Muscle Physiology

Muscle Fiber

Basic unit of a muscle that contracts and generates force.

Nucleus

Cell organelle that contains genetic material.

A Band

Dark bands in myofibrils that contain myosin filaments and parts of actin.

I Band

Light bands in myofibrils that contain only actin filaments.

Z Disc

Structure that anchors actin filaments and marks the boundary between sarcomeres.

Mitochondria

Organelles that produce energy through aerobic metabolism.

Transverse Tubules (T-tubules)

Invaginations of the sarcolemma that facilitate action potential propagation.

Sarcoplasmic Reticulum

Endoplasmic reticulum in muscle cells that releases calcium ions during contraction.

Triad

Structure formed by one T-tubule and two terminal cisternae of the SR.

Myofibrils

Bundles of myofilaments that contract to produce muscle tension.

Sarcoplasm

Cytoplasm of a muscle cell.

Myofilaments

Filaments that make up myofibrils; include thick and thin filaments.

Thick Filament

Filament made primarily of myosin proteins.

Thin Filament

Filament made mainly of actin, along with troponin and tropomyosin.

H Zone

Region in the A band where only thick filaments are present.

M Line

Middle line of the A band where thick filaments are anchored.

Cross Bridges

Projections from myosin filaments that bind to actin.

Sarcomere

Functional unit of muscle fiber, defined by Z discs.

Calcium Ions (Ca2+)

Essential for muscle contraction, released from sarcoplasmic reticulum.

Acetylcholine (ACh)

Neurotransmitter released at the neuromuscular junction to initiate contraction.

Action Potential (AP)

Electrical impulse that stimulates muscle contraction.

Excitation-Contraction Coupling (E-C Coupling)

Process that converts an electrical stimulus to a mechanical response in muscle.

Troponin

Protein that binds calcium and shifts tropomyosin to expose binding sites.

Tropomyosin

Protein that blocks myosin binding sites on actin filaments.

ATP (Adenosine Triphosphate)

Energy currency of the cell, required for muscle contraction.

Phosphocreatine

Energy source for short bursts of contraction.

Glycogen

Stored form of glucose that provides energy during prolonged exercise.

Isometric Contraction

Muscle contraction where the muscle does not change length.

Isotonic Contraction

Muscle contraction where the muscle changes length while maintaining tension.

Type I Fibers

Slow-twitch muscle fibers suited for endurance activities.

Type II Fibers

Fast-twitch muscle fibers suited for short bursts of strength.

Rigor Mortis

Postmortem state where muscles stiffen due to calcium retention.

Clostridium tetani

Bacteria causing tetanus, characterized by sustained muscle contractions.

Tetanus

Condition marked by prolonged muscle contraction; can be fatal.

Presynaptic Motor Neuron

Neuron that releases neurotransmitters to initiate muscle contraction.

GABA (Gamma-Aminobutyric Acid)

Inhibitory neurotransmitter that helps prevent excessive muscle contraction.

Risus Sardonicus

Facial muscle contraction symptom associated with tetanus.

Opisthotonos

Severe muscle spasm leading to arching of the back.

Muscle Contraction

Process by which muscle fibers develop tension and shorten.

Calcium Release Channel

Channel in the SR membrane that opens to release Ca2+ during contraction.

Active Sites

Binding sites on actin exposed for myosin cross-bridges during contraction.

Voltage-Sensitive Protein

Protein that detects changes in membrane potential during action potential.

Calcium Binding to Troponin

Triggers conformational change that allows for muscle contraction.

Cytosol

Intracellular fluid where metabolic processes occur.

Extracellular Space

Fluid environment outside of the muscle cell.

Neuromuscular Junction

Synapse between a motor neuron and muscle fiber.

Motor Unit

A motor neuron and the muscle fibers it innervates.

Myoglobin

Oxygen-binding protein in muscle tissues that supports aerobic metabolism.

Tetanization

Progressive increase in muscle contraction strength due to rapid stimulation.

Serum Calcium Levels

Concentration of calcium in blood that affects muscle function.

Inflammation in Muscle Tissue

Response of muscle tissues to injury or infection, often causing pain.

Electrolyte Balance

Maintaining the balance of ions that is critical for muscle function.

Muscle Fatigue

Decrease in muscle performance due to prolonged activity.

Respiratory Rate

Rate of breathing that can influence muscle oxygenation.

Cardiac Output

Volume of blood the heart pumps, affecting muscle and organ perfusion.

Metabolic Pathways

Series of chemical reactions within cells to create energy.

Endurance Training

Exercise designed to improve the ability of muscles to sustain activity.

Strength Training

Exercise designed to improve the strength of muscles.

Skeletal Muscle Function

Voluntary movement, posture maintenance, and heat generation.

Cardiac Muscle Function

Involuntary contraction to pump blood throughout the body.

Smooth Muscle Function

Involuntary control in hollow organs like intestines and blood vessels.

Hormonal Regulation of Muscles

Influences muscle metabolism and growth through hormones.

Cross-Bridge Cycling

Continuous process of cross-bridge formation and breaking during contraction.

Elastic Components of Muscle

Structures that allow muscles to return to original length after contraction.

CNS Signals

Nervous signals regulating muscle contractions based on need.

Muscle Fiber Recruitment

Process of activating more muscle fibers for greater force.

Plasma Membrane Depolarization

Change in membrane potential essential for muscle activation.

Resting Membrane Potential

Electrical charge difference across the plasma membrane at rest.

Muscle Temperature Regulation

Maintenance of optimal temperature for enzymes and metabolic rates.

Motor Neuron Health

Condition of motor neurons influencing muscle functionality.

Immediate Energy Sources

Energy systems that provide ATP for short-duration activities.

Creatine Kinase

Enzyme facilitating ATP regeneration from phosphocreatine.

High-Intensity Interval Training

Training method that alternates between intense bursts of activity.

Post-Exercise Recovery

Period where the body restores homeostasis after activity.

Anaerobic Metabolism

Energy production without oxygen, typically for short efforts.

Aerobic Metabolism

Energy production using oxygen, used during prolonged exercise.

Insulin's Role in Muscle

Hormone that helps absorb glucose and amino acids into muscle cells.

Muscle Stretch Receptors

Sensory receptors that monitor muscle stretch and help prevent injury.

Lactic Acid

Byproduct of anaerobic metabolism linked to muscle fatigue.

Apoptosis in Muscle Tissue

Programmed cell death that balances muscle growth and regeneration.

Sarcopenia

Age-related loss of muscle mass and strength.