Chapter 9 HW Assignment
Consider how the action potential that initiates contraction is delivered to the muscle cell. Which of the choices below correctly describes how an action potential generated at the neuromuscular junction (NMJ) is converted to excitation in the muscle fiber?
An action potential in the motor neuron causes ACh to be released into the synaptic cleft. Binding of ACh to sarcolemma receptors initiates graded potentials.
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.
Which selection best describes the initial event in contraction?
Myosin heads bind to the newly exposed myosin-binding sites on actin to form cross bridges.
Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?
calcium ions
What structure most directly stimulates a skeletal muscle fiber to contract?
motor neuron
Which of the following choices best summarizes excitation-contraction coupling?
A series of events in which an electrical stimulus is conveyed to a muscle fiber to enact 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.
The cross bridge cycle starts when...
Ca2+ from the sarcoplasmic reticulum binds to troponin
Which selection correctly describes the role of calcium in coupling?
Calcium binds to troponin, which moves tropomyosin and exposes 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?
Calcium release from the sarcoplasmic reticulum initiates the contraction.
A person dies, and within hours, the skeletal muscles develop a locked contraction known as rigor mortis. Calcium ions leak from the sarcoplasmic reticulum into cytoplasm. From your knowledge of cross bridge cycling, what best explains this rigor?
Cross bridge detachment cannot occur. Detachment requires ATP, which is produced only during life.
The action potential propagates along the sarcolemma. As the action potential spreads down the T tubules of the triads, voltage-sensitive tubule proteins change shape. How does the shape change of these proteins lead to contraction?
It allows calcium to exit the sarcoplasmic reticulum and enter the cytosol.
Inadequate calcium in the neuromuscular junction would directly affect which of the following processes?
Release of acetylcholine from the synaptic vesicles
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.
If troponin is a component of both cardiac and skeletal muscle, why is an elevated plasma troponin level useful in diagnosing myocardial damage?
The subunits of the troponin in cardiac muscle are unique to heart muscle.
A muscle cell runs out of ATP. Even though these are cyclic reactions, what step of the cross bridge cycle given is most directly inhibited or terminated?
cross bridge detachment
What is name given to the regularly spaced infoldings of the sarcolemma?
transverse or T tubules
