Chapter 12 Muscles

A motor unit consists of

one neuron and all skeletal muscle fibers it controls

Motor unit that control skeletal muscles involved with fine motor movements (eye muscles or the hands) have ____ muscle fibers than motor unis that control more gross movements (gastrocnemius muscle of the lower leg)


Which of the following statements is NOT correct regarding the motor units and their activation?

A weak contractile stimulus activates fast-twitch motor units.

Which fibers generate more force?

Fast-twitch fibers

Which fibers fatigue sooner?

Fast-twitch fibers

The neurons system avoids muscle fatigue during submaximal contraction by

asynchronous recruitment

Inward extensions of the muscle cell membrane


Highly organized bundles of contractile proteins within a skeletal muscle cell

Sarcomere, myofibril

A single muscle cell

muscle fiber

The muscle cell mebrane


A bundle of adjacent muscle cells


The structures that serve as the attachment site for the thin filaments and mark the boundaries for one sarcomere.

Z disk

The letter assigned to this structure stands for the German word for middle, it is the attachment site for the thick filaments.

M line

The band with the most overlap between thick and thin filaments, which unevenly scatters light leading to its dark appearance

A band

Which of the following is not a correct statement concerning the muscles in the body?

All types of muscle generate heat by shivering when we are cold

Groups of adjacent fibers bundled together into units are called ____. These bundles are surrounded by the proteins ______ and elastin as well as ______ that deliver nutrients to the muscle cells.

fascicles, collagen, blood vessels

The T-tubular membrane contains ____ receptors that are ____ and therefore respond to action potentials. The receptor is mechanically linked to ______ receptors in the adjacent sarcoplasmic reticulm

dihydropyridine (DHP), voltage sensing , ryanodine (RyR)

In order to contract and relax, muscle cells require energy in the form of ______. The immediate backup energy source is _____ that requires the enzyme ______.

ATP, phosphocreatine, creatin kinase

Calcium released by the sacroplasmic reticulum, binds to ____ to mobe the _____ which allows actin to form a high-force crossbridge with myosin

Troponin C, Tropomyosin

The heavy chain of myosin contains two important regions: the first acts as ______ to convert energy into movement whereas the second binds to ____.

ATPase, actin

As a muscle cell undergoes an accentric contraction, sarcomer length will _____ as the length of the A band ____.

Increase, does not change

Put these in the order they would be recruited as the body moves from a weak to a strong stimulus:
1. glycolitic fast-twitch fiber
2. fatigue-resistant oxidative fast-twitch fibers
3. fatigue-resistant slow-twitch fibers.


A contraction that generates enough force to move a load is known as ______, whereas one that generates force that equals the load is known as ______.

isotonic. isometric

Before the entire muscle can change length, the force generated by the muscle must stretch the

series elastic elements

In the lever system that characterizes the interaction between bones and muscle, the bones act as the _____ whereas the joint form the ______.

lever, fulcrums

In order for the bicep muscle to shorten, the force applied by the muscle must be ____ the load applied at the hand.

Greater than

Compared to skeletal muscle, contraction of smooth muscle cells is

A slower response to a stimulus and sustained without fatigue

Smooth muscle cells lack which protein(s)?

tropinin only

Which of the following is NOT a property of single-unit smooth muscles?

Each cell functions independent of its neighbor

The protien is activated by the Ca2+ calmodulin complex to phosphorylate the mysodin light chain protien.

Myosin light chain kinase

The calcium release channel in the smooth muscle sacroplasmic reticulum that is opened by increase in phospholipase C activity is the

inositol trisphosphate (IP3) receptor channel

A change in smooth muscle cell tension in the absence of a change in electrical potential of the cells is described as a

pharmacomechanical coupling

Which of the following is NOT a correct comparison of cardiac myocytes to other muscle cell types?

Like skeletal muscle, contraction of cardiac muscle is under autonomic nervous control.

In comparison to skeletal muscle, smooth muscle cells function over a ____ range of muscle lengths and exhibit a speed of contraction that is _____ than skeletal muscle

wider, slower

The gap junctions in cardiac muscle are part of specialized cell junctions that are localized to the

intercalated disks

Store-generated calcium channels open in response to

depleted intracellular stores of calcium

A myogenic contraction describes the opening of ____ channels in smooth muscle cells in response to a distortion of the cell membrane that is commonly observed in ______-.

stretch activated , blood vessels