MasteringA&P: Chapter 9 part 1
The smallest contractile unit within skeletal muscle would correspond to the distance between which two points in the figure? [Relationship between fibers composing a sarcomere.]
1 and 7 [The distance between points 1 and 7 spans a sarcomere, the smallest contractile unit of a muscle fiber.]
The molecular interaction described as a cross bridge involves the binding of which two proteins? [Interaction between thick and thin filaments during muscle contraction.]
A & c
Both actin and myosin are found in the ______________________
A Band
The myosin filaments are located in the ___________________
A Band
Which step precedes all of the other listed steps?
ACh is released by the motor neuron.
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.
Which of the following corresponds to a single fascicle? [Pop-out view of a skeletal muscle showing tissue sheaths and bundling patterns.]
B [A fascicle is an organized group of muscle fibers (cells) bounded by a perimysium.]
Which of the following interactions must occur first so that the others can take place? [Interaction between thick and thin filaments during muscle contraction.]
B binds to troponin.
Which structure in the figure corresponds to a single skeletal muscle cell? [Pop-out view of a skeletal muscle showing tissue sheaths and bundling patterns.]
C [Note that a skeletal muscle cell is commonly termed a muscle fiber.]
Which of the following is most directly required to initiate the coupling of myosin to actin?
Ca+
The ________ contains only the actin filaments.
I Band
The thicker filaments are the ____________ filaments.
Myosin
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.
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.
Based on what you know of the relationship between the thick and the thin filaments, what would happen if a disorder existed that caused a person to produce no tropomyosin?
The muscle tissues would never be able to relax. [The tropomyosin covers the myosin binding site on actin. Without tropomyosin, the myosin would constantly have access to those binding sites.]
What is the role of tropomyosin in skeletal muscles?
Tropomyosin serves as a contraction inhibitor by blocking the myosin binding sites on the actin molecules.
What is the functional unit of a skeletal muscle called?
a sarcomere
Although all the anatomical parts of muscle work together to give it its characteristics, which of the following proteins listed below would be most associated with the characteristics of excitability?
acetylcholine receptors in the motor end plate
After nervous stimulation stops, what prevents ACh in the synaptic cleft from continuing to stimulate contraction?
acetylcholinesterase destroying the ACh
The sliding filament model of contraction involves ________.
actin and myosin sliding past each other and partially overlapping
During muscle contraction, myosin cross bridges attach to which active sites?
actin filaments
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
Which of the following surrounds the individual muscle cell?
endomysium
What is the functional role of the T tubules?
enhance cellular communication during muscle contraction
Muscle tissue can be stimulated by the nervous system. This is because of the membrane potential in the muscle cell. Cells with a membrane potential have what property?
excitability [Excitability, also termed responsiveness, is the ability to receive and respond to a stimulus. For example, skeletal muscle contracts in response to receiving chemical stimulation from the central nervous system.]
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
Which of the following is the correct sequence of events for muscle contractions?
motor neuron action potential, neurotransmitter release, muscle cell action potential, release of calcium ions from SR, ATP-driven power stroke, sliding of myofilaments
Which term best identifies a muscle cell?
muscle fiber [Skeletal muscle cells fuse during development to form the mature, multinucleated muscle fibers.]
The contractile units of skeletal muscles are ________.
myofibrils
Which protein is indicated by the letter E? [Interaction between thick and thin filaments during muscle contraction.]
myosin
Rigor mortis occurs because ________.
no ATP is available to release attached actin and myosin molecules
Hypothetically, if a muscle were stretched to the point where thick and thin filaments no longer overlapped, ________.
no muscle tension could be generated
Approximately 80% of a muscle fiber's volume are the myofibrils. This characteristic reflects muscles ability to ________.
produce movement through contractile force
What is the function of the filaments found in ranges 1-2 and 6-7 but no other ranges? [Relationship between fibers composing a sarcomere.]
protection from overstretching [Elastic (titin) filaments help to protect the muscle from overstretching and also aid in returning it to normal length.]
The __________ shorten(s) during muscle contraction
sarcomere [As actin slides over myosin, the z lines are pulled closer together, shortening the sarcomere.]
What structure in skeletal muscle cells functions in calcium storage?
sarcoplasmic reticulum
Which of the following is NOT a normal function of muscle tissue?
secreting hormones
Muscle tissue has all of the following properties except ________.
secretion
Which of the following are correctly paired?
skeletal muscle; voluntary control
The connective tissue that covers structure A is continuous with which of the following? [Pop-out view of a skeletal muscle showing tissue sheaths and bundling patterns.]
tendon [The dense connective tissue at A is continuous with the tendon that connects the muscle to a bone or, in some cases, to another muscle or to the skin.]
Acetylcholine binds to its receptor in the sarcolemma and triggers __________.
the opening of ligand-gated cation channels
The contractile, or functional, unit of a muscle fiber is __________.
the sarcomere [The sarcomere is the contractile unit of a muscle fiber and the smallest functional unit of muscle. A sarcomere is the region of a myofibril between two successive Z discs; it primarily consists of thin and thick myofilaments.]
Although all the anatomical parts of muscle work together to give it it's characteristics, which of the following proteins listed below would be most associated with the characteristics of contractility?
thick (myosin) filaments
A sarcomere is the distance between two _____________
z Discs
