A+P Exam 3 Muscles

The following is a list of the events that occur during a muscle contraction. What is the correct sequence of these events? 1. Myosin cross-bridges bind to the actin. 2. The free myosin head splits ATP. 3. Calcium ion is released from the sarcoplasmic reticulum. 4. The myosin head pivots toward the center of the sarcomere. 5. Calcium ion binds to troponin.6. The myosin head binds an ATP molecule and detaches from the actin.

3, 5, 1, 4, 6, 2

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

A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. How are these components connected?

A series of proteins that control calcium release.

The post-synaptic reaction on the sarcolemma is short in duration. Which of the following explanations describes why the reaction of the sarcolemma is short in duration?

ACh diffuses out of the synaptic cleft, AChE acts to breakdown the ACh in the synaptic cleft.

Which of the following events most directly occurs due to an action potential generated by the motor neuron?

ACh is released at the synapse.

The characteristic muscle stiffness associated with rigor mortis is due to the inability of myosin filaments to detach from the active site on actin filaments. What molecule is essential for this detachment?

ATP

Which of the following molecules is NOT thought to accumulate during muscle fatigue?

ATP

After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment?

ATP binds to the myosin head

Action potential propagation in a skeletal muscle fiber ceases when acetylcholine is removed from the synaptic cleft. Which of the following mechanisms ensures a rapid and efficient removal of acetylcholine?

Acetylcholine is degraded by acetylcholinesterase

The neuromuscular junction is a well-studied example of a chemical synapse. Which of the following statements describes a critical event that occurs at the neuromuscular junction?

Acetylcholine is released by axon terminals of the motor neuron

Tamara's muscle weakness and fatigue becomes progressively worse over the course of the day. This is a hallmark sign of myasthenia gravis, an autoimmune disorder that affects the ability of a motor neuron to communicate with a muscle fiber. What synaptic events must happen first for excitation to occur?

Acetylcholine is released from the axon terminal and diffuses across the synapse to bind to a receptor in the surface of the motor end plate.

The injection that dramatically improved Tamara's symptoms was Tensilon, an acetylcholinesterase inhibitor. What is acetylcholinesterase, and why was this injection effective in relieving Tamara's symptoms?

Acetylcholinesterase is the enzyme that clears acetylcholine from the synapse. Inhibiting this enzyme will enable acetylcholine to be available for a longer period to bind to receptors.

For a weight to be lifted, which of the following must occur?

An isotonic muscle contraction with a force greater than the load.

The binding of the neurotransmitter to receptors on the motor end plate causes which of the following to occur?

Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate (junctional folds of the sarcolemma) and sodium enters the cell.

The cross bridge cycle starts when _________.

Ca2+ from the sarcoplasmic reticulum binds to troponin

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

What specific event triggers the uncovering of the myosin binding site on actin?

Calcium ions bind to troponin and change its shape.

Excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. What specific event initiates the contraction?

Calcium release from the sarcoplasmic reticulum initiates the contraction

Which of the following situations delay the development of muscle fatigue the longest?

Consistent interruptions of muscle stimulation

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

Excitation-contraction coupling is a series of events that occur after the events of the neuromuscular junction have transpired. The term excitation refers to which step in the process?

Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.

Myasthenia gravis is an autoimmune disorder that results in the production of antibodies that either block or cause the destruction of the ACh receptor. Why do you think that Tamara's symptoms become worse as the day progresses?

In the morning, the neuronal reserves of acetylcholine are larger, allowing for sufficient neurotransmitter release and resulting in effective muscle signaling. As the day progresses and the stores of acetylcholine become depleted, muscle function becomes progressively worse.

With both ends of the muscle fixed, which of the following occurs if the load attempted is equal to or greater than the force generated by a muscle?

Isometric muscle contraction occurs.

Why does wave summation occur?

Muscle fibers are partially contracted when the next stimulus arrives.

Which of the following occurs during the latent period of isotonic concentric contraction?

Muscle tension is produced, and the weight will not move.

Which of the following is true of the maximum stimulus frequency?

No greater muscle force can be generated and the muscle has reached maximal tetanic tension

Calcium entry into the axon terminal triggers which of the following events?

Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine.

The origin of the hamstring muscles is on the ischial tuberosity; where are their insertions?

The biceps femoris inserts on the head of the fibula and lateral condyle of the tibia, the semimembranosus inserts on the posterior surface of the medial condyle of the tibia, and the semitendinosus inserts on the medial surface of the tibia.

How does the myosin head obtain the energy required for activation?

The energy comes from the hydrolysis of ATP

David sustained a complete avulsion of his hamstring tendons from their origin on the ischial tuberosity. What classes of lever are the hamstring muscles?

The hamstrings are an example of third-class levers, where the applied force is between the load and the fulcrum.

Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels. Why?

The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients.

Which of the following occurs during isotonic concentric contraction?

The length of the muscle decreases with contraction.

Which of the following does NOT describe tetanus?

The muscle relaxes fully between contractions.

What happens immediately after the myosin head binds to the active site on actin?

The myosin head pivots, moving the actin strand

Which of the following statements about muscles of the forearm is true?

The pronator teres originates on the medial epicondyle and inserts on the radius.

Why are the muscles that move the fingers and wrist located in the forearm?

This design allows the hand to maintain fine motor control and strength without the interference of bulky muscles.

Define and describe the term sarcomere

This is the functional unit of skeletal muscle. The sarcomere extends from z line to z line. Within the sarcomere there are thin filaments (actin) and think filaments (myosin). The myofilaments interact to cause muscle tension/shortening

What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated?

Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.

Treppe is the phenomenon that results in _______.

a progressive increase in the force generated with repetitive stimulation

In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter?

acetylcholine (ACh)

Triggering of the muscle action potential occurs after

acetylcholine binds to chemically-gated channels in the motor end plate.

A myosin head binds to which molecule to form a cross bridge?

actin

Myosin molecules form cross-bridges when they attach to __________.

actin

Which of the following proteins contains the active site involved in cross-bridge formation?

actin

Which of the following is generated when cross-bridges form between actin and myosin?

active force

One of the actions of the latissimus dorsi muscle is to __________.

adduct the arm

The origin of the rectus femoris is the ____________.

anterior inferior iliac spine

The origin of the Sartorius muscle is from the __________ spine.

anterior superior iliac

At the completion of supinator action, the palm is turned __________.

anteriorly

A(n) ________ can be described as a broad tendinous sheet.

aponeurosis

What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell?

arrival of an actin potential

Forearm supination is assisted by the __________.

biceps brachii

What causes the myosin head to disconnect from actin?

binding of ATP

belly

body of muscle, between origin & insertion

Muscle twitches overlap with _______.

both fused and unfused tetanus

The muscle that generates the most power during elbow flexion is the __________.

brachialis

These modified structures contain a high concentration of the ion ___________, which is important in the process of muscle contraction.

calcium

Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?

calcium ions

Which of the following is matched correctly?

complete tetanus - fused tetanus

The deep posterior extensor of the wrist and fingers __________.

controls the thumb and index finger

Convergent

cover a broad area & converge on common point ex: pectoralis major, latissimus dorsi

Physical evidence that supports the sliding filament theory of muscle contraction includes

decreased width of the H band during contraction

The brachialis muscle is located __________ to the biceps brachii muscle.

deep

The forearm muscles can be divided into anterior flexors and posterior extensors, as well as __________.

deep and superficial layers

ATP binding leads to which of the following actions?

detaching and resetting cross-bridges

origin

end of muscle fixed point of attachment, attached to bone that doesn't move, usually proximal to insertion

insertion

end of muscle that is moveable (usually distal), attached to bone that moves, usually distal to origin

The delicate connective tissue that surrounds the skeletal muscle fibers and ties adjacent muscle fibers together is the

endomysium

The sequence of processes that links the action potential to contraction is called

excitation-contraction coupling

What means of membrane transport is used to release the neurotransmitter into the synaptic cleft?

exocytosis

Action potentials travel the length of the axons of motor neurons to the axon terminals. These motor neurons __________.

extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fiber

The semimembranosus __________ the thigh at the hip and __________ the leg at the knee.

extends; flexes

The gluteus maximus is the most powerful muscle during __________.

extension

The extensor muscle that branches to form four tendons on the back of the hand is the __________.

extensor digitorium

pennate

fascicles form a common angle with the tendon

Muscles that move the eyeball have ________ fibers.

fast

Parallel

fibers run parallel to long axis (VERY EFFICIENT) ex: triceps brachii, biceps brachii

The origin of the external obliques includes ribs __________.

five through twelve

A muscle that assists another by stabilizing its origin is called its __________.

fixator

Both heads of the biceps femoris muscle __________.

flex the leg at the knee

The brachioradialis is a strong forearm __________.

flexor

During muscle fatigue, the ____________ decreases.

force of contraction

The actions of the internal intercostals are most important during __________.

forced expiration

The rotator cuff is a term used to describe the group of muscles and tendons that stabilize and reinforce the __________.

glenohumeral joint

The infraspinatus inserts on the ____________ of the humerus.

greater tubercle of the humerus

circular

having the shape of a circle ex: orbicularis oculi, orbicularis oris

All the tendons of the rotator cuff muscles combine at which location?

humeral head

The majority of the fibers of the gluteus maximus insert onto the __________.

iliotibial tract

A muscle producing almost peak tension during rapid cycles of contraction and relaxation is said to be in

incomplete tetanus

The external intercostals elevate the rib cage during __________.

inspiration

The tibialis anterior muscle dorsiflexes the foot at the ankle and also assists in __________ of the foot

inversion

The long head of the biceps femoris muscle originates on the __________.

ischial tuberosity

A weight-lifter strains to lift a heavy weight and there is no movement of the person's arms holding on to the weight. This type of contraction is called a(n) ________ contraction.

isometric

The rectus femoris muscle extends the leg at the __________.

knee

The tensor fasciae latae stabilizes the hip joint and the __________ joint

knee

Muscle fatigue occurs because of a buildup of __________ and a(n) __________ in pH.

lactic acid; decrease

An origin of the supinator is the __________.

lateral epicondyl of the humerus

Both the Psoas major muscle and iliacus muscle insert on the __________.

lesser trochanter of the femur

The subscapularis muscle inserts on the __________.

lesser tubercle of the humerus

The muscle weakness of myasthenia gravis results from

loss of acetylcholine receptors in the end-plate membrane.

Myofibrils are __________.

made of a series of sarcomeres

Which of the following is a recognized function of skeletal muscle?

maintain posture, produce movement, maintain body temperature, and guard body entrances and exits

The insertion of the extensor carpi radialis longus muscle is on __________.

metacarpal two

When acetylcholine binds to receptors at the motor end plate, the sarcolemma becomes

more permeable to sodium ions

Which of the following terms are NOT used interchangeably?

motor unit - motor neuron

Active interactions between actin and myosin filaments within the sarcomere are responsible for

muscle contraction

Interactions between actin and myosin filaments of the sarcomere are responsible for

muscle contraction

In an isotonic contraction,

muscle tension exceeds the load and the muscle lifts the load

Which of the following is involved in the power stroke?

myosin

Each skeletal muscle fiber is controlled by a motor neuron at a single

neuromuscular junction

The insertions of the semispinatus capitus are on the __________.

occipital bone

The resting length of the muscle _______.

occurs when the muscle is relaxed

bipennate

on both sides of tendon ex: rectus femoris

The latissimus dorsi inserts __________.

on the intertubercular groove of the humerus

unipennate

one side of tendon ex: extensor digitorium

The biceps femoris is located in the __________.

posterior thigh

All fibers of the semimembranosus muscle converge to insert on the __________.

posterior tibia

The origins of the rectus abdominus muscle are on the __________.

pubic bone

The two heads of the biceps brachii combine to insert on the __________.

radial tuberosity

Where does the acetylcholine that stimulates muscle contraction bind?

receptors in the motor end plate

You try to pick up an object and discover that it is much heavier than you expected. Which process must occur in the muscle to increase tension so you can pick up the object?

recruitment

In complex movements, muscles commonly work in groups rather than individually. The hamstrings flex the knee. Which muscles are antagonists to the hamstrings?

rectus femoris, vastus intermedius, vastus lateralis, vastus medialis

A patient takes a medication that blocks ACh receptors of skeletal muscle fibers. What is this drug's effect on skeletal muscle contraction?

reduces the muscles ability for contraction

What causes the power stroke?

release of ADP and Pi

The infraspinatus muscle is included in the __________ muscles.

rotator cuff

The plasma membrane of a skeletal muscle fiber is called the

sarcolemma

The repeating unit of a skeletal muscle fiber (that gives it the striped appearance) is the

sarcomere

Z lines define the edges of which of the following?

sarcomeres

In response to an action potential along the transverse tubules, the __________ release(s) calcium ions into the sarcoplasm.

sarcoplasmic reticulum

The series of membranous channels that surrounded each myofibril is the

sarcoplasmic reticulum

The anterior muscles of the thigh that originate on the os coxae are __________.

sartorius; rectus femoris

Stem cells located between the endomysium and sarcolemma that function in the repair of damaged muscle tissue are called

satellite cells

Which of the following is NOT a phase of a muscle twitch?

shortening phase

The speed of muscle contraction is called the _______.

shortening velocity

Since each myofibril is attached at either end of the muscle fiber, when sarcomeres shorten, the muscle fiber

shortens

How is acetylcholine (ACh) removed from the synaptic cleft?

simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme)

The type of muscle fiber that is most resistant to fatigue is the ________ fiber.

slow

The sarcolemma of the muscle fiber form deep invaginations into sarcoplasm called

t-tubules

At each end of the muscle, the collagen fibers of the epimysium, perimysium, and endomysium, come together to form a

tendon

The bundle of collagen fibers at the end of a skeletal muscle that attaches to bone is called a(n)

tendon

multipennate

tendon branches within muscle ex: deltoid

These structures encircle a myofibril and are bordered on each side by special modified structures of the sarcoplasmic reticulum, the

terminal cisternae

The action potential on the muscle cell leads to contraction due to the release of calcium ions. Where are calcium ions stored in the muscle cell?

terminal cisterns (cisternae) of the sarcoplasmic reticulum

Which deep posterior extensor of the wrist originates on the radius and ulna and interosseous membrane?

the abductor pollicis longus

A motor unit is defined as _______.

the axon terminals of a single motor neuron and all of the muscle fibers that it stimulates

When acetylcholine binds to its receptors, it results in __________.

the end plate potential, a graded depolarization, and a change in ion permeability

NO force is generated during which of the following?

the latent period

When wave summation occurs, _______

the muscle force generated increases

Which of the following is proportional to the amount of tension produced by a skeletal muscle?

the number of motor units activated

Acetylcholine binds to its receptor in the sarcolemma and triggers __________.

the opening of ligand-gated cation channels

The graph of the length-tension relationship illustrates _______.

the optimal sarcomere length for muscle contraction and the amount of overlap between the thick and thin filaments in the resting muscle

What structure is the functional unit of contraction in a skeletal muscle fiber?

the sarcomere

Myosin molecules form what part of the sarcomere?

thick filament

Muscles that act on the knee joint form most of the mass of the __________.

thigh

Which of the following best matches the term Z-line?

thin filaments are anchored here

The biceps brachii-radius arrangement represents a __________-class lever system.

third

What is the minimum voltage needed to generate active force in the skeletal muscle?

threshold voltage

The tibialis posterior muscle originates at which three locations?

tibia, fibula, and interosseous membrane

What is name given to the regularly spaced infoldings of the sarcolemma?

transverse or T-tubules

The actin potential is conducted into skeletal muscle fiber by

transverse tubules

The prime mover of elbow extension is the __________.

triceps brachii

When the sarcomere is at rest, what is covering the active sites on actin?

tropomyosin

The binding of calcium to which molecule causes the myosin binding sites to be exposed?

troponin

When calcium is released inside a muscle cell, what does it bind to?

troponin

At rest, the tropomyosin molecule is held in place by

troponin molecules

A single contraction-relaxation cycle in a muscle fiber produces a(n)

twitch

When an action potential arrives at the axon terminal of a motor neuron, which ion channels open?

voltage-gated calcium channels

When the frequency of stimulation of a muscle is great enough, _______.

wave summation results and muscle twitches overlap.

The actions of the extensor carpi radialis brevis are localized to the __________.

wrist

In a sarcomere, cross-bridge attachment occurs specifically in the

zone of overlap