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• Who is this?
• Chelsey
Thomas.
Chapter 11
Muscular System
• What is her
problem?
• Moebius
syndrome?
• A rare disorder
which causes
paralysis of facial
muscles!!!
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Outline
Types and Functions of Muscles
– Smooth
– Cardiac
– Skeletal
Muscle Innervation
Whole Muscle Contraction
– Oxygen Deficit
– Athletics and Muscle Contraction
 Slow and Fast Twitch Fibers
Muscle Disorders
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Types and Functions of Muscles
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Smooth muscle is located in the walls of
hollow internal organs and contracts
involuntarily. (non-striated / involuntary,
visceral muscle)
Cardiac muscle forms the heart wall and
contracts involuntarily. (striated, involuntary)
Skeletal muscle runs the entire length of the
muscle and contracts voluntarily. (striated,
voluntary)
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Types of Muscle
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Functions of Skeletal Muscles
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Support
body.
Movement
of bones.
Maintenance
of constant body temperature.
Assist
movement in cardiovascular and
lymphatic vessels.
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Protect
•internal organs.
•Stabilize
•joints.
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SKELETAL MUSCLES
Macroscopic View
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Skeletal Muscles of the Body
A whole muscle contains bundles of skeletal
muscle fibers (= muscle cells), fascicles.
Muscles are covered with fascia (dense
connective tissue) that becomes tendons.
Muscles originate on the stationary bone
(origin), and insert on the bone that moves
(insertion).
Cooperating muscle pairs have prime
movers, synergists, and antagonists.
Muscles usually work in antagonistic pairs
which work opposite one another to move in
opposite directions.
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Skeletal Muscles of the Body
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Muscles only contract, never push.
Muscle spindles are modified muscle fibers
that have a sensory nerve fiber wrapped
around the middle of the muscle’s length so
as to inform the CNS as to the state of that
muscle for coordination with other muscles
and for posture and muscle tone.
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Names and Actions of Skeletal Muscles
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Skeletal muscles are named based on
characteristics.
– Size.
– Shape.
– Direction of muscle fibers.
– Number of attachments.
– Action.
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SKELETAL MUSCLES
Microscopic View
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Skeletal Muscle Fiber Contraction
 “Sliding Filament Theory”
 When muscle fibers are stimulated to
contract, myofilaments (actin –
anchored on Z line, myosin – in the
middle) slide past one another.
 This causes sarcomeres (muscle units)
to shorten and the whole muscle fiber
shortens.
 Thus, when you see the prefixes myoor sarco-, you will know these refer to
muscles.
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Skeletal Muscle Fiber Contraction
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Myosin filament heads break down ATP and
attach to an actin filament, forming crossbridges that pull the actin filament to the
center of the sarcomere.
– Contraction continues until nerve impulses
cease.
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“Sliding Filament Theory” Video Clips
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Concept 29 - Levels of Muscle Structure
Concept 30 - Sliding Filament Model
Concept 31 - Regulation of Muscle
Contraction
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Muscle Innervation
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Nerve impulses originate in the brain,
travel down motor neurons, and stimulate
muscle fibers at neuromuscular junctions
and muscle fibers are innervated. . . . .
Stimulated to contract by motor nerve
fibers.
 Signaled when nerve impulses bring
about release of neurotransmitter
molecules at a neuromuscular junction.
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Whole Muscle Contraction
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Method of study: when a muscle (frog’s calf
muscle) is attached to a physiograph
(machine), a myogram (a recording) will
result when muscle is stimulated to contract.
Characteristics of muscle contraction: a
muscle fiber, in contrast to a whole muscle,
will behave in an all-or-none manner when
a threshold stimulus is applied.
The force of contraction of a whole muscle
depends upon the number of fibers
contracting.
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Whole Muscle Contraction
Muscle Twitch - Single muscle contraction.
– Divided into three stages.
 Stimulation.
 Contraction.
 Relaxation.
If a muscle is given a rapid series of
threshold stimuli, muscle contraction
summates in a sustained contraction,
tetanus. . . .
which continues until the muscle fatigues
due to depletion of energy reserves.
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Physiology of Whole Muscle Contraction
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Whole Muscle Contraction
A motor neuron, together with all of the
muscle fibers that it innervates, is a motor
unit.
– As the intensity of nervous stimulation
increases, more motor units are activated
(recruitment) resulting in stronger and
stronger contractions.
Also important are the number of muscle
fibers within a motor unit. . . . for example:
– innervation ratio of 1 motor neuron / 23
muscle fibers (eye muscles). . . .
– 1 motor neuron / 1,000 muscle fibers (calf
muscle).
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The Effect of Exercise.
A regular exercise program will bring about
1. Increased endurance 2. Increased
strength of muscles.
Muscle enlarges, not due to increase in
number of muscle fibers, but increased
amounts of actin and myosin myofibrils
inside each muscle fiber making them
bigger and stronger.
“Use it or lose it !”
Benefits include: lower risk of heart attack,
increased capacity of heart and lungs,
decreased body fat and cholesterol levels.
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HEALTH FOCUS
Exercise, Exercise,
Exercise.
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Energy for Muscle Contraction
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ATP produced previous to strenuous
exercise lasts a few seconds.
Then muscles acquire new ATP in three
ways.
– Creatine phosphate (phosphocreatine)
breakdown. (anaerobic)
– Fermentation. (anaerobic)
– Cellular respiration. (aerobic)
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Oxygen Deficit
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When a muscle uses the anaerobic means
of supplying energy, it incurs an oxygen
deficit.
– Repaying an oxygen deficit requires
replenishing creatine phosphate supplies
and disposing of lactic acid.
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Athletics and Muscle Contraction
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Muscles that are not used, or are used in
only weak contractions can atrophy.
– Can cause muscle fibers to progressively
shorten, leaving body parts contracted in
contorted positions.
 Hypertrophy occurs if the muscle
contracts to at least 75% of its
maximum tension.
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Athletics and Muscle Contraction
Although all muscle fibers metabolize both
aerobically and anaerobically, some muscle
fibers utilize one method more than the
other.
Slow-twitch fibers produce most of their
energy aerobically and tire only when their
fuel supply is gone.
Fast-twitch fibers tend to be anaerobic and
seem to be designed for strength as their
motor units contain many fibers.
– Can develop greater, and more rapid,
maximum tension than slow-twitch fibers.
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Ben Johnson, 1988, Olympic gold medal 100-m sprint.
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BIOETHICAL FOCUS
Performance-Enhancing Drugs
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Anabolic steroids to promote muscle growth.
Testosterone or related chemicals.
Danger ! ?
Cardiovascular disease, liver and kidney
dysfunction, impotency and sterility, increase
in rash behavior called “roid mania”.
What is a misconception that some have of
these drugs?
Is becoming a problem with young people!
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Muscle Disorders – Spasms and Injuries
Spasms are sudden, involuntary muscular
contractions most often accompanied by pain.
– Multiple spasms of skeletal muscles are
called a seizure or convulsion.
A strain is an overstretching of a muscle near
a joint, while a sprain is a twisting of a joint
leading to swelling and injury.
Myalgia refers to inflammation (pain) of
muscle tissue.
Tendinitis is inflammation of a tendon due to
the strain of repeated athletic activity
(shoulder, elbow, hip, and knee).
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Muscular Disorders - Diseases
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Infection known as tetanus or lockjaw?
Muscular dystrophy is a broad term applied
to a group of disorders characterized by
progressive muscle degeneration and
weakening (ie. Duchenne MD).
Myasthenia gravis is an autoimmune
disease characterized by weakness that
especially affects the muscles of the eyelids,
face, neck, and extremities.
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Homeostasis
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Cardiac muscle contraction accounts for the
heartbeat, delivering blood to the tissues.
Smooth muscle contraction accounts for
peristalsis and urination.
Skeletal muscle contraction returns blood to
the heart and moves bones, allowing for
body movement.
SEE Human Systems Work Together in
the text.
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Review
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Types and Functions of Muscles
– Smooth
– Cardiac
– Skeletal
Muscle Innervation
Whole Muscle Contraction
– Oxygen Deficit
– Athletics and Muscle Contraction
 Slow and Fast Twitch Fibers
Muscle Disorders
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REVIEW
Remember:
•Use the “Study Questions” in the Student
Study Guide to guide your reading of the text
material before coming to class.
•Use the “Powerpoint handouts” to review
what you read before class and what we
covered in class.
•After studying the material and when you
believe you know and understand it – use the
End-of-Chapter material to check your
understanding.
•Also check your understanding by working in
groups.
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Skeletal Muscles
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Neurotransmitter Junction
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Slow-and-Fast Twitch Muscle Fibers
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