Anatomy and Physiology Chapter 9 Part 1

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The region between which two points corresponds to the entire A (dark) band? (img 1)

Relationship between fibers composing a sarcomere.

>1 and 2
>2 and 3
>3 and 5
>2 and 6

>2 and 6 The A band, also know as the dark band, is occupied by the entire length of thick myofilaments.

Which of the following statements is FALSE?

>Skeletal muscle cells have T tubules.
>Skeletal muscle cells use creatine phosphate instead of ATP to do work.
>Skeletal muscle cells are multinucleated.
>Skeletal muscle cells contain myoglobin.
>Skeletal muscle cells have glycosomes

Muscle cells, just like other cells, use ATP to do work. Creatine phosphate is used by muscle cells to directly phosphorylate (i.e., donate a high-energy phosphate group to) ADP to resynthesize ATP.

Which organelle can chemically regulate the shortening of the muscle?

>the sarcolemma
>the sarcoplasmic reticulum
>the myofibril
>glycosome

>the sarcoplasmic reticulum

What event directly triggers the release of neurotransmitter shown in A? (img 2)

Summary of events at a neuromuscular synapse.

>diffusion of Na+ into the axon terminal
>diffusion of Na+ out of the axon terminal
>diffusion of Ca2+ into the axon terminal
>diffusion of K+ into the axon terminal

>diffusion of Ca2+ into the axon terminal. 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.

diagram (img 3)

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

>ligament
>synovial membrane
>endomysium
>tendon

>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.

Which protein is indicated by the letter A? (img 5)

>actin
>troponin
>myosin
>keratin

>actin. Actin is the chief component of the thin myofilaments.

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 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
>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 overlap to a greater degree. 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.

Which of the following regions best identifies where myosin would have maximum cross-bridge access to actin? (img 1)

>the region between 1 and 2
>4
>the region between 3 and 5
>the region between 2 and 3

>the region between 2 and 3. Actin and myosin are components of thin and thick filaments, respectively. The region between points 2 and 3 includes the area of overlap between thin and thick filaments.

Which type of muscle requires voluntary nervous stimulation for activation?

>skeletal
>smooth
>cardiac
>visceral

>skeletal. 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.

Which statement accurately describes the event indicated by B? (img 2)

>The binding of acetylcholine directly causes the formation of a wave of depolarization.
>Diffusion of acetylcholine into the muscle fiber triggers the opening of an ion channel.
>Binding of acetylcholine to a receptor triggers the opening of an ion channel.
>Diffusion of Ca2+ into the muscle fiber triggers the diffusion of acetylcholine out of the muscle fiber.

>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.

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

>True
>False

>True. In the muscles of the limbs, the insertion is pulled toward the immobile origin.

Which protein functions as a motor protein that applies the power stroke during muscle contraction? (img 5)

>A
>B
>C
>D

>C. The myosin head groups (C) hydrolyze ATP to power molecular movement along the actin subunits of the thin myofilaments.

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

>secreting hormones
>generating heat
>stabilizing joints
>maintaining posture
>producing movement

>secreting hormones. Secreting hormones is a function of the endocrine system.

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

>tropomyosin; calcium ions
>troponin; calcium ions
>myosin; sodium ions
>troponin; sodium ions

>troponin; calcium ions. When calcium ions bind to troponin, troponin changes shape and moves tropomyosin away from its inhibitory position. As a result, the energized myosin heads can bind to the actin molecules and begin the cross bridge cycle, which shortens the muscle fiber.

Which protein is indicated by the letter E? (img 5)

>tropomyosin
>troponin
>actin
>myosin

>myosin. Myosin tail groups form the extended regions of the thick myofilament.

Which of the following corresponds to a single fascicle? (img 4)

>A
>B
>C
>D

>B. A fascicle is an organized group of muscle fibers (cells) bounded by a perimysium.

Which of the structures is surrounded by the connective tissue sheath known as the perimysium? (img 4)

A
B
C
D

>B. The structure at B is covered by the perimysium. Remember that the word root peri means "around," as in "perimeter."

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

>to facilitated transport of acetylcholine across the cleft
>to pump Ca2+ back out of the axon terminal
>to facilitate the entrance of acetylcholine into the muscle cell
>to break down acetylcholine

>to break down acetylcholine. Acetylcholinesterase breaks acetylcholine apart, terminating the synaptic transmission. Choline can be taken back into the axon terminal and reused.

Which term best identifies a muscle cell?

>sarcomere
>myofibril
>muscle fiber
>muscle fascicle

>muscle fiber. Skeletal muscle cells fuse during development to form the mature, multinucleated muscle fibers.

Which of the following are correctly paired?

>smooth muscle; striated
>skeletal muscle; voluntary control
>cardiac muscle; nonstriated
>cardiac muscle; voluntary control

>skeletal muscle; voluntary control.

The smallest contractile unit within skeletal muscle would correspond to the distance between which two points in the figure? (img 1)

>3 and 5
>1 and 3
>1 and 7
>2 and 6

>1 and 7. The distance between points 1 and 7 spans a sarcomere, the smallest contractile unit of a muscle fiber.

Which structure in the figure corresponds to a single skeletal muscle cell? (img 4)

>A
>B
>C
>D

>C. Note that a skeletal muscle cell is commonly termed a muscle fiber.

What cellular event is indicated by A?

>endocytosis
>facilitated diffusion
>active transport
>exocytosis

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

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

>the myofilament
>troponin
>the sarcomere
>the elastic filament

>the sarcomere. 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.

The __________ shorten(s) during muscle contraction

>Z lines
>thick filament
>actin
>sarcomere

>sarcomere. As actin slides over myosin, the z lines are pulled closer together, shortening the sarcomere.

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.
>The muscle would be weaker than normal.
>Actin will spontaneously fall apart.
>The muscle would never contract.

>The muscle tissues would never be able to relax. The tropomyosin covers the myosin binding site on actin. Without tropomyosin, the myosin would constantly have access to those binding sites.

The molecular interaction described as a cross bridge involves the binding of which two proteins? (img 5)

>A and C
>B and D
>A and D
>A and B

>A and C. Cross bridges between thin and thick myofilaments are formed by the specific interaction between actin (A) and myosin head groups (C).

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

>The muscle would become permanently contracted.
>The muscle would remain fixed at the length it was when the toxin contacted it.
>the loss of ability to contract the muscle

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

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?

>excitability
>extensibility
>elasticity
>contractility

>excitability. 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.

Which step precedes all of the other listed steps?

>The sarcoplasmic reticulum is activated.
>An action potential starts on the sarcolemma.
>Na+ rushes into the cell.
>ACh is released by the motor neuron.

>ACh is released by the motor neuron. The first step toward generating a skeletal muscle contraction is nervous stimulation of the muscle fiber in order to generate an action potential. The site of muscle stimulation, where the nerve ending communicates with the muscle fiber, is called the neuromuscular junction.

Excitation-contraction coupling includes all EXCEPT which of the following events?

>release of acetylcholine from axon terminals at the neuromuscular junction
>binding of calcium ions to troponin, which removes the blocking action of tropomyosin
>propagation of an action potential along the sarcolemma and down T tubules
>release of calcium ions from the terminal cisterns

>release of acetylcholine from axon terminals at the neuromuscular junction. Release of acetylcholine from axon terminals at the neuromuscular junction is an event that precedes excitation-contraction coupling, which begins with excitation of the T-tubules.

What is the function of the filaments found in ranges 1-2 and 6-7 but no other ranges? (Refer to img 1)

Relationship between fibers composing a sarcomere.

>neurological sensing of the muscle’s tension
>a connection between the myosin fibers and a calcium source
>adding strength to contraction
>protection from overstretching

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

Which of the following interactions must occur first so that the others can take place? (Refer to img 5)

Interaction between thick and thin filaments during muscle contraction.

>B binds to troponin.
>D is shifted from actin’s binding sites.
>C binds to actin.
>C releases ADP and P.

>B binds to troponin. Binding of calcium (B) to troponin removes the blocking action of tropomyosin along the thin myofilament. This allows myosin to bind to actin and form the cross bridge illustrated in this figure.

Which term best identifies a muscle cell?

>sarcomere
>muscle fascicle
>myofibril
>muscle fiber

>muscle fiber. Skeletal muscle cells fuse during development to form the mature, multinucleated muscle fibers.

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.
>Ca+ would leak out of the cell.
>The muscle would not contract.
>Ca+ would build up in the sarcoplasmic reticulum.

>It would be unable to concentrate Ca+ in the sarcoplasmic reticulum. To concentrate Ca+ in the sarcoplasmic reticulum, active transport must occur. With no ATP, there would be no active transport.

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