Worksheetsphysiology 1: Chương 7: sinh lý co cơ
Total questions: 109
Worksheet time: 2hrs 49mins
Which best describes a "myofibril"?
It is a single skeletal muscle cell
It is a cylindrical cellular organelle composed of myofilaments
It is a hollow membranous structure that stores calcium
It is composed of a single type of protein and forms cross-bridges
It is a fibrous junction between a muscle cell and a tendon
What protein is the principal component of skeletal muscle thick filaments?
Actin
Myosin
Troponin
Calmodulin
Tropomyosin
During concentric isotonic contraction of a skeletal muscle fiber, which of these occurs?
Sarcomeres lengthen
A bands shorten
I bands shorten
A bands lengthen
Thin filaments shorten
Which of the following statements regarding contraction of a skeletal muscle fiber is TRUE?
Thick filaments shorten when muscle cells contract
Some contractions occur without cross-bridge activation
Contracting muscle fibers do not always shorten
Contraction does not always require the occurrence of an action potential
Contraction only occurs following summation of action potentials from many motor neurons
In skeletal muscle cells, calcium initiates contraction by binding to
Tropomyosin
Actin
Troponin
Myosin
The thick filament
Binding of ________ to myosin permits cross-bridge ________ between actin and myosin in skeletal muscle cells.
ATP; attachment
ATP; detachment
calcium; attachment
calcium; detachment
actin; detachment
Which occurs FIRST as a result of ATP binding to myosin?
Cross-bridge heads are cocked into an "energized" state
Actin dissociates from myosin
Ca2+ is released from the sarcoplasmic reticulum
Actin binds to myosin
Cross-bridges rotate, sliding past the thin filament
What would be the result if the administration of a drug sequesters all the ATP in a cell?
All cross-bridges will remain tightly bound to actin
Calcium will remain in the cytosol, continuously stimulating cross-bridge cycling
Repeated, high-frequency action potentials will be fired at a skeletal muscle fiber causing sustained contraction
Calcium-activated proteases degrade all proteins in skeletal muscle fibers, making muscles limp
A build-up of K+ in T-tubules will cause constant, tetanic contractions of skeletal muscles
Rigor mortis is caused by:
Buildup of lactic acid
Lack of Ca2+
Depletion of glycogen
Lack of ATP
Deficient acetylcholine receptors
You have designed a drug that is supposed to bind to the myosin binding sites on actin. You inject it into a relaxed muscle, but find that none of the drug bound. Which of the following explains why?
There are no myosin binding sites on actin
Troponin molecules are covering myosin binding sites on actin
The myosin binding sites are covered by ATP
The myosin binding sites on actin are covered by tropomyosin
None of the choices are correct
In a laboratory experiment you have treated a muscle cell with a calcium channel blocker. The membrane still depolarizes, but the concentration of calcium never increases in the cytosol. Which of the following describes what will happen next?
Only one cross-bridge cycle will occur but no second cycle
Binding of myosin to actin will take place
Tropomyosin will continue to cover the myosin binding sites on actin and no cross-bridges will form
A single twitch in skeletal muscle but no sustained contraction
Contraction will occur, but the muscle will be stuck in the contracted state and unable to relax
What is the definition of a "motor unit"?
A single motor neuron plus all the muscle fibers it innervates
A single muscle fiber plus all of the motor neurons that innervate it
All of the motor neurons supplying a single muscle
A pair of antagonistic muscles
All of the muscles that affect the movement of any given joint
With an implanted electrode you are able to cause an individual motor neuron that connects to the bicep muscle to fire an action potential. Which of the following is the most likely result?
The entire bicep muscle contracts
A single muscle cell within the bicep muscle contracts
Between 10–1,000 muscle cells within the bicep muscle contract
It is impossible to predict based on this information alone
What is the function of the transverse tubules in a skeletal muscle fiber?
They store the calcium ions that are the main source of activation for the cross-bridge cycle
They form the Z lines that mark the end of each sarcomere
They allow action potentials to propagate deep into the center of skeletal muscle cells
They manufacture and store ATP
They run in parallel with the myofibrils, and have abundant Ca2+-ATPase proteins for pumping Ca2+ back into the sarcoplasmic reticulum
A build-up of K+ in the T-tubules can occur during periods of frequent muscle cell potentials. What will be the result?
Inhibition of neurotransmitter release from the motor neuron
Inhibition of muscle cell depolarization and contraction
Inhibition of relaxation, muscle stays in contracted state
None of the answer choices are correct
Based on its molecular properties, nicotine will have what effect on skeletal muscle contraction?
Increases in contraction or contraction is more likely to happen
Decreases in contraction or contraction is less likely to happen
Effects on the motor neuron, but not on the muscle tissue itself
Nicotine has no effect on muscle cells
As a muscle gets stronger the diameter of its individual muscle cells becomes larger. Which of the following structures ensures that the membrane potential change is translated into the depth of the cell?
Z lines
Sarcoplasmic reticulum
H zone
Transverse tubules
Pores in the plasma membrane
If a muscle cell expressed muscarinic ACh channels, which are only permeable to Na+ instead of nicotinic ACh channels, which are permeable to both Na+ and K+, which portion of a muscle cell would be inhibited?
Neurotransmitter release from the motor neuron
Muscle cell depolarization
Cross-bridge cycling
Relaxation
None of the answer choices are correct
A scientist labels ACh with fluorescent dye to be able to visualize under the microscope where ACh travels and binds. She takes an image of the motor end plate and see that ACh is
Bound to muscarinic receptors at the end plate
Inside the muscle cell sarcoplasm
Bound to acetylcholinesterase in the end plate membrane
Bound to receptors on the sarcoplasmic reticulum
Bound to Ca2+ ions
The chemical curare is a nicotinic receptor antagonist. How will curare affect skeletal muscle function?
It activates an autoimmune disease that destroys myelin
It will cause persistent twitches with short periods of rest in between
It will cause spastic paralysis (sustained, unwanted muscle contraction)
It will cause flaccid paralysis (no muscle contraction possible)
Muscle function is fine, but it will cause a loss of voluntary control
Tetanus toxin inhibits acetylcholinesterase activity. What will a person suffering from tetanus toxin poisoning look like?
All muscles of the body might exhibit frequent small twitches
All muscles of the body might present a tense, fully contracted state
All muscles of the body might present a limp, relaxed state known as flaccid paralysis
All muscles of the body will be completely normal in function
Myasthenia gravis is an autoimmune disease in which the immune system gradually destroys the receptors for acetylcholine at the neuromuscular junction. Which of the following drugs might initially be useful in treating the symptoms of this disease?
A drug that inhibits acetylcholinesterase
A drug that inhibits release of acetylcholine
Curare
Atropine (a muscarinic acetylcholine receptor antagonist)
A nicotinic acetylcholine receptor antagonist
Which of these occurs during an isometric contraction of a skeletal muscle?
The I bands shorten and the A bands stay the same length
The thick and thin filaments slide past each other
Sarcomere length does not change significantly
The A bands shorten and the I bands stay the same length
Cross-bridges lock onto actin, similar to what occurs in rigor mortis
During an isometric twitch in a skeletal muscle:
Tension generated by the muscle always exceeds the load on the muscle
Tetanus occurs
Sarcomeres do not significantly shorten
The whole muscle shortens
H zones shorten
Which of the following statements regarding skeletal muscle contraction is true?
During a lengthening contraction, the tension exerted by the muscle exceeds the load on the muscle
In every isotonic muscle contraction, the length of the muscle remains constant
During every muscle contraction, muscle fibers change length
During every muscle contraction, tension is developed in the muscle
Cross-bridges cycle faster during isometric contractions than during isotonic contractions
What is the best description of a tetanic contraction in a skeletal muscle cell?
A single action potential in the motor neuron causes a sustained contraction
Multiple action potentials in the motor neuron cause a sustained contraction
The action potential in the muscle cell is prolonged to last as long as the contraction
Repeated action potentials from the motor neuron summate into a sustained depolarization of the motor end plate, causing a sustained contraction
A very large amplitude action potential in the motor neuron causes a very strong contraction in the skeletal muscle cell
How is the length of a skeletal muscle cell related to the force it can generate?
The tension in a skeletal muscle cell is greatest when contractions occur at either very short or very long lengths
Skeletal muscle cells generate the same amount of force, regardless of their length
The shorter a skeletal muscle cell is when it begins to contract, the stronger the force generation will be
The longer a skeletal muscle cell is when it begins to contract, the stronger the force generation will be
Skeletal muscle cells generate the most force when the contraction occurs at an intermediate length
The optimal length (Lo) of a skeletal muscle cell is
The length at which the muscle can generate its maximum tetanic tension
The shortest length the muscle can achieve while attached to bone, because the amount of overlap between thick and thin filaments is maximal then
Generally the length attained when the joint it crosses is fully extended
The only length at which any tension can be generated by the muscle cell
The length at which thin filaments from opposite sides of a sarcomere overlap
In the first few seconds of skeletal muscle contraction, what is the main mechanism by which ATP is replenished?
Energy and phosphate are transferred from creatine phosphate to ADP
Oxidative phosphorylation rapidly generates ATP from glucose
Glycolysis produces ATP from glycogen
Oxidation of fatty acids into ATP occurs in the mitochondria
Myoglobin catalysis produces ATP
When a muscle has been repeatedly contracting at a moderate intensity for an extended period of time (more than a few minutes), what is the primary source of ATP?
Transfer of energy and phosphate from creatine phosphate to ADP
Glycolysis
Oxidative phosphorylation
Breakdown of myosin
Uptake of ATP from the blood plasma
Which of the following statements regarding myosin in skeletal muscle is TRUE?
Myosin cross-bridge heads contain two binding sites, one for actin and one for tropomyosin
Myosin is an ATPase
The rate of ATP hydrolysis by myosin is the same in all types of skeletal muscle
All of the myosin cross-bridge heads in a thick filament are oriented and rotate in the same direction
Troponin covers the binding site on myosin molecules until Ca2+ binds to troponin to remove it from its blocking position
Compared to type 1 (slow oxidative) skeletal muscle fibers, how are type 2X (fast-glycolytic) skeletal muscle fibers different?
Type 2X fibers have more abundant mitochondria
Type 2X fibers fatigue more readily
Type 2X fibers have more abundant myoglobin
Type 2X fibers are smaller in diameter
Type 2X motor units contain fewer fibers per alpha motor neuron
Unlike humans, cows eat all day. They spend hours and hours chewing with very little rest from the task in a 24-hour period. The food they eat (grass) is difficult to break down, requiring a lot of chewing. Understanding the endurance required for these chewing muscles, what fiber type would you expect to be predominant in their chewing muscles?
Type 1
Type 2A
Type 2X
Type 3
There is not enough information to predict a dominant muscle fiber type
The muscles in your fingers have a predominance of fast-glycolytic fibers, whereas the muscles of your feet have a predominance of slow-oxidative fibers. Which of the following statements accurately describes their differences?
The muscle fibers of the feet have a greater abundance of glycogen than do the muscle fibers of the hands
Muscle fibers of the feet have a greater abundance of myoglobin than do muscle fibers of the hands
Muscle fibers of the hands can generate greater tension than muscle fibers of the feet
Muscle fibers in both locations are innervated by alpha motor neurons of the same diameter
More oxidative phosphorylation occurs in the hands than the feet
Sarah is a girl with dreams of becoming an Olympic marathon runner. She just learned that she has a rare genetic mutation and does not produce functional creatine phosphate. What portion of Sarah's marathon experience will be effected?
Just the first few seconds of exercise
All muscle contractions after Sarah reaches her maximum heart rate (about 10 minutes into her run)
All muscle contractions after Sarah reaches fatigue (about an hour into her run)
Every moment of Sarah's runs
No effects on her running
Which of the following is NOT a determinant of whole-muscle tension?
The number of muscle fibers contracting
The tension produced by each contracting fiber
The numbers of motor units recruited
The frequency of motor neuron stimulation
The proportion of the muscle fibers within each motor unit that are contracting at any given time
Which of the following statements regarding skeletal muscle is TRUE?
Skeletal muscle fibers have pacemaker activity
Skeletal muscle fibers are joined together by gap junctions
A given skeletal muscle fiber will contract when excitatory nervous stimuli sufficiently exceed inhibitory nervous stimuli at the motor end plate
A given skeletal muscle fiber will contract if excitatory synaptic inputs sufficiently exceed inhibitory synaptic inputs on the motor neuron that innervates that fiber and the motor neuron fires an action potential
Skeletal muscle contraction is inhibited by inhibitory motor neurons that synapse onto skeletal muscle fibers
Which of these would increase the tension generated in a skeletal muscle?
Increasing the frequency of firing in alpha motor neurons innervating the muscle
Stretching the muscle to very long lengths
Resting the muscle for several weeks
Switching off fast-glycolytic motor units and activating an equal number of slow-oxidative motor units
Increasing the amplitude of action potentials in the alpha motor neurons that innervate the muscle
Which of the following statements regarding whole-muscle contraction is TRUE?
The order of recruitment of motor units in a muscle is such that the last units recruited are those that fatigue most readily
The order of recruitment of motor units in a muscle is such that the first units recruited generate the most tension
Motor units whose motor neurons have large-diameter cell bodies are recruited first, while motor units with smaller-diameter motor neurons are only activated as the level of activation in the spinal cord increases
The order of motor unit recruitment is independent of the size of the alpha motor neuron that innervates them
Recruitment of one fast-glycolytic motor unit provides a smaller increment in whole-muscle tension than recruitment of one slow-oxidative motor unit
Sarah is a sprinter who specializes in quick and powerful bursts of speed followed by periods of rest. Priya is a marathon runner who specializes in long, steady runs. Compared to Priya, Sarah is likely to have
Leg muscles with a larger diameter
Leg muscles with a smaller diameter
Hypertrophy of type I muscle fibers
A higher density of capillaries in her leg muscles
Lower concentrations of glycolytic enzymes in her leg muscles
Sarah is a sprinter who specializes in quick and powerful bursts of speed followed by periods of rest. Priya is a marathon runner who specializes in long, steady runs. Compared to Sarah's muscles, how are Priya's most likely to differ?
Priya muscles will have more glycogen stored in her type 2X muscle fibers
Priya's muscles will have more mitochondria in her type 1 and 2A muscle fibers
Priya's muscles will have less myoglobin in her type 1 muscle fibers
Priya's type 2X fibers will be larger in diameter
Priya will have a greater proportion of type 2 muscle fibers and a lower proportion of type 1 fibers than Sarah
If a biopsy of the quadriceps muscles (muscles on the front of the thigh) were taken from gold medal-winning speed skaters in the four following events, which would most likely have the SMALLEST percentage of type 1 muscle fibers?
10,000 meters
5,000 meters
1,000 meters
500 meters
Which of the following statements is FALSE?
Synaptic input onto skeletal muscle cells is always excitatory, whereas inputs to smooth muscle cells may be either excitatory or inhibitory
A single smooth muscle cell may be innervated by both a sympathetic neuron and a parasympathetic neuron
Contractile activity of smooth muscle cells does not normally require Ca2+
In the absence of any neural input, skeletal muscle cannot generate tension
Ca2+ that activates contraction of smooth muscles can come from either the ECF or from the sarcoplasmic reticulum
Which of these is a major difference between smooth muscle and skeletal muscle?
Myosin is the main regulatory protein in smooth muscle
Myosin is the main regulatory protein in skeletal muscle
Skeletal muscle usually exhibits spontaneous activity, while smooth muscle cannot contract spontaneously
Only skeletal muscle requires increased calcium ion concentration in the cytosol for contraction
Only skeletal muscle has both actin and myosin
Which is a TRUE statement about smooth muscle?
Smooth muscle is striated
Smooth muscle does not have thick and thin filaments
Smooth muscle does not use troponin-tropomyosin to regulate cross-bridge activity
Changes in cytosolic calcium do not regulate cross-bridge activity in smooth muscle
The myosin in smooth muscle requires phosphorylation before it can bind to ATP
Which is a TRUE statement about excitation-contraction coupling?
In skeletal muscle cells, it requires the influx of extracellular calcium ion
In smooth muscle cells, it must be preceded by an action potential in the cell membrane
In all kinds of muscle it requires the entry of calcium from the extracellular fluid
Calcium-induced calcium release plays a role in cardiac muscle cells, as well as in some smooth muscle cells
In skeletal muscle cells, excitation-contraction coupling begins when an action potential propagates along the sarcoplasmic reticulum membrane
Which of the following statements regarding contraction in skeletal and smooth muscle is TRUE?
In skeletal muscle, calcium initiates contraction by binding to troponin, while in smooth muscle calcium initiates contraction by binding directly to myosin
In skeletal muscle, calcium ions bind to a regulatory protein on thin filaments; in smooth muscle, calcium ions bind to a regulatory protein on thick filaments
In skeletal muscle, calcium initiates contraction by binding to myosin light-chain kinase, while in smooth muscle calcium initiates contraction by binding directly to tropomyosin
In skeletal muscle, calcium initiates contraction by binding to troponin, while in smooth muscle calcium initiates contraction by binding to calmodulin
All of the choices are true
Which of the following is FALSE regarding single-unit smooth muscle cells?
They have an individual neuron innervating each individual smooth-muscle cell
They have many gap junctions between cells
They may have pacemaker activity
They may respond to stretch by contracting
They exhibit tone
Which of the following properties of smooth muscle helps us to understand why, as pregnancy advances, women get more and more Braxton-Hicks (smooth muscle) contractions in the uterine wall?
Smooth muscle cells contract in response to stretch
Smooth muscle cells contract in response to NO
Smooth muscle cells contract in response to CO2
Smooth muscle cells contract in response to changes in pH
Multiunit smooth muscle cells
Generally have individual innervation of each cell
Have many gap junctions between cells
Respond to stretch by relaxing
Can only be excited, and not inhibited
Have abundant T-tubules
Which of the following does NOT correctly describe cardiac muscle cells?
They are arranged in layers surrounding hollow cavities in the heart
They are much shorter than skeletal muscle fibers, and generally have a single nucleus
Their membranes are depolarized initially by the influx of sodium ions
They depolarize prior to contraction
They can contract in the absence of external calcium
Which of the following choices lists a correct sequence of events following the depolarization of transverse tubules in excitation-contraction coupling in cardiac muscle?
Calcium release into cytosol, calcium ion influx through sarcolemma, actin and myosin attach, thin filaments slide toward the middle of sarcomeres
Actin and myosin attach, thin filaments slide toward the middle of sarcomeres, calcium release into cytosol
Calcium release into cytosol, actin and myosin attach, calcium ion influx through sarcolemma, thin myofilaments slide toward the middle of sarcomeres
Calcium release into cytosol, actin and myosin attach, thin filaments slide toward the middle of sarcomeres, calcium ion influx through sarcolemma
Calcium ion influx through sarcolemma, calcium release into cytosol, actin and myosin attach, thin myofilaments slide toward the middle of sarcomeres
The prolonged electrical depolarization of cardiac muscle cells that occurs during contraction is due primarily to the persistent influx of what ion?
Sodium
Calcium
Nitrate
Chloride
Potassium
You are trying to design a new drug to painlessly euthanize animals. Your plan is to design a molecule that blocks the action of one of the following pumps so that heart muscle stays contracted and blood movement is stopped. Which would be effective?
Ca2+-ATPase pumps on the cell membrane
Na+/K+-ATPase pumps on the cell membrane
Ca2+-ATPase pumps on the sarcoplasmic reticulum
Na+/Ca2+-exchangers on the cell membrane
None of these would result in sustained muscle contraction
Which best describes a role of L-type Ca2+ channels in cardiac muscle cells?
They function exactly the same in cardiac muscle cells as they do in skeletal muscle.
They are directly responsible for making cardiac muscle fatigue-resistant
They are responsible for preventing tetanic contractions
They cause the absolute refractory period to be very brief
They act as non-conducting voltage sensors that mediate excitation-contraction coupling
Which dietary supplement is most likely to contribute to greater skeletal muscle ATP availability in the first few seconds of skeletal muscle contraction?
Fatty acids
Sports drinks with electrolytes
Sugar
Protein
Creatine
Myasthenia gravis is a collection of muscle disorders that cause muscle fatigue and weakness. What is the major mechanism?
Overproduction of acetylcholinesterase
Autoimmune destruction of nicotinic acetylcholine receptors
Demyelination of axons in motor pathways
Autoimmune destruction of L-type Ca2+ channels
A tumor that overproduces acetylcholine
Skeletal muscles are made up of bundles of muscle fibers attached to bone by connective tissue called tendons
(a)
The name given to the repeating functional units that cause striations in a skeletal muscle myofibril is "sarcomere."
(a)
The force-generating sites in a myofibril are the Z lines
(a)
During skeletal muscle contraction, the distance between the Z lines of a sarcomere decreases because of shortening of the thick and thin filaments
(a)
During concentric contractions of skeletal muscle, the I band and H zone shorten but the A band stays the same
(a)
The step of the cross-bridge cycle that immediately follows the attachment of ATP to the myosin head is referred to as the "powerstroke."
(a)
The energy for muscle contraction is provided by the hydrolysis of ATP.
(a)
Actin has an ATPase enzyme.
(a)
If you tagged all ATPase enzymes in the muscle cell with fluorescent dye you would see tagging on both myosin and on the surface of the sarcoplasmic reticulum
(a)
The binding of ATP to myosin causes an allosteric change in myosin's actin-binding site such that the affinity of myosin for actin is decreased
(a)
In the absence of ATP, myosin can remain bound to actin; this can occur during times when there is a significant reduction in intracellular ATP
(a)
Binding of myosin to actin in skeletal muscle cells does not normally take place in the absence of Ca2+
(a)
Ca2+ or any other positive ion can enable cross-bridge cycling to begin
(a)
"Excitation-contraction coupling" refers to the binding of energized myosin to actin
(a)
The site of Ca2+ storage in muscle cells is the lateral sacs of the transverse tubules
(a)
Curare blocks neuromuscular transmission by preventing the release of neurotransmitters from the motor neuron
(a)
Organophosphate "nerve gases" induce paralysis by blocking neural stimulation of the neuromuscular junctions, while botulinum toxin produces the same effect by inhibiting acetylcholinesterase
(a)
The term "twitch" refers to the mechanical response of a muscle fiber during one cross-bridge cycle
(a)
When the load on a skeletal muscle is less than the tension the muscle generates, a concentric contraction results
(a)
During isometric contraction of a skeletal muscle fiber, tension increases but the fiber length stays the same.
(a)
The latent period of an isotonic twitch is shorter than the latent period of an isometric twitch
(a)
Sustained contraction and tension in a skeletal muscle is called tetanus
(a)
A skeletal muscle generates its greatest twitch tension when it is stretched to twice its resting length
(a)
Fast fibers can be distinguished from slow fibers by the rate at which their myosin-ATPases split ATP
(a)
Characteristics of slow-oxidative fibers include numerous mitochondria, abundant myoglobin, and large stores of glycogen
(a)
The difference in color between white muscle and red muscle is accounted for by the greater abundance of glycogen in white muscle
(a)
The fiber type intermediate between the two extremes of fast-glycolytic and slow-oxidative is slow-glycolytic
(a)
Muscles used for delicate, finely controlled movements have smaller motor units than muscles used for high power activities
(a)
In general, activating a slow-oxidative motor unit in a muscle will generate more tension than activating a fast-glycolytic motor unit
(a)
Endurance exercise, such as long-distance swimming, causes a preferential increase in glycolytic enzymes and increased mass of the exercising muscles.
(a)
If you took a drug that acts as an inhibitor of creatine kinase, you would still be able to contract your muscles, but in order to sustain a contraction you may notice an increase in ventilatory and heart rates
(a)
The larger the diameter of a skeletal muscle fiber, the greater the tension it can generate
(a)
Recruitment of different types of motor units in a muscle is one means of varying the amount of tension generated in that muscle
(a)
Being able to generate more force with a muscle could include variations in motor unit recruitment or muscle cell hypertrophy
(a)
The shortening velocity of a skeletal muscle fiber increases with decreasing load because the rate at which the cross-bridge cycle can occur increases with decreasing load
(a)
Flexor muscles generally pull on bone and decrease the angle at a joint, whereas extensor muscles push the bone to increase the angle
(a)
The decrease in mass and strength of muscle as a result of damage to the nerves innervating the muscle is called disuse atrophy
(a)
A Ca2+-binding protein in smooth muscle is calmodulin
(a)
The myosin in smooth muscle cells differs from that in skeletal muscle in that smooth muscle myosin requires phosphorylation before it can bind to actin
(a)
In smooth muscle cells that can produce action potentials, cell membrane depolarization usually opens voltage-sensitive sodium channels
(a)
Neuronal stimulation of skeletal muscle is always excitatory, whereas neuronal stimulation of smooth muscle may be excitatory or inhibitory
(a)
Smooth muscle cells may contract in the absence of neuronal stimulation
(a)
Multiunit smooth muscle is characterized by many gap junctions between cells
(a)
In cardiac muscle cells, the release of Ca2+ through L-type Ca2+ channels depolarizes the sarcoplasmic reticulum and inhibits the release of any additional Ca2+ necessary for excitation-contraction coupling
(a)
More mitochondria are typically found in type 1 muscle fibers
(a)
More myoglobin is typically found in type 2X skeletal muscle fibers
(a)
Compared to type 1, both forms of type 2 muscle fibers usually have a large diameter
(a)
Type 2X skeletal muscle fibers have fast myosin ATPase activity
(a)
Type 2 muscle fibers are generally recruited first during a muscle contraction.
(a)
You're holding a pose for a photograph. Your cheek muscles fatigue quickly from smiling, meanwhile your neck muscles feel fine from holding your head up. This is because your cheek muscles are predominantly type 2 muscle fibers
(a)
Type 2 muscle fibers typically have the fewer mitochondria than type 1
(a)
With athletic conditioning, type 2 muscle fibers can gain myoglobin
(a)
