LearnSmart Muscles - A&P I

Place in order the steps leading to the relaxation of the muscle.

1) Nerve signal ceases 2) Acetylcholine releases into the synaptic cleft stops; ACh already in synaptic cleft is broken down 3) Calcium is actively transported into the sarcoplasmic reticulum; Ca +2 diffuses away from troponin 4) Troponin returns to its relaxed configuration, causing tropomyosin to cover the myosin binding sites on actin

What is an isotonic contraction?

A muscle changes in length, but its tension stays constant.

What is a muscle twitch?

A single contraction of muscle fiber in response to a single stimulation.

When is ATP required by muscle cells?

During both relaxation & contraction

How many myofibrils and sarcomeres are found in a muscle fiber?

Each muscle fiber contains many myofibrils, each made of many sarcomeres joined end to end.

Actin (thin) filaments are attached to a Z line, which is located in the middle of what region of the striations?

I band

Match each striation band with its composition.

I band (light band) - actin (thin) filaments only A band (dark band) - myosin and actin filaments H zone - myosin (thick) filaments only

What is the role of creatine phosphate during skeletal muscle contraction?

It is used to quickly regenerate ATP from ADP.

Consider the naming of the temporalis muscle. What does the name tell you about the muscle?

It provides information about the locations of the origins and/or insertions for the muscle.

Consider the naming of the triceps brachii muscle. What does the name tell you about the muscle?

It provides information about the number of heads (origins).

Which statements correctly describe changes in a skeletal muscle cell during muscle contraction?

Muscles shorten during contraction Myofilaments overlap during contraction Sarcomeres shorten during contraction

List in order the events leading to excitation of a muscle fiber.

Nerve impulse arrives at distal end of axon. Acetylcholine is released. ACh diffuses across synaptic cleft. ACh binds to its receptors on muscle fiber sarcolemma. Permeability of sarcolemma to ion decreases.

Smooth muscle cells differ from skeletal muscle cells in numerous ways. Which of the following correctly describes one of those differences?

Smooth muscle cells lack striations.

During one of the steps of muscle contraction, ATP binds to myosin heads. What happens as a result of that?

The myosin heads are released from the actin filaments.

Match thick and thin filaments with the proteins found in them. Thin vs thick.

Thin - actin, troponin, tropomyosin Thick - myosin

As ATP is broken down to ADP by the myosin-head ATPase, what is the released energy used for?

To move the myosin head into its cocked position.

What is the role of neurotransmitters?

To stimulate a target cell.

True or false: Muscles generate heat when they contract.

True

For a typical muscle fiber in its optimal state, how many action potentials generated by a motor neuron must arrive at the neuromuscular junction to reach the threshold stimulus?

Typically, a single action potential is enough to bring the muscle fiber to the threshold.

A sarcomere extends from one ______ to the next.

Z line

What is a muscle fascicle?

a bundle of skeletal muscle fibers surrounded by perimysium

What is a motor unit composed of?

a single motor neuron, several muscle fibers

What is muscle fiber?

a single muscle cell

The supraspinatus and deltoid muscles are the primary ______ of the arm at the shoulder.

abductors

During excitation of a muscle fiber, which one of the following events comes immediately after the release of acetylcholine from the motor neuron?

acetylcholine diffuses across the synaptic cleft

What are the two major protein types found in myofibrils?

actin and myosin

The process of a neuron, its axon, conducts electrical impulses called BLANK BlANK towards the end of the axon that innervates a target cell.

action potentials

Choose two actions of the pectoralis major muscle.

adducts arm; medially rotates arm

The process of glycolysis is ______.

anaerobic

Glycolysis is used to produce ATP for muscle contraction and is best described as ______.

anaerobic breakdown of glucose to produce ATP

Neurons have extensions (processes) called BLANK that carry electrical impulses toward the cell they are innervating.

axons

What causes the myosin heads to move into their "cocked" positions prior to them attaching to actin?

breakdown of ATP into ADP and Pi

What are myofibrils?

bundles of proteins in a muscle cell

During muscle relaxation, calcium levels in the sarcoplasm fall because ______.

calcium is actively transported into the sarcoplasmic reticulum

Which of the following best describes the role of the sarcoplasmic reticulum (SR) when a skeletal myofiber is first stimulated?

calcium is released from the SR into the sarcoplasm

Muscle tissue that has a well-developed sarcoplasmic reticulum, many mitochondria, and branching cells with one nucleus is classified as ______ muscle.

cardiac

Which type of muscle have striated cells that form interconnected, branching, three-dimensional networks?

cardiac muscle

The "cocking" of the myosin heads, hydrolysis of ATP, and the power stroke occur during the ______ phase of skeletal muscle contraction.

contraction

Two flexors of the arm are ______.

coracobrachialis and pectoralis major

What is the first source of energy that is used to convert ADP to ATP after a contraction in a skeletal muscle cell begins?

creatine phosphate

When is lactic acid produced?

during anaerobic metabolism

The teres major and latissimus dorsi are the primary ______ of the arm at the shoulder.

extensors

True or false: Myofilaments shorten during contraction.

false

A bundle of skeletal muscle fibers enclosed by a perimysium forms a(n) BLANK within a muscle.

fascicle

Muscle cells are also known as muscle fibers. In a skeletal muscle, muscle fibers are found as bundles called BLANK, each enclosed in a connective tissue sheath, called the BLANK.

fascicle, perimysium

Only ______-twitch fibers can be predominantly glycolytic, using glycolysis to produce ATP.

fast

Prolonged or intense exercise can lead to a condition called muscle BLANK, defined as the loss of a muscle's ability to contract.

fatigue

Due to their shape, muscle cells are also called muscle BLANK.

fibers

What is the action of the coracobrachialis muscle?

flexes the arm at the shoulder

The coracobrachialis and pectoralis major are both ______ of the arm.

flexors

What is the immediate result of the opening of sodium channels along the sarcolemma (beyond the motor end plate)?

generation of an action potential

In muscles, ______ is stored in the form of glycogen.

glucose

Lactic acid produced by muscle cells travels via the blood to the liver where liver cells are able to convert it to ______.

glucose

Muscle cells store glucose in the form of BLANK.

glycogen

Muscle cells store glucose in the form of BlANK.

glycogen

Muscle contractions generate ______, which is important for the overall functioning of the body.

heat

What is the outcome of the movements of the cocked myosin heads?

increase in overlap between thin and thick filaments

What is the immediate effect of acetylcholine binding to its receptors on the motor end plate?

increased membrane permeability to sodium ions

What type of contraction is observed when a muscle shortens?

isotonic

During high-intensity exercise, anaerobic metabolism results in the production of pyruvic acid, which is then converted to BLANK acid.

lactic

Which type of motor unit produces more force when recruited?

large motor unites (more muscle fibers)

Cells of the BLANK can convert lactic acid to glucose.

liver

What four pairs of muscles are considered muscles of mastication?

masseter lateral pterygoid temporalis medial pterygoid

The muscles of mastication include the medial and lateral pterygoid, BLANK and BLANK.

masseter, temporalis

A motor unit is comprised of a ______ and the ______ that it controls.

motor neuron; muscle fibers

Indicate three characteristics of skeletal muscle fibers.

multinucleated elongated cells cylindrical shape

Long bundles of contractile proteins found in the sarcoplasm are called BLANK.

myofibrils

What generates the force that shortens the sarcomeres to bring about muscle contraction?

myosin cross-bridges pulling on the actin filaments

In order to communicate with a target cell at a synapse, a neuron releases BLANK.

neurotransmitters

What type of chemical is released by neurons? These chemicals then bind to effector cells.

neurotransmitters

The end of a muscle that is fixed (relatively immovable) is called its ______.

origin

The point of attachment for a muscle that remains relatively stationary is its BLANK.

origin

The trapezius, the rhomboid major and minor, and the levator scapulae are all muscles that move the BLANK girdle.

pectoral

Alternate contractions and relaxations of longitudinal and circular muscles in certain tubular organs produce a wavelike motion called BLANK.

peristalsis

The rhythmic contraction of the smooth muscle layers in the walls of tubular hollow organs is known as ______.

peristalsis

Name the process in which multiple motor units are activated in response to the increasing intensity of stimulation, increasing the strength of contraction.

recruitment

The increase in the number of activated motor units as the intensity of neuronal stimulation increases is called BLANK, or multiple motor unit summation.

recruitment

Which of the following is a characteristic of slow-twitch (type I) fibers?

red in color

During which phase are calcium ions actively transported into the sarcoplasmic reticulum?

relaxation

Which of the following are muscles that move the pectoral girdle?

rhomboid major, levator scapula, serratus anterior, trapezius

The teres minor and infraspinatus are the primary ______ of the arm at the shoulder.

rotators

Within myofibrils, the area between two successive Z lines is called a(n) ______.

sarcomere

Myofibrils are formed by many ______ positioned end-to-end.

sarcomeres

The coracobrachialis muscle runs from the BLANK to the middle of the humerus and it BLANK and adducts the arm.

scapula; flexes

Which muscle type has multi-nucleated cells that are cylindrical in shape?

skeletal

Fill in the blank question. The three types of muscle are BLANK muscle, BlANK muscle, and BLANK muscle.

skeletal, smooth, cardiac

What are the three types of muscles found in the human body?

skeletal, smooth, cardiac

______-twitch fibers always use aerobic metabolism and are therefore called oxidative fibers.

slow

Compared to skeletal muscle, smooth muscle is ______ to contract and ______ to relax.

slower; slower

Which type of motor unit is more easily stimulated and, thus, is recruited first?

small motor units (fewer muscle fibers)

Which type of muscle can change length without changing tautness?

smooth muscle

Place the following descriptions of smooth and skeletal muscle cells into the appropriate category.

smooth muscle cell - single nucleus lacks striations, lacks transverse tubules skeletal muscle cell - multiple nuclei per cell, striated, well-developed sarcoplasmic reticulum

Action potentials spreading along the sarcolemma of a muscle fiber result from the opening of ______ channels in the sarcolemma.

sodium

The binding of acetylcholine to its receptors on the motor end plate results in increased membrane permeability to BLANK ions and potassium ions.

sodium

The organization of the thin and thick filaments within a muscle cell results in the formation of what muscle feature?

striations

Which muscles rotate the arm at the shoulder?

subscapularis and teres minor

When a muscle fiber is stimulated at a high enough frequency that it doesn't have time to relax, the forces of the individual twitches combine. What is this process called?

summation

When the frequency of stimulation of a muscle fiber increases, eventually the individual twitches combine by the process of BLANK which results in a sustained contraction.

summation

What are the two major abductors of the arm?

supraspinatus and deltoid

Which of the following are major extensors of the arm?

teres major and latissimus dorsi

What forms the striations seen in skeletal muscle?

the arrangement of thin and thick filaments

Muscle fatigue is a condition described by ______ and is usually caused by prolonged use of a muscle.

the loss of a muscle's ability to contract

During muscle contraction, the sarcomeres shorten because ______.

thick and thin filament slide past one another, increasing their overlap

In a muscle contraction, the force that shortens the sarcomeres comes from the myosin cross-bridges pulling on the BLANK filaments.

thin or actin

If a muscle fiber is subjected to stronger and stronger electrical impulses, it will initially be unresponsive until a strong enough impulse is applied which causes it to contract. The level of electrical stimulation needed to stimulate contraction is called the ______.

threshold stimulus

What is the name of the invaginations of the sarcolemma that extend through the muscle fiber?

transverse (T) tubules

Numerous openings in the sarcolemma of a muscle fiber lead down into structures called the ______.

transverse tubules

What structures are positioned between adjacent cisternae of the sarcoplasmic reticulum?

transverse tubules

Of the following muscles, which one moves the pectoral girdle?

trapezius

In excitation-contraction coupling, the protein called BLANK moves to expose binding sites on the actin filaments that can form cross-bridges.

tropomyosin

During excitation-contraction coupling, calcium binds to ______.

troponin

True or false: ATP is needed for both muscle contraction and muscle relaxation.

true

True or false: The sarcoplasmic reticulum releases calcium into the cytoplasm when a muscle impulse moves down into the muscle fiber along the T tubules.

true

True or false: The transverse tubules are located between structures called cisternae.

true

When a single muscle fiber contracts when stimulated by a single impulse, the contractile response is called a(n) BLANK.

twitch

Muscle fibers with abundant mitochondria and myoglobin that are typically red in color are called ______ fibers.

type I