Muscle Tissues and Muscle Physiology

Vocabulary flashcards covering terms related to muscle tissue structure, function, contraction, metabolism, types, and clinical considerations from the lecture notes.

Excitability

The ability of muscle tissue to respond to a stimulus (nerve impulse) and initiate an action.

Contractility

The ability of muscle tissue to contract forcefully when stimulated.

Extensibility

The ability of muscle tissue to be stretched beyond its resting length.

Elasticity

The ability of muscle tissue to return passively to its original length after stretch.

Cardiac Muscle

Striated, involuntary muscle of the heart.

Smooth Muscle

Nonstriated, involuntary muscle found in walls of hollow organs.

Endomysium

Connective tissue surrounding each individual muscle fiber.

Perimysium

Connective tissue surrounding a fascicle of muscle fibers.

Epimysium

Dense connective tissue surrounding the entire muscle.

Direct Attachment

Epimysium fuses with the periosteum of bone.

Indirect Attachment

Epimysium fuses with tendons or aponeuroses.

Origin

The less mobile attachment site of a muscle.

Insertion

The more mobile attachment site of a muscle.

Myoblasts

Embryonic muscle cells that fuse to form multinucleated skeletal muscle fibers.

Sarcolemma

The plasma membrane of a muscle fiber.

Myofibril

Rod-like contracting structures inside a muscle fiber, composed of myofilaments.

Myofilaments

Filaments (actin, myosin, and titin) that make up myofibrils.

Actin (Thin Filament)

Filament primarily composed of actin; contains active sites for myosin binding.

Myosin (Thick Filament)

Filament with a rod-like tail and globular heads that form cross-bridges.

Titn (Elastic Filament)

Elastic filament that extends from Z-disc to M-line and helps recoil.

Sarcomere

Contractile unit from one Z-disc to the next Z-disc.

Z-disc

Z-line; anchors actin filaments in a sarcomere.

A Band

Dark region where thick (myosin) filaments reside; overlap with thin filaments.

I Band

Light region containing thin (actin) filaments only.

H Zone

Light stripe within the A band where thin and thick filaments do not overlap.

Troponin

Regulatory protein that binds actin and tropomyosin; calcium-regulated.

Tropomyosin

Protein that blocks actin active sites; moved by troponin during contraction.

Calcium (Ca2+)

Ion that triggers contraction by removing inhibitory proteins from actin.

Sarcoplasmic Reticulum (SR)

Extensive network storing Ca2+; releases it to trigger contraction.

T-Tubules

Transverse tubules that conduct action potentials into the muscle fiber.

Triad

Arrangement of two terminal cisternae and a T-tubule around a sarcomere.

Sliding Filament Mechanism

Muscle contraction occurs as thin and thick filaments slide past each other; sarcomeres shorten without filament shortening.

Contraction Cycle

Cycle of events: calcium binds troponin, cross-bridges form, power stroke, detachment by ATP, and re-cocking of myosin heads.

Neuromuscular Junction (NMJ)

Synapse where a motor neuron meets a muscle fiber; voltage changes trigger contraction.

Acetylcholine (ACh)

Neurotransmitter released at the NMJ to stimulate muscle fibers.

Acetylcholinesterase (AChE)

Enzyme that breaks down ACh to stop stimulation of the muscle.

Depolarization

Membrane potential becomes less negative, initiating an action potential.

Repolarization

Membrane potential returns to resting negative value after depolarization.

Excitation–Contraction Coupling

Process linking the action potential in the sarcolemma/T-tubules to Ca2+ release and muscle contraction.

Rigor Mortis

Post-mortem stiffening due to Ca2+ influx and absence of ATP for relaxation.

Muscular Dystrophy

Genetic disorder characterized by progressive muscle weakness and loss of dystrophin.

Dystrophin

Protein that stabilizes the sarcolemma; its deficiency leads to muscular dystrophy.

Botulism

Toxin that blocks ACh release, causing flaccid paralysis.

Myasthenia Gravis

Autoimmune loss of ACh receptors causing weakness that worsens with use.

Neostigmine

Acetylcholinesterase inhibitor used to treat myasthenia gravis.

Pyridostigmine

Acetylcholinesterase inhibitor used to treat myasthenia gravis.

Rhabdomyolysis

Breakdown of muscle tissue releasing myoglobin into the bloodstream; can cause kidney damage.

Contusion

Bruise of muscle tissue from a direct blow.

Plantar Fasciitis

Overstretching of the ligaments on the bottom of the foot.

Hernia

Weakness in the abdominal wall allowing tissue to protrude; inguinal and hiatal are common types.

Delayed Onset Muscle Soreness (DOMS)

Soreness after unfamiliar exercise due to microscopic muscle fiber tears.

Heat Production

Most energy output is released as heat; muscles contribute substantially to body heat.

Motor Unit

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

Muscle Tone

Continuous, partial contraction of muscles to maintain posture and readiness.

Isotonic Contraction (Concentric)

Contraction with movement where the muscle shortens and moves a load.

Isotonic Contraction (Eccentric)

Contraction with movement where the muscle lengthens while contracting.

Isometric Contraction

Contraction with no change in muscle length or joint position.

Treppe (Staircase Effect)

Increased tension with the second stimulation due to still-warmed fibers.

Tetanus (Tetanic Contraction)

Sustained, maximal contraction resulting from high-frequency stimulation.

Length–Tension Relationship

Optimal overlap of actin and myosin at a resting length produces maximal tension.

Motor Unit Recruitment

Activation of more motor units to increase overall muscle force.

EPOC (Oxygen Debt)

Continuation of oxygen use after exercise to restore muscle to resting state. Requires lactic acid conversion, ATP production, CP production, and glycogen regeneration as well as heat dissipation

Cori Cycle

Liver converts lactic acid back to glucose after intense exercise.

Aerobic vs. Anaerobic Respiration

Aerobic uses O2 to produce ATP; anaerobic yields less ATP and produces lactic acid.

Myoglobin

Oxygen-binding pigment in muscle that stores O2 for sustained contraction.