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Warm-Up
1.
2.
Based on what you know about Latin root words, what do you
think these terms refer to?

Sarcomere

Sarcoplasm

Myofibril

Epimysium

Perimysium

Endomysium
What structure connects muscle to bone?
Warm-Up
1.
2.
What is the organization of a skeletal muscle from the largest
to the smallest structures?
Draw and label the parts of a sarcomere. Be sure to include the
thick & thin filaments, I band, A band, and Z lines.
Warm-Up
1.
2.
3.
Describe what happens at the neuromuscular junction.
How would a drug that blocks acetylcholine (ACh) release
affect muscle contraction?
Which of the following pictures below shows a contracted
muscle? Explain your answer.
Warm-Up
Put the following events in muscle contraction in order:
A.
B.
C.
D.
E.
F.
Calcium binds to troponin  changes shape  myosin binding sites
exposed on actin
Myosin head pivots and pulls actin filament toward M line
ATP attaches to myosin and cross-bridge detaches
Action potential travels down sarcolemma along T-Tubules
Myosin cross-bridge forms with actin
Calcium is released from sarcoplasmic reticulum (SR)
Warm-Up
1.
Jay is competing in a chin-up competition. What types of
muscle contractions are occurring in his biceps muscles:
a)
b)
c)
2.
immediately after he grabs the bar?
as his body begins to move upward toward the bar?
when his body begins to approach the mat?
When a suicide victim was found, the coroner was unable to
remove the drug vial from his hand. Explain.
Chapter 8
Muscular System
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Introduction:
A. All movements require muscle which are organs using chemical
energy to contract.
B. The three types of muscle in the body are:
1. Skeletal – voluntary
a. Multinucleated
b. Striation
2. Smooth – involuntary
a. Single nuclei
b. No Striations
3. Cardiac – involuntary
a. Single nuclei
b. Intercalated discs and striations
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 Structure
of a Skeletal Muscle
A. Each muscle is an organ, comprised of:
1. skeletal muscle tissue
2. connective tissue
3. nervous tissue
4. blood
Prefixes:
My/myo  muscle
Sarco  flesh
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B. Connective Tissue Coverings
1. Fascia – dense connective tissue that surrounds and separates
each muscle
2. Tendons – extend past fascia; connect muscle to bone (via
periosteum)
3. Aponeuroses – broad sheets of connective tissue that connect
muscle
4. Epimysium – connective tissue that surrounds each whole
muscle
5. Perimysium – surrounds individual bundles (fascicles) within
each muscle
6. Endomysium – connective tissue covering each muscle cell
(fiber)
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Study Analogy
Pretend you are going to play a joke on someone and give them
100 pencils. The pencils will represent muscle fibers. First you
wrap each individual pencil in tissue paper (dense tissue paper
of course!). This would be endomysium. Then you take about
10 pencils in a bundle (a fascicle) and wrap them in paper
(perimysium). After that you take all the bundles and wrap
them in gift wrap (epimysium). But you are going to mail this
joke, so you also have to wrap it in brown paper
representing the fascia.
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C. Skeletal Muscle Fibers
1. Each muscle fiber is a single, long, cylindrical muscle cell.
2. Beneath the sarcolemma (cell membrane) lies sarcoplasm
(cytoplasm) with many mitochondria and nuclei; the sarcoplasm
contains myofibrils  key role in muscle contractions and made
up of:
a. Myosin  Thick protein filaments
b. Actin  Thin protein filaments
c. The organization of these filaments produces striations.
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3. Sarcomere extends from Z line to Z line.
a. I bands (light bands) made up of actin filaments are
anchored to Z lines.
b. A bands (dark bands) are made up of overlapping thick
and thin filaments.
c. In the center of A bands is an H zone, consisting of
myosin filaments only.
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4. Sarcoplasm composed of:
a. Sarcoplasmic reticulum (SR) – surround each
myofibril and run PARALLEL to it
b. Transverse (T) tubules – run perpendicular to SR;
passes all way through myofibril
1. lies between two cisternae of SR
2. open to the outside of the muscle fiber
BOTH ACTIVATE THE MUSCLE CONTRACTION
MECHANISM
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D. Neuromuscular Junction (NMJ)
1. Site where the motor neuron and muscle fiber meet
a. Motor neuron  nerve cell that connects to a muscle
fiber
b. Axon  appendage of nerve cell
c. Motor end plate  area where nuclei and mitochondria
are abundant
d. Synaptic vesicles  store neurotransmitters (ex.
Acetylcholine)
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E. Motor Units
1. Collective name for the motor neuron and muscle fiber
working together to cause a muscle contraction
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Skeletal Muscle Contraction
A. Shortening of sarcomeres and pulling of the muscle against
its attachments
B. Role of Myosin and Actin
1. Myosin  protein consists of cross-bridges
2. Actin  protein with myosin binding sites
a. Tropomysosin and Troponin two proteins of the
actin filament
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3. Sliding filament theory
a. Myosin cross-bridge attaches to the binding site on
the actin filament and bends  pulling on the actin
filament
b. It then releases and attaches to the next binding site
on the actin  pulling again.
4. Energy from the conversion of ATP to ADP is provided to
the cross-bridges from the enzyme ATPase, causing them
to be in a “cocked” position.
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C. Stimulus for Contraction
1. The motor neuron must release the
neurotransmitter acetylcholine from its synaptic vesicles into
the synaptic cleft in order to initiate a muscle contraction.
2. Protein receptors in the motor end plate detect the
neurotransmitters, and a muscle impulse spreads over the
surface of the sarcolemma and into the T tubules, where it
reaches the sarcoplasmic reticulum.
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3. Upon receipt of the muscle impulse, the sarcoplasmic
reticulum releases its stored calcium to the sarcoplasm of the
muscle fiber.
4. The high concentration of calcium in the sarcoplasm
interacts with the troponin and tropomyosin molecules, which
move aside, exposing the myosin binding sites on the actin
filaments.
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5. Myosin cross-bridges now bind and pull on the actin
filaments, causing the sarcomeres to shorten.
6. After the nervous impulse has been received,
acetylcholinesterase rapidly decomposes the acetylcholine.
7. Then, calcium is returned to the sarcoplasmic reticulum, and
the linkages between myosin and actin are broken.
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Study Analogy: Think of a very familiar love story. The actin
and myosin are in love and would love to bind (keep it clean,
think kiss). However, the actin is being guarded by the troponin
and tropomyosin (T-T complex), perhaps they are her parents or
guardians? But someone is looking out for the love birds,
maybe a fairy godmother? They send a messenger in the form
of a nerve impulse. This messenger isn’t someone allowed in
the house, so they send a second messenger
(acetylcholinesterase) by way of the trusty T-tubules. This
messenger releases a distractor (aka calcium). Pretend this is
a belly dancer or someone from Publisher’s clearing house or
some other such distraction.
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While the T-T complex is so occupied, actin and myosin are free to
bind. Of course this takes a lot of energy (who said love was easy?),
but the messenger has only been paid for so long (destroyed by
acetylcholinesterase) and the distractor can only dance (or whatever)
for so long and has to leave (calcium returns to sarcoplasmic
reticulum). Thus, the linkages are broken and they cannot live happily
every after. But wait, another impulse may come along at any time!
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D. Energy Sources for Contraction
1. ATP  limited supply (only for short timed
muscle contractions) and so must often be
regenerated
2. Creatine phosphate which stores excess energy
released by the mitochondria… present to
regenerate ATP from ADP and phosphate.
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E. Oxygen Supply and Cellular Respiration
1. Hemoglobin in red blood cells carries oxygen to muscle
a. Iron (Fe)  high affinity for oxygen
b. Anemia  low Fe in blood
2. Myoglobin stores oxygen in muscle tissue
a. Reduces need for continuous blood supply
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F. Oxygen Debt
1. Lacking oxygen due to
strenuous exercise
2. Convert to anaerobic
respiration
a. Pyruvic acid to
lactic acid
3. Must be repaid  may
take several hours
a. Equal amounts of
oxygen to convert
lactic acid back into
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G. Muscle Fatigue and Cramps
1. Fatigue  Loss of ability to contract during strenuous
exercise
a. Arises from the accumulation of lactic acid in the
muscle  lower pH due to accumulated lactic acid 
prevents the muscle from contracting
2. Muscle cramp occurs due to a lack of ATP required to return
calcium ions back to the sarcoplasmic reticulum so muscle fibers
can relax
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3. Rigor Mortis
A. Partial contraction that fixes the joints
B. Increase in calcium b/c membrane is more permeable
1. Decrease in ATP
2. Actin and myosin remain contracted - cannot relax
3. Muscle decomposition  relaxation
H. Heat Production
1. Contraction of skeletal muscle  important source of
heat for the body
2. Energy produced through cellular respiration  lost
as heat (another source of heat for the body)
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 Muscular Responses
A. Threshold Stimulus
1. A muscle fiber remains
unresponsive to stimulation
unless the stimulus is of a
certain strength  threshold
stimulus
B. Latent Period
1. Time delay between when
the stimulus is applied and when
the muscle contracts  less than
0.01 second
2. Followed by a period of
contraction and a period of
relaxation
C. All-or-None Response
1. When a muscle fiber contracts, it contracts to its full extent
(all-or-none response); it cannot contract partially.
D. Recruitment
1. Increase in # of motor units activated
E. Tetanic contraction  TETANUS
1. Forceful and lacks even partial relaxation
F. Sustained Contraction
1. Muscle Tone
G. Tonic Contraction
1. Holds muscles in place and counteracts gravity
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E. Fast Twitch Muscle Fibers
1. Used during strenuous exercise  weight lifting can exert more
than 75% of max. tension
2. Glycolytic and fatigable
F. Slow Twitch Muscle Fibers
1. Muscle contracts with low intensity  swimming or running
2. Oxidative and fatigue-resistant
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 Smooth Muscles
A. Smooth Muscle Fibers
1. Elongated with tapered ends
2. Lack striations
3. Single nuclei
4. Visceral
a. Rhythmicity (pattern or repeated contractions) 
Peristalsis (wave-like motion)
5. Ex. Hollow organs
6. Actin and myosin
a. slower to contract and relax
b. Neurotransmitters
1. Acetylcholine
2. Norepinephrine
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3. Hormones play a role too
Cardiac Muscle
A. Heart only
B. Striated cells join end to end
C. Single Nuclei
D. Actin and myosin
E. Intercalated disks
1. Myofibril attachment
2. Transmit rapidly (self-exciting)  whole
structure contracts
3. All or none response
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 Skeletal Muscle Actions
A. Origin and Insertion
1. Origin  immovable
end of muscle
2. Insertion  movable
end
3. Contraction 
insertion pulled toward
origin
4. Some muscles have
more than one insertion
or origin
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B. Interaction of Skeletal Muscles
1. Prime mover  main muscle doing work
2. Synergist  “helpers” contract and assist prime mover
3. Antagonist  muscles resisting prime mover’s action
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Major Skeletal Muscles
A. Muscles are named according to any of the following criteria:
1. size
2. shape
3. location
4. action
5. number of attachments
6. direction of its fibers
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Directions

The following terms refer to the direction the muscle fibers
run in relation to the midline.
Rectus

Parallel to the midline
Transverse

Perpendicular to the midline
Oblique

Diagonal to the midline
Size

Relative to other muscles in that group
Maximus

Largest
Minimus

Smallest
Longus or Longissimus

Longest
Latissimus

Widest; means “broadest muscle on the back”
Magnus

Large
Major

Larger
Minor

smaller
Vastus

great
Shape

General shape of the muscle
Deltoid

Triangle
Trapezius

Trapezoid
Serratus

Saw-toothed
Rhomboid

Diamond shaped
Orbicularis

Circular
Pectinate

Comb-like
Piriformis

Pear shaped
Platys

Flat
Quadratus

square
Gracilis

slender
Action

Based on the action the muscle performs
Flexor/Extensor
Flexor – decreases the angle between bones
 Extensor – increases the angle between bones

Abductor/Adductor
Abductor – moves a bone away from the
midline
 Adductor – moves a bone toward the midline

Levator/Depressor
Levator – elevates body part
 Depressor – lowers body part

Supinator/Pronator
Supinator – turns palms up
 Pronator – turns palms down

Sphincter

Decreases the size of an opening
Tensor

Makes a body part rigid
Number of Origins

Biceps – 2 heads

Triceps – 3 heads

Quadriceps – 4 heads
Location
Muscles named for the
structures that they are by.
 Examples include the
sternocleidomastoid muscle
(runs from the sternum
across the clavicle to the
mastoid process) and the
temporalis (near the
temporal bone)

B. Muscles of Facial Expression
1. Major muscles include epicranius, orbicularis oculi,
orbicularis oris, and buccinator
C. Muscles of Mastication
1. Chewing muscles include masseter, temporalis, and
zygomaticus
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D. Muscles that Move the Head
1. Major muscles include sternocleidomastoid, splenius capitis,
and semispinalis capitis
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E. Muscles that Move the Pectoral Girdle
1. The chest and shoulder muscles move the scapula
2. Major muscles include trapezius, rhomboideus major, levator
scapulae, serratus anterior, and pectoralis minor
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F. Muscles that Move the Arm
1. Muscles connect the arm to the pectoral girdle, ribs, and
vertebral column, making the arm freely movable
2. Flexors: coracobrachialis and pectoralis major
3. Extensors: teres major and latissimus dorsi
4. Abductors: supraspinatus and deltoid
5. Rotators: subscapularis, infraspinatus, and teres minor
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G. Muscles that Move the Forearm
1. Arise from the humerus or pectoral girdle and connect
to the ulna and radius
2. Flexors: biceps brachii, brachialis, and brachioradialis
3. Extensor: triceps brachii
4. Rotators: supinator, pronator teres, and pronator
quadratus
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H. Muscles that Move the Wrist, Hand, and Fingers
1. Muscles originating from the distal humerus, and the radius
and ulna
2. Flexors: flexor carpi radialis, flexor carpi ulnaris,
palmaris longus, and flexor digitorum profundus
3. Extensors: extensor carpi radialis longus, extensor carpi
radialis brevis, extensor carpi ulnaris, and extensor digitorum
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I. Muscles of the Abdominal Wall
1. Connects the rib cage and vertebral column to the pelvic girdle
a. Band of tough connective tissue, the linea alba,
extending from the xiphoid process to the symphysis
pubis, serves as an attachment for certain abdominal wall
muscles
2. These four muscles include:
a. external oblique, internal oblique, transverse abdominis,
and rectus abdominis
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J. Muscles of the Pelvic Outlet
1. Superficial urogenital
diaphragm fills the space
within the pubic arch, and
the deeper pelvic diaphragm
forms the floor of the pelvic
cavity
2. Pelvic diaphragm includes
the levator ani
3. Urogenital diaphragm
includes: superficial
transversus, perinei,
bulbospongiosus, and
ischiocavernosus
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K. Muscles that Move the Thigh
1. Muscles that move the thigh are attached to the femur and to
the pelvic girdle
2. Anterior group includes: psoas major and iliacus
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L. Muscles that Move the Leg
1. Connects the tibia or fibula to the femur or pelvic girdle.
2. Flexors: biceps femoris, semitendinosus, semimembranosus,
and sartorius
3. Extensor: quadriceps femoris group  made up of four
parts: rectus femoris, vastus lateralis, vastus medialis, and
vastus intermedius
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M. Muscles that Move the Ankle, Foot, and Toes
1. Muscles that move the foot are attached to the femur, fibula,
or tibia, and move the foot upward, downward, or in a turning
motion
2. Dorsal flexors: tibialis anterior, peroneus tertius, and extensor
digitorum longus
3. Plantar flexors: gastrocnemius, soleus, and flexor digitorum
longus
4. Invertor: tibialis posterior
5. Evertor: peroneus longus
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