Chapter 10: Muscle Tissue Study Guide

What is a muscle fiber?

skeletal muscle cells

Muscle tissue in a skeletal muscle is surrounded by three layers of connective tissue (CT).

Name each layer and describe where each is located and what it surrounds.

• Epimysium: A dense layer of collagen fibers that surrounds the entire muscle.

• Perimysium: Divides the skeletal muscle into a series of compartments.

• Endomysium: Surrounds individual skeletal muscle cells.

What is a fascicle?

A bundle of muscle fibers

What are myosatellite cells and what is their function?

Stem cells that help repair damaged muscle tissue

What are tendons and aponeuroses? What is their general function?

• A bundle formed when the collagen fibers of the epimysium, perimysium, and endomysium come together

• Function: Attach skeletal muscles to bones

What are aponeuroses? What is their general function?

• A broad sheet formed when the collagen fibers of the epimysium, perimysium, and endomysium come together

• Function: Attach skeletal muscles to bones

What are three differences between muscle fibers and typical cells?

Muscle Fibers

• Size: Much larger

• Multinucleate: Each contains hundreds of nuclei just internal to the plasma membrane

• Banded or striated

Skeletal muscle cells multinucleated. What advantage do these cells have because they possess multiple nuclei?

• Nuclei control the production of enzymes and structural proteins required for normal muscle contraction

• Assisting in the repair of the tissue

What are myoblasts? What do they fuse into?

• Groups of embryonic cells that fuse for my individual multinucleate skeletal muscle fibers.

What are non-fused myoblast cells called?

Myocytes

Skeletal muscle is also called striated muscle. What two proteins give skeletal muscle it striated appearance?

• Thin (actin)

• Thick (myosin)

What is a sarcolemma?

Plasma membrane of a muscle fiber

What is sarcoplasm?

Cytoplasm of the muscle fiber

What are transverse tubules (T tubules) and what is their function?

• Are narrow tubes whose surfaces are continuous with the sarcolemma and extend deep into the sarcoplasm

• Transmit electrical impulses (action potentials) from the sarcolemma into the cell interior to ensure a coordinated contraction of the entire cell

What are action potentials and what do they trigger in muscle fibers?

• Electrical Impulses

• Contractions

What is the sarcoplasmic reticulum?

• A tubular network similar to the smooth endoplasmic reticulum

What are terminal cisternae?

• Chambers that attach to T tubules

What structures form a triad?

• Two terminal cisternae plus a T tubule

What ions are stored and released by the sarcoplasmic reticulum?

• Calcium

Myofibrils consist of bundles of protein filaments called myofilaments. What is the primary protein that makes thin filaments? What is the primary protein that makes thick filaments?

• Actin makes thin

• Myosin makes thick

Scattered among the myofibrils are mitochondria and granules of glycogen. What is the function of these in myofibrils?

• They are responsible for skeletal muscle fiber contraction

What is a sarcomere?

• Thin and thick myofilaments are organized into repeating structural and functional units

Sarcomeres contain A bands and I bands. Which of these is thick and which is thin?

Which band, A or I, contain regions of overlapping thick and thin filaments?

Which band, A or I, contains thin filaments but no thick filaments?

• A bands is thick and I bands is thin

  • A bands: Contain regions of overlapping thick and thin filaments

  • I bands: Contains thin filaments but no thick filaments

What ion must bind to receptors on troponin to change the position of the troponin–tropomyosin complex? What does the change in position of the complex expose on G-actin?

• Calcium Ions

• Active Sites

What theory explains muscle contraction?

The Sliding-Filament Theory

What is the resting membrane potential for skeletal muscle fibers?

• - 85mV

What is the threshold potential value in mV of a muscle fiber?

• From - 85mV to - 55mV

What membrane channels open once the muscle fiber’s plasma membrane reaches the threshold potential?

Opening of these channels cause what ions to enter the cell?

• Voltage-gated sodium ion channels

  • Sodium ion

    • Depolarization

Once the muscle fiber’s membrane reaches +30mV, repolarization occurs. What channels close, what channels open, what ion is involved, and which way do the ions travel?

• Close: Voltage-gated sodium ion channels

• Open: Voltage-gated potassium ion

  • Potassium travel out of the cell

What pump is used to restore the initial concentrations of sodium and potassium in the cell during the refractory period?

• Sodium–potassium ion pumps

What is a neuromuscular junction (NMJ)? What three structures make up the NMJ?

• Synapse: The location where communication between a neuron and another cell

  • Axon terminal: expanded end of the axons of the motor neuron

  • Synaptic cleft: Narrow space between the axon

    terminal and the motor end plate

Which neurotransmitter is released into the synaptic cleft by a motor neuron axon terminal? You must know the name and the abbreviation.

• Neurotransmitter

  • acetylcholine (ACh)

When acetylcholine (ACh) binds to a membrane channel receptor on the motor end plate of the muscle fiber, which channels open? Make sure you state the type of channel and the ion.

• Chemically gated Na+ channel

  • Na+ ions

What are two ways that ACh is removed from the synaptic cleft?

• Diffusion

• Broken down by acetylcholinesterase (AChE) into choline and acetate

What enzyme breaks down ACh?

• Acetylcholinesterase (AChE)

Which transport mechanism is used to transfer acetylcholine out of the axon terminal?

• Transferred out of the axon terminal via exocytosis, a Ca²⁺-dependent process

What kind of molecule released by Clostridium causes tetanus?

• Tetanospasmin

What is the common name for tetanus?

• Lockjaw

What is excitation-contractions coupling?

• A muscle contraction

Cocking the myosin head requires energy. What energy source is used?

• Energy

At the beginning of the contraction cycle, what breakdown products of ATP remain bound to the myosin head?

ADP and phosphate

What forms a cross-bridge?

Once the active sites are exposed the energize myosin heads bind forming the bridge

What occurs when ADP and phosphate are released from the myosin head?

• The power stroke

What happens to allow cross-bridge detachment to occur?

• When another ATP binds to the myosin head

How does myosin reactivation occur?

When a free myosin head splits ATP into ADP and phosphate

List two mechanisms that are used to quickly return calcium levels in a muscle fiber to normal.

• Active Ca2+ transport into the SR

• Active Ca2+ transport across the sarcolemma into the extracellular fluid

What is a muscle twitch?

• A single stimulus- contraction-relaxation

  sequence

What is treppe, also known as the staircase effect?

• As a phenomenon in muscle contraction where the force of each successive contraction increases gradually when a muscle is stimulated with identical stimuli at a low frequency

What is wave summation?

• Increasing tension due successive stimuli that arrive before the relaxation phase has been completed

What is tetanus (not relating to lockjaw)?

• Maximum tension

What is the difference between incomplete and complete tetanus?

• One is near-maximum tension due to rapid cycles of contraction and very brief incomplete relaxation

• and the other

• is in continuous contraction due to high stimulation frequency which eliminates the relaxation phase

What is a motor unit?

• A motor neuron and all the muscle fibers it controls

What size motor units are in areas of the body that require precise movements?

• Small

What is recruitment?

• The increase in muscle tension due to the increase of active motor units

What is muscle tone?

• The resting tension of a skeletal muscle

What occurs to the muscle length when muscle tension is increased during an isotonic contraction?

• It shortens

What occurs to the muscle length when muscle tension is increased during an isometric contraction?

• It elongates

What is the function of creatine phosphate?

To participate in a reaction that provides energy to convert ADP back to ATP during a contraction

What is the function of creatine kinase?

To catalyze a reaction that takes ADP and creatine phosphate And produces ATP and creatine.

What are glycogen reserves in the sarcoplasm used for?

• When the muscle fiber begins to run short of ATP and creatine phosphate, enzymes split the glycogen molecules, releasing glucose, which can be used to generate more ATP.

What are pyruvate molecules produced by glycolysis converted to if oxygen cannot enter cells fast enough to support aerobic metabolism?

• Lactate

What is oxygen debt?

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

Active skeletal muscles release heat. What is the heat used for?

• Maintain normal body temperature

Which type of muscle fiber fatigues quickest due to relatively few mitochondria?

• Fast fibers

Which type of muscle fiber contains numerous mitochondria and myoglobin?

• Slow fibers

What is the difference between muscle hypertrophy and atrophy?

• One is muscle growth from heavy training

• and the other is

• reduction of muscle size, tone, and power due to lack of activity

List differences when comparing skeletal muscles and cardiac muscle. Focus on size, number of nuclei, branching, intercalated discs.

Size:

• Skeletal: Long

• Cardiac: Small

Number of nuclei:

• Skeletal: Multiple

• Cardiac: Singular

Branching:

• Skeletal: Unbranched

• Cardiac: Branched

Intercalated discs:

• Skeletal: Absent

• Cardiac: Present

What is an intercalated disc? How do they affect cardiac rhythm?

• Specialized connections that join the sarcolemmas memes of adjacent cardiac muscle cells by gapped junctions and desmosomes

  • Allow ions to move from one cell to the other

    • Enabling the cardiac muscle cells to beat in rhythm

What is automaticity in cardiac muscles?

• Able to contract without neural stimulation

What is the function of pacemaker cells in cardiac muscle?

• Generate the electrical signals that initiate contraction

Are cardiac muscle contractions voluntary or involuntary?

• Involuntary

What is the general function of smooth muscle?

• Coordinate the movement of substances through internal passageways

List several differences when comparing smooth muscle to skeletal muscle. Focus on spindle shape, nuclei, presence of T tubules, striations.

• Spindle shape:

  • Smooth: Long, slender

  • Skeletal: Cylindrical, long

• Nuclei:

  • Smooth: Singular

  • Skeletal: Multiple

• Presence of T tubules:

  • Smooth: Absent

  • Skeletal: Present

• Striations:

  • Smooth: Nonstriated

  • Skeletal: Striated

In skeletal and cardiac muscles, the trigger for contraction is the binding of calcium ions to troponin. What is the trigger for smooth muscle contraction?

• Appearance of free calcium ions in the cytoplasm

What is the name of the calcium binding protein in the sarcoplasm of smooth muscle?

• Calmodulin

What enzyme is activated by calmodulin, which enables myosin heads to attach to actin?

• Myosin light chain kinase

Are smooth muscle contractions voluntary or involuntary?

• Involuntary

Which type of muscle tissue has the greatest effect on the body's heat production?

Skeletal

The dense layer of connective tissue that surrounds an entire skeletal muscle is the

Epimysium

A(n) ________ is a broad, tendinous sheet.

Aponeurosis

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

Tendon

Titin is a(n) __________.

elastic protein

The muscle action potential penetrates deep into a fiber along the __________.

Transverse Tubules

Skeletal muscle is multinucleated because it

produces large amounts of muscle proteins.

Muscle fibers differ from "typical cells" in that muscle fibers

are multinucleate.

The area in the center of the A band that contains only myosin is the

H band

The region of the sarcomere that always contains thin filaments is the

I band

The most important factor in decreasing the intracellular concentration of calcium ion after contraction is

active transport of calcium into the sarcoplasmic reticulum.

After death, muscle fibers run out of ATP and calcium begins to leak from the sarcoplasmic reticulum into the sarcoplasm. This results in a condition known as

rigor mortis.

How would the loss of acetylcholinesterase from the motor end plate affect skeletal muscle?

It would cause muscles to stay contracted.

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 muscle's ability for contraction

Cross bridge detachment is caused by ________ binding to the myosin head.

ATP

Which of the following is not true of acetylcholine?

It enters the muscle fiber to release calcium.

Put the following events of the neuromuscular junction in the order in which they occur.

1. Action potential is propagated in the sarcolemma.

2. Acetylcholine binds to ligand gated sodium channels.

3. Action potential arrives at the neuromuscular junction.

4. Vesicles full of acetylcholine are stored at the axon terminal.

5. Acetylcholine is released into the synaptic cleft.

4,3,5,2,1

Put the following events of the contraction cycle in the order in which they occur.

1. Cross-bridge detachment

2. Cross-bridge formation

3. Active site exposure

4. Myosin reactivation

5. Calcium ions bind troponin

6. Myosin head pivoting

5,3,2,6,1,4

A muscle producing its maximum tension for a prolonged period is in __________.

Complete tetanus

What happens to sarcomere length if the zone of overlap is decreased? (Figure 10-14)

sarcomere length increases

If a second stimulus arrives before the relaxation phase has ended, a second, more powerful contraction occurs. This addition of one twitch to another is called

wave summation

What can the nervous system do to increase muscle tension?

All of the listed responses can increase muscle tension

The increase in muscle tension that is produced by increasing the number of active motor units is called

recruitment