Musculoskeletal System

Concept: Muscle System and Skeleton


Concept: Muscle Fibers and Sarcomeres


Concept: Sliding Filament Model


Concept: Motor Unit and Neuromuscular Junction


Concept: Fast and Slow Twitch Muscles


Concept: Endoskeleton


Concept: Joints


Musculoskeletal System Additional Practice Problems

Define the following terms: (a) absolute refractory period, (b) relative refractory period, (c) compound nerve-action potential, (d) synapse, (e) neuro- myo junction, (f) motor unit, (g) reflex arc.

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If cartilage is avascular, how do chondrocytes get nutrients and eliminate waste?

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Cartilage is found ____

a. surrounding organs such as the kidneys
b. in the heart
c. at the ends of bones such as the femur
d. covering the surface of your body
e. connecting one bone to another

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The sarcoplasmic reticulum is a specialized form of ER that surrounds each myofibril. The sarcoplasmic reticulum functions to control cytosolic Ca2+ levels in the muscle cell. Changes in cytosolic Ca2+ concentrations couple action potentials to muscle contraction. 

The concentration of Ca2+ ions in the sarcoplasmic reticulum is typically much higher than the Ca2+ concentration in the cytosol. This concentration gradient is key to the movement of Ca2+ in the muscle cell in response to an action potential. 

The cycle diagram below shows the sequence of events that affect Ca2+ levels in a muscle cell, beginning with the propagation of an action potential down a T tubule (top of the diagram). 

Drag the labels to their appropriate locations on the cycle diagram below. Note that SR stands for sarcoplasmic reticulum.

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Skeletal muscle is capable of which of the following?

a. wave summation

b. fused tetanus

c. autorhythmicity

d. wave summation and fused tetanus

e. wave summation, fused tetanus and autorhythmicity

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Explain why, during exercise, muscle cells need liver cells for regeneration of glucose from lactate.

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Drag the labels onto the diagram to label the steps of smooth muscle activation and deactivation.

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What is the primary function of wave summation?

a. prevent muscle fatigue

b. increase muscle tension

c. prevent muscle relaxation

d. produce smooth, continuous muscle contraction

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

a. troponin; sodium ions

b. myosin; sodium ions

c. tropomyosin; calcium ions

d. troponin; calcium ions

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The cross-bridge cycle starts when _________. select one

a. ATP binds to troponin and is hydrolyzed to ADP and Pi

b. acetylcholine diffuses away from the synaptic cleft

c. Ca2+ is actively transported into the sarcoplasmic reticulum

d. Ca2+ from the sarcoplasmic reticulum binds to tropomyosin

e. Ca2+ from the sarcoplasmic reticulum binds to troponin

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All types of muscle tissue have ________.

a. striated banding patterns seen under the microscope

b. cells that lengthen when appropriately stimulated

c. a response that can be consciously controlled

d. interactions between actin and myosin

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Blood is best classified as connective tissue because ________.

a. its cells are separated from each other by an extracellular matrix

b. it contains more than one type of cell

c. its cells can move from place to place

d. it is found within all the organs of the body

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A ball-and-socket joint connects ________.

a. the radius to the ulna

b. the radius to the humerus

c. the ulna to the humerus

d. the humerus to the scapula

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An endoskeleton is the primary body support for the ________.

a. annelids, including earthworms

b. insects, including beetles

c. cartilaginous fishes, including sharks

d. bivalves, including clams

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The venom of cobras contains a mixture of substances that have a variety of physiological effects. One substance in the venom works by preventing acetylcholine from binding to muscle receptors. How does the venom affect the prey of the cobra?

a. Action potentials would be continuously generated, causing convulsive muscle contractions.

b. Muscle contractions would be prevented, causing paralysis.

c. Muscle contractions could still occur, but relaxation of the muscle would be impaired.

d. Action potentials would be continuously generated, causing convulsive muscle contractions; muscle contractions would then be prevented, causing paralysis.

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Connective tissues typically have ________.

a. little space between the membranes of adjacent cells

b. the ability to transmit electrochemical impulses

c. the ability to shorten upon stimulation

d. relatively few cells and a large amount of extracellular matrix

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Action potentials in the heart move from one contractile cell to the next via ________.

a. chemical synapses using acetylcholine

b. chemical synapses using norepinephrine

c. intercalated disks

d. non-myelinated motor neurons

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The motor unit in vertebrate skeletal muscle refers to ________.

a. one actin binding site and its myosin partner

b. one sarcomere and all of its actin and myosin filaments

c. one myofibril and all of its sarcomeres

d. one motor neuron and all of the muscle fibers on which it has synapses

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Most of the ATP supplies for a skeletal muscle undergoing one hour of sustained exercise come from ________.

a. creatine phosphate

b. glycolysis

c. substrate phosphorylation

d. oxidative phosphorylation

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A skeletal muscle deprived of adequate ATP supplies will ________.

a. immediately relax

b. enter a state where actin and myosin are unable to separate

c. fire many more action potentials than usual and enter a state of "rigor"

d. sequester all free calcium ions into the sarcoplasmic reticulum

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