TEST 3 MASTERING A&P PHYSIO

According to the sliding- filament model of muscle contraction, which of the following is shortened: I band A band H zone sarcomere all of these except b

all of these except b I band, H zone and Sarcomere

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

calcium ions

The muscle generates force and shortens in this type of twitch. isometric isotonic

isotonic

Because of the correlation between the size of a motor unit and the type of fiber it contains, recruitment of fibers happen in a specific order. Which of the following fibers are recruited first? fast oxidative fibers fast glycolytic fibers slow glycolytic fibers slow oxidative fibers

slow oxidative fibers

What is name given to the regularly spaced infoldings of the sarcolemma? transverse or T tubules motor endplatest erminal cisternae sarcoplasmic reticulum

transverse or T tubules

A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. How are these components connected? gated sodium channels. Potassium leak channels. Myosin cross-bridge binding sites. A series of proteins that control calcium release.

A series of proteins that control calcium release.

The cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge? A. A myosin head bound to actin B. Calcium bound to troponin C. Troponin bound to tropomyosin D. ATP bound to a myosin head

A. a myosi head bound to actin As soon as the activated myosin head forms a cross bridge with actin, the power stroke begins

After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment? Acetylcholine binds to receptors in the junctional folds of the sarcolemma. ATP binds to the myosin head. ADP and inorganic phosphate are bound to the myosin head. Calcium ions bind to troponin.

ATP binds to the myosin head. The binding of ATP to the myosin head weakens the bond between myosin and actin, forcing the myosin head to detach. ATP also provides the energy for the next power stroke.

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. Calcium ions are stored in the nuclei. Calcium ions are stored in the transverse tubules. Calcium ions are stored in the mitochondria.

Calcium ions are stored in the sarcoplasmic reticulum. Sarcoplasmic reticulum is the specific name given to the smooth endoplasmic reticulum in muscle fibers. The sarcoplasmic reticulum is very elaborate in skeletal muscle fibers, allowing for significant storage of calcium ions.

What specific event triggers the uncovering of the myosin binding site on actin? Calcium ions bind to tropomyosin and change its shape. Calcium ions bind to troponin and change its shape. Calcium release channels open in the sarcoplasmic reticulum, and calcium levels rise in the sarcoplasm. Sodium ions bind to troponin and change its shape.

Calcium ions bind to troponin and change its shape. The shape change caused by the binding of calcium to troponin shifts tropomyosin away from the myosin binding sites on actin.

Excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. What specific event initiates the contraction? Sodium release from the sarcoplasmic reticulum initiates the contraction. Calcium release from the sarcoplasmic reticulum initiates the contraction. Action potentials propagate into the interior of the skeletal muscle fiber. Voltage-sensitive proteins change shape.

Calcium release from the sarcoplasmic reticulum initiates the contraction.

When does cross bridge cycling end? Cross bridge cycling ends when ATP binds to the myosin head. Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin. Cross bridge cycling ends when calcium ions are passively transported back into the sarcoplasmic reticulum. Cross bridge cycling ends when calcium release channels in the sarcoplasmic reticulum open.

Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin. The sarcoplasmic reticulum contains Ca2+-ATPases that actively transport Ca2+ into the SR. Without Ca2+, troponin returns to its resting shape, and tropomyosin glides over and covers the myosin binding sites on actin.

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-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 refers to the propagation of action potentials along the axon of a motor neuron. Excitation refers to the release of calcium ions from the sarcoplasmic reticulum. Excitation refers to the shape change that occurs in voltage-sensitive proteins in the sarcolemma.

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

What structure is the functional unit of contraction in a skeletal muscle fiber? The cross bridge The junctional folds of the sarcolemma The triad The sarcomere

The SARCOMERE A sarcomere is a regular arrangement of thin and thick myofilaments that extends from one Z disc to the next. A myofibril consists of a series of sarcomeres.

How does the myosin head obtain the energy required for activation? The energy comes from the hydrolysis of GTP. The energy comes from the direct phosphorylation of ADP by creatine phosphate. The energy comes from the hydrolysis of ATP. The energy comes from oxidative phophorylation.

The energy comes from the hydrolysis of ATP. Myosin is a large, complex protein with a binding site for actin. It also contains an ATPase. The energy released during the hydrolysis of ATP activates the myosin head.

What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated? A motor neuron typically innervates only one skeletal muscle fiber. Motor neurons always innervate thousands of skeletal muscle fibers. Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron. A skeletal muscle fiber is innervated by multiple motor neurons.

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