9.1 - 9.3

Question 1

The 3 basic types of muscle are ___ muscle, ___ muscle, and ___ muscle.

Answer 1

skeletal; smooth; cardiac

Question 2

Recognize a light micrograph of a skeletal (striated) muscle

Answer 2

x

Question 3

A single skeletal muscle cell is also called a muscle ___.

Answer 3

fiber

Question 4

What term describes bundles of collagen fibers that attach bone to muscle?

Answer 4

tendons

Question 5

Within each skeletal muscle fiber densely packed, striated subunits known as ___ extend in parallel rows from one end of the cell to the other leaving little room between for other organelles. The striations in these elongated structures are caused by the regular arrangement of thick and thin filaments into sarcomeres.

Answer 5

myofibrils

Question 6

T/F: On the basis of structure, contractile properties, and control mechanisms, two types of muscle tissue can be identified: skeletal muscle and cardiac muscle.

Answer 6

F (there’s also smooth)

Question 7

One end of each thin filament overlaps a portion of the thick filaments, whereas the other end is anchored to a network of interconnecting proteins known as the ___ ___.

Answer 7

Z line

Question 8

The most striking feature seen when viewing skeletal muscle through a microscope is a distinct series of alternating light and dark. Because of these bands, skeletal muscle is also referred to as ___ muscle.

Answer 8

striated

Question 9

In a muscle fiber, the ___ forms a series of sleeve-like segments around each myofibril.

Answer 9

sarcoplasmic reticulum

Question 10

Which best describes the term “muscle fiber?”

Answer 10

a skeletal muscle cell

Question 11

With reference to muscle physiology, which best defines the term “contraction?”

Answer 11

activation of cross-bridge cycling

Question 12

What are myofibrils?

Answer 12

bundles of proteins in a muscle cell

Question 13

The ___ define the limit of the sarcomere.

Answer 13

Z lines

Question 14

The neurons whose axons innervate skeletal muscle fibers are known as ___ neurons.

Answer 14

alpha motor

Question 15

Skeletal muscle fiber image- The web-like structure (in blue) is the ___ ___.

Answer 15

sarcoplasmic reticulum or SR

Question 16

What is the function of troponin in skeletal muscle cell contractile regulation?

Answer 16

To hold tropomyosin in a position that blocks the cross-bridge binding sites on actin when the Ca2+ concentration is low

Question 17

Recognize a single muscle fiber in the cartoon image of a skeletal muscle cell.

Answer 17

letter C on image

Question 18

During cross-bridge cycling when Ca2+ remains present in the cytosol, which step of the cycle happens immediately after the energizing of the cross-bridge?

Answer 18

Attachment of the cross-bridge to the thin filament

Question 19

In muscle physiology, the term contraction refers to activation of the force-generating sites within muscle fibers: these are called ___ ___.

Answer 19

cross bridges

Question 20

In skeletal muscle, thin and thick filaments are arranged in cylindrical bundles called ___.

Answer 20

myofibrils

Question 21

The force generated on an object when a skeletal muscle is stimulated to contract is called muscle ___.

Answer 21

tension

Question 22

Which of the following is the name for neurons that originate with cell bodies in the brainstem or spinal cord and whose axons innervate skeletal muscle fibers?

Answer 22

motor neurons

Question 23

A contraction known as a muscle ___ occurs when a muscle fiber is stimulated with a single action potential.

Answer 23

twitch

Question 24

In skeletal muscle, the protein ___ regulates the position of tropomyosin on actin, thereby regulating cross-bridging binding.

Answer 24

troponin

Question 25

Place in order the four steps of the cross-bridge cycle beginning in a resting cell, immediately after tropomyosin shifts to reveal the binding sites. This earliest step would go on top.

Answer 25

• attachment of the cross-bridge to a thin filament
• movement of the cross-bridge, producing tension in the thin filament and dissociation of ADP and Pi from the cross-bridge
• detachment of the cross-bridging from the thin filament
• re-energizing the cross-bridge by hydrolysis of ATP

Question 26

The velocity of skeletal muscle fiber shortening is ___ when there is no load and is ___ when the load is equal to the maximal isometric tension.

Answer 26

maximal; zero

Question 27

An external force on a muscle is known as the ___.

Answer 27

load

Question 28

The mechanical response of a muscle fiber to a single action potential is known as a(n) ___.

Answer 28

twitch

Question 29

Which of the following best describes the mechanism of twitch summation in a single skeletal muscle fiber?

Answer 29

Successive activation occurs before the fiber has relaxed from a previous twitch, so the number of bound cross-bridges increases.

Question 30

Which explains the role of Ca2+ in the regulation of skeletal muscle contraction?

Answer 30

It binds to troponin and causes the movement of tropomyosin.

Question 31

As the load on a muscle fiber increases, the velocity of shortening during a twitch contraction ___.

Answer 31

decreases

Question 32

The length at which skeletal muscle fibers develop the greatest isometric active tension is termed the ___ ___.

Answer 32

optimal length

Question 33

The force exerted on a muscle by an object is the ___, whereas the force exerted on an object by a contracting muscle is known as muscle ___.

Answer 33

load (resistance); tension (effort)

Question 34

When a skeletal muscle is at rest, the majority of the active sites for myosin binding on the actin molecule are covered by the protein ___.

Answer 34

tropomyosin

Question 35

The optimal length in skeletal muscle fibers is…

Answer 35

• the length where the most actin and myosin interactions can take place and the most force is generated
• close to the normal resting length of muscle due to tendon insertion points

Question 36

The protein ___ inhibits contraction of skeletal muscle fibers by blocking cross-bridge binding sites on actin. When Ca2+ binds to the protein ___, the binding sites are unblocked and cross-bridge cycling occurs.

Answer 36

tropomyosin; troponin