Test

Sequence of Events at the Neuromuscular Junction:

1. Ca2+ enters the axon terminal 2. Synaptic vesicles release ACh 3. ACh binds to ACh receptors. 4. Ligand-Gated cation channels open 5. Na+ enters K+ exits 6. Membrane potential is less negative.

The following is a list of the events that occur during a muscle contraction. What is the correct sequence of these events?

3.calcium ion is released from the sarcoplasmic reticulum, 5.calcium ion binds to troponin, 1.myosin cross bridges bind to actin, 4.the myosin head pivots toward the center of the sarcomere, 6.the myosin head binds an ATP molecule and detaches from the actin, 2.the free myosin head splits ATP

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

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.

sequence of events that occur during excitation-contraction coupling.

AP propagates along sarcolemma,AP travels down T tubules to triads,Voltage-sensitive proteins open Ca2+ channels,Sarcoplasmic reticulum releases Ca2+ and Ca2+ levels in sarcoplasm increase.

Cross bridge detachment is caused by ________ binding to the myosin head.

ATP

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.

The cross bridge cycle starts when _________.

Ca2+ from the sarcoplasmic reticulum binds to troponin

How is delayed-onset muscle soreness (DOMS) different from muscle fatigue?

Delayed-onset muscle soreness occurs a day or more after the physical exertion.

Which of the following is a way that muscle fibers get energy needed for contraction?

During peak activity levels, glycolysis is the only pathway by which ATP can be produced to supply energy to the muscle.

Put the following structures in order from superficial to deep. 1. muscle fiber 2. perimysium 3. myofibril 4. fascicle 5. endomysium 6. epimysium

Epimysium Perimysium Fascicle Endomysium Muscle Fiber Myofibril

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 spastic paralysis (muscles are contracted and unable to relax).

How would an elevated level of thyroid hormone in the body affect skeletal muscles?

It would stimulate energy use and heat production.

Which of the following processes produces 36 ATP?

Krebs cycle and oxidative phosphorylation

Which of the following statements is true concerning motor units?

Movement of the eyeball requires fewer muscle fibers with less tension being produced.

The "rest and recovery" period, where the muscle restores depleted reserves, includes all of the following processes EXCEPT __________.

Pyruvic acid is converted back to lactic acid.

Identify the incorrect statement about a single motor unit.

The more neurons involved, the more powerful the contraction.

Which of these statements about skeletal muscles is FALSE?

Their fibers branch

Events Involved in Generation of an Action Potential:

Threshold stimulus Na+ channels open, Na+ influx Depolarization, Na+ channels close K+ channels open, K+ efflux Repolarization, Hyperpolarization K+ channels close

complete tetanus

What is the contraction

Treppe

What is this contraction

The cytoplasm of the neuromuscular terminal contains vesicles filled with molecules of the neurotransmitter

acetylcholine

Thin filaments are mostly made of the protein

actin

The protein that is found in the Z line of a sarcomere is called

actinin

Decreased blood flow to a muscle could result in all of the following except

an increase in intracellular glycogen

A(n) ________ can be described as a broad tendinous sheet.

aponeurosis

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

Which of the following statements about excitation-contraction coupling is incorrect?

calcium ions travel through the transverse tubule

What is the type of chemical reaction used to rebuild ADP into ATP?

dehydration synthesis

Nerves and blood vessels that service a muscle fiber are located in the connective tissues of its

endomysium

The delicate connective tissue that surrounds the skeletal muscle fibers and ties adjacent muscle fibers together is the

endomysium

The dense layer of connective tissue that surrounds an entire skeletal muscle is the

epimysium

Synaptic vesicles contain neurotransmitters that are released by ________ when the action potential arrives.

exocytosis

Activities involving eccentric contractions more commonly lead to delayed-onset muscle soreness than concentric or isometric contractions. Which of the following activities is thus a candidate for delayed-onset muscle soreness?

extension of the biceps brachii

Large-diameter, densely packed myofibrils, large glycogen reserves, and few mitochondria are characteristics of

fast fibers

Which of the following processes produces molecules of ATP and has two pyruvic acid molecules as end products?

glycolysis

Each skeletal muscle fiber contains ________ myofibrils

hundreds of thousands

A muscle producing almost peak tension during rapid cycles of contraction and relaxation is said to be in

incomplete tetanus

The type of contraction in which the muscle fibers do not shorten is called

isometric

The muscle weakness of myasthenia gravis results from

loss of acetylcholine receptors in the end-plate membrane.

Receptors for acetylcholine are located on the

motor end plate

To produce a contraction similar to the one in graph (b), the muscle

must be stimulated again before it has relaxed from the previous stimulation

Skeletal muscle fibers are formed from embryonic cells called

myoblasts

Thick filaments are made of the protein.

myosin

Communication between axons and muscle fibers occurs at specialized synapses called

neuromuscular junctions

At peak levels of muscle exertion the mitochondria can supply

only about one-third of the energy required by the muscle.

The advantage of having many nuclei in a skeletal muscle fiber is the ability to

produce large amounts of muscle proteins

Which of the following is a recognized function of skeletal muscle?

produce movement maintain posture maintain body temperature guard body entrances and exits

Which of the following best describes the term titin?

protein that accounts for elasticity of resting muscle

The increase in muscle tension that is produced by increasing the number of active motor units is called

recruitment

The repeating unit of a skeletal muscle fiber is the

sarcomere

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

When comparing slow muscle fibers to fast muscle fibers, slow fibers

take about three times as long to reach peak tension. B) have much smaller fiber diameters. C) generate much less tension. D) are rich in the red protein myoglobin.

The contraction of a muscle exerts a pull on a bone because muscles attach to bones by

tendons

Which of the following hormones directly stimulates growth of muscle tissue, leading to increased muscle mass?

testosterone

When a skeletal muscle fiber contracts

the Z lines move further apart, zones of overlap get larger,width of the A band increases ,H bands and I bands get larger.

The Cross Bridge Cycle:

the activated myosin head binds to actin, forming a cross bridge, ADP is released and myosin slides the thin filament toward the center of the sarcomere,ATP binds to the myosin head and detaches it from actin and ATP is hydrolyzed to ADP and Pi and the energy released re-cocks the myosin head.

Which of the following acts as an ATPase during the contraction cycle of muscle?

the head portion of the myosin molecule

At rest, active sites on the actin are blocked by

tropomyosin molecules

Active sites become exposed when calcium ions bind to

troponin

A single contraction-relaxation cycle in a muscle fiber produces a(n)

twitch

Each thin filament consists of

two actin protein strands coiled helically around each other

Muscular force can be adjusted to match different loads by

varying the frequency of action potentials in motor neurons. B) recruiting larger motor units. C) recruiting more motor units D)involving more muscle fibers in the contraction.

The generation of an action potential in a neuron requires the presence what type of membrane channels?

voltage-gated channels

If a second stimulus arrives before the relaxation phase has ended, a second, more powerful contraction occurs. This addition of one twitch to another is called

wave summation

Which type of muscle fiber has a large quantity of glycogen and mainly uses glycolysis to synthesize ATP?

white fast twitch fibers

In a sarcomere, cross-bridge attachment occurs specifically in the

zone of overlap