Chapter 9 Mastering A&P – Flashcards
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Which of the following are correctly paired?
cardiac muscle; nonstriated
cardiac muscle; voluntary control
skeletal muscle; voluntary control
smooth muscle; striated
answer
skeletal muscle; voluntary control
question
Which type of muscle requires voluntary nervous stimulation for activation?
skeletal
visceral
cardiac
smooth skeletal
answer
skeletal
rationale: In order to contract, skeletal muscle fibers must be voluntarily stimulated by the nervous system. The site of muscle stimulation, where the nerve fiber communicates with the muscle fiber, is called the neuromuscular junction.
question
Muscle tissue can be stimulated by the nervous system. This is because of the membrane potential in the muscle cell. Cells with a membrane potential have what property?
extensibility
elasticity
contractility
excitability
answer
excitability
rationale: Excitability, also termed responsiveness, is the ability to receive and respond to a stimulus. For example, skeletal muscle contracts in response to receiving chemical stimulation from the central nervous system.
question
The contractile, or functional, unit of a muscle fiber is __________.
the myofilament
troponin
the sarcomere
the elastic filament
answer
the sarcomere
rationale: The sarcomere is the contractile unit of a muscle fiber and the smallest functional unit of muscle. A sarcomere is the region of a myofibril between two successive Z discs; it primarily consists of thin and thick myofilaments.
question
The sliding filament model of contraction states that __________.
during contraction, the thin myofilaments slide past T tubules so that the Z discs are overlapping
during contraction, the thin myofilaments slide past the thick myofilaments so that the actin and myosin myofilaments no longer overlap
during contraction, the thin myofilaments slide past the thick myofilaments so that the actin and myosin myofilaments overlap to a greater degree
during contraction, the thin myofilaments slide past the thick myofilaments so that calcium ions can be released from the sarcoplasmic reticulum
answer
during contraction, the thin myofilaments slide past the thick myofilaments so that the actin and myosin myofilaments overlap to a greater degree
rationale: The sliding filament model of contraction states that during contraction, the thin myofilaments slide past the thick myofilaments so that actin and myosin myofilaments overlap to a greater degree. In a relaxed muscle fiber, the thick and thin myofilaments overlap only at the ends of the A band.
question
Excitation-contraction coupling is a series of events that occur after the events of the neuromuscular junction have transpired. The term excitation refers to which step in the process?
Excitation refers to the propagation of action potentials along the axon of a motor neuron.
Excitation refers to the release of calcium ions from the sarcoplasmic reticulum.
Excitation refers to the shape change that occurs in voltage-sensitive proteins in the sarcolemma.
Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.
answer
Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.
rationale: These action potentials set off a series of events that lead to a contraction.
question
Excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. What specific event initiates the contraction?
Calcium release from the sarcoplasmic reticulum initiates the contraction.
Sodium release from the sarcoplasmic reticulum initiates the contraction.
Action potentials propagate into the interior of the skeletal muscle fiber.
Voltage-sensitive proteins change shape.
answer
Calcium release from the sarcoplasmic reticulum initiates the contraction.
rationale: Sarcoplasmic reticulum is the specific name given to the smooth endoplasmic reticulum in muscle cells. It is especially abundant and convoluted in skeletal muscle cells. It functions in the storage, release, and reuptake of calcium ions.
question
A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. How are these components connected?
A series of proteins that control calcium release.
Voltage-gated sodium channels.
Myosin cross-bridge binding sites.
Potassium leak channels.
answer
A series of proteins that control calcium release.
rationale: When action potentials propagate along T-tubules, a voltage-sensitive protein changes shape and triggers a different protein to open it's channels, resulting in the release of calcium from the terminal cisternae.
question
Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?
Sodium ions.
Action potentials.
Acetylcholine.
Calcium ions.
answer
calcium ions
rationale: Action potentials propagating down the T-tubule cause a voltage-sensitive protein to change shape. This shape change opens calcium release channels in the sarcoplasmic reticulum, allowing calcium ions to flood the sarcoplasm. This flood of calcium ions is directly responsible for the coupling of excitation to contraction in skeletal muscle fibers.
question
What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated?
A skeletal muscle fiber is innervated by multiple motor neurons.
Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.
Motor neurons always innervate thousands of skeletal muscle fibers.
A motor neuron typically innervates only one skeletal muscle fiber.
answer
Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.
rationale: There are many more skeletal muscle fibers than there are motor neurons. The ratio of neurons to fibers varies from approximately one to ten to approximately one to thousands.
question
Skeletal muscle cells are grouped into bundles called __________.
muscle fibers
fascicles
myofilaments
myofibrils
answer
fascicles
rationale: Skeletal muscle cells (or muscle fibers) are grouped into fascicles that resemble bundles of sticks.
question
Synaptic vesicles at the neuromuscular junction contain __________.
calcium
acetylcholine
synaptic potentials
ACh receptors
answer
acetylcholine
rationale: Acetylcholine (ACh) is the neurotransmitter contained in synaptic vesicles at the neuromuscular junction. ACh allows a motor neuron to stimulate the sarcolemma of a skeletal muscle fiber.
question
ACh receptors are found mainly in the __________.
axon terminal
terminal cisternae
synaptic vesicles
sarcolemma
answer
sarcolemma
rationale: The sarcolemma contains ACh receptors. The opening of these ACh receptors depolarizes the muscle fiber, which leads to the generation of a muscle action potential.
question
What most directly causes synaptic vesicles to release acetylcholine into the synaptic cleft?
depolarization of the sarcolemma
calcium entering the axon terminal
an action potential arriving at the axon terminal
sodium entering the muscle fiber
answer
calcium entering the axon terminal
rationale: Calcium entry causes synaptic vesicles to release acetylcholine into the synaptic cleft. Each synaptic vesicle contains thousands of acetylcholine molecules.
question
Acetylcholine receptors are best characterized as what type of channel?
voltage-gated Ca2+ channels
chemically gated Ca2+ channels
chemically gated Na+-K+ channels
voltage-gated Na+-K+ channels
answer
chemically gated Na+-K+ channels
rational: Chemically gated ion channels open due to the binding of a neurotransmitter, such as acetylcholine. Chemically gated Na+-K+ channels allow the diffusion of Na+ into the muscle fiber and K+ out of the muscle fiber
question
When the chemically gated ion channels open, which ion is mainly responsible for depolarizing the sarcolemma?
potassium
ACh
calcium
sodium
answer
sodium
rationale: The inward diffusion of sodium ions, through acetylcholine receptors, depolarizes the sarcolemma. Potassium also diffuses through acetylcholine receptors, but less potassium diffuses than sodium, and the outward movement of potassium is not depolarizing.
question
What is the primary mechanism by which ACh is cleared from the synaptic cleft?
diffusion away from the synaptic cleft
endocytosis by synaptic vesicles
broken down by acetylcholinesterase
reuptake into the synaptic terminal
answer
broken down by acetylcholinesterase
rationale: Acetylcholinesterase breaks down acetylcholine in the synaptic cleft. Inhibition of acetylcholinesterase, as some poisons can do, causes repeated muscle action potentials and near-constant muscle contraction.
question
What would happen if acetylcholine was not removed from the synaptic cleft?
Multiple action potentials would occur in the motor neuron.
The acetylcholine receptors would not open.
Multiple action potentials would occur in the muscle fiber.
Voltage-gated Ca2+ channels would remain open.
answer
Multiple action potentials would occur in the muscle fiber.
rationale: Action potentials will not cease until acetylcholine is removed from the synaptic cleft. Therefore, the constant presence of acetylcholine would cause multiple muscle action potentials and near-constant muscle contraction.
question
The cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge?
ATP bound to a myosin head
Troponin bound to tropomyosin
Calcium bound to troponin
A myosin head bound to actin
answer
A myosin head bound to actin
rationale: As soon as the activated myosin head forms a cross bridge with actin, the power stroke begins.
question
What structure is the functional unit of contraction in a skeletal muscle fiber?
The junctional folds of the sarcolemma
The cross bridge
The triad
The sarcomere
answer
The sarcomere
A sarcomere is a regular arrangement of thin and thick myofilaments that extends from one Z disc to the next. A myofibril consists of a series of sarcomeres.
question
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 transverse tubules.
Calcium ions are stored in the nuclei.
Calcium ions are stored in the sarcoplasmic reticulum.
Calcium ions are stored in the mitochondria.
answer
Calcium ions are stored in the sarcoplasmic reticulum.
rationale: Sarcoplasmic reticulum is the specific name given to the smooth endoplasmic reticulum in muscle fibers. The sarcoplasmic reticulum is very elaborate in skeletal muscle fibers, allowing for significant storage of calcium ions.
question
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.
Calcium ions bind to troponin.
ADP and inorganic phosphate are bound to the myosin head.
Acetylcholine binds to receptors in the junctional folds of the sarcolemma.
answer
ATP binds to the myosin head.
rationale: The binding of ATP to the myosin head weakens the bond between myosin and actin, forcing the myosin head to detach. ATP also provides the energy for the next power stroke.
question
How does the myosin head obtain the energy required for activation?
The energy comes from oxidative phosphorylation.
The energy comes from the hydrolysis of ATP.
The energy comes from the hydrolysis of GTP.
The energy comes from the direct phosphorylation of ADP by creatine phosphate.
answer
The energy comes from the hydrolysis of ATP.
Myosin is a large, complex protein with a binding site for actin. It also contains an ATPase. The energy released during the hydrolysis of ATP activates the myosin head.
question
What specific event triggers the uncovering of the myosin binding site on actin?
Calcium ions bind to troponin and change its shape.
Sodium ions bind to troponin and change its shape.
Calcium release channels open in the
sarcoplasmic reticulum, and calcium levels rise in the sarcoplasm.
Calcium ions bind to tropomyosin and change its shape.
answer
Calcium ions bind to troponin and change its shape.
rationale: The shape change caused by the binding of calcium to troponin shifts tropomyosin away from the myosin binding sites on actin.
question
When does cross bridge cycling end?
Cross bridge cycling ends when ATP binds to the myosin head.
Cross bridge cycling ends when calcium ions are passively transported back into the sarcoplasmic reticulum.
Cross bridge cycling ends when calcium release channels in the sarcoplasmic reticulum open.
Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin.
answer
Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin.
rationale: The sarcoplasmic reticulum contains Ca2+-ATPases that actively transport Ca2+ into the SR. Without Ca2+, troponin returns to its resting shape, and tropomyosin glides over and covers the myosin binding sites on actin.
question
What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell?
calcium ion pump
ATP
troponin
arrival of an action potential
answer
arrival of an action potential
rationale: an action potential in the T tubule causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum.
question
The binding of calcium to which molecule causes the myosin binding sites to be exposed?
tropomyosin
actin
myosin
troponin
answer
troponin
rationale: when calcium binds to troponin, troponin releases tropomyosin, exposing the myosin binding sites.
question
A myosin head binds to which molecule to form a cross bridge?
troponin
tropomyosin
actin
answer
actin
rationale: the myosin head binds to actin, the major component of thin filaments.
question
What causes the myosin head to disconnect from actin?
binding of ATP
hydrolysis of ATP
binding of troponin
binding of calcium
answer
binding of ATP
rationale: the binding of ATP causes the myosin head to disconnect from actin.
question
What causes the power stroke?
hydrolysis of ATP
binding of ATP
calcium
release of ADP and Pi
answer
release of ADP and Pi
rationale: the hydrolysis of ATP provides the energy for the power stroke. Energy is transferred from ATP to the myosin head.
question
In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter?
acetylcholine (ACh)
dopamine
norepinephrine
serotonin
answer
acetylcholine (ACh)
rationale: acetylcholine is the neurotransmitter found in neuromuscular junctions.
question
When an action potential arrives at the axon terminal of a motor neuron, which ion channels open?
voltage-gated potassium channels
chemically gated calcium channels
voltage-gated sodium channels
voltage-gated calcium channels
answer
voltage-gated calcium channels
rationale: the action potential opens voltage-gated calcium channels and calcium rushes into the axon terminal, leading to the release of the neurotransmitter.
question
What means of membrane transport is used to release the neurotransmitter into the synaptic cleft?
a protein carrier
a channel
exocytosis
answer
exocytosis
rationale: the synaptic vesicles (where the neurotransmitter is stored) merge with the membrane and release the neurotransmitter by exocytosis.
question
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 (junctional folds of the sarcolemma).
Binding causes voltage-gated sodium channels to open in the motor end plate (junctional folds of the sarcolemma).
Binding causes chemically gated potassium channels to open in the motor end plate (junctional folds of the sarcolemma).
Binding causes potassium voltage-gated channels to open in the motor end plate (junctional folds of the sarcolemma).
answer
Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate (junctional folds of the sarcolemma).
rationale: sodium enters the cell and causes depolarization. A small amount of potassium also leaves the motor end plate (junctional folds of the sarcolemma).
question
How is acetylcholine (ACh) removed from the synaptic cleft?
acetylcholinesterase (AChE; an enzyme) and endocytosis into the muscle fiber
acetylcholinesterase (AChE; an enzyme) only
simple diffusion away from the synaptic cleft and endocytosis into the muscle fiber
simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme)
answer
simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme)
rationale: Acetylcholinesterase breaks down acetylcholine in the synaptic cleft.
question
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?
cytosol
terminal cisterns (cisternae) of the sarcoplasmic reticulum
sarcolemma
T tubule
answer
terminal cisterns (cisternae) of the sarcoplasmic reticulum
rationale: calcium is stored in the terminal cisterns (cisternae) of the sarcoplasmic reticulum until it is released by an action potential.
question
What is the role of calcium in the cross bridge cycle?
Calcium binds to active sites on actin, forming the cross bridge.
Calcium binds to myosin, causing the myosin head to release from the actin myofilament.
Calcium binds to troponin, exposing the active site on troponin.
Calcium binds to troponin, altering its shape.
answer
Calcium binds to troponin, altering its shape.
rationale: Calcium binding to troponin causes tropomyosin to move away from the active sites on actin.
question
What role does tropomyosin play in the cross bridge cycle?
Tropomyosin moves the actin filament relative to the myosin filament.
The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form.
Tropomyosin binds to calcium, causing muscle relaxation.
Tropomyosin pushes the myosin head away, causing cross bridge detachment.
answer
The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form.
rationale: Tropomyosin covers active sites in relaxed muscle. When tropomyosin is displaced, the active sites are exposed for cross bridge formation.
question
How does troponin facilitate cross bridge formation?
Troponin gathers excess calcium that might otherwise block actin's progress.
Troponin hydrolyzes ATP, which provides the energy necessary for cross bridges to form.
Troponin controls the position of tropomyosin on the thin filament, enabling myosin heads to bind to the active sites on actin.
Troponin moves away from the active sites on actin, permitting cross bridge formation.
answer
Troponin controls the position of tropomyosin on the thin filament, enabling myosin heads to bind to the active sites on actin.
rationale: For cross bridges to form, tropomyosin must not block the active sites. The position of tropomyosin is controlled by the regulatory protein troponin. This protein-protein interaction couples the binding of calcium (to troponin) to the exposure of active sites.
question
What, specifically, is a cross bridge?
myosin binding to actin
calcium binding to troponin
ATP binding to the myosin head
tropomyosin covering the active sites on actin
answer
myosin binding to actin
rationale: The attachment of a myosin head from the thick filament to an active site on actin on the thin filament is a cross bridge. As soon as the cross bridge forms, the power stroke occurs, moving the thin filament toward the center of the sarcomere.
question
Which event causes cross bridge detachment?
ATP binding to the myosin head
release of ADP and inorganic phosphate from the myosin head
release of calcium from troponin
nervous input ends
answer
ATP binding to the myosin head
rationale: As ATP binds, the myosin head releases from the active site on actin
question
Where in the cross bridge cycle does ATP hydrolysis occur?
during the power stroke
during the movement of tropomyosin to expose the active sites on actin
during the cocking of the myosin head
during the removal of calcium from troponin
answer
during the cocking of the myosin head
rationale: As ATP is broken down, its energy is used to cock the myosin head in preparation for the next power stroke.
question
How/when does the myosin head cock back to store energy for the next cycle?
when ADP is released from the myosin head
The power stroke cocks the myosin head.
After the myosin head detaches, energy from ATP hydrolysis is used to re-cock the myosin head.
The sliding of the actin myofilament during the power stroke re-cocks myosin heads that have previously delivered their power stroke.
answer
After the myosin head detaches, energy from ATP hydrolysis is used to re-cock the myosin head.
rationale: In addition to breaking the cross bridge, ATP provides energy to cock the heads back after the previous power stroke.
question
BMD (2,3-butanedione 2-monoximime) inhibits myosin, such that ATP can bind to myosin but myosin is unable to hydrolyze the bound ATP. What effect would BMD have on the cross bridge cycle?
Myosin heads would remain detached, unable to cock.
Myosin heads would remain attached to actin, unable to perform the power stroke.
Myosin heads would remain attached to actin, unable to detach.
Tropomyosin would not move, and the active sites on actin would not be exposed.
answer
Myosin heads would remain detached, unable to cock.
rationale: The hydrolysis of ATP is required for the cocking of the myosin head. ATP would still bind to myosin, causing cross bridge detachment, but myosin would be stuck in this step of the cross bridge cycle.
question
During contraction, what prevents actin myofilaments from sliding backward when a myosin head releases?
There are always some myosin heads attached to the actin myofilament when other myosin heads are detaching.
The actin myofilament can only move in one direction relative to the myosin filament.
Calcium blocks the active sites on actin.
The cross bridge remains in place, preventing the actin myofilament from sliding.
answer
There are always some myosin heads attached to the actin myofilament when other myosin heads are detaching.
rationale: During contraction, about half of the myosin heads are attached, preventing the actin myofilament from sliding backwards when any single myosin head detaches. The situation is analogous to a game of tug-of-war. In tug-of-war, individual hands release after they pull on the rope, but not all hands release at the same time.
question
Muscle tissue has all of the following properties except ________.
extensibility
excitability
secretion
contractility
answer
secretion
question
Which term best identifies a muscle cell?
myofibril
sarcomere
muscle fascicle
muscle fiber
answer
muscle fiber
rationale: Skeletal muscle cells fuse during development to form the mature, multinucleated muscle fibers.
question
A sarcomere is the distance between two ________.
I band
Myosin
A band
Z discs
answer
Z discs
question
The ________ contains only the actin filaments.
I band
Myosin
A band
Z discs
answer
I band
question
The thicker filaments are the ________ filaments.
I band
Myosin
A band
Z discs
answer
myosin
question
Both actin and myosin are found in the ________.
I band
Myosin
A band
Z discs
answer
A band
question
The myosin filaments are located in the ________.
I band
Myosin
A band
Z discs
answer
A band
question
Which of the following is the correct sequence of events for muscle contractions?
muscle cell action potential, neurotransmitter release, ATP-driven power stroke, calcium ion release from SR, sliding of myofilaments
neurotransmitter release, motor neuron action potential, muscle cell action potential, release of calcium ions from SR, ATP-driven power stroke
motor neuron action potential, neurotransmitter release, muscle cell action potential, release of calcium ions from SR, ATP-driven power stroke, sliding of myofilaments
neurotransmitter release, muscle cell action potential, motor neuron action potential, release of calcium ions from SR, sliding of myofilaments, ATP-driven power stroke
answer
motor neuron action potential, neurotransmitter release, muscle cell action potential, release of calcium ions from SR, ATP-driven power stroke, sliding of myofilaments
question
What is the functional unit of a skeletal muscle called?
a sarcomere
a myofibril
a myofilament
the sarcoplasmic reticulum
answer
a sarcomere
question
The thin filaments (actin) contain a polypeptide subunit G actin that bears active sites for myosin attachment.
True
False
answer
true
question
Which of the following is/are mechanism(s) to end neural transmission at the neuromuscular junction?
Select all the correct answers.
ACh diffuses away from the synaptic cleft.
ACh is broken down into acetic acid and choline by the enzyme acetylcholinesterase (AChE).
ACh binds to ACh receptors.
ACh is taken up by the axon terminal via endocytosis.
answer
-ACh diffuses away from the synaptic cleft.
-ACh is broken down into acetic acid and choline by the enzyme acetylcholinesterase (AChE).
rationale: The chemical signal (ACh) at the neuromuscular junction is very short! Soon after ACh is released from the axon terminal, it is rapidly degraded by AChE or diffuses out of the synaptic cleft. These two mechanisms ensure that just enough ACh binds to its receptor to initiate an action potential and that the muscle fiber's response is quickly terminated.
question
What event directly triggers the release of neurotransmitter shown in A?
diffusion of K+ into the axonal terminus
diffusion of Na+ out of the axonal terminus
diffusion of Na+ into the axonal terminus
diffusion of Ca2+ into the axonal terminus
answer
diffusion of Ca2+ into the axon terminal
rationale: A nerve impulse arrives at the axon terminal triggering the opening of Ca2+ channels, which allows for the diffusion of Ca2+ into the terminal. This in turn leads directly to the release of neurotransmitters by exocytosis.
question
A resting potential is caused by a difference in the concentration of certain ions inside and outside the cell.
True
False
answer
true
question
The effect of a neurotransmitter on the muscle cell membrane is to modify its ion permeability properties temporarily.
True
False
answer
true
question
Of the following muscle types, which is the only one subject to conscious control?
A. Smooth
B. Skeletal
C. Cardiac
D. All of these muscle types are subject to conscious control.
answer
B. Skeletal
question
In order to receive a signal to contract, each skeletal muscle must be served by a(n) _________.
A. artery
B. nerve
C. vein'
D. ligament
answer
B. nerve
question
Which of the following surrounds the individual muscle cell?
A. perimysium
B. endomysium
C. epimysium
D. fascicle
answer
B. endomysium
question
What structure in skeletal muscle functions in calcium storage?
A. sarcoplasmic reticulum
B. mitochondria
C. intermediate filament network
D. myofibrillar network
answer
A. sarcoplasmic reticulum
question
The space between the neuron and the muscle is the axon terminal.
A. True
B. False
answer
False
Rationale: the space between the neuron and the muscle is called the synaptic cleft
question
The neurotransmitter that stimulates skeletal muscles is acetylcholine
A. True
B. False
answer
A. True
question
What is the significance of the muscle fiber triad relationship?
A. The terminal cisterns subdivide the sarcolemma.
B. The T tubules bring calcium to the sarcoplasmic reticulum.
C. The sarcoplasmic reticulum transfers calcium to the T tubules.
D. The T tubules conduct electrical impulses that stimulate calcium release from the sarcoplasmic reIculum
answer
D. The T tubules conduct electrical impulses that stimulate calcium release from the sarcoplasmic reIculum
question
What is calcium's function during muscle contraction?
A. Calcium binds to troponin, changing its shape and removing the blocking action of tropomyosin.
B. Calcium binds to troponin to prevent myosin from attaching to actin.
C. Calcium depolarizes the muscle fiber.
D. Calcium flows down the T tubules to stimulate the influx of sodium from the sarcoplasmic reticulum.
answer
A. Calcium binds to troponin, changing its shape and removing the blocking action of tropomyosin.
question
The sliding filament model of contraction involves ________.
A) actin and myosin sliding past each other and partially overlap
B) the shortening of thick filaments so that thin filaments slide past
C) actin and myosin shortening but not sliding past each other
D) the Z discs sliding over the myofilaments
answer
A) actin and myosin sliding past each other and partially overlap
question
The force exerted by a contracting muscle on an object is called ______.
A. musclesummation
B. muscle twitch
C. muscle tension
D. muscle load
answer
C. muscle tension
question
A single contraction in response to a single threshold stimulus is defined as _________.
a. summation
b. tetany
c. treppe
d. a twitch
answer
d. a twitch
question
Contraction of which sheet of smooth muscle results in shortening of the organ?
A. circular layer
B. transverse layer
C. longitudinal layer
D. square layer
answer
C. longitudinal layer
question
A major difference between smooth muscle fibers and skeletal muscle fibers in terms of calcium influx in that
A. smooth muscle fibers have a sarcoplasmic reticulum
B. calcium ions are stored in the sarcoplasm of smooth muscle
C. calcium ion influx occurs mostly from the extracellular fluid in smooth muscle
D. smooth muscle contraction does not involve calcium
answer
C. calcium ion influx occurs mostly from the extra cellular fluid in smooth muscle
question
What is name given to the regularly spaced infoldings of the sarcolemma?
transverse or T tubules
motor endplates
sarcoplasmic reticulum
terminal cisternae
answer
transverse or T tubules
rationale: T tubules penetrate a skeletal muscle fiber and provide a pathway for excitation into the interior.
