Muscle Physiology - Ch. 8

striated / unstriated

cardiac and skeletal muscle have a ___________ appearance while smooth muscle is ________

muscle fiber

a single skeletal muscle cell

myofibrils

specialized contractile elements, consists of a regular arrangement of thick and thin filaments; makes up 80% of volume of muscle fiber

myosin

thick filaments; lie only within A band

actin

thin filaments

A band

made up of a stacked set of thick filaments along with portions of thin filaments that overlap both ends of the thick filaments

H zone

lighter area in the middle of the A band and thin filaments do not reach, contains only the central portions of the thick filaments

I band

consists of the remaining portion of the thin filaments that do not project into the A band

Z line

dense, vertical line, boundaries create a sarcomere

sarcomere

functional unit of skeletal muscle, the area between the two z-lines; smallest component of muscle fiber that can contract

myosin molecule

protein consisting of two identical subunits, shaped like a golf club

actin molecules

primary structural proteins of the thin filaments; each contain a special bonding site for attachment with a myosin cross bridge

sliding filament theory

cross bridge interaction between actin and myosin brings about muscle contraction; thin filaments slide inward and sarcomere shortens

power stroke

occurs when myosin and actin make contact at a cross bridge, the bridge changes shape, binding inward toward the center of the sarcomere

transverse tubule (T-tubule)

runs perpendicularly from the surface of the muscle cell membrane into the central portions of the muscle fiber

sarcoplasmic reticulum

modified ER, a fine network of interconnected membrane-enclosed compartments surrounding each myofibril; Calcium stored in

calcium

spread of an action potential down a T-tuble triggers opening of ___________ channels in lateral sacs

ATPase site

enzymatic site that can bind to ATP and split to ADP before cross bridges form, creates high energy state of myosin

rigor mortis

skeletal muscle is locked in place because no more ATP is available to detach the cross bridges

relaxation

occurs when calcium is returned to the sarcoplasmic reticulum when local electrical activity stops and contractile process is turned off

whole muscle

groups of muscle fibers bundled up together and attached to bone

tendons

collagenous connective tissue that attaches muscle and bone

twitch

brief, weak contraction produced by a single action potential

one

each muscle fiber is supplied by ______ motor neuron

motor unit

one motor neuron plus all the muscle fibers its innervates

twitch (wave) summation

two twitches from two action potentials sum together to produce greater tension in the fiber than that produced by a single action potential

tetanus

occurs when a muscle fiber is stimulated so rapidly that its does not have a chance to relax at all between stimuli, a smooth, sustained contraction of maximal strength

aerobic

presence of oxygen (oxidative phosphorylation)

phosphocreatine (creatine phosphate)

high energy compound, can give up a high energy state phosphate group to convert ADP to ATP; low supply in muscle and used up quickly.

anaerobic glycolysis

pyruvate molecules are processed to produce ATP and end product is lactate.

lactic acid

formed by anaerobic glycolysis

anaerobic

with out oxygen

red fibers

contain a high amount of hemoglobin which attract and attach to oxygen

myoglobin

can store and increase the rate of transfer from the blood into the muscle fibers, gives fibers a red color

hypertrophy

increase in cross-sectional area of muscle/muscle enlargement, number of myofilaments increase; fiber thickening resulting from synthesis of myosin and actin filaments

atrophy

muscles that are immobilized, not being stimulated to produce force caused myosin and actin content to decrease; muscle mass decreases

epimysium

connective tissue covering the entire muscle

endomysium

connective tissue covering individual muscle cells

fascicle

bundle of fibers, covered by perimysium

perimysium

connective tissue covering muscle fiber bundles (fascicles)