings of a typical long bone?

A long bone consists of a central shaft (diaphysis) enclosing a medullary cavity and expanded ends (epiphyses), separated in growing individuals by the epiphyseal plate at the metaphysis. Externally, it is covered by a fibrous periosteum secured via collagenous perforating (Sharpey's) fibers.

What is the diploe, and what is its protective mechanical function in the skull?

The diploe is the middle layer of spongy bone sandwiched between two layers of compact bone in cranial bones. It absorbs impact forces from head trauma to protect the inner compact bone layer and brain from fracture.

Where is active red bone marrow typically harvested for bone marrow transplants in adults?

Active hematopoietically active red marrow (myeloid tissue) is commonly withdrawn from the ala of the hip bone (ilium).

What are the four primary cell types of osseous tissue and their specific functions?

Osteogenic cells are stem cells that produce osteoblasts. Osteoblasts are bone-forming surface cells that secrete osteoid and promote mineralization. Osteocytes are mature bone cells in lacunae that act as strain sensors and maintain matrix. Osteoclasts are multinucleated macrophage-derived cells with ruffled borders that dissolve mineralized bone using acid and enzymes.

What are the structural microscopic components that make up an osteon in compact bone?

An osteon consists of a central canal (housing blood vessels and nerves), surrounded by concentric lamellae of calcified matrix, lacunae containing osteocytes, and radiating canaliculi that allow cell communication and nutrient diffusion, linked together horizontally by perforating canals.

How does the composition of the bone matrix resemble 'steel rebar embedded in cement'?

Collagen fibers act like rebar to provide tensile strength and flexibility, while the calcium-phosphate-rich mineralized osteoid acts like cement to resist compressive forces.

What is the key developmental difference between intramembranous and endochondral ossification?

Intramembranous ossification forms bone directly within condensed sheets of mesenchymal membrane (mostly forming flat bones). Endochondral ossification forms bone indirectly by replacing a pre-existing hyaline cartilage model (mostly forming long bones).

What are the five distinct histological zones found within the epiphyseal growth plate shown here?

From the epiphyseal side to the diaphyseal side: (1) Zone of resting cartilage; (2) Zone of proliferating cartilage; (3) Zone of hypertrophic cartilage; (4) Zone of calcified cartilage; (5) Zone of ossification.

What does Wolff's Law of bone state, and at what rate does bone remodeling occur?

Wolff's Law states that bone remodels and architecture adapts in response to mechanical loads and physical stress placed upon it. The entire adult skeleton is remodeled at a rate of approximately $10\%$ per year, with the femur completely replaced every $4\text{ months}$.

What are the four chronological stages of bone fracture repair?

(1) Formation of a fracture hematoma; (2) Formation of a fibrocartilaginous (soft) callus; (3) Conversion into a bony (hard) callus; (4) Continual remodeling of the bone and callus over several months.

Why does post-menopausal estrogen decline increase the risk for osteoporosis?

Estrogen normally stimulates and maintains osteoblast activity. A loss of estrogen depresses osteoblast bone deposition while osteoclasts continue uninhibited bone resorption, disproportionately degrading metabolically active spongy bone trabeculae.

Which structural unit of skeletal muscle contraction is diagrammed here, and what bands/lines define it?

The sarcomere, defined between two Z discs. It contains a dark central A band (thick myosin and overlapping thin actin filaments), a pale central H band (thick filaments only) bisected by the M line, and light I bands (thin actin and elastic filaments only).

According to the sliding filament theory, what structural changes occur to the sarcomere during contraction?

Thin actin filaments slide inward over thick myosin filaments, pulling the Z lines closer together, narrowing the H band and I band, and shortening the overall sarcomere length while the A band width remains unchanged.

What are the three connective tissue investments surrounding skeletal muscle, and how do they attach to bone?

Endomysium surrounds individual muscle fibers, perimysium wraps fascicles, and epimysium encloses the entire muscle. Epimysium collagen blends into the tendon, which merges with the bone periosteum anchored via Sharpey's fibers.

Which cranial nerve innervates the muscles of facial expression, and what are the primary sphincter muscles of the eyes and mouth?

The facial nerve (CN VII) innervates muscles of facial expression. The orbicularis oculi closes the eyelid, and the orbicularis oris closes and purses the lips.

What are the four primary muscles of mastication, and what is their common innervation?

The temporalis, masseter, medial pterygoid, and lateral pterygoid muscles. They are all innervated by the mandibular division of the trigeminal nerve ($\text{CN V}_3$).

Which cranial nerves innervate the pharyngeal constrictors versus the intrinsic/extrinsic muscles of the tongue?

Pharyngeal constrictors (superior, middle, inferior) are innervated by the vagus nerve (CN X). Tongue muscles (hyoglossus, styloglossus, genioglossus) are innervated by the hypoglossal nerve (CN XII).

What three skeletal landmarks provide attachments for the sternocleidomastoid (SCM) muscle?

The manubrium of the sternum (sternal head), the clavicle (clavicular head), and the mastoid process of the temporal bone.

What are the actions of the abdominal wall obliques when contracted bilaterally versus unilaterally?

Bilateral contraction increases intra-abdominal pressure and promotes spinal posture/flexion. Unilateral contraction laterally flexes the vertebral column toward the active side.

Which four muscles comprise the rotator cuff ('SITS'), and which posterior scapular muscle is explicitly NOT part of the cuff?

The rotator cuff consists of the supraspinatus, infraspinatus, teres minor, and subscapularis. The teres major is NOT a rotator cuff muscle.

What are the three muscle columns of the erector spinae group from lateral to medial, and what innervates them?

From lateral to medial: Iliocostalis, Longissimus, and Spinalis (mnemonic: 'I Love Spaghetti'). They are innervated segmentally by the dorsal rami of spinal nerves.

What three muscle layers form the pelvic diaphragm of the pelvic floor?

The coccygeus, levator ani, and deep transverse perineal muscles.

Why does an infant have approximately $270$ bones at birth compared to the standard $206$ in adults?

Infants have unfused epiphyses and separate bony elements (such as cranial bones, pelvic bones, and sacral/coccygeal vertebrae) that fuse together into single bones throughout childhood and adolescence.

How is the human skeleton divided into axial and appendicular divisions, and how many bones are in each axial subgroup?

The axial skeleton forms the central axis and consists of $80$ bones: Skull ($22$), Hyoid ($1$), Vertebral column ($26$ in adult), and Thoracic cage ($25$). The appendicular skeleton consists of the limbs and the pectoral and pelvic girdles that attach them.

Which eight bones comprise the cranial cavity of the skull?

Unpaired: ethmoid, frontal, occipital, and sphenoid. Paired: parietal and temporal bones.

What are the three cranial fossae of the skull base, and what part of the brain does each accommodate?

The anterior cranial fossa (A) houses the frontal lobes; the middle cranial fossa (M) houses the temporal lobes; and the posterior cranial fossa (P) houses the cerebellum.

What bones form the anterior two-thirds and posterior one-third of the hard palate?

The anterior two-thirds is formed by the palatine processes of the paired maxillae, and the posterior one-third is formed by the horizontal plates of the paired palatine bones.

What critical endocrine structure is housed within the sphenoid bone, and in what depression does it sit?

The pituitary gland is housed within the sella turcica of the sphenoid bone.

What are the primary versus secondary curvatures of the human vertebral column, and when do the secondary curves develop?

Primary curvatures (thoracic and sacral) are present at birth in the C-shaped fetal spine. Secondary curvatures develop postnatally: the cervical curve develops as the baby learns to hold its head upright, and the lumbar curve forms around age $3$ when standing and walking begin.

Which three abnormal spinal curvatures are illustrated in this image?

(a) Scoliosis (abnormal lateral curvature); (b) Kyphosis (exaggerated posterior thoracic curvature, often called hunchback); (c) Lordosis (exaggerated anterior lumbar curvature, swayback).

What anatomical defect occurs during an intervertebral disc herniation?

The soft, gel-like central nucleus pulposus ruptures through the outer fibrocartilaginous ring (annulus fibrosus) and compresses adjacent spinal nerves.

What are the three distinct regions of the sternum indicated by numbers 1, 2, and 3?

(1) Manubrium; (2) Body (gladiolus); (3) Xiphoid process.

How are ribs classified, and which ribs belong to each group?

Ribs 1–7 are true ribs (attach directly to the sternum via independent costal cartilages); ribs 8–10 are false ribs (attach indirectly via the costal cartilage of rib 7); ribs 11–12 are floating ribs (lack any anterior attachment).

What structural features are found on a typical rib (ribs 2–10)?

A typical rib has a head with two articular demi-facets (for adjacent vertebral bodies), a neck, a tubercle with a facet (for the transverse process), a costal angle, a shaft with an inferior costal groove (protecting intercostal nerves/vessels), and a distal cup for costal cartilage.

What inverse biomechanical principle is illustrated across the joint spectrum shown in this diagram?

The trade-off between mobility and stability: joints with the greatest mobility (e.g., glenohumeral joint) have the least stability and highest dislocation risk, whereas joints with high stability (e.g., cranial sutures) are immobile.

What are the structural versus functional classifications of joints?

Structural: Fibrous (dense connective tissue), Cartilaginous (cartilage), and Synovial (joint cavity with fluid). Functional: Synarthrosis (immobile), Amphiarthrosis (slightly mobile), and Diarthrosis (freely mobile).

What is the structural difference between a synchondrosis and a symphysis joint?

A synchondrosis connects bones via hyaline cartilage (e.g., epiphyseal plates, costal cartilages), whereas a symphysis connects bones via fibrocartilage (e.g., intervertebral discs, pubic symphysis).

What anatomical structure differentiates a tendon sheath from a simple bursa?

A bursa is a flattened synovial fluid sac preventing friction between bone and soft tissues, whereas a tendon sheath is an elongated tubular synovial sac wrapping around a tendon, typically where it passes under fibrous retinacula.

What anatomical structures increase the depth and stability of the shoulder and hip joints?

A fibrocartilaginous labrum (the glenoid labrum in the shoulder and acetabular labrum in the hip).

Which muscle is the true prime mover of elbow flexion, and what is the primary action of the biceps brachii?

The brachialis muscle is the prime mover of elbow flexion. The biceps brachii is the primary supinator of the forearm (while also assisting in flexion).

What two deep anterior compartment muscles of the arm are shown, and what is their common innervation?

The coracobrachialis (attaching to the coracoid process) and the brachialis (attaching to the humeral shaft and coronoid process of the ulna). Both are innervated by the musculocutaneous nerve.

What nerve innervates all muscles in the posterior compartments of the arm and forearm?

The radial nerve of the brachial plexus.

What are the two muscle exceptions in the anterior forearm flexor compartment that are innervated by the ulnar nerve?

The flexor carpi ulnaris and the medial half of the flexor digitorum profundus (the rest of the anterior forearm flexors are innervated by the median nerve).

Which three major lower-limb nerves derived from the lumbar plexus are highlighted here?

The femoral nerve, the obturator nerve, and the sciatic nerve (with the lumbar plexus originating from spinal levels L2 to L5).

What are the three muscular compartments of the thigh, their primary actions, and their primary nerve supplies?

Anterior compartment: extends the knee/flexes hip, innervated by the femoral nerve. Medial compartment: adducts the thigh, innervated by the obturator nerve. Posterior compartment (hamstrings): extends the hip/flexes the knee, innervated by the sciatic nerve.

What are the three muscular compartments of the lower leg and their corresponding nerves?

Anterior compartment: dorsiflexes ankle and extends toes, innervated by the deep fibular nerve. Lateral compartment: everts foot and plantarflexes ankle, innervated by the superficial fibular nerve. Posterior compartment: plantarflexes foot and flexes toes, innervated by the tibial nerve.