1)In which of the following would the motor units have the fewest muscle fibers?
A)calf muscles
B)thigh muscles
C)muscles of the neck
D)muscles that control the eyes
E)postural muscles of the back
D)muscles that control the eyes
2)The following is a list of the events that occur during a skeletal muscle contraction.
- Myosin cross-bridges bind to the actin.
- The free myosin head splits ATP.
- Calcium ion is released from the sarcoplasmic reticulum.
- The myosin head pivots toward the center of the sarcomere.
- Calcium ion binds to troponin.
- The myosin head binds an ATP molecule and detaches from the actin.
The correct sequence of these events is
A)1, 3, 5, 4, 6, 2.
B)1, 4, 6, 2, 3, 5.
C)3, 5, 1, 4, 6, 2.
D)5, 1, 4, 6, 2, 3.
E)3, 5, 1, 2, 4, 6.
C)3, 5, 1, 4, 6, 2.
3)Muscle tension can be increased by increasing the number of active motor units this process is called
A)wave summation.
B)complete tetanus.
C)recruitment.
D)treppe.
E)incomplete tetanus.
C)recruitment.
4)Muscular force can be adjusted to match different loads by
A)recruiting larger motor units
B)varying the frequency of action potentials in motor neurons
C)recruiting more motor units
D)A, B, and C
E)None of the above muscle contraction is all-or-none.
D)A, B, and C
5)A single motor neuron together with all the muscle fibers it innervates is called
A)an end foot.
B)a dermatome.
C)an end plate.
D)a motor unit.
E)a myotome.
D)a motor unit.
6)Since each myofibril is attached at either end of the muscle fiber, when sarcomeres shorten, the muscle fiber
A)shortens.
B)weakens.
C)lengthens.
D)strengthens.
E)not enough information to say
A)shortens.
7)In rigor mortis
A)muscles are inextensible.
B)cross-bridge cycling is absent.
C)ATP is depleted.
D)the myosin heads are attached to actin.
E)all of the above
E)all of the above
8)Which feature of a skeletal muscle fiber is involved in the conduction of the action potential from the sarcolemma into the fiber?
A)transverse tubules.
B)neuromuscular junctions.
C)sarcoplasmic reticulum.
D)triads.
E)motor end plates.
A)transverse tubules.
9)How would a drug that blocks acetylcholine receptors at the motor end plate affect skeletal muscle?
A)It would cause flaccid paralysis (muscles are relaxed and unable to contract).
B)It would have little effect on skeletal muscles.
C)It would produce uncontrolled muscle spasms.
D)It would cause spastic paralysis (muscles are contracted and unable to relax).
E)It would make the muscles more excitable.
A)It would cause flaccid paralysis (muscles are relaxed and unable to contract).
10)The cytoplasm of the neuromuscular terminal bouton contains vesicles filled with molecules of the neurotransmitter
A)norepinephrine.
B)acetylcholine.
C)epinephrine.
D)antidiuretic hormone.
E)all of the above
B)acetylcholine.
11)When calcium ion binds to troponin,
A)active sites on the myosin are exposed.
B)myosin shortens.
C)muscle relaxation occurs.
D)tropomyosin moves into the groove between the helical actin strands.
E)actin heads will bind to myosin.
D)tropomyosin moves into the groove between the helical actin strands.
12)The repeating unit of a skeletal muscle fiber is the
A)myofibril.
B)myofilament.
C)sarcomere.
D)sarcoplasmic reticulum.
E)sarcolemma.
C)sarcomere.
13)Which statement about excitation-contraction coupling is incorrect?
A)Relaxation requires uptake of calcium ion by the sarcoplasmic reticulum.
B)Tropomyosin moves to expose myosin binding sites on actin.
C)Troponin binds calcium ion and signals tropomyosin to move.
D)Calcium ion is released from the sarcoplasmic reticulum.
E)Calcium ion is released from the transverse tubule.
E)Calcium ion is released from the transverse tubule.
14)The most important factor in decreasing the intracellular concentration of calcium ion after contraction is
A)active transport of calcium into the synaptic cleft.
B)diffusion of calcium into the sarcoplasmic reticulum.
C)active transport of calcium into the sarcoplasmic reticulum.
D)active transport of calcium across the sarcolemma.
E)diffusion of calcium out of the cell.
C)active transport of calcium into the sarcoplasmic reticulum.
15)Which of the following statements is false?
A)Skeletal muscle contractions may be summated.
B)Cardiocytes are interconnected through intercalated discs.
C)Skeletal muscle stimulation is neural.
D)Cardiac muscle stimulation is neural.
E)Cardiac muscle contractions cannot be summated
D)Cardiac muscle stimulation is neural.
16)Smooth muscle cell contraction occurs
A)Due to release of calcium primarily from the sarcoplasmic reticulum
B)Due to the action of primarily extracellular calcium activating myosin
C)Due to calcium binding to troponin
D)Due to the activation of T tubules
B)Due to the action of primarily extracellular calcium activating myosin
17)Cardiac muscle contraction is
A)initiated by the autonomic nervous system
B)increased by a decrease in permeability of the membrane to Na ions
C)initiated by extracellular calcium ions hyperpolarising the cell membrane
D)decreased by an increase in permeability of the membrane to K ions
D)decreased by an increase in permeability of the membrane to K ions