Chapter 2 Structure of Muscle Tissue and Muscle Contraction

Chapter 2 Structure of Muscle Tissue

and Muscle Contraction

Key Concepts

• “A” band• acetylcholine (ACH)• actin• action potential• adenosine

triphosphate (ATP)• cardiac muscle• cross-bridge recycli

ng

• cross-bridges• endomysium• epimysium• fasciculus• fast twitch glycotic

(FG)• fast twitch oxidative

glycotic (FOG)• H zone

• I band• mitochondria• motor unit• myofibrils• myofilaments• myosin• myosin ATPase

• neuromuscular junction

• perimysium• sarcolemma• sarcomere• sarcoplasm• sarcoplasmic

reticulum• skeletal muscle

• sliding filament model

• slow twitch oxidative (SO)

• smooth muscle

• synapse• tropomyosin• troponin• Z-line

Review Questions

Name the three types of human muscle tissue. Where are they found?

• Smooth, nonstriated muscle is found in the walls of the hollow viscera and blood vessels.

• Skeletal, striated muscle is attached to the skeleton and provides the force for movement of the bony leverage system.

• Cardiac, striated muscle is found only in the heart.

What nervous system innervates smooth muscle?

The autonomic nervous system

What nervous system innervates skeletal muscle?

The voluntary or somatic nervous system

Cardiac muscle contracts rhythmically and automatically, without ________.

outside stimulation

Describe the structure of smooth muscle.

• Long, spindle-shaped fibers.

• External shape may change to conform to the surrounding elements.

• Each fiber usually has only one nucleus.

Name four characteristics of the structure of skeletal muscle.

• Long, cylindrical muscle fibers.

• Each fiber is a large cell with up to several hundred nuclei.

• Each cell is structurally independent of its neighboring fiber or cell.

• The muscle has cross-striations of alternating light and dark bands.

Name three characteristics of the structure of cardiac muscle.

• A network (syncytium) of striated muscle fibers.

• Made up of discrete fibers that can contract individually.

• The network of fibers responds to innervation with a wavelike contraction that passes through the entire muscle.

In the following diagram of skeletal muscle, what do A, B, C, and D refer to?

A.B.C.D.

Fascia

EpimysiumFasciculusPerimysium

CB

DA

In the following diagram of an individual skeletal muscle fiber, what do A, B, C, and D refer to?

A.B.C.D.

EndomysiumSarcolemmaSarcoplasmMyofibrils

A

BC

D

• The motor unit consists of– A motor neuron– All the fibers the neuron innervates

• Do small muscles have few or many fibers?– Few

• Do large muscles have few or many fibers?– Many

• Muscles fibers within a motor unit are the same or different types?– Same

What are the three primary fiber types in human skeletal muscle?

• Slow twitch oxidative (SO)

• Fast twitch oxidative glycolytic (FOG)

• Fast twitch glycolytic (FG)

What are the characteristics of SO fibers?

1. Speed of contraction2. Strength of

contraction3. Fatigability4. Aerobic capacity5. Anaerobic capacity6. Size7. Capillary density

SlowLow

Fatigue resistantHighLow

Small

High

What are the characteristics of FG fibers?



Fast

Low

LargeHigh

Low

Most fatigable

High

What are the characteristicsof FOG fibers?



Fast

High

LargeMedium

Medium

Fatigable

High

There are significant differences between men and women with regard to fiber type distribution patterns. True or False?

False

Our fiber type pattern is genetically determined. True or False?

True

How can training affect muscle fiber?

Within fast twitch fibers, endurance andresistance training result in a shift from

FG toFOG fibers.

A person with a high percentage of SO fibers would be a good candidate for what sort of sports?

This person would be a good candidatefor distance running or other

enduranceevents, because SO fibers are highlyfatigue resistant.

A person with a high percentage of fast twitch (FT) fibers would be a good candidate for what sort of sports?

This person would be most successful inpower and sprint events.

In the following diagram of a sarcomere, what do the letters A through F correspond to?

A.B.C.D.

Z-Line

A bandH zoneI band

BD D

CA A A A

What is the series of events that leads to muscle contraction in the sliding filament model?

1. Neural stimulation causes the sarcoplasmic reticulum to release calcium.

2. Calcium binds to troponin, which removes the inhibitory effect of tropomyosin and actin-myosin bind.

3. Myosin cross-bridges swivel, pulling the actin and z-lines.

4. Fresh ATP binds to the myosin cross-bridges, leading to cross-bridge recycling.

5. Neural stimulation ceases and relaxation occurs

At Rest• Tropomyosin inhibits actin-myosin binding.• Calcium is stored in the sarcoplasmic reticulum.

Contraction

Fill in the blanks for the sliding filament model1. travels along to2. releases into and binds

to

3. creates that travels along the

4. moves into the through5. intersects with releasing

into the6. binds with which is bound to7. causes change in shape to

uncovering8. binds with9. breaks down to and providing

used in

Electrical impulse

motor neuron

end bulb.ACH synaps

eACH

motor end plate.

ACH binding

action potentialsarcolemma.

Action potential muscle fiber

t-tubules.Action potential sarcoplasmic reticulum

calcium sarcoplasm.

Calcium troponin tropomyosin.

Calcium-troponin bindingtropomyosin

moleculebinding sites on the actin molecule.Myosin cross-

bridgeactin molecule.

ATP

ADP inorganic phosphatemuscle contraction.

End bulb

energy

Explain Theory 1 regarding the way in which energy from the breakdown of ATP is used in muscle contraction.

1. Actin-myosin bind Activates myosin ATPase Breakdown of ATP molecule liberates energy

2. Energy causes myosin cross-bridge to swivel to center of sarcomere Myosin is bound to actin, which is bound to Z-lines Z-lines pulled closer together Sarcomere shortened

3. Fresh ATP molecule binds to myosin cross-bridge Actin-myosin binding released Myosin cross-bridge stands back up

4. Actin-myosin rebinds at new siteActivates myosin ATPase Breakdown of ATP molecule liberates energy

5. And process repeats

Explain Theory 2 regarding the way in which energy from the breakdown of ATP is used in muscle contraction.

1. Myosin cross-bridge stores energy from breakdown of ATP by myosin ATPase Actin-myosin binding releases stored energy

2. Energy causes myosin cross-bridge to swivel ADP and Pi are released from the myosin cross-bridge

3. Fresh ATP molecule binds to myosin cross-bridge Actin-myosin binding released ATP is broken down and energy causes myosin cross-bridge to stand back up (re-energized)

4. Fresh ATP molecule is broken down Energy reenergizes myosin cross-bridge

5. Repeat of process

How is Theory 1 similar to Theory 2 in explaining how energy from the breakdown of ATP is used in muscle contraction?

Both theories state that fresh ATP binds to the

myosin cross-bridge to release it from actin

during cross-bridge recycling.

How do the theories differ in describing how energy from the breakdown of ATP is used in muscle contraction?

Theory 2 states that after the myosin-actin bindingis released, the fresh ATP molecule is broken downand the energy released is used to reenergize themyosin cross-bridge. According to Theory 1, energyis not needed to cause the myosin cross-bridge tostand back up.

Useful Websites

Muscles

www.ultranet.com/~jkimball/BiologyPages/M/Muscles.html

Muscle Physiology—Myofilament Structurehttp://muscle.ucsd.edu/musintro/fibril.shtml

Muscle Histology

www.unomaha.edu/~swick/2740musclehistology.html

Histology of Musclehttp://views.vcu.edu/ana/OB/Muscle~1/index.htm

Selected Images

Figure 2.1 Skeletal muscle fibers showing cross-striations.

Figure 2.2 Muscle fibers and connective tissue sheaths.

Figure 2.3 A sarcomere extends from Z-line to Z-line. Also shown are the A, H, and I bands that give skeletal muscle its striated appearance.

Figure 2.4 Contractile proteins actin, myosin, troponin, and tropomyosin.

Figure 2.5 Aspects of the sliding filament model of muscle contraction.

Documents

Chapter 2 Structure of Muscle Tissue and Muscle Contraction