Question 1

Heterogeneity of muscle speed in different muscle fibers depends in part on the

Accepted Answer

The speed at which a muscle fiber contracts is influenced by the type of myosin isoform it expresses. Different myosin isoforms can cause the muscles to contract at different speeds, contributing to the heterogeneity of muscle speed among different muscle fibers.

Question 2

The velocity of muscle contraction at maximum recruitment depends on

Accepted Answer

A

Question 3

Myofibrils are

Accepted Answer

Myofibrils are indeed bundles of myofilaments within the muscle fiber. These myofilaments, primarily actin and myosin, are the contractile elements that allow muscles to contract and generate force.

Question 4

The thick filament is 1.6 :m long and the thin filament is 1.0 :m. At a sarcomere length of 2.2 :m, what fraction of the part of the thick filament containing m yosin heads is covered by a thin filament?

Accepted Answer

At a sarcomere length of 2.2 µm, the entire length of the thick filament (1.6 µm) is covered by thin filaments because the thin filaments (1.0 µm each) extend from both ends of the sarcomere towards the center, overlapping the thick filament entirely.

Question 5

The A band contains all of the following EXCEPT

Accepted Answer

The A band in a sarcomere contains myosin and actin filaments, as well as titin. Actinin is not found in the A band; it is associated with the Z line.

Question 6

The plateau at the top of the length -tension curve is due to

Accepted Answer

The plateau of the length-tension curve is due to the "bare zone" in the middle of the thick filament that lacks myosin heads, which limits the number of cross-bridges that can form, thus limiting tension.

Question 7

The thick filament is 1.6 :m long and the thin filament is 1.0 :m. At a sarcomere length of 2.2 :m, how much of the thin filament is covered by the thick filament?

Accepted Answer

The answer of The thick filament is 1.6 :m long...

Question 8

Isometric active force developed by skeletal muscle at long lengths (greater than the rest length)

Accepted Answer

The isometric active force developed by skeletal muscle at lengths greater than the rest length is influenced by several factors: it is indeed directly proportional to the overlap of thin and thick filaments, as this overlap determines the number of potential cross-bridges that can form. The force also depends on the number of cross-bridges that can be formed, which is a function of the filament overlap. While the relationship between muscle length and force generation is not strictly linear across all lengths, within certain ranges, there can be a roughly linear relationship. Finally, these phenomena are key pieces of evidence supporting the sliding filament hypothesis, which posits that muscle contraction occurs as a result of thin and thick filaments sliding past each other, rather than either filament type changing length.

Question 9

During a concentric contraction of muscle

Accepted Answer

During a concentric contraction, the I band and H zone shorten as the actin and myosin filaments slide past each other, while the A band remains constant in length.

Question 10

“Striations” are

Accepted Answer

Striations are the stripes that run across the muscle fiber at right angles to its long axis, typically seen in skeletal and cardiac muscle due to the arrangement of actin and myosin filaments.

Question 11

The thick filament is 1.6 :m long and the thin filam ent is 1.0 :m. At a sarcomere length of 2.2 :m, how wide is the H band?

Accepted Answer

The answer of The thick filament is 1.6 :m long...

Question 12

The I band does not contain

Accepted Answer

The I band in muscle fibers contains thin filaments, which are primarily made up of actin, tropomyosin, and troponin (including TnT and TnC), but does not contain myosin, which is a component of the thick filaments found in the A band.

Question 13

ATP hydrolysis associated with force development is carried out by

Accepted Answer

Myosin is the motor protein that uses ATP hydrolysis to move along actin filaments, generating force and causing muscle contraction.

Question 14

The “turnover number” refers to the

Accepted Answer

The "turnover number" refers to the number of substrate molecules that an enzyme can convert into product per unit time, essentially indicating the number of completed reactions per enzyme molecule per second.

Question 15

The thin filament contains all of the following proteins EXCEPT

Accepted Answer

Calsequestrin is not a component of the thin filament; it is found in the sarcoplasmic reticulum of muscle cells, where it binds calcium ions.

Question 16

The protein of the thick filam ent that extends to the Z line is

Accepted Answer

Titin is the protein that extends from the Z line to the M line in the center of the sarcomere, providing structural support and elasticity to the muscle fiber. It is a key component of the thick filament in muscle cells.

Question 17

The protein mainly responsible for anchoring the thin filam ents at the Z disc is

Accepted Answer

Actinin is the protein primarily responsible for anchoring thin filaments to the Z disc in muscle cells, providing structural support and organization necessary for muscle contraction.

Question 18

The sarcomere is defined as

Accepted Answer

The sarcomere, the basic contractile unit of muscle fiber, is defined as the segment between two neighboring Z discs. This encompasses the entire unit of myofibril necessary for muscle contraction, including both the A and I bands as well as the H zone and M line within its boundaries.

Question 19

Force developed by muscle

Accepted Answer

The force developed by muscle primarily derives from the interaction between the thick and thin filaments within the muscle fibers. This interaction is facilitated by the sliding filament theory, where the myosin heads (thick filaments) attach to and pull on the actin filaments (thin filaments), leading to muscle contraction.

Question 20

Proteins involved in the lateral transmisson of muscle force to the outside of the m uscle fiber include

Accepted Answer

All of the options listed (Dystrophin, Surface integrins, Syntrophin, Dystroglycan) are involved in the lateral transmission of muscle force to the outside of the muscle fiber, playing roles in the connection of the cytoskeleton of the muscle cells to the extracellular matrix, thus facilitating force transmission and structural integrity.

Quiz 21: Contractile Mechanisms in Skeletal Muscle