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Chapter 9

Movement (Skeletal)

muscles move bones and provide for facial expressions

Posture (Skeletal)

the ability to support the body against gravity

Stabilize Joints (Skeletal)

muscles (tendons and ligaments) help to stabilize poorly articulating joints

Generate Heat (Skeletal)

mitochondria makes ATP from glucose and oxygen; skeletal muscles use ATP for contractions and creates heat as a bi-product

Excitability (Muscle Characteristic)

muscles ability to react to a stimulus

Contractility (Muscle Characteristic)

muscle shortens upon stimulation

Elasticity (Muscle Characteristic)

muscle returns to normal length after stretching

Cardiac Muscle

involuntary; located in the heart; striated; unique features: branching pattern, intercalated discs, and muscle fibers are separate

Smooth Muscle

involuntary; located in walls of hollow organs (intestines, etc.); performs peristalsis; unique features: spindle shaped, and has NO striations

Skeletal Muscle

ONLY VOLUNTARY MUSCLE; location: attached to bones; has striations; unique features: cylindrical shaped, multinucleated, and fibers are close together


connective tissue that covers the outside of the entire muscle; connected to the fascia


wraps around the fascicle (several muscle fibers connected together); contains collagen and elastic fibers, nerves and blood vessels


each individual muscle cell (myofiber) in the fascicle is wrapped by this connective tissue; (membrane layer on the inside) endo

Tendon or Aponeurosis

at the end of each muscle cell where the endomysium and perimysium come together to form a tendon or aponeurosis; both connect skeletal muscles to bone; aponeurosis connects muscle to muscle


'flesh husk'- the plasma membrane of a cell that surrounds the sarcoplasm of the muscle cell


extend into the cell at the right angles to the cells surface to contract the entire muscle cell at the same time


long organelles found inside the muscle cell; tiny contract units that help to shorten the muscle during contraction; have banding patterns (striations)


a portion of the myofibril; runs from 1 Z line to another Z line

During muscle contraction, what happens to the sarcomere?

it shortens as the Z lines are pulled closer together


a portion of the sarcomere which contains ALL of the thick filaments and only a portion of the thin filaments

H Zone

a portion within the A Band which contains only the THICK filaments; no thin filaments are found when the muscle is relaxed

During muscle contraction, what happens to the H Zone?

it disappears since the thin filaments invade the H zone


a portion of the sarcomere which contains the Z Line and only the THIN filaments

During muscle contraction, what happens to the I Band?

it disappears since the thick filaments invade the I Band

Z Line (Disc)

zig-zag shaped line that is the membrane where thin filaments are attached

During muscle contraction, what happens to the Z Lines?

slides closer together since the myosin heads attach to the thin filaments and pull them


long proteins made of either actin or myosin

Thick Filaments/Myosin Filaments

possess heads which are crucial for muscle contraction; made of the protein, myosin; myosin heads attach to certain sites of the thin filaments so muscle contraction can occur

Myosin Heads

knobby, golf club shaped portions of the thick filaments; made of proteins that attach to a particular portion of the thin filaments during muscle contraction; often called a cross bridge

During muscle contraction, what is the role of the myosin heads?

myosin heads attach to thin filaments, pull them together, release and repeat; the thin filaments slide toward the center of the sarcomere, in turn, the Z Lines are moved closer together and the sarcomere shortens

Thin Filament/Actin Filament

anchored to the Z Line; made of actin, tropomyosin and troponin; for muscle contraction to occur, troponin-tropomyosin must change positions and expose active sites on actin

Sarcoplasmic Recticulum

organelle wrapped around the myofibril like a lacey sleeve; calcium ions are released into the sarcoplasm for muscle contraction to occur; ions diffuse into the sarcomere, the SR reabsorbs calcium ions after muscle contraction to help the muscle relax

Excitation-Contraction Coupling

link between the generation of action potential and the start of muscle contraction; takes about .03 seconds for action potential to create a muscle contraction

Motor Unit

motor neuron and all the skeletal muscle cells its stimulates

Neuromuscular Junction

location where individual axon terminals stimulate ONE muscle cell

Synaptic Cleft

gap between the sarcolemma of the muscle cell and the axon terminals of the nerve cell


as action potential reaches the synaptic knob, calcium ions diffuse into the axon terminal


a chemical packaged in vesicles that is released into the synaptic cleft by exocytosis


binds to receptors on the sarcolemma of the muscle cell; channel proteins open so that the voltage of the cell can change and the action potential can be transferred to the next cell; to keep it resting, the charge must be negative; action potential changes a negative charge to a positive on the interior of the muscle cell; causes sarcolemma to become selectively permeable to sodium ion (outside of cell) while potassium is inside


breaks down ACh

Action Potential

sodium ions that carry a positive charge, creates an electrical impulse, influx of sodium ions into the muscle cell causes the flow of an electrical current

Power Stroke

when myosin heads form cross bridges when attaching to the binding sites on actin filaments

Rigor Mortis

occurs when no ATP is available; muscles are locked in contracted state until ions drain and pool in the body

Isotonic Contractions

contractions that shorten and produce movement (flexion, extension, abduction, adduction)

Isometric Contractions

contractions that do not shorten (pushing against a wall)


AChE breaks down ACh, ACh is recycled and returned to the axon terminal, SR reabsorbs calcium ions, troponin-tropomyosin complex recovers the binding sites on acting and prevents the myosin heads from attaching, without cross bridge interaction, the contraction ends, muscle relaxes to its normal length

Smooth Muscles Contracting

lacks sarcomeres, troponin, and striations; uses same sliding filament theory of other muscles

Muscle Tension

produced by cross bridges -- constant state of mild stimulation

Graded Response

different degrees of muscle shortening affected by: changing frequency in muscle stimulation and changing the number of muscles being stimulated


single, brief, jerky contraction; not a normal way to operate; result in nervous system problems

Latent Period (Twitch)

excitation period- the contraction cycle has not yet begun; action potential is sweeping across the sarcolemma; SR is in the process of releasing calcium

Contraction Phase (Twitch)

tension rises as calcium ions bind to troponin and active sites on the thin filaments are now exposed; cross bridge interactions occur

Relaxation Phase

calcium levels fall and active sites are covered by tropomyosin, cross bridges detach and tension falls


skeletal muscle stimulated immediately after relaxation phase has ended; will produce a slightly higher tension than the first stimulus

Summation of Twitches

addition of twitches; if stimulation continues and the muscles is not allowed to relax completely, tension will begin to rise above treppe; reaches an imcomplete tetanus

Fused or Complete Tetanus

in most types of muscle activity; impulses sent so rapidly that the muscle doesn't get to relax completely between stimuli

How do muscles increase tension?

recruitment of additional motor units will produce higher tension

Muscle Tone

resting tension; not enough tension to create movement, but enough to tense and firm the muscle

Fast Fibers

reaches peak tension is 0.01 seconds; larger fiber possess, many packed myofibrils, large amounts of glycogen, few mitochondria; fatigue quickly; found in white meat in chicken

Slow Fibers

smaller in diameter; specialized to continue contractions over longer periods of time, has mitochondria and contains a pigment called myoglobin which leads to oxygen molecules that makes it more dependent on anaerobic cellular respiration; found in dark meat chicken


enlargement of a muscle due to repeated stimulation, builds muscle mass


loss of muscle size, tone or power; can be caused by wearing a cast or splint

Aerobic Cellular Respiration

most common way to generate ATP in a resting muscle by transforming fatty acids; exercise begins-- ATP made by pyruvic acid
glucose + oxygen > carbon dioxide + water + 34-36 ATP

Direct Phosphorylation

fastest way to regenerate ATP when supplies run low; creatine phosphate can be stored when muscles are inactive; this type of ATP regeneration can be exhausted in 15 seconds
CP interacts with ADP > Creatine and ATP

Anaerboic Cellular Respiration

generates 2 ATP molecules for each glucose molecule broken down, glucose retrieved from glycogen stored in the sarcoplasm; lactic acid builds up during exercise
Glycogen stored in muscle cells > Glucose > 2 ATP + Lactic Acid

What is muscle fatigue?

when muscles lack ATP to produce a muscle contraction

What causes oxygen debt?

when ATP and CP runs low

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