Chapter 9 Midterm Questions

Front 1

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

Back 1

sarcoplasmic reticulum

Front 2

a muscle is composed of numerous visible bundles called muscle

Back 2

Fasciculi

Front 3

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

Back 3

sarcomere

Front 4

what is a z-disk?

Back 4

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

Front 5

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

Back 5

Isotropic band or I band- (light)

Front 6

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

Back 6

H-zone, actin, myosin myofilaments, myosin myofilaments

Front 7

Three important properties of myosin heads

Back 7

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.

Front 8

What is part of the energy used for?

Back 8

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

Front 9

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

Back 9

sarcoplasm

Front 10

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

Back 10

Voltage-gated ion channels

Front 11

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

Back 11

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

Front 12

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

Back 12

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

Front 13

The resting membrane potential can be measured in units called______

Back 13

millivolts (mv=1/1000 volt)

Front 14

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

Back 14

Between -70 and -90 mV.

Front 15

Why is the potential difference reported as a negative #?

Back 15

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

Front 16

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

Back 16

Depolarization phase, positively charged.

Front 17

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

Back 17

Synaptic vesicles

Front 18

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

Back 18

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

Front 19

Acetycholine (ACh) is a _________

Back 19

neurotransmitter

Front 20

What is a neurotransmitter?

Back 20

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

Front 21

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

Back 21

By binding to ligand-gated ion channels

Front 22

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

Back 22

terminal cisternae

Front 23

What is a triad?

Back 23

A T tubule and 2 adjacent terminal cisternae

Front 24

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

Back 24

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

Front 25

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

Back 25

Power stroke

Front 26

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

Back 26

recovery stroke

Front 27

______cycles of power & recovery during each muscle contraction.

Back 27

Many

Front 28

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

Back 28

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

Front 29

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

Back 29

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

Front 30

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

Back 30

many muscle fibers - can be several hundred

Front 31

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

Back 31

fewer, greater control

Front 32

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

Back 32

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.

Front 33

what is tetanus?

Back 33

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

Front 34

Incomplete tetanus?

Back 34

muscle fibers partially relax between the contractions

Front 35

complete tetanus?

Back 35

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

Front 36

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

Back 36

multiple- wave summation

Front 37

what are eccentric contractions?

Back 37

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.

Front 38

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

Back 38

physiological contracture

Front 39

why is Physiological contracture caused?

Back 39

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.

Front 40

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

Back 40

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

Front 41

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

Back 41

Myosin ATPase

Front 42

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

Back 42

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

Front 43

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

Back 43

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.

Front 44

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

Back 44

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.

Front 45

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

Back 45

glycogen, anaerobic respiration.

Front 46

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

Back 46

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.

Front 47

what are the largest diameter fibers in men and women?

Back 47

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

Men- type IIa