Muscular System

Fascia

sheet of dense connective tissue that separates individual muscles and helps hold them in position

Epimysium

sheath of connective tissue that surrounds a skeletal muscle (beneath the fascia)

Perimysium

sheath of connective tissue that encloses a bundle of skeletal muscle fibers (fascicle)

Endomysium

sheath of connective tissue surrounding each skeletal muscle fiber

Tendon

cordlike connective tissue that connects muscle to bone

Tendinitis

inflammation of a tendon

Sprain

an injury to the ligament

Strain

an injury to a muscle or tendon

Skeletal muscle fiber

single cell that contracts (exerts a pulling force) in response to stimulation and relaxes when stimulation ends; also known as myofiber

Sarcolemma

the cell membrane in a muscle cell

Sarcoplasm

the cytoplasm in a muscle cell

Myofibril

contractile fiber in striated muscle cells that play a fundamental role in contractions

Sarcomere

structural unit of a myofibril and the functional unit of muscle contraction

Sarcoplasmic Reticulum

membranous network of channels and tubules within a muscle fiber; stores calcium ions

Transverse tubules

membranous channels that extend deep inward into the cell from the sarcolemma

Neuromuscular Junction

synapse between a motor neuron and a skeletal muscle fiber

Myosin

two twisted protein strands with globular heads; part of the thick filament

Actin

globular proteins with a binding site for myosin heads to attach; part of the thin filament

Troponin

complex of three proteins associated with tropomyosin

Tropomyosin

regulatory protein that blocks the myosin binding site on actin

Sliding Filament Model

the model for muscle contraction in which muscle proteins slide past each other to generate force

Rigor Mortis

the condition in which skeletal muscles partially contract and become rigid after death

Muscular Dystrophy

X-linked disorder caused by the mutation of the protein dystrophin; no anchoring of actin to the sarcolemma

Botulinum Toxin

neurotoxin produced by the bacteria clostridium bacterium; prevents fusion of acetylcholine to the cell membrane and leads to paralysis of muscles

Myasthenia Gravis

autoimmune disease caused by antibodies attaching ACh receptors on the sarcolemma; results in less muscle contraction

Creatine Phosphate

molecule in muscle that stores extra energy in phosphate bonds

Hemoglobin

oxygen-carrying protein in red blood cells

Myoglobin

oxygen-storing protein in muscle tissue

Oxygen Debt

the amount of oxygen that liver cells require, after anaerobic exercise, to convert the accumulated lactic acid into glucose, plus the amount muscle cells require to restore ATP and creatine phosphate to their original concentrations and return blood and tissue oxygen levels to normal

Fatigue

a condition where a muscle, after being exercised strenuously for an extended period, experiences a decreased ability to contract

Cramp

a painful condition in which a muscle undergoes a sustained involuntary contraction

Fast Twitch Fibers

fibers that fatigue easily, produce new filaments of actin & myosin and enlarge muscle fibers also known as white fibers

Slow Twitch Fibers

fibers that are fatigue resistant; develop more mitochondria & capillary networks; also known as red fibers

Muscular Hypertrophy

the enlargement of muscles that are forcefully exercised

Muscular Atrophy

the decrease in size and strength of an unused muscle

Twitch

single contraction of a muscle fiber followed by relaxation

Threshold Stimulus

minimum strength of stimulation required to cause a contraction

Latent Period

time between a stimulus and the beginning of a response in a muscle fiber

Summation

the combination of individual twitches where the muscle is unable to relax

Tetanus

a sustained contraction caused by high frequency stimulation that lacks any relaxation

Motor Unit

a motor neuron and the muscle fibers that it controls

Recruitment

increase in the number of motor units taking place in a muscle contraction

Muscle Tone

ongoing low-level contraction of some fibers in otherwise resting skeletal muscle

Isotonic Contraction

a contraction that creates force and moves a load by shortening the muscle

Isometric Contraction

a contraction that creates force without shortening

Origin

end of a muscle that attaches to a relatively immovable part

Insertion

end of a muscle attached to a moveable part

Prime Mover

muscle that provides most of the particular body movement; also called an agonist

Synergist

muscle that assists the action of an agonist

Antagonist

muscle that opposes a particular movement

Acetylcholine (ACh)

neurotransmitter that stimulates muscle fibers

Motor End Plate

specialized muscle fiber membrane that contains receptors for neurotransmitters