A&P LEC Ch. 10

As myosin heads complete the power stroke, actin filaments: -slide toward the M line of the sarcomere -move closer to myosin -move farther away from myosin -slide away from the M line of the sarcomere.

- slide toward the M line of the sarcomere As the myosin heads pivot and perform a power stroke, actin filaments slide toward the M line and the entire sarcomere shortens.

Which of the following steps of the contraction cycle triggers ATP hydrolysis? -the myosin head binds to actin -power stroke -the binding of ATP to the myosin head -The myosin head detaches from actin.

- the binding of ATP to the myosin head When ATP binds to the head of the myosin molecule, the ATPase in the myosin rapidly hydrolyzes the ATP. the energy liberated from this reaction "cocks" the myosin head

This is a __________. -thin filament -muscle fiber -thick filament -sarcomere

- thin filament Thin filaments consist of two intertwined actin strands, covered by long, ropelike strands of tropomyosin, which is held in place by the smaller globular protein troponin.

Which of the following is/are mechanism(s) to end neural transmission at the neuromuscular junction? -ACh binds to ACh receptors -ACh diffuses away from the synaptic cleft -ACh is taken up by the axon terminal via endocytosis -ACh is broken down into acetic acid and choline by the enzyme acetylcholinesterase (AChE).

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

Complete the reaction below: ADP + creatine phosphate -> creatine + _______________ -adp -lactic acid -creatine kinase - atp

-ATP ATP produced by this reaction provides the muscle with enough energy for about 10 sec of maximal activity

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 -Acetylcholine diffuses away from the cleft -Acetylcholine is transported into the postsynaptic neuron by receptor-mediated endocytosis -Acetylcholine is transported back into the axon terminal by a reuptake mechanism.

-Acetylcholine is degraded by acetylcholinesterase

Which of the following causes myosin to detach from actin? -A calcium ion binds to myosin -Troponin binds to myosin -An ADP molecule is hydrolyzed to ATP -An ATP molecule binds to myosin.

-An ATP molecule binds to myosin After the power stroke is complete, a new ATP molecule binds to the myosin head and causes it to detach from actin

The cross bridge cycle starts when _________. -Ca2+ from the sarcoplasmic reticulum binds to tropomyosin -acetylcholine diffuses away from the synaptic cleft -Ca2+ is actively transported into the sarcoplasmic reticulum -ATP binds to troponin and is hydrolyzed to ADP and Pi -Ca2+ from the sarcoplasmic reticulum binds to troponin

-Ca2+ from the sarcoplasmic reticulum binds to troponin

Creatine phosphate provides 30-40 seconds of energy for muscle activity -True -False

-False

This membrane protein is the __________. -voltage-gated Na+ channel -voltage-gated K+ channel -ligand-gates ion channel -Na+/K+ ATPase pump

-Na+/K+ ATPase pump As indicated in the figure, the Na+/K+ ATPase pump uses ATP to pump Na out of the cell and K into the cell, thus maintaining the concentration gradients of sodium and potassium ions across the sarcolemma.

ATP is required for a power stroke to be repeated during the contraction cycle. -true -false

-True

Electrical gradients exist because sodium and potassium ions are separated on either side of the plasma membrane. -True -False

-True

Greater muscle tension results when muscle fibers are repeatedly stimulated -True -False

-True

The loss of potassium ions from the cell during the repolarization stage restores a membrane potential of -85 mV. -True -False

-True

Type IIb fibers produce the fastest, strongest twitches of any fiber type. -True -False

-True

Compared to Type I fibers, Type II fibers__________. -are more "red" in appearance -can generate faster, more powerful contractions -have more mitochondria -can maintain longer periods of contraction, and therefore have more endurance

-can generate faster, more powerful contractions Type II fibers are larger in diameter than Type I fibers, and therefore contain more contractile proteins capable of generating more tension.

What is the type of chemical reaction used to rebuilt ADP into ATP? -rehydration synthesis -dehydration synthesis -hydrolysis

-dehydration synthesis Yes, a water molecule is removed, thus it is called dehydration synthesis. Building ATP from ADP requires a synthetic enzyme plus a source of energy to rebuild the high energy bond.

If the Na+ voltage-gated channels in a muscle cell open, what will be the result? -depolarization -repolarization -The cell will remain at resting membrane potential -The same result happens as if K+ voltage-gated channels have opened.

-depolarization If Na+ voltage-gated channels open, Na ions will enter the cell and make it less negative or more positive.

What means of membrane transport is used to release the neurotransmitter into the synaptic cleft? -a protein carrier -exocytosis -a channel

-exocytosis yes, the synaptic vesicles (where the neurotransmitter is stored) merge with the membrane and release the neurotransmitter by exocytosis

In a sarcomere, the light and dark bands are produced by alternating M lines and Z discs. -True -False

-false

Myofilaments shorten to produce muscle contractions according to the sliding filament mechanism. -True -False

-false

The Na+/K+ ATPase (Na+/K+ pump) maintains the concentration gradients for sodium and potassium ions by moving two sodium ions out of the cell and three potassium ions into the cell. -True -False

-false

The entry of acetylcholine into a muscle cell through ligand-gated ion channels depolarizes the sarcolemma locally -true -false

-false

Which of the following processes produces molecules of ATP and has two pyruvic acid molecules as end products? -krebs cycle & oxidative phosphorylation -hydrolysis of creatine phosphate -glycolysis

-glycolysis Yes, glucose is broken down in the process called glycolysis. This process takes place in the cytoplasm and does not require oxygen - hence it is called anaerobic respiration. If oxygen is available, the pyruvic acid moves into the mitochondria and glycolysis contributes to aerobic respiration.

The arrow points to the _____ region of myosin. -head -tail -neck -hinge

-hinge The hinge is the flexible point on each myosin molecule, where the neck meets the tail.

Excitation-contraction coupling results in an increase of calcium ion concentration: -in the synaptic cleft -in the sarcoplasmic reticulum -in the T-tubules -in the cytosol of the muscle fiber.

-in the cytosol of the muscle fiber Excitation-contraction coupling results in release of calcium ions from the SR, and therefore the cytoplasmic concentration of calcium ions can increase as much as 100 times

Which of the following processes produces 36 ATP? -glycolysis hydrolysis of creatine phosphate -krebs cycle and oxidative phosphorylation

-krebs cycle and oxidative phosphorylation Yes, 36 ATPs are produced for each glucose molecule. This process, which takes place in the mitochondria, is considered aerobic respiration because oxygen is required.

The immediate result of acetylcholine binding to receptors on the motor end plate is_________. -the axon propagates an action potential -the sarcolemma remains at its resting membrane potential -local repolarization of the sarcolemma -local depolarization of the sarcolemma

-local depolarization of the sarcolemma ACh receptors are ligand-gated ion channels that open and allow sodium ions to enter the muscle fiber, thus causing depolarization

The folded region of sarcolemma found at the neuromuscular junction (NMJ) is called the_________. -motor end plate -transverse tubule -axon terminal -sarcoplasmic reticulum

-motor end plate the motor end plate is a specialized region of the sarcolemma at the NMJ, whose folded surface contains many receptors for Each

The active ingredient of Botox, botulinum toxin, blocks the release of ACh from the axon terminal. An overdose of Botox will most likely result in: -decreased production of ACh -increased excitability of the muscle fibers at the site of injection -muscle paralysis at the site of injection -increased levels of ACh in the synaptic cleft

-muscle paralysis at the site of injection

The protein that binds to actin when tropomyosin moves off of the active sites of actin, is: -myosin -calcium ions -troponin -titin

-myosin Myosin heads bind to the exposed active sites on actin. that enables the muscle to contract

Which of the following proteins is a component of thick filaments? -troponin -tropomyosin -actin -myosin

-myosin Myosin is a contractile protein with a "tail," "neck," and "head" region. Clusters of myosin form thick filaments.

During the power stoke of ----=--myosin heads pull actin toward the center of the sarcomere -actin heads pull on the Z-disks of the sarcomere -myosin heads attach to actin's active sites -ATP breaks the attachment of myosin to actin

-myosin heads pull actin toward the center of the sarcomere During the power stroke, myosin heads pivot from their high-energy position to their relaxed position and pull actin towards the M line as they pivot

If a patient is given a drug that inhibits acetylcholinesterase (AChE), you would expect to see__________. -muscle paralysis -There will be less ACh released from the axon terminal -There will be no effect on the muscle -prolonged muscle contraction

-prolonged muscle contraction If AChE is inhibited, ACh will be available in the synaptic cleft for a prolonged period of time and therefore contraction will last longer

The "rest and recovery" period, where the muscle restores depleted reserves, includes all of the following processes EXCEPT __________. -Glycogen is synthesized from glucose molecules. -Oxygen rebinds to myoglobin. -ATP is used to rephosphorylate creatine into creatine phosphate. -Pyruvic acid is converted back to lactic acid.

-pyruvic acid is converted back to lactic acid Yes, this is NOT a part of the "rest and recovery" period. When oxygen is available, lactic acid is converted back to pyruvic acid (not vice versa) that then enters the Krebs cycle. Lactic acid is the end product of the anaerobic pathway.

What causes the power stroke? -calcium -release of ADP and Pi -hydrolysis of ATP -binding of ATP

-release of ADP and Pi Yes, the hydrolysis of ATP provides the energy for the power stroke. Energy is transferred from ATP to the myosin head

What is the plasma membrane of skeletal muscle called? -sarcoplasmic reticulum -sarcolemma -sarcoplasm -sarcomere

-sarcolemma The plasma membrane of skeletal muscle is called sarcolemma, from sarco meaning "flesh" and lemma meaning "shell."

During excitation contraction coupling calcium is released from the__________. -motor end plate -vesicles in the axon terminal -sarcoplasmic reticulum -T-tubules

-sarcoplasmic reticulum when t-tubules depolarize, that in turn, opens calcium in the sarcoplasmic reticulum, and calcium ions enter the cytosol

How is acetylcholine (ACh) removed from the synaptic cleft? -simple diffusion away from the synaptic cleft and endocytosis into the muscle fiber -acetylcholinesterase (AChE; an enzyme) and endocytosis into the muscle fiber -simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme)

-simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme) acetylcholinesterase breaks down acetylcholine in the synaptic cell

While studying the properties of a muscle in the laboratory, you observe that the muscle is involuntary and does not have striations or T-tubules. You determine that this muscle is__________. -cardiac muscle -smooth muscle -areolar muscle -skeletal muscle

-smooth muscle Smooth muscles are involuntary and do not have striations, T-tubules, or motor end plates.

What does this figure show? -skeletal muscle -smooth muscle -myofibrils -cardiac muscle

-smooth muscle The figure depicts smooth muscle, which consists of spindle-shaped cells, with a single, oval nucleus and no striations.

Stimulation of acetylcholine (ACh) receptors by ACh will primarily result in: -ACh entering the muscle fiber -potassium ions entering the muscle fiber -sodium ions entering the muscle fiber -chloride ions entering the muscle fiber.

-sodium ions entering the muscle fibers ACh receptors are ligand-gated cation channels that allow sodium to enter the muscle cell down its concentration gradient

In the absence of ATP in the muscle, which of the following is most likely to occur? - Some myosin heads will remain attached to actin molecules, but are unable to perform a power stroke -The crossbridge cycle will be much slower -All myosin heads will continuously be in the "cocked" position -The crossbridge cycle will continue as normal, because ATP is not necessary for muscle contraction.

-some myosin heads will remain attached to actin molecules, but are unable to perform a power stroke Myosin heads detach from actin when a new ATP binds to them; then they hydrolyze the ATP to become cocked

The narrow space between the axon terminal and the motor end plate is called the: -synaptic left -sarcolemma -vesicle -axon

-synaptic cleft The synaptic cleft is the narrow space between the axon terminal and the muscle fiber. it is filled with collagen fibers and an extracellular gel that anchors the neuron in place.

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 cisterns (cisternae) of the sarcoplasmic reticulum -sarcolemma -T tubule -cytosol

-terminal cisterns (cisternae) of the sarcoplasmic reticulum yes, calcium is stored in the terminal cisterns (cisternae) of the sarcoplasmic reticulum until it is released by an action potential

When the sarcomere contracts and shortens__________. -the I-band becomes larger -the A band stays the same -the zones of overlap become smaller -the Z-disks move further apart

-the A band stays the same The A band contains the thick filaments, and the length of the thick filament does not change during contraction

According to this graph, ______________ -the muscle fiber is the relaxation period -the muscle fiber is not allowed to relax between stimuli -the muscle fiber relaxes completely between stimuli -the muscle fiber relaxes between stimuli, but not completely

-the muscle fiber is not allowed to relax between stimuli Each consecutive stimulus arrives before relaxation begins and this results in fused tetanus

The neurons of patients with multiple sclerosis are unable to transmit action potentials down the axon. How will that affect skeletal muscle stimulation? -The muscle will be stimulated, but will not be able to contract -The muscle will be stimulated and will contract -The muscle will not be stimulated and therefore will not contract -The muscle will not be stimulated, but will still contract.

-the muscle will not be stimulated and therefore will not contract Skeletal muscle will contract only if stimulated by a neuron. If action potentials do not reach the axon terminal, ACh will not be released and the muscle will not be stimulated to contract.

Predict the effect of Tetrodotoxin, a powerful blocker of voltage-gated sodium ion channels: -There will be no action potential generated in the muscle fiber -There will be multiple end-plate potentials generated in the muscle fiber -There will be no end-plate potential generated in the muscle fiber -There will be multiple action potentials generated in the muscle fiber.

-there will be no action potential generated in the muscle fibers

Which of the following proteins forms elastic filaments? -myosin -titin -actin -troponin

-titin Titin forms elastic filaments. They run through the core of the thick filament and help to stabilize the myofibril structurally.

In preparation for contraction, calcium ions bind to: -troponin -sodium ions -tropomyosin -myosin

-troponin

The binding of calcium to which molecule causes the myosin binding sites to be exposed? -myosin -tropomyosin -troponin -actin

-troponin Yes, when calcium binds to troponin, troponin releases tropomyosin, exposing the myosin binding sites.

The function of the sarcoplasmic reticulum (SR) is to store and release calcium ions. -True -False

-true

The return of calcium ions to the sarcoplasmic reticulum during muscle relaxation decreases the calcium ion concentration in the cytosol -true -false

-true

The three types of myofilaments are thin, thick and elastic. -True -False

-true

The type of contraction represented by a single stimulus/contraction/relaxation sequence is a(n)__________. -twitch -unfused tetanus -fused tetanus -wave summation

-twitch a twitch is the smallest muscle contraction and can only be produces in a laboratory setting

What are the components of a triad? -Two terminal cisternae of the SR and one calcium ion -One actin and one myosin -Two terminal cisternae of the sarcoplasma reticulum (SR) and one T-tubule -Two thin filaments and one T-tubule

-two terminal cristernae of the sarcoplasm reticulum (SR) and one t-tubule Triads are formed by one T-tubule and two terminal cristernae of the sarcoplasmic reticulum on either side

Wave summation, in which the muscle can only partially relax between contractions, will lead to__________. -fused tetanus -latent period -unfused tetanus -twitch

-unfused If the muscle is stimulated about 50 times per second, it can only partially relax between contractions. A sustained contraction called unfused (or incomplete) tetanus results.

When an action potential arrives at the axon terminal of a motor neuron, which ion channels open? -voltage-gated potassium channels -voltage-gated sodium channels -voltage-gated calcium channels -chemically gated calcium channels

-voltage-gated calcium channels yes, the action potential opens voltage-gated calcium channels and calcium rushes into the axon terminal, leading to the release of the neurotransmitter

During the repolarization stage of a muscle action potential__________. -voltage-gated potassium ion channels open and potassium ions enter the cell -voltage-gated sodium ion channels open and sodium ions leave the cell -voltage-gated sodium ion channels open and sodium ions enter the cell -voltage-gated potassium ion channels open and potassium ions leave the cell

-voltage-gated potassium ion channels open and potassium ions leave the cell During the repolarization stage, potassium voltage-gated ion channels open and potassium ions move out of the cell driven by their concentration gradient. This loss of positively-charged ions causes the sarcolemma to return to its negative resting potential.

Which type of muscle fiber has a large quantity of glycogen and mainly uses glycolysis to synthesize ATP? -white fast twitch fibers -red slow twitch fibers

-white fast twitch fibers

Increase in tension by increasing the number of motor units that are stimulated is called __________________. -autorhythmicity -hypertonia -recruitment -muscle tone

Recruitment when greater force of contraction is needed, more motor units are activated, a phenomenon called recruitment

Which of the following steps of the crossbridge cycle occurs immediately before the power stroke? -Myosin heads detach from actin -Calcium ions bind to myosin.A crossbridge forms -ATP hydrolysis "cocks" the myosin head.

-a crossbridge forms Immediately before the power stroke, myosin heads bind to the active site on actin to form a crossbridge.

The end-plate potential is: -a depolarization caused by sodium ion movement into the extracellular fluid -a depolarization caused by sodium ion movement into the cytosol -a repolarization caused by sodium ion movement into the extracellular fluid -a repolarization caused by sodium ion movement into the cyto

-a depolarization caused by sodium ion movement into the cytosol. When ACh receptor ligand-gated cation channels open, they allow diffusion of sodium ions into the muscle fiber's cytosol. Sodium ions are the major extracellular ion, so by diffusion they will enter the muscle fiber, causing the membrane potential to become more positive.

A crossbridge forms when: -a myosin head binds to ATP -a myosin head binds to actin -an actin head binds to ATP -an actin head binds to myosin

-a myosin head binds to actin A structure known as the crossbridge forms when a "cocked" myosin head binds to an active site on actin

The neurotransmitter used at the neuromuscular junction (NMJ) is__________. -acetylcholinesterase -norepinephrine -acetylcholine -calcium

-acetylcholine Acetylcholine or ACh is stored in the axon terminal and released to stimulate receptors on the muscle motor end plate

In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter? -acetylcholine (ACh) -dopamine -serotonin -norepinephrine

-acetylcholine (ACh) yes, acetylcholine is the neurotransmitter found in neuromuscular junctions

A myosin head binds to which molecule to form a cross bridge? -tropomyosin -actin -troponin

-actin yes, the myosin head binds to actin, the major component of thin filaments

If oxygen is not available, the muscle fiber will produce ATP by__________. -oxidative catabolism -using fatty acids for energy -synthesis of creatine phosphate -anaerobic catabolism

-anaerobic catabolism AC involves glycosides and the production of lactic acid.

What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell? -arrival of an action potential -ATP -troponin -calcium ion pump

-arrival of an action potential Yes, an action potential in the T tubule causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum.

What causes the myosin head to disconnect from actin? -binding of ATP -hydrolysis of ATP -binding of troponin -binding of calcium

-binding of ATP yes, the binding of ATP causes the myosin head to disconnect from actin