Muscles, Bones, Neurons, and Sensory Systems

Comprehensive review flashcards covering muscles, bones, neurophysiology, nervous systems, and sensory biology across four course chapters.

Skeletal Muscle Tissue

Striated muscle tissue attached to bones that is under voluntary control of the somatic nervous system.

Cardiac Muscle Tissue

Striated, involuntary contractile tissue forming the walls of the vertebrate heart.

Smooth Muscle Tissue

Non-striated, involuntary muscle tissue found in internal organs and blood vessel walls.

Tendons

Cords of connective tissue that attach vertebrate skeletal muscles to bones.

Skeletal Muscle-Tendon-Bone Attachment

The structural linkage wherein skeletal muscle connects via fibrous tendons to bone levers, enabling voluntary movement across joints.

Muscle Fibers

Elongated, multinucleate contractile cells that run the entire length of a skeletal muscle.

Myofibrils

Cylindrical contractile elements packed inside muscle fibers that run lengthwise throughout the cell.

Thick Filaments

Myofibril filaments with a diameter of $13\text{--}18\,\text{nm}$ composed of parallel bundles of myosin molecules.

Thin Filaments

Myofibril filaments with a diameter of $5\text{--}8\,\text{nm}$ composed primarily of actin chains, troponin, and tropomyosin.

Striations

The microscopic pattern of alternating dark and light bands produced by the precise arrangement of thick and thin filaments.

A Band

Dark bands spanning the stacked thick filaments, including the outer edges where thin filaments overlap.

H Zone

The lighter center region of an A band that contains only thick filaments and no overlapping thin filaments.

M Line

A disc of proteins situated in the center of the H zone that anchors and holds the stack of thick filaments together.

I Band

Light bands in a myofibril consisting exclusively of thin filaments that do not overlap with the A band.

Z Line

A thin disc in the center of each I band to which the thin filaments are anchored.

Sarcomere

The basic contractile unit of a myofibril, defined as the region between two adjacent Z lines.

Sarcomere Striation Pattern

The repeating banding structure of a myofibril consisting of alternating A bands, I bands, H zones, M lines, and boundary Z lines.

Myosin Molecule

Protein consisting of two subunits that form a globular head connected to a long double-helix tail.

Crossbridge

The functional linkage formed when a myosin head binds to an adjacent thin actin filament.

Actin

The primary structural protein of thin filaments, configured as two linear chains wound into a double helix.

Tropomyosin

An elongated, fibrous protein bound to actin that blocks myosin-binding sites in the relaxed state.

Troponin

A three-subunit globular protein complex bound at intervals along thin filaments that binds $\text{Ca}^{2+}$ to shift tropomyosin.

Sliding Filament Model

The mechanism of muscle contraction described in 1954 where thin filaments slide past thick filaments without either filament changing length.

A. F. Huxley and R. Niedergerke (1954)

Researchers who published experimental evidence in Nature demonstrating structural changes in striated muscle during contraction.

H. Huxley and J. Hanson (1954)

Researchers who published findings in Nature detailing cross-striation alterations during contraction and stretch supporting the sliding filament model.

Crossbridge Detachment Step

Phase of the crossbridge cycle wherein ATP binds to the myosin head, causing it to release actin.

Myosin Head Cocking Step

Hydrolysis of bound ATP into ADP and $\text{P}_i$ by the myosin head ATPase that resets the head into its high-energy conformation.

Power Stroke

The release of ADP and $\text{P}_i$ from the myosin head causing it to pivot and slide the thin filament toward the sarcomere center.

T (Transverse) Tubule

Infolding of the muscle fiber plasma membrane at A band–I band junctions that conducts depolarizations deep into the fiber.

Sarcoplasmic Reticulum

A complex network of membrane-bound vesicles modified from smooth ER that wraps around myofibrils and stores $\text{Ca}^{2+}$.

Neuromuscular Junction (NMJ)

The specialized chemical synapse formed between the axon terminal of an efferent motor neuron and a skeletal muscle fiber.

Motor Endplate

The specialized, folded region of the muscle fiber sarcolemma situated directly beneath the motor neuron axon terminal.

Low Intracellular $\text{Ca}^{2+}$ State

Physiological condition where tropomyosin physically obstructs the myosin-binding sites on actin, inhibiting crossbridge formation.

Tropomyosin Displacement by Calcium

Structural transition where elevated cytoplasmic $\text{Ca}^{2+}$ binds troponin, shifting tropomyosin aside to expose myosin-binding sites on actin.

Excitation-Contraction Coupling

Sequence of events linking motor neuron action potentials to acetylcholine release, T tubule depolarization, $\text{Ca}^{2+}$ release, and sarcomere shortening.

Botulinum Toxin

Bacterial neurotoxin that paralyzes skeletal muscles, including the diaphragm, by blocking acetylcholine release at neuromuscular junctions.

Curare

Plant-derived toxin that induces fatal flaccid paralysis by blocking acetylcholine receptors on muscle fibers.

Rigor Mortis

Postmortem muscle stiffness occurring within hours of death caused by $\text{Ca}^{2+}$ leakage into cytoplasm without ATP available for crossbridge release.

Muscle Twitch

A single, weak contraction produced in a muscle fiber in response to a single isolated action potential.

Twitch Summation

The additive increase in contraction strength that occurs when a muscle fiber is restimulated before completely relaxing.

Tetanus

A peak level of continuous, maximal muscle contraction produced when action potentials arrive approximately $25\,\text{msec}$ apart without relaxation.

Slow Muscle Fibers

Red muscle fibers containing abundant myoglobin and mitochondria that contract slowly, resist fatigue, and produce ATP via oxidative phosphorylation.

Fast Aerobic Muscle Fibers

Red muscle fibers with high myosin-ATPase activity, abundant mitochondria, and intermediate glycolytic capacity that contract rapidly.

Fast Anaerobic Muscle Fibers

Pale muscle fibers containing high glycogen, few mitochondria, and low myoglobin that generate rapid bursts of force via glycolysis and fatigue quickly.

Myoglobin

An iron-containing oxygen-binding pigment in muscle fibers that gives aerobic fibers their red coloration and enhances intracellular oxygen availability.

Postural Muscles

Muscles specialized for sustained, slow contractions that feature a high proportion of fatigue-resistant slow muscle fibers.

Finger Muscles

Skeletal muscles specialized for quick, delicate movements that possess a high proportion of fast muscle fibers.

Muscle Fiber Proportions (Distance Runner vs. Sprinter)

Athletic muscle adaptation showing a dominance of red slow-twitch oxidative fibers in distance runners versus pale fast-twitch glycolytic fibers in sprinters.

Motor Unit

A single efferent motor neuron and all the uniform muscle fibers it innervates, which contract simultaneously.

Delicate Movement Motor Control

Motor organization characterized by numerous small motor units distributed across a small area, each containing relatively few muscle fibers.

Large Movement Motor Control

Motor organization featuring fewer motor units per tissue volume, with each individual motor unit containing thousands of muscle fibers.

Muscle Fatigue

Decline in muscle force caused primarily by failure of excitation-contraction coupling and related intracellular events rather than lactate accumulation.

Central Fatigue

Mechanisms of muscle exhaustion originating within the CNS, including psychological effects and protective inhibitory reflexes.

Peripheral Fatigue

Muscle performance decline originating at the neuromuscular junction, sarcolemma, sarcoplasmic reticulum, or contractile crossbridges.

Hydrostatic Skeleton

Support system consisting of incompressible fluid-filled compartments under pressure on which muscles contract to produce movement.

Hydrostatic Skeleton Movement

Locomotory mechanism in annelids where contraction of circular muscles lengthens segments and contraction of longitudinal muscles shortens and widens them.

Earthworm Circular Muscles

Body wall muscle layer whose contraction reduces body diameter and increases body length.

Earthworm Longitudinal Muscles

Body wall muscle layer whose contraction shortens overall body length and increases diameter.

Vertebrate Hydrostatic Structure

The erectile tissue of the vertebrate penis, which becomes rigid when filled with pressurized fluid.

Exoskeleton

A rigid external body covering that protects internal tissues and provides mechanical levers against which internal muscles apply force.

Mollusk Exoskeleton

A hard calcium carbonate shell secreted by specialized glands situated within the mantle tissue.

Arthropod Exoskeleton

A protective chitinous cuticle secreted by underlying hypodermal tissue with muscles extending across internal joint surfaces.

Vertebrate Exoskeletal Structures

External protective armor found in certain vertebrates, such as turtle shells and the bony scutes and skull plates of the American alligator.

Endoskeleton

An internal skeletal framework of hard structures, such as bones or cartilage, that protects soft organs and anchors muscles.

Echinoderm Endoskeleton

Internal skeletal framework consisting of ossicles formed from crystalline calcium carbonate.

Sand Dollar Endoskeleton

The internal rigid calcium carbonate test of an irregular echinoid supporting internal organs and spines.

Vertebrate Endoskeleton Functions

Body support, internal organ protection, mineral storage for calcium and phosphate ions, and site of hematopoiesis.

Axial Skeleton

Division of the vertebrate skeleton comprising the skull, vertebral column, and rib cage along the body's central longitudinal axis.

Appendicular Skeleton

Division of the vertebrate skeleton comprising the limb bones and the pectoral and pelvic girdles that attach limbs to the axial core.

Compact Bone

Dense, highly organized bone tissue that forms the exterior surfaces and shafts of vertebrate bones.

Spongy Bone

Porous, open bone tissue consisting of interconnected trabeculae located in the interior regions and ends of bones.

Osteon

The cylindrical structural unit of compact bone consisting of concentric lamellae surrounding a central neurovascular canal.

Central (Osteonic) Canal

The central longitudinal channel of an osteon containing nerves, arteries, and blood vessels.

Perforating Canal

Transverse channels in compact bone that connect central canals with the periosteum and medullary cavity.

Lacuna

A small chamber or space within the mineralized bone matrix that houses an individual osteocyte.

Canaliculus

Microscopic canal linking adjacent lacunae, allowing cytoplasmic extensions of osteocytes to communicate and exchange nutrients.

Compact Bone Microstructure

The histological architecture of cortical bone displaying osteons, central osteonic canals, lacunae housing osteocytes, canaliculi, and trabeculae.

Periosteum

The tough, fibrous connective tissue sheath covering the external surfaces of compact bone.

Endosteum

The cellular membrane lining the inner surfaces, trabeculae, and canals of bone tissue.

Red Marrow

Hematopoietic tissue filling the interior cavities of flat bones (such as ribs and hip bones) that produces new red blood cells.

Yellow Marrow

Adipose-rich tissue filling the central medullary canal of long bones (such as the femur) that serves as a source of white blood cells.

Synovial Joint

A freely movable joint where cartilage-covered bone ends are enclosed by a connective tissue capsule containing synovial fluid and stabilized by ligaments.

Cartilaginous Joint

A joint where the cartilage-covered ends of bones are united by fibrous connective tissue without a fluid-filled capsule.

Hinge Joint

A synovial joint, such as the elbow or knee, that allows movement strictly in a single plane to open or close the angle between flanking bones.

Ball-and-Socket Joint

A synovial joint, such as the shoulder or hip, capable of multiaxial rotation and providing the greatest range of motion in the body.

Fulcrum

The fixed pivot point around which a skeletal lever rotates when muscular force is applied.

Elbow Lever Mechanics

A third-class lever configuration where the fulcrum is at one end, the load is at the other, and effort is applied in between, trading force for amplified movement distance.

Agonist Muscle

A muscle that causes a specific joint movement through its active contraction.

Antagonistic Muscle Pairs

Opposing muscle arrangements wherein contraction of an extensor extends a joint while contraction of a flexor closes it.

Flexor Muscle

A muscle, such as the biceps brachii, whose contraction decreases the angle across a joint.

Extensor Muscle

A muscle, such as the triceps brachii, whose contraction increases the angle across a joint.

Antagonistic Muscle Pair Operation

Reciprocal muscle action wherein contraction of the biceps flexes the forearm while the triceps relaxes, and contraction of the triceps extends the forearm while the biceps relaxes.

Mole Limb Adaptation

Skeletal limb morphology characterized by short lever arms adapted for generating slow, high-power burrowing forces.

Deer Limb Adaptation

Skeletal limb morphology characterized by elongated lever arms optimized for maximizing movement velocity and running speed.

Osteocyte

A mature bone cell entrapped within mineralized extracellular matrix that maintains bone tissue metabolism.

Osteoblast

A bone-forming cell derived from mesenchymal stem cells that synthesizes and secretes unmineralized osteoid matrix.

Osteoclast

A large multinucleate cell derived from monocyte precursors that resorbs mineralized bone tissue.

Osteoid

The unmineralized organic extracellular matrix secreted by osteoblasts prior to calcification.

Trabeculae

The branching, lattice-like bony struts and plates that make up the internal network of spongy bone.

Synovial Fluid

Viscous, lubricating fluid contained within the connective tissue capsule of a synovial joint.