Comprehensive Study Guide: Cartilage, Bone, Articulations, and Muscle Tissue

Chapter 6: Cartilage and Bone

  • Types of Tissues Found in Bone

    • Osseous Tissue (Bone Tissue): Primary connective tissue component consisting of a calcified extracellular matrix and specialized cells.
    • Connective Tissue Proper: Includes dense irregular connective tissue forming the outer fibrous periosteum, and collagenous fibrous networks.
    • Cartilage Tissue: Hyaline cartilage present at articular surfaces and growth plates (epiphyseal plates).
    • Adipose Tissue: Yellow bone marrow functioning as a energy reserve inside the medullary cavity.
    • Hemopoietic Tissue: Red bone marrow producing blood cellular elements.
    • Nervous Tissue: Innervates bone matrix and periosteum to detect pain and mechanical stress.
    • Vascular/Epithelial/Smooth Muscle Tissue: Endothelium lining blood vessels and smooth muscle within blood vessel walls running through canals.

  • Functions of Bone and Bone Connective Tissue

    • Support: Structural framework for the body, supporting soft tissues and providing attachment points for tendons.
    • Protection: Shields internal vital organs (e.g., cranium protects brain, vertebrae protect spinal cord, rib cage protects heart and lungs).
    • Movement / Leverage: Skeletal muscles attach to bones via tendons; contraction pulls on bones to produce movement acting as levers.
    • Mineral Storage and Homeostasis: Stores critical minerals, mainly calcium (Ca2+Ca^{2+}) and phosphate (PO43−PO_4^{3-}), releasing them into the blood as needed to maintain ionic balance.
    • Hemopoiesis (Blood Cell Production): Red bone marrow produces red blood cells, white blood cells, and platelets.
    • Energy Storage: Yellow bone marrow consists primarily of adipocytes storing triglycerides as an energy reserve.

  • Bone Classification by Shape

    • Long Bones: Greater length than width, consisting of a shaft (diaphysis) and variable ends (epiphyses), slightly curved for strength. Examples: Femur, tibia, fibula, humerus, radius, ulna, phalanges.
    • Short Bones: Cube-like in shape, equal in length and width. Examples: Carpals (wrist bones) and tarsals (ankle bones).
    • Flat Bones: Thin, parallel plates of compact bone enclosing a layer of spongy bone; provide extensive protection and broad areas for muscle attachment. Examples: Cranial bones (frontal, parietal), sternum, ribs, scapulae.
    • Irregular Bones: Complex shapes that cannot be grouped into previous categories. Examples: Vertebrae, hip bones (os coxae), certain facial bones (e.g., sphenoid, ethmoid).
    • Sesamoid Bones: Specialized bones developed within tendons where considerable pressure/tension exists. Example: Patella (knee cap).

  • General Structure of a Long Bone

    • Diaphysis: The elongated tubular shaft forming the main axis of the long bone.
    • Epiphysis: The expanded distal and proximal ends of the bone.
    • Metaphysis: The region between the diaphysis and epiphysis containing the epiphyseal plate (growth plate of hyaline cartilage) in growing bones, which later becomes the epiphyseal line.
    • Articular Cartilage: A thin layer of hyaline cartilage covering the epiphysis at joint surfaces to reduce friction and absorb shock.
    • Medullary Cavity: Hollow space within the diaphysis containing yellow bone marrow (in adults) and blood vessels.
    • Periosteum: Tough outer sheath surrounding the bone surface where not covered by articular cartilage.
      • Outer Fibrous Layer: Composed of dense irregular connective tissue providing attachment for tendons and ligaments.
      • Inner Osteogenic Layer: Contains osteoprogenitor cells, osteoblasts, and osteoclasts responsible for bone growth in width and repair.
      • Perforating (Sharpey's) Fibers: Thick collagen bundles attaching the periosteum to underlying bone matrix.
    • Endosteum: Thin delicate membrane lining internal bone surfaces, including the medullary cavity, trabeculae of spongy bone, and central canals. Contains osteoprogenitor cells, osteoblasts, and osteoclasts.

  • Evolution and Types of Bone Cells

    • Osteoprogenitor (Osteogenic) Cells: Stem cells derived from mesenchyme; located in the periosteum, endosteum, and central canals. They undergo mitosis to produce osteoblasts.
    • Osteoblasts: Bone-forming cells synthesized from osteoprogenitor cells. They secrete osteoid (unmineralized organic bone matrix containing collagen) and initiate calcification/mineralization.
    • Osteocytes: Mature bone cells trapped within matrix cavities called lacunae. Formed when osteoblasts become embedded in their own matrix. They maintain daily bone cellular activities, monitor matrix strain, and communicate via cellular processes located in canaliculi.
    • Osteoclasts: Large, multinucleated bone-resorbing cells derived from the fusion of bone marrow monocytes/macrophages. Located in resorption lacunae (Howship's lacunae). Release lysosomal enzymes and acids (HCl) to dissolve matrix and release calcium into blood.

  • Microscopic Anatomy of Compact Bone

    • Structural Unit: Osteon (Haversian System), elongated cylinders parallel to bone's long axis.
    • Central (Haversian) Canal: Longitudinal channel running through center of osteon containing blood vessels and nerves.
    • Perforating (Volkmann's) Canals: Transverse or oblique canals running perpendicular to central canals, carrying neurovascular supply from periosteum/endosteum into osteons.
    • Concentric Lamellae: Rings of hard, calcified extracellular matrix surrounding the central canal.
    • Interstitial Lamellae: Incomplete rings between osteons representing remnants of old partially resorbed osteons.
    • Circumferential Lamellae: Rings extending around the entire outer (outer circumferential) and inner (inner circumferential) circumferences of the diaphysis.
    • Lacunae: Small spaces between lamellae housing individual osteocytes.
    • Canaliculi: Tiny, radiating microscopic channels connecting lacunae with each other and central canals, housing osteocyte cytoplasmic processes and gap junctions for nutrient/waste exchange.

  • Microscopic Anatomy of Spongy (Cancellous/Trabecular) Bone

    • Structure: Composed of an irregular latticework of thin bone columns called trabeculae.
    • Absence of True Osteons: Lacks central canals and complete osteons; osteocytes are housed in lacunae within parallel lamellae of trabeculae.
    • Nutrients: Obtained via diffusion through canaliculi directly from surrounding red bone marrow spaces.
    • Alignment: Trabeculae align precisely along lines of stress to distribute mechanical force.

  • Comparison: Spongy Bone vs. Compact Bone

    • Structure: Compact bone is dense, solid, and heavily organized into osteons; Spongy bone is porous, lightweight, organized into mesh-like trabeculae.
    • Location: Compact bone forms external layer of all bones and diaphysis of long bones; Spongy bone forms interior of epiphyses, interior of flat/short/irregular bones, and border of medullary cavity.
    • Function: Compact bone provides protection, support, and resistance to linear loads; Spongy bone reduces total skeleton weight, resists multi-directional stress, and houses red bone marrow.

  • Steps of Intramembranous Ossification

    1. Development of Ossification Center: Mesenchymal cells aggregate, differentiate into osteoprogenitor cells, and then into osteoblasts, which secrete osteoid.
    2. Calcification: Osteoblasts become trapped in matrix and transform into osteocytes; calcium and other mineral salts deposit, hardening the matrix.
    3. Formation of Trabeculae: Matrix develops into trabeculae that fuse to form spongy bone around blood vessels.
    4. Development of Periosteum: Mesenchyme condenses on the outer surface to form periosteum; compact bone replaces surface layers of spongy bone, leaving spongy bone sandwiched in the middle.

  • Steps of Endochondral Ossification

    1. Development of Cartilage Model: Mesenchymal cells assemble into the shape of the future bone and differentiate into chondroblasts, forming a hyaline cartilage model surrounded by perichondrium.
    2. Growth of Cartilage Model: Chondrocytes hypertrophy, burst, and alter matrix pH, triggering calcification of surrounding cartilage matrix, causing chondrocytes to die and leave empty cavities.
    3. Development of Primary Ossification Center: A nutrient artery penetrates perichondrium; perichondrial cells differentiate into osteoblasts (forming periosteum and periosteal collar). Blood vessels grow into disintegrating cartilage model (periosteal bud), bringing osteoblasts and osteoclasts to replace calcified cartilage with spongy bone in diaphysis center.
    4. Development of Medullary Cavity: Osteoclasts break down central spongy bone to form hollow medullary cavity, extending towards epiphyses.
    5. Development of Secondary Ossification Centers: Epiphyseal arteries enter epiphyses, usually around birth, creating secondary ossification centers in epiphyses (spongy bone remains, no central cavity created).
    6. Formation of Articular Cartilage and Epiphyseal Plate: Hyaline cartilage remains covering epiphysis ends (articular cartilage) and between diaphysis/epiphysis (epiphyseal plate).

  • Interstitial vs. Appositional Growth

    • Interstitial Growth: Growth in length occurs at the epiphyseal plate via chondrocyte proliferation within cartilage model followed by replacement with bone.
    • Appositional Growth: Growth in width/thickness occurs at the periosteal surface, where osteoblasts in inner periosteum secrete new matrix while osteoclasts along endosteum resorb old bone to enlarge medullary cavity.

  • Hormones Involved in Bone Remodeling

    • Parathyroid Hormone (PTH): Secreted by parathyroid glands in response to hypocalcemia (low blood Ca2+Ca^{2+}). Stimulates osteoclasts to resorb bone, increases renal calcium reabsorption, and promotes active Vitamin D production to raise blood calcium levels.
    • Calcitonin: Secreted by parafollicular (C cells) of thyroid gland in response to hypercalcemia (high blood Ca2+Ca^{2+}). Inhibits osteoclasts and promotes calcium deposition into bone matrix.
    • Growth Hormone (GH) / Somatotropin: Secreted by anterior pituitary gland; stimulates liver to produce IGFs (insulin-like growth factors), promoting chondrocyte proliferation at epiphyseal plate.
    • Thyroid Hormone (T3T_3 & T4T_4): Secreted by thyroid gland; promotes metabolic activity of osteoblasts.
    • Sex Hormones (Estrogen and Testosterone): Secreted during puberty; cause dramatic surge in osteoblast activity, rapid growth, and eventual closure/ossification of epiphyseal plate.

  • Vitamins Essential for Bone Remodeling

    • Vitamin A: Stimulates activity of osteoblasts and proper bone growth balance.
    • Vitamin C (Ascorbic Acid): Required for collagen synthesis (cross-linking matrix proteins); deficiency leads to scurvy and fragile bones.
    • Vitamin D (Calcitriol): Enhances absorption of dietary calcium and phosphate from gastrointestinal tract into blood.
    • Vitamin K and B12B_{12}: Necessary for synthesis of bone proteins such as osteocalcin.

  • Exercise and Bone Remodeling

    • Mechanical stress (weight-bearing exercise, resistance training) generates electrical currents in bone tissue and triggers osteocytes to stimulate osteoblasts.
    • Results in increased deposition of mineral salts and collagen fibers, thickening bones and strengthening structural density. Unused bones undergo demineralization and atrophy.

  • Types of Bone Fractures

    • Avulsion: Fragment of bone pulled off by tendon or ligament traction.
    • Open (Compound): Broken end of bone pierces through skin.
    • Closed (Simple): Bone is broken cleanly, skin remains intact.
    • Colles: Fracture of distal radius where distal fragment is displaced posteriorly.
    • Stress: Thin microscopic cracks resulting from repetitive overuse/impact without structural trauma.
    • Spiral: Twisted fracture line resulting from violent torsional forces along shaft.
    • Oblique: Fracture line diagonal across bone long axis.
    • Transverse: Fracture line at right angles (90∘90^\circ) to bone long axis.
    • Linear: Fracture parallel to long axis of bone.
    • Greenstick: Partial break where one side breaks while other side bends (common in children).
    • Epiphyseal: Separation or break across epiphyseal plate, potentially impacting future length growth.
    • Displaced: Anatomical alignment of bone fragments is lost.
    • Pathologic: Fracture occurring in bone weakened by underlying disease (e.g., bone cancer, osteoporosis).

  • Steps in Fracture Repair

    1. Fracture Hematoma Formation: Torn blood vessels form a localized blood clot (hematoma) within 6-8 hours post-injury; inflammation occurs and dead cells removed.
    2. Fibrocartilaginous (Soft) Callus Formation: Capillaries grow into hematoma; fibroblasts produce collagen fibers and chondroblasts form fibrocartilage bridging broken ends (takes ~3 weeks).
    3. Bony (Hard) Callus Formation: Osteoprogenitor cells differentiate into osteoblasts, replacing fibrocartilage with spongy bone to form hard callus (lasts 3-4 months).
    4. Bone Remodeling: Osteoclasts resorb dead bone fragments and excess callus; compact bone replaces spongy bone on outer margins, restoring original shape and strength.

  • Bone Markings and Meanings

    • Articulating Surfaces:
      • Head: Prominent, rounded articular end.
      • Condyle: Large, smooth, rounded articular process.
      • Facet: Small, flat, smooth articular surface.
      • Trochlea: Smooth, grooved pulley-like articular process.
    • Depressions and Openings:
      • Fossa: Shallow, flattened basin or depression.
      • Sulcus (Groove): Narrow elongated ditch or channel.
      • Foramen: Rounded hole or opening through bone for blood vessels/nerves.
      • Canal / Meatus: Passageway or tube-like tunnel through bone.
      • Fissure: Narrow slit-like crack or opening.
      • Sinus: Cavity or hollow air-filled space within bone.
    • Non-articulating Projections and Processes:
      • Crest: Prominent, narrow ridge of bone.
      • Epicondyle: Raised projection adjacent to or above a condyle.
      • Process: Any marked bony outgrowth or extension.
      • Spine: Sharp, slender, pointed projection.
      • Tubercle: Small rounded projection.
      • Tuberosity: Large, rough, rounded elevation.
      • Trochanter: Massive, blunt, irregular process (found only on femur).

  • Osteopenia and Osteoporosis

    • Osteopenia: Inadequate ossification or lower-than-normal bone mineral density resulting from age-related decrease in osteoblast activity relative to osteoclast activity (typical start around age 30-40).
    • Osteoporosis: Severe reduction in bone mass causing bone density to fall below critical threshold, leading to structural microarchitectural deterioration, highly porous bones, and susceptibility to pathological fractures.

Chapter 9: Articulations

  • Definition of an Articulation (Joint)

    • A junction or point of contact between two or more bones, between cartilage and bone, or between teeth and bone.

  • Structural Classification of Joints (by Connective Tissue)

    • Fibrous Joints: Articulating bones held together tightly by dense fibrous connective tissue; no joint cavity.
    • Cartilaginous Joints: Articulating bones connected by cartilage (hyaline or fibrocartilage); no joint cavity.
    • Synovial Joints: Articulating bone surfaces enclosed within a fluid-filled synovial cavity surrounded by an articular capsule.

  • Functional Classification of Joints (by Movement Permitted)

    • Synarthrosis: Immovable joint.
    • Amphiarthrosis: Slightly movable joint.
    • Diarthrosis: Freely movable joint (all synovial joints).

  • Fibrous Joints: Types, Movement, and Locations

    • Gomphoses: Peg-in-socket joint where tooth root is anchored into alveolus by periodontal ligament; Functional class: Synarthrosis (immovable); Location: Teeth roots in maxilla and mandible.
    • Sutures: Interlocking margins of cranial bones bound by short dense fibrous tissue; Functional class: Synarthrosis (immovable); Location: Skull sutures (e.g., Coronal, Sagittal, Lambdoid sutures).
    • Syndesmoses: Bones connected by longer sheets or cords of dense fibrous connective tissue (interosseous membrane/ligament); Functional class: Amphiarthrosis (slightly movable); Location: Distal tibiofibular joint, interosseous membranes between radius/ulna and tibia/fibula.

  • Cartilaginous Joints: Types, Movement, and Locations

    • Synchondroses: Bones joined by hyaline cartilage; Functional class: Synarthrosis (immovable); Location: Epiphyseal growth plates in long bones, joint between First Rib and Sternum (manubriosternal/first sternocostal).
    • Symphyses: Bones joined by a broad, flat pad of fibrocartilage; Functional class: Amphiarthrosis (slightly movable); Location: Pubic symphysis, intervertebral discs.

  • Anatomy of Synovial Joints

    • Articular Capsule: Two-layered sleeve enclosing joint cavity.
      • Fibrous Layer: Outer dense irregular connective tissue layer continuous with periosteum; provides mechanical strength.
      • Synovial Membrane: Inner delicate layer of loose vascular connective tissue lining capsule except over articular cartilage; secretes synovial fluid.
    • Joint (Synovial) Cavity: Physical space separating articulating bones containing lubricating fluid.
    • Articular Cartilage: Hyaline cartilage covering epiphysis ends to decrease friction.
    • Synovial Fluid: Viscous, egg-white-like fluid containing hyaluronic acid and interstitial fluid.
    • Accessory Ligaments: Extracapsular (outside capsule) and Intracapsular (inside capsule) dense connective tissue bands strengthening joint.
    • Menisci / Articular Discs: Pads of fibrocartilage extending from capsule to improve fit and stability.
    • Sensory Nerves & Blood Vessels: Abundant nerve endings monitor pain and proprioception; rich blood capillaries deliver nutrients.

  • Function of Synovial Fluid

    • Lubrication: Reduces friction between moving articular surfaces.
    • Nutrient Distribution: Supplies oxygen and nutrients to avascular chondrocytes and removes metabolic wastes.
    • Shock Absorption: Distributes mechanical pressure evenly across joint surfaces.

  • Bursa and Tendon Sheath

    • Bursa: Fibrous, sac-like structure lined with synovial membrane and containing synovial fluid; located where friction occurs (between skin/bone, muscle/bone, or ligament/bone).
    • Tendon Sheath: Elongated, tubular bursa wrapped around tendons subjected to high friction (e.g., wrist and ankle tendons).

  • Tendons vs. Ligaments

    • Tendon: Dense regular connective tissue band attaching muscle to bone.
    • Ligament: Dense regular connective tissue band attaching bone to bone.

  • Shapes of Articulating Surfaces in Synovial Joints, Movement Planes, and Locations

    • Planar (Gliding) Joint: Flat or slightly curved articular surfaces; Nonaxial / Uniaxial (sliding motion, no rotation axis); Locations: Intercarpal joints, intertarsal joints, acromioclavicular joint.
    • Hinge Joint: Convex surface fits into concave surface; Uniaxial (1 plane of movement - flexion/extension); Locations: Elbow (humeroulnar), knee (tibiofemoral), interphalangeal joints.
    • Pivot Joint: Rounded or pointed surface articulates within ring formed by bone and ligament; Uniaxial (1 plane - rotation); Locations: Atlantoaxial joint (C1−C2C_1-C_2), proximal radioulnar joint.
    • Condylar (Ellipsoid) Joint: Oval convex condyle fits into elliptical depression; Biaxial (2 planes - flexion/extension, abduction/adduction, circumduction); Locations: Metacarpophalangeal (MCP) joints (knuckles 2-5), radiocarpal (wrist) joint.
    • Saddle Joint: Articular surfaces are saddle-shaped (concave in one direction, convex in other); Biaxial (2 planes - flexion/extension, abduction/adduction, opposition); Location: First carpometacarpal (CMC) joint of thumb.
    • Ball-and-Socket Joint: Spherical head fits into cup-like socket; Multiaxial / Triaxial (3 planes - flexion/extension, abduction/adduction, rotation, circumduction); Locations: Shoulder (glenohumeral) joint, hip (coxal) joint.

  • Synovial Joint Movements and Body Locations

    • Angular Movements:
      • Flexion: Decreases angle between articulating bones (e.g., bending knee/elbow).
      • Extension: Increases angle between articulating bones, returning to anatomical position.
      • Hyperextension: Extension beyond normal anatomical position (e.g., looking up at ceiling).
      • Abduction: Movement of bone away from midline.
      • Adduction: Movement of bone toward midline.
      • Circumduction: Circular movement combining flexion, abduction, extension, and adduction in sequence (e.g., tracing circle with arm).
    • Rotational Movements:
      • Rotation: Bone turns around its long axis (e.g., turning head "no").
      • Medial (Internal) Rotation: Turning anterior surface toward midline.
      • Lateral (External) Rotation: Turning anterior surface away from midline.
    • Special Movements:
      • Pronation: Medial rotation of forearm causing palm to face posteriorly.
      • Supination: Lateral rotation of forearm causing palm to face anteriorly (anatomical position).
      • Dorsiflexion: Lifting foot toward shin (pointing toes up).
      • Plantarflexion: Depressing foot (pointing toes down/standing on tiptoes).
      • Inversion: Turning sole of foot inward medially.
      • Eversion: Turning sole of foot outward laterally.
      • Protraction: Moving structure anteriorly in horizontal plane (e.g., jutting jaw out).
      • Retraction: Moving structure posteriorly in horizontal plane (e.g., pulling jaw back).
      • Elevation: Superior movement of body part (e.g., shrugging shoulders).
      • Depression: Inferior movement of body part (e.g., lowering shoulders).
      • Opposition: Thumb movement touching tip of fingers across palm.

Chapter 10: Muscle Tissue and Organization

  • Three Types of Muscle Tissue & Distinguishing Features

    • Skeletal Muscle: Striated, multinucleated (nuclei located peripherally), long cylindrical unbranched fibers; under voluntary control.
    • Cardiac Muscle: Striated, single central nucleus (occasionally two), branched fibers connected by intercalated discs (containing desmosomes and gap junctions); under involuntary control.
    • Smooth Muscle: Non-striated, single central nucleus, spindle-shaped (fusiform) unbranched fibers; located in walls of hollow organs; under involuntary control.

  • Five Properties of Muscle Tissue

    • Excitability: Ability to respond to electrical stimuli (action potentials) or chemical signals by producing electrical signals.
    • Conductivity: Ability to propagate electrical signals along the cell membrane (sarcolemma).
    • Contractility: Ability to shorten forcefully when stimulated, generating tension.
    • Extensibility: Ability to stretch beyond resting length without undergoing structural damage.
    • Elasticity: Ability to recoil and return to original resting length after stretching or contracting.

  • Functions of Skeletal Muscle Tissue

    • Body Movement: Contraction pulls on bones to move skeleton.
    • Maintenance of Posture: Continuous muscle contractions stabilize head and trunk.
    • Protection and Support: Layers of muscle shield internal abdominal and pelvic organs.
    • Storage and Movement of Materials: Sphincters regulate entry/exit of substances in conduits.
    • Heat Production (Thermogenesis): Metabolic energy converted during muscle contraction releases heat to maintain normal body temperature.

  • Gross Anatomy of Skeletal Muscle and Connective Tissue Layers

    • Epimysium: Dense irregular connective tissue sheath surrounding the entire skeletal muscle organ.
    • Perimysium: Connective tissue sheath wrapping around groups of muscle fibers, organizing them into bundles called fascicles; houses blood vessels and nerves.
    • Endomysium: Delicate loose connective tissue layer surrounding each individual muscle fiber/cell; contains capillaries and nerve axons.
    • Hierarchy (Largest to Smallest): Skeletal Muscle Organ →\rightarrow Muscle Fascicle →\rightarrow Muscle Fiber (Cell) →\rightarrow Myofibril →\rightarrow Myofilaments (Thick and Thin).

  • Tendons and Aponeuroses

    • Tendon: Thick cord-like structure formed by merging epimysium, perimysium, and endomysium, anchoring muscle to periosteum of bone.
    • Aponeurosis: Thin, broad, flattened sheet of dense fibrous connective tissue acting as a broad tendon attachment.

  • Muscle Attachments: Origin vs. Insertion

    • Origin: Less movable or fixed attachment point of a muscle (usually proximal).
    • Insertion: More movable attachment point of a muscle pulled toward origin during contraction (usually distal).

  • Blood and Nerve Supply Distribution

    • Extensive vascular and neural supply branches throughout perimysium and endomysium to deliver oxygen/nutrients, remove wastes, and stimulate each individual skeletal muscle fiber.

  • Microscopic Anatomy of Skeletal Muscle

    • Sarcolemma: Plasma membrane of skeletal muscle fiber that conducts action potentials.
    • Sarcoplasm: Cytoplasm of skeletal muscle cell containing glycogen and myoglobin (oxygen-binding protein).
    • T-tubules (Transverse Tubules): Deep invaginations of sarcolemma extending into sarcoplasm to carry action potentials rapidly into interior cell regions.
    • Sarcoplasmic Reticulum (SR): Fluid-filled network of smooth ER surrounding myofibrils, expanded into terminal cisternae on both sides of T-tubule (forming a Triad = 1 T-tubule + 2 terminal cisternae); stores high concentrations of calcium ions (Ca2+Ca^{2+}).

  • Development of Skeletal Muscle Fibers

    • Multinucleated structure arises during embryonic development from fusion of multiple uninucleated myoblasts. Unfused satellite cells remain as adult stem cells for limited repair.

  • Myofilaments: Types and Descriptions

    • Thick Filaments: Composed of bundles of myosin protein molecules; each molecule features a tail and two globular heads (containing actin-binding sites and ATP-binding sites).
    • Thin Filaments: Composed of double helix of actin molecules (containing myosin-binding sites) intertwined with regulatory proteins:
      • Tropomyosin: Filamentous protein blocking myosin-binding sites on actin at rest.
      • Troponin: Globular protein complex bound to tropomyosin with binding site for Ca2+Ca^{2+}.

  • Sarcomere Structure and Contraction Changes

    • Definition: Functional microscopic contractile unit of myofibril bounded by two adjacent Z-discs.
    • Z-disc (Z-line): Structural protein plate anchoring thin filaments.
    • I band: Light region containing only thin filaments; bisected by Z-disc.
    • A band: Dark region spanning full length of thick filaments (includes region of thick and thin overlap).
    • H zone: Central region of A band containing only thick filaments (no thin overlap).
    • M line: Meshwork of proteins in center of H zone anchoring adjacent thick filaments.
    • Changes During Contraction (Sliding Filament Theory):
      • Z-discs move closer together (sarcomere shortens).
      • I band narrows / shortens.
      • H zone narrows and vanishes/disappears.
      • A band width remains unchanged.

  • Neuromuscular Junction (NMJ) and Motor Unit

    • Neuromuscular Junction: Specialized synapse between motor neuron axon terminal and motor end plate of muscle fiber sarcolemma.
    • Neurotransmitter: Acetylcholine (ACh), stored in synaptic vesicles and released into synaptic cleft.
    • Motor Unit: Single somatic motor neuron plus all individual skeletal muscle fibers it innervates.
    • Motor Unit Size vs. Control:
      • Small Motor Units: 1 neuron innervates few fibers (e.g., 3-6 fibers in extraocular eye muscles); yields precise, fine motor control.
      • Large Motor Units: 1 neuron innervates hundreds to thousands of fibers (e.g., 1000+ fibers in gastrocnemius); yields coarse, powerful control.
    • Force Production & Recruitment: Increased force achieved by recruitment (spatial summation)—activating progressively larger/more motor units.

  • Muscle Tone and Types of Contractions

    • Muscle Tone: Continuous, involuntary partial contraction of resting muscle to maintain posture and joint stability.
    • Isometric Contraction: Muscle generates tension without changing length (no movement, load exceeds tension).
    • Concentric (Isotonic) Contraction: Muscle shortens while generating tension to overcome resistance (e.g., lifting weight).
    • Eccentric (Isotonic) Contraction: Muscle lengthens while generating tension (e.g., controlled lowering of weight).

  • Skeletal Muscle Fiber Organizations and Examples

    • Circular (Sphincters): Concentric rings around orifices; Example: Orbicularis oris, Orbicularis oculi.
    • Parallel: Fascicles run parallel to long axis of muscle; Example: Rectus abdominis, Sartorius.
    • Convergent: Triangular/fan-shaped with broad origin converging to single tendon; Example: Pectoralis major.
    • Pennate: Short fascicles attach obliquely to central tendon running length of muscle:
      • Unipennate: Fascicles on one side of tendon (e.g., Extensor digitorum).
      • Bipennate: Fascicles on both sides of central tendon (e.g., Rectus femoris).
      • Multipennate: Branches of central tendon inside muscle (e.g., Deltoid).

  • Functional Muscle Classifications

    • Agonist (Prime Mover): Muscle primarily responsible for producing a specific movement.
    • Antagonist: Muscle opposing or resisting action of agonist.
    • Synergist: Muscle assisting agonist by producing same movement or stabilizing intermediate joints.

  • Naming Conventions of Skeletal Muscle

    • Direction of muscle fibers (e.g., Rectus = straight, Transverse = perpendicular).
    • Relative size (e.g., Maximus = largest, Minimus = smallest, Longus = long).
    • Location / Bone region (e.g., Frontalis, Tibialis anterior).
    • Number of origins / heads (e.g., Biceps = 2, Triceps = 3, Quadriceps = 4).
    • Shape (e.g., Deltoid = triangular, Trapezius = trapezoid).
    • Origin and insertion points (e.g., Sternocleidomastoid).
    • Action / Movement (e.g., Flexor, Extensor, Adductor).

  • Features of Cardiac and Smooth Muscle

    • Cardiac Muscle Features: Located exclusively in heart wall; involuntary; striated; short, branched cells with 1-2 central nuclei; connected by intercalated discs (gap junctions and desmosomes); autorhythmic; abundant mitochondria.
    • Smooth Muscle Features: Located in walls of hollow organs, blood vessels, respiratory tract; involuntary; non-striated (fusiform, single central nucleus); unbranched; controlled by autonomic nervous system; lacks sarcomeres and T-tubules; uses calmodulin instead of troponin for calcium binding.

Lab Activities 3, 4, 5, and 6

  • Skull Structures, Bones, and Features

    • Major Cranial Bones: Frontal, Parietal (2), Temporal (2), Occipital, Sphenoid, Ethmoid.
    • Major Facial Bones: Maxilla (2), Zygomatic (2), Nasal (2), Lacrimal (2), Palatine (2), Inferior nasal conchae (2), Vomer, Mandible.
    • Skull Foramina / Passageways and Parent Bones:
      • Foramen Magnum: Occipital bone (passage of spinal cord / brainstem).
      • Jugular Foramen: Between Occipital and Temporal bones (passage of internal jugular vein, CN IX, X, XI).
      • Carotid Canal: Temporal bone (passage of internal carotid artery).
      • Optic Canal: Sphenoid bone (lesser wing, passage of CN II / optic nerve).
      • Superior Orbital Fissure: Sphenoid bone (passage of CN III, IV, V1V_1, VI).
      • Foramen Rotundum: Sphenoid bone (greater wing, passage of CN V2V_2).
      • Foramen Ovale: Sphenoid bone (greater wing, passage of CN V3V_3).
      • Foramen Spinosum: Sphenoid bone (passage of middle meningeal artery).
      • Internal Acoustic Meatus: Temporal bone (petrous part, passage of CN VII, VIII).
      • Stylomastoid Foramen: Temporal bone (passage of CN VII / facial nerve).
      • Olfactory Foramina in Cribriform Plate: Ethmoid bone (passage of CN I).
      • Infraorbital Foramen: Maxilla.
      • Mental Foramen: Mandible.
    • Paranasal Sinuses: Air-filled, mucosa-lined cavities communicating with nasal cavity:
      • Frontal sinus (Frontal bone)
      • Ethmoidal sinuses / air cells (Ethmoid bone)
      • Sphenoidal sinus (Sphenoid bone)
      • Maxillary sinus (Maxilla bone - largest sinus)
    • Bones Forming the Orbit:
      • Roof: Frontal bone, Sphenoid (lesser wing).
      • Floor: Maxilla, Zygomatic, Palatine bone.
      • Medial Wall: Ethmoid, Lacrimal, Maxilla, Sphenoid body.
      • Lateral Wall: Zygomatic, Sphenoid (greater wing).

  • Bone Feature Terminology Summary

    • Process: Generic term for bony projection.
    • Fossa: Shallow depression.
    • Foramen: Hole/aperture.
    • Meatus / Canal: Tubular passage.
    • Condyle: Rounded articular knob.
    • Crest: Narrow ridge.
    • Tuberosity: Large rounded rough process.

  • Rotator Cuff Muscles (SITS)

    • Supraspinatus:
      • Origin: Supraspinous fossa of scapula.
      • Insertion: Greater tubercle of humerus.
      • Action: Abduction of arm (initiates first 15∘15^\circ).
    • Infraspinatus:
      • Origin: Infraspinous fossa of scapula.
      • Insertion: Greater tubercle of humerus.
      • Action: Lateral (external) rotation of arm.
    • Teres Minor:
      • Origin: Lateral border of scapula.
      • Insertion: Greater tubercle of humerus.
      • Action: Lateral (external) rotation and adduction of arm.
    • Subscapularis:
      • Origin: Subscapular fossa of scapula.
      • Insertion: Lesser tubercle of humerus.
      • Action: Medial (internal) rotation of arm.

  • Lab Muscles, Attachments, and Actions

    • Head and Neck Muscles:
      • Epicranius (Frontalis & Occipitalis): Raises eyebrows / wrinkles forehead (Frontalis); retracts scalp (Occipitalis).
      • Orbicularis Oculi: Closes eyes / winking / blinking.
      • Orbicularis Oris: Closes and pouts/puckers lips ("kissing muscle").
      • Zygomaticus Major: Pulls corners of mouth superiorly/laterally ("smiling muscle").
      • Masseter: Elevates mandible (chewing/mastication).
      • Temporalis: Elevates and retracts mandible.
      • Sternocleidomastoid: Unilateral: rotates head to opposite side; Bilateral: flexes neck/head.
    • Anterior Torso and Abdominal Muscles:
      • Pectoralis Major: Adducts, medially rotates, and flexes humerus/arm.
      • Pectoralis Minor: Depresses and protracts scapula.
      • Serratus Anterior: Protracts and rotates scapula upward ("boxer's muscle").
      • Rectus Abdominis: Flexes vertebral column, compresses abdominal viscera.
      • External Oblique: Flexes and rotates trunk/vertebral column.
      • Internal Oblique: Flexes and rotates trunk/vertebral column.
      • Transverse Abdominis: Compresses abdominal contents.
    • Posterior Torso and Shoulder Muscles:
      • Trapezius: Elevates, rotates, retracts, and depresses scapula; extends neck.
      • Latissimus Dorsi: Extends, adducts, and medially rotates humerus ("swimmer's muscle").
      • Rhomboid Major & Minor: Retracts (adducts) and elevates scapula.
      • Deltoid: Anterior fibers flex/medially rotate arm; Middle fibers abduct arm (after 15∘15^\circ); Posterior fibers extend/laterally rotate arm.
    • Upper Limb Muscles:
      • Biceps Brachii: Flexes forearm, supinates forearm (at radioulnar joint), flexes arm.
      • Brachialis: Primary flexor of forearm at elbow.
      • Brachioradialis: Flexes forearm at semi-prone position.
      • Triceps Brachii: Primary extensor of forearm at elbow; long head extends arm.
      • Pronator Teres: Pronates forearm.
      • Supinator: Supinates forearm.
    • Lower Limb Muscles:
      • Gluteus Maximus: Primary extensor of thigh/hip; laterally rotates thigh.
      • Gluteus Medius & Minimus: Abducts and medially rotates thigh; stabilizes pelvis while walking.
      • Iliopsoas (Iliacus + Psoas Major): Primary flexor of thigh/hip.
      • Quadriceps Femoris (Rectus Femoris, Vastus Lateralis, Vastus Medialis, Vastus Intermedius): Extends leg at knee joint; Rectus Femoris also flexes thigh at hip joint.
      • Sartorius: Flexes, abducts, and laterally rotates thigh at hip; flexes leg at knee ("tailor's muscle").
      • Hamstrings (Biceps Femoris, Semitendinosus, Semimembranosus): Flexes leg at knee joint; extends thigh at hip joint.
      • Adductor Group (Adductor Longus, Adductor Brevis, Adductor Magnus, Gracilis): Adducts thigh at hip joint.
      • Tibialis Anterior: Dorsiflexes foot at ankle; inverts foot.
      • Gastrocnemius & Soleus (Calf muscles): Plantarflexes foot at ankle joint; Gastrocnemius also flexes leg at knee joint.