MUSCULAR SYSTEM
Muscle Facts!
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The human body has 640 voluntary/skeletal muscles. This means
muscles which we can control, as opposed to muscles of the heart
and intestines which we can not voluntarily control.
Muscles are made of microscopic filaments which contract and slide
over each other causing the the muscles to shorten and therefore
contract.
No matter how much you exercise you can not increase the number
of muscle cells you have. By getting bigger, via strength training, you
are simply increasing the size of each muscle cell. The quantity of
muscle cells remain the same.
The strongest muscles are:
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The Soleus, part of the calf muscle, below the calf muscles, as it can
apply the most force.
The Masseter, also known as the jaw muscles.
The tongue. Yes, the tongue is a muscle! And for its size it's very strong.
Major Muscles
The functions of muscles
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Producing movement – facial
expressions, movement of food
stuffs through digestions and
blood through the heart.
Maintaining posture (skeletal
only), very fatigue resistant
muscles, ex. erector spinae; and
stabilizing joints (holding the
skeleton together)
Generating heat to maintain
body temperature. Muscles
make up 40% of body weight
and ¾ of energy given off by
ATP is heat.
Three types of Muscle: Skeletal,
smooth and cardiac
Skeletal muscle fibers contain numerous
nuclei and mitochondria --> Energy
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The muscle fiber membrane is called the
SARCOLEMMA and the cytoplasm is called the
SARCOPLASM. Within the sarcoplasm are many
parallel fibers known as MYOFIBRILS
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Each myofibril is
made of many
protein filaments
called
MYOFILAMENTS.
There are two types
MYOSIN - thick
filaments
ACTIN - thin
filaments
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Muscles are made of muscle fibers (cells)
Muscle fibers (cells) are made of myofibrils which
contain the functioning units of contraction called
sarcomeres
Muscle Structure
Relaxed vs. Contracted Sarcomere
How the muscle fiber contracts – The
Sliding Filament Theory
Basic structure of
sarcomere.
 1. Sarcomere is
the functional
contracting unit
of the muscle fiber.
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Steps in the Sliding Filament Theory
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1. Nerve impulse
reaches the
synaptic cleft
between the nerve
and the muscle
fiber (each fiber
must be
individually
stimulated). This is
called the
neuromuscular
junction.
Steps in the Sliding Filament Theory
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2. Signal
causes Calcium
(Ca) to be
released from
the
sarcoplasmic
reticulum. (as
soon as nerve
impulse is over
Ca is
reabsorbed)
Steps in the Sliding Filament Theory
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3. Calcium causes
the protein
complex on actin to
move away from
the binding site.
Steps in the Sliding Filament Theory
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4. ATP activates the myosin head to form the
cross bridge (myosin head )attached to actin
and pivots toward the H-zone. Causing a
shortening of the sarcomere.
Steps in the Sliding Filament Theory
5. This action occurs
simultaneously through out the
entire muscle fiber and
through out the entire muscle
causing the muscle itself to
contract/shorten. In order to
maintain a contraction (ex.
hold your arm out in front of
you for several seconds) the
nerve must constantly
restimulate the muscle fiber.
Energy for muscle contractions
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Muscle fibers typically keep 4 to 6 seconds
worth of ATP stored. Therefore the cell
must very quickly begin generating more
ATP
First, use of creatine phosphate to make
more ATP. (about 20 seconds)
Aerobic respiration. Used during light
exercise and rest. 95% of all muscle
energy is generated this way. Requires
oxygen.
Anaerobic respiration. During more intense
exercise (30 to 60 seconds) but results in the
build up of lactic acid (byproduct) in the
muscles which promotes muscle fatigue and
soreness.
Sliding Filament Theory Videos
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http://bcs.whfreeman.com/thelifewire/content/chp
47/4702001.html
 Good
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simple animation
http://www.youtube.com/watch?v=GC_CUfLP6Pc
 song
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http://www.wisconline.com/objects/ViewObject.aspx?ID=AP2904
http://www.youtube.com/watch?v=sJZm2YsBwMY
 Cartoon
version
Types of Muscle Contractions
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Isotonic – the muscle shortens and movement occurs
lifting weights
running
Isometric – muscle contracts or shortens but no
movement occurs (pushing against a brick wall)
Types of Body Movements
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A. Flexion- bending movement that brings
two
articulating bones closer
together.
B. Extension- reverse of flexion, moves the
bones further apart.
C. Abduction- movement of limb away from
the mid-line
D. adduction- movement of limb toward the
mid-line.
Body Movements continued
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E. Circumduction- moving a limb so it
describes a cone in space
F. Rotation- turning of a bone on its long axis,
this also includes lateral and medial rotation
of hip and shoulder
G. Supination- palm up
H. Pronation palm down
Special Body Movements
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Inversion: sole of foot is turned medially
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Eversion- sole of foot is turned laterally
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plantar flexion- point toes
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dorsiflexion- pull toes towards shin
Muscle Movements
Muscle Movements
Types of Muscles
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A. Prime mover- provide the major force for
producing a specific movement.
Ex. Biceps Brachii for forearm flexion
B. Antagonist- oppose or reverses a particular
movement
Ex. Triceps brachii for forearm
extension (oppose biceps)
C. synergist- aid prime movers by promoting the
same movement or reducing undesireable or
unnecessary movements that might occur as the
prime mover contracts.
Ex. Semimembranosis helps the biceps
femoris with thigh extension and knee
flexion
Types of Muscles
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D. Fixators- a synergist that immobilizes or stabilizes
a bone or a muscle’s origin
Ex. Rotator cuff muscles (terest minor, infraspinatus,
supraspinatus, subscapularis)
E. Example of movement of all four involved in a
movement
a. prime mover= pectoralis major (shoulder flexion)
b. antagonist= lattisimus dorsi
c. synergist= biceps brachii
d. fixator= rotator cuff
Skeletal muscles are named according
to certain criteria
1. Location- may indicate bone or body
region that muscle is associated with
Ex. Zygomaticus- associated with the
zygomatic arch in the skull
 2. Shape- Muscles often have a definitive
shape, after which they are name
Ex. Deltoid means triangle (and the
deltoid muscle is triangular)
 3. Relative Size
 Maximus= largest
 Minimus= smallest
 Longus= long
 Brevis= short
 Ex. Gluteus maximus (larger) and minimus
(smaller)
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4. Direction of Muscle Fibersmay reflect the direction of the
fibers in relation to midline or
other axis
Rectus= straight (runs parallel)
Transversus/oblique ( right
angles)/ obliquely
Ex. Rectus femoris- muscle that
runs parallel with the femur
 5. Number of Origins
Biceps= two origins
Triceps= three origins
Quadriceps= four origins
Ex. Biceps Brachii
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6. Location of origin and insertions may be named according to the
attachment points
 Origin is always named first
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Ex. Sternocleidomastoid (dual origin on sternum and clavicle; insertion on
mastoid process
 7. Action
Uses words such as flexor, extensor, or adductor
Ex. Adductor longus on thigh adducts the thigh
Sometimes several criteria are combined in a name.
Ex. Extensor carpi radialis longus
 muscle’s action (extensor)
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joint it acts on (carpi= wrist)
 Where it is (radialis = radius of forearm)
 size (long relative to other wrist muscles
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