MasteringA&P 07 Muscles
The heart's pacemaker is the:
sinoatrial node.
Describe the pressures in the atria and ventricles that would cause the opening of the AV valves.
Pressure in the atria would be greater than the pressure in the ventricles.
Slow oxidative muscle fibers are best suited for:
endurance activities.
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.
Cardiac muscle makes most of its ATP via anaerobic mechanisms.
False
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.
Which of the following is a factor that affects the velocity and duration of muscle contraction?
load on the fiber
What special feature of smooth muscle allows it to stretch without immediately resulting in a strong contraction?
stress-relaxation response
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 calcium calmodulin system of contraction regulation is found in:
smooth muscle only.
z disc, H zone, I band, M line etc
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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.
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 is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?
Calcium ions.
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 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
Increased pressure in the ventricles would close what valve(s)?
AV valves only
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.
Brian decided to enter a 5-mile race designed to raise money for a class trip. He did not do any preconditioning, nor has he ever jogged before. The morning after the race, Brian had so much pain in both his legs that he was unable to go to school. What caused this pain, and why?
Brian has shin splints. This is a condition in which the anterior tibialis muscle is irritated, inflamed, and swollen. The circulation is impaired by the tight fascial wrappings, causing pain.
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.
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.
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.
Which of the following is correct about the filling of the ventricles?
Most blood flows passively into the ventricles through open AV valves.
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.
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 causes the aortic semilunar valve to close?
greater pressure in the aorta than in the left ventricle
Put the phases of the cardiac cycle in the correct order, starting after ventricular filling.
isovolumetric contraction, ventricular ejection, isovolumetric relaxation
Immediately following the arrival of the stimulus at a skeletal muscle cell there is a short period called the ________ period during which the events of excitation-contraction coupling occur.
latent
The mechanism of contraction in smooth muscle is different from skeletal muscle in that ________.
the site of calcium regulation differs
What is name given to the regularly spaced infoldings of the sarcolemma?
transverse or T tubules
Isovolumetric relaxation and ventricular filling (two phases of the cardiac cycle) take place during __________.
ventricular diastole
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
SA node, AV node, AV bundle, bundle branches, purkinje fibres on heart and graph: QRS complex, T wave, P wave, Atrial depolarisation, ventricular depolarisation and repolarisation.
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