Adaptive follow up Anatomy ch.9 Muscles

What is the role of calcium in the cross bridge cycle?

calcium binds to troponin, altering its shape

The type of muscle found in the walls of most hollow organs is ________.

unitary smooth muscle

What role does tropomyosin play in the cross bridge cycle?

The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form.

Which of the following best describes the events of "contraction" in "excitation-contraction coupling"?

cross bridge formation

What is the type of chemical reaction used to rebuild ADP into ATP?

dehydration synthesis

If both of the neurons in the figure were activated, more muscle fibers would contract than if either neuron alone were active. This mechanism for control of the force of muscle contraction is known as ______.

recruitment

In muscle fibers, which regulatory protein blocks the attachment of myosin heads to actin?

tropomyosin

Which type of muscle fiber has a large quantity of glycogen and mainly uses glycolysis to synthesize ATP?

white fast switch fibers

How do calcium ions initiate contraction in skeletal muscle fibers?

Calcium ions bind to troponin, changing troponin's shape.

Muscle cells initiate nerve impulses. T/F

TRUE

The cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge?

A myosin head bound to actin

The final "go" signal for skeletal muscle contraction is __________.

an increase in intracellular calcium ion levels

Synaptic vesicles at the neuromuscular junction contain __________.

ACh (acetylcholine)

Which event causes cross bridge detachment?

ATP binding to the myosin head

After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment?

ATP binds to the myosin head

Action potential propagation in a skeletal muscle fiber ceases when acetylcholine is removed from the synaptic cleft. Which of the following mechanisms ensures a rapid and efficient removal of acetylcholine?

Acetylcholine is degraded by acetylcholinesterase.

The neuromuscular junction is a well-studied example of a chemical synapse. Which of the following statements describes a critical event that occurs at the neuromuscular junction?

Acetylcholine is released by axon terminals of the motor neuron.

How/when does the myosin head cock back to store energy for the next cycle?

After the myosin head detaches, energy from ATP hydrolysis is used to re-cock the myosin head.

What specific event triggers the uncovering of the myosin binding site on actin?

Calcium ions bind to troponin and change its shape.

Which of the following is true concerning the anatomy of a skeletal muscle fiber?

Myofibrils contain thick and thin filaments.

When does cross bridge cycling end?

Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin.

Duchenne muscular dystrophy is more common in females than in males. T/F

FALSE

What would happen if acetylcholine was not removed from the synaptic cleft?

Multiple action potentials would occur in the muscle fiber.

When the chemically gated ion channels open, which ion is mainly responsible for depolarizing the sarcolemma?

Na+

The "rest and recovery" period, where the muscle restores depleted reserves, includes all of the following processes EXCEPT __________.

Pyruvic acid is converted back to lactic acid.

Calcium entry into the axon terminal triggers which of the following events?

Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine.

The __________ are extensions of the sarcolemma, and serve as a rapid communication system that ensures that every myofibril in the muscle fiber contracts at virtually the same time.

T tubules

Skeletal muscle fibers contain sarcomeres; smooth muscle fibers do not. T/F

TRUE

Smooth muscle depends on the calcium-calmodulin system to regulate contraction while skeletal muscle relies on the calcium-troponin system to regulate contraction. T/F

TRUE

Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels. Why?

The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients.

During contraction, what prevents actin myofilaments from sliding backward when a myosin head releases?

There are always some myosin heads attached to the actin myofilament when other myosin heads are detaching.

How does troponin facilitate cross bridge formation?

Troponin controls the position of tropomyosin on the thin filament, enabling myosin heads to bind to the active sites on actin.

The response of a motor unit to a single action potential of its motor neuron is called ________.

a muscle twitch

The thin myofilaments of skeletal muscle are composed chiefly of __________.

actin

The sequence of electrical changes that occurs along the sarcolemma when a muscle fiber is stimulated is known as the ___________.

action potential

What event most directly triggers the release of calcium from the terminal cisternae?

action potential propagating down the T tubule

Acetylcholinesterase is responsible for?

breaking down acetylcholine

What is the primary mechanism by which ACh is cleared from the synaptic cleft?

broken down by acetylcholinesterase in the synaptic cleft

What most directly causes synaptic vesicles to release acetylcholine into the synaptic cleft?

calcium entering the axon terminal

What is the cause of rigor mortis?

calcium influx into the sarcoplasm after death

Calcium ions couple excitation of a skeletal muscle fiber to contraction of the fiber. Where are calcium ions stored within the fiber?

calcium ions are stored in the sarcoplasmic reticulum

what causes smooth muscles contractions?

calmodulin

Acetylcholine receptors are best characterized as what type of channel?

chemically gated Na+ and -K+ channels

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 overlap to a greater degree

Where in the cross bridge cycle does ATP hydrolysis occur?

during the cocking of the myosin head

Which of the following allows recoil of the muscle fiber when contraction ends?

elastic filaments

Action potentials travel the length of the axons of motor neurons to the axon terminals. These motor neurons __________.

extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fiber

Skeletal muscle cells are grouped into bundles called __________.

fascicles

Which of the following processes produces molecules of ATP and has two pyruvic acid molecules as end products?

glycosis

Properly controlled skeletal muscle contractions produced by changing the frequency of stimulation or the strength of stimulation are accomplished by __________.

grades muscle response

Which of the following best describes the events of "excitation" in "excitation-contraction coupling"?

propagation of the action potential along the sarcolemma

Myasthenia gravis is sometimes treated medically by a treatment that involves ________.

inhibiting the action of acetylcholinesterase

The major role of the sarcoplasmic reticulum is to regulate ________.

intracellular levels of Ca2+

Which of the following processes produces 36 ATP?

krebs cycle and oxidative phosphorylation

A motor neuron and all the muscle fibers it supplies is called a(n) ____________.

motor unit

Which of the following is thought to be an autoimmune disease of acetylcholine receptors?

myasthenia gravis; it is thought to be an autoimmune disease of the acetylcholine receptors on the skeletal muscle cell because antibodies that destroy these receptors can be detected in the patients.

What is a special adaptation present in skeletal muscle cells, but absent in most other cells?

myoglobin

What protein functions as a motor protein?

myosin

What, specifically, is a cross bridge?

myosin binding to actin

BMD (2,3-butanedione 2-monoximime) inhibits myosin, such that ATP can bind to myosin but myosin is unable to hydrolyze the bound ATP. What effect would BMD have on the cross bridge cycle?

myosin heads would remain detached, unable to cock

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

peristalsis

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

repolarization

Slow oxidative muscle fibers are best suited for ________.

running a marathon

ACh receptors are found mainly in the __________.

sarcolemma

The smallest contractile unit of a muscle fiber is ________.

sarcomere

Myofibrils are composed of repeating contractile elements called __________.

sarcomeres

Which type of muscle CANNOT contract without being stimulated by the nervous system?

skeletal

Which of the following muscle types is both voluntary and striated?

skeletal muscle only

Binding of calcium to calmodulin is a step in excitation-contraction coupling of ________ cells.

smooth muscle

The first step toward generating a skeletal muscle contraction is ________.

stimulation of the muscle by a nerve ending

The space between the neuron and the muscle is the ___________.

synaptic cleft

The calcium that initiates skeletal muscle contraction is released from what structure(s)?

terminal cisternae

What is unique about smooth muscle?

the absence of striated; only smooth muscle is non-striated

The force of a muscle contraction is NOT affected by __________.

the amount of ATP stored in the muscle cells

How does the myosin head obtain the energy required for activation?

the energy comes from the hydrolysis of ATP

Acetylcholine binds to its receptor in the sarcolemma and triggers __________.

the opening of ligand-gated cation channels

When an action potential arrives at the neuromuscular junction, the most immediate result is __________.

the release of acetylcholine form the motor neuron

What structure is the functional unit of contraction in a skeletal muscle fiber?

the sarcomere

Which of the following are composed of myosin?

thich filaments