Chapter 9 homework

A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. How are these components connected ? a) A series of proteins that control calcium release. b) Myosin cross-bridge binding sites. c) Potassium leak channels. d) Voltage-gated sodium channels.

a) A series of proteins that control calcium release.

A myosin head binds to which molecule to form a cross bridge? a) actin b) troponin c) tropomyosin

a) actin

Which of the following is NOT a role of ATP in muscle contraction? a) exposing myosin binding sites on actin b) Detaching the cross bridge from actin c) Transporting calcium ions into the sarcoplasmic reticulum d) Energizing the power stroke of the cross bridge

a) exposing myosin binding sites on actin

What causes the power stroke? a) release of ADP and Pi b) calcium c) hydrolysis of ATP d) binding of ATP

a) release of ADP and Pi

The action potential on the muscle cell leads to contraction due to the release of calcium ions. Where are calcium ions stored in the muscle cell? a) terminal cisterns (cisternae) of the sarcoplasmic reticulum b) sarcolemma c) cytosol d) T tubule

a) terminal cisterns (cisternae) of the sarcoplasmic reticulum

What is name given to the regularly spaced infoldings of the sarcolemma? a) transverse or T tubules b) terminal cisternae c) motor endplates d) sarcoplasmic reticulum

a) transverse or T tubules

The binding of the neurotransmitter to receptors on the motor end plate causes which of the following to occur? a) Binding causes voltage-gated sodium channels to open in the motor end plate (junctional folds of the sarcolemma ) and sodium enters the cell. b) Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate (functional folds of the sarcolemma ) and sodium enters the cell c) Binding causes chemically gated potassium channels to open in the motor end plate (junctional folds of the sarcolemma) and potassium enters the cell. d) Binding causes potassium voltage-gated channels to open in the motor end plate junctional folds of the sarcolemmaand potassium enters the cell.

b) Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate (functional folds of the sarcolemma ) and sodium enters the cell

Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers? a) Sodium ions b) Calcium ions c) Action potentials . d) Acetylcholine.

b) Calcium ions

Which of the following is responsible for muscle relaxation? a) Sodium ions enter into the sarcopiasm through voltage-gated channels. b) Calcium ions are removed from the sarcoplasm by active transport. c) ATP binds to the myosin head to cause cross bridge detachment. d) Calcium ions are released from the terminal cisterns during depolarization of the T tubule.

b) Calcium ions are removed from the sarcoplasm by active transport.

Based on what you know of the relationship between the thick and the thin filaments , what would happen if a disorder existed that caused a person to produce no tropomyosin ? a) The muscle would never contract . b) The muscle tissues would never be able to relax c) actin will spontaneously fall apart . d) The muscle would be weaker than normal .

b) The muscle tissues would never be able to relax

In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter ? a) serotonin b) acetylcholine (ACh) c) dopamine d) norepinephrine

b) acetylcholine (ACh)

What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell? a) troponin b) arrival of an action potential c) calcium ion pump d) АТР

b) arrival of an action potential

How is acetylcholine (ACh) removed from the synaptic cleft? a) acetylcholinesterase (AChE; an enzyme) and endocytosis into the muscle fiber b) simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme) c) acetylcholinesterase (ACHE ; an enzyme ) only d) simple diffusion away from the synaptic cleft and endocytosis into the muscle fiber

b) simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme)

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? a) Excitation refers to the propagation of action potentials along the axon of a motor neuron. b) Excitation refers to the shape change that occurs in voltage-sensitive proteins in the sarcolemma . c) Excitation, in this case, refers to the propagation of action potentials along the sarcolemma . d) Excitation refers to the release of calcium ions from the sarcoplasmic reticulum .

c) Excitation, in this case, refers to the propagation of action potentials along the sarcolemma .

What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated? a) A skeletal muscle fiber is innervated by multiple motor neurons b) A motor neuron typically innervates only one skeletal muscle fiber. c) Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron . d) Motor neurons always innervate thousands of skeletal muscle fibers .

c) Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron .

What causes the myosin head to disconnect from actin? a) binding of troponin b) binding of calcium c) binding of ATP d) hydrolysis of ATP

c) binding of ATP

What means of membrane transport is used to release the neurotransmitter into the synaptic cleft? a) protein carrier b) a channel c) exocytosis

c) exocytosis

Botulism and myasthenia gravis are conditions that cause muscle weakness. Which of these statements is NOT true? a) In myasthenia gravis, acetylcholine is released, but the receptors on the junctional folds of the sarcolemma cannot receive the acetylcholine. b) Both conditions affect normal activity at the neuromuscular junction. c) Botulium toxin impairs the release of acetylcholine from the presynaptic neuron. d) Both conditions are caused by an inability of the body to produce adequate acetylcholine.

d) Both conditions are caused by an inability of the body to produce adequate acetylcholine

Excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. What specific event initiates the contraction? a) Action potentials propagate into the interior of the skeletal muscle fiber. b) Sodium release from the sarcoplasmic reticulum initiates the contraction. c) Voltage-sensitive proteins change shape. d) Calcium release from the sarcoplasmic reticulum initiates the contraction.

d) Calcium release from the sarcoplasmic reticulum initiates the contraction.

The binding of calcium to which molecule causes the myosin binding sites to be exposed? a) actin b) tropomyosin c) myosin d) troponin

d) troponin

When an action potential arrives at the axon terminal of a motor neuron, which ion channels open? a) chemically gated calcium channels b) voltage-gated sodium channels c) voltage-gated potassium channels d) voltage- gated calcium channels

d) voltage- gated calcium channels