chapter 9 questions
what is the minimum voltage needed to generate active force in the skeletal muscle?
threshold voltage
Both actin and myosin are found in the
A band
the myosin filaments are located in the
A band
After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge attachment?
ATP binds to the myosin head the binding of ATP to the myosin head weakens the bond between myosin and actin, forcing the myosin head to detach. ATP also provides the energy for the next powerstroke.
During muscle contraction, myosin cross bridges attach to which active site?
Actin filaments
The cross bridge cycle begins when
Ca2+ from the sarcoplasmic reticulum binds to troponin
when does cross bridge cycling end?
Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin. The sarcoplasmic reticulum contains Ca2+ ATPase that actively transport Ca2+ into the SR. Without Ca2+, troponin returns to it's resting shape, and tropomyosin glides over and covers the myosin binding sites on actin.
contain abundant amounts of glycogen
Fast (oxidative or glycolytic), fatigable fibers
A neurotransmitter released at motor end plate by the axon terminals
acetylcholine
the_____contains ony the actin filaments.
I band
A relatively high percentage are found in successful marathon runners
Slow (oxidative), fatigue-resistant fibers
Red fibers, the smallest of the fiber types.
Slow (oxidative), fatigue-resistant fibers
abundant in muscles used to maintain posture
Slow (oxidative), fatigue-resistant fibers
depends on oxygen delivery and aerobic mechanisms
Slow (oxidative), fatigue-resistant fibers
When a sarcomete contracts and thin filaments move over thin filaments you would expect to see
The I bands to appear smaller
As the stimulus voltage increased in this activity, which of the following occurred?
The muscle force generated increased
Which of the following is proportional to the amount of tension produced by a skeletal muscle?
The number of motor units activated
Which of the following describes the relaxation phase?
The sarcomeres are increasing in length, and the force generated decreases.
The mechanism of contraction in smooth muscle is different from skeletal muscle in that
The site of calcium binding site differs
what is the role of tropomyosin in skeletal muscles?
Tropomyosin serves as a contraction inhibitor by blocking the myosin binding sites on the actin molecules
A sacromere is the distance between two
Z discs
Most skeletal muscles contain ________.
a mixture of fiber types
the cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge?
a myosin head bound to actin as soon as a myosin head forms a cross bridge with actin, the power stroke begins.
Although all the anatomical parts of muscle work together to give it it's characteristics, which of the following proteins listed below would be most associated with the characteristics of excitability?
acetylcholine receptors in the motor end plate
Breaks down ACh into its building blocks, rendering it ineffective.
acetylcholinesterase
Activates synaptic vesicles in axon terminals to fuse with plasma membrane of axon terminal
calcium ions
The final chemical messenger and "trigger" for muscle contraction. It binds to troponin
calcium ions
calcium ions couple excitation of a skeletal muscle fiber to contraction of the fiber. Where are calcium ions stored within the fiber?
calcium ions are stored in the sarcoplasmic reticulum sarcoplasmic reticulum is the specific name given to the smooth endoplasmic reticulum in muscle fibers. The sarcoplasmic reticulum is very elaborate in skeletal muscle fibers, allowing for significant storage of calcium ions.
What specific event triggers the uncovering of the myosin binding site on actin?
calcium ions bind to troponin and change it's shape the shape change caused by the binding of calcium to troponin shifts tropomyosin away from the myosin binding sites on actin.
Which of the following occurs during the latent period of muscle contraction?
calcium is releases from the sarcoplasmic reticulum
Sarcomeres are functional units of
cardiac and skeletal muscles only
The ability of muscle to shorten forcibly when adequately stimulated is known as and sets muscle apart from other tissue types.
contractibility
An anaerobic metabolic pathway that results in the production of two net ATPs per glucose plus two pyruvic acid molecules is
direct phosphorylation of ADP by creatine phosphate the rapid ATP-synthesizing pathway only lasts for about 15 seconds
which of the following surrounds an individual muscle cell?
endomysium
which of the following properties is most directly associated with changes to a muscle cell's membrane potential (the voltage across the plasma membrane)?
excitability
Exhaustion of glycogen storage within muscle fiber would have the biggest effect on
fast glycolytic fibers
Addition to more myoglobin to a muscle fiver would have the largest effect on
fast oxidative and slow oxidative fibers
skeletal muscles are composed of hundreds of thousands of individual cells called
fibers
It diffuses across the cell membrane resulting in depolarization.
sodium ions
Which of the following statements is not true regarding ATP production in muscles during periods of prolonged energy use, such as exercise?
in the absence of oxygen, creatine phosphate can drive aerobic respiration pathways for a few minutes
When muscle tension develops but the load is not moved
isometric contraction
When the muscle tension developed overcomes the load and muscle shortening occurs
isotonic contraction
during vigorous exercise, there may be insufficient oxygen available to completely break down pyruvic acid for energy. As a result, the pyruvic acid is converted to
lactic acid
No force is generated during which of the following?
latent period
Which of the following is the correct sequence of events for muscle contractions?
motor neuron action potential, neurotransmitter release, muscle cell action potential, release of calcium ions from SR, Self-defense power stroke, sliding of myofilaments
Each neuron shown in this figure innervates a group of muscle fibers. What is the term for a group of muscle fibers innervated by a single neuron?
motor unit
how a smooth muscle increase in muscle force is produced
multiple motor unit summation
determined by alternating motor units of a muscle organ even when the muscle is at rest
muscle tone
The thicker filaments are the
myosin filaments
If a muscle fiber were to suddenly and permanently stop producing ATP the fiber would no longer be able to actively transport calcium out of the cytoplasm (sarcoplasm) and the intracellular calcium concentration would rise. Which of the following would you expect to happen?
myosin would be able to bind to the exposed binding sites on thin filaments but it would not be able to detach
The motor neuron and muscle fiber intersect at what is called
neuromuscular junction
Where the axon of a motor neuron connects with the muscle fibers
neuromuscular junction
Hypothetically, if a muscle were stretched to the point where thick and thin filaments no longer overlapped
no muscle tension could be generated
A twitch is
one contractile response to a single action potential
The term motor unit refers to
one motor neuron and all of the skeletal muscle fibers it innervates
troponin, a major protein in thin filament, is globular protein with three polypeptide subunits. Which of the following is not a function of the troponin?
one subunit binds to potassium ions
When a muscle is unable to respond to stimuli temporarily, it is in which of the following periods?
refractory
Which of the following can trigger a muscle twitch?
release of acetylcholine or electrical stimulation
it diffused across the cell membrane resulting in depolarization
sodium ions
which of the following is NOT a normal function of muscle tissue?
secreting hormones
which type of muscle requires somatic (voluntary) nervous stimulation for activation?
skeletal in order to contract muscle fibers must be voluntarily stimulated by motor neurons of the somatic nervous system
which of the following are correctly paired?
skeletal muscle, voluntary control
Reduction in blood flow to a muscle fiver would gave the greatest effect on
slow oxidative fibers
Which muscle cells have the greatest ability to regenerate?
smooth
Oxygen starved tissues can release chemical signals into the blood that can change the diameter of nearby blood vessels delivering oxygen and nutrients to the tissues. In doing so the blood vessels will respond through vasodilation (widening of the vessel). Which muscle type is responsible for this vasodilation?
smooth muscle
myoglobin
stores oxygen in muscle cells
creatine phosphate functions in the muscle cell by
storing energy that will be transferred to ADP to resynthesize ATP
unlike skeletal muscle, smooth muscle may spontaneously contract when it is stretched. What feature of smooth muscle allows it to stretched without immediately resulting in a strong contraction?
stress-relaxation response Stretching of smooth muscle provokes contraction; however, the increased tension persists only briefly, and soon the muscle adapts to it's new length and relaxes, while still retaining the ability to contract on demand. The stress-relaxation response of smooth muscle allows a hollow organ to fill or expand slowly to accommodate greater volume without promoting strong contractions that would expel it's contents.
skeletal muscles are connected to bones by
tendons
continued sustained smooth contraction due to rapid stimulation
tetanus
A motor unit is defined as
the axon terminals of a single motor neuron and all of the muscle fibers that it stimulates
How does the myosin head obtain the energy required to activation?
the energy comes from the hydrolysis of ATP myosin is a large, complex protein with a binding site for actin. It also contains an ATPase. The energy released during the hydrolysis of ATP activated the myosin head.
What structure is the functional unit of contraction in a skeletal muscle fiber?
the sarcomere a sarcomere is a regular arrangement of thin and thick myofilaments that extends from one Z disc to the next. A myofibril consists of a series of sarcomeres.
Smooth muscle is characterized by all of the following except
there are more thick filaments than thin filaments
Although all the anatomical parts of muscle work together to give it it's characteristics, which if the following proteins listed below would be most associated with the characteristics of contractibility?
thick (myosin) filaments
Which type of muscle is found in the body wall of hollow organs?
unitary smooth muscle
which of the following is/are mechanism(s) to end neural transmission at the neuromuscular junction?
•ACH is broken down into acetic acid and choline by the enzyme acetylcholinesterase •ACH diffused away from the synaptic cleft
The conversion of an action potential (AP) generated by a motor neuron to contraction of skeletal muscle fiber is called excitation-contraction coupling. This activity will test your understanding of the sequence of events that occur during excutation-coupling.
•AP propagates along sarcolemma •AP travels down T tubules to triads •voltage-sensitive proteins open Ca2+ channels •sarcoplasmic reticulum releases Ca2+ •Ca2+ levels in sarcoplasm increase
identify the correct sequence of the following events
•Ca++ binds to troponin •troponin removes tropomyosin from G actin • myosin binds to actin • myosin generates a power stroke • the sarcomete shortens • ATP recharges the myosin head
The site where a motor neuron excites a skeletal muscle fiber is called the neuromuscular junction. This activity will test your understanding of the sequence of events that occur at the neuromuscular junction.
•Ca2+ enters the axon terminal •synaptic vesicles release ACH Ach binds to act receptions •ligand-gated cation channels open •Na+ enters cation channels open •membrane potential is less negative