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Muscular System
Types of Muscle
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Skeletal
– Striated
– Voluntary
– Multinucleated
Smooth
– Nonstriated
– Involuntary
Cardiac
– Striated
– Involuntary
– Intercalated disks
~ 50% of body weight
Work in groups to perform a function
General Functions of Muscular
System

Movement
– Skeletal muscle contractions move body in
whole or part

Heat Production
– Muscle cells produce heat via catabolism to
maintain temperature homeostasis

Posture
– Continued partial contraction of muscle in
order to perform many functions
Characteristics of all Muscle
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Excitability
– Respond to stimuli
Contractility
– Actively shorten to exert a pull
– Tension that can be harnessed by CT
Extensibility
– Continue to contract over range of resting lengths
– Ex: smooth muscle can be stretched to several times its original
length and still contract on stimulation
Elasticity
– Return to original length after contraction
-mysium=CT membrane
and tendon sheath
Muscle Fiber Arrangement
Parallel
Convergent
Pennate
Bipennate
Sphincter
Muscle Attachment
Does NOT move when
muscle contracts
Naming Muscles
Location
 Function
 Shape
 Fiber direction
 Number of heads/divisions
 Points of attachment
 Muscle size

Location
Function
Frontalis
Frontal bone
Abductor
Moves part away from body
Femoris
Femur
Adductor
Moves part toward body
Gluteus
Posterior of hip/thigh
Depressor
Lowers a part
Oculi
Eye
Extensor
Extends a part
Oris
Mouth
Flexor
Flexes a part
Radialis
Radius
Levator
Elevates a part
Ulnaris
Ulna
Rotator
Rotates a part
Brachialis
Arm
Fiber Direction
Shape
Oblique
Diagonal to midline
Deltoid
Shaped like delta ∆
Rectus
Parallel to midline
Orbicularis
Circular
Sphincter
Circling an opening
Platy
Flattened; platelike
Transversus
Right angle to midline
Quadratus
Square
Rhomboideus
Diamond-shaped
Trapezius
Trapezoidal
Number of divisions
Bicep
Two heads
Tricep
Three heads
Quadricep Four heads
Size
Brevis
Short
Longus
Long
Magnus
Large
Maximus
Largest
Medius
Moderately sized
Minimus
Smaller
Raises eyebrows
Frowning
Mastication
Blinking
Laughing
Whistling, smiling
Puckering
Mastication
Flexes head
Moves head
Moves head
Flexes head
Superficial Back Muscles
•Large, fan-shaped muscles provide force in a wide range of body positions
-EX: leaning back to straight vertical and all points in between.
Shrugging, pulling
scapulas together and
down
Shoulder movement
Pull the arm down,
Stabilize torso during
many movements (EX:
bench press)
Rotator cuff
muscles
Stabilize
shoulder joint,
pull arm back
Trunk Muscles - Thorax
Elevate ribs
Trunk Muscles
Abdomen
Flexes trunk
Compresses
abdomen
Stabilizes
Lower back
Upper Arm
Extends
forearm
Flexes
Upper arm
Flexors
Extensors
Upper Leg
Deep muscle
Vastus intermedius
Biceps femoris
Semimembranosus
Quadricep
Femoris
Semitendinosus
Lower Leg
Plantar flexion
Foot
Anal and Urogenital Muscles
Posture
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Good Posture – body alignment that favors function with
least work
– Standing Position
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Head and chest held high
Chin, abdomen, buttocks pulled in
Knees slightly bent
Feet firmly on ground 6 in. apart
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Poor Posture - puts abnormal strain on ligaments and
bones
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Maintenance
– Tonicity (muscle tone): muscles exert a pull against gravity
 Continuous and passive partial contraction of muscles
Classification of Muscle Group Actions
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Agonist (Prime Mover)
– Muscle most responsible for movement
Antagonist
– Opposes prime mover
– Provides precision and control during prime mover contraction
– Relaxes when prime mover contracts
Synergist
– Aid prime mover
– Contract at same time as prime mover
Fixator
– Joint stabilizer
– Maintains posture/balance during prime mover contraction
L
e
v
e
r
S
y
s
t
e
m
s
1st Class
2nd Class
3rd Class
P = Force (push or pull)
Contracting Muscle
F = Fulcrum
Joint
L = Load
Weights, etc
Muscles & Age
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Infancy & Childhood
– Muscle coordination and control allows
developmental sequences to occur

Aging
– Muscles degenerate with age
 Replaced with CT
Muscle cell (fiber)
cytoplasm
Basic contractile unit
of muscle fiber
H zone
Space between
actin
Sarcoplasm
Z line
Muscle fiber
membrane
I band
Z line
A band
Bundle of
microfilaments;
almost fill
sarcoplasm
Length of
myosin
heads
(wide,
dark
stripes)
Allows impulses to travel
along sarcolemma deeper
into muscle cell (fiber)
Length of
actin (thin,
light
stripes)
Network of tubules and sacs:
pumps calcium ions in from
sarcoplasm to store in sacs
Allows impulse traveling
down T tubule to stimulate
adjacent sacs
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter10/animation__sarcomere_c
ontraction.html
Myofilaments
protein molecules
Holds tropomyosin in place
Covers active site on actin
Attracted to actin and
forms crossbridge
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__breakdown_of_atp_and_crossbridge_movement_during_muscle_contraction.html
Contraction
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter10/animation__action_potentials_an
d_muscle_contraction.html
tropomyosin
1.
2.
3.
4.
5.
6.
7.
8.
9.
troponin
Synaptic vesicle travels down motor neuron and binds to motor endplate
Acetylcholine released into synaptic cleft
Ach binds to receptor on sarcolemma
Impulse travels along sarcolemma and down t-tubules
Calcium released from sarcoplasmic reticulum
Calcium binds to troponin causing conformation change
tropomyosin shifts to expose active site on actin
myosin heads bind to actin
actin filaments are pulled past the myosin head; head unattaches and reattaches to a
new site….repeat
Sliding Filament Theory - sliding of thin filaments toward center of each sarcomere shortens
the myofibril and muscle fiber.
Excitation
&
Contraction
Impulse sent to muscle fiber
Muscle fiber creates movement
Synaptic cleft
Motor endplate
Synaptic vesicle
Neuromuscular junction
(neurotransmitter)
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter10/animation__function_of_the_neuromuscular_junctio
n__quiz_1_.html
Motor Unit
Smaller # fibers – more precise movement
Larger # fibers – more powerful contraction
SR releasing Ca+2
Ca+2 bind to troponin;
Cross-bridging
All or NONE
•Quick jerk due to brief
threshold stimulus
•One twitch – 1/10 sec
•Rarely occur
•Gradual, step-like increase in contraction
strength
•Series of twitch contractions 1 sec apart
•Muscle contracts more forcefully after it has
contracted a few times, then when it first
contracts
•Warm-up before exercise
•Smooth, sustained contractions
•Coordinated contractions of different motor
units
•Multiple twitch waves add together to
sustain
muscle tension for longer time
•Very short periods of relaxation between
peaks
of tension
•Twitch waves fused into a single, sustained
peak
Tonicity
Continual, partial contraction of a muscle
 Flaccid
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– Muscles with less tone than normal
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Spastic
– Muscles with more tone than normal
Length-tension Relationship
Optimal length
Strongest max
contraction
possible
Overstretched
Sarcomere
compressed
Muscle can’t
develop tension
Muscle can’t
develop tension
due to filaments
too far apart
Energy Sources
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ATP
– Hydrolysis into ADP yields energy required for contraction
– ATP binds to myosin head in order to pull actin
– Fibers continually resynthesize ATP from breaking down creatine
phosphate (requires glucose and oxygen)
Glucose & oxygen
– Hemoglobin transfers O2 to muscle fiber
– Fiber stores glucose as glycogen
– At rest: Excess O2 in sarcoplasm is bound to myoglobin
temporarily
– Exercise: O2 concen. Decreases in muscle, so myoglobin
resupplies muscle with O2
Respiration
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Aerobic Respiration
– Requires O2
– Produces max amount of energy available from each
glucose molecule
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Anaerobic Respiration
– Occurs when lack of O2
– Forms lactic acid
 During exercise
 Muscles “burn”
– O2 debt
 Heavy breathing during exercise in order to process lactic
acid
Muscle Fatigue
Muscles loses ability to contract due to
lack of ATP
 Lactic acid build up
 Cramp – muscle contracts spasmodically,
but does not relax completely
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Most body movements are a result of both types
Change in Muscle Size
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Atrophy – decrease in muscle size
– Bed Rest: lose 1% muscle strength/day
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Hypertrophy – increase in muscle size
Myopathies
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Myalgia - muscle pain due to overstretching/tearing of muscle fibers
Fibromyalgia – widespread muscle and CT pain
Strain – caused by overexertion/trauma and can lead to muscle tear
Myositis - any muscle inflammation
Fibromyositis - tendon inflammation along with myositis
Cramps
– Painful muscle spasms
– Due to mild myositis, fibromyositis, irritation, iron, and water imbalance
– Charley Horse
 Intense muscle spasms
 Last few seconds to few hours
 Caused by injury or overuse
– Dehydration
– Low K+ or Ca+2
– Nerve irritated
 Treatment
– Stop activity
– Stretch and massage
– Heat to relax muscle
– Ice when spasm is over
Myopathies
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Contusion
– Muscle bruise, local internal bleeding and inflammation
– Crush injury: severe trauma to muscle, releasing fibers into
bloodstream (life threatening)
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Poliomyelitis (Poilio)
– Viral infection of nerves controlling skeletal movement
– Causes partial or full paralysis and death
– Vaccine created in US in 1950s, but not everywhere
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Muscular Dystrophy
– Genetic disease caused by muscle atrophy
– Some forms are fatal
– Most common form is Duchenne Muscular Dystrophy (DMD)
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Myasthenia Gravis
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Autoimmune disease that attacks muscle cells at NM junction
Muscle weakness
Can become a crisis and affect all four limbs
Could die of respiratory failure
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Hernias
Myopathies
– “protrusion”
– Reducible – can manipulate protruding organ back into abdominal cavity
– Strangulated – blood flow to organ is stopped; obstruction, gangrene, pain.
Vomiting, emergency surgery
– Types
 Inguinal – hernia extends into inguinal canal into scrotum or labia;
affects more males
 Femoral – affects more women below groin area due to pregnancy