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Chapter 12a. Muscles. About this Chapter. Skeletal muscle Mechanics of body movement Smooth muscle Cardiac muscle. Three Types of Muscle. Nucleus. Muscle fiber (cell). Striations. (a) Skeletal muscle . Figure 12-1a. Three Types of Muscle. Striations. Muscle fiber. Intercalated disk.

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about this chapter
About this Chapter
  • Skeletal muscle
  • Mechanics of body movement
  • Smooth muscle
  • Cardiac muscle
three types of muscle
Three Types of Muscle

Nucleus

Muscle fiber(cell)

Striations

(a) Skeletal muscle

Figure 12-1a

three types of muscle1
Three Types of Muscle

Striations

Muscle fiber

Intercalated disk

Nucleus

(b) Cardiac muscle

Figure 12-1b

three types of muscle2
Three Types of Muscle

Muscle fiber

Nucleus

(c) Smooth muscle

Figure 12-1c

skeletal muscle
Skeletal Muscle
  • Usually attached to bones by tendons
  • Origin: closest to the trunk
  • Insertion: more distal
  • Flexor: brings bones together
  • Extensor: moves bones away
  • Antagonistic muscle groups: flexor-extensor pairs
antagonistic muscle groups
Antagonistic Muscle Groups

Tricepsmusclerelaxes

Biceps musclecontracts (flexor)

(a) Flexion

Figure 12-2a

antagonistic muscle groups1
Antagonistic Muscle Groups

Triceps musclecontracts (extensor)

Bicepsmusclerelaxes

(b) Extension

Figure 12-2b

organization of skeletal muscle
Organization of Skeletal Muscle

Skeletal muscle

Nerve andblood vessels

Tendon

Connective tissue

Muscle fascicle:bundle of fibers

Connectivetissue

Nucleus

Muscle fiber

(a)

Figure 12-3a (1 of 2)

organization of skeletal muscle1
Organization of Skeletal Muscle

Figure 12-3a (2 of 2)

ultrastructure of muscle
Ultrastructure of Muscle

ANATOMY SUMMARY

ULTRASTRUCTURE OF MUSCLE

Mitochondria

Sarcoplasmicreticulum

Thickfilament

Thinfilament

Nucleus

T-tubules

Myofibril

Sarcolemma

(b)

A band

Sarcomere

Z disk

Z disk

Myofibril

(c)

M line

I band

H zone

Titin

(d)

Z disk

Z disk

M line

Myosincrossbridges

M line

Thick filaments

Thin filaments

Titin

(e)

Troponin

Nebulin

Myosin heads

Hingeregion

Myosin tail

Tropomyosin

G-actin molecule

Actin chain

Myosin molecule

(f)

Figure 12-3b-f

ultrastructure of muscle1
Ultrastructure of Muscle

ULTRASTRUCTURE OF MUSCLE

Mitochondria

Sarcoplasmicreticulum

Thickfilament

Thinfilament

Nucleus

T-tubules

Myofibril

Sarcolemma

(b)

Figure 12-3b

ultrastructure of muscle2
Ultrastructure of Muscle

Sarcomere

A band

Z disk

Z disk

Myofibril

(c)

M line

H zone

I band

Figure 12-3c

ultrastructure of muscle3
Ultrastructure of Muscle

Titin

(d)

Z disk

Z disk

Myosincrossbridges

M line

Figure 12-3d

ultrastructure of muscle4
Ultrastructure of Muscle

M line

Thick filaments

(e)

Myosin

heads

Hinge

region

Myosin tail

Myosin molecule

Figure 12-3e

ultrastructure of muscle5
Ultrastructure of Muscle

Thin filaments

Titin

Troponin

Nebulin

Tropomyosin

G-actin molecule

Actin chain

(f)

Figure 12-3f

ultrastructure of muscle6
Ultrastructure of Muscle

Sarcomere

A band

Z disk

Z disk

Myofibril

(c)

M line

H zone

I band

Titin

(d)

Z disk

Z disk

Myosin

crossbridges

M line

M line

Thick filaments

Thin filaments

Titin

(e)

Troponin

Nebulin

Myosin

heads

Hinge

region

Myosin tail

Tropomyosin

G-actin molecule

Myosin molecule

Actin chain

(f)

Figure 12-3c-f

t tubules and the sarcoplasmic reticulum
T-Tubules and the Sarcoplasmic Reticulum

T-tubule brings actionpotentials into interiorof muscle fiber.

Thin filament

Thick filament

Sarcolemma

Triad

Sarcoplasmic reticulumstores Ca2+

Terminalcisterna

Figure 12-4

the two and three dimensional organization of a sarcomere
The Two- and Three-Dimensional Organization of a Sarcomere

Sarcomere

A band

I band

H zone

I band

Thin filament

Thick filament

(a)

M line

Z disk

Z disk

(b)

Z disk

Z disk

I bandthin filamentsonly

H zonethick filamentsonly

M linethick filamentslinked withaccessory proteins

Outer edgeof A bandthick and thinfilaments overlap

(c)

Figure 12-5

anatomy review animation
Anatomy Review Animation

PLAY

Interactive Physiology® Animation: Muscular System:

Anatomy Review: Skeletal Muscle Tissue

muscle contraction
Muscle Contraction
  • Muscle tension: force created by muscle
  • Load: weight that opposes contraction
  • Contraction: creation of tension in muscle
  • Relaxation: release of tension
  • Steps leading up to muscle contraction:
    • Events at the neuromuscular junction
    • Excitation-contraction coupling
    • Contraction-relaxation cycle
events at the neuromuscular junction
Events at the Neuromuscular Junction

PLAY

Events at the Neuromuscular Junction

PLAY

Interactive Physiology® Animation: Muscular System: Events at the Neuromuscular Junction

changes in a sarcomere during contraction
Changes in a Sarcomere During Contraction

I band

Myosin

Z

Z

A band

Actin

Musclerelaxed

Zline

Z

M

Z

A band

Half ofI band

H zone

Half ofI band

Sarcomere shortenswith contraction

Half ofI band

Mline

Zline

H

Z

Z

A band constant

Musclecontracted

I

H

I

H zone and I band both shorten

Figure 12-8

sliding filament theory
Sliding Filament Theory

PLAY

Interactive Physiology® Animation: Muscular System: Sliding Filament Theory

the molecular basis of contraction
The Molecular Basis of Contraction

Troponin

G-Actin

TN

Myosin head

Tropomyosinblocks bindingsite on actin

ADP

Pi

(a) Relaxed state. Myosin head cocked.

Figure 12-9a

the molecular basis of contraction1
The Molecular Basis of Contraction

1

Cytosolic Ca2+

1

Ca2+ levels increase

in cytosol.

3

Tropomyosin shifts,

exposing binding

site on actin

2

2

Ca2+ binds to

troponin (TN).

TN

3

Troponin-Ca2+

complex pulls

tropomyosin

away from actin’s

myosin-binding site.

5

Actin

moves

ADP

4

Power stroke

Pi

4

Myosin binds to

actin and completes

power stroke.

5

Actin filament

moves.

(b) Initiation of contraction

Figure 12-9b

the molecular basis of contraction2
The Molecular Basis of Contraction

G-actin molecule

Myosinbinding sites

Myosinfilament

ATP binds to myosin.Myosin releases actin.

1

Tight binding in the rigor state

ATP

ADP

Myosin hydrolyses ATP. Myosinhead rotates and binds to actin.

2

Myosin releases ADP.

4

Contraction-relaxation

Actin filament movestoward M line.

Sliding filament

ADP

Pi

Ca2+signal

Pi

Power stroke

3

Relaxed state with myosin heads cocked

Figure 12-10

the molecular basis of contraction3
The Molecular Basis of Contraction

G-actin molecule

Myosin

binding sites

Myosin

filament

Tight binding in the rigor state

Figure 12-10, step 0

the molecular basis of contraction4
The Molecular Basis of Contraction

G-actin molecule

Myosin

binding sites

Myosin

filament

ATP binds to myosin.

Myosin releases actin.

1

T

ight binding in the rigor state

ATP

Figure 12-10, steps 0–1

the molecular basis of contraction5
The Molecular Basis of Contraction

ATP binds to myosin.

Myosin releases actin.

Myosin hydrolyses ATP. Myosin

head rotates and binds to actin.

1

2

ADP

ATP

Pi

Relaxed state with myosin heads cocked

Figure 12-10, steps 1–2

the molecular basis of contraction6
The Molecular Basis of Contraction

Myosin hydrolyses ATP. Myosin

head rotates and binds to actin.

Power stroke

3

2

Actin filament moves

toward M line.

Ca2+

signal

ADP

Pi

Pi

Relaxed state with

myosin heads cocked

Figure 12-10, steps 2–3

the molecular basis of contraction7
The Molecular Basis of Contraction

Power stroke

Myosin releases ADP.

3

4

Actin filament moves

toward M line.

ADP

Pi

Figure 12-10, steps 3–4

excitation contraction coupling
Excitation-Contraction Coupling

Axon terminal of

somatic motor neuron

1

Somatic motor neuron releases

ACh at neuromuscular junction.

1

Muscle fiber

ACh

2

2

Net entry of Na+ through ACh

receptor-channel initiates a

muscle action potential

Na+

Motor end plate

RyR

T-tubule

Sarcoplasmic

reticulum

Ca2+

DHP

Z disk

Troponin

Actin

Tropomyosin

M line

Myosin head

Myosin thick filament

(a) Initiation of muscle action potential

KEY

RyR = ryanodine receptor-channel

DHP = dihydropyridine L-type calcium channel

Figure 12-11a

excitation contraction coupling1
Excitation-Contraction Coupling

Axon terminal of

somatic motor neuron

1

Somatic motor neuron releases

ACh at neuromuscular junction.

1

Muscle fiber

ACh

Motor end plate

RyR

T-tubule

Sarcoplasmic

reticulum

Ca2+

DHP

Z disk

Troponin

Actin

Tropomyosin

M line

Myosin head

Myosin thick filament

(a) Initiation of muscle action potential

KEY

RyR = ryanodine receptor-channel

DHP = dihydropyridine L-type calcium channel

Figure 12-11a, step 1

excitation contraction coupling2
Excitation-Contraction Coupling

Axon terminal of

somatic motor neuron

1

Somatic motor neuron releases

ACh at neuromuscular junction.

1

Muscle fiber

ACh

2

2

Net entry of Na+ through ACh

receptor-channel initiates a

muscle action potential

Na+

Motor end plate

RyR

T-tubule

Sarcoplasmic

reticulum

Ca2+

DHP

Z disk

Troponin

Actin

Tropomyosin

M line

Myosin head

Myosin thick filament

(a) Initiation of muscle action potential

KEY

RyR = ryanodine receptor-channel

DHP = dihydropyridine L-type calcium channel

Figure 12-11a, steps 1–2

excitation contraction coupling3
Excitation-Contraction Coupling

Action potential in t-tubule alters

conformation of DHP receptor.

3

4

DHP receptor opens RyR Ca2+

release channels in sarcoplasmic

reticulum and Ca2+ enters

cytoplasm.

4

3

Ca2+ binds to troponin, allowing

actin-myosin binding.

5

Ca2+ released

7

5

Myosin heads execute power

stroke.

6

6

Actin filament slides toward center

of sarcomere.

Myosin thick filament

7

Distance actin moves

KEY

(b) Excitation-contraction coupling

DHP = dihydropyridine L-type calcium channel

RyR = ryanodine receptor-channel

Figure 12-11b

electrical and mechanical events in muscle contraction
Electrical and Mechanical Events in Muscle Contraction
  • A twitch is a single contraction-relaxation cycle

Muscle fiber

+30

Action potentialfrom CNS

Neuronmembranepotentialin mV

-70

Motorend plate

Time

Recordingelectrodes

+30

Axonterminal

Muscle fibermembranepotentialin mV

Muscle actionpotential

-70

2msec

Time

Latentperiod

Relaxationphase

Contractionphase

Developmentof tensionduring onemuscle twitch

Tension

10–100 msec

Time

Figure 12-12

phosphocreatine
Phosphocreatine

Creatine phosphate

Glycolysis

Krebs cycle

Figure 12-13

causes of muscle fatigue during exercise
Causes of Muscle Fatigue During Exercise
  • Extended submaximal exercise
    • Depletion of glycogen stores
  • Short-duration maximal exertion
    • Increased levels of inorganic phosphate
    • May slow Pi release from myosin
    • Decrease calcium release
  • Maximal exercise
    • Potassium (K+) leaves muscle fiber, leading to increased concentration that is believed to decrease Ca2+