Ch 12 (EXAM 3) Muscle Physiology - Study Modules

The neurotransmitter that signals the contraction of skeletal muscle fibers is ________.

acetylcholine -Specifically, the motor neuron synapses with skeletal muscle at the neuromuscular junction. An action potential traveling down the axon of the motor neuron stimulates the opening of voltage-gated calcium channels located on axon terminal (terminal bouton). As a result, a calcium influx occurs, causing synaptic vesicles to fuse with the axon terminal membrane releasing acetylcholine into the neuromuscular junction. The acetylcholine binds to nicotinic cholinergic receptors on the motor end plate resulting in a net sodium influx that depolarizes the muscle fiber. - Dopamine is involved in the reticular activating system and the basal ganglia (nuclei) in the brain. - Epinephrine is involved in the reticular activating system in the brain and released from the adrenal medulla. -Serotonin is a central nervous system neurotransmitter.

A molecule(s) common to both skeletal and smooth muscle crossbridge cycling include ________.

actin

Contraction in smooth muscle is initated when ________.

calcium binds to calmodulin

When myosin is bound to actin during the crossbridge cycle ________.

calcium is bound to the troponin complex, and myosin is in a high-energy form -Two events must occur prior to myosin binding to actin forming crossbridges. First, the myosin head must be in a high-energy cocked position. By hydrolyzing ATP to ADP and Pi, the energy released is utilized to cock the myosin head. Second, calcium (released from the smooth endoplasmic reticulum) must bind to troponin for the tropomyosin to move aside, exposing the myosin binding sites on the actin filament. Following these two events, myosin binds to actin.

In what way(s) is cardiac muscle similar to smooth muscle?

It contains gap junctions, possesses pacemaker cells, and is innervated by autonomic neurons.

Which receptors are located at a skeletal muscle motor end plate?

Nicotinic cholinergic receptors - The release of acetylcholine from a somatic motor neuron binds to nicotinic receptors, leading to an end plate potential by the influx of sodium ions. This end plate potential then initiates an action potential across the sarcolemma.

Are the terms muscle organ and muscle cell interchangeable? Why or why not?

No. The terms muscle organ and muscle cell are not interchangeable because a muscle organ is comprised not only of many muscle cells, but additional tissues (such as sensory nerves, motor nerves, and connective tissue).

The function of skeletal muscle transverse tubules is to ________.

conduct action potentials and excite the sarcoplasmic reticulum

During skeletal muscle contraction, thick and thin filaments bind together forming __________.

crossbridges

During complete tetanus ________.

cytosolic calcium levels are high enough to saturate all the troponin molecules

The latent period of a muscle twitch is due to the time it takes for ________.

excitation-contraction coupling -This represents time between the action potential production in the muscle cell and muscle contraction. -Tension is generated during the cross bridge cycle. The production of ATP should be continuous. An action potential does not occur at the motor end plate, only graded end plate potentials (EPPs).

Put the following in order of largest to smallest: a) myofibril b) muscle fiber c) fascicle d) thick filament

fascicle muscle fiber myofibril thick filament -A fascicle is a bundle of muscle fibers. Muscle fibers are muscle cells and myofibrils are found in the cytoplasm of muscle fibers. Thick filaments are found in sarcomeres, which are contained in myofibrils.

Smooth muscle is similar to skeletal muscle in which of the following ways?

Presence of actin and myosin

Which of the following skeletal muscle types have a high capillary density, high myoglobin content, and high resistance to fatigue?

Red, slow oxidative muscle fibers - these muscle fibers are small in diameter and generate minimal amounts of tension.

Muscle fibers can obtain energy from the conversion of pyruvate to________ when the oxygen supply for aerobic respiration is too slow to meet the ATP demands of heavy exercise.

lactic acid

The burning sensation that is felt in muscles during exercise is due to the buildup of ________.

lactic acid

As the load on a muscle increases, which of the following also increase(s)?

latent period

Contraction in smooth muscle is terminated when ________.

myosin is dephosphorylated by a phosphatase

Which type of molecules are more likely to be found in higher concentrations in a fast glycolytic fiber?

pyruvate and lactic acid -These muscle fibers are utilized to perform high intensity exercise for brief periods. They tend to be larger in diameter and are surrounded by fewer capillaries.

An increase in the force generated by a muscle is achieved by the ________ of more motor units.

recruitment

Put the events of the crossbridge cycle in the correct order, starting with the binding of myosin to actin: a) binding of ATP b) release of Pi c) release of ADP d) power stroke

release of Pi power stroke release of ADP binding of ATP

When a muscle is stimulated at a high frequency such that the twitches build on each other, ________ is observed.

summation

Small motor units ________.

tend to be recruited first during a contraction

The amount of force a muscle can generate depends on __________.

the number of sarcomeres in parallel, the length of individual sarcomeres, and the cross-sectional diameter of the muscle fiber - If a muscle has more sarcomeres in parallel, it means that there are more thin and thick filaments available to generate force.

Muscle tension decreases at short muscle lengths when ________.

thin filaments at opposite ends of the sarcomere overlap

The force generated by an entire muscle organ depends directly or indirectly on the ________.

- number of active cross bridges formed - force generated by individual muscle fibers - number of muscle fibers contracting

Which of the following statements about muscle contractions is true?

Sarcomeres shorten during each isometric and isotonic contractions.

Which of these statements best characterize single-unit smooth muscle?

Single-unit smooth muscle has gap junctions and light innervation by the autonomic nervous system.

Which muscle fiber type experiences slow-wave potentials?

Smooth muscle

Which type of muscle is subject to the several types of hormonal control?

Smooth muscle

Which of the following statements about muscles is true?

Smooth muscle thin and thick filaments are arranged obliquely. -This arrangement allows the contraction to occur on various axes.

In which types of muscle does myosin have ATPase activity?

Smooth, cardiac, and skeletal

Sarcomere thick and thin filaments overlap within the __________.

A band - The overlap of the thick and thin filaments permits crossbridge cycling to occur. - The H zone = where only thick filaments are found. - The I band = where only thin filaments are found. - The Z line is the boundary lines for a sarcomere and runs perpendicular to the long axis. It is made of protein, which anchors the thin filaments on one end.

During the crossbridge cycle, once myosin ATPase hydrolyzes ATP into ADP + Pi, ________.

ADP + Pi are bound to the myosin head and the myosin head binds to a G-actin molecule (It is now primed for a power stroke.) -The myosin has to first bind to a G-actin of a thin filament before it can complete the power stroke. -ADP + Pi presence activates the crossbridge. -The myosin head binds to a G-actin of a thin filament when ADP + Pi are present.

Muscle relaxation requires ________ added to the myosin crossbridge.

ATP -In doing so, the myosin head can detach from actin. This is illustrated in step 4 in the image below. During the crossbridge cycle, when the myosin head hydrolyzes ATP to ADP and Pi, the released energy is utilized to re-cock the myosin head.

Skeletal muscle thick filaments have __________.

ATPase activity and actin binding sites - Thick filaments have ATPase activity in the myosin head and actin binding sites. Thick filaments are made of myosin molecules grouped together. Each myosin molecule has two heads and two intertwined tails. Each myosin head has two binding sites; one site binds ATP and the other site binds actin. It is important to note that the myosin head cannot bind both ATP and actin at the same time. The myosin head has a greater affinity for ATP than for actin. This is important because a myosin head will detach from an actin filament in order to bind ATP.

Which of the following statements about smooth muscle is true?

Actin and myosin generate force through the crossbridge cycle. -Unlike skeletal muscle, actin and myosin in smooth muscle are not organized in sarcomeres

Why is there a high degree of overlap between the action potential and the contraction in cardiac fibers?

An overlap of cardiac action potential and contraction prevents summation of muscle contractions so that the heart has time to relax and fill with blood before the next contraction.

In which type of muscle is the function of gap junctions of the greatest importance in maintaining life?

Cardiac

Which is the fastest way that a skeletal muscle cell can generate ATP to power muscle contraction?

Creatine phosphate (phosphocreatine) phosphorylation of ADP -The fastest way a skeletal muscle cell can generate ATP to power muscle contraction is by use of creatine phosphate (phosphocreatine) to phosphorylate ADP -Oxidation of glucose generates considerably more ATP than the amount of ATP produced from utilization of creatine phosphate, but it requires more time.

When the conduction of an action potential along a skeletal muscle cell membrane leads to the release of calcium from the sarcoplasmic reticulum, why will the calcium release eventually stop?

The rising concentration of cytosolic calcium triggers the closure of calcium channels in the sarcoplasmic reticulum. -A drop in cytosolic calcium concentration results in calcium dissociating from troponin and tropomyosin moves into its original position.

Which of the following have a large muscle fiber diameter and a high force-generating capacity?

White, fast glycolytic fibers

Which of the following statements about muscle contraction is true?

Each myosin head completes about five crossbridge cycles per second, but each thick filament has hundreds of myosin heads.

Which of these statements best characterize multi-unit smooth muscle?

Multi-unit smooth muscle lacks gap junctions but has dense innervation by the autonomic nervous system.

The functional unit within a muscle fiber is called a sarcomere. Which of the following does not make up part of the sarcomere?

Myofibril - Actin, myosin and tropomyosin are proteins found within a sarcomere. Specifically, actin and tropomyosin are found in the thin filaments while myosin constitutes the thick filaments. - Sarcomeres packaged end-to-end within a myofibril

Skeletal muscle troponin complex of thin filaments can bind __________.

Tropomyosin, calcium, and actin