Muscular System

skeletal muscle

attached to skeleton; voluntary

cardiac muscle

wall of heart; involuntary

smooth muscle

walls of internal organs; involuntary

skeletal muscles composition

skeletal muscle tissue, nervous tissue, blood, connective tissue

fascia

thin covering of connective tissue around a muscle

tendon

cord-like mass of connective tissue that connects muscle to bone

aponeurosis

sheet-like mass of connective tissue that connects a muscle to bone, skin, or another muscle

epimysium

surround whole muscle & lies beneath fascia; connective tissue

perimysium

surrounds fascicles within a muscle; connective tissue

endomysium

surrounds muscle fibers (cells) within a fascicle

compartment

space containing group of muscles, blood vessels, and nerves enclosed by fascia

compartment syndrome

fluid accumulation within a compartment which results in increase of pressure in compartment; leads to deficiency of oxygen & nutrients; causes severe pain

deep fascia

surrounds muscles

subcutaneous fascia

under skin

subserous fascia

fascia of serous membranes

cells of muscle

muscle fibers

characteristics of skeletal muscle fibers

multinucleated, sarcolemma, & sarcoplasm; many myofibrils, sarcoplasmic reticulum, transverse tubule & triad (consists of 1 tubule & 2 SR cisternae

sarcolemma

cell membrane of muscle fiber

sarcoplasm

cytoplasm of muscle fiber

myofibrils

long, parallel structures that run down fiber; consists of thin actin filaments & thick myosin filaments

sarcomeres

units that connect end to end to make up myofibrils

what does the sarcoplasmic reticulum store?

calcium

function of transverse tubules

relays electrical impulses to the SR

what causes the striation pattern in skeletal muscle?

the arrangement of myofilaments & myofibrils

I band of sarcomere

light band; composed of thin actin filaments

A band of sarcomere

dark band; thick myosin filaments with portions overlapped with thin actin filaments

H zone

center of A band; thick myosin filaments

Z line

sarcomere boundary; in center of I band anchors filaments in place

M line

center of sarcomere and A band; anchors thick filaments

thick filaments

composed of myosin; heads form cross-bridges with thin filaments

thin filaments

composed of actin; troponin & tropomyosin prevents cross-bridge when muscle is at rest

how does a skeletal muscle contract?

actin & myosin filaments slide past each other, shortening the sarcomeres

neuromuscular junction

site where an axon of motor neuron and skeletal fiber interact; skeletal muscles only contract when stimulated by motor neuron

motor neuron

neuron that controls skeletal muscle fiber

motor end plate

specialized folded portion of skeletal muscle fiber, where fiber finds to neurotransmitter

synaptic cleft

space between neuron and muscle fiber, across which neurotransmitter travels

synaptic vesicles

membrane-bound sacs containing neurotransmitters

neurotransmitters in neuromuscular junction

chemicals released by motor neuron to deliver message to muscle fiber

neurotransmitter for muscle contraction

acetylcholine

first step of skeletal muscle contraction

nerve impulses causes release of ACh from synaptic vesicles

second step of skeletal muscle contraction

ACh binds to ACh receptors on motor end plate

third step of skeletal muscle contraction

ACh causes changes in membrane permeability to sodium & potassium ions, which generates a muscle impulse (action potential)

last step in skeletal muscle contraction

impulse causes release of calcium ions from SR, which leads to muscle contraction

myasthenia gravis

autoimmune disorder where antibodies attack ACh receptors; leads to widespread weakness & muscle fatigue

muscular dystrophy

deficiency or mutation in dystrophin which holds cell membrane in place during contraction; cells lose normal structure & die

clostridium botulinum

bacteria that produce a toxin that causes food poisoning; causes digestive, musclular, & respiratory symptoms

excitation-contraction coupling

connection between muscle fiber stimulation & muscle contraction

when a muscle is at rest

calcium ions are stored in SR & troponin-tropomyosin complexes cover binding sites on actin filaments

when a muscle is stimulated

calcium ion binds to troponin to change its shape, binding sites are now exposed, myosin heads bind to actin, forming cross-bridges

process of sliding filament model

H zone and I bands narrow, Z lines move closer together, thin & thick filaments do not change in length, overlap between filaments increase

first step of cross-bridge cycling

myosin head attaches to actin binding site, forming cross bridge

second step of cross-bridge cycling

myosin cross-bridge pulls thin filament toward center of sarcomere

third step of cross-bridge cycling

ADP & phosphate are released from myosin

fourth step of cross-bridge cycling

new ATP binds to myosin

fifth step in cross-bridge cycling

linkage between actin & myosin cross-bridge break & ATP splits

last step in cross-bridge cycling

myosin cross bridge goes back to original position, ready to bind to another binding site on actin

first step in muscle relaxation

acetylcholinesterase (enzyme) rapidly decomposes ACh remaining in the synapse; muscle impulse stops once ACh is decomposed

second step in muscle relaxation

calcium pump moves calcium back to SR

last step in muscle relaxation

troponin-tropomyosin complex covers binding sites on actin which prevents myosin & actin binding & muscle fibers relax

first source of energy for muscle contraction

ATP

initial source of energy to regenerate ATP from ADP & P

creatine phosphate; stores energy in phosphate bond

ATP & creatine phosphate can fuel how many seconds of intense muscle contraction?

10 seconds

what is needed to fuel longer periods of muscle contraction?

cellular respiration; glucose is stores as glycogen in muscles

anaerobic phase of cellular respiration

glycolysis; occurs in cytoplasm & produces little ATP

aerobic phase of cellular respiration

citric acid cycle & electron transport system; in mitochondria & produces most ATP

myoglobin

stores extra oxygen in muscles

anaerobic (lactic acid) threshold

shift in metabolism from aerobic to anaerobic during strenuous exercise when systems cannot supply enough O2; lactic acid is produced

oxygen debt

the amount of oxygen needed by liver cells to convert the accumulated lactic acid to glucose, and to restore muscle ATP & creatine phosphate concentrations

muscle fatigue

inability to contract muscle

common causes of muscle fatigue

decreased blood flow, ion imbalances in sarcolemma, loss of desire to continue exercise, & accumulation of lactic acid (controversial)

muscle cramp

sustained, involuntary muscle contraction; may be caused by changes in electrolyte concentration in extracellular fluids in the area

muscle cells are a major source of

body heat

more than half of the energy released by cellular respiration becomes…

heat

threshold stimulus

minimum strength of of stimulation of a muscle fiber required to cause contraction

when strength of stimulus reaches threshold…

an action potential is generated

twitch

contractile response of a single muscle fiber to a single impulse

latent period

delay between stimulation & start of contraction

period of contraction

fiber pulls at attachments

period of relaxation

pulling force decreases

length of muscle fiber before stimulation determines..

amount of force it can develop

optimum starting length

resting length of the muscle fiber

overly stretched or shortened muscle fibers

develop less force

summation

the force of individual muscle fiber twitches combine, when frequency of stimulation increases; leads to sustained contractions

partial tetany

occurs at higher frequencies of stimulation; time spent in relaxation between twitches becomes very brief

complete tetany

occurs at very high frequencies; does not occur in body; forceful sustained contraction with no relaxation between twitches

motor unit

a motor neuron plus all the muscle fibers it controls

coarse movements

produced with large numbers of fibers in a motor unit

precise movements

produced with fewer muscle fibers in a motor unit

recruitment

increase in the number of motor units activated, to produce more force

smaller motor units in a sustained contraction are recruited…

first

larger motor units in a sustained contraction are recruited…

later

muscle tone (tonus)

continuous state of partial contraction in resting muscles

isotonic contractions

muscle contracts & changes length

concentric

shortening contraction; occurs when lifting an object

eccentric

lengthening contraction; occurs when force is not enough to life object

isometric contractions

muscle contracts but does not change length

slow twitch fibers

always oxidative, resistant to fatigue, red fibers, abundant myoglobin, good blood supply, many mitochondria, slow ATPase activity, slow to contract

fast twitch fatigue resistant fibers

intermediate twitch fibers, oxidative capacity, & myoglobin; white fibers, resistant to fatigue, rapid ATPase activity

fast twitch glycolytic fibers

anaerobic respiration(glycolysis), white fibers(less myoglobin); poorer blood supply, fewer mitochondria, more SR, susceptible to fatigue, & fast ATPase activity; rapid contraction

hypertrophy

enlargement of skeletal muscle that is exercised