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47 Cards in this Set

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  • Back

The T, or transverse tubules, are also associated w/the highly organized smooth endoplasmic reticulum called the______ in skeletal fibers

sarcoplasmic reticulum

a muscle is composed of numerous visible bundles called muscle


this is considered the smallest contractile unit of skeletal muscle. It extends from z-disk to z-disk.


what is a z-disk?

a filamentous network of protein forming a disklike structure for the attachment of actin myofilaments.

each______includes a z-disk and extends from each side of the z-disk to the ends of the myosin myofilaments.

Isotropic band or I band- (light)

In the center of each A band is a smaller band called the _______, where the _________ and _______ do not overlap and only _______ are present.

H-zone, actin, myosin myofilaments, myosin myofilaments

Three important properties of myosin heads

1. Bind to active sites on the actin molecules to form Cross-bridges

2. Heads are attached to the rod portion by a hinge region that can bend & straighten during contraction

3. The heads are ATPase enzymes, which breakdown adenosine triphosphate (ATP), releasing energy.

What is part of the energy used for?

to bend the hinge region of the myosin molecule during contraction (causes contraction).

The equivalent to a cytoplasm of a cell is called a _______ in muscles


These channels are gated membrane channels that open and close in response to a particular membrane potential.

Voltage-gated ion channels

the voltage-gated channels that play a major role in an action potential are

voltage-gated Na+, K+, and Ca2+ channels.

Do voltage-gated channels allow all ions to cross the plasma membrane?

No, they are specific to an ion. For example, the Na+ channel only allows Na+ to cross through the plasma membrane.

The resting membrane potential can be measured in units called______

millivolts (mv=1/1000 volt)

What are the potential differences across the plasma membranes of neurons and muscle fibers?

Between -70 and -90 mV.

Why is the potential difference reported as a negative #?

because the inner surface of the plasma membrane is negative compared with the outside.

The ________ of the action potential is a brief period during which further depolarization occurs & the inside of the cell becomes_______.

Depolarization phase, positively charged.

Each presynaptic terminal contains numerous mitochondria and many small, spherical sacs approx. 45um in diameter, called________

Synaptic vesicles

every vesicle contains acetycholine (ACh), what is it composed of?

It is an organic molecule composed of acetic acid and choline.

Acetycholine (ACh) is a _________


What is a neurotransmitter?

A substance released from a presynaptic membrane that diffuses across the synaptic cleft and alters the activity of the postsynaptic cell.

How can neurotransmitters stimulate or inhibit the production of an action potential in the postsynaptic membrane?

By binding to ligand-gated ion channels

Near the t-tubules the sarcoplasmic reticulum is enlarged to form

terminal cisternae

What is a triad?

A T tubule and 2 adjacent terminal cisternae

Is the concentration of Ca2+ higher or lower within the sarcoplasmic reticulum compared to the sarcoplasm of a resting muscle fiber?

It is higher, approximately 2000 times higher. Since the sarcoplasmic reticulum actively transports Ca2+ into its lumen.

Movement of the myosin molecule while the cross-bridge is attached is called the

Power stroke

Return of the myosin head to its original position after cross-bridge release is called the

recovery stroke

______cycles of power & recovery during each muscle contraction.


What happens when Ca2+ is released from the sarcoplasmic reticulum in response to an action potential?

The cycle of cross-bridge formation, movement, and release, which results in contraction, begins.

muscles performing delicate and precise movements have motor units with a ______

small number of muscle fibers - can be as little as 10

muscles performing more powerful but less precise contractions have motor units with____

many muscle fibers - can be several hundred

The _______ fibers there are in motor units of a muscle, the _______ a person has over that muscle.

fewer, greater control

what is a possible explanation for treppe (a phenomenon where a muscle fiber contracts w/greater force w/each subsequent stimulus)?

an increase in Ca2+ levels around the myofibrils. The Ca2+ released in response to the 1st stimulus is not taken up completely by the sarcoplasmic reticulum before the 2nd stimulus causes the release of additional Ca2+, even though the muscle relaxes completely between the muscle twitches.

what is tetanus?

a period of sustained contraction of muscle fibers due to the increase of action potential and contraction frequency.

Incomplete tetanus?

muscle fibers partially relax between the contractions

complete tetanus?

muscle fibers produce action potentials so rapidly that no relaxation occurs between them

as the frequency of contractions increases, the increased tension produced is called

multiple- wave summation

what are eccentric contractions?

isotonic contractions in which tension is maintained in a muscle, but the opposing resistance is great enough to cause the muscle to increase in length.

As a result of extreme muscle fatigue, muscles occasionally become incapable of either contracting or relaxing- a condition called

physiological contracture

why is Physiological contracture caused?

Due to lack of ATP in muscle fibers. When ATP levels are low, active transport of Ca2+ into the sarcoplasmic reticulum slows, Ca2+ accumulate in the sarcoplasm, & ATP is unavailable to bind to the myosin molecules that have formed cross-bridges w/the actin myofilaments. So, the previously formed cross-bridges cannot release, causing Physiological Contracture.

Slow-twitch oxidative (SO) muscle fibers (type I fibers)

contract more slowly, have a better-developed blood supply, have more mitochondria, and are more fatigue-resistant than fast-twitch muscle fibers.

The enzymes on the myosin heads responsible for the breakdown of ATP are called_____, which are broken down slowly by slow-twitch fibers.

Myosin ATPase

what is the primary source for ATP synthesis in slow-twitch muscles?

Aerobic respiration-which is enhanced by plentiful blood supply and the presence of numerous mitochondria

Fast-twitch muscle fibers (type II fibers)....

respond rapidly to nervous stimulation, &

their myosin heads have a fast form of myosin ATPase, which allows the rapid breakdown of ATP. This allows the cross-bridges to release & form more rapidly.

Muscles containing a high percentage of fast-twitch fibers have a.....

less-well-developed blood supply than muscles containing a high percentage of slow-twitch muscle fibers. Fast-twitch fibers have very little myoglobin & fewer & smaller mitochondria.

Fast-twitch muscle fibers have large deposits of______ and are well adapted to perform______.

glycogen, anaerobic respiration.

what are the 2 forms of fast-twitch muscle fibers?

Type IIa, or fast-twitch oxidative glycolytic fibers (FOG), which rely on both anaerobic and aerobic ATP production.

Type IIb, or fast-twitch glycolytic fibers (FG), which almost exclusively rely on anaerobic glycolysis for ATP production.

what are the largest diameter fibers in men and women?

Women- type I alone, or in conjunction with type IIa.

Men- type IIa