Muscle and Muscle Tissue (Mastering A&P)

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

which of the choices below correctly describes how an action potential generated at the neuromuscular junction is converted to excitation in the muscle fiber?

an action potential in the motor neuron causes ACh to be released into the synaptic cleft. binding of ACh to sarcolemma receptors initiates graded potentials

Which selection correctly describes the role of calcium in coupling?

calcium binds to troponin, which moves tropomyosin and exposes the myosin-binding sites on actin

synaptic vescile

container of many neurotransmitter molecules

Troponin

the protein that binds to calcium

Ca2+

ion triggering exocytosis

the action potential propagates along the sarcolemma. as the action potential spreads down the T tubules of the triads, voltage-sensitive tubule proteins change shape. how does the shape of these proteins lead to contraction?

it allows calcium to exit the sarcoplasmic reticulum and enter the cytosol

synaptic cleft

location of acetylcholinesterase

sarcolemma

membrane surrounding muscle fiber

When a muscle is unable to respond to stimuli temporarily, it is in which of the following periods?

refractory period

myoglobin

stores oxygen in muscle cells

What does excess postexercise oxygen consumption represent?

the difference between the amount of oxygen needed for totally aerobic muscle activity and the amount actually used

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 sarcolemma is negatively charged compared to the outside surface. sodium ions diffuse inward along favorable chemical AND electrical gradients

neurotransmitter at neuromuscular junction

ACh

which of the following is most directly required to initiate the coupling of myosin to actin?

Ca++

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

Calcium ions

voltage-sensitive tubule protein

a protein that changes shape as a result of an action potential

Which step precedes all of the other listed steps?

ACh is released by the motor neuron.

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

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 refers to the propagation of action potentials along the sarcolemma

ion entering muscle fiber through open chemically gated ion channels

Na+

the end plate potential is primarily, and most directly, caused by the movement of

Na+

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

Transverse or T tubules

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 an actin

Exhaustion of glycogen storage within a muscle fiber would have the biggest effect on ________.

fast glycolytic fibers

What part of the sarcolemma contains acetylcholine receptors?

motor end plate

which of the following is the correct sequence of events for muscle contractions?

motor neuron action potential, neurotransmitter release, muscle cell action potential, release of calcium ions from SR, ATP-driven power stroke, sliding of myofilaments

which term best identifies a muscle cell?

muscle fiber

which selection best describes the initial event in contraction?

myosin heads bind to the newly exposed myosin-binding sites on actin to form cross bridges

the cross bridge cycle starts when

Ca2+ from the sarcoplasmic recticulum binds to troponin

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

myosin

a protein with heads that attach in cross bridging

Steps of Excitation-Contraction Coupling

1. action potential is generated at the sarcolemma. 2. action potential goes down the T tubule 3. voltage-gated tubule protein changes shape. 4. calcium ion channels open. 5. calcium exits the cistern into sarcoplasm. 6. calcium binds to troponin. 7. actin sites are exposed. 8. cross bridges form between actin and myosin

what are the steps of the cross bridge cycle?

1. the activated myosin head binds to actin, forming a cross bridge 2. ADP is released and myosin slides the thin filament toward the center of the sarcomere 3. ATP binds to the myosin head and detaches it from actin 4. ATP is hydrolyzed to ADP and Pi and the energy released re-cocks the myosin head

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

which of the following best describes how ACh changes the ion permeability of the sarcolemma?

ACh binds to receptors in the junctional folds

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.

which of the following choices best summarizes excitation-contraction coupling?

a series of events in which an electrical stimulus is conveyed to a muscle fiber to enact contraction

T tubule

a structure that forms a path from the membrane to the cell interior

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 acetylchoniesterase

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 axon terminals of the motor neuron

which of the following best describes the role of acetylcholinesterase molecules at the neuromuscular junction?

acetylcholinesterase breaks down ACh, which allows chemically gated ion channels to close

signals flowing through the neuromuscular junction pass through several structures in a single direction

axon, axon terminal, synaptic cleft, and sarcolemma

Why would inflammation of the knee joint be a "good thing" when there's been an acute quadriceps injury?

because fluid accumulation reduces joint movement

Proper application of RICE --rest, ice, compression, and elevation--can effectively control inflammation due to an ankle sprain. why would compression provided by a correctly wrapped elastic Ace bandage be helpful in preventing further inflammation?

because it immobilizes/stabilizes an injured ankle

ACh

binds to ACh receptors, causing them to open chemically gated ion channels

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 changes it shape

Curare is a poisonous plant extract. Curare molecules have a chemical structure like the neurotransmitter ACh. Curare can bind to the ACh receptor site on the chemically gated ion channels in the motor end plate. Even though curare will bind to the receptor site it will not open the ion channel and no ions will pass through. What do you think the symptoms of curare poisoning would look like?

curare will only affect muscles with ACh receptors, paralyzing them

Na+

diffuses into the muscle fiber through open chemically gated ion channels

K+

diffuses out of the muscle fiber through open chemically gated ion channels

the sliding filament model of contraction states that

during contraction, the thin myofilaments slide past the thick myofilaments so that the actin and myosin myofilaments overlap to a greater degree

which of the following surrounds an individual muscle cell?

endomysium

which of the following properties is most directly associated with changes to a muscle's cell's membrane potential (the voltage across the plasma membrane)?

excitability

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 a skeletal muscle fiber

Cross bridge formation between myosin heads and actin molecules is caused by the elevation of calcium ion concentration in the cytosol. During rigor mortis, this elevation of calcium ion concentration in the cytosol is permanent because ________.

mitochondria stop producing ATP molecules required by the sarcoplasmic reticulum's calcium ion pumps

Rigor mortis occurs because ________.

no ATP is available to release attached actin and myosin molecules

Hypothetically, if a muscle were stretched to the point where thick and thin filaments no longer overlapped, ________.

no muscle tension could be generated

junctional folds

portion of sarcolemma containing ACh receptors

ACh receptor

protein in sarcolemma

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

sarcomere

the ___ shorten(s) during muscle contraction

saromere

which type of muscle requires somatic (voluntary) nervous stimulation for activation?

skeletal

Of the following items listed below, which is the best description for why skeletal muscle stores glycogen?

skeletal muscle is a heavy consumer of energy

which of the following are correctly paired?

skeletal muscle, voluntary control

Addition of more mitochondria to a muscle fiber will have the greatest effect on ________.

slow oxidative fibers

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

What is the most distinguishing characteristic of muscle tissue?

the ability to transform chemical energy into mechanical energy to move the body

based on what you know of the relationship between the thick and thin filaments, what would happen if a disorder existed that caused a person to produce no tropomyosin

the muscle tissues would never be able to relax

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

the opening of the ligand-gated cation channels

cistern

the swollen chamber of an organelle that lies on either side of a T tubule

Although all the anatomical parts of muscle work together to give it its characteristics, which of the following proteins listed below would be most associated with the characteristics of contractility?

thick (myosin) filaments