Muscle Physiology

When a muscle fibre shortens, the following also shortens: Sarcomere Myosin Filament Z-Line Actin filament

Sarcomere

The dense layer of collagen fibers that surround an entire skeletal muscle is the ___________. endomysium epimysium perimysium tendon

epimysium

ATP can be made in muscles from stored glucose. In muscles, glucose is stored in the form of __________. fat creatine glycogen energy

fat

"Cross bridges" that link between the thick and thin filaments are formed by the ___________. globular actin F actin tails of myosin filaments globular head of thick filaments

globular head of thick filaments

The type of muscle contraction in which the muscle fibers produce increased tension, but the muscle neither shortens nor lengthens, is called _____________. treppe isotonic concentric isometric

isometric

Which of the following substances increases in quantity during repetitive muscle contraction during oxygen deficit? lactic acid oxygen glucose adenosine triphosphate (ATP)

lactic acid

A motor neuron and all the muscle fibers it supplies is called a(n) ____________. motor unit motor end plate neuromuscular junction axon terminal

motor unit

In the sliding filament model of muscle contraction, the myofilaments slide over each other, resulting in the overlapping of actin and _________. troponin thin filaments myosin tropomyosin

myosin

Each skeletal muscle fiber is controlled by a neuron at a single ___________. synaptic cleft sarcomere neuromuscular junction transverse tubule

neuromuscular junction

Which of the following is true about muscle structure? Even the largest (thickest) muscle fibres would contain only about 100 myofibrils. Myofibrils make up about 15% of the contents of a muscle fibre. Actin filaments are arranged so that 6 actin filaments surround each myosin filament. Myosin filaments are about twice as thick as actin filaments.

Actin filaments are arranged so that 6 actin filaments surround each myosin filament.

In regard to the force-length relationship, it is true that: The muscle length at which maximal active force occurs is called optimal length. All of the above are true. Beyond resting length, passive force increases from short to long muscle lengths. Total force is equal to the sum of active and passive force.

All of the above are true.

Concentric contractions are weaker than isometric and eccentric contractions partly because, in concentric contractions: There may a small decrease in the force per cross-bridge. There is a smaller number of cross-bridges bound to actin at any time. All of the above. Some attached cross-bridges may exert a "drag" effect on the actin filament.

All of the above.

Select the trait that does not characterize muscle tissue in general. All of these are traits of muscle. extensibility irritability contractility

All of these are traits of muscle.

What is the ion released from the terminal cisternae that combines with troponin and removes the blocking action of tropomyosin, resulting in the formation of cross bridges? Calmodulin myosin Calcium Troponin

Calcium

Which of the following does NOT occur during skeletal muscle contraction? The I bands shorten and H zones disappear. Calcium concentration in the sarcoplasm increases. Calcium binds to myosin heads. Myosin heads bind to actin.

Calcium binds to myosin heads.

Curare is a naturally-occurring compound that competitively binds to nicotinic acetylcholine receptors on muscle cells. Which of the following symptoms might be seen in a patient who has been exposed to curare? Diaphragmatic paralysis Muscle spasticity Cardiac arrest Excessive salivation

Diaphragmatic paralysis

Which of the following correctly identifies muscle components in order from largest to smallest? Muscle fiber, fasciculus, myofibril Fasciculus, muscle fiber, myofibril Sarcolemma, sarcoplasm, fasciculus Fasciculus, muscle bundle, myofibril

Fasciculus, muscle fiber, myofibril

Which of the following statements about smooth muscle is true? Smooth muscle is striated and involuntary. Nuclei are peripherally located in the fibers. Contractions are rapid and forceful. Fibers are small and spindle-shaped.

Fibers are small and spindle-shaped.

In regard to the cross-bridge (CB) power stroke, it is true that: In isometric contractions, the CB power stroke pulls the actin filament straight down, preventing shortening or lengthening. All of the above are true. In concentric contractions, the CB power stroke pulls the actin filament toward the center of the sarcomere, causing sarcomere shortening. In eccentric contractions, the CB power stroke pushes the actin filament away from the centre of the sarcomere, causing sarcomere lengthening.

In concentric contractions, the CB power stroke pulls the actin filament toward the center of the sarcomere, causing sarcomere shortening.

The sarcoplasmic reticulum does not: Make up about 85% of the contents of a muscle fibre. Release Ca2+ in response to a muscle action potential. Surround each myofibril. Has a Ca2+ "pump" in its membrane.

Make up about 85% of the contents of a muscle fibre.

The force of a tetanic contraction is greater than that of a twitch contraction because: The muscle action potentials travel faster along the transverse tubules. More Ca2+ is released in a tetanic contraction. More acetylcholine is released at the neuromuscular junction per nerve impulse. The muscle action potentials are smaller during a tetanic contraction.

More Ca2+ is released in a tetanic contraction.

We would expect to find smooth muscle in all of the following EXCEPT: Myocardial tissue Small intestine Pulmonary circulatory tissue Esophagus

Myocardial tissue

Which is most likely to extend the entire length of a muscle fiber? M-Line Myosin filaments Myofibril Sarcomere

Myofibril

The sensitivity of the smooth muscle contractile apparatus to calcium is known to increase in the steady-state under normal conditions. This increase in calcium sensitivity can be attributed to a decrease in the levels of which of the following substances? Actin Calmodulin Adenosine Triphosphate (ATP) Calcium-calmodulin complex Myosin light chain phosphatase (MLCP)

Myosin light chain phosphatase (MLCP)

Which of the following statements is INCORRECT? Skeletal muscles support the weight of some internal organs. Skeletal muscles form valves regulating the passage of substances through internal openings of the digestive and urinary tracts. Skeletal muscles are responsible for the pumping action of the heart. Skeletal muscle contractions help maintain body temperature.

Skeletal muscles are responsible for the pumping action of the heart.

What is the role of acetylcholine in calcium release? Stimulates postsynaptic acetylcholine receptors to release intracellular calcium Binds to the T-tubules, causing calcium release Stimulates cellular contraction by opening voltage-gated ion channels Binds to sarcoplasmic reticulum, causing calcium release

Stimulates cellular contraction by opening voltage-gated ion channels

Which of the following is NOT innervated by the autonomic nervous system? Striated skeletal muscle cell Branching muscle cell Myocardial cell Intestinal muscle cell

Striated skeletal muscle cell

In excitation-contraction coupling: Ca2+ released from the sarcoplasmic reticulum binds to tropomyosin. Relaxation occurs when Ca2+ is excreted from the muscle fibre. The muscle action potential propagates along the sarcolemma and down the transverse tubules. Troponin blocks binding of myosin heads to actin filaments.

The muscle action potential propagates along the sarcolemma and down the transverse tubules.

Calcium ions are released from the sarcoplasmic reticulum to initiate muscle contraction and are reabsorbed upon muscle relaxation. Which of the following occurs if calcium ions are not completely reabsorbed? The next muscle contraction will be weaker than the previous muscle contraction. There won't be a second muscle contraction until all the calcium ions are reabsorbed. The next muscle contraction will be greater than the previous muscle contraction.

The next muscle contraction will be greater than the previous muscle contraction.

What is the role of tropomyosin in muscle contraction? To release calcium from the sarcoplasmic reticulum To prevent myosin from continuing to slide up the actin filament To release troponin from tropomyosin, allowing myosin to bind to the actin filament To aid in myosin 'cocking' on the actin filament

To prevent myosin from continuing to slide up the actin filament

Eccentric contractions are stronger than isometric and concentric contractions partly because, in eccentric contractions: More muscle fibres within a muscle are activated. More ATP is used in each cross-bridge cycle. Muscle fibres are conducting muscle action potentials at a higher frequency. Within each muscle fibre, more cross-bridges are attached to actin at a given time

Within each muscle fibre, more cross-bridges are attached to actin at a given time

The sequence of electrical changes that occurs along the sarcolemma when a muscle fiber is stimulated is known as the ___________. motor end plate potential membrane repolarization action potential resting potential

action potential

Lactic acid, a byproduct of cellular respiration, is typically produced during __________ respiration. Isotonic aerobic anaerobic isometric

anaerobic

What is the cause of rigor mortis? diffusion of potassium out of the cell after death breakdown of protein in the cell after death high levels of sodium in the cell after death calcium influx into the sarcoplasm after death

calcium influx into the sarcoplasm after death

Which one of the following binds calcium ions in a smooth muscle, causing contraction? tropomyosin troponin actin calmodulin

calmodulin

When the cross‐bridges bind to actin, they will pivot in such a manner to cause the actin filaments to slide. This pivoting action causes the actin filaments to slide __________. closer together farther apart toward the Z lines

closer together

All of the following terms refer to the ability to receive and respond to a stimulus, EXCEPT ___________. contractility irritability excitability responsiveness

contractility

Which of the following allows recoil of the muscle fiber when contraction ends? myosin tropomyosin elastic filaments actin

elastic filaments

Individual fibers of skeletal muscle have fine sheath of connective tissue called a(n) ________________. fascia endomysium perimysium epimysium

endomysium

An entire skeletal muscle is surrounded by ___________. endomysium epimysium perimysium sarcolemma

epimysium

The alternating contraction and relaxation of opposing layers of smooth muscle is referred to as ___________. peristalsis isotonic contraction automatic contraction isometric contraction

peristalsis

In order to make ATP (adenosine triphosphate) in muscles, creatine phosphate (CP) transfers __________ to adenosine diphosphate (ADP). phosphate oxygen adenosine

phosphate

The refractory period in which the muscle will NOT contract if stimulated occurs during __________ of the muscle cell. repolarization hyperpolarization polarization depolarization

repolarization

The functional unit of contraction in a skeletal muscle fiber is the ____________. sarcomere sarcolemma myofibril myofilament

sarcomere

What is the membranous network that surrounds each myofibril? sarcoplasmic reticulum myolemma sarcoplasm sarcolemma

sarcoplasmic reticulum

The space between the neuron and the muscle is the ___________. synaptic cleft motor unit motor end plate synaptic knob

synaptic cleft

Which of the following best describes the composition of the structure known as a triad in a skeletal muscle fiber? actin, troponin, and tropomyosin sarcolemma, sarcoplasm, and sarcoplasmic reticulum A band, I band, and H band terminal cisterna, transverse tubule, and terminal cistern

terminal cisterna, transverse tubule, and terminal cistern

Which of the following characteristics is unique to smooth muscle? response to stretch hyperplasia the ability of ATP to energize the sliding process the absence of striations

the absence of striations

The term that means a continued mild or partial contraction of a muscle that keeps it healthy and ready to respond is muscle ___________. summation tetanus stimulation tone

tone

When muscle contracts upon stimulation, calcium ions bind to __________, which exposes the binding sites for the myosin cross‐bridges to attach to. actin myosin Tropomyosin troponin

troponin