Chapter 6

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.

Cardiac muscle tissue

Muscle tissue composed of branching cells and intercalated discs

Cardiac muscle tissue

Muscle tissue found only in the heart

Smooth muscle tissue

Muscle tissue that activates arrector pili muscles to stand hairs on end

Smooth muscle tissue

Muscle tissue that dilates and constricts the pupils of our eyes

Skeletal muscle tissue

Muscle tissue that is multinucleate

8. Skeletal muscle tissue

Muscle tissue that maintains posture, body position, and stabilizes joints

Smooth muscle tissue

Performs very slow, sometimes rhythmic, contractions

Cardiac and skeletal muscle both possess striations.

True

Skeletal muscle tissue

Voluntary muscle tissue

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

acetylcholine (ACh)

What specific event triggers the uncovering of the myosin binding site on actin?

Calcium ions bind to troponin and change its shape.

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

The sarcomere

Cardiac muscle fibers are joined by special gap junctions called intercalated discs; these discs allow heart activity to be closely coordinated.

True

The sarcoplasmic reticulum wraps like a sleeve around the myofibril and stores and releases calcium.

True

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

actin

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

Which of the following is NOT a function of the muscular system?

blood cell formation

Striated involuntary muscle tissue is classified as ________ muscle.

cardiac

Striated involuntary muscle tissue found in the heart is ________.

cardiac muscle

What type of muscle tissue is both striated and involuntary?

cardiac muscle

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

exocytosis

Which of these characteristics applies only to cardiac muscle tissue?

intercalated discs

What causes the power stroke?

release of ADP and Pi

The plasma membrane of a skeletal muscle cell is called the ________.

sarcolemma

What organelle wraps and surrounds the myofibril and stores calcium?

sarcoplasmic reticulum

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

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

Which term does NOT describe smooth muscle cells?

skeletal

The type of muscle tissue pictured in the figure is ________.

smooth muscle

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 Submit

A sarcomere is ________.

the contractile unit between two Z discs

Which one of the following is composed mostly of the protein myosin?

thick filaments

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

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.

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.

Smooth muscles stabilize joints of the skeleton.

False

What creates the alternating light and dark bands that provides the striation pattern on skeletal muscle tissue?

A bands and I bands

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

A myosin head bound to actin

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.

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

The energy comes from the hydrolysis of ATP.