Free Anatomy: Skeletal & Muscular System Flashcards

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What are the 5 classifications of bones? Give an example of each.

Long (femur, humerus), Short (carpals, tarsals), Flat (sternum, scapula, cranial bones), Irregular (vertebrae, sphenoid), Sesamoid (patella)

What is the periosteum?

Dense irregular connective tissue membrane covering the outer surface of bone (except at joint surfaces). Contains osteoblasts, osteoclasts, nerve fibers, and blood vessels. Anchors tendons and ligaments via Sharpey's fibers.

Describe compact (cortical) bone vs. spongy (cancellous/trabecular) bone.

Compact: dense, solid, forms diaphysis; organized into osteons (Haversian systems). Spongy: porous, lattice of trabeculae; found in epiphyses and interior of flat bones; contains red marrow for hematopoiesis.

What is an osteon (Haversian system)?

Structural unit of compact bone. Consists of concentric lamellae surrounding a central (Haversian) canal containing blood vessels and nerves. Osteocytes sit in lacunae connected by canaliculi. Perforating (Volkmann's) canals connect adjacent osteons.

Define: epiphysis, diaphysis, metaphysis, and medullary cavity.

Epiphysis: expanded ends of long bone (articular cartilage). Diaphysis: shaft of long bone (compact bone). Metaphysis: region between; contains epiphyseal plate/line. Medullary cavity: hollow center of diaphysis; contains yellow marrow in adults.

Name the 8 cranial bones.

Frontal (1), Parietal (2), Temporal (2), Occipital (1), Sphenoid (1), Ethmoid (1). Total = 8 bones forming the cranial vault and floor.

Name the major facial bones.

Maxilla (2), Mandible (1 — only movable skull bone), Zygomatic (2), Nasal (2), Lacrimal (2), Palatine (2), Inferior nasal conchae (2), Vomer (1). Total = 14.

Describe the regions and curvatures of the vertebral column.

7 Cervical (lordotic curve), 12 Thoracic (kyphotic curve), 5 Lumbar (lordotic curve), Sacrum (5 fused — kyphotic), Coccyx (3-5 fused). Total ~33 vertebrae, 26 bones in adult. Abnormal curves: scoliosis (lateral), excessive kyphosis, excessive lordosis.

What are the unique features of C1 (atlas) and C2 (axis)?

Atlas (C1): ring-shaped, no body or spinous process; supports the skull; allows 'yes' nodding. Axis (C2): has the dens (odontoid process) projecting superiorly; atlas pivots around it for 'no' head rotation.

How are ribs classified?

True ribs (1-7): attach directly to sternum via costal cartilage. False ribs (8-10): attach to sternum indirectly through rib 7's cartilage. Floating ribs (11-12): no sternal attachment at all. Total = 12 pairs (24 ribs).

What bones make up the pectoral (shoulder) girdle?

Clavicle (collarbone) and Scapula (shoulder blade) on each side. The pectoral girdle is light and allows great mobility but sacrifices stability. It attaches to the axial skeleton only at the sternoclavicular joint.

Name the bones of the upper extremity in order (proximal to distal).

Humerus (arm) → Radius (lateral forearm, thumb side) and Ulna (medial forearm, pinky side) → 8 Carpals (wrist) → 5 Metacarpals (palm) → 14 Phalanges (fingers: 2 in thumb, 3 in each finger).

What is the difference between the radius and the ulna?

Radius: lateral (thumb side), rotates over ulna during pronation, articulates with carpals at wrist. Ulna: medial (pinky side), forms olecranon process (elbow point), main forearm bone at elbow joint (trochlear notch articulates with humerus trochlea).

What bones make up the pelvic (hip) girdle?

Two os coxae (hip bones), each formed by fusion of 3 bones: ilium (superior, largest), ischium (posterior-inferior, sit bones), pubis (anterior). They join anteriorly at pubic symphysis and posteriorly at sacroiliac joints.

Name the bones of the lower extremity in order.

Femur (thigh, longest bone) → Patella (sesamoid, in quadriceps tendon) → Tibia (medial, weight-bearing shin bone) and Fibula (lateral, non-weight-bearing) → 7 Tarsals (ankle, including calcaneus and talus) → 5 Metatarsals (foot) → 14 Phalanges (toes).

Define synarthrosis, amphiarthrosis, and diarthrosis.

Synarthrosis: immovable joint (e.g., skull sutures, gomphoses of teeth). Amphiarthrosis: slightly movable joint (e.g., pubic symphysis, intervertebral discs). Diarthrosis: freely movable joint; all are synovial joints (e.g., knee, shoulder, hip).

Name the 6 types of synovial joints with examples.

Hinge (elbow, knee), Ball-and-socket (shoulder, hip), Pivot (atlantoaxial, proximal radioulnar), Saddle (thumb CMC), Condyloid/ellipsoidal (wrist, MCP joints), Gliding/plane (intercarpal, intertarsal, acromioclavicular).

What structures make up a synovial joint?

Articular cartilage (hyaline), joint (synovial) cavity, articular (joint) capsule (fibrous capsule + synovial membrane), synovial fluid (lubricant, nourishes cartilage). May also have menisci, bursae, fat pads, ligaments, and tendons.

What are the 3 types of muscle tissue?

Skeletal: voluntary, striated, multinucleated, attached to bones. Cardiac: involuntary, striated, branched, intercalated discs, autorhythmic. Smooth: involuntary, non-striated, spindle-shaped, single nucleus; found in walls of hollow organs and blood vessels.

Describe the sliding filament theory of muscle contraction.

Thick (myosin) and thin (actin) filaments slide past each other, shortening the sarcomere. Myosin heads bind to actin (cross-bridge), pivot (power stroke) pulling actin toward the M-line, then release and re-cock. Requires ATP and Ca²⁺. The H-zone and I-band shorten; A-band stays the same length.

What is the neuromuscular junction (NMJ)?

The synapse between a motor neuron's axon terminal and a skeletal muscle fiber's motor end plate. The motor neuron releases acetylcholine (ACh) into the synaptic cleft; ACh binds nicotinic receptors on the sarcolemma, causing depolarization and initiating muscle contraction.

List the steps of skeletal muscle contraction (excitation-contraction coupling).

1) ACh released at NMJ → 2) Action potential on sarcolemma → 3) AP travels down T-tubules → 4) Sarcoplasmic reticulum (SR) releases Ca²⁺ → 5) Ca²⁺ binds troponin, moving tropomyosin off actin binding sites → 6) Myosin cross-bridges form and cycle (power stroke) → 7) Ca²⁺ pumped back into SR (relaxation) → 8) ATP needed for detachment and re-cocking.

What is the role of calcium and troponin in muscle contraction?

Ca²⁺ released from the SR binds to troponin (on the thin filament). This causes a conformational change that shifts tropomyosin away from myosin-binding sites on actin, allowing cross-bridge formation. Without Ca²⁺, tropomyosin blocks the binding sites and the muscle remains relaxed.

What is the role of ATP in muscle contraction?

ATP serves 3 roles: 1) Energizes the myosin head (cocking it for the power stroke), 2) Detaches myosin from actin after the power stroke, 3) Powers the Ca²⁺ pump (SERCA) to return Ca²⁺ to the SR. Without ATP, cross-bridges cannot detach (rigor mortis).

Tendons vs. Ligaments: structure and function.

Tendons: dense regular connective tissue connecting muscle to bone; transmit force of contraction. Ligaments: dense regular connective tissue connecting bone to bone; stabilize joints and prevent excessive movement. Both are composed primarily of collagen fibers.

Deltoid muscle: origin, insertion, and action.

Origin: clavicle (anterior fibers), acromion (middle fibers), spine of scapula (posterior fibers). Insertion: deltoid tuberosity of humerus. Action: Abduction of the arm (middle fibers primarily); anterior fibers flex and medially rotate; posterior fibers extend and laterally rotate the arm.

Biceps brachii: origin, insertion, and action.

Origin: Long head — supraglenoid tubercle; Short head — coracoid process of scapula. Insertion: radial tuberosity and bicipital aponeurosis. Action: Flexion of the elbow, supination of the forearm, weak shoulder flexion.

Triceps brachii: origin, insertion, and action.

Origin: Long head — infraglenoid tubercle of scapula; Lateral head — posterior humerus (above radial groove); Medial head — posterior humerus (below radial groove). Insertion: olecranon process of ulna. Action: Extension of the elbow. Primary elbow extensor (anconeus also assists).

Quadriceps femoris: name the 4 muscles and their shared action.

1) Rectus femoris (only one crossing the hip — also flexes hip), 2) Vastus lateralis, 3) Vastus medialis, 4) Vastus intermedius. All insert via the patellar tendon/ligament onto the tibial tuberosity. Shared action: extension of the knee.

Hamstrings: name the 3 muscles and their shared action.

1) Biceps femoris (long & short heads), 2) Semimembranosus, 3) Semitendinosus. Origin: ischial tuberosity (except biceps femoris short head from linea aspera). Action: Flexion of the knee and extension of the hip. Antagonists to quadriceps.

Gastrocnemius: origin, insertion, and action.

Origin: medial and lateral condyles of the femur (two heads). Insertion: calcaneus via the calcaneal (Achilles) tendon. Action: plantarflexion of the foot and weak knee flexion. The soleus (deep to it) also plantarflexes but does not cross the knee.

Pectoralis major: origin, insertion, and action.

Origin: medial clavicle, sternum, and upper costal cartilages. Insertion: lateral lip of intertubercular (bicipital) groove of humerus. Action: flexion, adduction, and medial rotation of the arm. Major chest muscle.

Latissimus dorsi: origin, insertion, and action.

Origin: spinous processes of T7-L5, thoracolumbar fascia, iliac crest, lower 3-4 ribs. Insertion: intertubercular groove of humerus (floor). Action: extension, adduction, and medial rotation of the arm. Key muscle in pull-ups and swimming.

Trapezius: origin, insertion, and action.

Origin: occipital bone, nuchal ligament, spinous processes C7-T12. Insertion: clavicle, acromion, and spine of scapula. Action: upper fibers elevate scapula (shrug), middle fibers retract scapula, lower fibers depress scapula. Also rotates scapula upward.

Rectus abdominis: origin, insertion, and action.

Origin: pubic crest and pubic symphysis. Insertion: xiphoid process and costal cartilages of ribs 5-7. Action: flexion of the vertebral column (trunk), compression of the abdomen. Divided by tendinous intersections (the 'six-pack').

Diaphragm: structure and function.

Primary muscle of inspiration. Dome-shaped skeletal muscle separating the thoracic and abdominal cavities. Origin: xiphoid process, lower ribs, lumbar vertebrae. Insertion: central tendon. Contraction flattens the dome, increasing thoracic volume and decreasing intrathoracic pressure → air flows in. Innervated by the phrenic nerve (C3-C5).

Gluteus maximus: origin, insertion, and action.

Origin: ilium (posterior gluteal line), sacrum, coccyx, sacrotuberous ligament. Insertion: iliotibial (IT) band and gluteal tuberosity of femur. Action: powerful extension and lateral rotation of the hip. Most important for climbing stairs, rising from seated position, and running.

What is an agonist, antagonist, synergist, and fixator?

Agonist (prime mover): muscle primarily responsible for a movement. Antagonist: opposes the agonist (e.g., triceps opposes biceps). Synergist: assists the agonist in performing the movement. Fixator: stabilizes the origin of the agonist so it can act efficiently (e.g., rotator cuff stabilizing the shoulder).

What is the motor unit?

A motor unit = one motor neuron + all the muscle fibers it innervates. Small motor units (e.g., eye muscles, ~10 fibers) allow fine control. Large motor units (e.g., quadriceps, ~1000 fibers) generate powerful but coarse movements. Recruitment of additional motor units increases force.

Differentiate between isotonic and isometric contractions.

Isotonic: muscle changes length while tension remains relatively constant. Includes concentric (muscle shortens, e.g., lifting a curl) and eccentric (muscle lengthens under load, e.g., lowering a curl). Isometric: muscle generates force but does not change length (e.g., holding a plank, pushing against a wall).

What are the types of bone fractures?

Transverse: perpendicular to bone axis. Oblique: diagonal. Spiral: twisting injury. Comminuted: bone shatters into 3+ fragments. Greenstick: incomplete fracture in children (bone bends). Compound (open): bone pierces skin. Simple (closed): no skin break. Compression: vertebrae crushed (osteoporosis). Stress: hairline fracture from repetitive force.

What is the difference between a sprain and a strain?

Sprain: stretching or tearing of a LIGAMENT (connects bone to bone). Common at ankle, knee, wrist. Strain: stretching or tearing of a MUSCLE or TENDON (connects muscle to bone). Common in hamstrings and lower back. Both graded I (mild), II (partial tear), III (complete rupture).

What is an ACL tear? Clinical significance?

The anterior cruciate ligament (ACL) prevents anterior translation of the tibia on the femur and resists internal rotation. Commonly torn during sudden pivoting, deceleration, or landing (non-contact injury common in sports). Positive anterior drawer test and Lachman test. Often requires surgical reconstruction (ACL reconstruction using graft).

What are the menisci of the knee?

Medial and lateral menisci are C-shaped fibrocartilage discs between femoral condyles and tibial plateau. Functions: shock absorption, load distribution, joint stability, lubrication. Medial meniscus is more commonly torn (attached to MCL, less mobile). Tears may cause locking, clicking, swelling. The 'unhappy triad' = ACL + MCL + medial meniscus injury.

What are osteoblasts, osteoclasts, and osteocytes?

Osteoblasts: bone-building cells; secrete osteoid (organic matrix) that mineralizes. Osteoclasts: large multinucleated cells that resorb (break down) bone using acid and enzymes; derived from monocytes. Osteocytes: mature bone cells trapped in lacunae; maintain bone matrix and sense mechanical stress. Bone remodeling requires balance between osteoblast and osteoclast activity.

What is the epiphyseal (growth) plate?

Hyaline cartilage plate at the metaphysis of long bones in children/adolescents. Site of longitudinal bone growth (endochondral ossification). Has 5 zones: resting, proliferation, hypertrophy, calcification, ossification. Closes at skeletal maturity (~18-25 years) and becomes the epiphyseal line. Fractures through growth plate (Salter-Harris) can affect growth in children.

Describe intramembranous vs. endochondral ossification.

Intramembranous: bone forms directly from mesenchymal tissue (no cartilage model). Produces flat bones of the skull and clavicle. Endochondral: bone replaces a hyaline cartilage model. Produces most bones of the skeleton. Both involve osteoblast activity and result in woven bone that is remodeled into lamellar bone.

What are the rotator cuff muscles? (SITS)

Supraspinatus: initiates abduction (most commonly torn). Infraspinatus: lateral rotation. Teres minor: lateral rotation. Subscapularis: medial rotation. They stabilize the glenohumeral (shoulder) joint by holding the humeral head in the glenoid fossa. Mnemonic: SITS.

What is the difference between fast-twitch and slow-twitch muscle fibers?

Slow-twitch (Type I): fatigue-resistant, aerobic metabolism, lots of mitochondria and myoglobin (red), used for endurance (postural muscles, marathon). Fast-twitch (Type IIa): moderately fatigue-resistant, aerobic and anaerobic. Fast-twitch (Type IIx/IIb): fatigue quickly, anaerobic/glycolytic, powerful and fast, few mitochondria (white), used for sprinting and heavy lifting.

What is Wolff's Law?

Bone remodels and strengthens in response to mechanical stress placed upon it. Increased stress (weight-bearing exercise) stimulates osteoblast activity, increasing bone density. Decreased stress (immobilization, sedentary lifestyle, microgravity) leads to bone resorption by osteoclasts and decreased density. Clinically important for osteoporosis prevention and rehabilitation.

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