lab 10

The characteristic muscle stiffness associated with rigor mortis is due to the inability of myosin filaments to detach from the active site on actin filaments. What molecule is essential for this detachment?

ATP

Tamara's muscle weakness and fatigue becomes progressively worse over the course of the day. This is a hallmark sign of myasthenia gravis, an autoimmune disorder that affects the ability of a motor neuron to communicate with a muscle fiber. What synaptic events must happen first for excitation to occur?

Acetylcholine is released from the axon terminal and diffuses across the synapse to bind to a receptor in the surface of the motor end plate.

The injection that dramatically improved Tamara's symptoms was Tensilon, an acetylcholinesterase inhibitor. What is acetylcholinesterase, and why was this injection effective in relieving Tamara's symptoms?

Acetylcholinesterase is the enzyme that clears acetylcholine from the synapse. Inhibiting this enzyme will enable acetylcholine to be available for a longer period to bind to receptors.

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 (junctional folds of the sarcolemma) and sodium enters the cell.

How is delayed-onset muscle soreness (DOMS) different from muscle fatigue?

Delayed-onset muscle soreness occurs a day or more after the physical exertion.

Myasthenia gravis is an autoimmune disorder that results in the production of antibodies that either block or cause the destruction of the ACh receptor. Why do you think that Tamara's symptoms become worse as the day progresses?

In the morning, the neuronal reserves of acetylcholine are larger, allowing for sufficient neurotransmitter release and resulting in effective muscle signaling. As the day progresses and the stores of acetylcholine become depleted, muscle function becomes progressively worse.

The muscle action potentials that initiate contraction are transmitted from the sarcolemma into the interior of the muscle fiber by __________.

T tubules

Malignant hyperthermia (MH) is a rare genetic disease in which the sarcoplasmic reticulum leaks calcium when the patient is put under general anesthesia. Which of the following best describes how anesthesia would affect the skeletal muscles of a patient with MH?

The muscles would contract because of calcium binding to troponin.

What happens immediately after the myosin head binds to the active site on actin?

The myosin head pivots, moving the actin strand.

Why do the disease tetanus and the normal sustained muscle contraction called tetanus share the same name?

They both eliminate the relaxation phase in the affected muscle fibers.

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

acetylcholine (ACh)

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

actin

Myosin molecules form cross-bridges when they attach to __________.

actin

Which of the following proteins contains the active site involved in cross-bridge formation?

actin - Correct The active site on actin is where myosin heads bind. In the absence of calcium, these active sites are covered by the regulatory protein tropomyosin.

Considering that the likelihood of nerve damage due to intramuscular injections into bulky muscles with fewer nerves is greatly reduced, into which of the following muscles would you NOT want to receive an intramuscular injections?

adductor longus

What causes the vesicles inside a neuron to fuse with the plasma membrane?

an action potential in the neuron

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

arrival of an action potential

What causes the myosin head to disconnect from actin?

binding of ATP

The sarcoplasmic reticulum contains __________.

calcium

ATP binding leads to which of the following actions?

detaching and resetting cross-bridges

A hiatal hernia develops when abdominal contents protrude into the thoracic cavity through openings in the muscle that separates the thoracic and abdominal cavities. What is the name of the muscle?

diaphragm

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

exocytosis

Activities involving eccentric contractions more commonly lead to delayed-onset muscle soreness than concentric or isometric contractions. Which of the following activities is thus a candidate for delayed-onset muscle soreness?

extension of the biceps brachii

Inside a muscle, bundles of single muscle fibers form __________.

fascicles

In an inguinal hernia, abdominal contents protrude through an enlarged inguinal canal. Which of the following muscles is not superficial to the inguinal canal?

latissimus dorsi

Myofibrils are __________.

made of a series of sarcomeres

Bacteria that cause tetanus release a neurotoxin called tetanospasmin. Which of the following components of the neuromuscular junction (NMJ) does this neurotoxin affect directly?

motor neurons

The neuromuscular junction is a connection between a neuron and a __________.

muscle fiber

Which of the following is involved in the power stroke?

myosin

Acetylcholine receptors are primarily located __________.

on the motor end plate

What causes the power stroke?

release of ADP and Pi

The role of acetylcholinesterase in the neuromuscular junction is to __________.

remove acetylcholine from the synaptic cleft

Z lines define the edges of which of the following?

sarcomeres

Which organelle completely surrounds each myofibril inside a muscle fiber?

sarcoplasmic reticulum

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

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

The end of a neuron, where acetylcholine-filled vesicles are located, is called the __________.

synaptic terminal

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 cisterns (cisternae) of the sarcoplasmic reticulum

During an intramuscular injection temporary paralysis of the deltoid muscle occurred. Which of the following nerves was accidentally pierced during this injection?

the axillary nerve

Which of the following most correctly describes excitation in the context of excitation-contraction coupling in skeletal muscle?

the generation of an action potential in the sarcolemma

An action potential in the muscle fiber causes __________.

the muscle fiber to contract

What is the synaptic cleft?

the space between the synaptic terminal and the motor end plate

Myosin molecules form what part of the sarcomere?

thick filament

Which of the following phrases best describes how excitation is coupled to contraction in skeletal muscle fibers?

through calcium release from the sarcoplasmic reticulum

T tubules and the terminal cisternae are clustered into structures called __________.

triads

When the sarcomere is at rest, what is covering the active sites on actin?

tropomyosin

Which of the following causes the active site on actin to be exposed or uncovered?

tropomyosin shifting position

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

troponin

To what regulatory protein does calcium bind during the initiation of the contraction cycle in skeletal muscle fibers?

troponin

When calcium is released inside a muscle cell, what does it bind to?

troponin

Inside a neuron, acetylcholine is contained within __________.

vesicles

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

voltage-gated calcium channels