Skeletal Muscle

Question 1

Give the anatomical arrangement of skeletal muscle

Answer 1

Muscle fibers - myofibrils - myofilaments (contractile element)

Question 2

___ lines delineate the sarcomere

Answer 2

Z

Question 3

__ bands represent the thin filaments that are anchored to Z lines and extend in each direction.

Answer 3

I

Question 4

Do I bands overlap with thick filaments?

Answer 4

no

Question 5

The ___ band includes the ___ zone, which is only myosin thick filaments with no overlapping thin filaments and some degree of overlap of thin and thick and thin filaments

Answer 5

A; H

Question 6

Thin filaments are polymers composed of two strands of F-actin wrapped around each other in a helical arrangement with ___ and ____

Answer 6

troponin; tropomyosin

Question 7

In regards to thin filaments, ____ is arranged in parallel with the actin strands

Answer 7

tropomyosin

Question 8

For each of the following Troponin subunits, give its function:
Troponin T
Troponin I
Troponin C

Answer 8

Troponin T: binds troponin to tropomyosin
Troponin I: inhibits the interaction between myosin and actin
Troponin C: binding site for Ca2+

Question 9

Thick filaments are composed of several hundred ___ molecules. It is made up of __ heavy chains and ___ light chain head units. The head units have ___ activity.

Answer 9

myosin; 2; 2; ATPase

Question 10

This protein connects the Z line to the M line of the sarcomere. It acts as a molecular spring and contributes to the passive elasticity of muscle, and contributes to force transmission at the Z line and resting tension at the I band

Answer 10

Titin

Question 11

This protein is a large molecule that forms a rod connecting the actin filaments to the transmembrane protein B-dystroglycan in the sarcolemma by smaller proteins in the cytoplasm known as syntrophins (forms scaffold that connects myofibrils to external environment)

Answer 11

Dystrophin

Question 12

Disruption in the structure of Dystrophin can lead to specific muscular pathologies such as ___ ____

Answer 12

muscular dystrophy

Question 13

T-tubules come in close contact with the SR in skeletal muscle, forming ____

Answer 13

triads

Question 14

The SR contains the Ca2+ binding protein, ____, which facilitates the storage of large quantities of Ca2+

Answer 14

calsequestrin

Question 15

Skeletal muscle fibers are innervated by ___ motor neurons. These are large, myelinated neurons with rapid conduction velocity.

Answer 15

alpha

Question 16

The resting membrane potential in skeletal muscle is approx ___ mV

Answer 16

-90

Question 17

The AP duration in skeletal muscle is only __-__ ms, while the duration of muscle contraction is about ___-___ ms

Answer 17

3-5; 20-100

Question 18

Voltage-gated Ca2+ channels called _____ receptors are present in the t tubules.

Answer 18

dihydropyridine (DHPR)

Question 19

Activation of the DHPR physically opens the ____ receptor in the terminal cisternae of the SR, allowing Ca2+ to leave

Answer 19

ryanodine

Question 20

The Ca2+ released from the SR into the cytosol is pumped back into the SR by what?

Answer 20

SERCA (ATPase)

Question 21

SERCA has a greater affinity for Ca2+ than troponin C and starts pumping Ca2+ back into the SR immediately after it is released into the cytosol. True or false?

Answer 21

true - very transient event

Question 22

The increase in cytosolic Ca2+ results in Ca2+ binding to troponin C which weakens the interaction between troponin ___ and ____.

Answer 22

I; actin

note: this causes conformational shift of both the troponin and tropomyosin that uncovers the actin binding site for myosin and leads to the formation of anti-myosin crossbridges

Question 23

The binding of actin and myosin results in the release of ___ and ___

Answer 23

ADP; Pi

Question 24

After ADP and Pi have been released, there is a conformational change in the myosin head unit that moves the ___ filament relative to the ___ filament and constitutes the “power stroke”

Answer 24

thin; thick

Question 25

The power stroke shortens the sarcomere by about ___ nm

Answer 25

10

Question 26

After the power stroke, ATP binds to the open site on myosin. What is the result?

Answer 26

detachment of the myosin head from the thin filament

Question 27

After the myosin head detaches from the thin filament, the ATP is hydrolyzed and Pi is released, causing "___" of the myosin head unit

Answer 27

cocking

Question 28

If there is no ATP available, the actin remains bound to the myosin leading to a state of "___" If the transport of Ca2+ back into the SR is inhibited, the muscle will remain in a state of "____"

Answer 28

rigor; contracture

Question 29

Ca2+ is pumped back into the SR by SERCA, and as cytosolic levels fall, Ca2+ detaches from troponin C leading to what?

Answer 29

cessation of the actin-myosin interaction

Question 30

The coordinated shortening of many sarcomeres results in force generation and movement. Muscle has elastic components that must be overcome to accomplish muscle shortening. These are in ___ and in ___ with the contractile elements

Answer 30

parallel; series

Question 31

Parallel elastic elements include?

Answer 31

sarcolemma, intracellular architectural components, extracellular CT

Question 32

Series elastic elements represent the ___ and regions within the ___

Answer 32

tendons; myosin

Question 33

____ contractions represent a single contractile event resulting in a brief (20-100 ms) contraction.

Answer 33

twitch

Question 34

In regards to twitch contractions, the velocity of shortening is inversely related to the initial load on the muscle. If the load exceeds the force generated during the contraction, what is the result?

Answer 34

no shortening, and the velocity will be zero (isometric contraction).

Question 35

In regards to twitch contractions, as the load ___, the velocity of shortening increases to a theoretical Vmax at zero initial load.

Answer 35

decreases

Question 36

____ contractions are characterized by contractions that result in sarcomere shortening (internal shortening), but do not result in external shortening (same length). In such cases, the load exceeds the ability to overcome the elastic elements and there is no external work

Answer 36

isometric

Question 37

_____ contractions are characterized by contractions that result in sarcomere shortening and external shortening. In such cases, the load is less than the tension that can be generated by the contractile elements resulting in external work.

Answer 37

Isotonic

Question 38

_____ contractions occur when the muscle contractile elements are contracting, but the muscle is being externally lengthened forcefully. These type of contractions usually result in muscle damage.

Answer 38

eccentric

Question 39

Contractile elements do not display ____ so as soon as another action potential fires, another contraction can be initiated. If the cytosolic Ca2+ is still elevated the resulting contractile tension will be greater because there is a greater intracellular Ca2+ level

Answer 39

refractoriness

Question 40

Describe incomplete tetany

Answer 40

if the stimulus frequency is increased, the developed tension will increase. As the stimulation frequency increases, the phasic nature of the twitch contraction begins to disappear and tension does not return to baseline

Question 41

Describe tetanic contraction

Answer 41

if the stimulation frequency increases sufficiently there will be less time for relaxation between stimulations and muscle force will be sustained, resulting in a complete or fused tetany.

Question 42

At compltete tetany, the muscle tension will be about ___ times greater than a single twitch contraction

Answer 42

4

Question 43

When muscle is stretched from an unstressed length, the resting or ____ tension increases as a function muscle length.

Answer 43

passive note: this is due to the progressive stretch on the elastic elements within the muscle

Question 44

If the muscle is contracted at each of the same muscle lengths, from the unstressed length, the ___ tension development will increase to some maximum

Answer 44

active

Question 45

The sarcomere length at which active tension is greatest represents the "optimal length" and is typically ___-___ um

Answer 45

2.0-2.2

Question 46

Define motor unit

Answer 46

single alpha motor neuron and all the muscle fibers it innervates

Question 47

The exception of a single motor neuron leading to an AP ("all or nothing") will cause every muscle fiber in that motor unit to contract simultaneously. True or false?

Answer 47

true

Question 48

Motor neurons also influence muscle fibers in a trophic manner. What does this mean?

Answer 48

the properties of all muscle fibers in the motor unit are similar

Question 49

``` The following describes what type of muscle fiber: diameter: small myosin ATPase: slow rate of Ca2+ sequestration: moderate mitochondria: abundant oxidative enzymes: high glycolytic enzymes: moderate myoglobin: abundant capillary density: high tension/motor unit: low control: fine ```

Answer 49

Type I

Question 50

``` The following describes what type of muscle fiber: diameter: moderate myosin ATPase: fast rate of Ca2+ sequestration: high mitochondria: abundant oxidative enzymes: moderate glycolytic enzymes: high myoglobin: moderate capillary density: high tension/motor unit: moderate control: moderate ```

Answer 50

Type IIA

Question 51

``` The following describes what type of muscle fiber: diameter: large myosin ATPase: fast rate of Ca2+ sequestration: high mitochondria: sparse oxidative enzymes: low glycolytic enzymes: high myoglobin: none capillary density: low tension/motor unit: high control: coarse ```

Answer 51

Type IIB

Question 52

Motor units are recruited in an orderly manner, from smallest to largest, as the need for tension generation increases. This is known as the ___ _____ and permits smooth, graded development of muscle tension

Answer 52

size principle

Question 53

Maximum tension development can be attained when all of the largest motor units are recruited. However, while these large motor units generate the greatest tension, they are not well-suited for what?

Answer 53

prolonged activity (fatigue very quickly)