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Chapter 9
Muscular System
Functions of a Muscle Tissue
1. Movement:
1. Skeletal - locomotion , vision, facial expression.
2. Cardiac – blood pumping
3. Smooth – food digestion
2. Posture - (skeletal)
3. Joint Stability - (skeletal)
4. Heat Generation - (skeletal)
Chapter 9
Muscular System
Three Types of Muscle Tissues
Cardiac Muscle
Skeletal Muscle
• wall of heart
• involuntary - not
under conscious
control
• striated
• usually attached
to bones
• voluntary- under
conscious control
• striated
Smooth Muscle
• walls of most viscera,
blood vessels, skin
• involuntary - not under
conscious control
• not striated
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Structure of a Skeletal Muscle
Skeletal Muscle
• organs of the muscular system
• skeletal muscle tissue
• nervous tissue
• blood
Connective tissues and muscle
tissue:
1.fascia – covers the muscle
2.tendon – attaches the
muscle
3.aponeuroses – muscle to
muscle
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Functional Characteristics of Muscle
• Excitability – receive and respond to stimuli
• Contractility – shorten forcibly and when stimulated
• Extensibility – stretched or extended
• Elasticity – bounce back to original length
Structure of a Skeletal Muscle
Coverings of a muscle
1. Epimysium - outter
2. Perimysium - middle
3. Endomysium - inner
Organization of Muscle
• muscle
• fascicles
• muscle fibers
• myofibrils
• thick and thin filaments
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Structure of a Skeletal Muscle
Coverings of a muscle
1. Epimysium – connective tissue surrounding the entire muscle
2. Perimysium – connective tissue surrounding a fascicle
3. Endomysium – thin connective tissue surrounding each
muscle cell
Organization of Muscle
• muscle
• fascicles – bundle of muscle cells
• muscle fibers – a muscle cell
• myofibrils – a long, filamentous organelle found within muscle cells
that has a banded appearance
• thick and thin filaments (myofilament)- actin &myosin filaments
• sarcomere – contractile unit of muscle
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Skeletal Muscle Fiber
• sarcolemma • sacroplasm
• sarcoplasmic reticulum
• transverse tubule
• triad
• cisterna of sarcoplasmic
reticulum
• transverse tubule
• myofibril
• actin filaments
• myosin filaments
• sarcomere
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Skeletal Muscle Fiber
• sarcolemma – Plasma membrane surrounding each
muscle fiber
• sarcoplasm – specialized cytoplasm
• sarcoplasmic reticulum – network of tubes and sacs
• transverse tubule – tubular organelles that run across
fibers, right angles
• triad
• cisternae of sarcoplasmic reticulum
• transverse tubule
• myofibril – consists of the many, bundled myofilaments
• actin filaments – thin filaments
• myosin filaments – thick filaments
• sarcomere – basic contractile unit of muscle
ActingActin
and Myosin
Filaments
and Myosin
Sarcomere
• I band
• A band
• H zone
• Z line
• M line
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Sarcomere Structure
A sarcomere is defined as the segment between two neighboring Zlines .
• Z-line- the disc in between the I bands. Appears as a series of
dark lines.
• I-band is the zone of thin filaments that is not superimposed by
thick filaments.
• A-band contains the entire length of a single thick filament.
• H-band is the zone of the thick filaments that is not superimposed
by the thin filaments.
• Finally, inside the H-zone is a thin M-line formed of crossconnecting elements of the cytoskeleton.
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Sliding Filament Theory
When
sarcomeres
shorten, actin
and myosin
filaments slide
past one another
VIDEO#1
VIDEO #2
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Skeletal Muscle Contraction
?
How does a muscle contract?
Sequence of a Muscle Contraction
Brain
Spinal Cord
Nerve
(Action potential)
Motor Unit
Neuromuscular Junction
(Calcium is released)
Acetylcholine
(Neurotransmitter)
Contraction
Motor Unit
• single motor neuron (a single nerve)
• one motor neuron and many skeletal muscle fibers
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Neuromuscular Junction
• site where a motor
nerve fiber and a
skeletal muscle fiber
meet
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Muscle Contraction
• Action potential causes
the release of Ca at the
NMJ.
•a neurotransmitter
releases a chemical
substance from the motor
end fiber, causing
stimulation of the muscle
fiber
•That substance is called
acetylcholine (ACh)
•ACh causes the muscle
fibers to become
stimulated and contract
(shorten).
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Relaxation of a Muscle
• acetylcholinesterase – an enzyme that
breaks down acetylcholine. NMJ
• muscle impulse stops
• calcium moves back into sarcoplasmic
reticulum
• myosin and actin action prevented
• muscle fiber relaxes
• Cd
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Sequence of a Muscle Contraction
Brain
Spinal Cord
Nerve
(Action potential)
Motor Unit
Neuromuscular Junction
(Calcium is released)
Acetylcholine
(Neurotransmitter)
Contraction
Recruitment of Motor Units
Recruitment - increase in the number of motor units
activated
• whole muscle composed of many motor units
• as intensity of stimulation or contraction increases,
recruitment of motor units continues until all motor
units are activated = all or none principle
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Question ????
We now know how a muscle contracts and relaxes, so
is energy needed for that to happen?
NO
or
YES
?
How is energy that is stored in
carbohydrates released?
Cellular Respiration
Oxygen
Glucose
H2O + CO2
Useable Energy is Adenosine triphosphate (ATP)
Adenosine triphosphate (ATP)
• It serves as a source of energy for many
metabolic processes.
• ATP releases energy when it is broken down
into ADP by hydrolysis during cell metabolism.
ENERGY
The energy used to power the interaction
between actin and myosin filaments comes from
ATP (useable chemical energy) produced by
cellular respiration.
ATP stored in skeletal muscle last only about six
seconds.
ATP must be regenerated continuously if
contraction is to continue
Two Energy Sources
for Contraction
1) Creatine phosphate (ADP)
2) Cellular respiration
• creatine phosphate – stores energy that quickly converts
unusable energy (ADP) to usable energy (ATP) 6 Seconds!!
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Cellular Respiration (CR)
THREE SERIES OF REACTIONS in CR
1. Glycolysis
2. Citric acid cycle
3. Electron transport chain
Produces
• carbon dioxide
• water
• ATP (chemical energy)
• heat
Two Types of Reactions
• Anaerobic Respiration (without O2) - produce little ATP
• Aerobic Respiration (requires O2) - produce most ATP 4-11
Anaerobic Reaction (Glycolysis)
• Recall that glycolysis results in pyruvate acid.
If O2 is not present, pyruvate can be
fermented into LACTIC ACID.
• Lactic Acid
• It is a waste product of pyruvate acid.
• Occurs in many muscle cells.
• Accumulation causes muscle soreness and fatigue.
Oxygen Supply and
Cellular Respiration
• Anaerobic Phase
•Steps are called glycolysis.
•occur in the cytoplasm
• no oxygen
• produces pyruvic acid
and produces lactic acid
• little ATP
• Aerobic Phase
•Steps are called citric acid
cycle and electron transport
chain.
• occur in the mitochondrion
•oxygen
•produces most ATP / CO2/
H2O
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Summary of Cellular Respiration
Total ATP Production
2 ATP – Glycolysis
2 ATP – Citrus Acid Cycle
34 ATP – Electron Transport Chain
38 ATP – Total energy released from one
molecule of glucose.
Oxygen Debt
Oxygen debt – amount of oxygen needed by liver to convert
lactic acid to glucose
• oxygen not available
• glycolysis continues
• pyruvic acid converted
to lactic acid
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What happens to the lactic acid once
it has accumulated?
• The liver filters the blood and rids the
body of toxins. Lactic acid is a toxin.
• liver converts lactic acid to glucose
Muscle Fatigue
• Muscle fatigue- is a state of physiological
inability to contract
• commonly caused from
– decreased blood flow
– ion imbalances
– accumulation of lactic acid
Cramp – sustained, involuntary contraction
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Muscle
MuscleCramp
Cramp
The exact cause of muscle cramps is still
unknown, but the theories most commonly
cited include:
– Altered neuromuscular control
– Dehydration
– Electrolyte depletion
– Poor conditioning
– Muscle fatigue
– Doing a new activity
Muscle Tone
Muscle tone – continuous state of partial contraction
-Even when a muscle appears to be at rest, a certain
amount of sustained contraction is occurring in its
fibers.
Atrophy – a wasting away or decrease in size of an
organ or tissue.
Hypertrophy – Enlargement of an organ or tissue.
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Types of Contractions
Two Types
1. Isometric – muscle contracts but does not change length
2. Isotonic – muscle contracts and changes length
Two Types of Isotonic Contractions
1. Eccentric – (negative) lengthening contraction
2. Concentric – (positive) shortening contraction
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Types of Contractions
Smooth and Cardiac Muscle
Smooth Muscle Fibers
Compared to skeletal muscle fibers
• shorter
• single nucleus
• elongated with tapering ends
• myofilaments randomly organized
• no striations
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Two Types of Smooth Muscle
Multiunit Smooth Muscle
• irises of eye
• walls of blood vessels
• contractions are rapid and vigorous
• similar to skeletal muscle tissue
Visceral Smooth Muscle
Location - walls of most hollow organs (intestine)
• contractions are slow and sustained
•exhibit rhythmicity – pattern of repeated
contractions
• exhibit peristalsis – wave-like motion that helps
substances through passageways.
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Smooth Muscle Contraction
• Resembles skeletal muscle contraction
• interaction between actin and myosin
• both use calcium and ATP
• both depend on impulses
• Different from skeletal muscle contraction
• hormones affect smooth muscle
• stretching can trigger smooth muscle contraction
• smooth muscle slower to contract and relax
• smooth muscle more resistant to fatigue
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Cardiac Muscle
Anatomy
• only in the heart
• striated uninuclear cells join end-to-end forming a network
• arrangement of actin and myosin are not as organized as
skeletal muscle
Physiology
• self-exciting tissue (Pacemaker)
• rhythmic contractions
• involuntary, all or nothing contractions
Pumps blood to:
• 1. lungs for oxygenation
• 2. body for distribution of O2 and nutrients
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