Chapter 10

An adult has more muscle mass than a child. How did that increase in muscle mass occur?

Transverse tubules

Are actually tiny pockets of plasma membrane that extends to the muscle cell

Are filled with interstitial fluid

Prevent the spread of an action potential to the interior of a myofiber

A and b are correct

A, b, and c are correct

The sarcoplasm

Is the extracellular fluid around a myofiber

Is enriched with glycogen

Contains hemoglobin to store O2

Contains few mitochondria

Includes many nuclei

The sarcoplasmic reticulum of muscle tissue

Stores Ca2 ions required for muscle contraction

Is called rough endoplasmic reticulum in other tissues

Is part of the transverse tubules

Is a thread of protein running the length of the muscle tissue

Removes Ca2 from the sarcoplasm so that an action potential can be generated

Muscular atrophy

Is an increase in muscle mass due to increased number of myofibrils

Is an increase in muscle mass due to increased numbers of myofibers

Is a decrease in muscle mass due to loss of myofibrils

Is the result of overuse of muscles

Is always reversible, no matter what the cause

Which of the following accurately describes the filaments of skeletal muscle tissue?

The thin filaments have twice the diameter and half the numbers of the thick filaments

The filaments extend through the entire length of the myofiber

Neither thick nor thin filaments are directly involved in muscle contraction

Thin filaments are more abundant than thick filaments in the H zone of the A band

Thick and thin filaments overlap each other within the A band of the sarcomere

Myofibrils

Include contractile proteins which stabilize the structure of the sarcomere

Include the contractile proteins actin actin and myosin

Include regulatory proteins that keep thick and thin filaments in proper alignment

Include structural proteins that decrease the extendibility and elasticity of the myofiber

Include structural proteins the turn the contraction process off or on

Thick filaments

Are composed primarily of myosin

Are able to convert mechanical energy into chemical energy

Are primarily regulatory proteins

Are primarily structural proteins

Are composed of different types of proteins that appear as beds on string

Thin filaments

Are composed of the titin

Are connected to the M lines

Are able to convert chemical energy to mechanical energy

Are composed of actin, troponin and tropomyosin

Are the proteins that anchor thick filaments to the Z discs

Which of the following does not happen during a muscle contraction?

The myosin heads bind to actin

The myosin heads pull the thin filaments toward the M line

The sarcomere shortens

The myofiber and the muscle itself shortens

The thick and thin filaments shorten

A contraction cycle

Cannot begin until Ca2 has bound to troponin

Cannot begin until the myosin- binding sites on actin are exposed

Cannot begin until Ca2 has bound to tropomyosin

A and b are correct

B and c are correct

Place the events of a contraction cycle in the order in which they occur: 1. ATP hydrolysis 2. Detachment of myosin head from actin 3. Power stroke 4. Crossbridge formation

Repetition of the contraction cycle

Requires the absence of ATP

Requires the presence of an adequate number of Ca2 ions

Requires the action of the ATPase found on actin

A and b are correct

A, b, and c are correct

How is excitation of the sarcolemma coupled to the contraction of a muscle fiber?

Excitation continues into the T-tubules causing Ca2 active transport channels to open, thus removing Ca2 from the cytoplasm

Excitation causes synthesis from calsequestrin, thus allowing more Ca2 to be stored in the sarcoplasmic reticulum

Excitation continues into the T-tubules causing Ca2 release channels to open, thus starting a contraction cycle

Excitation causes Ca2 to be released from troponin, thus allowing more cross-bridges to form between myosin and actin

Excitation causes a number of intracellular events, which lower Ca2 levels, thus stimulating a contraction cycle

Under what condition can muscle fibers generate the most tension?

When fibers are stretched so that there is no overlap between thick and thin filaments

When fibers have atrophied and there are fewer thin filaments to overlap thick filaments

When fibers are compressed so much that the thick and filaments crumple

When fibers have sufficient ATPase to initiate power strokes

When fibers have an overlap of thick and thin filaments that is close to their resting length

How does muscle tissue contribute to homestasis?

By generating heat that helps maintain body temperature

By moving materials through the body

By pulling on bones to move the body

A and b are correct

A, b, and c are correct

The primary function of muscle is

Conversion of chemical energy into mechanical energy

Conversion of chemical into radiant energy

Conversion of mechanical energy into heat energy

Conversion of heat energy into mechanical energy

Conversion of heat energy into chemical energy

Skeletal muscle

Is striated

Is largely under voluntary control

Is primarily regulated by hormones from the endocrine system

A and b are correct

A, b, and c are correct

Cardiac muscle

Is found in the walls of blood vessels and in the heart

Is largely under voluntary control

Is striated

Contraction is dependent on stimulation by the nervous system

Is unaffected by hormones

Smooth muscle

Is largely under voluntary control

Is located in the coverings of solid organs

Is striated

Moves blood through the heart

Is regulated by the autonomic division of the nervous system

Which of the following is a function of muscle tissue?

Absorbing heat from the environment

Storage of triglycerides

Controlling flow of materials out of the stomach and urinary bladder

Destabilizing body position

Strong calcium

The ability to respond to stimuli by producing action potentials

The ability of a muscle tissue to stretch without being damaged is called

Superficial fascia

Is composed primarily of dense connective tissue

Provides a route for lymphatic and blood vessels as well as nerves to enter muscles

Is found between the skeletal muscles and the bones

Stores most of the body's proteins

Promotes heat loss

Deep fascia

Is composed of loose (aerolar) connective tissue

Is found between the muscles and the skin

Holds muscles with similar functions together

Limits movement of muscles

Blocks the penetration of nerves and blood vessels into muscles

A tendon

Attaches a muscle to a bone

Is an extension of the fused endomysium, perimysium, and epimysium of a muscle

Contains parallel bundles of collagen fibers

A and b are correct

A, b, and c are correct

Which of the following is not true?

Several nerves accompany each artery that penetrates a muscle cell

Muscle tissue is highly vascular

Somatic motor neurons control skeletal muscle contraction

Somatic motor neurons branch; each branch may control a muscle fiber

A muscle fiber uses large amounts of ATP during contraction

A skeletal myofiber

Has one centrally located nucleus

Is derived from embryonic cells called myoblasts

Retains miotic potential even in the adult

A and b are correct

A, b, and c are correct

A neuromuscular junction (NMJ)

Is the synapse of a motor neuron with a muscle fiber

Includes the synaptic end bulbs of the muscle fiber

Includes the motor endplates of the motor neuron

Use Na as a nuerotransmitter

All of the above are correct

Place the events of the neuromuscular junction (NMJ) in the order in which they occur: 1. Release of acetylcholine (ACh) 2. Activation of ACh receptors on motor endplate 3. Termination of ACh activity by acetylcholinesterase (AChE) 4. Arrival of an action potential at the synaptic end bulb 5. Diffusion of ACh across the synaptic cleft 6. Opening of Na channels in the motor endplate 7. Production of muscle fiber action potential

Which of the following acts on the NMJ to block stimulation of muscle contraction?

How do muscle fibers produce ATP?

Creatine phosphate

Is produced when ATP levels in a muscle cell are depressed

Production requires the activity of creatine kinase

Is much less plentiful in the cytoplasm than is ATP

Provides enough energy for 15 minutes of muscle activity

Enough energy to run a 10 Km race

Anaerobic cellular respiration

Converts glucose to pyruvic acid and ultimately to lactic acid

Can produce energy for 30-40 seconds of contraction

Requires O2

A and b are correct

A, b, and c are correct

Aerobic cellular respiration

Converts the pyruvate from glycolysis into CO2, H2O, heat, and ATP

Occurs in the mitochondria

Requires O2, which can be obtained from hemoglobin or myoglobin

Is required for muscle activities lasting longer than one minute

All of these are correct

Each of the following contributes to muscle fatigue except:

Depressed Ca2 levels in the sarcoplasm

Presence of adequate amounts of O2 in the mitochondria

Elevated levels of lactic acids in the sarcoplasm and blood

Depletion of glycogen and other nutrients from the sarcoplasm

Elevated ADP levels

Oxygen debt (recovery oxygen uptake)

Is the amount of O2 required by the body to convert glycogen into lactic acid

Is the amount of O2 required by the body to remove O2 from myoglobin

Is the amount of O2 required by the body to recuperate from exercise

Is the amount of O2 required by the body to convert ATP to ADP

Is the amount of O2 required by the body to convert creatine phosphate to pyruvate

Each of the following is true except that:

A single muscle fiber is controlled by through a single neuromuscular junction

A single motor neuron controls a single muscle fiber

The strength of a muscle contraction depends on the number of motor units stimulated

The strength of a muscle contraction depends on the size of the motor units stimulated

a motor unit consists of a somatic motor neuron and the skeletal muscle fibers it controls

Motor unit recruitment

Occurs when the number of motor units involved in muscle contraction decreases

Contributes to the production of smooth rather than jerky movements

Promotes muscle fatigue

Prevents sustained contraction of a muscle group

Inhibits fine adjustments to muscle strength

Muscle tone

Is maintained by conscious control from the autonomic division of the nervous system

Blocks muscle contractions not needed for movement of the body

Is a property of skeletal, but not, smooth muscle tissue

Result from involuntary contractions of alternating small groups of motor units

Increases when motor nerves to a muscle group are damaged

Isotonic contractions

Generates low muscle tension but allow little change in muscle length

Generate high low muscle tension but allow little change in muscle length

Are used to move objects or to move the body

Are important in maintaining posture

Are concentric if the length of the muscle increases during the contraction

Cardiac muscle tissue

Is autorhythmic

Contains branched cells that are connected by intercalated discs

Obtains Ca2 required for contraction from the sarcoplasmic reticulum and the interstitial fluid

Maintains contractions for longer periods of time than skeletal muscle tissue

All of the above are correct

Smooth muscle tissue

May be stimulated to contract by hormones

Has briefer contractions that skeletal muscle tissue

Used calmodulin to remove Ca2 from the cytoplasm

A and c are correct

B and c are correct

Property allowing muscle to shorten forcefully when stimulated by an action potential

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