41.The energy for cross bridge cycling during muscle contraction provided : 1417084
41.The energy for cross bridge cycling during muscle contraction is provided by:
42.Which of the following is involved in the relaxation of a muscle cell?
a.Synthesis of ACh by acetylcholinesterase
b.Initiation of action potentials
c.The troponin-tropomyosin complex slipping back into its blocking position
d.Detachment of actin from tropomyosin
e.T tubules actively absorbing Ca2+
43.A lack of ATP in a contracted skeletal muscle cell would most likely cause
a.cross bridges to detach from actin
b.the sarcomeres to remain shortened
c.an inability to relax
d.both a and c
e.both b and c
44.Which of the following is involved in muscle relaxation?
a.Acetylcholinesterase removes ACh and the muscle cell returns to resting potential.
b.Ca2+ is actively taken up by the lateral sacs when there is no longer an action potential.
c.The cross bridges pull the filaments back to their original resting positions.
d.Both a and b
e.Both b and c
45.Whole muscle tension depends on all of the following except
a.number of muscle fibers contracting
b.tension produced by each contracting fiber
c.extent of motor-unit recruitment
d.frequency of stimulation
e.the proportion of each motor unit used at any given time
46.A motor unit refers to
a.a single motor neuron plus all of the muscle fibers it innervates
b.a single muscle fiber plus all of the motor neurons that innervate it
c.all of the motor neurons supplying a single muscle
d.a pair of antagonistic muscles
e.a sheet of smooth muscle cells connected by gap junctions
47.In twitch summation, the muscle fiber
a.is stimulated again before the fibers returns to resting potential.
b.is stimulated again before it completely returns to resting position.
c.contracts stronger but stronger action potentials do not occur.
d.experiences a and b
e.experiences b and c
a.is a means by which gradation of muscle contraction may be accomplished
b.results from the additional release of Ca2+ within the cytosol of muscle fibers
c.results from increasing the frequency at which motor units are firing within a muscle
d.results from more cross bridges binding to actin within muscle fibers
e.has all of the above characteristics
a.results from increases in cytosolic calcium levels
b.results from pumping of calcium into the sarcoplasmic reticulum
c.can be enhanced by allowing a cell to completely relax
d.rarely results in tetany
e.is not characterized by any of the above
50.To pick up something heavier than your pencil, your nervous system could
a.stimulate larger motor units
b.decrease the frequency of stimulation to allow a more prolonged contraction to occur
c.decrease the refractory periods
d.block acetylcholinesterase at the neuromuscular junction to allow acetylcholine to function longer
e.do all of the above