MUSCULAR SYSTEM:
FUNCTIONS OF MUSCULAR SYSTEM
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Body movement
Maintain posture
Respiration
Produce body heat
Communication
Constriction of organs and blood vessels
Heartbeat
Muscle Types
 Skeletal: elongated
 striated
 Voluntary
 Moves the skeleton
 Smooth: spindle shaped
 no striations
 Involuntary
 Found in organs and lining of blood vessels
 Cardiac: cylindrical shaped
 striated
 involuntary (only responds to direct electrical stimulation)
SKELETAL MUSCLE: Connective Tissue Sheaths
 The MUSCLE FASCIA is loose fibrous connective tissue on the outside of the
muscle. It creates a slippery surface for muscles to rub against each other. Deep
to the fascia is the
 EPIMYSIUM, (dense irregular fibrous connective tissue), and which eventually
becomes the tendon (which is connected to bone). The epimycium extends into
the muscle belly to form compartments called FASICLES. This tissue
surrounding the fascicles is now called the PERIMYCIUM. Each fascicle
contains MUSCLE FIBERS, which are individual muscle cells, each one
surrounded by ENDOMYCIUM. When you eat steak and find it’s stringy, each
string is a fascicle, and the fat around the whole outside of the slice of meat is
near where the fascia is.
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TYPES OF MUSCLE PATTERNS
 PARALLEL
 PENNATE
 CONVERGENT
 CIRCULAR
PARALLEL MUSCLE
The fascicles are parallel. They are long fibers, which can contract to 75% of their
length. They contract a long way, but they are relatively weak, because there are
relatively few fascicles. E.g. Sternocleidomastoid.
PENNATE
PENNATE (means “feather shape”) MUSCLES: three types:
 UNIPENNATE; looks like half a feather. The fascicles are short, but
there are more of them. They are stronger, but do not have the same
length contraction ability of the parallel muscles.
 BIPENNATE are fascicles that insert into the tendon from both sides;
they are stronger than unipennate.
 MULTIPENNATE are the strongest (biceps femoris). The fascicles are
in multiple bundles inserting on one tendon
CONVERGENT
CONVERGENT MUSCLE has more fibers than parallel, but contracts a greater
distance than pinnate. E.g. Pectoralis major.
CIRCULAR MUSCLE
CIRCULAR MUSCLE (Sphincter) is arranged in a circle, with a small area of tendon
on the sides. It allows closure of the eyes, mouth, etc. They are not very strong, but they
don’t need to be.
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TERMS:
 ORIGIN = The region which usually doesn’t move when the muscle contracts.
Look at the biceps brachii; does the shoulder move when I bend my arm? No; the
shoulder = origin.
 INSERTION= The point of attachment that moves; bend arm, radial tuberosity =
attachment.
 AGONIST = The main muscle for a particular action; bend arm, biceps = agonist.
 ANTAGONIST = Does the opposite action; bend elbow, antagonist extends.
Every muscle in the body has to have an antagonist.
 SYNERGIST = The muscle that helps the agonist. There are several muscles
that assist when the arm is bent.
Skeletal Muscle Characteristics
 Contractility
 The ability to shorten with force
 However, they lengthen passively, by gravity or by the contraction of an
opposing muscle.
 Excitability
 Capacity to respond to a stimulus (nerves)
 Extensibility
 Can be stretched
 After a contraction, they can be stretched to their normal resting length
and beyond to a limited degree.
 Elasticity
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 Can recoil to their original resting length after they have been
stretched
 Has several nuclei per cell, unlike smooth and cardiac muscle
SKELETAL MUSCLE
 Theses are very long fibers (biceps muscle can be 8-10 cm).
 They have thousands of nuclei because they start from many stem cells that fuse
together into one skeletal muscle fiber.
 Myoblasts exist in adults, so muscle heals well.
 A muscle cell torn in half can regenerate.
 There are almost no muscle diseases for this reason (muscular dystrophy is the
main muscle disease).
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In skeletal muscle fibers, there are light and dark stripes called striations, which
can be seen under a microscope.
 The plasma membrane of muscles is called a SARCOLEMMA.
 The cytoplasm of muscle cells is called SARCOPLASM.
 Muscle cells contain many mitochondria and other organelles.
 One type of unusual organelle found only in muscle cells is called a myofibril.
They are packed in bundles and fill up most of the cell.
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MUSCLE MYOFIBRILS
• Cylindrical organelles found within muscle cells
• Contain actin and myosin myofilaments
• Extend from one end of the muscle fiber (muscle cell) to the other
• Contain sarcomeres joined end to end.
These striations (stripes) are caused by dark and light bands.
The dark band is called an A band. (There is an “A” in dark)
The light band is called an I band. There is an “I” in light)
Every dark band + light band is one sarcomere
In the center of each light I band is a Z disc
One sarcomere is the area from one Z disc to the next Z disc.
So, each sarcomere extends from the middle of one light band to the middle of the next
light band. In the center of the dark band is a lighter colored area called the H zone. It is
the area of the myosin without heads.
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SARCOMERES
 The striations result from the internal structure of SARCOMERES within the
sarcoplasm.
 The sarcomere is the basic structural and functional unit of skeletal muscle.
The sarcomere is what contracts.
 Each sarcomere
 Extends from one Z disc to the next Z disc
 Has a light colored H zone in the center (found in the middle of the dark
band, which is in the center of the sarcomere. It is the area of myosin in
the center that does not have myosin heads).
 Contains parts of two I (light) bands and all of one A (dark) band
 Contains overlapping actin and myosin myofilaments.
Actin and Myosin
 Sarcomeres consist of two types of myofilaments made out of protein:
 thin (ACTIN) myofilaments
 Look like two strands of beads twisted together.
 Actin myofilaments are attached to the Z disc at one end.
 thick (MYOSIN) myofilaments.
 Both ends of a thick filament are studded with knobs called myosin
heads (look like little golf clubs).
 Myosin is NOT attached to the Z disc.
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Don’t confuse these terms!
MUSCLE FASCICLE: a group of muscle fibers, surrounded by perimysium.
MUSCLE FIBER: a single muscle cell
MYOFIBRIL: a long organelle inside a muscle fiber, contains actin and myosin
myofilaments.
MYOFILAMENTS: these are proteins, and there are two types: actin (with troponin and
tropomyosin) and myosin. The myofilament is the lowest level of organization that is
composed of actin, troponin, and tropomyosin proteins.
Therefore, a myofilament is part of a myofibril, which is inside a muscle fiber, which is
inside a muscle fascicle.
MECHANISM OF CONTRACTION
The Sliding Filament Theory
 Contraction results as the myosin heads of the thick filaments attach like hooks to
the thin actin filaments at both ends of the sarcomere and pull the thin filaments
toward the center of the sarcomere.
 The myosin head is like a hook with a hinge. After a myosin head pivots at its
hinge, it draws the actin closer, then lets go, springs up again to grab the actin
filament again, pulls it closer, and it keeps repeating this until the entire actin
filament has been drawn in as far as it can go.
 The sites where the myosin heads hook onto the actin are called cross-bridges.
 The complete process of contraction of the sarcomere takes only a fraction of a
second.
 The actin and myosin filaments do not shorten; they merely slide past each
other.
 The energy required is ATP.
 The A band (dark stripe) in a sarcomere does not change length in a contraction.
 This sliding filament mechanism begins whenever calcium ions bind to the thin
filament.
 Where does the calcium come from?
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SARCOPLASMIC RETICULUM AND T TUBULES
 Within the cytoplasm of all body cells is an endoplasmic reticulum.
 The endoplasmic reticulum in muscle cells is called the SACROPLASMIC
RETICULUM.
 It surrounds each sarcomere like the sleeve of a loosely crocheted sweater.
 Most of the “yarn fibers” of this “knit sweater” run longitudinally, but some run
perpendicular to them and surround structures called T tubules.
Calcium is needed for muscle contraction
 The sarcoplasmic reticulum stores a lot of calcium ions, which are released
when the muscle is stimulated to contract.
 The calcium diffuses through the sarcoplasmic reticulum to the actin filaments,
where they trigger the sliding filament mechanism of contraction.
 After the contraction, the calcium ions are pumped back into the sarcoplasmic
reticulum for storage.
 ACTIVE TRANSPORT is required to return the calcium ions to the
sarcoplasmic reticulum.
 It also requires energy to break the cross-bridge so the myosin head can cock back
again, ready to spring onto the next binding site.
 Therefore, ATP is used.
 ATP is used to return calcium to the sarcoplasmic reticulum
 ATP is used to cock back the myosin heads
 ATP attaches to the myosin myofilaments
 Provides energy for the movement of the cross bridges
 ATP is required for muscle relaxation
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 ATP releases part of its energy as heat.
 That is why we get hot when we exercise
 When we are cold, we shiver (muscle contraction) to warm up.
 In order for the mitochondria to produce enough ATP, it needs oxygen and the
sugars that are in storage.
For contraction to take place, you need a nerve signal and calcium
 For skeletal muscle to contract, the synaptic knob of a neuron must first release a
chemical called ACETYLCHOLINE onto the region where it sits on the muscle
cell, known as the ENDPLATE.
 Calcium is also needed for muscle contraction.
 The nerve signal is called an ACTION POTENTIAL.
 It causes a release of calcium from the sarcoplasmic reticulum, which causes
contraction.
 In a muscle fiber, an action potential results in muscle contraction. How does this
happen?
 The action potential continues to travel along the sarcolemma (cell membrane of
the muscle).
 Part of this electrical impulse breaks away from the sarcolemma and travels down
the T-tubules, while the rest of the electrical impulse continues longitudinally
down the muscle cell to the next sarcomere and T-tubule.
 T TUBULES (“T” stands for “transverse”) are continuations of the sarcolemma
(cell membrane) which invaginate to the deepest regions of the muscle cell.
 Since the T tubules conduct the nerve impulse throughout the muscle cell, all the
sarcomeres of that cell contract at the same time.
 The action potential of the nerve goes down the T-tubules and causes calcium to
leak out of the sarcoplasmic reticulum.
 The calcium causes the muscle fibers to contract.
 After a while, the calcium gets pumped back where it came from, the muscle
fibers relax, although it requires gravity or another muscle to pull the sarcomere
back to its original length.
 How does the calcium cause the muscle fibers to contract?
TROPOMYOSIN is a single long protein strand like a piece of yarn that winds around
the actin filament.
• Tropomyosin blocks actin’s attachment site for the myosin head, so the myosin
“hook” has nothing to grab onto, thus preventing contraction.
TROPONIN is a globular complex of three proteins, and is found in clumps around the
tropomyosin protein.
• Troponin is the specific molecule that provides the calcium binding site on
actin.
• Calcium binds to troponin and causes troponin to move a little, taking the
tropomyosin thread with it, so the attachment sites on the actin molecule are now
exposed. The myosin heads can now hook into the exposed sites on the actin
myofilament.
Both troponin and tropomyosin cover the actin filament when the muscle is relaxed.
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This is an illustration of an actin molecule. You can see the thready tropomyosin and the
globular troponin proteins wrapping around the double-stranded actin.
When calcium binds to the globular troponin, it moves, taking the tropomyosin thread
with it. This exposes the myosin binding site on the actin.
Calcium in muscle contraction
 When the muscle cell is stimulated to contract by an action potential, calcium
channels open in the sarcoplasmic reticulum and release calcium into the
sarcoplasm.
 Some of this calcium attaches to troponin, causing a conformational change that
moves tropomyosin out of the way so that the myosin heads can attach to actin
and produce muscle contraction.
 When the calcium gets pumped back where it came from, the tropomyosin protein
blocks the myosin head again so it can no longer get its hook into the actin
filament, and the muscle will relax.
Rigor Mortis
 A new ATP molecule must bind to the myosin before the cross-bridge can be
release. When ATP is not available after a person dies, the cross-bridges that have
formed are not released, causing muscle to become rigid (rigor mortis)
 NOTE: Sarcomeres lengthen during muscle relaxation, but only if gravity or an
opposing muscle pulls the sarcomere back to its original length.
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Sequence of events
 The action potential reaches the cell membrane
 The action potential reaches the T-tubules
 The ion channels in the sarcoplasmic reticulum open
 Calcium ions move along their concentration gradient
 Actin forms cross-bridges to myosin
 The actin myofilaments move closer to each other, causing contraction of the
sarcomere.
 NOTE: A muscle fiber will not respond to a stimulus until that stimulus reaches
the threshold level.
 Troponin is found in both skeletal muscle and cardiac muscle, but not in smooth
muscle.
 Both cardiac and skeletal muscles are controlled by changes in the intracellular
(“inside the cell”) calcium concentration (not blood calcium concentration).
 When muscle calcium levels rise, the muscles contract, and when muscle calcium
levels fall the muscles relax.
Muscle Contraction
A muscle TWITCH is one single muscle fiber contraction.
 It takes 1/20th of a second.
 How is it that I can pick up and hold a chair if the fiber only contracts for 1/20th
second?
 There are ten thousand fibers per muscle; each one contracts at different intervals,
so contraction is maintained, just like tug-of-war. One person in ten can drop the
rope and get a better grip because the others are maintaining the tension.
Motor Units
A MOTOR UNIT is a single neuron and all of the muscle fibers on which it synapses.
If one neuron sends a signal, only its muscle fibers contract (the motor unit). This allows
for strength variations in lifting a chair vs. an eraser. For full strength, all the motor units
contract. For half strength, half of the motor units contract. The more motor units there
are, the more precisely the muscle can respond.
 The action potential continues from one motor neuron to the next motor neuron
until the last neuron lands on its target cells; in this case, skeletal muscle fibers.
 A single motor neuron and all the skeletal muscle fibers it innervates constitute a
motor unit.
 A muscle in your tongue may only have a few muscle fibers innervated by a
neuron to allow for precise movement. However, large thigh muscles may have as
many as 1000 muscle fibers per neuron, since precision is not necessary.
 The muscles of the back are larger motor units (more muscle fibers per neuron),
but there are fewer motor units present = strength, but less precision.
 The muscles that move the tongue are smaller motor units (10 fibers per neuron),
but there are many motor units present = less strength, more precision.
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Muscle Twitch Phases
A muscle twitch has three phases
 The lag phase is the time between the application of a stimulus and the beginning
of contraction.
 The contraction phase is the time of contraction.
 The relaxation phase is the time during which the muscle relaxes.
 The refractory period is the time between muscle twitches.
Force of Contraction
 The strength of muscle contraction can vary from weak to strong. For example,
the force generated by muscles to lift a feather is much less than the force
required to lift a 25 pound weight.
 The force of contraction produced by a muscle is increased in two ways:
 Summation, which involves increasing the force of contraction of the muscle
fibers within the muscle
 Recruitment, which involves increasing the number of muscle fibers
contracting
Summation
 The force of contraction of individual muscle fibers is increased by rapidly
stimulating them.
 Stimulus frequency is the number of times a motor neuron is stimulated per
second.
 When the stimulus frequency is low, there is time for complete relaxation of
muscle fibers between twitches.
 As stimulation frequency increases, there is not enough time between contractions
for muscles to completely relax.
 Thus, one contraction summates, or is added onto, a previous contraction. As a
result, the overall force of contraction increases.
 Tetanus is the condition in which a muscle remains contracted between stimuli
without relaxing.
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TETANUS TOXIN
 A toxin caused by a certain bacteria can cause muscle to remain contracted (in
tetanus).
 It quickly results in death because the diaphragm and other respiratory muscles
cannot function properly, and the person suffocates.
 The bacteria that make this toxin live deep in the soil and cannot survive in air.
 If you step on something that imbeds soil deeply into your tissues (like a rusty
nail), you might contract the bacteria.
 You will need a tetanus vaccine before the toxins accumulate.
Recruitment
 In recruitment, the strength of contraction of the muscle is increased by
increasing the number of motor units stimulated.
 When only a few motor units are stimulated, a small force of contraction is
produced, because only a small number of muscle fibers are contracting.
 As the number of motor units stimulated increases, more muscle fibers are
stimulated to contract, and the force of contraction increases.
 Maximum force of contraction is produced in a given muscle when all the motor
units of that muscle are stimulated, or recruited.
 Motor unit recruitment allows muscles to have slow, smooth sustained
contractions so our movements are not jerky.
 If all the motor units in a muscle could be stimulated simultaneously, a quick,
jerky motion would occur.
 Because the motor units are recruited gradually so that some are stimulated and
held in tetanus while additional motor units are recruited, slow, smooth, sustained
contractions occur.
Types of Muscle Contractions
Muscle contractions are classified as either isometric or isotonic. Most muscle
contractions are a combination.
 Isometric (equal distance)
 tension increases during contraction
 length of the muscle does not change
 Example is when you push against a wall or try to pick up an
object that is too heavy to lift
 Isotonic (equal tension)
 tension is generally constant during contraction
 Although in one type of isotonic contraction, the tension
increases
 Length of the muscle changes (either increases or decreases).
 Example is when you lift a weight.
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Concentric and Eccentric Contractions
 Two types of isotonic contractions:
 CONCENTRIC CONTRACTIONS are isotonic contractions in which the
muscle tension increases as the muscle shortens. Most movements performed by
muscle contractions are of this type.
 ECCENTRIC CONTRACTIONS are isotonic contractions in which tension is
maintained as the muscle lengthens. An example is when a person lets down a
heavy weight slowly. Substantial force is produced in the muscles and injuries
can occur from repetitive eccentric contractions, such as in the hamstring muscles
when a person runs downhill.
Muscle Tone
 Even when muscles are relaxed, some of their fibers are still contracting, giving
the muscle some tone.
 Therefore, the normal state of a muscle, with some contraction, is called
muscle tone. This is important in posture so you can stand upright but mostly
relaxed.
 Muscle tone refers to the constant tension produced by muscles of the body over
long periods of time. It is responsible for keeping the back and legs straight, the
head held in an upright position, and the abdomen from bulging. it declines during
REM sleep.
 Hypertonia
 Can present clinically as either spasticity or rigidity
 Hypotonia
 Seen in lower motor neuron diseases
 Can present clinically as muscle flaccidity, where the limbs appear floppy,
stretch reflex responses are decreased, and the limb’s resistance to passive
movement is also decreased.
Muscle Spasticity
 Spasticity is a feature of altered skeletal muscle performance in muscle tone
involving hypertonia, which is also referred to as an unusual "tightness" of
muscles. Clinically spasticity is defined as velocity dependent resistance to
stretch, where a lack of inhibition from the CNS results in excessive contraction
of the muscles.
 Passively moving an elbow quickly will elicit increased muscle tone, but
passively moving elbow slowly may not elicit increased muscle tone
 It mostly occurs in disorders of the central nervous system (CNS) impacting the
upper motor neuron in the form of a lesion, but it can also present in various types
of multiple sclerosis, which are autoimmune conditions.
 Precise cause aside, whenever there is a loss of muscle tone inhibition from the
brain to the spinal cord such that muscles become overactive, this loss of
inhibitory control can cause an ongoing level of contraction, with decreased
ability for the affected individual to volitionally control the muscle contraction,
and increased resistance felt on passive stretch.
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 There is a difference in cause of two of the most common spasticity conditions,
spastic diplegia and multiple sclerosis.
 In spastic diplegia, the upper motor neuron lesion arises often as a result of
neonatal asphyxia (lack of oxygen in a newborn), while in conditions like
multiple sclerosis, spasticity is from autoimmune destruction of the myelin
sheaths around nerve endings.
 A defining feature of spasticity is that the increased resistance to passive stretch is
velocity-dependent.
 There is a velocity-dependent increase in tonic stretch reflexes (muscle tone) with
exaggerated tendon jerks, resulting from hyper-excitability of the stretch reflex.
 Causes of muscle spasticity include
 Cerebral palsy
 Spastic diplegia (a form of Cerebral palsy)
 Multiple sclerosis
 Spinal cord injury
 Stroke
Muscle Rigidity
 Unlike spasticity, rigidity is velocity-independent resistance to passive stretch.
 There is uniform increased tone whether the elbow is passively moved quickly or
slowly.
Muscle Clonus
 Clonus (from the Greek for "violent, confused motion") is a series of involuntary
muscular contractions and relaxations.
 Clonus is a sign of certain neurological conditions, and is particularly associated
with upper motor neuron lesions such as in stroke, multiple sclerosis, spinal cord
damage.
 Clonus causes large motions that are usually initiated by a reflex.
 Clonus is most common in the ankles, where it is tested by rapidly dorsiflexing
the foot. If the foot then jerks 5 times or more, clonus is present.
 It can also be tested in the knees by rapidly pushing the patella (knee cap),
towards the toes.
 Only sustained clonus (5 beats or more) is considered abnormal.
Muscle Fasciculations
 These are small, local, involuntary muscle contraction and relaxation visible
under the skin arising from the spontaneous discharge of a bundle of skeletal
muscle fibers (muscle fascicle).
 Fasciculations have a variety of causes, the majority of which are benign, but can
also be due to disease of the lower motor neurons.
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 Benign causes of fasciculations include:
 Magnesium deficiency
 Diarrhea
 Overexertion
 Inadequate intake from diet (almonds are a good source of
magnesium)
 Dehydration
 Fatigue
 They can also be caused by long-term use of:
 Benadryl (antihistamine)
 Dramamine (for nausea and motion sickness).
 Caffeine
 Sudafed
 Asthma medicines
 ADD medicines
 More serious conditions causing fasciculations include
 Fibromyalgia
 Myasthenia Gravis
 Lyme Disease
 Rabies
Hyperreflexia
 The most common cause of exaggerated reflexes is spinal cord injuries (upper
motor neuron diseases).
 Other causes include
 Medication
 Stimulants
 Hyperthyroidism
 Electrolyte imbalance
 Severe brain trauma.
Hyporeflexia
 This means diminished or absent reflexes.
 The most common cause is lower motor neuron diseases.
Muscle Contractures
 Muscle contractures can occur from paralysis, muscular atrophy, muscular
dystrophy, immobilization from a cast, and chronic spastic conditions like
cerebral palsy.
 Fundamentally, the muscle and its tendons shorten, resulting in reduced
flexibility.
 Muscle contractures in tendons are caused from the fibrinogen leaking out of the
fibroblasts, which turn the elastic fibers into inelastic fibers.
 Most treatments involve surgery, so physical therapy efforts focus on prevention
of contractures.
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Exercise
 Average adults have roughly equal numbers of slow and fast twitch fibers.
 However, of their fast twitch fibers, they have three times as many type IIa
(slower, better endurance fast-twitch) fibers as they have type IIx fibers (faster,
but fatigue faster).
 A sprinter may have 80% of type IIa fibers (slower, better endurance), while a
marathon runner might have 95% of type I fibers (even slower and even better
endurance). The ratio is due to genetics, but can be influenced by training.
 Exercise increases the vascularature (blood supply) to the muscles, increases the
number of mitochondria per muscle fiber, and causes enlargement of muscle
fibers by increasing the number of myofibrils and myofilaments (there is no
increase in the number of muscle cells).
 With weight training, fast-twitch type IIx (fastest, but fatigue easiest) can be
replaced by fast-twitch type IIa (less fast, fatigue less quickly) as muscles enlarge,
but you cannot change a fast twitch to a slow twitch fiber.
 When exercise stops, the genes turn off and the muscles return to their previous
condition.
Energy Requirements of Muscle
 What fuel does a car use?
 Gasoline
 What fuel does a candle use?
 Wax
 What fuel do humans use?
 Oxygen?
 NO
 Sugars?
 NO
 ATP
 YES
ATP
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


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Where do we get ATP?
We can make a little ATP in the cytoplasm of our cells, but not enough to live on.
Most of our ATP is made by the mitochondria inside our cells.
Mitochondria are like little protozoa (animals) that live in our cells. Each cell has
hundreds of them. Muscle cells have thousands of them.
What is their fuel?
 Oxygen and glucose
THAT is why we need to inhale oxygen and consume sugars….to feed our
mitochondria so they can make ATP for us!
In order for the muscle mitochondria to produce enough ATP, they need oxygen
(for their own aerobic respiration) and sugars that are in storage.
Mitochondria can only perform aerobic respiration.
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 What can we do to make ATP if our muscle cells run out of oxygen?
 Start performing anaerobic respiration.
 We can do this ourselves in the cytoplasm of our cells.
Making ATP by Aerobic Respiration
Aerobic respiration
 Takes place in the mitochondria
 Requires oxygen
 Breaks down glucose to produce ATP
 Waste products are CO2 and H2O (we exhale them)
 The good thing about making ATP from our mitochondria is that we can make a
LOT of it.
 The bad things are that it takes longer to make it, and it requires oxygen, and a
muscle cell may have used up all the oxygen during a sprinting run.
Making ATP by Anaerobic Respiration
Anaerobic respiration
 Takes place in the cytoplasm
 Does not require oxygen
 Breaks down glucose to produce ATP
 Waste product is lactic acid
 The good thing about making ATP this way is that we can make it FAST.
 The bad thing is that it does not make much ATP, and we deplete the reserves
quickly.
Lactic Acid
 The waste product of aerobic respiration is carbon dioxide and water. These are
not a problem…we eliminate them by exhaling.
 The waste product of anaerobic respiration is lactic acid, which can irritate muscle
fibers, causing muscle pain (stitch in your side) and muscle cramps.
 We deactivate lactic acid by adding oxygen to it. Therefore, breathing heavily
adds the oxygen to our system to deactivate lactic acid, and the muscle pains go
away.
ATP and Creatine Phosphate
 What do we do when we run out of ATP?
 Muscle fibers cannot stockpile ATP in preparation for future periods of activity.
 However, they can store another high energy molecule called creatine
phosphate.
 Creatine phosphate is made from the excess ATP that we accumulate when we are
resting.
 During short periods of intense exercise, the small reserves of ATP existing in
a cell are used first.
 Then creatinine phosphate is broken down to produce ATP.
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Aerobic vs. Anaerobic Respiration
 When do we use aerobic respiration?
 Resting (can breathe easily)
 Running marathons (can breathe easily on long runs)
 Marathon runners want to make sure there will be enough readily
available energy for the muscles, so they eat a lot of
carbohydrates over a two-day period before the marathon. That’s
why they load up on pasta before a marathon.
 When do we use anaerobic respiration?
 Sprint running (can’t talk while sprinting!)
 Why does sprinting require anaerobic respiration?
 We use up all of the ATP faster than we can make it.
 When we run out of ATP, we break down creatine phosphate to make more ATP.
 When we run out of ATP and creatine phosphate, we start using anaerobic
respiration to make more ATP.
 When we run out of glucose, or too much lactic acid is built up, we have to stop
and rest.
 Anaerobic metabolism is ultimately limited by depletion of glucose and
buildup of lactic acid within the muscle fiber.
Sprint Runners
 Why do sprint runners tire out during the last part of a fast run?
 Sprinting is an anaerobic activity…the oxygen requirement is quickly exceeded,
so the muscle has to use anaerobic respiration to continue to contract. This
requires a lot of glucose and also results in a buildup of lactic acid.
 Once the sprint-runner has used up the available glucose, or has produced
too much lactic acid, the muscles fatigue.
Oxygen Debt
 Anaerobic respiration produces lactic acid, which causes the painful cramps
because it creates an oxygen debt.
 The amount of oxygen needed to replenish the supply following aerobic
demand is called the oxygen debt.
 When you continue to breathe heavily after exercising, it means you have an
oxygen debt.
 Muscles can do without oxygen for a while pretty well, unlike the brain.
 To pay back a minor oxygen debt, you just have to breathe heavily for a while.
 This heavy breathing brings in oxygen, which is used to convert lactic acid to
glucose, replenish the depleted ATP and creatinine phosphate stores in the muscle
fibers, and to replenish oxygen stores in the lung, blood, and muscles.
 After the oxygen debt has been paid back, breathing returns to normal.
 People who are in good physical condition can carry out both aerobic and
anaerobic activities efficiently, and do not suffer from an oxygen debt for very
long.
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Myoglobin
 Myoglobin is an iron- and oxygen-binding protein found in the muscle tissue of
mammals.
 It is related to hemoglobin, which is the iron- and oxygen-binding protein in
blood, specifically in the red blood cells.
 The only time myoglobin is found in the bloodstream is when it is released
following muscle injury. It is an abnormal finding, and can be diagnostically
relevant when found in blood.
 Myoglobin binds to oxygen more strongly than hemoglobin.
 It acts as an oxygen-storage molecule and delivers the oxygen to cells when
needed.
 High concentrations of myoglobin in muscle cells allow organisms to hold their
breaths longer.
 Diving mammals such as whales and seals have muscles with particularly high
myoglobin levels.
 Myoglobin forms pigments responsible for making meat red. The color that meat
takes is partly determined by the oxidation states of the iron atom in myoglobin.
 When meat is raw, the iron atom is in the +2 oxidation state (Fe+2).
 Meat cooked well done is brown because the iron atom is now in the +3 oxidation
state (Fe+3), having lost an electron.
 Under some conditions, meat can also remain pink all through cooking, despite
being heated to high temperatures. If meat has been exposed to nitrites, it will
remain pink because the iron atom is bound to NO, nitric oxide (e.g., corned beef
or cured hams). Grilled meats can also take on a pink "smoke ring" that comes
from the iron binding to a molecule of carbon monoxide.
 Rhabdomyolysis is the condition when myoglobin is released from damaged
muscle tissue.
 Released myoglobin is filtered by the kidneys, but it damages them, so it can lead
to renal failure.
 High blood levels may indicate the person is having a heart attack, or it could just
be a muscle injury.
 Therefore, CK, cTnT, ECG, and clinical signs should be taken into account to
make the diagnosis of a heart attack.
Creatine kinase (CK)
 CK is the enzyme used to get ATP out of storage (ATP is stored as creatine).
 High blood levels of CK may indicate myocardial infarction (heart attack),
rhabdomyolysis (severe muscle breakdown), muscular dystrophy, the
autoimmune myositides, or acute renal failure.
Troponin (cTnT)
 Troponin levels in the blood can be used as a test of several different heart
disorders, including myocardial infarction.
 Troponin-I is highly specific for cardiac muscle necrosis. Serum levels rise 4-8
hrs after onset of chest pains, peak at 12-16 hrs and return to baseline within 5-9
days.
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EXERCISE
 There are many physiological benefits of exercise:
1. Improved muscular strength, endurance, flexibility
2. Improved cardio-respiratory endurance
3. Increased bone density and strength
4. Relief from depression
5. Increased HDLs
Hypertrophy
 Weight training and other exercises can cause muscles to hypertrophy ( enlarge).
This occurs as more myofilaments and myofibrils are produced inside a myofiber,
causing them to enlarge. The number of mitochondria also increases, causing
additional enlargement.
 However, you don’t grow new muscle cells. The number of cells in a skeletal
muscle remains relatively constant following birth.
 Hypertrophy can happen in two ways:
 Increase in number of fibers inside a muscle cell
 Increase in size of individual fibers
 Muscle hypertrophy is greater in males due to the hormone testosterone.
 A professional athlete may have many muscles that exhibit hypertrophy.
 Eating protein does not automatically increase muscle. The average person only
needs one ounce of protein a day, two if you work out.
 Two ounces is like one mini hamburger.
 Most people eat too much meat.
 Most people need around 0.8 grams of protein per day per 2.2 pounds of body
weight, according to registered dietitian Reed Mangels.
 Consuming around 46 grams of protein per day if you're female and 56 grams per
day if you're male will meet your protein needs, whether you get your protein
from meat or from plant sources.
 A 3-ounce portion of meat contains 21 to 24 grams of protein.
 Three 3-ounce meat servings per day would supply all your protein needs, but this
much meat could include a large amount of saturated fat, which could increase
your risk of heart disease.
Atrophy
 Lack of use causes muscle ATROPHY. This happens quickly. Astronauts can
lose 40% of their muscle in two weeks! It is regained quickly, too.
 Atrophy is a decrease in muscle size because of the decrease in myofilaments
within muscle fiber.
 Severe atrophy involves the permanent loss of skeletal muscle fiber and the
replacement of those fibers by connective tissue.
 Damage to the nervous system, or a severed motor nerve can cause atrophy. The
muscle becomes flaccid (having no tone) .
 Casting a broken limb also leads to temporary atrophy.
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Muscular Dystrophy
 This refers to a group of inherited muscle disorders in which skeletal, cardiac, and
smooth muscle tissue degenerates and the person experiences progressive
weakness and other symptoms, including heart problems.
 The disorders are characterized by the progressive degeneration of muscle fibers
leading to atrophy and their eventual replacement by fat and other connective
tissue.
 This is a genetic lack of a protein called DISTROPHIN. It causes the muscle
tissue to harden, inhibiting contraction, causing progressive paralysis.
 Duchenne muscular dystrophy is more common in males.
Muscle Problems
 Tendonitis is an inflammation of the tendon or its attachment point. It usually
occurs in athletes who overuse the muscle to which the tendon is attached.
 A strain is a tear in a muscle. Remember, a sprain is a tear in a ligament.
 A muscle strain will heal faster than a torn ligament because muscles have good
blood supply and ligaments do not.
Treatment for Injuries: RICE
 Rest
 Ice
 20 minutes on, 20 minutes off
 Ice pack or frozen bag of peas!
 Compression
 Ace wrap from distal to proximal
 Don’t leave any openings while wrapping
 Elevation
 Above the heart
Treatment for Injuries: RICE
 Ice for the first 72 hours (NO heat!)
 Anti-inflammatory medicines
 Ibuprofin, 600 mg TID (3x a day)
 Over the counter (OTC) pills are 200 mg
 Heat and massage as needed after third day.
 Can try a muscle stimulator too…works pretty well!
Muscle Spasms
 Muscle spasms/cramps are sudden and involuntary muscle contractions. They
are painful, spastic contractions that are usually caused from overexertion. Lactic
acid builds up and irritates the overused muscles, causing inflammation. If the
muscle remains in spasm for longer than a few minutes, might need heat and
massage to increase circulation.
 Avoid spasms by stretching before and after activities.
 For people with frequent low back spasms throughout the day, a portable muscle
stimulator that clips to the belt will help a great deal.
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Fibromyalgia (muscle and tissue pain)
 Common disorder in adults, especially women
 Painful muscles, debilitating fatigue, sleep disturbance, and joint stiffness
 Many trigger points: painful lumps in muscles
 Treatment includes anti-inflammatory medicines, physical therapy, acupuncture,
and exercise.
 Muscle stimulators help
Ganglion Cysts
 Ganglion cysts arise as outpouchings from fluid filled areas such as the fluid
around tendon sheaths.
 When the fluid, called synovial fluid, leaks out from these spaces, it can become a
cystic structure.
 Treatment is to drain the fluid with a needle, but they frequently grow back.
 Then you do a surgery to scoop out the whole cyst, find the stalk and tie it off.
Baker’s Cyst
 A Baker's Cyst, or popliteal cyst, is a collection of fluid in the back of the knee
joint.
 A Baker's cyst is usually a symptom of another problem, or it may be an
incidental finding with no significant meaning.
 Most often in adults the Baker's cyst is found in conditions where there is chronic
swelling or fluid accumulation in the knee joint.
 These conditions include knee arthritis, meniscus injuries, and ligamentous
injuries.
 Treatment of a Baker's cyst that is the result of a problem within the knee consists
of treating the underlying problem. These treatments may include antiinflammatory medications and cortisone injections.
 The cyst can be drained with a needle, but the fluid can be jelly-like and difficult
to remove.
 If conservative treatments fail to correct the cyst, an operation can be done to
excise the cyst.
AGING
 With aging, fibrous connective tissue replaces some muscle fibers, causing
decreased strength.
 As people age, the number of muscle fibers decreases, and new ones cannot be
added.
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Smooth and Cardiac muscle
SMOOTH MUSCLE CELLS
Found around internal organs (intestines, uterus, etc). They are involuntary and not
striated. When smooth muscle contracts around the intestines, the movement is called
PERISTALSIS.
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•
•
•
•
•
•
•
•
Smooth muscle cells are small and spindle shape, usually with one nucleus per
cell.
They contain less actin and myosin, and the microfilaments are not organized into
sarcomeres.
As a result, smooth muscle cells are not striated.
They contract more slowly and do not develop an oxygen debt.
Smooth muscle cells can spontaneously generate action potentials that cause the
cell to contract.
Smooth muscle is under involuntary control, whereas skeletal muscle is voluntary.
Some hormones in the digestive system can stimulate smooth muscles to contract.
They have specialized cell to cell contacts that allow the action potential to spread
to all of the smooth muscle cells in a given tissue.
This allows them to function as a unit and contract at the same time.
Characteristics of smooth muscle
 There are no distinct sarcomeres
 They contract more slowly than skeletal muscle…their twitch time is very long =
several seconds
 It doesn’t get tired (“I’m too tired to urinate!”)
 They contract in response to neurons as well as hormones and changes in local
environment (amount of oxygen, lactic acid, etc).
 They may be autorhythmic (self-exciting); they can contract spontaneously
without being stimulated (like cardiac muscle).
 They do not develop oxygen debt.
CARDIAC MUSCLE: Only found in heart. Has both smooth/skeletal characteristics.
It’s involuntary and striated. It is made up of individual cells.
Cardiac muscle has INTERCALATED DISCS which join each cell. These are a
series of gap junctions (communication) and desmosomes (holds cells together).
 Cardiac cells are long, striated, and branching, with one nucleus per cell.
 The actin and myosin myofilaments are organized into sarcomeres, but not as
uniformly as in skeletal muscle.
 As a result, cardiac muscle cells are striated, but not as distinctly as skeletal
muscle.
 Cardiac muscle is involuntary and does not fatigue.
 Cardiac muscle cells are connected to one another by intercalated discs which
facilitate action potential conduction between themselves.
 This allows them to function as a unit and they all contract together.
 Contraction of cardiac cells is influenced by hormones, such as epinephrine.
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 As one cell contracts, the action potential goes through all the cells, and they all
contract as a unit. That’s why the heart contracts all at once.
 It has an intrinsic beat. The cells contract on their own, without a signal.
 Even if you chop a heart up, each piece will beat by itself!
Involuntary or
voluntary?
Striated or
non-striated
Where is it
found?
Skeletal muscle
Voluntary
Smooth muscle
Involuntary
Cardiac muscle
Involuntary
Striated
Non-striated
Striated
Inserts onto bones
Myometrium of
uterus, intestines,
blood vessels,
bladder, other organs
Myocardium of heart
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