Joints, Muscular Tissue, and the Muscular System

Comprehensive vocabulary flashcards covering anatomical joints, structural and functional classifications, synovial joint types and motions, muscular tissue properties, sarcomere mechanics, excitation-contraction coupling, energetics, motor units, musculoskeletal levers, and major skeletal muscles based on lecture presentations.

Synarthrosis

An immovable joint, such as the fibrous suture joints found between the bones of the skull.

Amphiarthrosis

A slightly movable joint, such as the cartilaginous pubic symphysis.

Diarthrosis

A freely movable joint, exemplified by synovial ball-and-socket joints of the shoulder and hip.

Fibrous Joint

A joint that lacks cartilage and a synovial cavity, where articulating bones are held closely together by dense irregular connective tissue.

Cartilaginous Joint

A joint consisting of a solid bar of cartilage between two articulating bones that lacks a synovial cavity and permits little to no movement.

Synovial Joint

A freely movable diarthrotic joint characterized by a synovial cavity enclosed by a two-layered articular capsule and reinforced by ligaments.

Synovial Fluid

A lubricating secretion produced by the synovial membrane that reduces friction, absorbs shocks, supplies oxygen and nutrients to articular cartilage, and removes metabolic wastes.

Bursae

Fluid-filled saclike structures strategically situated to minimize friction between skin, muscles, tendons, ligaments, and bones in synovial joints.

Menisci

Pads of dense fibrocartilage (articular discs) situated between articular bone surfaces that provide superior structural strength and permit bones of different shapes to fit together tightly.

Planar Joint

A synovial joint with flat or slightly curved articulating surfaces that permits back-and-forth and side-to-side gliding movements without altering joint angles significantly.

Hinge Joint

A uniaxial synovial joint in which the convex surface of one bone fits into the concave surface of another bone, producing an opening-and-closing action.

Pivot Joint

A uniaxial synovial joint where the rounded or pointed surface of one bone articulates with a ring formed partly by another bone and partly by a ligament, permitting rotation around its longitudinal axis.

Condyloid Joint

A biaxial synovial joint wherein the convex, oval-shaped projection of one bone fits neatly into an oval-shaped depression of another bone.

Saddle Joint

A modified condyloid synovial joint in which the articular surface of one bone is saddle-shaped, permitting movement around all three axes.

Ball-and-Socket Joint

A triaxial synovial joint where the rounded, ball-like surface of one bone fits into a cup-like depression of another bone, allowing the widest range of motion.

Range of Motion (ROM)

The range, measured in degrees of a circle, through which the articulating bones of a joint can be moved.

Flexion

An angular movement that results in a decrease in the angle between articulating bones, typically in the sagittal plane.

Extension

An angular movement that results in an increase in the angle between articulating bones, typically in the sagittal plane.

Abduction

The movement of a bone away from the body midline, typically occurring in the frontal plane.

Adduction

The movement of a bone toward the body midline, typically occurring in the frontal plane.

Circumduction

A composite movement involving flexion, abduction, extension, adduction, and rotation in succession, wherein the distal end of a body part moves in a circle.

Inversion

A special movement of the foot that turns the sole medially at the intertarsal joints.

Eversion

A special movement of the foot that turns the sole laterally at the intertarsal joints.

Dorsiflexion

Bending of the foot at the ankle joint in an upward direction toward its superior surface (dorsum).

Plantar Flexion

Bending of the foot at the ankle joint in a downward direction toward the sole (plantar surface).

Opposition

The special movement of the opposable thumb across the palm at the carpometacarpal joint to touch the tips of the fingers on the same hand.

Temporomandibular Joint (TMJ)

A combined hinge and planar joint formed by the condylar process of the mandible and mandibular fossa of the temporal bone; the only movable joint in the skull.

Arthroplasty

The surgical replacement or implantation of an artificial joint, most frequently performed on hips, knees, and shoulders.

Excitability (Irritability)

The property of muscular and nervous tissue that allows them to respond to specific chemical or electrical stimuli by producing electrical signals.

Contractility

The ability of muscular tissue to contract forcefully and shorten in length when stimulated by an action potential.

Extensibility

The ability of muscular tissue to stretch or extend within physiological limits without sustaining damage.

Elasticity

The ability of muscular tissue to return to its original length and shape after undergoing contraction or extension.

Skeletal Muscle Tissue

Voluntary, striated muscle tissue composed of long, parallel, multinucleated fibers with eccentrically located nuclei, primarily functioning to move the skeleton.

Cardiac Muscle Tissue

Involuntary, striated, autorhythmic muscle tissue located exclusively in the heart wall, composed of branched fibers containing a single central nucleus that pump blood continuously.

Visceral (Smooth) Muscle Tissue

Involuntary, non-striated muscle tissue located in the walls of hollow internal structures (such as blood vessels and the G.I. tract), featuring tapered cells with a single central nucleus.

Myoblasts

Embryonic progenitor cells that fuse together during development to form a single, elongated, multinucleated skeletal muscle fiber.

Epimysium

The outermost dense connective tissue sheath that encircles an entire muscle belly, extending continuously to form tendons and deep fascia.

Perimysium

A connective tissue partition that groups individual skeletal muscle fibers into discrete bundles known as fascicles.

Endomysium

An invaginating, delicate layer of connective tissue that surrounds each individual skeletal muscle fiber.

Aponeurosis

A broad, thick, sheetlike tendon or fascia that connects muscle bellies together or attaches muscle to bone, such as the epicranial aponeurosis.

Sarcolemma

The plasma membrane of an individual skeletal muscle fiber lying directly beneath the endomysium.

Sarcoplasm

The cytoplasm of a muscle fiber, packed with glycogen, myoglobin, and contractile proteins organized into myofibrils.

Transverse (T) Tubules

Deep, perpendicular invaginations of the sarcolemma that tunnel from the fiber surface inward to conduct muscle action potentials toward the sarcoplasmic reticulum.

Sarcoplasmic Reticulum (SR)

A specialized fluid-filled system of membranous tubules surrounding each myofibril that stores calcium ions ($\text{Ca}^{2+}$) and releases them to trigger muscle contraction.

Sarcomere

The basic functional contractile unit of a muscle fiber, consisting of ordered arrays of thick and thin filaments bounded on each end by a Z disc.

Myosin

A motor contractile protein that forms thick filaments, featuring twisted tails and outward-projecting heads shaped like golf clubs that bind actin to generate tension.

Actin

The primary structural contractile protein of thin filaments, arranged like twisted beads of pearls, containing binding sites for myosin heads.

Tropomyosin

A strandlike regulatory protein that blocks myosin-binding sites on actin thin filaments in relaxed muscle tissue to prevent cross-bridge interaction.

Troponin

A globular regulatory protein on thin filaments that binds calcium ions ($\text{Ca}^{2+}$), causing a conformational change that pulls tropomyosin away from actin's binding sites.

Titin

An enormous structural protein extending from the Z disc to the M line; the third most plentiful protein in muscle that accounts for myofibril elasticity and stability.

Power Stroke

The step in the contraction cycle during which bound myosin cross-bridges swivel toward the center of the sarcomere, pulling thin filaments past thick filaments.

Neuromuscular Junction (NMJ)

The chemical synapse formed between the synaptic end bulb of a somatic motor neuron and the motor end plate of a skeletal muscle fiber.

Motor End Plate

The specialized, folded region of the sarcolemma opposite the synaptic terminal that is rich in ligand-gated sodium channels that act as receptors for acetylcholine.

Acetylcholinesterase

An enzyme present within the synaptic cleft of the NMJ that rapidly degrades acetylcholine, stopping generation of continuous muscle action potentials.

Creatine Phosphate

An energy-rich phosphagen found in muscle fibers that rapidly phosphorylates ADP to regenerate ATP, supporting maximal contraction for approximately $15\text{ seconds}$.

Anaerobic Glycolysis

A metabolic pathway that degrades muscle glycogen and blood glucose to pyruvic acid and lactic acid in the absence of oxygen, yielding $2\text{ ATP}$ per glucose for $30\text{--}40\text{ seconds}$ of activity.

Aerobic Cellular Respiration

Oxygen-dependent mitochondrial catabolism of pyruvate, fatty acids, and amino acids that yields $36\text{ ATP}$ along with $\text{CO}_2$, $\text{H}_2\text{O}$, and heat to power activity lasting minutes to hours.

Oxygen Debt (EPOC)

Excess post-exercise oxygen consumption required after exertion to restore ATP, creatine phosphate, and myoglobin stores, and to convert accumulated lactic acid back to pyruvate.

Motor Unit

A physiological motor unit consisting of a single somatic motor neuron along with every skeletal muscle fiber it innervates.

All-or-None Principle

The physiological rule stating that an individual skeletal muscle fiber or all fibers within a single motor unit contract maximally once depolarized to threshold.

Slow Oxidative (SO) Fibers

Small-diameter, fatigue-resistant skeletal muscle fibers rich in myoglobin and mitochondria that appear dark red and are suited for aerobic endurance tasks such as marathon running.

Fast Glycolytic (FG) Fibers

Large-diameter, white skeletal muscle fibers adapted for intense, short-duration anaerobic tasks due to high glycogen content and rapid, powerful ATP hydrolysis.

Latent Period

The brief interval between the delivery of a muscle stimulus and the initial generation of tension, during which the action potential sweeps over the sarcolemma and $\text{Ca}^{2+}$ is released from the SR.

Tetanus

A sustained, steady muscle contraction without relaxation, generated by rapid, repetitive action potentials fusing twitches together.

Motor Unit Recruitment

The progressive activation of increasing numbers of motor units within a muscle to produce gradations in total contractile force.

Concentric Isotonic Contraction

A dynamic contraction in which the muscle generates tension sufficient to overcome a load and shortens in length to produce movement.

Eccentric Isotonic Contraction

A dynamic contraction in which the resistance exceeds the developed tension, causing the actively contracting muscle to lengthen under load.

Isometric Contraction

A static muscle contraction in which internal tension matches the load, producing no joint movement or change in muscle length.

Myofibrosis

The pathological replacement of healthy muscle fibers by excessive fibrous scar connective tissue following chronic metabolic injury or severe trauma.

Myosclerosis

The abnormal hardening and loss of flexibility in a muscle resulting from calcification following trauma or metabolic disturbances.

Origin

The anatomical attachment of a muscle's tendon to a stationary, typically proximal bone or connective structure.

Insertion

The attachment point of a muscle's tendon to the movable, typically distal bone that moves when the muscle contracts.

Fulcrum

The fixed pivot point around which a lever pivots, represented anatomically by the joints of the musculoskeletal system.

First-Class Lever

A lever mechanism where the fulcrum lies between the applied effort and the opposing load, such as the head resting on the atlanto-occipital joint.

Second-Class Lever

A lever system where the load is positioned between the fulcrum and the effort, producing a distinct mechanical advantage for force production, such as standing on tiptoes.

Third-Class Lever

The most common lever system in the human body, where the effort is applied between the fulcrum and the load, favoring speed and range of motion over force.

Agonist (Prime Mover)

The primary muscle directly responsible for producing a specific intended movement around an articulating joint.

Antagonist

A muscle that yields to and stretches in response to the action of an agonist, producing the opposite functional movement.

Synergist

A muscle that contracts alongside the prime mover to prevent unwanted movement at intermediate joints or to directly aid the action.

Fixator

A specialized synergist muscle that stabilizes the proximal origin of the prime mover to establish a firm base for action.

Sternocleidomastoid

A prominent neck muscle originating on the sternum and clavicle and inserting onto the mastoid process of the temporal bone, acting to flex and rotate the head.

Masseter

A powerful muscle of mastication originating from the maxilla and zygomatic arch and inserting onto the mandible to elevate and close the mouth.

Orbicularis Oris

A circular sphincter muscle surrounding the oral opening that closes and protrudes the lips during speech and kissing.

Diaphragm

The primary dome-shaped muscle of inspiration, originating from the inferior six ribs and lumbar vertebrae and inserting into a central tendon.

Latissimus Dorsi

A broad superficial back muscle ('swimmer's muscle') originating from thoracic and lumbar vertebrae and ilium, inserting onto the mid-humerus to drive the arm inferiorly and posteriorly.

Brachioradialis

A forearm muscle originating on the humerus and inserting on the distal radius that acts to supinate the forearm at the radioulnar joint.

Hamstrings

The posterior thigh muscle group consisting of the biceps femoris, semitendinosus, and semimembranosus, originating on the ischial tuberosity and acting to flex the leg and extend the thigh.

Quadriceps Femoris

The large anterior thigh muscle group consisting of the rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis, which extends the leg at the knee joint.

Tibialis Anterior

An anterior leg muscle originating from the tibia and inserting on the first cuneiform and first metatarsal, responsible for dorsiflexing and inverting the foot.