Human Anatomy & Physiology- MyLab & Mastering AandP- Muscle Physio I

An enzyme known as acetylcholinesterase is present in the synaptic cleft. What is its role?

to break down acetylcholine

The sliding filament model of contraction states that __________.

during contraction, the thin myofilaments slide past the thick myofilaments so that the actin and myosin myofilaments overlap to a greater degree

During muscle contraction, myosin cross bridges attach to which active sites?

actin filaments

Exhaustion of glycogen storage within a muscle fiber would have the biggest effect on ________.

fast glycolytic fibers

Which step precedes all of the other listed steps?

ACh is released by the motor neuron.

The sliding filament model of contraction involves ________.

actin and myosin sliding past each other and partially overlapping

The cross bridge cycle starts when _________.

Ca2+ from the sarcoplasmic reticulum binds to troponin

Curare is a poisonous plant extract. Curare molecules have a chemical structure like the neurotransmitter ACh. Curare can bind to the ACh receptor site on the chemically gated ion channels in the motor end plate. Even though curare will bind to the receptor site it will not open the ion channel and no ions will pass through. What do you think the symptoms of curare poisoning would look like?

Curare will only affect muscles with ACh receptors, paralyzing them.

The __________ shorten(s) during muscle contraction

sarcomere

Duchenne muscular dystrophy could theoretically be cured if a technique was developed that would _________.

none of the above

Which term best identifies a muscle cell?

muscle fiber

Oxygen starved tissues can release chemical signals into the blood that can change the diameter of nearby blood vessels delivering oxygen and nutrients to the tissues. In doing so the blood vessels will respond through vasodilation (widening of the vessel). Which muscle type is responsible for this vasodilation?

smooth muscle

What part of the sarcolemma contains acetylcholine receptors?

motor end plate

The contractile units of skeletal muscles are ________.

myofibrils

After nervous stimulation stops, what prevents ACh in the synaptic cleft from continuing to stimulate contraction?

acetylcholinesterase destroying the ACh

Reduction in blood flow to a muscle fiber would have the greatest effect on ________.

slow oxidative fibers

ATP is required to cause the power stroke in the myosin head.

False

Which of the following is/are mechanism(s) to end neural transmission at the neuromuscular junction?

ACh is broken down into acetic acid and choline by the enzyme acetylcholinesterase (AChE). ACh diffuses away from the synaptic cleft.

Muscle tissue has all of the following properties except ________.

secretion

Identify the correct sequence of the following events. Myosin generates a power stroke. Ca+ binds to troponin. ATP recharges the myosin head. Troponin removes tropomyosin from G actin. The sarcomere shortens. Myosin binds to actin.

The Ca+ binds to the troponin, which removes the tropomyosin from actin. This allows the myosin to bind to actin and generate a power stroke, shortening the sarcomere. ATP is used to recharge the myosin.

If given the exact same amount of ATP, which of the three fiber types would be able to contract for the longest amount of time?

slow oxidative fibers

When a muscle fiber contracts, the I bands diminish in size, the H zones disappear, and the A bands move closer together but do not diminish in length.

True

Which type of muscle requires voluntary nervous stimulation for activation?

skeletal

Of the following items listed below, which is the best description for why skeletal muscle stores glycogen.

Skeletal muscle is a heavy consumer of energy.

Addition of more mitochondria to a muscle fiber will have the least effect on ________.

fast glycolytic fibers

When a sarcomere contracts and thin filaments move over thick filaments you would expect to see ________.

the I bands to appear smaller

Action potential propagation in a skeletal muscle fiber ceases when acetylcholine is removed from the synaptic cleft. Which of the following mechanisms ensures a rapid and efficient removal of acetylcholine?

Acetylcholine is degraded by acetylcholinesterase.

The neuromuscular junction is a well-studied example of a chemical synapse. Which of the following statements describes a critical event that occurs at the neuromuscular junction?

Acetylcholine is released by axon terminals of the motor neuron.

Action potentials travel the length of the axons of motor neurons to the axon terminals. These motor neurons __________.

extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fiber

Calcium entry into the axon terminal triggers which of the following events?

Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine.

Acetylcholine binds to its receptor in the sarcolemma and triggers __________.

the opening of ligand-gated cation channels

Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels. Why?

The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients.

Cross bridge formation between myosin heads and actin molecules is caused by the elevation of calcium ion concentration in the cytosol. During rigor mortis, this elevation of calcium ion concentration in the cytosol is permanent because ________.

mitochondria stop producing ATP molecules required by the sarcoplasmic reticulum’s calcium ion pumps

During development embryonic cells will fuse to form muscle fibers. This will result in ________.

multinucleated muscle fibers that can extend as long as 30 centimeters

What does excess postexercise oxygen consumption represent?

the difference between the amount of oxygen needed for totally aerobic muscle activity and the amount actually used

If the cell could no longer produce ATP, what would be the effect on the sarcoplasmic reticulum?

It would be unable to concentrate Ca+ in the sarcoplasmic reticulum.

In the muscles of the limbs, the origin is usually the immobile muscle attachment.

True

Which of the following statements is FALSE?

Skeletal muscle cells use creatine phosphate instead of ATP to do work.

Which of the following is true concerning the anatomy of a skeletal muscle fiber?

Myofibrils contain thick and thin filaments.

The calcium that initiates skeletal muscle contraction is released from what structure(s)?

terminal cisternae

Which of the following are composed of myosin?

thick filaments

In muscle fibers, which regulatory protein blocks the attachment of myosin heads to actin?

tropomyosin

What event most directly triggers the release of calcium from the terminal cisternae?

action potential propagating down the T tubule

How do calcium ions initiate contraction in skeletal muscle fibers?

Calcium ions bind to troponin, changing troponin’s shape.

Which of the following best describes the events of "excitation" in "excitation-contraction coupling"?

propagation of the action potential along the sarcolemma

Which of the following best describes the events of "contraction" in "excitation-contraction coupling"?

cross bridge formation

Myasthenia gravis is sometimes treated medically by a treatment that involves ________.

inhibiting the action of acetylcholinesterase

Which of the following are correctly paired?

skeletal muscle; voluntary control

The contractile, or functional, unit of a muscle fiber is __________.

the sarcomere

Rigor mortis occurs because ________.

no ATP is available to release attached actin and myosin molecules

What level of structural organization do voltage-gated sodium channels in muscle sarcolemma represent?

molecule

What is the function of the filaments found in ranges 1-2 and 6-7 but no other ranges?

protection from overstretching Elastic (titin) filaments help to protect the muscle from overstretching and also aid in returning it to normal length.

Myasthenia gravis is a disease that is believed to be caused by autoimmune disorder, resulting in the loss of ACh receptors at the motor end plate of muscle fibers. Which of the following is likely to be a symptom of myasthenia gravis?

weakness of muscle

What is the role of calcium in the cross bridge cycle?

Calcium binds to troponin, altering its shape.

What role does tropomyosin play in the cross bridge cycle?

The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form.

How does troponin facilitate cross bridge formation?

Troponin controls the position of tropomyosin on the thin filament, enabling myosin heads to bind to the active sites on actin.

What, specifically, is a cross bridge?

myosin binding to actin

Which event causes cross bridge detachment?

ATP binding to the myosin head

Where in the cross bridge cycle does ATP hydrolysis occur?

during the cocking of the myosin head

How/when does the myosin head cock back to store energy for the next cycle?

After the myosin head detaches, energy from ATP hydrolysis is used to re-cock the myosin head.

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.

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.

Which protein is indicated by the letter A?

actin Actin is the chief component of the thin myofilaments.

Which of the following is the correct sequence of events for muscle contractions?

motor neuron action potential, neurotransmitter release, muscle cell action potential, release of calcium ions from SR, ATP-driven power stroke, sliding of myofilaments

The connective tissue that covers structure A is continuous with which of the following?

tendon The dense connective tissue at A is continuous with the tendon that connects the muscle to a bone or, in some cases, to another muscle or to the skin.

If a muscle fiber were to suddenly and permanently stop producing ATP the fiber would no longer be able to actively transport calcium out of the cytoplasm (sarcoplasm) and the intracellular calcium concentration would rise. Which of the following would you expect to happen?

Myosin would be able to bind to the exposed binding sites on thin filaments but it would not be able to detach.

Based on what you know of the relationship between the thick and the thin filaments, what would happen if a disorder existed that caused a person to produce no tropomyosin?

The muscle tissues would never be able to relax.

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, in this case, refers to the propagation of action potentials along the sarcolemma.

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.

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.

What is name given to the regularly spaced infoldings of the sarcolemma?

transverse or T tubules

Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?

Calcium ions.

What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated?

Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.

An increase in the calcium ion level in the sarcoplasm starts the sliding of the thin filaments. When the level of calcium ions declines, sliding stops.

True

Which organelle can chemically regulate the shortening of the muscle?

the sarcoplasmic reticulum

What is the most distinguishing characteristic of muscle tissue?

the ability to transform chemical energy into mechanical energy to move the body

What structure in skeletal muscle cells functions in calcium storage?

sarcoplasmic reticulum

What cellular event is indicated by A?

exocytosis Neurotransmitters stored in synaptic vesicles are released into the synaptic cleft by exocytosis.

What is the functional unit of a skeletal muscle called?

a sarcomere

Hypothetically, if a muscle were stretched to the point where thick and thin filaments no longer overlapped, ________.

no muscle tension could be generated

Which of the following is most directly required to initiate the coupling of myosin to actin?

Ca+

The interaction between which protein and ion initiates contraction of skeletal muscle?

troponin; calcium ions

Skeletal muscle cells are grouped into bundles called __________.

fascicles

Synaptic vesicles at the neuromuscular junction contain __________.

acetylcholine

ACh receptors are found mainly in the __________.

sarcolemma 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.

What most directly causes synaptic vesicles to release acetylcholine into the synaptic cleft?

calcium entering the axon terminal

Acetylcholine receptors are best characterized as what type of channel?

chemically gated Na+-K+ channels

When the chemically gated ion channels open, which ion is mainly responsible for depolarizing the sarcolemma?

sodium

What is the primary mechanism by which ACh is cleared from the synaptic cleft?

broken down by acetylcholinesterase

What would happen if acetylcholine was not removed from the synaptic cleft?

Multiple action potentials would occur in the muscle fiber.

What is the functional role of the T tubules?

enhance cellular communication during muscle contraction

Which of the following surrounds the individual muscle cell?

endomysium

Which statement accurately describes the event indicated by B?

Binding of acetylcholine to a receptor triggers the opening of an ion channel. Binding of acetylcholine to its receptor opens chemically (ligand) gated ion channels that allow Na+ and K+ to diffuse across the sarcolemma

A toxin released by certain bacteria can block the release of neurotransmitters into a neuromuscular synapse. What would result from such a block?

the loss of ability to contract the muscle Without acetylcholine, the muscle would not be able to contract or even maintain tone

Which of the following is NOT a normal function of muscle tissue?

protecting organs