Understanding Chap 12

Drag and drop each of the following events in their correct sequential order

1. Somatic motor neuron delivers action potential 2. Acetylcholine is released from the axon terminal onto the motor end plate 3. Net Na+ influx through nick tonic receptors 4. Muscle fiber depolarizes 5. Action potential travels down the T-tubule of the muscle fiber

Put these events in the correct chronological sequence: 1. End-plate potentials trigger action potentials. 2. Transverse tubules convey potentials into the interior of the cell. 3. Acetylcholine binds to receptors on the motor end plate. 4. Ca2+ is released from the sarcoplasmic reticulum.

3, 1, 2, 4

The cross bridge cycle is a series of molecular events that occur after excitation if the sarcolemma. What is a cross bridge?

A mysosjn head bound to actin

Occurs when myosin crossbridges attach to actin filaments and pull them toward the middle of the sarcomere

A power stroke

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.

A structure that when bound to a ligand opens a divalent channel for the movement of both Na+ and K+

ACh receptor-channel

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

In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter?

Acetylcholine (ACh)

Which of the following best describes the contraction phase of the excitation-contraction coupling reaction?

Actin and myosin filaments slide past each other to shorten the sarcomere, bringing Z disks closer together.

An area that contains many synaptic vesicles filled with acetylcholine

Axon terminal of motor neuron

What causes the myosin bead to disconnect from actin?

Binding of ATP

The binding of the neurotransmitter to receptors on the motor end plate causes which of the following to occur?

Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate and sodium enters the cell

How does the process of smooth muscle contraction differ from contraction in skeletal muscle?

Ca2+ comes from the extracellular fluid as well as the SR.

Which of the following is the most direct cause of muscle relaxation?

Ca2+ unbinds from troponin, which results in tropomyosin re-covering myosin binding sites.

Which of the following best describes the role of calcium in the excitation-contraction coupling reaction?

Ca2+ will bind to troponin, which leads to a conformational switch in tropomyosin, allowing for actin and myosin to attach

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.

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.

Which of the following processes produces 36 ATP?

Krebs cycle and oxidative phosphorylation

Which of the following structures is/are necessary to imitate the muscle action potential?

Motor end plate Motor neuron Acetylcholine ACh receptor channels Muscle fiber

Which of the following best summarized the events of excitation-contraction coupling?

Muscle action potentials initiate calcium signals that activate a contraction-relaxation cycle

Which of the following is the smallest structure?

Myosin

Which loss of function would occur if you introduced a chemical that functioned as an inhibitor of the ryanodine receptor channel?

Myosin would not be able to bind to actin in order to cause shortening of the sarcomere

Which of the following would stop muscle contraction?

Pumping of calcium ions into the SR

The "rest and recovery" period, where the muscle restores depleted reserves, includes all of the following except

Pyruvic acid is converted back to lactic acid

How is acetylcholine (ACh) removed from the synaptic cleft?

Simple diffusion away from the synaptic cleft acetylcholinesterase (AChE; an enzyme)

Which of the following statements best describes the pathology associated with periodic paralysis?

Skeletal muscles are plagued by being flaccid for short periods.

How does the myosin head obtain the energy required for activation?

The energy comes from the hydrolysis of ATP.

How does the permanent depolarization of the skeletal muscle result in a flaccid (non-contracted) paralysis?

The muscle cell would not be able to depolarize a second time because the voltage-gated sodium channel never inactivates.

What name is given to the regularly spaced infoldings of the sarcolemma?

Transverse or T Tubules

What happens when calcium binds troponin?

Tropomyosin is pulled away from the actin active site.

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.

Compared to skeletal muscle, contraction of smooth muscle cells is

a slower response to a stimulus and sustained without fatigue.

A myosin head binds to which molecule to form a cross bridge?

actin

Each myosin head has a binding site for

actin and ATP

A change in membrane voltage that travels down the t-tubule to cause opening of CA2+ channels

action potential

What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell?

arrival of an action potential

Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?

calcium ions

What is the type of chemical reaction used to rebuild ADP into ATP?

dehydration synthesis

What means of membrane transport is used to release the neurotransmitter into the synaptic cleft?

exocytosis

Motor units that control skeletal muscles involved with fine motor movements (eye muscles or the hands) have ________ muscle fibers than motor units that control more gross movements (gastrocnemius muscle of the lower leg).

fewer

which of the following processes produces molecules of atp and has two pyruvic acid molecules as end products

glycolysis

An area of muscle fiber membrane that is in close association with the axon terminal of the motor neuron, contain receptors for acetylcholine

motor end plate

Because of their shape, muscle cells are also known as

muscle fibers

A motor unit consists of

one neuron and all the skeletal muscle fibers it controls.

What causes the power stroke?

release of ADP and Pi

What immediately follows hydrolysis of atp during muscle contraction?

rotation of the myosin head to the cocked position

What structure is the functional unit of contraction in a skeletal muscle fiber?

sarcomere

What are the ions directly associated with all forms of periodic paralysis due to the fact that the channels for these ions are defective?

sodium and calcium

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?

terminal cisternae of the sarcoplasmic reticulum

Which of the following statements best describes the neuromuscular junction?

the point of synapse between a motor neuron and the muscle fiber that it innervates

The binding of calcium to which molecule causes the myosin binding sites to be exposed?

troponin

When an action potential arrives at the axon terminal of a motor neuron, which ion channels open?

voltage-gated calcium channels

Which type of muscle fiber has a large quantity of glycogen and mainly uses glycolysis to synthesize ATP?

white fast twitch fibers