Human Anatomy Chapter 10
Put the following structures in order from superficial to deep. 1. muscle fiber 2. perimysium 3. myofibril 4. fascicle 5. endomysium 6. epimysium
6, 2, 4, 5, 1, 3
What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell?
Arrival of an action potential
The binding of the neurotransmitter to receptors on the motor end plate causes which of the following to occur?
Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate.
Calcium ions couple excitation of a skeletal muscle fiber to contraction of the fiber. Where are calcium ions stored within the fiber?
Calcium ions are stored in the sarcoplasmic reticulum.
The region of the sarcomere that always contains thin filaments is the
I band
How does the myosin head obtain the energy required for activation?
The energy comes from the hydrolysis of ATP.
Which of the following is important to increasing efficiency in tension production?
a shortened relaxation phase
Fatigued muscles signify
decreased pH
Muscles that move the eyeball have ________ fibers
fast
A fascicle is a
group of muscle fibers that are encased in the perimysium.
Fast fibers
have low resistance to fatigue and quick twitches.
A muscle producing almost peak tension during rapid cycles of contraction and relaxation is said to be in
incomplete tetanus
Heat energy gained from muscle contraction is released by the ________ system.
integumentary
The type of contraction in which the muscle fibers do not shorten is called
isometric
A single motor neuron together with all the muscle fibers it innervates is called a(n)
motor unit
Interactions between actin and myosin filaments of the sarcomere are responsible for
muscle contraction
The neuromuscular junction is a connection between a neuron and a __________.
muscle fiber
Acetylcholine receptors are primarily located __________
on the motor end plate
The plasma membrane of a skeletal muscle fiber is called the
sarcolemma
The repeating unit of a skeletal muscle fiber is the
sarcomere
Which organelle completely surrounds each myofibril inside a muscle fiber?
sarcoplasmic reticulum
At each end of the muscle, the collagen fibers of the epimysium, perimysium, and endomysium, come together to form a
tendon
An action potential in the muscle fiber causes __________.
the muscle fiber to contract
What is the synaptic cleft?
the space between the synaptic terminal and the motor end plate
T tubules and the terminal cisternae are clustered into structures called __________.
triads
A single contraction-relaxation cycle in a muscle fiber produces a(n)
twitch
Aerobic metabolism normally provides ________ percent of the ATP demands of a resting muscle cell.
95
The region of the sarcomere containing the thick filaments is the
A band
The cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge
A myosin head bound to actin
Cross bridge detachment is caused by ________ binding to the myosin head.
ATP
The characteristic muscle stiffness associated with rigor mortis is due to the inability of myosin filaments to detach from the active site on actin filaments. What molecule is essential for this detachment?
ATP
After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment?
ATP binds to the myosin head.
Tamara's muscle weakness and fatigue becomes progressively worse over the course of the day. This is a hallmark sign of myasthenia gravis, an autoimmune disorder that affects the ability of a motor neuron to communicate with a muscle fiber. What synaptic events must happen first for excitation to occur?
Acetylcholine is released from the axon terminal and diffuses across the synapse to bind to a receptor in the surface of the motor end plate.
The injection that dramatically improved Tamara's symptoms was Tensilon, an acetylcholinesterase inhibitor. What is acetylcholinesterase, and why was this injection effective in relieving Tamara's symptoms?
Acetylcholinesterase is the enzyme that clears acetylcholine from the synapse. Inhibiting this enzyme will enable acetylcholine to be available for a longer period to bind to receptors.
What specific event triggers the uncovering of the myosin binding site on actin?
Calcium ions bind to troponin and change its shape.
When does cross bridge cycling end?
Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin.
The dense layer of connective tissue that surrounds an entire skeletal muscle is the
Epimysium
The area in the center of the A band that contains no thin filaments is the
H band
Myasthenia gravis is an autoimmune disorder that results in the production of antibodies that either block or cause the destruction of the ACh receptor. Why do you think that Tamara's symptoms become worse as the day progresses?
In the morning, the neuronal reserves of acetylcholine are larger, allowing for sufficient neurotransmitter release and resulting in effective muscle signaling. As the day progresses and the stores of acetylcholine become depleted, muscle function becomes progressively worse.
How would the loss of acetylcholinesterase from the motor end plate affect skeletal muscle?
It would cause muscles to stay contracted.
Skeletal muscles does each of these except...
Pump Blood
Which of the following statements is false?
Skeletal muscle and cardiac muscle stimulation is neural.
What structure is the functional unit of contraction in a skeletal muscle fiber?
The sarcomere
Which of these statements about skeletal muscles is false?
Their fibers branch
The skeletal muscle complex known as the triad consists of
a transverse tubule and two terminal cisternae
During neuromuscular transmission, the axon terminals release
acetylcholine
In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter?
acetylcholine (ACh)
Triggering of the muscle action potential occurs after
acetylcholine binds to chemically-gated channels in the motor end plate.
The cytoplasm of the neuromuscular terminal contains vesicles filled with molecules of the neurotransmitter
acetylcholine.
How is acetylcholine (ACh) removed from the synaptic cleft?
acetylcholinesterase (AChE; an enzyme)
A myosin head binds to which molecule to form a cross bridge?
actin
Thin filaments are mostly made of the protein
actin
The most important factor in decreasing the intracellular concentration of calcium ion after contraction is
active transport of calcium into the sarcoplasmic reticulum.
Creatine phosphate
acts as an energy reserve in muscle tissue.
During the recovery period the body's need for oxygen is increased because
additional oxygen is required to restore energy reserves.
A resting muscle generates most of its ATP by
aerobic metabolism of fatty acids
What causes the vesicles inside a neuron to fuse with the plasma membrane?
an action potential in the neuron
Decreased blood flow to a muscle could result in all of the following except
an increase in intracellular glycogen.
After heavy exercise, if energy reserves in a muscle are depleted, ________ occurs.
an oxygen debt
What causes the myosin head to disconnect from actin?
binding of ATP
The sarcoplasmic reticulum contains
calcium
Active sites on the actin become available for binding after
calcium binds to troponin
In response to action potentials arriving along the transverse tubules, the sarcoplasmic reticulum releases
calcium ions
Smooth muscle contracts when calcium binds to __________ and activates __________.
calmodulin; myosin light chain kinase
Muscle tissue, one of the four basic tissue groups, consists chiefly of cells that are highly specialized for
contraction
Physical evidence that supports the sliding filament theory of muscle contraction includes
decreased width of the H band during contraction.
What means of membrane transport is used to release the neurotransmitter into the synaptic cleft?
exocytosis
Inside a muscle, bundles of single muscle fibers form
fascicles
Which of the following is not a function of smooth muscle tissue?
forcing blood from the heart into the major arteries
In the liver, during the Cori cycle,
glucose is produced from lactic acid.
When comparing slow muscle fibers to fast muscle fibers, slow fibers
have much smaller fiber diameters. are rich in the red protein myoglobin. take about three times as long to reach peak tension. generate much less tension. All of the answers are correct.
Which of the following would not lead to increased oxygen consumption?
increased anaerobic respiration by muscle cells
The muscle weakness of myasthenia gravis results from
loss of acetylcholine receptors in the end-plate membrane
In a sarcomere, the central portion of thick filaments are linked laterally by proteins of the
m line
When acetylcholine binds to receptors at the motor end plate, the sarcolemma becomes
more permeable to sodium ions.
During activities requiring aerobic endurance,
most of the muscle's energy is produced in mitochondria.
Receptors for acetylcholine are located on the
motor end plate
During the recovery period following exercise, all of the following are true except
muscle fibers are unable to contract.
In an isotonic contraction,
muscle tension exceeds the load and the muscle lifts the load.
In which of the following would the motor units have the fewest muscle fibers?
muscles that control the eyes
Skeletal muscle fibers are formed from embryonic cells called
myoblasts
Thick filaments are made of the protein
myosin
What area of the thick filament binds to actin once its active binding sites are exposed?
myosin cross bridge
Cross-bridges are portions of
myosin molecules
Each skeletal muscle fiber is controlled by a motor neuron at a single
neuromuscular junction
At peak levels of muscle exertion the mitochondria can supply
only about one-third of the energy required by the muscle.
During anaerobic glycolysis,
oxygen is not consumed. pyruvic acid is produced. carbohydrate is metabolized. ATP is produced. All of the answers are correct.
The ability of smooth muscle to function over a wide range of lengths is called
plasticity.
Which of the following best describes the term titin?
protein that accounts for elasticity of resting muscle
You try to pick up an object and discover that it is much heavier than you expected. Which process must occur in the muscle to increase tension so you can pick up the object?
recruitment
What causes the power stroke?
release of ADP and Pi
The role of acetylcholinesterase in the neuromuscular junction is to __________.
remove acetylcholine from the synaptic cleft
In response to an action potential along the transverse tubules, the __________ release(s) calcium ions into the sarcoplasm.
sarcoplasmic reticulum
Which type of muscle tissue has the greatest effect on the body's heat production?
skeletal
The structural theory that explains how a muscle fiber contracts is called the ________ theory
sliding filament
The type of muscle fiber that is most resistant to fatigue is the ________ fiber.
slow
Which of the following types of muscle fibers are best adapted for prolonged contraction such as standing all day?
slow fibers
Which of the following best describes the term sarcoplasmic reticulum?
storage and release site for calcium ions
In rigor mortis
sustained contractions occur. ATP is depleted. calcium ions keep binding to troponin. the myosin heads are attached to actin. All of the answers are correct.
The narrow space between the synaptic terminal and the muscle fiber is the
synaptic cleft
The end of a neuron, where acetylcholine-filled vesicles are located, is called the __________.
synaptic terminal
The muscle action potentials that initiate contraction are transmitted from the sarcolemma into the interior of the muscle fiber by
t tubtules
The action potential on the muscle cell leads to contraction due to the release of calcium ions. Where are calcium ions stored in the muscle cell?
terminal cisternae of the sarcoplasmic reticulum
A muscle produces its highest tension when in complete
tetanus
Which of the following acts as an ATPase during the contraction cycle of muscle?
the head portion of the myosin molecule
Which region of the sarcomere gives rise to the structure (band or line) indicated by the arrow?
the point of connection for adjacent tails of the thick filaments
All of the following proteins are part of the thin filaments except
titin
The action potential is conducted into a skeletal muscle fiber by
transverse tubules
At rest, active sites on the actin are blocked by
tropomyosin molecules
When calcium ion binds to troponin,
tropomyosin rolls away from the active site.
The binding of calcium to which molecule causes the myosin binding sites to be exposed?
troponin
To what regulatory protein does calcium bind during the initiation of the contraction cycle in skeletal muscle fibers?
troponin
What component of the thin filament binds to calcium once calcium is released from the terminal cisternae of the sarcoplasmic reticulum?
troponin
Each thin filament consists of
two actin protein strands coiled helically around each other.
Inside a neuron, acetylcholine is contained within __________.
vesicles
When an action potential arrives at the axon terminal of a motor neuron, which ion channels open?
voltage-gated calcium channels