DAT BIO BITES muscular system

At which point of a twitch contraction do we experience the highest muscle tension?

beg of relax phase

Contraction of which muscles causes forearm lifting and extension, respectively?

biceps, triceps Forearm lifting is generated by contracting biceps, pictured below. Forearm extension is the opposite motion, and it is generated by contracting triceps, which are located on the posterior side of the upper arm

During a contraction, how does myosin release its grip on actin?

binding of ATP Now that the myosin is in its low energy state (not cocked back), it doesn't have the power to pull actin any closer to the center of the sarcomere. However, passing ATP binds to myosin, causing myosin to release its grasp from actin.

Which of the following events alters the shape of troponin?

binding to calcium When calcium binds to troponin-C, it alters the shape of troponin. Troponin can no longer hold tropomyosin in the proper location to prevent myosin binding to actin. Myosin now has the potential of binding to actin's exposed binding sites.

What can the organization of skeletal muscles be best compared to?

braided rope When you look at a braided rope from afar, it looks like one big piece; but, as you get closer, you notice the smaller bundles. If you look even closer at each bundle, you would see many woven threads. Skeletal muscles are similar. They are bundles of fibers, much like a rope. Each bundle has a name; further, each bundle is encased in a protective sheath.

How are thin actin filaments oriented within the sarcomere?

branch from z lines and extend toward m lines

What type of muscle cells are joined by intercalating discs?

cardiac Cardiac muscle cells are connected by intercalated discs. Smooth and skeletal muscle cells do not have this feature.

What type of muscle does NOT have inherent muscle tone?

cardiac Cardiac muscle has no inherent muscle tone. Resting muscle tone affects motor units in smooth muscle as well as skeletal muscle

Which of the following can have varied force?

contraction Despite the fact that a muscle fiber's twitch will always be the same size, the overall force of contraction varies. This is accomplished through summation.

During which phase of a twitch contraction do the H zones of sarcomeres begin to shrink?

contraction The contraction phase describes the period of time when calcium binds to troponin-C, triggering a shape change in troponin that causes it to pull tropomyosin away from actin's myosin binding sites. Cross-bridges are established and the H zone begins to shrink.

What is the function of tropomyosin?

cover actin's binding site for myosin n the relaxed state, actin's binding site for myosin is covered by tropomyosin. Tropomyosin is held in place by troponin. Tropomysin covers the binding sites on the actin filament so that myosin cannot bind or slide up the filament.

What are intercalated discs made up of?

desmosomes and gap junctions Intercalated discs contain a desmosome and a gap junction. The desmosome is a inter-cell connection that holds the cells tightly together. The gap junction is like a tube between heart muscle cells that lets the cells quickly pass key ions from cell to cell

What type of contraction occurs as a muscle is lengthening?

eccentric Isotonic contractions can further be broken down into concentric and eccentric contractions. Eccentric contractions occur when a muscle lengthens, despite tension being applied to the muscle fibers. Whereas concentric contractions occur when a muscle shortens as it pulls the bone it inserts onto closer to the bone it originates from.

Which of the following represent a correct order from outermost to innermost?

endomysium, sarcolemma, sarcoplasm, myofibril The endomysium is a layer of connective tissue that surrounds each individual muscle fiber (aka muscle cell). The plasma membrane of a muscle fiber is called the sarcolemma. Contained within the sarcoplasm of the muscle fiber are many strands of contractile protein called myofibrils.

Which layer encases an entire skeletal muscle?

epimysium The epimysium is a layer of connective tissue that surrounds the entire skeletal muscle.

Which of the following is NOT one of the three main types of muscle?

epithelial There are three main types of muscle: Smooth Cardiac Skeletal

Powerful movements are created by what arrangement of motor units?

few large motor units Large motor units are those which have many muscle fibers innervated by one motor neuron. Powerful movements are created by large muscles with few motor units.

Which of the following is a true statement concerning muscle contractions?

filaments of actin and myosin do not shorten the filaments of actin and myosin do not get shorter during a contraction: the sarcomere shortens because the filaments slide past each other. This is why this is referred to as the sliding filament model.

Which of the following gives the correct order from smallest to largest?

Myofibril, muscle fiber, muscle fascicle, skeletal muscle Myofibrils are strands of contractile protein that are found within each muscle fiber (aka muscle cell). A bundle of multiple muscle fibers is called a fascicle. Many fascicles bundled together forms a whole skeletal muscle.

the neuromuscular junction is the space between a which of the following?

The neuromuscular junction is the space between the presynaptic motor neuron and postsynaptic muscle fiber.

Which of the following areas of the sarcomere does not shorten during a muscular contraction?

A band Because the A band includes where the overlap of thick and thin filaments occur, the A band is the only zone/band that does not shorten during muscle contraction.

What causes different types of muscle fibers to vary in speed? A. Distance between T-tubules B. Number of sarcoplasmic reticulum units C. Type of ATPase on myosin head D. Thick filament/thin filament ratios Check Answer

Type of ATPase on myosin head Muscle fiber types vary in speed of contraction due to the type of ATPase on their myosin heads, which allows for the hydrolysis of ATP into ADP + Pᵢ and ultimate cross-bridge cycling. Type I fibers have the slowest acting myosin ATPase, while type IIb fibers have the quickest acting myosin ATPase.

Which of the following is a correct statement?

a motor unit is all the muscle fibers innervated by one motor neuron A motor unit is all the muscle fibers innervated by one motor neuron. A single motor neuron can innervate multiple muscle fibers, but since neuron action potentials are all or none, one motor neuron will cause all of its associated muscle fibers to contract together as a single motor unit. Therefore, one motor neuron cannot coordinate the activity of multiple motor units.

Which of the following is NOT one of the two twitch summation mechanisms?

action potential summation Wave summation (temporal summation) Motor unit summation

How does the sarcoplasmic reticulum recapture calcium once a muscle contraction is no longer desired?

active transport The sarcoplasmic reticulum recaptures calcium by pumping it back inside via active transport. This allows troponin to return to its original shape and pull tropomyosin back over actin's binding site.

Which type of skeletal muscle functional group performs the primary movement?

agonists Agonists are the primary muscles involved in performing a desired motion.

What is the primary function of gap junctions in intercalated discs?

allow heart tissue to contract in unison Gap junctions allow ions (like the Na+ that causes an action potential) to spread through cardiac muscles cells quickly, which ensures that the heart tissue can depolarize and contract in unison.

Which of the following organisms move via pseudopodia?

amoeba There are various types of movement experienced by different types of animals. For example, protozoans move via cilia and flagella, while amoeba move via pseudopodia. These are examples of unicellular movements. Nematoda and annelida move via hydrostatic skeletons, which is an example of invertebrate movement.

What is myosin bound to when it is in its high energy state?

ADP + Pi Myosin heads are ATPases, and when they hydrolyze an ATP molecule into ADP and inorganic phosphate (Pi), the myosin head cocks back into a high energy state and binds to actin, forming a complex called the cross-bridge.

What does the release of acetylcholine into the neuromuscular junction trigger?

Acetylcholine facilitates the opening of ligand gated sodium channels on the muscle fiber.

What represents the area of the sarcomere where only myosin is present

h zone Finally, the area where only myosin is present is called the H zone.

Where are cardiac muscle cells located?

heart

Which of the following is NOT a location where one would expect to find smooth muscle?

heart can find: blood vessels, organ lining, airways

What does the sliding filament model of muscle contraction explain?

how myofilaments slide past each other The sliding filament model of muscle contraction explains how myofilaments slide past one another to shorten the sarcomeres of a muscle cell, leading to contraction of the muscle as a whole.

Which of the following conditions often occurs as a result of damage to the peripheral nervous system?

hypotonicity Hypotonicity is when muscles lose tone and thus feel flaccid. Hypotonicity occurs as the result of damage to the peripheral nervous system, as well as reduced electrolytes. Hypertonicity is when muscles gain tone and thus feel spastic and rigid. Hypertonicity occurs as the result of damage to the central nervous system. Examples: compression of a peripheral nerve, as in carpal tunnel syndrome, can leave your hand feeling weak (hypotonicity). Damage to the central nervous system, as in the case of a stroke, can result in muscles feeling stiff (hypertonicity

What represents the area of the sarcomere where only actin is present? A. A band B. H zone C. I band D. Z line Check Answer

i band The areas where only actin is present are called I bands, and these include the Z line itself.

Which of the following is NOT one of the main types of contractions in vertebrate movement?

isolateral Vertebrate movement involves two main types of muscular contraction: Isotonic contractions Isometric contractions

Which type of contraction involves no movement?

isometric sometric contractions are the muscular contractions that occur when the muscle does not change length and the angle across the joint between the muscle's origin and insertion does not change. These types of contraction occur because the tension on the muscle is equal to the load the muscle is contracting against.

What is the reason behind "rigor mortis," i.e. muscles remaining stiff after death?

lack of ATP In the case of dead animals, rigor mortis occurs because no ATP is being produced to stimulate the release of myosin from actin. This results in muscle becoming "stiff" because the resting state of a muscle is contracted.

Which phase of a twitch contraction takes up the least amount of time?

latent

Which phase of a twitch contraction describes when an action potential makes its way through T-tubules and calcium is released into the sarcoplasm?

latent The latent phase describes the period where an action potential spreads over the sarcolemma and down the T-tubules, signaling the sarcoplasmic reticulum to release its calcium ions into the sarcoplasm.

What represents the midpoint of each sarcomere?

m line

Precision movements are created by what arrangement of motor units?

many small motor units Small motor units are those which have a few muscle fibers innervated by a single motor neuron. Precision movements are created by small muscles containing many motor units. Example: the rectus muscle of the eye has many, small motor units. They are not powerful muscles, but they are very precise.

In motor unit summation, small motor units and large motor units are innervated by what types of neurons, respectively?

most excitable, least excitable In motor unit summation, small motor units with small fibers are innervated by the most excitable neurons. Conversely, large motor units with large fibers are innervated by the least excitable neurons.

What stimulates muscle contractions?

motor neuron firing A muscle contraction is triggered when the motor neuron fires at the neuromuscular junction.

Which twitch summation mechanism involves action potentials traveling to different motor units at different times`

motor unit summation

What does the size principle of motor unit recruitment refer to?

motor units are recruited from smallest to largest The size principle of motor unit recruitment explains how we recruit small motor units before we recruit larger and larger motor units until we have achieved the tension we were aiming for. It helps us to avoid fatigue because different motor units within the same muscle are being stimulated at different times, giving them a chance to relax.

A twitch will always be the same size and duration as long as what happens?

muscle fiber depolarizes above the threshold voltage

The perimysium groups which of the following structures into a bundle?

muscle fibers The perimysium is a layer of connective tissue that surrounds each individual fascicle. Recall that a fascicle is a bundle of muscle fibers.

Repeating units of sarcomeres are found within which structure?

myofibrils An even closer look at a myofibril would reveal many repeating units, called sarcomeres.

Sarcomeres contain an array of which of the following?

myofilaments Sarcomeres contain an array of long, filament proteins called myofilaments.

Which of the following are main source(s) of ATP expenditure during tetany? A. Myosin ATPases only B. Active transport for calcium only C. Myosin ATPases and active transport of calcium D. Action potential reception Check Answer

myosin ATPases and active transport of calcium

What happens during a power stroke?

myosin head pulls actin toward the center of the sarcomere When the cross-bridge is formed, myosin releases ADP + Pᵢ and a 'power stroke' occurs. The power stroke is when the myosin head contracts from its high energy state and pulls actin towards the center of the sarcomere. This shortens the sarcomere and causes the muscle to contract.

What will happen if a depolarization approaches, but does not reach the threshold potential?

none of the muscle fibers within the motor unit twitch Either the depolarization of the muscle fibers within a motor unit is above threshold, in which all the fibers twitch, or it is below threshold and none twitch. This is known as the all-or-none principle of muscle contraction

Which of the following represents the correct order of skeletal muscle structures, from most superficial to most deep?

perimysium, myofibril, myosin You must remember the parts of muscle anatomy, which is made up of various bundles from large to small. The largest is the muscle itself, which is covered in a sheath called the epimysium. Next are muscle fascicles that are covered in a sheath called the perimysium. Inside of muscle fascicles are muscle fibers, which have a sheath around them called the endomysium. Lastly, muscle fibers have strands of contractile proteins called myofibrils, which contain thin actin filaments and thick myosin filaments.

Which of the following is NOT one of the main functional groups of skeletal muscles?

protagonists There are three main functional groups of skeletal muscles, which work together to coordinate movement. They are: Agonists Antagonists Synergists

How do muscle contractions move bones?

pull insertion bone closer to origin bone Muscles pull the bone they insert upon closer to the bone they originate from. It's important to note that because of this, muscular contraction is always a pull (a contraction). It is never a push.

During which phase is calcium actively transported into the sarcoplasmic reticulum? A. Latent B. Contraction C. Relaxation Check Answer

relax

During which phase of twitch contractions does muscle tension begin to decrease? A. Latent B. Contraction C. Relaxation Check Answer

relax

What stimulates the removal of tropomyosin from actin binding sites by troponin?

release of calcium After an action potential and the release of calcium in our muscle cell, this release of calcium then encourages troponin to remove tropomyosin from the binding sites on actin, thereby allowing the two myofilaments to interact and slide over each other.

Postural skeletal muscles (e.g. neck muscles that keep our head upright) remain firm due to which of the following?

resting tone the two summation mechanisms support the idea that skeletal muscle contracts voluntarily. However, we never really think about standing straight or keeping our head upright. This is because all of our muscles have a resting tone that keeps them firm.

Which of the following is a membrane that encases each muscle cell?

sarcolemma The sarcolemma is the protective sheath encasing the muscle fiber (aka muscle cell). The sarcolemma is the muscle fiber's cell membrane.

What are the functional units of muscle fibers?

sarcomeres

What gives certain muscles a striated appearance?

sarcomeres Sarcomeres give skeletal and cardiac muscle a striated appearance. Smooth muscle lacks sarcomeres, which is why it does not appear striated.

What surrounds the myofibrils?

sarcoplasm There is no sheath covering individual myofibrils. Instead, they lie in the muscle fiber's sarcoplasm, which is the cytoplasm of the muscle fiber (aka muscle cell)

Where is calcium released from?

sarcoplasmic reticulum The sarcoplasmic reticulum stores and releases calcium ions, which go on to bind the C site of troponin.

How do sarcomeres facilitate muscle contractions?

shortening Sarcomeres shorten to facilitate muscle contraction. That is why muscles can only pull and not push.

What type of muscle inserts directly into bones?

skeletal

Which of the following types of muscles operate under voluntary control?

skeletal

What types of muscles are striated?

skeletal and cardiac

Which of the following types of muscle contain one nucleus per cell?

smooth and cardiac

Which type of skeletal muscle functional group has a role of supporting the joints? A. Agonists B. Antagonists C. Synergists Check Answer

synergists Synergists are the muscles that help primary movers and provide support to the joints.

How is an action potential spread through the muscle fiber?

t tubules T-tubules (which are invaginations of the sarcolemma) allow the action potential initiated on the muscle fiber to spread throughout the cell very quickly, ensuring a coordinated contraction.

Which of the following statements best defines a twitch contraction?

the contraction of a muscle fiber due to single action potential stimulating an entire motor neuron A twitch contraction is the brief contraction a muscle fiber experiences as the result of a single action potential stimulating an entire motor unit.

What happens after acetylcholine binds to ligand gated sodium channels?

the depolarization opens nearby voltage gated sodium channels When acetylcholine binds to ligand gated sodium channels on the muscle fiber, the channels open. This allows some sodium to enter the muscle fiber; therefore, creating a graded potential. This small depolarization opens nearby voltage-gated sodium channels. When the voltage-gated sodium channels open, we have successfully transferred an action potential from a neuron to a muscle!

Why do wave summation twitches become progressively stronger?

there is leftover calcium in the sarcoplasm from previous twitch Remember, we actively pump calcium into the sarcoplasmic reticulum during the relaxation period. If another action potential stimulates the voltage-gated calcium channels on the sarcoplasmic reticulum to open as relaxation is occurring, we will experience a stronger contraction because there is leftover calcium in the sarcoplasm from the previous twitch. This means more myosin binding sites will be exposed on the actin, leading to more cross-bridges (more tension).

What is the implication of referring to myosin heads as ATPases?

they catalyze the hydrolysis of an ATP molecule into ADP + Pi Myosin heads are ATPases, which means that they hydrolyze an ATP molecule into ADP and inorganic phosphate (Pi).

Which of the following is NOT a type of myofilament?

thick tubulin Thin actin filaments and thick myosin filaments are both subtypes of myofilaments. Whereas tubulin is a protein that makes up microtubules.

Which type of muscle fibers appear to have a dark red color?

type 1 and 2 a fibers

Which type of muscle fiber undergoes the most energy efficient contractions?

type 1 fibers

Which type of muscle fiber has the smallest diameter?

type 1 fibers Slow oxidative fibers are small in diameter; therefore, they have weak contractions. The tradeoff is that their twitch lasts the longest of the three types of muscle fibers, and their contractions are extremely efficient and resistant to fatigue.

Which type of muscle fiber does not rely on oxygen for its contractions?

type 2 - b fibers Fast glycolytic fibers (aka type II-b fibers) rely on anaerobic metabolism of stored glycogen to generate ATP; therefore, they have little use for oxygen.

Which type of muscle fiber may utilize aerobic or anaerobic respiration to generate ATP?

type 2 a fibers

Which type of muscle fiber twitches about two times as fast as type I fibers?

type 2 a fibers

Which type of muscle fiber can undergo the strongest contractions?

type 2 b fibers

Which type of muscle fiber contains the lowest number of mitochondria?

type 2 b fibers Fast glycolytic fibers (aka type II-b fibers) contain few mitochondria. This is due to the fact that they rely on anaerobic metabolism of stored glycogen to generate ATP, which occurs in the sarcoplasm and does not require the use of mitochondria organelles.

Which of the following factors has the most influence on the speed of a twitch contraction? A. Type of motor unit B. Type of muscle fiber C. Size of muscle fiber D. Which neurotransmitter is used Check Answer

type of muscle fiber

How long can tetany be sustained?

until muscle fibers fatigue Eventually, the prolonged tension and significant energy demands associated with tetany will cause fatigue and the contraction will cease completely.

What can be found along the membrane of a sarcoplasmic reticulum?

voltage gated calcium channels The sarcoplasmic reticulum is a specialized endoplasmic reticulum found in muscle fibers that stores calcium ions. A depolarization traveling through the T-tubules triggers voltage-gated calcium channels on the sarcoplasmic reticulum to open. This results in calcium being released from the sarcoplasmic reticulum and rushing into the sarcoplasm.

Which of the following is not a phase of a twitch contraction?

wave Each twitch has three phases: Latent phase Contraction Relaxation

Which of the following refers to the process of depolarizing muscle fibers again while they are in their relaxation phase?

wave summation Wave summation refers to the process of depolarizing muscle fibers in a motor unit again during their relaxation period. This causes another twitch contraction to occur before completion of the previous twitch; therefore, subsequent twitches stack on top of the first twitch contraction, and the overall contraction is larger (summation of waves of contraction).

What causes muscle tone (or tonus)?

weak involuntary twitches Muscle tone (or tonus) is due to weak and involuntary twitches of small groups of motor units within a muscle, due to a continuous output of action potentials from the brain and spinal cord. We never feel fatigued by our tonus because different motor units of a muscle are being stimulated at different times.

At which point of a muscle contraction is a cross bridge formed?

when myosin cocks back into its high energy state When the myosin head cocks back into a high energy state, it binds to actin to form a complex called the cross-bridge

What represents the endpoints of each sarcomere?

z line