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The body depends on muscles to...

-generate heat
-generate force
-generate motion

The purpose of transverse tubules is to...

rapidly conduct action potentials to the interior of the muscle fiber.

When the myosin heads are loosely bound to the actin filaments, the __________ span the space between the parallel thick and thin filaments.

Crossbridges span the gap.

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

Z disk are the boundaries for the sarcomere and attachement site for the thin filaments

The lightest color bands of the sarcomere, occupied only by thin filaments.

I band is the lightest colored band because it is occupied by only thin filaments.

The darkest band, with the most overlapping filaments, its abbreviation derives from its property of scattering light unevenly.

A band is the darkest band with the most overlapping filaments.

A muscle can create force without becoming physically shorter.

isometric contraction

Excitation-contraction coupling refers to...

the chemical and electrical events that trigger the mechanical events in a muscle fiber.

The membrane of the T-tubule contains receptors that are sensitive to


What are the events of excitation-contraction coupling

-ACh binds to receptors in the motore end plate
-ligand binding ion channels open causing depolarization
-end plate potential triggers action potential
-t-tubes convey action potential
-Ca is released from the SR
-Ca binds to troponin
-actin binding sites are uncovered, myosin binds to actin initiating the power-stroke

Muscles require __________ constantly; they can only store enough of it for about eight twitches.


Fatigue may be associated with...

-depletion of glycogen
-a shift in K levels which decreases Ca release
-accumulation of H from lactic acid
-increased levels of inorganic phosphate

A motor unit consists of...

one neuron and the muscle fibers it controls

Which fibers generate more force?

fast-twitch fibers

A contraction that generates force and moves a load is known as __________, whereas one that generates force without movement is known as __________.

isotonic, isometric

In the body, the bones act as __________ whereas the joints form the __________, so that the muscles attached to the bones can create force when they contract.

levers, fulcrums

Skeletal muscles are attached to bones by ...


A muscle is referred to as a(n) __________ if the bones it connects move closer to each other when that muscle contracts.


An alternate term for a muscle cell is __________.


The structures in smooth muscle that are analogous to the Z disks of sarcomeres are __________.

dense bodies

One of the factors determining the speed and duration of a twitch in various types of fibers is the speed of the...

-removal of Ca ions from the cytosol
-hydrolysis of ATP

Within a single fiber, the tension developed during a twitch can vary because...

the amount of overlap of thick and thin filaments must be sufficient to allow crossbridge formation

Explain the events leading up to a skeletal muscle twitch, starting with the arrival of neurotransmitter in the neuromuscular junction.


This graph was generated by students in a physiology lab. The top trace shows contraction force, the bottom shows the electrical stimulus. On the graph, label a muscle twitch. What is happening to the muscle and why?

The clearest single twitch is the first few and last few peaks on the myogram. The muscle is being stimulated at an increasing rate, as evidenced by the decreasing time between subsequent stimulus pulses. This caused fusion of the twitches, producing partial then complete tetanus, as well as an increase in peak force produced. Though the stimulus is maintained, the peak force starts to fall as the muscle fatigues. The students then decreased the stimulus frequency, allowing recovery from fatigue, and the muscle was able to contract again.

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