anatomy chapter 10

functions of muscular tissue

producing body movements, stabilizing body positions, storing and mobilizing substances within the body, generating heat

properties of muscular tissue

electrical excitability, contractility, extensibility, elasticity

skeletal muscle tissue

striated; works mainly in a voluntary manner

cardiac muscle tissue

striated; forms most of the heart wall, works mainly in an involuntary manner

smooth muscle tissue

nonstriated; located in the walls of hollow internal structures (blood vessels, airways, most organs in the abdominopelvic cavity), skin, and hair follicles; works mainly in an involuntary manner

electrical excitability

ability to respond to certain stimuli by producing electrical signals (action potentials)

contractility

ability of muscular tissue to contract forcefully when stimulated by a nerve impulse

extensibility

ability of muscular tissue to stretch, within limits, without being damaged

elasticity

ability of muscular tissue to return to its original length and shape after contraction or extension

subcutaneous tissue

separates muscle from skin, composed of areolar and adipose CT

epimysium

the outer layer, encircling the entire muscle, consists of dense irregular CT

perimysium

a layer of dense irregular CT that surrounds groups of 10-100 muscle fibers

endomysium

penetrates the interior of each muscle fascicle and separates individual muscle fibers from one another, mostly reticular fibers

tendon

attaches a muscle to the periosteum of a bone

sarcolemma

plasma membrane of a muscle fiber

T tubules

tunnel in from the surface toward the center of each muscle fiber, open to the outside of the fiber and are filled with interstitial fluid

sarcoplasm

the cytoplasm of a muscle fiber

myoglobin

red-colored protein, found only in muscle; binds oxygen molecules that diffuse into muscle fibers

myofibrils

contractile organelles of skeletal muscle; extend the entire length of a muscle fiber; prominent striations make the entire skeletal muscle fiber appears striped

sarcoplasmic reticulum

encircles each myofibril, fluid filled system of membranous sacs

terminal cisterns

dilated end sacs of the sarcoplasmic reticulum

triad

three; T tubule and two terminal cisterns

sarcomeres

basic functional units of a myofibril; extend from one Z disc to another

Z discs

narrow, plate-shaped regions of dense protein material, separate one sarcomere from the next

A band

darker middle part of the sarcomere

I band

lighter, less dense area that contains the rest of the thin filament but no thick filmanets

H band

narrow in the center of each A band, contains thick but not thin filaments

M line

middle of the sarcomere; supporting proteins that hold the thick filaments together at the center of the H band

myosin

main component of thick filaments and functions as a motor protein in all three types of muscle tissue

motor proteins

pull various cellular structures to achieve movement by converting chemical energy in ATP to the mechanical energy of motion; production of force

myosin tail

twisted golf club handles; points toward the M line in the center of the sarcomere; tails of neighboring myosin molecules lie parallel to one another, forming the shaft of the thick filament

myosin head

two projections of each myosin molecules, with two binding sites (1. actin-binding site and 2. ATP-binding site)

actin

THIN protein molecules join to form an actin filament that is twisted into a helix; contain a myosin-binding site where a myosin head can attach

tropomyosin and troponin

regulatory proteins in thin filament; strands of tropomyosin cover myosin-binding sites on actin in relaxed muscle

contractile

myosin and actin

regulatory

troponin and tropomyosin

contractile proteins

proteins that generate force during muscle contractions

structural proteins

align thick and thin filaments properly, provide elasticity and extensibility, link myofibrils to the sarcolemma (titan, myosin, nebula, dystrophin)

somatic motor neurons

neurons that stimulate skeletal muscle fibers to contract

neuromuscular junction (NMJ)

muscle action potentials arise here; the synapse between a somatic motor neuron and a skeletal muscle fiber

synapse

a region where communication occurs between two neurons, or between a neuron and a target cell; between a somatic motor neuron and a muscle fiber

synaptic cleft

a small gap at most synapses; separates the two cells; action potentials can “jump the gap”

neurotransmitter

chemical released by the initial cell communicating within the second cell

synaptic vesicles

sacs suspended within the synaptic end bulb containing molecules of the neurotransmitter acetylcholine

motor end plate

the region of the muscle cell membrane opposite the synaptic end bulbs; contain acetylcholine receptors

step 1 of muscle action potential

voltage-gated calcium channels in a neuron’s synaptic end bulb open, resulting in an influx of calcium; causes exocytosis of a neurotransmitter into the synaptic cleft

step 2 of muscle action potential

neurotransmitter binds to ligand-gated sodium channels on the motor endplate; influx of sodium into the muscle

step 3 of muscle action potential

depolarization of muscle, calcium release from sarcoplasmic reticulum

step 4 of muscle action potential

neurotransmitter gets broken down by acetylcholinesterase

excitation-contraction coupling

connects events of a muscle action potential with sliding filament mechanism

sliding filament mechanism

myosin pulls on actin, causing the thin filament to slide inward; Z disc move toward each other and sarcomere shortens; transmission of force throughout the entire muscle, resulting in whole muscle contraction

step 1 of contraction cycle

myosin head hydrolyzes ATP and becomes energized and oriented

step 2 of contraction cycle

myosin head binds to actin, forming a cross-bridge

step 3 of contraction cycle

myosin head pivots, pulling the thin filament past the thick filament toward center of the sarcomere; power stroke

step 4 of contraction cycle

as myosin head binds ATP, the cross bridge detaches from actin

how we move

as cells of a skeletal muscle start to shorten, they pull on CT coverings and tendons that become taught, tension passes through tendons to pull on bones

ATP

inside muscle fibers powers contraction for only a few seconds, must be produced by the muscle fiber after reserves are used up

creatine phosphate

energy-rich molecule that is founding muscle fibers; creatine catalyzes the transfer of one of the high-energy phosphate groups from ATP to creatine, forming creatine and ADP; 3-6x more plentiful than ATP in sarcoplasm of relaxed muscle fiber

anaerobic cellular respiration

breakdown of glucose gives rise to lactic acid when oxygen is absent or at a low concentration; each molecule of glucose yields 2 molecules of lactic acid and 2 molecules of ATP

aerobic cellular respiration

series of oxygen-requiring reactions that produce ATP, CO2, water and heat; yields more ATP than anaerobic; supplies enough ATP for muscles during periods of rest or light to moderate exercise provided sufficient oxygen and nutrients

oxygen consumption after exercise

heavy breathing continues and oxygen consumption remains above the resting level to “repay” the oxygen debt

muscle fatigue

inability of a muscle to maintain force of contraction after prolonged activity

factors that contribute to muscle fatigue

inadequate release of calcium ions from the SR, depletion of creatine phosphate, insufficient oxygen, depletion of glycogen and other nutrients, buildup of lactic acid and ADP, failure of the motor neuron to release enough acetylcholine

oxygen debt

added oxygen, over and above the resting oxygen consumption, that is taken into the body after exercise, used to “pay back” or restore metabolic conditions to resting level

types of skeletal muscle fibers

slow oxidative, fast oxidative-glycolytic, fast glycolytic

slow oxidative fibers

appear dark red because of myoglobin and many blood capillaries; have many large mitochondria, fibers generate ATP mainly by aerobic respiration; very resistant to fatigue and are capable of prolonged contractions for many hours

fast oxidative-glycolytic fibers

largest fibers; contain large amounts of myoglobin and many blood capillaries, dark red appearance; generate considerable ATP by aerobic respiration, moderately high resistance to fatigue

fast glycolytic fibers

have low myoglobin content, relatively few blood capillaries, and few mitochondria; appear white in color, contain large amounts of glycogen and generate ATP mainly by glycolysis; adapted for intense movements of short duration, fatigue quickly