The document summarizes key aspects of muscle contraction and function. It describes how motor neurons stimulate skeletal muscles to contract via motor units. It explains the neuromuscular junction and how the neurotransmitter acetylcholine is released, causing sodium to rush into muscle cells and generate an action potential for contraction. It outlines the sliding filament theory where myosin binds actin fibers and pulls them inward, shortening the muscle. Finally, it notes how exercise increases muscle size, strength and endurance through aerobic or resistance training.

1. PowerPoint®
Lecture Slide Presentation
by Patty Bostwick-Taylor,
Florence-Darlington Technical College
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
PART B
6
The Muscular
System

2. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
The Nerve Stimulus and Action Potential
 Skeletal muscles must be stimulated by a motor
neuron (nerve cell) to contract
 Motor unit—one motor neuron and all the skeletal
muscle cells stimulated by that neuron

3. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
The Nerve Stimulus and Action Potential
 Neuromuscular junction
 Association site of axon terminal of the motor
neuron and muscle

4. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
The Nerve Stimulus and Action Potential
Figure 6.5a

5. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
The Nerve Stimulus and Action Potential
 Synaptic cleft
 Gap between nerve and muscle
 Nerve and muscle do not make contact
 Area between nerve and muscle is filled with
interstitial fluid

6. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
The Nerve Stimulus and Action Potential
Figure 6.5b

7. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Transmission of Nerve Impulse to Muscle
 Neurotransmitter—chemical released by nerve
upon arrival of nerve impulse
 The neurotransmitter for skeletal muscle is
acetylcholine (ACh)
 Acetylcholine attaches to receptors on the
sarcolemma
 Sarcolemma becomes permeable to sodium (Na+)

8. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Transmission of Nerve Impulse to Muscle
 Sodium rushes into the cell generating an action
potential
 Once started, muscle contraction cannot be
stopped

9. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
The Sliding Filament Theory
of Muscle Contraction
 Activation by nerve causes myosin heads (cross
bridges) to attach to binding sites on the thin
filament
 Myosin heads then bind to the next site of the thin
filament and pull them toward the center of the
sarcomere
 This continued action causes a sliding of the
myosin along the actin
 The result is that the muscle is shortened
(contracted)

10. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
The Sliding Filament Theory
of Muscle Contraction
Figure 6.7a–b

11. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Effect of Exercise on Muscles
 Exercise increases muscle size (by increasing
muscle fiber size, NOT increasing # of muscle
fibers), strength, and endurance
 Aerobic (endurance) exercise (biking, jogging)
results in stronger, more flexible muscles with
greater resistance to fatigue
 Makes body metabolism more efficient
 Improves digestion, coordination
 Resistance (isometric) exercise (weight lifting)
increases muscle size and strength

12. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Effect of Exercise on Muscles
Figure 6.11