Chapter 11: Muscle
T/F: All of the myosin heads of a given thick filament do not proceed through the steps of the contraction cycle at the same time. At any one instant, some myosin heads are attaching to actin, others are engaging in power strokes and generating tension (force), and still others are detaching from actin and getting ready to bind to another actin molecule farther along the thin filament. With repeated contraction cycles, sequential power strokes from different myosin heads of a thick filament continuously pull the thin filament closer and closer toward the center of the sarcomere.
All TRUE
______________________ is a test that measures the electrical activity (muscle action potentials) in resting and contracting muscles. In the procedure, a ground electrode is placed over the muscle to be tested to eliminate background electrical activity. Then a fine needle electrode attached by wires to a recording instrument is inserted into the muscle. The electrical activity of the muscle is displayed as waves on an oscilloscope and heard through a loudspeaker. EMG helps to determine if muscle ___________ or __________ is due to a malfunction of the _______ itself or the ______ supplying the muscle. EMG is also used to diagnose certain muscle disorders, such as __________ __________.
Electromyography; weakness; paralysis; muscle; nerves muscular dystrophy
Both cardiac muscle and smooth muscle are regulated by motor neurons that are part of the ________ nervous system and by hormones released by ________ glands.
autonomic; endocrine
_________ motor neurons convey action potentials to skeletal muscles, whereas ________ motor neurons convey action potentials to cardiac muscle, smooth muscle, and glands
Somatic; autonomic
When Ca2+ binds to troponin, troponin undergoes a change in _______; this conformational change moves tropomyosin _______ from the myosin-binding sites on actin, and muscle contraction subsequently begins as _______ attaches to actin.
shape; away; myosin
Dilated end sacs of the sarcoplasmic reticulum called _____________ ____________ butt against a T tubule from both sides.
terminal cisternae (also known as lateral sacs)
Cardiac muscle contractions are not under ________ control. Instead, the heart beats because it has a __________ that initiates each contraction. This built-in rhythm is termed ________________.
conscious; pacemaker; autorhythmicity.
The myosin tail is composed of portions of the ______ chains that wrap around each other to form a double-stranded helix.
heavy
Because each mature skeletal muscle fiber arises during embryonic development from the fusion of many small, undifferentiated cells called ________. A mature skeletal muscle fiber has multiple ________.
myoblasts; nuclei
The asynchronous activity of the myosin heads during repeated contraction cycles is responsible for the continuous movement of the _____ filament If all of the myosin heads attached to and then detached from actin at the same time, the thin filament would slide back to its ________ position between power strokes. Because the myosin heads at opposite ends of a thick filament are arranged in _______ directions, as power strokes from each end pull a thin filament toward the ________ of the sarcomere, the Z discs are drawn ________ each other, and the sarcomere shortens. During a maximal muscle contraction, the distance between two Z discs can _______ to half the resting length. The Z discs in turn pull on neighboring _______, and the whole muscle fiber ______.
inward; thin; resting; opposite; center; toward decrease; sarcomeres; shortens
In an _________ contraction, the tension developed by the muscle remains almost constant while the muscle changes its length.
isotonic (isotonic = constant tension)
The name of the I band is derived from the fact that it is ________ to polarized light, which means that it refracts polarized light ____________ in all directions.
isotropic; uniformly
The myosin heads contain the ______ chains and the remaining portions of the heavy chains
light
A ________ skeletal muscle fiber is a long, cylindrical structure with a diameter that ranges from 10 to 100 μm and a length that is typically about 10 cm (4 in.), although some are as long as 30 cm (12 in.)
mature
This load-velocity relationship works as follows: (1) When the load is zero, the velocity of shortening is _________; (2) as the load increases, the velocity of shortening ____________; and (3) when the load is equal to or exceeds the maximum tetanic tension that the muscle can produce, the velocity of shortening is ______ and the contraction becomes __________.
maximal; decreases; zero; isometric
Fatigue results mainly from changes within __________ _______.
muscle fibers
Organization of Skeletal Muscle: Each of your skeletal muscles is composed of hundreds to thousands of muscle cells, called _______ _________, arranged parallel to one another
muscle fibers
1. Regular, repeated activities such as jogging or walking on the treadmill is Aerobic respiration or Anaerobic glycolysis? 2. Alternating sprints is Aerobic respiration or Anaerobic glycolysis? 3. Weight lifting is Aerobic respiration or Anaerobic glycolysis?
1. Aerobic respiration 2. Anaerobic glycolysis 3. Anaerobic glycolysis
1. ________ _________: slow-twitch, fatigue-resistant fibers are adapted for maintaining posture and for aerobic, endurance-type activities such as running a marathon. 2. ________ ____________: fibers contribute to activities such as walking and sprinting. 3. __________ __________: fast-twitch fibers are adapted for intense anaerobic movements of short duration, such as weight lifting or throwing a ball, but they fatigue quickly. Match the correct term to the described statement: Slow oxidative (SO) Fast glycolytic (FG) Fast oxidative-glycolytic (FOG)
1. Slow oxidative 2. Fast oxidative-glycolytic 3. Fast glycolytic
Primary functions of fibers: 1. Maintaining posture and aerobic endurance activities. 2. Walking, sprinting. 3. Rapid, intense movements of short duration. Match the correct term to the described statement: Slow oxidative (SO) Fast glycolytic (FG) Fast oxidative-glycolytic (FOG)
1. Slow oxidative 2. Fast oxidative-glycolytic 3. Fast glycolytic
Several key structural proteins are ______, _______, ______, _______, and _________.
1. titin 2. α-actinin 3. myomesin 4. nebulin 5. dystrophin
A single thick filament contains about ____ myosin molecules.
300
The ATP-binding site also functions as an ________. _______ is an enzyme that hydrolyzes ATP to generate energy for muscle contraction.
ATPase; ATPase
___________ released at the neuromuscular junction triggers a muscle action potential, which leads to muscle contraction.
Acetylcholine
Skeletal muscle works mainly in a ________ manner: Its activity can be __________ controlled by motor neurons that are part of the somatic nervous system A. Voluntary; unconscious B. Involuntary; conscious C. Voluntary; conscious D. Involuntary; unconscious
C. voluntary; consciously
Which type of muscle is striated and involuntarily controlled?
Cardiac muscle is striated and involuntarily controlled.
Which special property of muscle allows tension to be generated? A. Electrical excitability B. Contractility C. Extensibility D. Elasticity
Contractility
________ is the ability of muscle to contract forcefully when adequately stimulated. A. Electrical excitability B. Contractility C. Extensibility D. Elasticity
Contractility
________ is the ability of muscle to return to its original length and shape after contraction or extension. A. Electrical excitability B. Contractility C. Extensibility D. Elasticity
Elasticity
A narrow ___ ______ in the center of each A band contains thick filaments but no thin filaments.
H zone
Skeletal muscle fibers that have a ______ myoglobin content are termed red muscle fibers and appear _______ (the dark meat in chicken legs and thighs). Those that have a low content of myoglobin are called ______ muscle fibers and appear ________ (the white meat in chicken breasts). Red muscle fibers also contain more ____________ and are supplied by _______ blood capillaries.
High; darker White; lighter mitochondria; more
What would happen if ATP suddenly were not available after the sarcomere had started to shorten?
If ATP were not available, the myosin crossbridges would not be able to detach from actin. The muscles would remain in a state of rigidity, as occurs in rigor mortis
When a muscle fiber is relaxed, the concentration of Ca2+ in its sarcoplasm is very ________, only about 0.1 micromole per liter (0.1 μmol/L). However, a huge amount of Ca2+ is stored inside the ________ ___________.
LOW; sarcoplasmic reticulum (SR)
Unlike most cells of the body, skeletal muscle fibers often switch between a ______ level of activity, when they are relaxed and using only a _________ amount of ATP; And a high level of activity, when they are contracting and using ATP at a _____ pace.
LOW; Modest; Rapid
Creatine is a small, amino acid-like molecule that is synthesized in the _______, _________, and ___________ and then transported to muscle fibers.
Liver, Kidneys, and Pancreas
The myosin tail of each myosin molecule points toward the ___ _____ in the center of the sarcomere. A. H zone B. M line C. A band D. I band E. Z discs
M line
The other energy-generating mechanisms in a muscle fiber (anaerobic glycolysis and aerobic respiration) take ________ time to produce ATP.
MORE
________ muscle is located in the walls of hollow internal structures, such as blood vessels, the airways, stomach, intestines, and uterus
Smooth
Skeletal Muscle Mechanics: A skeletal muscle receives neural input from many ___________ motor neurons.
Somatic
T/F: Muscle action potentials travel along the sarcolemma and through the Transverse (T) tubules, quickly spreading throughout the muscle fiber. This arrangement ensures that an action potential excites all parts of the muscle fiber at essentially the same instant.
TRUE
A transverse tubule and the two terminal cisternae on either side of it form a ________
triad
Besides binding to ATP, what other function does the ATP-binding site on the myosin head perform?
The ATP-binding site also functions as an ATPase that hydrolyzes ATP to generate energy for muscle contraction.
Without ____________, end plate potentials are not generated, and the production of muscle action potentials ends.
acetylcholine (ACh)
Organization of Skeletal Muscle: An individual muscle fiber is surrounded by a sheath of _________ tissue. In addition, connective tissue surrounds groups of 10 to 100 or more muscle fibers, separating them into bundles called ____________. T/F: Connective tissue also surrounds the entire muscle itself.
connective; fascicles; True
During prolonged periods of muscle contraction, _________ in breathing rate and blood flow enhance __________ delivery to muscle tissue.
increases; oxygen
Muscle Fiber Diameter: Muscle fibers that have a thicker diameter have ______ myofibrils and can generate ______ tension compared to muscle fibers that have a thinner diameter. This relationship between muscle fiber diameter and muscle strength is evident in a ____________, whose huge, thick muscles can exert more force than the smaller, thinner muscles of an average person.
more; more bodybuilder
******** The total tension a whole muscle can produce depends on the number of muscle fibers that are contracting in unison, which is determined by the size and number of _______ _________ that are activated.
motor units
Release of Ca2+ from the terminal cisternae of the sarcoplasmic reticulum triggers _________ __________.
muscle contraction
The hinge region allows the myosin head to _____ during the ___________ process.
pivot; contraction
Creatine phosphate is three to six times more plentiful than ATP in the ________ of a _________ muscle fiber.
sarcoplasm; relaxed
What is a tendon?
A tendon is a cord of connective tissue that attaches muscle to a bone.
After a crossbridge forms, the myosin head pivots, changing its position from a 90° angle to a 45° angle relative to the thick and thin filaments. As the myosin head changes to its new position, it pulls the thin filament past the thick filament toward the center of the sarcomere, generating tension (force) in the process. This event is known as the ___________________. The energy required for the ______________ is derived from the energy stored in the myosin head from the hydrolysis of ATP. Once the ____________ occurs, ADP is released from the myosin head. Which of the following contraction cycle step is described? A. ATP hydrolysis B. Attachment of myosin to actin C. Power stroke D. Detachment of myosin from actin
Power Stroke
Is skeletal muscle striated or not striated? Is cardiac muscle striated or not striated? Is smooth muscle striated or not striated?
Skeletal muscle is striated; Cardiac muscle is striated; Smooth muscle is NOT striated
T/F: Although its exact mechanism is unknown, fatigue may be a protective mechanism to stop a person from exercising before muscles become damaged.
TRUE
T/F: Although the total number of skeletal muscle fibers usually does NOT increase, the characteristics of those present can change to some extent. Various types of exercises can induce changes in the fibers in a skeletal muscle.
TRUE
T/F: As the axon of a somatic motor neuron enters a skeletal muscle, it divides into a number of branches, each supplying a different muscle fiber.
TRUE
T/F: Normally, resting muscle fiber length is held very close to the optimum by firm attachments of skeletal muscle to bones (via their tendons) and to other inelastic tissues.
TRUE
********** Total Tension by the whole muscle depends on?
1. Motor unit size 2. Motor unit recruitment
A twitch consists of three sequential phases?
1. The latent period 2. The contraction period 3. The relaxation period
The skeletal muscle action potential consists of which two main phases?
1. a depolarizing phase 2. a repolarizing phase.
Skeletal muscle contractions stabilize joints and help maintain body positions, such as standing or sitting. Postural muscles contract continuously when you are awake; for example, sustained contractions of your neck muscles hold your head upright. Which of the following muscle function below is being described? A. producing body movements B. stabilizing body positions C. storing and moving substances within the body D. generating heat.
B. Stabilizing body positions
MOST skeletal muscle is attached to _______ and moves parts of the _________
Bone; skeleton
Frequency of stimulation: Wave summation and both kinds of tetanus (unfused and fused) occur when additional _________ is released from the sarcoplasmic reticulum by subsequent stimuli while the levels of Ca2+ in the sarcoplasm are still elevated from the first stimulus. Because of the buildup in the Ca2+ level, the peak tension generated during fused tetanus is 5 to 10 times ________ than the peak tension produced during a single twitch. Even so, fused tetanus ______ occurs in muscles of the body, except for those occasions when __________ strength is necessary (for example, attempting to lift part of a car away from someone who is trapped beneath one of its tires). Most smooth, sustained voluntary muscle contractions in the body are achieved by out-of-synchrony ________ ______ in different motor units.
Ca2+; Larger; Rarely; tremendous; unfused tetanus
Slow Oxidative Fibers Have a ________ Resistance to Fatigue. Fast Oxidative‐Glycolytic Fibers Have a _________ Resistance to Fatigue. Fast Glycolytic Fibers Have a ______ Resistance to Fatigue
High; Moderate; LOW
Skeletal muscle fibers are classified into what three main types?
(1) slow oxidative fibers (2) fast oxidativ-glycolytic fibers (3) fast glycolytic fibers
******** Tension (graded contractions) generated by a fiber depends on?
1. Action potential frequency 2. Muscle fiber length 3. Muscle fiber diameter
The dark middle part of the sarcomere is the ____ band, which extends the entire length of the thick filaments.
A
Movements of the whole body such as walking and running, and localized movements such as grasping a pencil or nodding the head, rely on the integrated functioning of skeletal muscles, bones, and joints. Which of the following muscle function below is being described? A. producing body movements B. stabilizing body positions C. storing and moving substances within the body D. generating heat.
A. producing body movements
Because of the arrangement of its thick and thin filaments, a sarcomere contains an __ band, __ bands, an __ zone, and an __ line.
A; I; H; M
Glycogen can be broken down into individual glucose molecules that can be used to synthesize _______.
ATP
Only the heart contains ______ muscle, which forms most of the heart wall
Cardiac
How is most ATP produced in a skeletal muscle fiber during a long-term event such as a marathon race?
During a long-term event such as a marathon race, most ATP is produce by aerobic respiration.
Organization of Skeletal Muscle: A skeletal muscle consists of individual muscle fibers (cells) bundled into _________.
Fascicles
Individual actin molecules are known as ___ _____ because they are globular proteins.
G actin
What happens to the velocity of shortening if the load equals or exceeds the amount of tension that the muscle can produce?
If the load becomes equal to or exceeds the amount of tension that a muscle can produce, the velocity of shortening is zero and the contraction becomes isometric.
What are the two major categories of muscle contractions?
Isotonic and Isometric contraction
Narrow, plate-shaped regions of dense protein material called ___ _____ separate one sarcomere from the next.
Z discs
While muscle fibers are relaxed, they produce ______ ATP than they need for resting metabolism.
more
Myosin functions as a _______ protein in all three types of muscle tissue
motor
Also present in the sarcoplasm are molecules of _______, a red-colored, oxygen-binding protein that is found only in muscle.
myoglobin
The main component of the thin filament is the protein ______.
actin
Most of the excess ATP is used to synthesize __________ ____________.
creatine phosphate
Muscle tone Is established by ________ motor units that are ______________ active and inactive; And help maintain _____ ______ and _______.
different; alternately blood pressure and posture
The action of smooth muscle is usually ___________, and some smooth muscle tissue, such as the muscles that propel food through your gastrointestinal tract, has __________.
involuntary; autorhythmicity
The dense material of the Z discs contains molecules of __________. __________ bind to actin molecules of the thin filament and to titin. A. titin B. α-actinin C. myomesin D. nebulin E. dystrophin
α-actinin; α-actinin
At the end of the power stroke, the crossbridge remains firmly attached to actin until it binds another molecule of ATP. As ATP binds to the ATP-binding site on the myosin head, the myosin head detaches from actin. Which of the following contraction cycle step is described? A. ATP hydrolysis B. Attachment of myosin to actin C. Power stroke D. Detachment of myosin from actin
Detachment of myosin from actin
A muscle fiber develops its greatest tension when there is an _________ zone of overlap between thick and thin filaments.
optimal
________ proteins: which help switch the contraction process on and off A. contractile proteins B. regulatory proteins C. structural proteins D. Support proteins
regulatory
A ___________ phase, caused by closure of the voltage-gated Na+ channels and the opening of voltage-gated K+ channels
repolarizing (falling)
_________ contractions are used for body movements and for moving objects. What are the two types of isotonic contractions?
Isotonic; concentric and eccentric.
The sarcolemma surrounds the ___________, which is the cytoplasm of a muscle fiber
sarcoplasm
Muscle tone is also important in ________ muscle tissues, such as those found in the gastrointestinal tract, where the walls of the digestive organs maintain a steady _________ on their contents.
Smooth; pressure
_________ _______ partial paralysis in which the muscles exhibit spasticity.
Spastic paralysis
True or False. Several neurotransmitters and hormones can adjust heart rate by speeding up or slowing down the pacemaker.
TRUE
When an action potential travels along the T tubule, the ___________ receptors detect the change in voltage and undergo a conformational change that ultimately causes the Ca2+ release channels to ______. Once these channels open, large amounts of Ca2+ flow out of the sarcoplasmic reticulum into the ______________ around the thick and thin filaments. As a result, the Ca2+ concentration in the sarcoplasm rises _____ or more. The released calcium ions combine with ________, which in turn undergoes a conformational change that causes tropomyosin to move away from the myosin-binding sites on actin. Once these binding sites are free, ________ heads bind to them to form ____________, and the contraction cycle begins.
Dihydropyridine; open sarcoplasm; tenfold; troponin; troponin; crossbridges
The sarcoplasm also contains ____________, a large polysaccharide consisting of thousands of glucose molecules covalently linked together.
Glycogen
1. ________ ________ and _________ ___________ appear dark red because they contain large amounts of myoglobin and many blood capillaries. 2. ________ ____________ can generate the most powerful contractions. They ave low myoglobin content, relatively few blood capillaries, few mitochondria, and appear white in color. Match the correct term to the described statement: Slow oxidative (SO) Fast glycolytic (FG) Fast oxidative-glycolytic (FOG)
1. Slow oxidative and Fast oxidative-glycolytic 2. Fast glycolytic
T/F: An increase in Ca2+ concentration in the sarcoplasm starts muscle contraction, and a decrease stops it.
TRUE
T/F: Overall, a myosin molecule is shaped like two golf clubs twisted together: the myosin tail resembles the twisted golf club handles and the myosin heads look like the golf club heads.
TRUE
Organization of Skeletal Muscle: A __________ is a cord of connective tissue that attaches the muscle to a bone
Tendon
Tails of neighboring myosin molecules lie parallel to one another, forming the shaft of the _____ filament. The myosin heads project ________ from the shaft in a spiraling fashion, each extending toward one of the six thin filaments that surround each thick filament.
Thick; outward
EC coupling occurs at the _______ of the skeletal muscle fiber. At a given triad, the T tubule and terminal cisternae are mechanically linked together by two groups of integral membrane proteins: _______________ receptors and ______ release channels
Triads; dihydropyridine; Ca2+
T/F: The thin and thick filaments inside a myofibril do not extend the entire length of a muscle fiber. Instead, they are arranged in compartments called _________, which are the repeating units of a myofibril
True; sarcomeres
A __________ is the brief contraction of a group of muscle fibers within a muscle in response to a single action potential.
Twitch
*********** The total force or tension that a single muscle fiber can produce depends on the _________ of stimulation, the __________ of the muscle fiber BEFORE contraction begins, and the __________ of the muscle fiber.
1. frequency of stimulation (the rate at which the muscle fiber is stimulated by a motor neuron) 2. length of the muscle fiber 3. diameter of the muscle fiber
What are the three types of muscle tissue?
1. skeletal 2. cardiac 3. smooth
_________ is a cytoskeletal protein that links thin filaments of the sarcomere to integral membrane proteins of the sarcolemma, which are attached in turn to proteins in the connective tissue extracellular matrix that surrounds muscle fibers. A. titin B. α-actinin C. myomesin D. nebulin E. dystrophin
Dystrophin
For muscle cells, two main types of stimuli trigger action potentials. One is chemical stimuli, such as neurotransmitters released by neurons and hormones distributed by the blood. The other is autorhythmic electrical signals arising in the muscle tissue itself, as in the heart's pacemaker. This is an example of which of the 4 muscle special properties? A. Electrical excitability B. Contractility C. Extensibility D. Elasticity
Electrical excitability
_____________ is the ability to respond to certain stimuli by producing action potentials. A. Electrical excitability B. Contractility C. Extensibility D. Elasticity
Electrical excitability
Where in a skeletal muscle fiber does excitation-contraction coupling occur?
Excitation-contraction coupling occurs at the TRIADS of a skeletal muscle fiber. A triad consists of a transverse (T) tubule and two opposing terminal cisternae of the sarcoplasmic reticulum (SR).
When the motor neurons serving a skeletal muscle are damaged or cut, the muscle becomes _________
Flaccid
_________ is a state of limpness in which muscle tone is lost.
Flaccid
________ _________ is characterized by loss of muscle tone (hypontonia), loss or reduction of tendon reflexes, and atrophy (wasting away) and degeneration of muscles.
Flaccid paralysis
Glycogen serves as a storage form of ________.
Glucose
What type of contraction occurs in your neck muscles to keep your head upright while you are walking?
Holding your head upright without movement involves mainly isometric contractions of neck muscles.
The neurotransmitter released at the NMJ is ______________ and it has an excitatory effect on neuromuscular transmission.
acetylcholine (ACh)
A _________ phase, caused by the opening of voltage-gated Na+ channels
depolarizing (rising)
The sequence of events that links the muscle action potential to muscle contraction is known as?
excitation-contraction (EC) coupling.
Each Ca2+ release channel has four projections called _______ ________ or _______ ______. T/F: Each foot process comes in contact with one of the four Dihydropyridine receptors in a tetrad. When the T tubule is at resting membrane potential, the part of the Ca2+ release channel that extends into the sarcoplasm is blocked by a given cluster of __________ receptors, which prevents Ca2+ from leaving the sarcoplasmic reticulum.
foot processes or junctional feet. True; Dihydropyridine
A flexible ______ is located where the myosin heads join the myosin tail
hinge
_________ refers to decreased or lost muscle tone. Such muscles are said to be _________. Flaccid muscles are ______ and appear _______ rather than rounded. Certain disorders of the nervous system and disruptions in the balance of electrolytes (especially sodium, calcium, and—to a lesser extent—magnesium) may result in ________ _________.
Hypotonia; Flaccid; loose; flattened; Flaccid paralysis
On either side of the A band is a light area called the ____ band, which contains the rest of the thin filaments but no thick filaments.
I band
Supporting proteins that hold the thick filaments together at the center of the H zone form the ___ ______, named for its position in the middle of the sarcomere.
M line
Molecules of the protein _________ form the M line. A. titin B. α-actinin C. myomesin D. nebulin E. dystrophin
myomesin
Together, all of the ________ muscles of the body comprise the muscular system.
Skeletal
___________ is the cytoplasm of a muscle fiber.
sarcoplasm
A fluid-filled system of membranous sacs called the ___________ ___________ encircles each myofibril.
sarcoplasmic reticulum (SR)
_________ muscle contractions promote the flow of lymph and aid the return of blood to the heart. Which of the following muscle function below is being described? A. producing body movements B. stabilizing body positions C. storing and moving substances within the body D. generating heat.
Skeletal; C. moving substances within the body
Most skeletal muscles are a mixture of all three types of skeletal muscle fibers; about half the fibers in a typical skeletal muscle are _________ ______ fibers.
Slow oxidative
T/F: The components of a sarcomere are organized into a variety of bands and zones
true
The resting membrane potential of a skeletal muscle fiber is about ________ mV.
−90
T/F: Skeletal muscle fibers are not all alike in composition and function. For example, muscle fibers vary in their content of myoglobin, the red-colored protein that binds oxygen in muscle fibers.
TRUE
Which structure shown here releases calcium ions to trigger muscle contraction?
The sarcoplasmic reticulum releases calcium ions to trigger muscle contraction.
A single somatic motor neuron innervates ___________ muscle fibers, but each muscle fiber is innervated by only _________ somatic motor neuron.
several; one
Before a skeletal muscle fiber can contract, it must be stimulated by a ________ motor neuron.
somatic
The metabolic changes that occur during exercise can account for only ______ of the extra oxygen used after exercise.
some
The energized myosin head attaches to the myosin-binding site on actin and releases the previously hydrolyzed phosphate group. When a myosin head attaches to actin during the contraction cycle, the myosin head is referred to as a _____________. Although a single myosin molecule has a double head, only one head binds to actin at a time. Which of the following contraction cycle step is described? A. ATP hydrolysis B. Attachment of myosin to actin C. Power stroke D. Detachment of myosin from actin
crossbrige; Attachment of myosin to actin
****** The extra oxygen is used to "pay back" or restore metabolic conditions to the resting level in three ways. What are the three ways?
(1) to convert lactic acid back into glycogen stores in the liver (2) to resynthesize creatine phosphate and ATP in muscle fibers (3) to replace the oxygen removed from myoglobin.
T/F: During muscle contraction, thin filaments move toward the M line of each sarcomere
TRUE
T/F: Most activities that occur throughout the day include both isotonic and isometric contractions.
TRUE
T/F: Twitches of skeletal muscle fibers last anywhere from 20 to 200 msec. This is very long compared to the brief 1-2 msec that a muscle action potential lasts.
True
True or False Your muscular strength reflects the primary function of muscle—the transformation of chemical energy into mechanical energy to generate force, perform work, and produce movement.
True
True or False. In addition, muscle stabilizes body position, regulates organ volume, generates heat, and propels fluids and food matter through various body systems.
True
True or False. Movements such as throwing a ball, riding a bike, and walking result from the contraction of muscle, which makes up 40-50% of total adult body weight.
True
True or False. The different types of muscle tissue differ from one another in their microscopic structure, their location, and how they are controlled by the nervous system.
True
T/F: Toward each end of the A band is a zone where the thick and thin filaments overlap. A cross section through this zone of overlap reveals that each thick filament is surrounded by a hexagonal arrangement of ____ thin filaments, and each thin filament is surrounded by a triangular arrangement of ____ thick filaments
True; six; three
Unlike skeletal muscle, cardiac muscle is __________ A. Voluntary B. Involuntary
involuntary
Depending on the intensity of the exercise, the recovery period may be just a ______ minutes, or it may last as _______ as _________ hours.
few; long; several
Dystrophin and its associated proteins are thought to reinforce the __________ and help transmit the _________ generated by the sarcomeres to the tendons.
sarcolemma; Dystrophin
What are the four steps of the contraction cycle?
1. ATP hydrolysis 2. Attachment of myosin to actin 3. Power stroke 4. Detachment of myosin from actin
What roles do the dihydropyridine receptors play in excitation-contraction coupling in a skeletal muscle fiber?
DHP is Voltage gated Ca2+ channel that allow Ca2+ to come in AND at the same time Activate Ryanodin Ca2+ release channel on SR to release Ca2+ in sarcoplasm
What is the contractile elements of the skeletal muscle fiber?
Myofibrils
The A band is so-named because it is ___________ to polarized light, meaning that it refracts polarized light _________ in different directions.
anisotropic; unevenly
The tone of smooth muscle fibers in the walls of blood vessels plays a crucial role in maintaining _______ ________.
blood pressure.
In a relaxed muscle fiber, the sarcoplasmic reticulum stores ________ _____.
calcium ions (Ca2+)
A _____________ is a record of a muscle contraction.
myogram
The tropomyosin strands in turn are held in place by molecules of __________.
troponin
Myofibrils are built from what three kinds of proteins?
(1) contractile proteins (2) regulatory proteins (3) structural proteins
What are the three ways that skeletal fibers have to produce ATP?
(1) from creatine phosphate (2) by anaerobic glycolysis (3) by aerobic respiration
What are three functions of ATP in muscle contraction?
(1) hydrolysis of ATP by myosin ATPase activates the myosin head so it can bind to actin and undergo the power stroke (2) binding of ATP to myosin causes detachment from actin after the power stroke (3) ATP powers the pumps that transport Ca2+ from the sarcoplasm back into the sarcoplasmic reticulum.
________ ________ __________ is the process of increasing the number of active motor units.
Motor unit recruitment
Muscle tone keeps skeletal muscles firm, but it does not result in a force _______ enough to produce ________. For example, when the muscles in the back of the neck are in normal tonic contraction, they keep the head upright and prevent it from slumping forward on the chest.
Strong; movement
__________ is a rod-shaped protein that joins with other ________________ molecules to form two long strands that wrap around the F actin double helix.
Tropomyosin; Tropomyosin
1. _________ _______ have many large mitochondria, so they generate ATP mainly by aerobic respiration, which is why they are called oxidative fibers. 2. _________ ___________ fibers can generate considerable ATP by aerobic respiration, which gives them a moderate resistance to fatigue. Because their intracellular glycogen level is high, they also generate ATP by anaerobic glycolysis. 3. ___________ ___________ contain large amounts of glycogen and generate ATP mainly by anaerobic glycolysis. Match the correct term to the described statement: Slow oxidative (SO) Fast glycolytic (FG) Fast oxidative-glycolytic (FOG)
1. Slow oxidative 2. Fast oxidative-glycolytic 3. Fast glycolytic
___________ ____________ is a energy-rich molecule that is found in muscle fibers.
creatine phosphate
Due to _______ _________, the tension produced during a sustained contraction is greater than that produced by a single twitch.
Wave summation
What is the purpose of calsequestrin?
(Directs calcium back to SR after muscle contraction) Molecules of a calcium-binding protein inside the sarcoplasmic reticulum that bind to the Ca2+, enabling even more Ca2+ to be sequestered (stored) within the sarcoplasmic reticulum. As a result, the concentration of Ca2+ is 10,000 times higher in the sarcoplasmic reticulum than in the sarcoplasm in a relaxed muscle fiber.
The duration of the skeletal muscle action potential is very brief, lasting only about _____ msec. Once an action potential is generated in a skeletal muscle fiber, it propagates along the _________ and _____ _________ via continuous ___________. T/F: The same mechanism used for propagation of nerve action potentials along unmyelinated axons.
1-2 msec; sarcolemma and Transverse Tubules; conduction TRUE
1. What is skeletal muscle's main source of ATP during rest? 2. During periods of light to moderate exercise? 3. During heavy exercise?
1. Aerobic respiration 2. Aerobic respiration 3. Anaerobic glycolysis
Muscle has four special properties that has that enable it to function and contribute to homeostasis. What are the 4 special properties?
1. Electrical excitability 2. Contractility 3. Extensibility 4. Elasticity
1. _______ _______ fibers are largest in diameter and contain the most myofibrils. 2. _______ ________ fibers are smallest in diameter and thus are the least powerful type of muscle fibers. 3. ________ __________ fibers are intermediate in diameter between the other two types of fibers. Match the correct term to the described statement: Slow oxidative (SO) Fast glycolytic (FG) Fast oxidative-glycolytic (FOG)
1. Fast glycolytic (FG) 2. Slow oxidative (SO) 3. Fast oxidative-glycolytic (FOG)
1. ___________ _________ fibers are said to be "slow" because the ATPase in the myosin heads hydrolyzes ATP relatively slowly and the contraction cycle proceeds at a slower pace than in "fast" fibers. As a result, _______ ________ fibers have a slow speed of contraction. Their twitch contractions last from 100-200 msec, and they take longer to reach peak tension. However, slow fibers are very resistant to fatigue and are capable of prolonged, sustained contractions for many hours. 2. _________ _______ fibers are fast because the ATPase in their myosin heads hydrolyzes ATP three to five times faster than the myosin ATPase in SO fibers, which makes their speed of contraction faster. Thus, twitches of ________ ________ fibers reach peak tension more quickly than those of SO fibers but are briefer in duration—less than 100 msec. 3. Due to their large size and their ability to hydrolyze ATP rapidly, _________ __________fibers contract strongly and quickly. Match the correct term to the described statement: Slow oxidative (SO) Fast glycolytic (FG) Fast oxidative-glycolytic (FOG)
1. Slow oxidative 2. Fast oxidative-glycolytic 3. Fast glycolytic
1. Postural muscles of the neck, back, and legs have a high proportion of _________ ________ fibers. 2. Muscles of the shoulders and arms, are used briefly now and then to produce large amounts of tension, such as in lifting and throwing. These muscles have a high proportion of __________ ________ fibers. 3. Leg muscles, which not only support the body but are also used for walking and running, have large numbers of both ________ ________ and ___________ __________ fibers.
1. Slow oxidative 2. Fast glycolytic 3. Slow oxidative and Fast oxidative-glycolytic
What are the four key functions of a muscle?
1. producing body movements 2. stabilizing body positions 3. storing and moving substances within the body 4. generating heat.
Together, stores of creatine phosphate and ATP provide enough energy for muscles to contract maximally for about ______ seconds.
15
Why is tension maximal at a sarcomere length of 2.2 μm?
A sarcomere length of 2.2 μm gives a generous zone of overlap between the parts of the thick filaments that have myosin heads and the thin filaments, without the overlap being so extensive that sarcomere shortening is limited.
When an action potential occurs in a somatic motor neuron, it releases ______ molecules stored in the synaptic vesicles of the synaptic end bulbs. ACh then diffuses across the synaptic cleft and binds to _______ ______ receptors on the motor end plate, generating a depolarizing graded potential called an _____ _____ ________. A single EPP is typically large enough to depolarize adjacent regions of sarcolemma to threshold, resulting in the generation of a muscle ________ _____. Because the NMJ is usually near the midpoint of the muscle fiber, once the muscle action potential arises, it ________ through the muscle fiber membrane in ______ directions away from the NMJ toward the ends of the fiber. As the muscle action potential passes through the membrane (sarcolemma and T tubules), it triggers a chain of events that ultimately leads to ___________ of the muscle fiber. Thus, a ________ action potential in a somatic motor neuron elicits a ________ action potential in a skeletal muscle fiber, which in turn causes the skeletal muscle fiber to _______. The events just described repeat as long as _____ action potentials continue to occur in the ________ motor neuron, causing the release of ACh. Once nerve action potentials in the somatic motor neuron cease, ACh is no longer released and the enzyme ________________, located on the end plate membrane, breaks down any ACh that is present in the synaptic cleft.
ACh; nicotinic ACh; end plate potential (EPP); action potential; propagates; both; contraction; single, single; contract; nerve; somatic; acetylcholinesterase (AChE)
A myosin head includes an ATP-binding site that functions as an ATPase—an enzyme that hydrolyzes ATP into ADP (adenosine diphosphate) and a phosphate group. The energy generated from this hydrolysis reaction is stored in the myosin head for later use during the contraction cycle. The myosin head is said to be energized when it contains stored energy. The energized myosin head assumes a "cocked" position, like a stretched spring. In this position, the myosin head is perpendicular (at a 90° angle) relative to the thick and thin filaments and has the proper orientation to bind to an actin molecule. Notice that the products of ATP hydrolysis—ADP and a phosphate group—are still attached to the myosin head. Which of the following contraction cycle step is described? A. ATP hydrolysis B. Attachment of myosin to actin C. Power stroke D. Detachment of myosin from actin
ATP hydrolysis
Recall that skeletal muscle contracts only after it is activated by acetylcholine released by action potentials in its motor neurons. Hence, MUSCLE TONE is established by neurons in the _____ and _____ ______ that excite the muscle's motor neurons.
Brain and spinal cord
The membrane of the sarcoplasmic reticulum (SR) also contains active transport proteins called ______________ pumps that constantly transport Ca2+ from the sarcoplasm into the Sarcoplasmic reticulum.
Ca2+-ATPase
As a muscle action potential propagates along the sarcolemma and into the T tubules, it causes the release of ______ from the sarcoplasmic reticulum into the sarcoplasm, and muscle ________ begins.
Ca2+; contraction
______ muscle contractions of the heart pump blood through the blood vessels of the body. Contraction and relaxation of ______ muscle in the walls of blood vessels help adjust blood vessel diameter and thus regulate the rate of blood flow. Which of the following muscle function below is being described? A. producing body movements B. stabilizing body positions C. storing and moving substances within the body D. generating heat.
Cardiac; Smooth; C. moving substances within the body
When a muscle contracts, it generates tension (force of contraction) while pulling on its attachment points. If the tension generated is great enough to overcome the resistance of the object to be moved, the muscle shortens and movement occurs. This is an example of which of the 4 muscle special properties? A. Electrical excitability B. Contractility C. Extensibility D. Elasticity
Contractility
During the ____________ period, which lasts 10-100 msec, Ca2+ binds to troponin, myosin-binding sites on actin are exposed, and myosin crossbridges form. As a result, peak tension develops in the muscle fiber. A. Contraction Period B. Relax Period C. Latent Period D. Stiff Period
Contraction Period
____________ receptors, which are so-named because the drug dihydropyridine binds to them, are located in the T-tubule membrane.
Dihydropyridine (DHP)
What events occur during the latent period?
During the latent period, the events of excitation-contraction coupling occur: The muscle action potential sweeps along the sarcolemma and into the T tubules, causing the release of calcium ions from the sarcoplasmic reticulum.
_______________ is a property of both neurons and muscle cells. A. Electrical excitability B. Contractility C. Extensibility D. Elasticity
Electrical excitability
On a cellular level, what causes muscle hypertrophy?
Exercises that require great strength for short periods produce an increase in the size and strength of Fast Glycolytic fibers. The increase in size is due to increased synthesis of thick and thin filaments. The overall result is muscle enlargement (hypertrophy), as evidenced by the bulging muscles of bodybuilders.
Normally, smooth muscle is subject to the greatest amount of stretching. For example, each time your stomach fills with food, the muscle in its wall is stretched. Cardiac muscle is also stretched each time the heart fills with blood. These are examples of which of the 4 muscle special properties? A. Electrical excitability B. Contractility C. Extensibility D. Elasticity
Extensibility
___________ allows a muscle to contract forcefully even if it is already stretched. A. Electrical excitability B. Contractility C. Extensibility D. Elasticity
Extensibility
_____________ is the ability of muscle to stretch without being damaged. A. Electrical excitability B. Contractility C. Extensibility D. Elasticity
Extensibility
A single thin filament contains two ____ actin strands arranged in a double helix like two strands of pearls that are twisted together.
F actin
G actin molecules are linked together to form a long polymer called ____ ______, which is so-named because it has a fibrous structure.
F actin
Tropomyosin strands wrap around the _____ actin double helix. Each of the tropomyosin molecules within a given strand extends along approximately seven ____ actin molecules.
F actin; G actin
The relative ratio of _______ _______ and ________ _________ fibers in each muscle is genetically determined and helps account for individual differences in physical performance. For example, people with a higher proportion of _______ _______ fibers often excel in activities that require periods of intense activity, such as weight lifting or sprinting. People with higher percentages of ____________ __________ fibers are better at activities that require endurance, such as long-distance running.
Fast glycolytic and Slow oxidative; Fast glycolytic; Slow oxidative
Endurance-type (aerobic) exercises, such as running or swimming, cause a gradual transformation of some ________ ________ fibers into _________ _____________ fibers. The transformed muscle fibers show slight _____________ in diameter, number of mitochondria, blood supply, and strength. Endurance exercises also result in cardiovascular and respiratory changes that cause skeletal muscles to receive _________ supplies of oxygen and nutrients, but they do not _______ muscle mass.
Fast glycolytic; Fast oxidative-glycolytic; increases; better; increase
A ______ amount of ATP is needed to power the contraction cycle, to pump Ca2+ into the sarcoplasmic reticulum, and for other metabolic reactions involved in muscle contraction. However, the ATP present inside muscle fibers is enough to power contraction for only a ________ seconds. If muscle contractions continue past that time, the muscle fibers must make ________ ATP.
Huge; few; More
_________ refers to increased muscle tone and is expressed in two ways: spasticity or rigidity. ____________ is characterized by increased muscle tone (stiffness) associated with an increase in tendon reflexes and pathological reflexes (such as the Babinski sign, in which the great toe extends with or without fanning of the other toes in response to stroking the outer margin of the sole). Certain disorders of the nervous system and electrolyte imbalances such as those previously noted may result in _________ _________. ___________ refers to increased muscle tone in which reflexes are not affected, as occurs in the disease tetanus.
Hypertonia; Spasticity; Spastic paralysis; Rigidity
A Z disc passes through the center of each ___ band.
I band
Would the peak tension of the second contraction in (b) be larger or smaller if the second stimulus were applied a few milliseconds later?
If the second stimulus were applied a little later, the second contraction would be smaller than the one illustrated in part (b) of Figure 11.15
Which component of the thin filament prevents myosin from binding to actin when a muscle fiber is relaxed?
In a relaxed muscle, TROPOMYOSIN prevents myosin from binding to actin.
By contrast, exercises that require great strength for short periods produce an ____________ in the size and strength of _______ ________ fibers. The increase in size is due to increased synthesis of _____ and _____ filaments. T/F: The overall result is muscle enlargement (hypertrophy), as evidenced by the bulging muscles of bodybuilders.
Increase; Fast glycolytic; Thick and thin; TRUE
____________ contractions occur when you try to lift an object that is too heavy for you to move. Muscles also contract isometrically in order to maintain posture and for supporting objects in a ________ position. An example of the latter is holding a book ______ using an outstretched arm. The book pulls the arm downward, stretching the shoulder and arm muscles. The isometric contraction of the shoulder and arm muscles ____________ the stretch. Although isometric contractions do not result in body movement, ________ is still expended.
Isometric; fixed; steady; counteracts; energy
Dihydropyridine receptors are ___-type voltage-gated _______ channels (L for long-lasting because they remain open for a relatively long period of time in response to activation) that are arranged in clusters of four known as _______.
L-type voltage-gated Ca2+; tetrads
During the _______ period, the events of excitation-contraction coupling occur: The muscle action potential sweeps along the sarcolemma and into the T tubules, causing the release of calcium ions from the sarcoplasmic reticulum. A. Contraction Period B. Relax Period C. Latent Period D. Stiff Period
Latent Period
The _______ period, which lasts about 2 msec, is a brief delay that occurs between application of the stimulus (time zero on the graph) and the beginning of contraction. A. Contraction Period B. Relax Period C. Latent Period D. Stiff Period
Latent period
Skeletal muscle is striated; that is, striations, or alternating _____ and ________ bands, are visible under a light microscope
Light; dark
Motor Unit Recruitment: When a muscle needs to generate more force during a contraction, ______ of its motor units are activated. The process of increasing the number of active motor units is called _______ ___________ _______. ______________ is one factor responsible for producing smooth movements rather than a series of jerks. Typically, the different motor units of an entire muscle are not stimulated to contract in ________. While some motor units are contracting, others are relaxed, a phenomenon known as ____________ recruitment of motor units. This pattern of motor unit activity delays muscle _______ and allows contraction of a whole muscle to be sustained for _______ periods. The smallest motor units are recruited ________, with progressively ________ motor units added if the task requires more force. For this reason, when a motor unit is recruited or turned off, only _________ changes occur in muscle tension.
More; Motor unit recruitment; Recruitment; Unison; asynchronous; fatigue; long; first; larger; slight
Why does motor unit recruitment occur?
Motor unit recruitment allows a muscle to generate more force when necessary, and it also helps to make muscle movements smooth (instead of a series of jerks).
What is the effect of the size of a motor unit on its strength of contraction? (Assume that each muscle fiber can generate about the same amount of tension.)
Motor units having many muscle fibers are capable of more forceful contractions than those having only a few fibers.
_________ is the he contractile protein that makes up the thick filaments of muscle fibers.
Myosin
________ helps anchor the thin filaments to the Z discs and regulates the length of thin filaments during development. A. titin B. α-actinin C. myomesin D. nebulin E. dystrophin
Nebulin
_________ is a long, nonelastic protein wrapped around the entire length of each thin filament. A. titin B. α-actinin C. myomesin D. nebulin E. dystrophin
Nebulin
Because the formation of ATP from creatine phosphate occurs very __________, creatine phosphate is the _______ source of energy when muscle contraction begins.
Rapidly; first
During the _________ period, also lasting 10-100 msec, Ca2+ is actively transported back into the sarcoplasmic reticulum, myosin-binding sites are covered by tropomyosin, myosin heads detach from actin, and tension in the muscle fiber decreases. A. Contraction Period B. Relax Period C. Latent Period D. Stiff Period
Relaxation Period
To sustain muscle tone, ______ groups of motor units are alternately active and inactive in a constantly shifting pattern.
Same
___________ cells retain the capacity to fuse with one another or with damaged muscle fibers to ___________ ___________ muscle fibers. T/F: However, the number of new skeletal muscle fibers formed is not enough to compensate for significant skeletal muscle damage or degeneration.
Satellite; regenerate functional; True
If weak contractions suffice to perform a task, only ______ _________ motor units are activated. If more force is needed, the motor units of _________ __________ fibers are also recruited. Finally, if maximal force is required, motor units of __________ ______ fibers are also called into action. Activation of various motor units is controlled by the _______ and ________ _________.
Slow oxidative; Fast oxidative-glycolytic; Fast glycolytic Brain and spinal cord
_____ muscle contractions also move food and substances such as bile and enzymes through the gastrointestinal tract, push gametes (sperm and oocytes) through the passageways of the reproductive systems, and propel urine through the urinary system. Which of the following muscle function below is being described? A. producing body movements B. stabilizing body positions C. storing and moving substances within the body D. generating heat.
Smooth C. moving substances within the body
Fast glycolytic fibers: __________ training programs that engage a person in activities requiring _______ strength for short times increase the size, strength, and glycogen content of fast glycolytic fibers. The FG fibers of a weight lifter may be _______ larger than those of a sedentary (sitting down) person or an endurance athlete. The increase in size is due to increased synthesis of muscle ___________. The overall result is muscle enlargement due to _______ of the FG fibers.
Strength; great; 50%; proteins; hypertrophy
Frequency of stimulation: If a second stimulus occurs in a skeletal muscle fiber AFTER the refractory period of the first stimulus is OVER but BEFORE the muscle fiber has relaxed, the second contraction will actually be _________ than the first. This phenomenon, in which stimuli arriving at different times cause contractions with greater tension, is called ________ ________.
Stronger; wave summation
T/F: Skeletal muscle fibers also contract and relax at different speeds, vary in which metabolic reactions they use to generate ATP, and differ in how quickly they fatigue. For example, a fiber is categorized as either slow or fast depending on how rapidly the ATPase in its myosin heads hydrolyzes ATP.
TRUE
T/F: When a region of sarcolemma adjacent to the motor end plate is depolarized to threshold by an end plate potential, an action potential is generated in the skeletal muscle fiber.
TRUE
T/F: Within a particular motor unit, all of the skeletal muscle fibers are of the same type. The different motor units in a muscle are recruited in a specific order, depending on need.
TRUE
T/F: The actual duration of these periods depends on the type of skeletal muscle fiber. Some fibers, such as the fast-twitch fibers that move the eyes, have contraction periods as brief as ____ msec and equally brief relaxation periods. Others, such as the slow-twitch fibers that move the legs, have contraction and relaxation periods of about _____ msec each.
TRUE; 10; 100
Motor Unit Size: The size of the motor units that are activated in a muscle affects the amount of _________ the muscle can generate. Muscles that control precise movements, which involve only small amounts of force, contain ______ motor units. T/F: For instance, muscles of the larynx (voice box) that control voice production have as few as two or three muscle fibers per motor unit, and muscles controlling eye movements may have 10 to 20 muscle fibers per motor unit. By contrast, muscles responsible for large-scale and powerful movements have _________ motor units. T/F: For example, the biceps muscle in the arm and the gastrocnemius muscle in the calf of the leg have as many as 2000 to 3000 muscle fibers in some motor units.
Tension; Small; TRUE; Large; TRUE
_____________ inhibits Ca-dependent release of Glycine and GABA- Neurotransmitters that activate inhibit interneurons. Lack of these cannot inhibit antagonistic muscles - So lock the movement of Jaw - _______-______ disease
Tetanospasmin; Lock-Jaw
What happens to the I band and H zone as muscle contracts? Do the lengths of the thick and thin filaments change?
The I bands and H zones narrow and eventually disappear when muscle is maximally contracted; The lengths of the thin and thick filaments do not change.
Which components of a sarcomere are responsible for the striations in skeletal and cardiac muscle fibers?
The striations that can be seen in skeletal and cardiac muscle fibers are created by alternating dark A bands and light I bands.
Are the voltage-gated channels involved in the skeletal muscle action potential the same as or different from those that are involved in the nerve action potential?
The voltage-gated channels involved in the skeletal muscle action potential are the SAME as those involved in the nerve action potential.
________ is the third most plentiful protein in skeletal muscle (after actin and myosin). This molecule's name reflects its huge size. With a molecular weight of about 3 million daltons, ______ is 50 times larger than an average-sized protein. A. titin B. α-actinin C. myomesin D. nebulin E. dystrophin
Titin; titin
Recall that a ______ consists of a transverse (T) tubule and two opposing terminal cisternae (lateral sacs) of the SR.
Triad
T/F: A sarcomere extends from one Z disc to the next Z disc.
True
___________: Narrow, plate-shaped regions of dense material that separate one sarcomere from the next. ___________: The dark, middle part of the sarcomere that extends the entire length of the thick filaments and also includes those parts of the thin filaments that overlap with the thick filaments. ___________: The lighter, less dense area of the sarcomere that contains the rest of the thin filaments but no thick filaments. A Z disc passes through the center of each band. ___________: A narrow region in the center of each A band that contains thick filaments but no thin filaments. ___________: A region in the center of the H zone that contains proteins that hold the thick filaments together at the center of the sarcomere. Match the correct term to one of the above descriptions: H zone M line A band I band Z discs
Z discs; A band; I band; H zone; M line
A thin filament contains? HINT: three
actin, troponin, and tropomyosin.
Each myosin head has two binding sites : (1) an ______-binding site and (2) an _____-binding site.
actin; ATP
The term oxygen debt refers to the ________ oxygen, over and above the resting oxygen consumption, that is taken into the body after ___________.
added; exercise
At the onset of contraction, the sarcoplasmic reticulum releases _______ _______ into the sarcoplasm. There, they bind to ________. Troponin then moves ____________ away from the myosin-binding sites on actin. Once the binding sites are "free," the _________ cycle begins.
calcium ions (Ca2+); troponin; tropomyosin; contraction
Once fusion has occurred, the muscle fiber loses its ability to undergo ______ _______. T/F: Thus, the number of skeletal muscle fibers is set before you are born, and most of these cells will last you a lifetime
cell division; True
********** Even before actual muscle fatigue occurs, a person may have feelings of tiredness and the desire to cease activity; this response, called _______ _______, is caused by changes in the ________ nervous system.
central fatigue; central (brain and spinal cord)
Motor proteins push or pull various cellular structures to achieve movement by converting the ________ energy in ATP to the _______ energy of motion or the production of force.
chemical; mechanical
Hydrolysis of the newly bound ATP molecule by the myosin ATPase causes the myosin head to pivot back to its ______ position (perpendicular relative to the thick and thin filaments), and a new contraction cycle begins. The contraction cycle repeats as long as ____ is available and the ____ level near the thin filament is sufficiently high.
cocked; ATP; Ca2+
In a ___________ isotonic contraction, the tension generated is great enough to exceed the load and the muscle shortens, pulling on another structure (such as a tendon) to produce movement.
concentric
Picking a book up off a table involves _________ isotonic contractions of the biceps muscle in the arm
concentric
After muscle contraction has stopped, heavy breathing _________ for a while, and oxygen consumption remains ________ the resting level.
continues; above
___________ proteins: which generate force during contraction A. contractile proteins B. regulatory proteins C. structural proteins D. Support proteins
contractile
The ________ cycle is the repeating sequence of events that causes the filaments to slide.
contraction
The enzyme _________ __________ catalyzes the transfer of one of the high-energy phosphate groups from ATP to creatine, forming creatine phosphate and ADP. This reaction is _________.
creatine kinase (CK); reversible
During the power stroke of the contraction cycle, ________ pivot, pulling the ____ filaments past the _____ filaments toward the center of the sarcomere.
crossbridges; thin; thick
Muscle Fiber Length: As sarcomere lengths become increasingly shorter than the optimum (understretched), the tension that can develop again _______. This is because the ______ filaments crumple as they are compressed by the Z discs, resulting in ______ myosin heads making contact with thin filaments.
decreases; thick; fewer
By contrast, as you lower the book to place it back on the table, the previously shortened biceps lengthens in a controlled manner while it continues to contract. When the length of a muscle increases during a contraction, the contraction is an ______________ isotonic contraction.
eccentric
During an _________ isotonic contraction, the tension exerted by the myosin crossbridges resists movement of a load (the book, in this case) and slows the lengthening process. For reasons that are not well understood, repeated eccentric isotonic contractions (for example, walking downhill) produce more muscle _________ and more delayed-onset muscle soreness than concentric isotonic contractions.
eccentric; damage
Although L-type voltage-gated Ca2+ channels allow ____________ Ca2+ to enter the sarcoplasm when activated, their main role in EC coupling is to serve as voltage _________ that trigger the _______ of the Ca2+ release channels. Ca2+ release channels are present in the _________ ___________ membrane of the sarcoplasmic reticulum.
extracellular; sensors; opening; terminal cisternal
Within myofibrils are smaller structures called _________, which can have either a thin or thick diameter. _______ filaments are 8 nm in diameter and 1-2 μm long, while _______ filaments are 16 nm in diameter and 1-2 μm long. Both thin and thick filaments are directly involved in the ______ process.
filaments; Thin; thick contraction
Frequency of stimulation: If two stimuli are applied to a skeletal muscle fiber, one immediately after the other, the muscle fiber will respond to the _____ stimulus but not to the _____. When a muscle fiber receives enough stimulation to contract, it temporarily ______ its excitability and _______ respond for a time. The period of lost excitability, called the _________ ________, is a characteristic of all muscle and nerve cells. T/F: The duration of the refractory period varies with the muscle involved. Skeletal muscle has a short refractory period of about 1 msec; cardiac muscle has a longer refractory period of about 250 msec.
first; second; loses; cannot; refractory period; TRUE;
Frequency of stimulation: If a skeletal muscle fiber is stimulated at an even higher rate, it does not relax at all. The result is ________ ___________, a smooth, sustained contraction in which individual twitches cannot be detected and maximum tension is reached.
fused (complete) tetanus
********** Although the precise mechanisms that cause muscle fatigue are still not clear, several factors are thought to contribute: One is __________ release of calcium ions from the SR, resulting in a decline of Ca2+ concentration in the ______________. Depletion of ________ _________ is also associated with fatigue, but surprisingly the ATP levels in fatigued muscle often are not much _________ than those in resting muscle. Other factors that contribute to muscle fatigue include insufficient _______, depletion of ________ and other nutrients, buildup of ______ ______ and ________, and failure of action potentials in the motor neuron to release enough ___________.
inadequate; sarcoplasm; creatine phosphate; lower; oxygen, glycogen; lactic acid; ADP; acetylcholine
In an _________ contraction, the tension generated is not enough to exceed the load, and the muscle does not change its length.
isometric (isometric = constant length)
In an ______________ contraction, tension remains constant as muscle length decreases or increases; in an ____________ contraction, tension increases greatly without a change in muscle length.
isotonic; isometric
Muscle Fiber Length: The ________-________ relationship for a skeletal muscle fiber, which indicates how the forcefulness of muscle contraction (tension) depends on the length of the __________ within a muscle fiber BEFORE contraction begins.
length-tension; sarcomeres
A major factor that determines the velocity of muscle shortening is the ______.
load
For concentric isotonic contractions, the _______ and ______ of shortening are inversely related.
load and velocity
Within the sarcoplasm are ______________, which produce large amounts of ATP for muscle contraction.
mitochondria
A ________ ________ consists of a somatic motor neuron plus all the muscle fibers it innervates
motor unit
********** The inability of a muscle to maintain force of contraction after prolonged activity is called _________ ________.
muscle fatigue
Even at rest, a skeletal muscle exhibits ________ _______, a small amount of tautness or tension in the muscle due to weak, involuntary contractions of its motor units.
muscle tone
Extending throughout the sarcoplasm are ___________, the contractile elements of the skeletal muscle fiber
myofibrils
The contractile elements of muscle fibers, the __________, contain overlapping thick and thin filaments.
myofibrils
On each G actin molecule is a ______-binding site, where a myosin head can attach.
myosin
The two contractile proteins in muscle are ______ and ______, which are the main components of thick and thin filaments, respectively
myosin and actin
The synapse between a somatic motor neuron and a skeletal muscle fiber is known as the __________ ____________.
neuromuscular junction (NMJ)
While muscle action potentials continue to propagate through the T tubules, the Ca2+ release channels are _______. Calcium ions flow into the sarcoplasm more ________ than they are transported back into the sarcoplasmic reticulum by the pumps. After the last action potential has propagated throughout the T tubules, the Ca2+ release channels ______. As the pumps move Ca2+ back into the SR, the concentration of calcium ions in the sarcoplasm quickly ________. Inside the sarcoplasmic reticulum, molecules of a calcium-binding protein, appropriately called ____________, bind to the Ca2+, enabling even more Ca2+ to be sequestered (stored) within the sarcoplasmic reticulum. As a result, the concentration of Ca2+ is 10,000 times _______ in the sarcoplasmic reticulum than in the sarcoplasm in a relaxed muscle fiber. As the Ca2+ level in the sarcoplasm drops, Ca2+ dissociates from ________, tropomyosin covers the _______-binding sites on _____, and the muscle fiber ______.
open; rapidly; closes; decreases; calsequestrin; higher; troponin; myosin; actin; relaxes
Muscle Fiber Length: At a sarcomere length of about 2.0-2.4 μm (which is very close to the resting length in most muscles), the zone of overlap in each sarcomere is __________, and the muscle fiber can develop _________ tension (100%).
optimal; maximum;
Myoglobin stores ___________ until it is needed by mitochondria to generate ______.
oxygen; ATP
Based on the law of mass action, when contraction begins and the ADP level starts to _______, creatine kinase catalyzes the transfer of a high-energy phosphate group from ___________ ____________ back to ADP. This direct phosphorylation reaction quickly regenerates new ______ molecules.
rise; creatine phosphate; ATP
Ca2+ release channels are also known as _________ receptors because the plant alkaloid ryanodine binds to them.
ryanodine
The multiple nuclei of a skeletal muscle fiber are located just beneath the _____________.
sarcolemma
________________ is the plasma membrane of a muscle fiber
sarcolemma
Each titin molecule spans half a _________, a distance of 1 to 1.2 μm in relaxed muscle. Each titin molecule connects a ___ ______ to the ___ _____ of the sarcomere, thereby helping stabilize the position of the ________ filament. The part of the titin molecule that extends from the Z disc is very _____. Because it can stretch to at least four times its resting length and then spring back unharmed, titin accounts for much of the ____________ and ____________ of myofibrils. Titin probably helps the sarcomere return to its _________ length after a muscle has contracted or been stretched, may help prevent __________ of sarcomeres, and maintains the central location of the ____ bands.
sarcomere (from a Z disc to an M line) Z disc; M line; thick elastic; extensibility; elasticity resting; overextension; A bands
A few myoblasts do persist in mature skeletal muscle as ________ cells
satellite
Muscle Fiber Length: As the sarcomeres of a muscle fiber are stretched to a longer length (overstretched), the zone of overlap ______, and ______ myosin heads can make contact with thin filaments. Therefore, the tension the fiber can produce _______. When a skeletal muscle fiber is stretched to 170% of its optimal length, there is no ________ between the thick and thin filaments. Because none of the myosin heads can bind to thin filaments, the muscle fiber cannot ________, and tension is _____.
shortens; fewer; decreases; overlap; contract; zero
A single nerve action potential in a somatic motor neuron elicits a _______ muscle action potential in _____ the skeletal muscle fibers with which it forms synapses. Action potentials always have the ______ size in a given neuron or muscle fiber. By contrast, the force of muscle fiber contraction can _____; a muscle fiber is capable of generating a much ________ force than the one that results from a single twitch. Hence, skeletal muscles can produce _______ ________. _______ _________ are contractions that vary in strength depending on how much force is needed by the muscle to support a particular object.
single; all; size; vary; greater; graded contractions (tension); graded contractions (tension)
When scientists examined the first electron micrographs of skeletal muscle in the mid-1950s, they were surprised to see that the lengths of the thick and thin filaments were the same in both relaxed and contracted muscle. It had been thought that muscle contraction must be a folding process, somewhat like closing an accordion. Instead, researchers discovered that skeletal muscle shortens during contraction because the thick and thin filaments slide past one another. The model describing this process is known as the ______ _______ __________ of muscle contraction.
sliding filament mechanism
Only a _______ amount of glycogen resynthesis occurs from lactic acid. Instead, most glycogen is made much later from _________ _____________. Much of the lactic acid that remains after exercise is converted back to ________ _______ and used for ATP production via ________ ____________ in the heart, liver, kidneys, and skeletal muscle. Oxygen use after exercise is also boosted by ongoing _____________. First, the elevated body temperature after strenuous exercise ___________ the rate of chemical reactions throughout the body. Faster reactions use ATP more _________, and _________ oxygen is needed to produce the ATP. Second, the heart and the muscles used in breathing are still working _________ than they were at rest, and thus they consume _______ ATP. Third, tissue repair processes are occurring at an ___________ pace. For these reasons, _________ _________ _______ is a better term than oxygen debt for the elevated use of oxygen after exercise.
small; dietary carbohydrates; pyruvic acid; aerobic respiration; changes; increases; rapidly; more; harder; more; increased; recovery oxygen uptake
Temporary storage of food in the stomach or urine in the urinary bladder is possible because __________ muscle ___________ close off the outlets of these organs.
smooth muscle sphincters
A muscle ______ is a sudden, involuntary contraction of one or more muscles. A spasm results from an _________ sustained muscle ___________ and is often painful. Various muscles may develop spasms, including the small intrinsic hand muscles of a musician to the larger "charley horse" calf muscles of a ru
spasm; abnormally; contraction
Storage is accomplished by sustained contractions of ringlike bands of smooth muscle called _______, which prevent outflow of the contents of a hollow organ.
sphincters
The alternating dark A bands and light I bands create the ___________ that can be seen in both myofibrils and in whole skeletal and cardiac muscle fibers.
striations
Under the light microscope, smooth muscle lacks the _______ that are present in skeletal and cardiac muscle. For this reason, it looks _______, which is why it is referred to as smooth
striations; nonstriated
In addition to contractile and regulatory proteins, muscle contains about a dozen _____________ proteins, which contribute to the alignment, stability, extensibility, and elasticity of myofibrils.
structural
___________ proteins: which keep the thick and thin filaments in the proper alignment, give the myofibril extensibility and elasticity, and link the myofibrils to the sarcolemma and extracellular matrix. A. contractile proteins B. regulatory proteins C. structural proteins D. Support proteins
structural
Many skeletal muscles are also controlled _________ to some EXTENT. For example, your diaphragm continues to alternately contract and relax ______ conscious control so that you don't stop breathing. In addition, the skeletal muscles that maintain posture or stabilize body position contract _______ conscious control.
subconsciously; without; without
Organization of Skeletal Muscle: All of the connective tissues of a muscle are continuous with its _______.
tendons
As muscle contracts, it produces heat, a process known as ___________. Much of the heat generated by muscle is used to maintain __________ body temperature. Involuntary contractions of _________ muscles, known as shivering, can increase the rate of heat production.
thermogenesis; normal; skeletal
Muscle contraction occurs because myosin heads attach to and "walk" along the _______ filaments at both ends of a sarcomere, progressively pulling the _____ filaments toward the M line As a result, the thin filaments slide _____ and meet at the _______ of a sarcomere. They may even move so far inward that their ends _______. As the thin filaments slide inward: The ___ band and ___ _____, narrow and eventually disappear altogether when the muscle is maximally contracted. However, the width of the A band and the individual lengths of the thick and thin filaments remain _________. Since the thin filaments on each side of the sarcomere are attached to Z discs, when the thin filaments slide inward, the Z discs come ________ together and the sarcomere _________. Shortening of the sarcomeres causes ___________ of the whole muscle fiber, which in turn leads to ____________ of the entire muscle.
thin; thin; inward; center; overlap; I band; H zone; unchanged; closer; shortens shortening; shortening
The M line (Myomesin) proteins bind to ______ and connect adjacent ______ filaments to one another.
titin; thick
Thousands of tiny invaginations (a cavity or pouch so formed) of the sarcolemma, called _________ ____________. Transverse (T) tubules tunnel in from the surface toward the center of each muscle fiber because they ________ to the outside of the fiber, they are filled with __________ _______.
transverse (T) tubules; Open; Extracellular fluid
In a relaxed muscle, myosin is blocked from binding to actin because the strands of _________ cover the myosin-binding sites on actin.
tropomyosin
What are the smaller amounts of TWO regulatory proteins and are also part of the thin filament?
tropomyosin and troponin
Troponin is a protein that consists of three globular subunits—one that binds to ____________, one that binds to ______, and one that has binding sites for _________ ______.
tropomyosin; actin; calcium ions (Ca2+)
A myosin molecule consists of six polypeptide chains: ____ large heavy chains and _____ small light chains. T/F: These polypeptide chains are arranged in such a way that the myosin molecule has a rodlike tail and two globular heads
two; four; True
Frequency of stimulation: If a skeletal muscle fiber is stimulated at a higher rate, it can relax only slightly between stimuli. The result is a sustained but wavering contraction called _______ ___________.
unfused (incomplete) tetanus
When a somatic motor neuron is activated, all of the muscle fibers in its motor unit contract in ________. Thus, the motor unit serves as the functional _________ unit of skeletal muscle. Typically, the muscle fibers of a motor unit are _________ throughout a muscle rather than _________ together.
unison; contractile; dispersed; clustered
Muscle tone is a small amount of tautness or tension in the muscle due to _______, ________ contractions of its motor units.
weak, involuntary
