MasteringA&P 6: Chapter 12- Muscles
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.
Acetylcholine binds to its receptor in the sarcolemma and triggers __________.
the opening of ligand-gated cation channels
What structure is the functional unit of contraction in a skeletal muscle fiber?
The sarcomere
Action Potential
A change in membrane voltage that travels down the T-tubule to cause opening of Ca2+ channels
Isometric; elastic elements stretch
A muscle moving a load goes through two phases of contraction. Which phase occurs first, and what happens inside the muscle during this phase?
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
One motor unit
A patient has damage to one somatic motor neuron. What will this affect?
smooth
A patient is born with a mutation in her calmodulin gene. This could affect the contraction of ________ muscles.
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.
ACh Receptor-channel
A structure that when bound to a ligand opens a divalent channel for the movement of both Na+ and K+
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.This degradation results in a rapid cessation of the acetylcholine signal and a swift removal from the cleft.
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.
Motor End Plate
An area of muscle fiber membrane that is in close association with the axon terminal of the motor neuron, contain receptors for acetylcholine
Axon terminal of motor neuron
An area that contains many synaptic vesicles filled with acetylcholine
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 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 most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?
Calcium ions.
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.
1. Acetylcholine is release from motor neuron. 2. Action potential travels down the T-tubule. 3. Ca2+ is released from the sarcoplasmic reticulum. 4. Myosin generates the power stroke. 5. Ca2+ -ATPase channels actively pump Ca2+ back into the sarcoplasmic reticulum. 6. Ca2+ unbinds from troponin. 7. Actin filament slip back to rest position.
Events of Excitation and Contraction Together in Order
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.
Ca2+ comes from the extracellular fluid and the SR.
How does the process of smooth muscle contraction differ from contraction in skeletal muscle?
It causes rotation of the myosin head, thus "cocking" it.
How is the energy released by ATP hydrolysis used during the contractile cycle in skeletal muscle?
*see image*
Label: Muscle Fiber Motor End Plate Axon Terminal of Motor Neuron Acetylcholine
1. Somatic motor neuron delivers action potential. 2. Acetylcholine is released from the axon terminal onto the motor endplate. 3. Net Na+ influx through nicotinic receptors. 4. Muscle fiber depolarizes. 5. Action potential travels down the T-tubule of the muscle fiber.
Putting the Events at the Neuromuscular Junction in Order
1. An action potential that travels down the T-tubule changes the structural confirmation of the DHP L-type Ca2+ channel. 2. Ryanodine receptor channels open. 3. Ca2+ leaves the sarcoplasmic reticulum. 4. Actin and myosin bind to one another. 5. Myosin heads utilize energy from ATP hydrolysis to produce the power stroke. 6. Actin filaments slide toward the M line, shortening the sarcomere.
Putting the Events of Contraction in Order
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.
How does the myosin head obtain the energy required for activation?
The energy comes from the hydrolysis of ATP.
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.
myosin
Thick filaments are made up of __________.
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.
Tropomyosin is pulled away from the myosin-binding site on actin.
What happens when calcium binds troponin?
Rotation of the myosin head to the cocked position
What immediately follows hydrolysis of ATP during muscle contraction?
Thin and thick filaments slide past each other, but do not change in length.
Which happens when a myofibril contracts?
In both, muscle action potentials are shorter than muscle contraction.
Which is a similarity between summation and tetanus?
Myosin would not be able to bind to actin in order to cause shortening of the sarcomere
Which loss of function would occur if you introduced a chemical that functioned as an inhibitor of the ryanodine receptor channel? Choose the best answer.
Actin and myosin filaments slide past each other to shorten the sarcomere, bringing Z disks closer together.
Which of the following best describes the contraction phase of the excitation-contraction coupling reaction? Choose the best answer.
Ca2+ will bind to troponin, which leads to a conformational shift in tropomyosin, allowing for actin and myosin to attach.
Which of the following best describes the role of calcium (Ca2+ ) in the excitation-contraction coupling reaction? Choose the best answer.
Muscle action potentials initiate calcium signals that activate a contraction-relaxation cycle.
Which of the following best summarizes the events of excitation-contraction coupling? Choose the best answer.
Both involve depolarizations followed by repolarizations
Which of the following is a similarity between slow wave potentials and pacemaker potentials?
Ca2+ unbinds from troponin, which results in tropomyosin re-covering myosin binding sites.
Which of the following is the most direct cause of muscle relaxation? Choose the best answer.
the point of synapse between a motor neuron and the muscle fiber that it innervates
Which of the following statements best describes the neuromuscular junction? Choose the best answer.
Myosin heavy chain
Which of the following structural protein of skeletal muscle also acts as an enzyme?
muscle fiber motor end plate ACh receptor-channels motor neuron acetylcholine
Which of the following structures is/are necessary to initiate the muscle action potential?
Pumping of calcium ions into the SR
Which of the following would stop muscle contraction?
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
What is name given to the regularly spaced infoldings of the sarcolemma?
transverse or T tubules
