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Muscular System Functions
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Body movement
Maintenance of posture
Production of body heat
Communication
Constriction of organs and vessels
Heart beat
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Muscle Tissue Types
Skeletal
Attached to bones
 Striated, Voluntary and involuntary (reflexes)
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Smooth
Walls of hollow organs, blood vessels, eye,
glands, skin
 Not striated, involuntary
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Cardiac
Heart
 Striations, involuntary, intercalated disks
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Smooth Muscle
Smooth muscle is found in the walls of blood vessels, tubular organs such as the stomach
and uterus. It has the ability to stretch and maintain tension for long periods of time. It is
not under voluntary control and each cell exists as a discreet independent unit that is
innervated by a single nerve ending. The myofilaments are loosely organized and attached
to dense bodies.
Cardiac Muscle
Skeletal Muscles
Biceps
Triceps
Biceps-Triceps Muscles Represent an Antagonistic Pair.
One contracts while it’s antagonist relaxes.
Organization III:
Structure of Skeletal Muscle:
Connective Tissue Covering
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Epimysium (upon, outside)
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Surrounds entire muscle
Perimysium (around)
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Surrounds bundles of muscle fibers
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Fascicles (bundle)
Endomysium (within)
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Surrounds individual muscle fibers
Connective Tissue, Nerve, Blood Vessels
Muscle cell (myofiber) Structure
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Sarcolemma
 Muscle cell membrane
Myofibrils
– contractile protein
strands
– Striations due to
presence of sarcomeres
Contraction
Sarcomere – the functional unit
of myofibrils
Sarcoplasmic reticulum – storage for
calcium ions that are used for muscle
contractions
CONTRACTILE PROTEINS
1. THIN FILAMENT
Has 3 parts;
i) ACTIN PROTEIN
(i.e. the main molecule of this filament).
FUNCTION: Binds to myosin head of thick filament.
ii) TROPONIN
FUNCTION: Regulatory function by binding to Ca
2+
iii) TROPOMYOSIN
FUNCTION: Has a regulatory function by blocking/unblocking
the binding site of actin to the myosin head
CONTRACTILE PROTEINS
1. THICK FILAMENT
– made of myosin protein
- has 2 main parts
i) MYOSIN HEAD - forms cross-bridge with actin.
ii) MYOSIN TAIL – forms the shaft of thick bands.
Calcium ?
• Click for video
Sliding Filament Model I:
• Actin myofilaments sliding over myosin to
shorten sarcomeres
Actin and myosin do not change length
 Shortening sarcomeres responsible for
skeletal muscle contraction
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• During relaxation, sarcomeres lengthen
Mechanism of muscle
contraction
SLIDING FILAMENT THEORY
MOTOR UNIT
Motor Unit
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Single motor neuron & muscle fibers it
innervates
Eye muscles – 1:1 muscle/nerve ratio
Hamstrings – 300:1 muscle/nerve ratio
The Neuromuscular Junction
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Site where motor neuron meets the muscle
fibre
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Motor end plate
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Separated by gap called the neuromuscular cleft
Pocket formed around motor neuron by
sarcolemma
Acetylcholine is released from the motor
neuron
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Causes an end-plate potential (EPP)
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Depolarisation of muscle fibre
Neuromuscular Junction
• Click for a Video
Rigor Mortis
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Rigor mortis is one of the recognizable signs of death (Latin mors, mortis) that is caused by a chemical
change in the muscles after death, causing the limbs of the corpse to become stiff (Latin rigor) and difficult
to move or manipulate.[1]
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After death, respiration in organisms ceases to occur, depleting the corpse of oxygen used in the making of
ATP. ATP is no longer provided to operate the SERCA pumps in the membrane of the sarcoplasmic
reticulum, which pump calcium ions into the terminal cisternae.[1] This causes calcium ions to diffuse from
the area of higher concentration (in the terminal cisternae and extracellular fluid) to an area of lower
concentration (in the sarcomere), binding with troponin and allowing for crossbridging to occur between
myosin and actin proteins. [2]
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Unlike normal muscle contractions, the body is unable to complete the cycle and release the coupling
between the myosin and actin, creating a perpetual state of muscular contraction, until the breakdown of
muscle tissue by digestive enzymes during decomposition.
Rigor Mortis
• Respiration ceases and Oxygen used in making ATP
is depleted.
• ATP is no longer provided to operate the pumps in
the membrane of the sarcoplasmic reticulum, which
pump calcium ions.
• Unlike normal muscle contractions, the body is
unable to complete the cycle and release the
crossbridges between the myosin and actin, creating
a perpetual state of contraction until the breakdown
of muscle during decomposition.
Muscle Function
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All or none law – fibre contracts
completely or not at all
Muscle strength gradation
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Multiple motor unit summation – more
motor units per unit of time
Wave summation – vary frequency of
contraction of individual motor units
Animation Links!!
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http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter10/animation__action_potentials_and_muscle_c
ontraction.html
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http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter10/animation__sarcomere_contraction.html
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http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter10/animation__breakdown_of_atp_and_crossbridge_movement_during_muscle_contraction.html
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http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter10/animation__function_of_the_neuromuscular_j
unction__quiz_1_.html