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Essentials of Human Anatomy & Physiology
Elaine N. Marieb
Seventh Edition
Chapter 6
The Muscular System
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
The Muscular System
 Essential function is contraction (shorten)
 Three basic muscle types are found in the body
 Skeletal muscle
 Cardiac muscle
 Smooth muscle
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.1
Role of Muscles in the Body
 Produce movement
 Maintain posture
 Stabilize joints
 Generate heat
 Propel Substances
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.8
Skeletal muscle
• Functions
– Locomotion and breathing
– Maintain posture
– Heat production
• Form smooth contours of
body
• Vary in shape (spindle, fan
or circle shape)
Skeletal Muscle Characteristics
 Striated – have visible banding
 Cells are multinucleate
 Voluntary – subject to conscious control
 Attached to bones
 Slow to fast contraction
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.3
Skeletal Muscle Activity
• Contract rapidly but tire
easily
• Can exert much power
without ripping
• Cells are surrounded by
connective tissue
• Adds strength and
support
Connective Tissue Wrappings of
Skeletal Muscle
 Notice how
Skeletal muscle
looks like a
cross section of
fiber optic
cable.
Figure 6.1
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.4a
Smooth muscle
• Lines walls of hollow
organs
• Ex: stomach, bladder
• Two layers
• Causes Peristalsis
• Function:
– Propels substances
along a tract
Smooth Muscle Characteristics
 No striations
 Single nucleus
 Involuntary – no
conscious control
 Found mainly in
the walls of hollow
organs
 Slow contraction
Figure 6.2a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.6
Cardiac muscle
• Pumping mass of heart
• Arranged in spiral or
figure 8 shape
• Heart muscle cell
behave as one unit
• Heart muscle always
contracts to it’s full
extent
Cardiac Muscle Characteristics
 Striations
 Single nucleus
 Involuntary
 Found only in the heart
 Contracts at slow, steady rate
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.7
Properties of Skeletal Muscle
Fibers
 Irritability – ability to receive and
respond to a stimulus
 Contractility – ability to shorten when an
adequate stimulus is received
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.13
Transmission of Nerve Impulse to
Muscle
 Neurotransmitter – chemical released
by nerve upon arrival of nerve impulse
 The neurotransmitter for skeletal muscle is
acetylcholine
 Neurotransmitter attaches to receptors
on the sarcolemma
 Sarcolemma becomes permeable to
sodium (Na+)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Transmission of Nerve Impulse to
Muscle
 Sodium rushing into the cell generates
an action potential
 Once started, muscle contraction
cannot be stopped
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Contraction of a Skeletal Muscle
 Muscle fiber contraction is “all or none”
 Not all fibers may be stimulated at the
same time
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Slide 6.19
Contraction of a Skeletal Muscle
 Muscle force depends upon the number
of fibers stimulated
 More fibers contracting results in
greater muscle tension
 Muscles can continue to contract unless
they run out of energy
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.22
2.
Energy for Muscle Contraction
a. Initially, muscles use stored ATP for energy
i.
ATP bonds are broken to release energy
ii. Only 4–6 seconds worth of ATP is
stored by muscles
b. After this initial time, other pathways must
be utilized to produce ATP
Energy for Muscle Contraction
c. Direct phosphorylation of ADP by
creatine phosphate (CP)
i.
Muscle cells store CP
i.
CP is a high-energy molecule
ii. After ATP is depleted, ADP is left
iii. CP transfers energy to ADP, to
regenerate ATP
iv. CP supplies are exhausted in less
than 15 seconds
Energy for Muscle Contraction
Figure 6.10a
Energy for Muscle Contraction
d. Aerobic respiration
i.
Glucose is broken down to carbon
dioxide and water, releasing energy
(ATP)
ii. This is a slower reaction that requires
continuous oxygen
iii. A series of metabolic pathways occur
in the mitochondria
Energy for Muscle Contraction
Figure 6.10b
Energy for Muscle Contraction
e. Anaerobic glycolysis and lactic acid formation
i.
Reaction that breaks down glucose without
oxygen
ii. Glucose is broken down to pyruvic acid to
produce some ATP
iii. Pyruvic acid is converted to lactic acid
f.
This reaction is not as efficient, but is fast
i.
Huge amounts of glucose are needed
ii. Lactic acid produces muscle fatigue
Energy for Muscle Contraction
Figure 6.10c
Muscle Fatigue and Oxygen Debt
 When a muscle is fatigued, it is unable to
contract
 The common reason for muscle fatigue is
oxygen debt
 Oxygen must be “repaid” to tissue to remove
oxygen debt
 Oxygen is required to get rid of accumulated
lactic acid
 Increasing acidity (from lactic acid) and lack
of ATP causes the muscle to contract less
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.27
4.
Types of Muscle Contractions
a. Isotonic contractions
i.
Myofilaments are able to slide past each
other during contractions
ii. The muscle shortens and movement
occurs
b. Isometric contractions
i.
Tension in the muscles increases
ii. The muscle is unable to shorten or
produce movement
C.
Naming Skeletal Muscles
1. By direction of muscle fibers
a. Example: Rectus (straight)
2. By relative size of the muscle
a. Example: Maximus (largest)
3. By location of the muscle
a. Example: Temporalis (temporal bone)
4. By number of origins
a. Example: Triceps (three heads)
Naming Skeletal Muscles
5. By location of the muscle’s origin and insertion
a. Example: Sterno (on the sternum)
6. By shape of the muscle
a. Example: Deltoid (triangular)
7. By action of the muscle
a. Example: Flexor and extensor (flexes or extends
a bone)
Muscles and Body Movements
 Muscles are
attached to at
least two points
 Origin –
attachment to a
moveable bone
 Insertion –
attachment to an
immovable bone
Figure 6.12
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Effects of Exercise on Muscle
 Results of increased muscle use
 Increase in muscle size
 Increase in muscle strength
 Increase in muscle efficiency
 Muscle becomes more fatigue resistant
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 6.31
Types of Ordinary Body
Movements
 Complete Exercise Lab
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Slide 6.32
Disorders relating to the
Muscular System
• Muscular Dystrophy: inherited, muscle
enlarge due to increased fat and connective
tissue, but fibers degenerate and atrophy
• Duchenne MD: lacking a protein to
maintain the sarcolemma
• Myasthemia Gravis: progressive weakness
due to a shortage of acetylcholine receptors