Muscular Tissue

Recruitment

The smooth but steady increase in muscular tension produced by increasing the number of active motor units

Automaticity

The spontaneous depolarization to threshold

Fibromyalgia

A chronic disorder characterized by widespread musculoskeletal pain, fatigue, and localized tenderness

Epimysium

A dense layer of collagen fibers that surrounds the entire muscle; separates the muscle from nearby tissues and organs; connected to the deep fascia

A. One Z disk to an adjacent Z disk B. One T tubule to the next T tubule C. The middle of the I band to the middle of the A band D. The H zone to the I band E. The M line to the next M line

A. One Z disk to an adjacent Z disk

Which type of muscle tissue would cause flexion and extension of the arm? A. Skeletal Muscle B. Cardiac Muscle C. Smooth Muscle

A. Skeletal Muscle

Fascia: A. Surrounds individual muscles B. Separates muscle fibers C. Connects muscle to bone D. Is a type of muscular tissue E. Is a type of nerve tissue

A. Surrounds individual muscles

Which of the following is composed of myosin molecules? Α. Thick filaments B. I Bands C. Z disks D. Sarcolemma E. Tropomyosin

A. Thick filaments

The active sites to which cross-bridges attach are found on the: A. Sarcoplasmic reticulum B. Actin myofilaments C. Z discs D. T tubules E. Myosin myofilaments

B. Actin myofilaments

What causes the tropomyosin to cover back over the actin binding sites?

Calcium ions fall off the troponin and calcium is taken back up into the sarcoplasmic reticulum, which leads to tropomyosin covering the actin binding sites.

Myofilament

Fine protein filaments composed primarily of the proteins actin (thin filaments) and myosin (thick filaments), which contains titin, the elastic filament associated with thick filaments

M Line

Located in the center of the A band; connects the central portion of each thick filament to neighboring thick filaments; helps stabilize the positions of thick filaments

Describe muscle fatigue.

Muscle fatigue is a muscle's reduced ability to contract due to low pH (hydrogen ion buildup), low ATP levels, or other problems.

Define oxygen debt.

Oxygen debt is the amount of oxygen required to restore normal, pre-exertion conditions in the muscle tissue.

Isotonic Contraction

When the muscle changes length with a constant force; either concentric or eccentric

Glycolysis

The anaerobic breakdown of glucose to pyruvate in the cytosol of a cell; an anaerobic process that does not require oxygen; provides a net gain of 2 ATP molecules and generates 2 pyruvate molecules to form each glucose molecule

Chemically Gated Na+ Channel

The membrane channel receptor on the motor end plate of the muscle fiber which ACh binds to

Hyperpolarization

The movement of potassium ions out of a cell leads to this, as the membrane potential becomes more negative

Synaptic Cleft

The narrow space between the motor end plate of the sarcolemma and the synaptic terminal of the neuron in a neuromuscular junction

Describe the neuromuscular junction.

The neuromuscular junction is the synapse between a motor neuron and a skeletal muscle cell (fiber). This connection enables communication between the nervous system and a skeletal muscle fiber.

Acetylcholine (ACh)

The neurotransmitter that is emitted during muscle contraction

Stimulus Frequency

The number of stimuli per unit of time

Myosin

The protein component of thick filaments; binds to actin

Cori Cycle

The shuffling of lactate produced in the muscles to the liver and glucose back to the muscle cells

Isometric Contraction

When the muscle does not change length with a constant force, and the tension produced never exceeds the load; when performed, the contracting muscles bulges

Isotonic Concentric Contraction

When the muscle tension exceeds the load and the muscle shortens

Power Stroke

When the myosin head pivots, using the energy released from the hydrolysis of ATP, causing it to swing towards the M line; the key step in muscle contraction

Isotonic Eccentric Contraction

When the peak muscle tension developed is less than the load, and the muscle elongates due to the contraction of another muscle or the pull of gravity; these types of contractions are very common; in these movements, you exert precise control over the amount of tension produced

Asynchondrous Motor Unit Summation

When, during a sustained contraction, motor units are activated on a rotating basis, so some of them are resting and recovering while others are actively contracting, when each motor unit can recover before it is stimulated again

Intercalated Disc

Where the sarcolemmas of two adjacent cardiac muscle cells are extensively intertwined and bound together by gap junctions and desmosomes; helps stabilize the positions of adjacent cells and maintain the three-dimensional structure of the tissue

Predict what would happen to a muscle if the motor end plate lacked acetylcholinesterase (AChE).

Without acetylcholinesterase (AChE), the motor end plate would be stimulated continuously by acetylcholine, locking the muscle in a state of contraction.

List the six important chemicals involved in muscle contraction.

1. Myosin 2. Actin 3. Troponin 4. Tropomyosin 5. ATP 6. Calcium ions

Neurotransmitter

A chemical signal released from an axon terminal to transmit messages

Triad

A combination of a pair of terminal cisternae and a T tubule

The Zone of Overlap

A dark region where thin filaments are located between the thick filaments; here, three thick filaments surround each thin filament, and six thin filaments surround each thick filament

Why does a muscle that has been overstretched procure minimal tension?

A muscle's ability to contract depends on he formation of cross-bridges between the myosin and actin myofilaments in the muscle. In a muscle that is overstretched, the myofilaments would overlap very little, so very few cross-bridges between myosin and actin could form and, thus, the contraction would be weak. If the myofilaments did not overlap at all, then no cross-bridges would form and the muscle would not contract.

Sphincter

A muscular ring that contracts to close the entrance or exit of an internal passageway

Botulism

A severe, potentially fatal paralysis of skeletal muscles, resulting from the consumption of a bacterial toxin

Muscle Fiber

A single cell in muscle tissue

Twitch

A single stimulation that produces a single contraction that may last 7-100 milliseconds, depending on the muscle stimulated; a single stimulus-contraction-relaxation sequence in a muscle fiber

Creatine

A small molecule that muscle cells assemble from filaments of amino acids

Why would a sprinter experience muscle fatigue before a marathon runner would?

A sprinter requires large amounts of energy for a short burst of activity. To supply this energy, the sprinter's muscles rely on anaerobic metabolism. Anaerobic metabolism is less efficient in producing energy than aerobic metabolism, and the process also produces acidic wastes; this combination contributes to muscle fatigue. Conversely, marathon runners derive most of their energy from aerobic metabolism, which is more efficient and produces fewer wastes than anaerobic metabolism does.

Refractory Period

A time period when the muscle cannot fire again

Filamentous Actin (F-Actin)

A twisted strand composed of two rows of 300-400 individual globular molecules (monomers) of G-actin

Muscular Dystrophies

A varied collection of inherited diseases that produce progressive muscle weakness and deterioration

Polio

A virus attacks motor neurons in the spinal cord and brain, causing muscular paralysis and atrophy

In which of the following situations does a resting membrane potential exist? A. A relaxed muscle fiber B. A conducting neuron C. A stimulated sensory receptor in the skin D. A contracting cardiac muscle cell E. The eye seeing an image

A. A relaxed muscle fiber

You are hired to work in a laboratory to measure the rate of human muscle contraction. Which of the following might decrease in quantity in muscle cells undergoing contractions? A. ATP B. Carbon dioxide C. Water D. Lactic acid E. Sodium

A. ATP

Tetanus of muscles is described as: A. Action potential frequency is high enough that no relaxation of muscle fibers occurs B. A muscle produces constant tension during contraction C. A muscle produces an increasing tension during contraction D. A muscle produces an increasing tension as it shortens E. A muscle produces tension, but the length of the muscle is increasingly

A. Action potential frequency is high enough that no relaxation of muscle fibers occurs

The sarcolemma is the: A. Cell membrane of a muscle fiber B. Cytoplasm of muscle cells C. Structural and functional unit of the skeletal muscle cell D. Contractile thread that extends the length of the muscle fiber E. Protein strand composed of actin

A. Cell membrane of a muscle fiber

The capability of a muscle cell to shorten forcefully is known as: A. Contractility B. Excitability C. Extensibility D. Elasticity

A. Contractility

If sodium ions cannot enter a muscle fiber in response to a stimulus: A. Contraction cannot occur B. Relaxation cannot occur C. Sodium ions will be released from the sarcoplasmic reticulum instead D. The active sites are left exposed E. The action potential travels into the muscle anyway

A. Contraction cannot occur

Rigor mortis occurs after death because: A. Cross-bridges form but can't release B. Calcium is actively transported back to the sarcoplasmic reticulum C. Anaerobic respiration is occurring D. Myosin levels decline at death E. Cross-bridges never form

A. Cross-bridges form but can't release

The electrical properties of cells are the result of: A. Ion concentration differences across the plasma membrane B. Receptor sites that are present on the plasma membrane C. Phosphorylation reactions within the cytoplasm D. Phospholipids in the cell membrane E. None of these choices are correct

A. Ion concentration differences across the plasma membrane

The sites where a chemical substance is transmitted from the presynaptic terminal of an axon to the postsynaptic membrane of a muscle fiber are called: A. Neuromuscular junction B. Sarcomeres C. Myofilaments D. Z-disks E. Cell body of neuron

A. Neuromuscular junction

The outside of the resting plasma membrane is _____ relative to the inside of the resting plasma membrane: A. Positively charged B. Negatively charged C. Electrically neutral D. Recharged E. None of these choices are correct

A. Positively charged

Endomysium is a delicate network of loose connective tissue that: A. Surrounds each muscle fiber B. Forms a sheath around a fasciculus C. Is composed of elastic fibers D. Separates individual muscles E. Penetrates muscle fibers

A. Surrounds each muscle fiber

Fascia is what? A. Surrounds individual muscles B. Separates muscle fibers C. Connects muscles to bones D. Is a type of muscle tissue E. Is a type of nerve tissue

A. Surrounds individual muscles

Which of the following is composed of myosin molecules? A. Thick filaments B. I Bands C. Z disks D. Sarcolemma E. Tropomyosin

A. Thick filaments

RICE (rest, ice, compression, and elevation)

Acronym for the standard treatment for muscle injuries, bruises, strains, and sprains

Which activity would be more likely to create an oxygen debt: swimming laps or lifting weights?

Activities that require short periods of strenuous activity produce a greater oxygen debt, because such activities rely heavily on energy production by anaerobic metabolism. Because lifting weights is more strenuous over the short term than swimming laps, which is an aerobic activity, weight lifting would likely produce a greater oxygen debt than swimming laps.

Improvements in aerobic endurance result from what?

Alterations in the characteristics of muscle fibers, and improvements in cardiovascular function

Lactate

An anion released by the dissociation of lactic acid, or formed from the reduction of pyruvate

Myosin Light Chain Kinase

An enzyme activated by calmodulin which enables myosin heads to attach to actin

Hypertrophy

An increase in tissue size without cell division; occurs in muscles that have been stimulated to produce near-maximal tension

Lactic Acidosis

An increased lactate blood level and metabolic acidosis

Depolarization

An influx of sodium ions leads to this, as the membrane potential becomes less negative

Fasciculation

An involuntary muscle twitch that involves more than one muscle fiber

Which type of respiration do resting muscles depend upon? A. Anaerobic respiration B. Aerobic respiration C. Both anaerobic and aerobic respiration

B. Aerobic respiration

Which of the following statements regarding the sliding filament theory is false? A. Actin and myosin do not shorten during contraction. B. Both actin and myosin myofilaments shorten during contraction C. The sarcomere shortens D. The I band and the H zone become narrower during contraction E. The A band remains constant in length

B. Both actin and myosin myofilaments shorten during contraction

Lack of acetylcholinesterase in the synaptic cleft would result in: A. A decrease in acetylcholine production by the motor neuron B. Continuous stimulation of the postsynaptic membrane C. Rapid degredation of acetylcholine D. Relaxation of the muscle E. Continuous stimulation of the presynaptic membrane

B. Continuous stimulation of the postsynaptic membrane

A drug that interfere with the active transport of calcium ions from the sarcoplasm back to the sarcoplasmic reticulum would result in: A. Relaxation of the muscle fibers B. Contraction with no relaxation C. Muscle hypertrophy D. Fibrosis of the muscle E. An imbalance of blood calcium

B. Contraction with no relaxation

Sarcoplasm is the: A. Cell membrane of a muscle fiber B. Cytoplasm of muscle cells C. Structural and functional unit of the skeletal muscle cell D. Contractile thread that extends the length of the muscle fiber E. Protein strand composed of actin

B. Cytoplasm of muscle cells

Sarcoplasm is the: A. Cell membrane of a muscle fiber B. Cytoplasm of muscle cells C. Structural and functional unit of the skeletal muscle cell D. Contractile thread that extends the length of the muscle fiber E. Protein strand composed of myosin or actin

B. Cytoplasm of muscle cells

Which of the following would contribute to muscular fatigue in the muscle fiber? A. The emotional state of an individual B. Depletion of ATP reserves C. Inability of the motor neuron to produce sufficient quantities of acetylcholine D. Depletion of neurotransmitter E. Blocked receptors in the postsynaptic membrane

B. Depletion of ATP reserves

Acetylcholine binds to a membrane bound receptor and causes ligand-gated sodium channels to open and results in: A. Hyperpolarization B. Depolarization C. Hypopolarization D. No change in membrane potential E. There is not enough information to predict the outcome

B. Depolarization

Which of the following actions is caused by contraction of skeletal muscle? A. Contraction of the heart B. Locomotion C. Movement of food through the digestive tract D. Emptying of the urinary bladder

B. Locomotion

Skeletal muscle develops from multinucleated cells called: A. Fascicles B. Myoblasts C. Myofibrils D. Myotomes

B. Myoblasts

In excitation-contraction coupling: A. Calcium ions must bind with myosin to expose active sites on actin B. Myosin heads bind to exposed active sites on actin C. Cross-bridges form between myosin head and calcium ions D. Movement of the troponin-tropomyosin complex causes actin myofilaments to slide E. ATP binds to actin myofilaments

B. Myosin heads bind to exposed active sites on actin

When the myosin head flexes into a bend, pulling the actin filament along with it, this is called the: A. Action reaction B. Power stroke C. Recovery stroke D. Muscle tone E. Action potential

B. Power stroke

Hypertrophy of skeletal muscles from weight lifting is caused by the increase in the: A. Number of muscle fibers B. Size of muscle fibers C. Number of striations D. Number of muscle cells

B. Size of muscle fibers

How would severing the tendon attached to a muscle affect the muscle's ability to move a body part?

Because tendons attach muscles to bone, severing the tendon would disconnect the muscle from the bone, and so the muscle could not move a body part.

Z Line

Bisects the A bands; marks the boundary between adjacent sarcomeres; consists of actinin proteins

Muscle myofibrils: A. Are found in the sarcolemma B. Extend from the sarcolemma to the T tubule C. Contain myosin and actin myofilaments D. Hold muscle cells together E. Do not appear striated

C. Contain myosin and actin myofilaments

Which type of the following connective tissue layers is outside all the others? A. Perimysium B. Endomysium C. Epimysium D. Paramysium E. Sarcolemma

C. Epimysium

Which of the following is true about skeletal muscle? A. Sensory neurons stimulate muscles to contract B. There are very few blood vessels in skeletal muscle C. Every muscle fiber receives a branch of an axon from the nerve D. There are very few nerve fibers in a muscle E. All of these choices are true

C. Every muscle fiber receives a branch of an axon from the nerve

A byproduct of of anaerobic respiration in muscle cells is: A. Uric acid B. Hydrochloric acid C. Lactic acid D. Carbonic acid E. Pyruvic acid

C. Lactic acid

The model that describes the contraction of the muscle is called the: A. Contraction cycle B. Power stroke C. Sliding filament model D. Slipping fibril mechanism E. Paddle model

C. Sliding filament model

A sarcomere is the: A. Cell membrane of a muscle fiber B. Cytoplasm of muscle cells C. Structural and functional unit of the skeletal muscle cell D. Contractile thread that extends the length of the muscle fiber E. Protein strand composed of actin

C. Structural and functional unit of the skeletal muscle cell

What causes the tropomyosin to move away from myosin binding sites on actin?

Calcium ions are released from the terminal cisternae, and they then bind to troponin, causing tropomyosin to move away from the myosin binding sites on actin.

What causes the myosin binding sites on actin to be exposed?

Calcium ions are released from the terminal cisternae, then they bind to troponin, and tropomyosin moves away from the myosin binding sites.

What feature of cardiac muscle tissue allows the heart to act as a functional syncytium?

Cardiac muscle cells are joined by gap junctions, which allow ions and small molecules to flow directly between cells. As a result, action potentials generated in one cell spread rapidly to adjacent cells. Thus, all the cells contract simultaneously, as if they were a single unit (syncytium).

Pacesetter Cells

Cells that allow for rhythmic waves of contraction that spread through the entire muscular sheet

Functional Syncytium

Cells that are physically, chemically, and electrically connected to one another

Perimysium

Dense layer of collagen and elastic fibers that divides the skeletal muscle into a series of compartments, which contains a bundle of muscle fibers called a fascicle; also contains the blood vessels and nerves that supply the muscle fibers within the fascicles

Myopathy

Disease of muscle tissue

Tropomyosin

Double-stranded protein that covers seven active sites; strands that cover the active sites on G-actin and prevents actin-myosin interaction; bound to one molecule of troponin midway along its length

Nebulin

Holds the F-actin strand together; extends along the F-actin strand in the cleft between the rows of G-actin molecules

Cardiac Muscle Cells

Muscle cells that are only found in the tissues of the heart

How do muscle fibers continuously synthesize ATP?

Muscle fibers synthesize ATP continuously by utilizing creatine phosphate (CP) and metabolizing glycogen and fatty acids. Most cells generate ATP only though aerobic metabolism in the mitochondria and through glycolysis in the cytosol.

Slow Fibers

Muscle fibers that are only about half the diameter of fast fibers, and take three times as long to reach peak tension after stimulation; surrounded by a more extensive network of capillaries; contains myoglobin

Intermediate Fibers

Muscle fibers that contain little myoglobin and are relatively pale; have average amounts of capillary networks, and are more resistant to fatigue than fast fibers

Smooth Muscle Tissue

Muscle tissue in the walls on many visceral organs; characterized as nonstriated, involuntary muscle

Striated Muscle

Muscle tissue in which the contractile fibrils in the cells are aligned in parallel bundles, so that their different regions form stripes visible in a microscope

Cardiac Muscle Tissue

Muscle tissue only found in the heart

Identify the common properties shared by muscle tissues.

Muscle tissues share the common properties of excitability (the ability to receive and respond to a stimulus), contractility (the ability of a muscle cell to shorten when it is stimulated), extensibility (stretching movement of a muscle), and elasticity (the ability of a muscle to recoil to its resting length).

White Muscles

Muscles dominated by fast fibers

Red Muscles

Muscles dominated by slow fibers

Opposing Muscles

Muscles that perform opposite reactions, such as the biceps and triceps

Describe the components of a sarcomere.

Sarcomeres, the smallest contractile units of a striated muscle cell, are segments of myofibrils. Each sarcomere has a dark A band and light I band. The A band contains the M line, the H band, and the zone of overlap. Each I band contains thin filaments, but not thick filaments. Z lines bisect the I bands and mark the boundaries between adjacent sarcomeres.

Which types of muscle tissue is least affected by changes in extracellular Ca2+ concentration during contraction?

Skeletal muscle contractions are least affected by changes in extracellular Ca2+ concentrations. In skeletal muscle, most of the calcium ions come from the sarcoplasmic reticulum. Most of the calcium ions that trigger a contraction in cardiac and smooth muscles come from the extracellular fluid.

Which type of muscle fibers would you expect to predominate in the leg muscles of someone who excels at endurance activities, such as cycling or long-distance running?

People who excel at endurance activities have a higher than normal percentage of slow fibers. Slow fibers are physiologically better adapted to this type of activity than are fast fibers, which are less vascular and fatigue faster.

What are the functions of skeletal muscle?

Producing movement, maintaining posture and body position, supporting soft tissues guarding body entrances and exits, storing nutrients, and maintaining body temperature

Contractility

The ability of a muscle cell to shorten when it is stimulated

Elasticity

The ability of a muscle to recoil to it's resetting length

Plasticity

The ability to function over a wide range of lengths

Wave Summation

The addition of one twitch to another, causing a second, more powerful contraction

Oxygen Debt (Excess Postexercise Oxygen Consumption)

The amount of oxygen required to restore normal, pre-exertion conditions

Synaptic Terminal

The area of the neuron in the neuromuscular junction that connects via the synapse to the motor end pate of the sarcolemma

Motor End Plate

The area of the sarcolemma in the neuromuscular junction that connects via the synapse to the synaptic terminal of the neuron

Cross-Bridge

The binding of a myosin head that projects from the surface of a thick filament at the active site of a thin filament in the presence of calcium ions

Aerobic Endurance

The length of time a muscle can continue to contract which supported by mitochondrial activities; does not promote muscular hypertrophy

Anaerobic Endurance

The length of time muscular contraction can continue to be supported by the existing energy reserves of ATP and CP and by glycolysis; limited by the amount of ATP and CP available, the amount of glycogen available for hydrogen ions generated during the period of anaerobic metabolism

Excitation-Contraction Coupling

The link between the generation of an action potential in the sarcolemma and the start of a muscle contraction; occurs at the triads

Graded Potential

The localized change limited by the presence or absence of stimulation that does not continue to spread over the plasma membrane

Why can smooth muscle contract over a wider range of resting lengths than skeletal muscle can?

The looser organization of actin and myosin filaments in smooth muscle allows smooth muscle to contract over a wider range of resting lengths than skeletal muscle.

Force

The maximum amount of tension produced by a particular muscle or muscle group

Tetanus

The maximum tension possible created by a single muscle fiber

Where is myosin found in skeletal muscle cells?

Thick filaments

Latent Period

This phase begins at stimulation and lasts about 2 milliseconds (for this muscle fiber); during this period, the action potential sweeps across the sarcolemma, and the sarcoplasmic reticulum releases calcium ions; the muscle fiber does not produce tension during this period, because the contraction cycle has yet to begin A in picture

Identify the primary functions of skeletal muscle.

Skeletal muscles produce skeletal movement, maintain posture and body position, support soft tissues, guard body entrances and exits, maintain body temperature, and store nutrients.

What are the three types of muscle tissue in human bodies?

Skeletal, cardiac, and smooth

Identify the structural characteristics of smooth muscle tissue.

Smooth muscle cells lack sarcomeres, and thus smooth tissue is nonstriated. Additionally, the thin filaments are anchored to dense bodies.

Multiunit Smooth Muscle Cells

Smooth muscle cells that are innervated in motor units comparable to those of skeletal muscles, but may be connected to more than one motor neuron; have excitable plasma membranes; resembles skeletal muscle fibers and cardiac muscle cells in that neural activity produces an action potential that travels over the sarcolemma; contract more slowly than skeletal or cardiac muscle cells; located in the iris of the eye (regulates the diameter of the pupil), within the walls of large arteries, in the arrector pili muscles of the skin, and along portions of the male reproductive tract

Endurance

The amount of time during which a person can perform a particular activity

List the six steps of the sliding filament theory.

1. Exposure of binding sites on actin 2. Binding of myosin to actin 3. Power stroke of the cross-bridge 4. Disconnecting the cross-bridge 5. Re-energizing the cross-bridge 6. Removal of the calcium ions

What two important binding sites are found on cross-bridges of myosin?

ATP and actin

How would a drug that blocks acetylcholine release affect muscle contraction?

Acetylcholine (ACh) release from the axon terminal is necessary for skeletal muscle contraction, because it serves as the first step in the process that leads to the formation of cross-bridges in the sarcomeres. A muscle's ability to contract depends on the formation of cross-bridges between the myosin heads and actin myofilaments. A drug that blocks ACh release would interfere with this cross-bridge formation and prevent muscle contraction.

What three protein molecules are thin filaments made of?

Actin, tropomyosin, and troponin

Excitability

Also know as responsiveness or irritability; the ability to receive and respond to a stimulus; muscle tissue responds to a chemical stimulus from a nerve cell with a change in membrane potential

An isometric contraction is described as: A. Action potential frequency is high enough that no relaxation of muscle fibers occurs B. A muscle produces constant tension during contraction C. A muscle produces an increasing tension as the length remains constant D. A muscle produces increasing tension as it shortens E. A muscle produces tension, but the length of the muscle is increasing

C. A muscle produces an increasing tension as the length remains constant

Pacemaker Cells

Cells of the sinoatrial node that set the pace of cardiac contraction

List the following structures in order from smallest to largest: 1. muscle fiber, 2. myofilament, 3. myofibril, 4. muscle fasciculus A. 4, 2, 3, 1 B. 2, 1, 3, 4 C. 2, 1, 4, 3 D. 2, 3, 1, 4 E. 4, 2, 1, 3

D. 2, 3, 1, 4

Titin

Elastic protein that extends from the tips of the thick filaments to attachment sites at the Z line; helps keep the thick and thin filaments in proper alignment and aids in restoring resting sarcomere length after retraction; also helps the muscle fiber resist extreme stretching that would otherwise disrupts the contraction mechanism

Relaxation Phase

For this muscle fiber, this phase lasts about 25 milliseconds; during this period, the Ca2+ level is decreasing as calcium ions are pumped back into the sarcoplasmic reticulum, active sites are being covered by tropomyosin, and the number of active cross-bridges is declining as they detach; as a result, tension decreases to the resting level C in picture

Active Site

Found in G-actin; a place where myosin can bind

Describe general age-related effects on skeletal muscle tissue.

General age-related effects on skeletal muscles include decreased skeletal muscle fiber diameters, diminished muscle elasticity, decreased tolerance for exercise, and a decreased ability to recover from muscular injuries.

Myoglobin

Globular protein similar to hemoglobin; reversibly binds oxygen molecules; most abundant in slow muscle fibers

Muscle Tone

In any skeletal muscle, some motor units are always active, even when the entire muscle is not contracting, but do not produce enough tension to cause movement

Fast Fibers

Muscle fibers that can reach peak twitch tension in 0.01 seconds or less after stimulation; large in diameter and contain densely packed myofibrils, large glycogen reserves, and relatively few mitochondria; muscles with these fibers produce powerful contractions; fatigue rapidly because the contractions use massive amount of ATP

Sarcolemma

Plasma membrane of a muscle fiber that surrounds the sarcoplasm

Why do skeletal muscle fibers appear striated when viewed through a light microscope?

Skeletal muscle fibers appear striated when viewed through a light microscope because the Z lines and thick filaments of the myofibrils within the muscle fibers are aligned.

Visceral Smooth Muscle Cells

Smooth muscle cells that are not innervated by motor neurons; arranged in sheets or layers

Myosatellite Cells

Stem cells that help repair damaged muscle tissue

Can a muscle contract without shortening? Explain.

Yes, a skeletal muscle can contract without shortening. The muscle can shorten (isotonic concentric contraction), elongate (isotonic eccentric contraction), or remain the same length (isometric contraction), depending on the relationship between the load (resistance) and the tension produced by actin-myosin interactions.

How to remember the difference between the A and I bands?

You can remember that actin occurs in thin filaments by associating the "tin" in actin with the word "thin". Then remember that th"I"n filaments look l"I"ght and form the "I" band. Similarly, the "A" bands are d"A"rk.

Where would you expect to find the greatest concentration of Ca2+ in a resting skeletal muscle fiber?

You would expect the greatest concentration of calcium ions in a resting skeletal muscle fiber to be in the terminal cisternae of the sarcoplasmic reticulum.

What is the function of tropomyosin?

It covers the binding sites on actin subunits, and prevents myosin cross-bridge binding

Contraction Cycle

A series of molecular events that enables muscular contraction

What happens in a sarcomere as the skeletal muscle fiber contracts?

The H bands and I bands of the sarcomeres narrow, the zones of overlap widen, the Z lines move closer together, and the width of the A band remains constant

Voltage-Gated Ion Channels

Electrical channels that become activated when the membrane of neurons and skeletal muscle fibers first depolarize from the resting potential to a threshold potential (from -70 to -60mV for neurons, and from -85 to -55mV for skeletal muscle fibers)

Action Potential

Electrical impulses that trigger muscle fiber contractions

Myoblasts

Embyronic muscle forming cells

A myofilament is the: A. Cell membrane of a muscle fiber B. Cytoplasm of muscle cells C. Structural and functional unit of the skeletal muscle cell D. Contractile thread that extends the length of the muscle cell E. Protein strand composed of myosin or actin

D. Contractile thread that extends the length of the muscle cell

The region of the sarcomere that contains both actin and myosin myofilaments is called the: A. I band B. A band C. Z disk D. H zone

D. H zone

Identify the statement concerning skeletal muscle that is true. A. It compromises about 20% of the body's weight. B. It propels urine through the urinary tract. C. It function is largely under involuntary control D. It is powered by ATP

D. It is powered by ATP

Terminal Cisternae

Enlarged areas of the sarcoplasmic reticulum that surround transverse tubules; contains the protein calsequestrin

Which of the following events occur on the postsynaptic membrane? A. Acetylcholine production B. Rapid degradation of acetylcholine C. Release of neurotransmitter D. Neurotransmitter combines with a receptor molecule E. Release of calcium ions

D. Neurotransmitter combines with a receptor molecule

Muscles exhibit the property of excitability. This means that the muscle: A. Shortens its length B. Recoils to its original resting length C. Stretches beyond its normal length D. Responds to stimulation by the nervous system

D. Responds to stimulation by the nervous system

What are the three roles of ATP in the sliding filament theory?

1. ATP transfers its energy to the myosin cross-bridge, which in turn, energizes the power stroke. 2. ATP disconnects the myosin cross-bridge from the binding site on actin. 3. ATP fuels the pump that actively transports calcium ions back into the sarcoplasmic reticulum.

Calmodulin

A calcium-binding protein protein found in the sarcoplasm of smooth muscle cells

Aponeurosis

A broad sheet where the collagen fibers of the epimysium, perimysium, and endomysium come together at either end of the muscle; usually attaches skeletal muscle to bone

Tendon

A bundle of the collagen fibers of the epimysium, perimysium, and endomysium that come together at either end of the muscle; usually attaches skeletal muscle to bone

Myasthenia Gravis

A general muscular weakness resulting from a reduction in the number of ACh receptors on the motor end plate

Myogram

A graphic representation showing development of twitches in muscle fibers from various skeletal muscles

Creatine Phosphate (CP) or Phosphocreatine

A high-energy compound in muscle cells; during muscle activity, the phosphate group is donated to ADP, regenerating to ATP

H Band

A lighter region on either side of the M line; contains thick filaments #5 in picture

Sarcoplasmic Reticulum

A membrane complex that forms a tubular network around each myofibril; similar to the smooth endoplasmic reticulum of other cells; specialized for the storage and release of calcium ions

Motor Unit

A motor neuron and all the muscle fibers that it controls

Incomplete Tetanus

A muscle fiber producing almost maximum tension during rapid cycles of contraction and relaxation

Complete Tetanus

A muscle fiber producing almost maximum tension during rapid cycles of contraction caused by higher stimulation frequency; in this situation, action potentials arrive so rapidly that the sarcoplasmic reticulum does not have time to reclaim the calcium ions

Actinin

A protein that interconnects thin filaments of adjacent sarcomeres

I (Isotropic) Band

A region of the sarcomere that contains thin filaments; but no thick filaments; extends from the A band of one sarcomere to the A band of another sarcomere #2 in picture

Repolarization

A return to the resting potential

Voltage-Gated Sodium Ion Channels

Channels that open and let in positively charged sodium ions into the cell

Compare and contrast skeletal muscle tissue and cardiac muscle tissue.

Compared to skeletal muscle tissue, cardiac muscle tissue (1) has relatively small cells; (2) has cells with a centrally located nucleus (some may contain two or more nuclei); (3) has T tubules that are short and broad and do not form triads; (4) has a sarcoplasmic reticulum that lacks terminal cisternae and has tubules that are nearly totally dependent on aerobic metabolism as an energy source; and (6) contains intercalated discs that assist in stabilizing tissue structure and spreading action potentials.

Troponin

Consists of three subunits, one of which binds to tropomyosin, locking them together as a troponin-tropomyosin complex, a second which binds to one G-actin, holding the troponin-tropomyosin complex into position, and a third which has a receptor that binds two calcium ions

Multinucleate

Containing two or more nuclei; skeletal muscle cells are an example

Thick Filament

Contains about 300 myosin molecules, each made up of a pair of myosin subunits twisted around one another; has a titin core; 10-12nm in diameter, and 1.6μm long

Thin Filament

Contains four main proteins: F-actin, nebulin, tropomyosin, and troponin; 5-6nm in diameter, and 1μm long

A concentric contraction is described as: A. Action potential frequency is high enough that no relaxation of muscle fibers occurs B. A muscle produces constant tension during contraction C. A muscle produces an increasing tension during contraction D. A muscle produces increasing tension as it shortens E. A muscle produces tension, but the length of the muscle is increasing

D. A muscle produces increasing tension as it shortens

During short periods of intense exercise, energy in muscles is primarily derived from: A. Aerobic respiration B. Anaerobic respiration C. Creatine phosphate breakdown D. Nuclear reactions E. Both anaerobic respiration and creatine phosphate breakdown

E. Both anaerobic respiration and creatine phosphate breakdown

Which of the following connective tissue layers is inside all of the others? A. Perimyisum B. Paramysium C. Epimysium D. Sarcolemma E. Endomysium

E. Endomysium

Muscle tone is what? A. Is a time during which the tissue cannot respond again B. Results in complete and incomplete tetanus C. Is a condition in which the muscle fiber only partially relaxes between contraction D. Is a condition in which stimuli occur so rapidly that there are no interning relaxations E. Is constant tension produced by muscles for long periods of time

E. Is constant tension produced by muscles for long periods of time

Treppe

If a skeletal muscle fiber is stimulated a second time immediately after the relaxation phase of a twitch has ended, the resulting contraction will develop a slightly higher maximum tension than did the first contraction; this increase will continue over the first 30-50 stimulations, then the amount of tension produced will remain constant; most skeletal muscles do not undergo this, but cardiac muscle does

What would happen to a resting skeletal muscle if the sarcolemma suddenly became very permeable to calcium ions?

If the sarcolemma of a resting skeletal muscle suddenly became permeable to Ca2+, the cytosolic concentration of Ca2+ would increase, and the muscle would contract. In addition, because the amount of calcium ions in the cytosol must decrease for relaxation to occur, the increased permeability of the sarcolemma to Ca2+ might prevent the muscle from relaxing completely.

Contraction Phase

In this phase, tension increases to a peak; as the tension increases, calcium ions are binding to troponin, active sites on thin filaments are being exposed, and cross-bridge interactions are occurring; for this muscle fiber, the contraction phase ends roughly 15 milliseconds after stimulation B in picture

G-Actin

Individual globular molecules (monomers) that are found in F-actin; contains an active site

Excitable Membranes

Membranes that permit rapid communication between different parts of a cell; contain voltage-gated ion channels that are activated and inactivated by changes in the membrane potential

Myofibril

Organized collections of myofilaments in skeletal and cardiac muscle; 1-2μm in diameter, and as long as the entire muscle; anchored to the inner surface of the sarcolemma at each end of a skeletal fiber

Skeletal Muscles

Organs composed mainly of skeletal muscle tissue, but also contains connective tissues, blood vessels, and nerves

Action contains binding sites for...

Myosin

Transverse Tubules (T Tubules)

Narrow tubes whose surfaces are continuous with the sarcolemma and extend deep into the sarcoplasm; contraction signals are propagated through these tubules; filled with extracellular fluid and form passageways though the muscle fiber

Duchenne Muscular Dystrophy (DMD)

One of the most common and best understood of the muscular dystrophies

Calsequestrin

Protein that reversibly binds Ca2+

What is required to move calcium ions from the cytosol back into the sarcoplasmic reticulum?

Specialized ion pumps in the membrane of the sarcoplasmic reticulum

Dense Bodies

Structures distributed throughout the sarcoplasm in a network of intermediate filaments composed of desmin

Sliding Filament Theory

The concept that a sarcomere shortens as the thick and thin filaments slide past one another

Muscle Metabolism

The consumption of energy by muscle tissue cells to perform work

Sarcoplasm

The cytoplasm of the muscle fiber

A (Anisotropic) Bands

The dark bands on the sarcomere; contains regions of overlapping thick (myosin) and thin (actin) filaments; about as long as a typical thick filament; contains the M line, the H band, and the zone of overlap #7 in picture

Endomysium

The delicate connective tissue that surrounds the individual skeletal muscle cells, and loosely interconnects adjacent muscle fibers; contains capillary networks that supply blood to the muscle fibers, myosatellite cells that help repair damaged muscle tissue, and nerve fibers that control the muscle

Muscle Metabolism during Moderate Activity

The demand for ATP increases There is still enough oxygen for the mitochondria to meet the increased demand, but no excess ATP is produced ATP is generated primarily by aerobic metabolism of glucose from stored glycogen If the glycogen reserves are low, the muscle fiber can also break down other substrates, such as fatty acids All of the ATP being generated is used to power muscle contraction

Muscle Metabolism during Peak Activity

The demand for ATP is enormous; oxygen cannot diffuse into the fiber fast enough for the mitochondria to meet that demand; only a third of the cell's ATP needs can be met by the mitochondria (not shown) The rest of the ATP comes from glycolysis, and when this produces pyruvate faster than the mitochondria can utilize it, the pyruvate builds up in the pyruvate builds up in the cytosol The pyruvate is converted to lactate; hydrogen ions from ATP hydrolysis are not absorbed by the mitochondria The buildup hydrogen ions increases cytosol acidity, which inhibits muscle contraction, leading to rapid fatigue

Muscle Metabolism in a Resting Muscle Fiber

The demand for ATP is low and sufficient oxygen is available for mitochondria to meet that demand Fatty acids are absorbed and broken down in the mitochondria creating a surplus of ATP Some mitochondrial ATP is used to convert absorbed glucose to glycogen Mitochondrial ATP is also used to convert creatine to creatine phosphate (CP) This results in the buildup of energy reserves (glycogen and CP) in the muscle

Creatine Kinase

The enzyme that catalyzes the reverse reaction that changes ADP and creatine phosphate to ATP and creatine; a high concentration of this usually indicates severe muscle damage

Describe the three connective tissue layers associated with skeletal muscle tissue.

The epimysium is a dense layer of collagen fibers that surrounds the entire muscle; the perimysium divides the skeletal muscle into a series of compartments, each containing a bundle of muscle fibers called a fascicle; and the endomysium surrounds individual skeletal muscle cells (muscle fibers). The collagen fibers of the epimysium, perimysium, and endomysium come together to form either bundles known as tendons, or broad sheets called aponeuroses. Tendons and aponeuroses generally attach skeletal muscles to bones.

What is the function of troponin?

The function of troponin is to move the tropomyosin aside, exposing the myosin binding sites.

Sarcomere

The smallest contractile unit of a striated muscle cell; has a resting length of about 2μm; contains thick filaments, thin filaments, proteins that stabilize the positions of the thick and thin filaments, and proteins that regulate the interactions between thick and thin filaments

Extensibility

The stretching movement of a muscle

Neuromuscular Junction

The synapse between a neuron and a muscle fiber; made up of an axon (synaptic) terminal of a neuron, a specialized region of the sarcolemma called the motor end plate, and the narrow space between the two, called the synaptic cleft

Length-Tension Relationship

The tension produced by the entire muscle fiber is directly proportional to the length of the individual sarcomeres

According to the sliding filament theory, when a muscle contracts, what happens?

The thin filaments slide past the thick filaments, and the sarcomere shortens.

Identify the three types of muscle tissue and cite their major functions.

The three types of muscle tissue are skeletal muscle, cardiac muscle, and smooth muscle. Skeletal muscle tissue moves the body by pulling on our bones, cardiac muscle tissue pumps blood through the cardiovascular system, and smooth muscle tissue pushes fluids and solids along the digestive tract and other internal organs, and regulates the diameters of small arteries.

Identify the three types of skeletal muscle fibers.

The three types of skeletal muscle fibers are (1) fast fibers (also called white muscle fibers, fast-twitch glycolytic fibers, Type II-B fibers, and fast fatigue fibers); (2) slow fibers (also called red muscle fibers, slow-twitch oxidative fibers, Type I fibers, and slow oxidative fibers); and (3) intermediate fibers (also called fast-twitch oxidative fibers, Type II-A fibers, and fast-resistant fibers).

Atrophy

The wasting away of tissues from a lack of use, ischemia, or nutritional abnormalities

Fatigue

When a muscle cell can no longer perform at the required activity level

Fibrosis

When an aging skeletal muscle develops increasing of fibrous connective tissue, which makes the muscles less flexible, and causes the collagen fibers to restrict movement and circulation

Recovery Period

When the conditions in the muscle fiber are returned to a normal, pre-exertion level; may take several hours to occur; completion of this phase may take up to a week