Muscular Tissue Vocabulary

Glossary

A

• Absolute refractory period – The time during which a muscle or nerve cell cannot respond to a new stimulus.
• Acetylcholine (ACh) – A neurotransmitterChemicals that transmit signals across synapses. that stimulates muscle contraction.
• Acetylcholinesterase (AChEAn enzyme that breaks down acetylcholine to stop muscle contraction.) – An enzyme that breaks down acetylcholinealso know as ACh A neurotransmitter that stimulates muscle contraction. to stop muscle contraction.
• ACh receptorsProteins on the motor end plate of the sarcolemma that bind acetylcholine to trigger contraction. – Proteins on the muscle cell membrane that bind acetylcholine to trigger contraction.
• Action potential – A rapid electrical signal traveling along a muscle or nerve cell.
• Actin subunits – the small spheres of actin in the thin filament
• Active site – The location on actin where myosin heads bind during contraction.
• ADPA molecule produced when ATP releases energy. (Adenosine Diphosphate) – A molecule produced when ATPThe energy currency of cells used for muscle contraction. releases energyThe capacity to do work or cause change..
• ADP accumulation – The buildup of ADP in fatigued muscles, reducing contraction efficiency.
• Aerobic respirationThe process of gas exchange, including ventilation, external and internal respiration. – ATP production using oxygen, producing large amounts of energy.
• Anaerobic fermentationprocess of regenerating NAD with either an inorganic or organic compound serving as the final elect – ATP production without oxygen, generating lactate as a byproduct.
• Anaerobic thresholdThe minimum voltage needed to trigger an action potential. – The point where muscles switch from aerobic to anaerobicprocess that does not use oxygen metabolismThe sum of all chemical reactions in the body..
• ATP (Adenosine Triphosphate) – The energy currency of cellsThe basic structural and functional units of life. used for muscle contraction.
• Axon terminal – The end of a motor neuron that releases neurotransmittersChemicals released by neurons to transmit signals across a synapse..

C

• Calmodulin – A protein in smooth muscle that binds calcium to initiate contraction.
• Cardiomyocytes – Heart muscle cells responsible for pumping action.
• Caveolae – Small indentations in smooth muscle cells that aid in calcium storage.
• Complete (fused) tetanusIn this context, sustained muscle contractions due to calcium or electrolyte imbalances. – A sustained, maximal muscle contraction without relaxation.
• Concentric contractions – Muscle contractions where the muscle shortens while generating force.
• Conductivity – The ability of muscle or nerve cells to transmit electrical impulses.
• Contractile proteinsLarge molecules made of amino acids with various functions in the body. – Proteins (actin and myosin) responsible for muscle contraction.
• Contractility – The ability of muscle tissue to shorten with force.
• Contraction – The process of muscle fibers shortening and generating force.
• Contraction phase – The period of increasing muscle tension during a twitch.
• Creatine kinase – An enzyme that helps transfer energy for muscle contraction.
• Creatine phosphate (CP) – A molecule that stores high-energy phosphate to quickly regenerate ATP.
• Cross bridge – The connection formed between myosin heads and actin filaments.

D

• Dark (A) band – The part of the sarcomere containing thick filaments.
• Dense bodies – Structures in smooth muscle that anchor actin filaments.
• Depolarization – The loss of electrical charge across a membrane, triggering an action potentialA rapid, temporary electrical charge that travels along neurons, allowing signal transmission..
• Dystrophin – A protein that stabilizes muscle cell membranes.

E

• Eccentric contractionsMuscle contractions where the muscle lengthens while generating force. – Muscle contractions where the muscle lengthens while generating force.
• Elasticity – The ability of muscle fibers to return to their original length.
• Electrochemical gradient – The difference in charge and ion concentration across a membrane.
• Electrolyte loss – The depletion of ionsCharged atoms or molecules. like sodium(Na⁺): Major ECF cation; important for fluid balance, nerve function. and potassium(K⁺): Major ICF cation; essential for muscle and nerve function., affecting muscle function.
• Endomysium – A connective tissue layer surrounding individual muscle fibers.
• End-plate potential (EPP) – A localized depolarizationThe loss of electrical charge across a membrane, triggering an action potential. at the neuromuscular junctionThe connection between a motor neuron and a muscle fiber..
• Endurance exercise – Physical activity that improves oxygen use in muscles.
• Epimysium – A connective tissue sheath covering an entire muscle.
• Excess post-exercise oxygen consumption (EPOCThe extra oxygen used to restore muscle function after exercise.) – The extra oxygen used to restore muscle function after exercise.
• Excitability – The ability of muscle fibers to respond to stimuliChanges in the environment that are detected by sensory receptors..
• Excitation – The process of stimulating a muscle fiber to contract.
• Excitation-contraction coupling – The link between muscle excitation and contraction.
• Extensibility – The ability of a muscle to stretch without being damaged.

F

• Fast glycolytic fibers – Muscle fibers specialized for short bursts of powerful movementA fundamental property of life involving motion of the body or its parts..
• Fast oxidative fibersMuscle fibers that use both aerobic and anaerobic energy. – Muscle fibers that use both aerobic and anaerobic energy.
• Fatigue – A decline in muscle power due to prolonged activity.
• Fibrous (F) actin – A form of actin found in muscle filaments.
• Fuel depletion – The exhaustion of energy sources in muscle tissue.

G

• Gap junctionsCell connections that allow ion flow between adjacent muscle cells. – Cell connections that allow ion flow between adjacent muscle cells.
• Globular (G) actin – The monomer subunit of actin filaments.
• Glycogen – A stored form of glucoseA simple sugar that is the main source of energy for cells. in muscles and the liverA large organ that produces bile, detoxifies blood, and stores nutrients..
• Glycogen-lactate system – A metabolic pathway providing ATP during anaerobic conditions.

H–M

• H zoneThe middle of the sarcomere where only thick filaments are present. – The middle of the sarcomere where only thick filaments are present.
• Incomplete tetanus – A muscle contraction with brief periods of relaxation between stimuli.
• Intercalated discs – Structures in cardiac muscle that allow electrical connectivity.
• Internal tension – Tension generated inside the muscle fiber.
• Involuntary – Muscle actions not under conscious control.
• Isometric contractionsMuscle contractions that generate force without changing length. – Muscle contractions that generate force without changing length.
• Isotonic contractionsMuscle contractions that generate force while changing length. – Muscle contractions that generate force while changing length.
• Junctional folds – Infoldings of the sarcolemma that increase surface area at the NMJ.
• Lactate threshold – The point during exercise where lactate accumulates faster than it can be removed.
• Latch-bridge mechanism – A process that allows smooth muscle to sustain contractions with little energy.
• Latent period – The short delay between muscle stimulation and contraction.
• Length-tension relationship – The relationship between sarcomere length and contraction force.
• Light (I) Bands – The part of the sarcomere containing only thin filaments

M–R

• M lineThe middle line of a sarcomere that stabilizes thick filaments. – The middle line of a sarcomere that stabilizes thick filaments.
• Maximum oxygen uptake – The highest amount of oxygen muscles can use during exercise.
• Motor end plate – The part of the muscle fiber membrane involved in neuromuscular transmission.
• Motor unit – A motor neuron and all the muscle fibers it controlsVariables that remain constant to ensure a fair test..
• MyoblastsMuscle cell precursors. – Muscle cell precursors.
• MyofibrilsCylindrical structures within muscle fibers that contain myofilaments. – Cylindrical structures within muscle fibers that contain myofilaments.
• Myosin – A thick filament protein that helps in muscle contraction.
• Neuromuscular junction (NMJ) – The connection between a motor neuron and a muscle fiber.
• Neurotransmitters – Chemicals that transmit signals across synapses.
• Oxygen debt – The amount of oxygen needed to restore muscle energy levels after exercise.
• Perimysium – A connective tissue sheath surrounding muscle fasciclesBundles of nerve fibers within a nerve.
  or
  Bundles of nerve fibers within a muscle..
• Phosphagen system – The immediate energy system for muscle contraction.

S–Z

• Sarcolemma – The plasma membraneThe outer boundary of a cell that controls what enters and exits. of a muscle fiber.
• Sarcomere – The functional contractile unit of muscle fibers.
• Sarcoplasm – The cytoplasmThe gel-like substance within a cell that contains organelles and cytosol. of a muscle fiber.
• Sarcoplasmic reticulum (SR) – A specialized organelle that stores calcium for muscle contraction.
• Sliding filament theoryA well-tested and widely accepted explanation. – The concept that muscles contract by actin and myosin sliding past each other.
• Slow oxidative fibers – Muscle fibers specialized for endurance activities.
• Temporal summation – The addition of multiple stimuli to increase contraction strength.
• Terminal cisterns – Enlarged areas of the sarcoplasmic reticulum that store calcium.
• Tropomyosin – A protein that blocks active sites on actin when a muscle is relaxed.
• Troponin – A protein that binds calcium and moves tropomyosin during contraction.
• Wave summation – The increasing force of contraction with repeated stimulation.
• Z discThe boundary of a sarcomere that anchors actin filaments. – The boundary of a sarcomere that anchors actin filaments.