What causes the myosin head to disconnect from actin?

binding of ATP

Yes, the binding of ATP causes the myosin head to disconnect from actin.

What energizes the power stroke?

hydrolysis of ATP

Yes, the hydrolysis of ATP provides the energy for the power stroke. Energy is transferred from ATP to the myosin head.

In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter?

acetylcholine (ACh)

Yes, acetylcholine is the neurotransmitter found in neuromuscular junctions

When an action potential arrives at the axon terminal of a motor neuron, which ion channels open?

voltage-gated calcium channels

Yes, the action potential opens voltage-gated calcium channels and calcium rushes into the axon terminal, leading to the release of the neurotransmitter.

What means of membrane transport is used to release the neurotransmitter into the synaptic cleft?

exocytosis

The binding of the neurotransmitter to receptors on the motor end plate causes which of the following to occur?

Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate

Excitation-contraction coupling is a series of events that occur after the events of the neuromuscular junction have transpired. The term excitation refers to which step in the process?

Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.

Excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. What specific event initiates the contraction?

Calcium release from the sarcoplasmic reticulum initiates the contraction.

A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. How are these components connected?

A series of proteins that control calcium release.

What is name given to the regularly spaced infoldings of the sarcolemma?

transverse or T tubules

Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?
Action potentials.
Calcium ions.
Acetylcholine.
Sodium ions

Calcium ions

Yes! Action potentials propagating down the T-tubule cause a voltage-sensitive protein to change shape. This shape change opens calcium release channels in the sarcoplasmic reticulum, allowing calcium ions to flood the sarcoplasm. This flood of calcium ions is directly responsible for the coupling of excitation to contraction in skeletal muscle fibers.

What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated?

Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.

The A band is occupied by the entire length of _________

thick myofilaments.

In which phase would the net movement of Ca2+ into the sarcoplasmic reticulum (SR) be greatest?
1. Latent Period (initial)
2. Period of contraction (middle)
3. Period of Relaxation (end)

3. Period of Relaxation (end)

During the period of relaxation (C), Ca2+ is transported by active transport into the SR. Decreased Ca2+ concentrations in the sarcoplasm leads to detachment of cross bridges and, consequently, decreased contractile force.

Excitation-contraction coupling includes all EXCEPT which of the following events?
1. propagation of an action potential along the sarcolemma and down T tubules
2. release of calcium ions from the terminal cisterns
3. release of acetylcholine from axon terminals at the neuromuscular junction
4. binding of calcium ions to troponin, which removes the blocking action of tropomyosin

3. release of acetylcholine from axon terminals at the neuromuscular junction

What is a cross bridge cycle?

It is the cycle in which an energized myosin head binds to actin and performs a power stroke, then binds to ATP in order to detach and re-energize

Which muscle fiber type is best suited for endurance activities, such as long-distance jogging?
slow glycolytic fibers
fast glycolytic fibers
fast oxidative fibers
slow oxidative fibers

slow oxidative fibers

Slow oxidative fibers are best suited for endurance (long duration) activities because they produce ATP aerobically, and are thus, fatigue-resistant. Fast glycolytic fibers, and to a lesser extent fast oxidative fibers, rely more on anaerobic glycolysis, and thus produce more lactic acid, which is a major cause of fatigue.

Which of the following factors influence the velocity and duration of muscle contraction?
load placed on the muscle
length of muscle fibers activated
frequency of stimulation
muscle fiber size

load placed on the muscle

Cross bridge formation between myosin heads and actin molecules is caused by the elevation of calcium ion concentration in the cytosol. During rigor mortis, this elevation of calcium ion concentration in the cytosol is permanent because ________.

mitochondria stop producing ATP molecules required by the sarcoplasmic reticulum's calcium ion pumps

In a bedridden patient recovering from a badly fractured femur, disuse atrophy in the thigh muscles is caused by _________.

decreased synthesis of muscle proteins and/or increased breakdown of muscle proteins

What special feature of smooth muscle allows it to stretch without immediately resulting in a strong contraction?

stress-relaxation response