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Acetylcholine (ACh) is released from motor neurons and enters the __________________.
answer
synaptic cleft
question
Acetylcholine causes an *end-plate potential* by triggering the ______________________. (depolarization of the membrane)
answer
opening of sodium channels
question
Thin filaments connect to and extend from either side of a ___________. These thin filaments are composed largely of the myofilament ____________.
answer
z disc; actin
question
Myosin heads directly use ______________ to transition to their _____________________ conformation, which enables them ready to bind to actin.
answer
ATP; energized
question
Steps in Process of Excitation
answer
Excitation is the process, in which action potentials in the nerve fiber lead to action potentials in the muscle fiber.
The process begins with a nerve signal stimulating a voltage-gated calcium ion channel to open, allowing the ions to enter the synaptic knob.
The ions stimulate the release of acetylcholine into the synaptic cleft.
There is then a rapid fluctuation in membrane voltage at the motor end plate, called the end-plate potential.
Areas of the sarcolemma near the motor plate have gates that open, moving ions, which causes the action potential that excites the muscle fiber.
question
An action potential enters the depths of a muscle fiber by way of __________.
diffusion
the T tubules
the calcium ion channels
the sarcoplasmic reticulum
the actin myofilament
answer
the T tubules
question
Which structure do the calcium ions bind to when muscle contraction is initiated?
The actin myofilament
The troponin molecule
The tropomyosin molecule
The sarcoplasmic reticulum
The sarcolemma
answer
The troponin molecule
question
Cross-bridges form between the __________ and the __________.
troponin; tropomyosin
calcium; sodium
sarcolemma ; sarcoplasmic reticulum
T tubules; sarcolemma
actin filaments; myosin heads
answer
actin filaments; myosin heads
question
An action potential introduced at the neuromuscular junction is propagated along the sarcoplasmic reticulum.
True
False
answer
False
propagated along sarcolemma
question
In response to an action potential entering the neuron, calcium ions diffuse from the sarcolemma into the sarcoplasm.
True
False
answer
False
In response to an action potential entering the neuron, calcium ions diffuse from the SARCOPLASMIC RETICULUM into the sarcoplasm
question
Which of the following best describes the role of Ca2+ in muscle contraction?
It binds to tropomyosin, moving troponin, so that myosin heads can bind to actin.
It binds to tropomyosin, moving troponin, so that actin heads can bind to myosin.
It binds to troponin, moving tropomyosin, so that myosin heads can bind to actin.
It binds to troponin, moving tropomyosin, so that actin heads can bind to myosin.
It binds to actin, moving myosin, so that troponin can bind to tropomyosin.
answer
It binds to troponin, moving tropomyosin, so that myosin heads can bind to actin.
question
All muscle types will respond to an electrical stimulus because all muscle cells are _________.
excitable
contractile
striated
involuntary
isometric
answer
excitable
question
Skeletal muscle is called ___________, because it is usually subject to conscious control.
excitable
contractile
striated
voluntary
isometric
answer
voluntary
question
When a skeletal muscle lengthens, its __________ helps resist excessive stretching and subsequent injury to the muscle.
thick filaments
collagen
actin
troponin-tropomyosin complex
varicosities
answer
collagen
question
The sarcoplasmic reticulum is the smooth endoplasmic reticulum of a muscle fiber.
True
False
answer
True
question
A deficiency of acetylcholine receptors leads to muscle paralysis in myasthenia gravis.
True
False
answer
True
question
An isometric contraction does not change muscle length.
True
False
answer
True
question
Which of the following marks the boundaries of a sarcomere?
I bands
H bands
Z discs
M lines
A bands
answer
Z discs
question
Which of the following is predominately made up of myosin?
G actin
F actin
The thin filament
The thick filament
The elastic filament
answer
The thick filament
question
Which of the following contains overlapping thick and thin filaments?
A band
H band
I band
M line
Z discs
answer
A band
question
Which muscle type depends solely on the sarcoplasmic reticulum as its calcium source?
Skeletal muscle
Smooth muscle
Cardiac muscle
Skeletal and smooth muscle
Smooth and cardiac muscle
answer
Skeletal muscle
question
80% of the lactic acid produced by skeletal muscle is converted to pyruvic acid by the __________.
kidneys
liver
muscle tissue
sarcoplasmic reticulum
neuromuscular junction
answer
liver
question
Shortening a muscle while it maintains constant tension is called __________.
complete tetanus
incomplete tetanus
an isokinetic contraction
an isometric contraction
an isotonic contraction
answer
an isotonic contraction
question
Michael Jordan was arguably the best player in professional basketball history. Scientifically, one would expect him to have highly developed __________ fibers.
red
white
intermediate
fast twitch
slow oxidative
answer
white
question
Where would you expect to find numerous gap junctions in muscular tissue?
The sarcoplasmic reticulum of skeletal muscle
The A bands of skeletal and cardiac muscle
The sarcolemma of skeletal muscle
The intercalated discs of cardiac muscle
Multiunit smooth muscle
answer
The intercalated discs of cardiac muscle
question
Why is the contraction strength of smooth muscle relatively independent of its resting length?
It gets nearly all of its Ca2+ from the extracellular fluid.
It does not have intercalated discs.
It does not have sarcomeres.
It is regulated by a length-tension relationship.
It is involuntary muscle.
answer
it does not have sarcomeres
question
Which of the following is an accurate comparison of skeletal muscle to smooth muscle?
Smooth muscle contracts more slowly but relaxes more rapidly.
Smooth muscle contracts more rapidly but relaxes more slowly.
Smooth muscle contracts and relaxes more slowly.
Smooth muscle consumes more ATP to maintain a given level of muscle tension.
Smooth muscle depends on a nerve fiber to supply the calcium needed for contraction.
answer
Smooth muscle contracts and relaxes more slowly.
question
The minimum stimulus needed to cause muscle contraction is called the __________.
threshold
latent period
twitch
motor unit
innervation
answer
threshold
question
If one nerve stimulus arrives at a muscle fiber so soon that the fiber has only partially relaxed from the previous twitch, the most likely result will be __________.
fatigue
spasm
incomplete tetanus
complete tetanus
flaccid paralysis
answer
incomplete tetanus
question
Which of the following has the largest mitochondria?
Slow oxidative fibers
Fast glycolytic fibers
Cardiac muscle
Smooth muscle
Intermediate fibers
answer
Cardiac muscle
question
To stimulate muscle contraction, acetylcholine is released from the ___________ into the synaptic cleft.
synaptic vesicles
junctional folds
sarcoplasmic reticulum
sarcolemma
terminal cisterna
answer
synaptic vesicles
question
The absence or inhibition of acetylcholinesterase at a synapse would lead to __________.
flaccid paralysis
tetanus
atrophy
numbness
muscle wasting
answer
tetanus
question
Which statement best describes the goal of medications used to treat myasthenia gravis?
To increase the number of acetylcholine receptors
To decrease the number of synaptic vesicles
To promote multiple motor unit summation
To inhibit Ca2+ release from the sarcoplasmic reticulum
To inhibit the function of cholinesterase
answer
To inhibit the function of cholinesterase
question
Aerobic respiration produces approximately _________ more ATPs per glucose molecule than glycolysis does.
12
24
36
48
100
answer
36
question
Athletes who train at high altitudes increase their red blood cell count, which increases their oxygen supply during exercise. Increased oxygen supply results in __________.
increased glycolysis
increased use of myokinase
longer aerobic respiration
longer anaerobic fermentation
reduced ATP consumption
answer
longer aerobic respiration
question
Which of the following would be caused by a contraction of smooth muscle?
Goose bumps
Blood leaving the left ventricle of the heart
Elevating the eyebrows
Blinking the eyelids
Deep inspiration
answer
Goose bumps
question
The triads of a muscle fiber consist of __________.
two A bands and one I band
two T tubules and one terminal cisterna
two terminal cisternae and one T tubule
two thin myofilaments and one thick myofilament
two thick myofilaments and one thin myofilament
answer
two terminal cisternae and one T tubule
question
As you are lifting a box, someone places extra weight on top of it. For your muscle to continue contracting and lifting the box, the muscle must __________.
recruit more muscle fibers
lower its threshold
reduce its wave summation
shift from isometric to isotonic contraction
shift from slow-twitch to fast-twitch mode
answer
recruit more muscle fibers
question
As you are lifting a box, someone places extra weight on top of it. For your muscle to continue contracting and lifting the box, the muscle must __________.
recruit more muscle fibers
lower its threshold
reduce its wave summation
shift from isometric to isotonic contraction
shift from slow-twitch to fast-twitch mode
answer
troponin
question
Drugs called calcium channel blockers may be used to lower blood pressure by causing arteries to vasodilate. How do you suppose these drugs work?
They prevent calcium from entering the sarcoplasmic reticulum of smooth muscle.
They stimulate the calcium pump in smooth muscle, thus removing calcium from the calmodulin.
They prevent calcium from exiting the sarcoplasmic reticulum in skeletal muscle.
They prevent calcium from entering cardiac muscle, thus slowing down the heart rate.
They prevent calcium from entering smooth muscle, thus allowing the muscle to relax.
answer
They prevent calcium from entering smooth muscle, thus allowing the muscle to relax.
question
What happens when acetylcholine stimulates its receptors in the neuromuscular junction?
The release of Ca2+ from the sarcoplasmic reticulum decreases.
The permeability of the sarcolemma to Na+ increases.
The positive charge on the sarcolemma decreases.
The threshold of the muscle fiber lowers.
The inhibitory effect of acetylcholinesterase is overridden.
answer
The permeability of the sarcolemma to Na+ increases.
question
Which of the following best describes the resting membrane potential (RMP)?
The intracellular environment is negatively charged.
The intracellular environment has more positively charged sodium.
The extracellular environment is negatively charged.
It has a voltage of about +75 mV.
It is dependent upon the absorption of potassium ions by the muscle fiber.
answer
The intracellular environment is negatively charged.
question
The sarcolemma of a resting muscle fiber is most permeable to __________.
calcium
potassium
sodium
lithium
magnesium
answer
potassium
question
What is the purpose of the triad?
The triad stores sodium.
The triad synthesizes ATP.
The triad maintains the resting membrane potential.
The triad removes acetylcholine from the synaptic cleft.
The triad allows for Ca2+ release when a muscle fiber is excited.
answer
The triad allows for Ca2+ release when a muscle fiber is excited.
question
Which of the following individuals would have more mitochondria in her skeletal muscle?
A 50-year-old sedentary computer programmer
A 22-year-old soccer player
A long-term hospice patient
A model on a reduced-calorie diet
A newborn
answer
A model on a reduced-calorie diet
question
Which of the following systems would provide energy for a racquetball player, while playing a point?
The respiratory system
The glycolysis system
The phosphagen system
The anaerobic system
The glycogen-lactic acid system
answer
The phosphagen system.
question
Loss of muscle mass from lack of activity is called __________.
myopathy
dystrophy
apathy
atrophy
tetanus
answer
atrophy
question
A myofilament that runs throught the core of a thick filament and anchors it to a Z disc is called a(n) __________.
myofibril
thin filament
T tubule
sarcolemma
elastic filament
answer
elastic filament
question
The synaptic knob releases acetylcholine into the synaptic cleft, which is received by receptors on the motor end plate. Which structure does this describe?
A sarcomere
The thick filament
The varicosity of a smooth muscle cell
The neuromuscular junction of a skeletal muscle
A motor unit
answer
The neuromuscular junction of a skeletal muscle
question
When acetylcholinesterase outlasts the release of acetylcholine from the synaptic vesicles, the skeletal muscle __________.
contracts
gets stronger
relaxes
releases Ca++
opens its Na+ channels
answer
relaxes
question
A volleyball player depends on the gastrocnemius muscles for plantar flexion, whereas a marathon runner depends more on the soleus muscles for the same action. What characteristic of the soleus muscles makes this so?
They have smaller mitochondria.
They have more glycogen in them.
They don't have as many blood capillaries per gram of tissue.
They make more use of aerobic respiration.
They break ATP down to ADP and Pi faster.
answer
They make more use of aerobic respiration
question
Why does one continue to breathe heavy after rigorous physical activity has stopped?
The diaphragm is waiting for its acetylcholine to run out.
The body requires more oxygen to restore levels of ATP and creatine phosphate.
The lungs can't stop breathing until the heart rate slows down.
Myosin heads need more oxygen to fully detach from actin.
The kidneys require oxygen to dispose of excess lactic acid.
answer
The body requires more oxygen to restore levels of ATP and creatine phosphate.
question
In skeletal muscle, the term that describes the alternating light and dark bands is ___________.
strabismus
striations
tetanus
myofibrils
myoblasts
answer
striations
question
The training regimen of a competitive weight lifter is designed partly to __________.
convert certain parallel muscles into stronger pennate muscles
increase the average number of myofibrils per muscle fiber
convert white muscle tissue to red muscle
increase the size of his motor units
lower the threshold for muscle excitation
answer
increase the average number of myofibrils per muscle fiber
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