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MUSCLE and MOVEMENTChapters 20, 8, 21

1. LocomotionA. Movement

B.

2. RepositioningA.

3. Internal movementA.

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Muscle Cells

1. Contractile

2. Myocytes

3. StriatedA. Skeletal

B. Cardiac

4. Smooth

5. Striated is voluntary

6. Smooth is involuntary

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The Musculoskeletal system

1. Provides the basic form and shape of the organism

2. Support

3. Protection

4. Body movement

5. Heat production

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Skeletal Muscle

1. Bundles of muscle fibers

2. Attaches via connective tissue to bone

3. Antagonistic muscle groups

bicepstriceps

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Figure 20.1 The organization of skeletal muscles

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Figure 20.1 The organization of skeletal muscles

Muscle fiber

MYOFYBRIL

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MYOFYBRIL

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Figure 20.2 Thick (myosin) and thin (actin) myofilaments are arranged in parallel in a sarcomere

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Figure 20.3 Muscle contraction produced by sliding filaments

1. Myosin heads pull on thin filaments

2. Sarcomere unit shortens

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Figure 20.4

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Fig 20.5 Molecular interactions that underlie muscle contraction

1.Rigor Conformation

2 Breaking the Cross-bridge

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3. Hydrolyzing the ATP causes the angle of the head to change

4 And bind to the actin

145. power stroke

6 The myosin unbinds ADP and remains bound to the actin

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Thin Filament

1. ACTINA. binding site for myosin

2. Two regulatory proteins A. TROPOMYOSIN

B. TROPONIN

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Figure 20.6 The regulation of contraction

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MUSCLE, HOW IT WORKS

1. Sequence of events in stimulation and contraction of muscle

A. Stimulation

B. Contraction

C. Relaxation

D. Rigor mortis happens when ATP is gone and myosin heads bind permanently to actin filaments

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Sarcolemma

(Sarcolemma)

1. Sarcolemma.

2. T (transverse) tubule

3. Sarcoplasmic reticulum:

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Microscopic structure of skeletal muscle cell

T-tubules with sarcomere unit

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Figure 20.7 Excitation–contraction coupling

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Figure 20.7 Excitation–contraction coupling

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Figure 20.7 Excitation–contraction coupling

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Fig. 20.9 Myogram: graph of a muscle contraction.

1. In isometric contraction muscle does not shorten

2. In isotonic contraction, the muscle shortens as it moves a constant load

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Fig. 20.10 Summation and Tetanus

1. Twitch

2. Summation

3. Tetanus

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Box 20.1 The electric eel Electrophorus electricuspossesses both strong and weak electric organs

1.Electric organs – modified skeletal muscle

2.Electrocytes – stacked in columns

A.Respond to signals from motor neurons

B.All electrocytes in column depolarize spontaneously

C.Up to 600 V discharge

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Muscle, How It Works: Contraction1. Energy Sources

A. glucose., glycogen, fat2. Anaerobic respiration (glycolysis)

A. 2 ATP/glucoseB. Lactic acidC. Rapid

3. Aerobic respiration (Fig. 20.13)A. 36 ATP/glucoseB. only enough ATP for 2-4 seconds of work

a. creatine phosphate, which converts into ATPb. glycogen and fat are also kept in cell for longer workc. even longer work gets energy from metabolism of food

and fat stores in the liver

1. Oxygen debt (Fig. 8.6)A. if not enough oxygen, glycogen is

metabolized anerobically and lactic acid builds up until muscle can’t work

2. Muscle Fatigue (Fig. 8.8)

3. Muscle cramps

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Classification of Skeletal Muscle Fibers

1. Tonic Fibers do not generate action potentials

A. Relatively rareB. Mainly in postural muscles of lower

vertebrates C. Slow cross-bridge cycling produces long

sustained

2. Twitch Fibers generate action potentials

Twitch Muscles: Fig. 8.13

1. Fast glycolytic fibers (FG) A. Contract quickly, generate lots of power. Mainly

fueled by glycolysis; high levels of glycolytic enzymes & low mitochondrial volume.

2. Slow oxidative fibers (SO): A. Contract relatively slowly. primarily fueled by

oxidative metabolism, high levels of aerobic enzymes and lots of mitochondria and myoglobin.

B. High levels of myoglobin and mitochondria make SO fibers more resistant to fatigue

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Figure 20.14 Whole muscles typically consist of mixtures of different types of fibers

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The Motor Unit (Fig 20.15)

1. one somatic motor neuron & all the skeletal muscle cells (fibers) it stimulates

A. One nerve cell supplies on average 150 muscle cells that all contract in unison.

2. muscle fiber in contact with only one motor neuron

3. When a motor neuron fires, all muscle fibers in the motor unit contract.

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Figure 20.15 Total strength of a contraction

depends on how many motor units

are activated & how large the motor

units are

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1. Graded Contraction A. Contractions of muscle fibers are all or none

B. Vary the frequency of action potentials

C. Rate of stimulation that is very fast results in tetanus

D. The neuron can cause many muscle fibers to contract at the same time

2. Muscle ForceA. proportional to cross-sectional diameter and

sarcomere length

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1. Graded Contraction A. Contractions of muscle fibers are all or none

B. Vary the frequency of action potentials

C. Rate of stimulation that is very fast results in tetanus

D. The neuron can cause many muscle fibers to contract at the same time

2. Muscle ForceA. proportional to cross-sectional diameter and

sarcomere length

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Skeletal muscle

1. attaches to bone, skin or fascia

2. striated with light & dark bands visible with scope

3. voluntary control of contraction & relaxation

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Cardiac Muscle

1. Striated

2. Short, branched fibers joined end-to-end A. gap junctions pass the electrical signal for

contraction

3. Contraction in one part sends wave of contraction throughout

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Cardiac Muscle

1. Contracts rhythmically

2. Sustained contraction is not possible

3. more mitochondria, works non-stop

4. Vertebrates are Myogenic

5. in some invertebrates it is controlled by the brain (neurogenic)

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Smooth Muscle

1. Small, involuntary muscle cellsA. autonomic nervous system,

hormones, local chemicals

2. Tapering at ends

3. Single, oval, centrally located nucleus

4. found in organs and blood vessels

5. Slow, regular contractions

6. Prolonged contractions

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Smooth Muscle

1. actin and myosin structure2. fibers are not in register with each other3. Sliding of thick & thin filaments

transferred to intermediate filaments & dense bodies attached to sarcolemma

4. Muscle fiber contracts and twists into a helix as it shortens

5. relaxes by untwisting