APk2100c - Ch. 10: The Muscular System

contractility, excitability, extensibility, elasticity

(4) functional properties of muscle that distinguish it from other tissues

contractility

property of muscle tissue: forceful shortening of muscle cells via myofilaments

excitability

property of muscle tissue: nerve cells send signals that travel the length of the muscle cell membrane, initiating a response

extensibility

property of muscle tissue: can be stretched (either by opposing muscle contraction, in skeletal muscles, or by contents of the organ, in smooth muscle-lined hollow organs)

elasticity

property of muscle tissue: recoils passively to resting length

sarcolemma

plasma membrane of a muscle cell

sarcoplasm

cytoplasm of a muscle cell

sarcoplasmic reticulum

specialized endoplasmic reticulum of muscle cells; stores calcium

produce movement, open and close passageways, maintain posture and stabilize joints, generate heat

(4) main functions of muscle tissue

striated muscle

muscle consisting of cross-striped fibers; skeletal and cardiac muscle

muscle fibers

either a smooth or skeletal muscle cell; long, slender, and cyllindrical; multinucleated

epimysium

a sheath of dense irregular CT proper covering a muscle (organ)

fascicle

discrete bundle of muscle cells, segregated from the rest of the muscle by a dense irregular CT sheath

perimysium

a sheath of dense irregular CT proper covering a fascicle

endomysium

a sheath of loose (areolar) CT proper covering a myofibril

myofibril

rodlike contractile organelle that occupies most of the muscle cell volume; composed of sarcomeres and arranged withs bands aligned to adjacent members

sarcomere

the contractile unit of a myofibril, composed of contractile proteins

thick (myosin) filaments

located in the center of the sarcomere; contain ATPase enzymes

thin (actin) filaments

extend from Z disc toward the center of the sarcomere; contain contractile protein as well as regulator proteins troponin and tropomyosin

cardiac muscle

muscle tissue of the heart wall

smooth muscle

musculature consisting of spindle-shaped, nonstriated muscle cells; present in the wall of most visceral organs

visceral muscle

muscle connected to internal organs; cardiac and smooth muscle

tendon

cord of dense regular CT proper that attached muscle to bone; continuous with epimysium, perimysium, and endomysium

origin

attachment of a muscle that remains relatively fixed during muscular contraction

insertion

movable part or attachment of a muscle

direct (fleshy) attachment

epimysium fused to periosteum of bone or perichondrium of cartilage

indirect attachment

connective tissue wrappings extend beyond muscle as ropelike tendon or sheetlike aponeurosis

aponeurosis

fibrous sheet connecting a muscle to the body part it moves

Z discs

narrow, plate-shaped regions of dense material that separate one sarcomere from the next; runs through the center of an I band

actin

contractile protein composing most of the thin filaments in a scarcomere

troponin

globular regulatory protein that binds to actin, tropomyosin, and calcium; attached tropomyosin to actin molecule

tropomyosin

thin, strand-like regulatory protein that spirals around actin molecule, covering binding sites for the thick myofilament, myosin

A band

dark area in a sarcomere; extends length of the thick filaments (including overlap with thin filaments)

H zone

the central part of an A band, where no thing filaments reach

M line

supporting proteins that hold the thick filaments together in the H zone

I bands

two regions on either side of an A band that contain only thin filaments

titin

springlike molecule in sarcomeres that resists overstretching; extend from Z disc to thick filament and run within the thin filament to attach to the M line

Holds thick filaments in place; helps recoil after stretch; resists excessive stretching

functions (3) of titin

terminal cisterns

dilated end-sacs of sarcoplasmic reticulum that form perpendicular cross channels over A-I junctions

T (transverse) tubules

invagination of the sarcolemma that conduct action potentials to the deepest regions of the muscle fiber

triad

complex of the T-tubule flanked by two terminal cisterns

concentric contraction

muscle shortens and does work

eccentric contraction

muscle generates force as it lengthens

sliding filament mechanism

how thick and thin filaments slide relative to one another during striated muscle concentric contraction to decrease sarcomere length

motor neurons

nerve cells that innervate muscle fibers

Neuromuscular Junction (NMJ)

synapse between the axon terminal of a motor neuron and the section of the membrane of a muscle fiber with receptors for the acetylcholine released by the terminal

synaptic cleft

the narrow gap that separates the presynaptic neuron from the postsynaptic muscle cell

Acetylcholine (ACh)

the neurotransmitter that triggers muscle contraction

active

exocytosis of neurotransmitters from an axon terminal is an __________ process

Acetylcholinesterase (AChE)

the enzyme that breaks down acetylcholine in the synaptic cleft; stored in the basal lamina of the sarcolemma's invaginations

motor unit

a motor neuron and all the fibers it innervates

fine

muscles that require _______ control have few muscle fibers per motos unit

powerful

muscles that require _____________ movement have many muscle fibers per motor unit

recruitment

the addition of motor units to accomplish a movement; the more force required, the more motor units are stimulated

slow oxidative fibers (SO)

obtain energy from aerobic metabolic interactions; least powerful

myoglobin

oxygen-binding pigment in muscle fibers; its concentration determines how "dark" a muscle fiber appears under a microscope

postural muscles

slow-oxidative fibers are resistant to fatigue, and are therefore found in large proportion in...

Fast Glycolytic Fibers (FG)

obtain energy via anaerobic pathways; contain few mitochondria but many glycosomes; most myofilaments per fiber; most powerful

Fast Oxidative Fibers (FO)

"intermediate" muscle fibers in terms of myoglobin concentration, fiber diameter, power, and energy pathway

lower limbs

fast oxidative fibers are not as powerful or fast as FG fibers, but more fatigue-resistant than SO fibers; therefore, they are found in abundance in the...

satellite cells

small immature muscle cells scattered in muscle tissue outside fibers; when myofilaments increase in number (due to resistance training), they fuse with the stimulated fibers to contribute the additional nuclei needed to accommodate the protein demands of the additional myofilaments