Chapter 10 MAP

which of the following is a recognized function of skeletal muscle?

-guard body entrances and exits -maintain body temp -produce movement -maintain posture

what can the nervous system do to increase muscle tension?

-increase the number of active motor units -increase stimulation frequency -recruit larger motor units

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

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 cross bridge cycle starts when _____.

Ca2+ from the sarcoplasmic reticulum binds to troponin

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.

a fascicle is a

a group of muscle fibers that are encased in the perimysium

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 bind to actin

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.

Action potential propagation in a skeletal muscle fiber ceases when acetylcholine is removed from the synaptic cleft. Which of the following mechanisms ensures a rapid and efficient removal of acetylcholine?

acetylcholine is degraded by acetylcholinesterase

The neuromuscular junction is a well-studied example of a chemical synapse. Which of the following statements describes a critical event that occurs at the neuromuscular junction?

acetylcholine is released by xox terminals of the motor neuron

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.

which of the following situations could contribute to prolonged muscle contraction?

acetylcholinesterase not being produced

the most important factor in decreasing the intracellular concentration of calcium ions after contraction is

active transport of calcium into the sarcoplasmic reticulum

what causes the release of calcium ions into the sarcoplasm from the terminal cisterns?

an action potential traveling along the t tubule

muscles are attached to bones by tendons or ______.

aponeuroses

a(n) _______ can be described as a broad tendinous sheet

aponeurosis

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

which of the following statements about excitation-contraction coupling is incorrect? a. calcium ion is released from the sarcoplasmic reticulum b. calcium ions travel through the transverse tubule c. tropomyosin moves to expose myosin binding sites on actin d. troponin binds calcium ion and signals tropomyosin to move e. relaxation requires uptake of calcium ion by the sarcoplasmic reticulum.

b. calcium ions travel through the transverse tubule

the role of acetylcholinesterase is to

break down acetylcholine in acetate and chlorine components

triads in skeletal muscle fibers function in ______

calcium ion release

what do terminal cisternae release?

calcium ions

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 the troponin and change its shape

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

calcium ions.

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.

muscle tissue, one of the four basic tissue groups, consists chiefly of cells that are highly specialized for

contraction

conduction of an action potential along the sarcolemma depends upon _______.

diffusion of sodium ions through voltage-gated channels

what is the function of the T tubules?

distribute action potentials throughout the interior of the skeletal muscle cells

identify the incorrect statement about a single motor unit. a. muscle fibers of one motor unit intermingle with the fibers of another motor unit b. the smaller the number of muscle fibers, the more precise the movement c. some motor units include as many as 2000 muscle fibers d. fine motor skills depend on the development of small motor units e. the more neurons involved, the more powerful the contraction

e. the more neurons involved, the more powerful the contraction

titin is a(n) ______.

elastic protein

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.

action potentials travel the length of the axons of motor neurons to the axon terminals. these motor neurons _____.

extend from the brain or spinal cord to the sarcolemma of the skeletal muscle fiber

which of the following allows muscles to return to their original shape during relaxation?

gravity, opposing muscle contractions, and elastic forces

what is the function of the nuclei?

houses the genetic material (DNA) of the cell

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.

a weight-lifter strains to lift a heavy weight and there is no movement of the person's arms holding on to the weight. this type of contraction is called a(n) ______ contraction.

isometric

what is the function of the mitochondria?

making of energy (ATP); "power house" of the cell

where is ATP produced in a skeletal muscle cell?

mitochondria

where is ATP consumed?

mitochondria and sarcoplasma reticulum

what structure most directly stimulates a skeletal muscle fiber to contract?

motor neuron

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

motor neurons

a single motor neuron together with all the muscle fibers it innervates is called a(n)

motor unit

interactions between actin and myosin filaments of the sarcomere are responsible for?

muscle contraction

in an isotonic contraction,

muscle tension exceeds the load and the muscle lifts the load

in which of the following would the motor units have the fewest muscle fibers?

muscles that control the eyes

thick filaments are made of the protein

myosin

what area of the thick filaments binds to actin once actin's binding sites are exposed?

myosin cross-bridge (head)

the increase in muscle tension that is produced by increasing the number of active motor units is called

recruitment

a patient takes a medication that blocks ACh receptors of skeletal muscle fibers. what is this drug's effect on skeletal muscle contraction?

reduces the muscle's ability for contraction

inadequate calcium in the neuromuscular junction would directly affect which of the following processes?

release of acetylcholine from the synaptic vesicles

After death, muscle fibers run out of ATP and calcium begins to leak from the sarcoplasmic reticulum into the sarcoplasm. This results in a condition known as

rigor mortis

the repeating unit of a skeletal muscle fiber is the

sarcomere

in response to an action potential along the transverse tubules, the ______ releases calcium ions into the sarcoplasm.

sarcoplasmic reticulum

since each myofibril is attached at either end of the muscle fiber, when sarcomeres shorten, the muscle fiber

shortens

what is the function of the triad?

storage of calcium

the narrow space between the synaptic terminal and the muscle fiber is the

synaptic cleft

Calcium entry into the axon terminal triggers which of the following events?

synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine

at each end of the muscle, the collagen fibers of the epimysium, perimysium, and endomysium, come together to form a

tendon

which of the following statements correctly describes the structure of the sarcomere indicated by the arrow? (Z line)

the boundary between adjacent sarcomeres

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

the energy comes from the hydrolysis of ATP

Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels. Why?

the inside surface of the sacrolemma is negatively charged compared to the outside surface. sodium ions diffuse inward along favorable chemical and electrical gradients.

Acetylcholine binds to its receptor in the sarcolemma and triggers __________.

the opening of ligand-gated cation channels

which of the following statements correctly describes the structure of the sarcomere indicated by the arrow?

the point of connection for adjacent tails of the thick filaments

which of the following statements correctly describes the structure of the sarcomere indicated by the arrow? (A and H band)

the region of the resting sarcomere that only contains thick filaments

which of the following statements correctly describes the structure of the sarcomere indicated by the arrow? (I band)

the region of the sarcomere that contains only thin filaments

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

the sarcomere

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

which of the following best describes the term Z line?

thin filaments are anchored here

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

transverse or T tubules

at rest, the tropomyosin molecule is held in place by

troponin molecules

each thin filament consists of

two actin protein strands coiled helically around each other

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.