Muscle Tissue and Physiology Vocabulary

Vocabulary flashcards covering key terms and concepts from Chapter 10: Muscle Tissue and Physiology.

Muscle Tension

The force generated by muscle tissue that creates movement, maintains posture, stabilizes joints, generates heat, and regulates material flow through hollow organs.

Myocytes

Individual muscle cells that make up muscle tissue along with the surrounding extracellular matrix.

Endomysium

The extracellular matrix surrounding muscle cells that holds them together and transmits tension to neighboring cells.

Skeletal Muscle Tissue

Voluntary muscle tissue consisting of long, thin, striated, multinucleated cells arranged parallel to each other and mostly attached to the skeleton.

Cardiac Muscle Tissue

Involuntary striated muscle tissue found only in the heart, consisting of short, wide, branching cells with intercalated discs and one or two nuclei.

Smooth Muscle Tissue

Involuntary non-striated muscle tissue consisting of long, flattened cells with two pointed ends and a single central nucleus, lining hollow organs, skin, eyes, and gland ducts.

Intercalated Discs

Specialized cell junctions in cardiac muscle tissue containing modified gap junctions and tight junctions that unite cells for coordinated contraction as a single unit.

Contractility

The ability of muscle cells to contract, where cellular proteins draw closer together.

Excitability

The ability of a cell to respond to a chemical, mechanical, or electrical stimulus.

Conductivity

The ability of a cell to conduct electrical charges across its plasma membrane.

Distensibility

The ability of a cell to be stretched without being ruptured.

Elasticity

The ability of a cell to return to its original length after being stretched.

Sarcoplasm

The cytoplasm of a muscle cell.

Sarcolemma

The plasma membrane of a muscle cell.

Myofibrils

Cylindrical bundles of specialized proteins in a muscle cell involved in muscle contraction, measuring about $1\,\mu\text{m}$ in diameter and occupying 50–80% of the cell volume.

Sarcoplasmic Reticulum (SR)

A modified smooth endoplasmic reticulum surrounding each myofibril that stores and releases calcium ions.

Myoblasts

Embryonic cells that fuse together during development to form multinucleated skeletal muscle fibers.

Transverse Tubules (T-tubules)

Inward extensions of the sarcolemma that form a tunnel-like network diving into the muscle fiber and surrounding each myofibril.

Terminal Cisternae

Enlarged portions of the sarcoplasmic reticulum that flank each side of a Transverse tubule.

Triad

A three-structure complex composed of a single T-tubule flanked on both sides by terminal cisternae.

Myofilaments

Protein bundles within myofibrils composed of contractile, regulatory, and structural proteins.

Thick Filaments

Myofilaments with the largest diameter, composed of intertwining chains and globular heads of the contractile protein myosin.

Thin Filaments

Myofilaments composed of the contractile protein actin along with the regulatory proteins tropomyosin and troponin.

Actin

A bead-shaped contractile protein in thin filaments containing active sites that bind to myosin heads.

Tropomyosin

A long, ropelike regulatory protein that spirals around actin strands and blocks actin's active sites when the muscle is at rest.

Troponin

A small globular regulatory protein that holds tropomyosin in place over actin's active sites.

Nebulin

A structural protein that regulates and sets the length of thin filaments in myofibrils.

Elastic Filaments

The thinnest myofilaments, composed of the massive spring-like structural protein titin.

Titin

A massive, spring-shaped structural protein in elastic filaments that anchors thick filaments, resists excessive stretching, and provides elasticity.

Dystrophin

A structural protein in skeletal and cardiac muscle fibers that anchors the sarcolemma to the endomysium and myofibrils.

Duchenne Muscular Dystrophy (DMD)

A degenerative muscular disease occurring almost exclusively in boys, caused by a defective gene for the structural protein dystrophin.

Sarcomere

The functional contractile unit of a myofibril, extending from one Z-disc to the next Z-disc.

I Band

The light region of a sarcomere striation that contains only thin filaments.

A Band

The dark region of a sarcomere striation that contains thick filaments as well as overlapping thin filaments.

H Zone

The middle region of an A band that contains only thick filaments.

M Line

A dark line in the center of the A band consisting of structural proteins that hold thick filaments in place.

Z-disc

A line composed of structural proteins that bisects the I band, anchors thin and elastic filaments, and attaches adjacent myofibrils to one another.

Sliding-Filament Mechanism

The process of muscle contraction where thin filaments slide past thick filaments toward the M line, shortening the sarcomere without altering filament length.

Electrophysiology

The branch of physiology that studies electrical charges across plasma membranes and their accompanying physiological processes.

Electrical Gradient

A separation of unequal positive and negative electrical charges across a barrier, such as a cell plasma membrane.

Voltage

The difference in electrical potential energy between two points, measured in millivolts ($\text{mV}$) across cell membranes.

Resting Membrane Potential

The voltage difference across the plasma membrane of an unstimulated cell, measuring approximately $-90\,\text{mV}$ in skeletal muscle fibers.

Polarized

The state of a cell membrane when its electrical potential is not at $0\,\text{mV}$, but measures to either a positive or negative value.

Leak Channels

Membrane ion channels that remain open continuously, allowing ions to diffuse down their concentration gradients.

Gated Channels

Membrane ion channels that are closed at rest and open only in response to specific chemical or electrical stimuli.

Ligand-Gated Channels

Ion channels in the plasma membrane that open or close in response to the binding of a specific chemical signal (ligand).

Voltage-Gated Channels

Ion channels in the plasma membrane that open or close in response to changes in membrane potential.

Sodium-Potassium Ion Pump

An active transport pump ($\text{Na}^+/\text{K}^+$ ATPase) that uses ATP to move three sodium ions out of the cell and two potassium ions into the cell.

Electrochemical Gradient

The sum of the concentration gradient and electrical gradient driving the movement of an ion across a membrane.

Action Potential

A quick, temporary reversal and restoration of membrane potential across a region of the plasma membrane.

Depolarization

The initial stage of an action potential where voltage-gated $\text{Na}^+$ channels open, allowing $\text{Na}^+$ entry and making the membrane potential positive (peaking around $+30\,\text{mV}$).

Repolarization

The stage of an action potential where $\text{Na}^+$ channels close and voltage-gated $\text{K}^+$ channels open, allowing $\text{K}^+$ efflux to restore the negative resting potential ($-90\,\text{mV}$).

Neuromuscular Junction (NMJ)

The functional synapse between a motor neuron axon terminal and the motor end plate of a skeletal muscle fiber.

Axon Terminal

The swollen bulb at the end of a motor neuron axon that contains synaptic vesicles filled with neurotransmitters.

Acetylcholine (ACh)

The neurotransmitter stored in motor neuron synaptic vesicles that triggers action potentials in skeletal muscle fibers.

Synaptic Cleft

The narrow extracellular space between the axon terminal and the motor end plate into which ACh is released.

Motor End Plate

A specialized, highly folded region of the sarcolemma that contains receptors for acetylcholine.

End-Plate Potential

A local depolarization at the motor end plate produced by cation influx through ACh-gated channels.

Acetylcholinesterase (AChE)

An enzyme in the synaptic cleft that rapidly degrades acetylcholine to end muscle stimulation.

Crossbridge

The binding structure formed when a cocked myosin head attaches to an exposed active site on an actin subunit.

Power Stroke

The pivoting action of a myosin head following phosphate release that pulls the thin filament toward the M line.

Rigor Mortis

The progressive stiffening of skeletal muscles starting 3–4 hours postmortem due to ATP depletion, which prevents calcium pumping and myosin head detachment.

Creatine Phosphate

A high-energy cytosolic compound that rapidly donates a phosphate group to ADP to synthesize ATP during initial muscle activity.

Creatine Kinase

The enzyme that catalyzes the transfer of a phosphate group between creatine phosphate and ADP.

Glycolytic Catabolism

An anaerobic metabolic process in cytosol that breaks down glucose into two pyruvate molecules, producing a net yield of $2\,\text{ATP}$.

Oxidative Catabolism

An aerobic metabolic process in mitochondria that uses oxygen to break down fuel molecules and yield large amounts of ATP.

Myoglobin

An oxygen-binding protein in muscle cells that stores oxygen for use during oxidative catabolism.

Muscle Twitch

The brief response and contraction of a single muscle fiber to a single action potential from a motor neuron.

Myogram

A laboratory recording of muscle tension generated over time during a twitch or contraction cycle.

Latent Period

The $1\text{--}2\,\text{ms}$ delay between stimulus arrival and tension development, during which the action potential spreads across the sarcolemma.

Contraction Period

The phase of a muscle twitch during which crossbridge cycling actively generates increasing tension.

Relaxation Period

The phase of a muscle twitch during which cytosolic calcium decreases and tension declines, lasting $10\text{--}100\,\text{ms}$.

Refractory Period

The brief time interval (about $5\,\text{ms}$) following stimulation during which a muscle fiber cannot respond to another stimulus.

Wave Summation

The addition of successive twitches resulting in greater total tension when a muscle fiber is stimulated repeatedly before fully relaxing.

Unfused Tetanus

A state of sustained, pulsating muscle tension produced when a fiber is stimulated approximately 50 times per second.

Fused Tetanus

A smooth, continuous maximal muscle contraction produced when stimulation frequency reaches 80–100 times per second without relaxation between stimuli.

Optimal Length

The resting length of a sarcomere at which the maximum number of crossbridges can form, allowing maximal tension production.

Type I Fibers

Slow-twitch, slow oxidative muscle fibers with small diameter, high myoglobin content, numerous mitochondria, and high fatigue resistance.

Type II Fibers

Fast-twitch muscle fibers with high myosin ATPase activity that contract rapidly, rely heavily on glycolytic catabolism, and fatigue quickly.

Motor Unit

A single motor neuron together with all the individual muscle fibers it innervates.

Recruitment

The activation of additional motor units to produce greater contraction force as required by a muscle.

Muscle Tone

The continuous, small amount of involuntary tension maintained in a relaxed muscle by alternating active motor units.

Hypotonia

An abnormal condition characterized by abnormally low muscle tone, causing muscles to feel loose and soft.

Hypertonia

An abnormal condition characterized by abnormally high muscle tone, causing muscles to feel rigid or hard.

Isotonic Concentric Contraction

A muscle contraction in which generated force exceeds the external load, causing the muscle to shorten.

Isotonic Eccentric Contraction

A muscle contraction in which generated force is less than the external load, causing the muscle to lengthen under tension.

Isometric Contraction

A muscle contraction in which muscle length remains unchanged because generated force equals the load or the load is immovable.

Delayed-Onset Muscle Soreness (DOMS)

Post-exercise muscle soreness caused by minor structural damage to myofilaments, predominantly from isotonic eccentric contractions.

Principle of Myoplasticity

The rule stating that a muscle fiber will alter its internal structure and biochemistry to adapt to functional demands.

Hypertrophy

An increase in muscle fiber diameter and myofibril count resulting from resistance training.

Atrophy

A decrease in muscle fiber diameter and loss of myofibrils resulting from physical inactivity or disuse.

Muscle Fatigue

The inability of a muscle to maintain a given level of exercise intensity due to metabolite depletion, chemical accumulation, or oxygen deficits.

Excess Postexercise Oxygen Consumption (EPOC)

The elevated rate of oxygen consumption post-exercise required to dissipate heat, restore ion gradients, and correct metabolic disturbances.

Peristalsis

Rhythmic waves of alternating smooth muscle contraction and relaxation that propel contents through hollow organs.

Pacemaker Cells

Specialized non-contractile cells that spontaneously depolarize in a rhythmic fashion to initiate contraction waves in smooth or cardiac muscle.

Calmodulin (CaM)

A cytosolic calcium-binding protein in smooth muscle that activates myosin light-chain kinase when bound to calcium ions.

Myosin Light-Chain Kinase (MLCK)

An enzyme in smooth muscle activated by the calcium-calmodulin complex that phosphorylates myosin ATPase to initiate crossbridge cycling.

Latch State

A condition in smooth muscle cells where crossbridges remain attached long-term, maintaining tension with minimal ATP consumption.

Single-Unit Smooth Muscle

Visceral smooth muscle tissue with cells coupled by gap junctions that contract together as a single synchronized unit.

Multi-Unit Smooth Muscle

Smooth muscle tissue composed of independent cells controlled individually by nerves for precise force regulation.