Physio Exercise 2 - Frog Skeletal Muscle

AI Generated

Gastrocnemius Muscle

Large calf muscle of the frog commonly dissected for in-vitro contraction experiments due to its size and robustness.

Kymograph

19th-century rotating drum with smoked paper that recorded muscle movement as waveforms via a writing lever.

Carl Ludwig

Physiologist who invented the kymograph, enabling quantitative recording of muscle contractions.

Luigi Galvani

18th-century scientist who demonstrated that electricity can elicit muscle movement, coining the idea of “animal electricity.”

BIOPAC

Modern electronic transducer and software system that digitally measures force, duration, and fatigue in muscle experiments.

Skeletal Muscle Fiber

Long, multinucleated, cylindrical cell containing myofibrils that perform voluntary contractions.

Sarcomere

Fundamental contractile unit bounded by two Z-discs and composed of interdigitating actin and myosin filaments.

Z-Disc

Protein boundary of a sarcomere to which actin filaments anchor.

Actin (Thin Filament)

Protein filament that slides past myosin during contraction; contains binding sites for myosin heads.

Myosin (Thick Filament)

Motor protein with ATP-powered heads that form cross-bridges with actin to generate force.

Sliding Filament Theory

Model stating that muscle shortens as actin and myosin filaments slide past each other without changing length.

Excitation-Contraction Coupling

Sequence converting a neural action potential into mechanical muscle contraction via Ca²⁺ release.

Neuromuscular Junction

Synapse where a motor neuron releases acetylcholine to initiate a muscle action potential.

Sarcolemma

Plasma membrane of a muscle fiber that depolarizes in response to acetylcholine.

Transverse Tubules (T-Tubules)

Invaginations of the sarcolemma that conduct action potentials deep into the muscle fiber.

Sarcoplasmic Reticulum (SR)

Specialized endoplasmic reticulum that stores and releases Ca²⁺ during contraction.

Calcium Ions (Ca²⁺)

Key intracellular messenger that binds troponin to initiate cross-bridge formation.

Troponin

Regulatory protein that, when bound to Ca²⁺, shifts tropomyosin away from actin’s binding sites.

Tropomyosin

Protein that blocks myosin-binding sites on actin until moved by Ca²⁺-activated troponin.

Cross-Bridge Cycle

Series of events where myosin heads attach, pivot, detach, and re-cock, driven by ATP hydrolysis.

Motor Unit

A single motor neuron and all the muscle fibers it innervates.

Motor Unit Recruitment (Spatial Summation)

Increase in contraction force produced by activating additional motor units as stimulus intensity rises.

Temporal Summation

Stronger contraction produced when a muscle receives repeated stimuli before full relaxation, allowing Ca²⁺ buildup.

Tetanus

Sustained maximal contraction from high-frequency stimuli; incomplete (unfused) shows slight tension dips, complete (fused) shows none.

Length-Tension Relationship

Bell-shaped relationship showing maximal force is generated at an optimal resting muscle length.

Muscle Fatigue

Decline in the muscle’s ability to generate force after prolonged activity due to metabolic and synaptic factors.

Acidosis (Low pH)

Condition often caused by lactic acid accumulation that inhibits myosin ATPase and Ca²⁺ handling, weakening contractions.

Myosin ATPase

Enzyme on myosin head that hydrolyzes ATP; its activity governs cross-bridge cycling speed and is pH-sensitive.

Reactive Oxygen Species (ROS)

Metabolic byproducts that accumulate during intense activity and can impair muscle enzymes and calcium regulation.