Chapter 9 Part 1- Muscles, Muscle Fibers

a muscle fiber is a

skeletal muscle cell

bundles of protein in a muscle cell

myofibrils

The dark lines that can be seen in the middle of each I band and which mark the ends of a sarcomere are known as the

z line

the sarcoplasmic reticulum is homologous to the _______ ________ found in most cells

endoplasmic reticulum

bundles of muscle fibers attaching bone to muscle

ligaments

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

activation of cross-bridge cycling

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

z line

the web-like structure around a skeletal muscle fiber

sarcoplasmic reticulum

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

myofibrils

The axon terminals of a somatic motor neuron contain vesicles that hold the neurotransmitter

acetylcholine

the axons of motor neurons are (myelinated or unmyelinated)

myelinated

the axons of motor neurons are the (longest or shortest) in the body

longest

The specialized region of the sarcolemma of a muscle fiber at the neuromuscular junction is called the

motor end plate

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

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

During the shortening of the sarcomeres, there is no change in the lengths of either the thick or thin filaments. This is known as the _______-_________ mechanism of muscle contra tion

sliding filament

the force exerted on a muscle by an object is the

load

the force exerted on an object by the muscle

tension

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

It binds to troponin and causes the movement of tropomyosin.

What is the term describing the contraction and relaxation that occurs in a muscle fiber after it is stimulated by a single action potential?

twitch

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?

Attachment of the cross-bridge to the thin filament

Maximum isometric tetanic tension is produced at optimal length (L₀) of a sarcomere. Stretching a fiber beyond L₀ or decreasing it below L₀ decreases the tension generated, because of reduced ____________ access to thin filaments at short and long sarcomere lengths.

cross bridge

inhibits of skeletal muscle fibers by blocking cross-bridge binding sites on actin

tropomyosin

When Ca2+ binds to the protein _______ the binding sites are unblocked and the cross-bridge cycling occurs

troponin

What molecule can be used by muscle to recharge ADP into ATP during short intense bouts of exercise?

creatine phosphate

The increase in muscle tension from successive action potentials occurring during the phase of mechanical activity is known as

summation

During the first 5 to 10 minutes of moderate intensity exercise, the fuel used by skeletal muscle fibers to produce ATP by oxidative phosphorylation is mainly

glucose from muscle glycogen

• is the length where the most actin and myosin interactions can take place and the most force is generated

• is close to the normal resting length of muscle due to tendon insertion points

optimal muscle length in skeletal muscle fibers

Which is a function of tropomyosin in skeletal muscle contractile regulation?

blocks myosin from binding to actin

During bouts of extremely intense exercise, glycolysis produces most of the ATP for muscle contraction, with a corresponding increase in the production of

lactic acid

When a skeletal muscle experiences a reduction in its ability to produce tension during prolonged intense exercise, it is due to a phenomenon called muscle

fatigue

During moderate intensity exercise, most of the ATP used for muscle contraction is formed by

oxidative phosphorylation

If prolonged exercise intensity exceeds about 70% of the maximum rate of ATP breakdown, Blank______ contributes an increasingly significant fraction of the total ATP generated within skeletal muscle

glycolysis

rod like structures within muscle fibers that contain the contractile proteins actin and myosin

myofibrils

composed of repeating units called sarcomeres, which are responsible for muscle contraction

myofibrils

released from the sarcoplasmic reticulum, binds to troponin

calcium

a regulatory protein that undergoes a conformational change

troponin

a protein that blocks myosin-binding sites on actin; when troponin changes shape, it shifts ______ exposing the binding sites for myosin, allowing contraction to occur

tropomyosin

does generate tension, does not shorten muscle

isometric twitch

does shortenthe muscle

isotonic tension

oxidative fibers have

lots of mitochondria

have few mitochondria, but a higher concentration of glycolitic enzymes

glycolytic fibers