Chapter 10: Muscular Tissue

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Which connective tissue coat surrounds groups of muscle fibers, separating them into fasicles?

Perimysium bundles groups of muscle fibers into fasicles.

Which structure releases calcium ions to trigger muscle contraction?

The sarcoplasmic reticulum releases calcium ions to trigger muscle contraction.

Which of the following is the smallest: muscle fiber, thick filament, or myofibril? Which is largest?

The following are arranged from smallest to largest: thick filament, myofibril, muscle fiber.

Which proteins connect into the Z disc?

Actin and titin anchor into the Z disc.

Which proteins are present in the A band? In the I band?

A bands contain myosin, actin, troponin, tropomyosin, and titin; I bands contain actin, troponin, tropomyosin, and titin.

What happens to the I band and H zone as muscle contracts? Do the lengths of the thick and thin filaments change?

The I bands and H zones disappear during muscle contraction; the lengths of the thin and thick filaments do not change.

What would happen if ATP suddenly were not available after the sarcomere had started to shorten?

If ATP were not available, the cross-bridges would not be able to detach from actin. The muscles would remain in a state of rigidity, as occurs in rigor mortis.

What are three functions of ATP in muscle contraction?

Three functions of ATP in muscle contraction are the following: (1) Its hydrolysis by an ATPase activates the myosin head so it can bind to actin and rotate; (2) Its binding to myosin causes detachment from actin after the power stroke; and (3) It powers the pumps that transport calcium ions from the cytosol back into the sarcoplasmic reticulum.

Why is tension maximal at a sarcomere length of 2.2 micrometers?

A sarcomere length of 2.2 micrometers gives a generous zone of overlap between the parts of the thick filaments that have myosin heads and the thin filaments without the overlap's being so extensive that sarcomere shortening is limited.

What part of the sarcolemma contains acetylcholine receptors?

The part of the sarcolemma that contains acetylcholine receptors is the motor end plate.

Which steps in the contraction and relaxation in skeletal muscle fiber are part of excitation-contraction coupling?

Muscle action potential traveling along transverse tubule opens calcium ion release channels in the sarcoplasmic reticulum membrane, which allows calcium ions to flood into the sarcoplasm.

Calcium ion binds to troponin on the thin filament, exposing the binding sites for myosin.

Contraction; power strokes use ATP; myosin heads bind to actin, swivel, and release; thin filaments are pulled toward center of sarcomere.

Where inside a skeletal muscle fiber does production of ATP for muscle contraction occur?

Glycolysis, exchange of phosphate between creatine phosphate and ADP, and glycogen breakdown occur in the cytosol. Oxidation of pyruvic acid, amino acids, and fatty acids (aerobic cellular respiration) occurs in mitochondria.

What is the effect of the size of a motor unit on its strength of contraction? (Assume that each muscle fiber can generate about the same amount of tension)

Motor units having many muscle fibers are capable of more forceful contractions than those having only a few fibers.

What events occur during the latent period?

During the latent period, the muscle action potential sweeps over the sarcolemma and calcium ions are released from the sarcoplasmic reticulum.

What type of contraction occurs in your neck muscles while you are walking?

Holding your head upright without movement involves mainly isometric contractions.

Which type of smooth muscle is more like cardiac muscle than skeletal muscle, with respect to both its structure and function?

Visceral smooth muscle is more like cardiac muscle; both contain gap junctions, which allow action potentials to spread from each cell to its neighbors.

Which part of a somite differentiates into skeletal muscle?

The myotome of a somite differentiates into skeletal muscle.

What is the functional unit of a skeletal muscle called?

A Sarcomere

What is the role of tropomyosin in skeletal muscles?

Tropomyosin serves as a contraction inhibitor by blocking the myosin binding sites on the actin molecules.

The oxygen-binding protein found in muscle cells is ________.

Myoglobin

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

Actin Filaments

The strongest muscle contractions are normally achieved by ________.

Increasing the stimulation up to the maximal stimulus.

True or False: Striated muscle cells are long and cylindrical with many nuclei.

True

True or False: Certain smooth muscle cells can actually divide to increase their numbers.

True

Rigor mortis occurs because ________.

No ATP is available to release attached actin and myosin molecules.

Muscle tone is ________.

A state of sustained partial contraction.

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

No muscle tension could be generated.

What is the main factor that determines the power of a muscle?

The total number of muscle cells available for contraction.

The main effect of the warm-up period of athletes, as the muscle contractions increase in strength, is to ________.

Enhance the availability of calcium and the efficiency of enzyme systems.

What produces the striations of a skeletal muscle cell?

The Arrangement of Myofilaments

The sliding filament model of contraction involves ________.

Actin and myosin sliding past each other and partially overlapping.

Excitation-contraction coupling requires which substances?

Calcium Ions and ATP

How much of the total body weight of an average adult is muscle tissue?

40-50%

The different types of muscle tissue differ from each other by

Microscopic anatomy, location, and type of control.

What are the major functions of muscle?

Producing body movements, stabilizing body positions, storing and moving substances within the body, and generating heat.

This is the property of muscle that gives it the ability to stretch without damage.

Extensibility

This is the outermost layer of connective tissue surrounding a skeletal muscle.

Epimysium

The type of tendon formed when the connective tissue elements of a skeletal muscle extend as a broad flat layer.

Aponeurosis

In neuromuscular junctions, synaptic vesicles containing acetylcholine are found suspended in the cytosol of

Synaptic End Bulbs

After the fusion of myoblasts, the muscle fiber loses its ability to do what?

Go through cell division

List the sequence of structures that action potentials must move through to excite skeletal muscle contraction.

Axon of neuron, sarcolemma, T tubules

The contractile organelles of a skeletal muscle fiber are thread-like structures called

Myofibrils

Release of calcium from these structures triggers skeletal muscle contraction.

Terminal cisterns of sarcoplasmic reticulum

Which regions of a sarcomere contain thin filaments?

I band and A band

Myofibrils contain

Contractile proteins, regulatory proteins, and structural proteins.

Which protein functions as a motor protein in all three types of muscle tissue?

Myosin

What regulatory proteins can be found in the thin filaments of skeletal muscle fibers?

Tropomyosin and Troponin

Which of the regions of a sarcomere contain titin?

From M line to Z disc

Which protein is used to reinforce the sarcolemma and to help transmit the tension generated by the sarcomeres to the tendons?

Dystrophin

During muscle contraction by the sliding filament mechanism, thin filaments are pulled towards the

M Line

Calcium ions are released from the sarcoplasmic reticulum into the cytosol when?

At the Beginning of Contraction

What energizes the myosin head?

ATP Hydrolysis Reaction

Skeletal muscle contraction will continue to occur as long as the following chemicals are available in the cytosol of the muscle fiber.

Calcium Ions and ATP

To stimulate skeletal muscle contraction, acetylcholine must cross the __________ of the neuromuscular junction and bind to receptors on the motor endplate.

Synaptic Cleft

What is commonly used to produce ATP during skeletal muscle contraction?

Creatine phosphate, anaerobic cellular respiration, and aerobic cellular respiration.

In skeletal muscles, the combined amounts of creatine phosphate and ATP provide enough energy for the muscle to contract maximally for approximately

15 Seconds

This consists of a somatic motor neuron and all the skeletal muscle fibers it stimulates.

Motor Unit

A brief contraction of all muscle fibers in a motor unit in response to a single action potential moving down the somatic motor neuron is known as

Twitch Contraction

This is also referred to as the period of lost excitability in skeletal muscle fibers.

Refractory Period

A period of sustained skeletal muscle contraction in which individual twitches cannot be detected is called

Fused Tetanus

Increasing the number of active motor units within a skeletal muscle is called

Motor Unit Recruitment

This is the least powerful type of skeletal muscle fiber.

Slow Oxidative Fiber

Which microscopic structures are only found in the cardiac muscle tissue?

Intercalated Discs

Which types of muscle tissue contract when excited by their own autorhythmic muscle fibers?

Cardiac muscle and visceral smooth muscle

Smooth muscle tone is maintained by the prolonged presence of ______ in the muscle cell's cytosol?

Calcium Ions

Hyperplasia is

An increase in the number of muscle fibers.

Which disorder is characterized by the wasting away of muscles due to the progressive loss of myofibrils?

Muscular Atrophy

What is seen in exercise-induced muscle damage?

Disrupted Z discs, torn sarcolemmas, damaged myofibrils, and sore muscles.

Which is the sequence of events in the onset of rigor mortis?

Cellular membranes become leaky -> calcium ions leak into the sarcoplasm -> myosin heads bind to actin -> muscles are in a state of rigidity.

What are the side-effects of anabolic steroid use by male athletes?

Diminished testosterone secretion, atrophy of the testes, sterility, and baldness.

What are the side-effects of anabolic steroid use by female athletes?

Atrophy of the breasts and uterus, menstrual irregularities, sterility, facial hair growth, and deepening of the voice.

Which type of abnormal contractions of skeletal muscle is a rhythmic, involuntary, purposeless quivering or shaking movement?

Tremor

Describe aerobic cellular respiration in skeletal muscles.

Cellular respiration is the set of the metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products. The reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy in the process as they break high-energy bonds. Respiration is one of the key ways a cell gains useful energy to fuel cellular activity.

After prolonged strenuous exercise has stopped, heavy breathing will often continue for several minutes in order to provide the oxygen needed to

Convert the lactic acid produced during exercise back into glycogen, resynthesize creatine phosphate, and replace oxygen displaced by muscle myoglobin.

Which type of muscle tissue is capable of undergoing the stress-relaxation response when they are stretched?

Single-unit smooth muscle fibers.

Cross bridges are formed during muscle contraction when _____ on the thick filaments binds to ______ on the thin filaments.

Myosin; Actin

In a neuromuscular junction, the effect of acetylcholine (ACh) binding to receptors on the motor end plate lasts only briefly due to

Rapid destruction of ACh in the synaptic cleft by acetylcholinesterase.

During this period of a twitch contraction, the muscle action potential moves along the sarcolemma of the muscle cell and triggers calcium release into the sarcoplasm.

Latent Period

What is a common characteristic of fast glycolytic (FG) skeletal muscle fibers?

High amount of glycogen in the sarcoplasm.

Myasthenia Gravis is an autoimmune disorder that targets the ACh receptors at the NMJ and ultimately reduces the number of available receptors. Predict what happens if you treat the patient with a drug that inhibits the activity of acetylcholinesterase?

Normal Contraction

Leg muscles are predominantly composed of which type of muscle fiber?

Fast Oxidative-Glycolytic

On which protein is the enzyme ATPase located?

Myosin

After several visits to the gym and serious "iron pumping" (strength training) you notice that your biceps have enlarged. What has happened to your muscles?

Hypertrophy

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