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Muscular System
BMLS II-E (2012) Human Anatomy and Physiology 1
UNDERSTANDING WORDS
Calat - something inserted e.g. interalated disc—membranous band that
connects cardiac muscle cells Erg – work
e.g. synergist – muscle that works with a prime mover to produce a movement
Fasc – bundles e.g. fasciculus – bundles of muscle of fibers
Gram – something written e.g. myogram – recording of a muscular
contraction Hyper – over, more
e.g. muscle hypertrophy – enlargement of muscle fibers
Inter – between e.g. intercalated disc – membranous band that
connects cardiac muscle cells Iso – equal
e.g. isotonic contraction – contraction during which the tension in a muscle remains unchanged
Laten – hidden e.g. latent period – period between a stimulus
and the beginning of a muscle contraction Myo – muscle
e.g. myofibril – contractile fiber of a muscle cell Reticul – a net
e.g. sarcoplasmic reticulum – network of membranous channels within a muscle fiber
Sarco – flesh e.g. sarcoplasm – substance (cytoplasm) within
a muscle fiber Syn – together
e.g. synergist – muscle that works with a prime mover to produce a movement
Tetan – stiff e.g. titanic contraction – sustained muscular
contraction Tonic – stretched
e.g. isotonic contraction – contraction during which the tension of a muscle remains unchanged
Troph – well fed
e.g. muscular hypertrophy – enlargement of muscle fibers
Voluntar – of one’s free will e.g. voluntary muscle – muscle that can be
controlled by conscious effort STRUCTURE OF A SKELETAL MUSCLE
- it is composed primarily of skeletal muscle tissue, nervous tissue, blood and connective tissue
- CONNECTIVE TISSUE COVERINGS
- An individual skeletal muscle is separated from
adjacent muscles and held in position by layers
of dense connective tissue called fascia. This
connective tissue surrounds each muscle and
may project beyond the ends of its muscle
fibers to form a cord-like tendon. Fibers in a
tendon may intertwine with those in the
periosteum of a bone, attaching the muscle to
the bone or the connective tissue associated
with a muscle from broad, fibrous sheets called
aponeuroses which may attach to bone or the
coverings of adjacent muscles
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BMLS II-E (2012) Human Anatomy and Physiology 2
- The layer of connective tissue that closely
surrounds a skeletal muscle is called the
epimysium. Another layer of connective tissue
called the perimysium, extends inward form the
epimysoum and separates the muscle tissue
into small sections. These sections contain
bundles of skeletal muscle fibers called
fascicles. Each muscle fiber within a fascicle lies
within a layer of connective tissue in the form
of a thin covering called endomysium.
DEEP FASCIA
- The portion of the network that surrounds and
penetrates the muscles
SUBCUTANEOUS FASCIA
- Deep fascia is continuous with this
- It lies just beneath the skin, forming the
subcutaneous layer.
SUBSEROUS FASCIA
- Subcutaneous fascia is also continuous with this
that forms the connective tissue layer of the
serous membranes covering organs in various
body cavities and lining those cavities
SKELETAL MUSCLE FIBERS
Myofibrils
- The sarcoplasm also has abundant, parallel,
thread-like structures called myofibrils
- Play a fundamental role in the muscle
contraction mechanism
MYOSIN (thick filaments) – composed of protein
ACTIN (thin filaments) composed primarily of
the protein actin
Sarcomeres
- Striations form a repeating pattern of units
STRIATION PATTERN
I Bands (light bands)
Composed of thin actin filaments held by
direct attachments to structures called Z
line
Z line – appear in the center of the I bands
A Bands (dark bands)
Composed of thick myosin filaments
overlapping thin actin filaments
H zone – slightly lighter cental region of A
band
It includes a thickening known as M line
M line – consists of proteins that help hold
the thick filaments in place
* TTIN – large protein
Cross-bridges
- Two twisted protein strands with globular parts
that project outward along their lengths
TWO OTHER TYPES OF PROTEIN
Troponin
Have 3 protein subunits and are attached to
actin
Tropomyosin
Are rod-shaped and occupy the longitudinal
grooves of the actin helix
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BMLS II-E (2012) Human Anatomy and Physiology 3
Troponin-tropomyosin complex
- This is form when each tropomyosin is held in
place by a troponin molecule
Sarcoplamic Reticulum
- Within the sarcoplasm of a muscle fiber is a
network of membranous channels that
surrounds each myobfibril and runs parallel to
it. This membranous form the sarcoplasmic
reticulum
- Corresponds to the endoplasmic reticulum of
other cells
Transverse tubule (T-tubules)
- A set of membranous channels
- It extends into the sarcoplasm as an
invaginations continuous with the sarcolemma
and contains extracellular fluid
Cisternae
- transverse tubule lies between two enlarges
portions of the sarcoplasmic reticulum
Triad
- formed by the 3 structures (sarcoplasmic
reticulum, T-tubules, cisternae) near the region
where the actin and myosin filaments overlap
SKELETAL MUSCLE CONTRACTION
- A muscle fiber contraction is a complex
interaction of several cellular and chemical
constituents. The final result is a movement
within the myofibrils in which the filaments of
actin and myosin slide past one another,
shortening the sarcomeres. When this happens,
the muscle fiber shortens and pulls on its
attachments
NEUROMUSCULAR JUNCTION
Motor Neurons
- Neurons that control effectors, including
skeletal muscle
Synapse
- It is a space through which information can pass
Neurotransmitters
- Neurons communicate with the cells that they
control by releasing these chemicals
Neuromuscular Junction
- The site where an axon and a muscle fiber meet
Motor end plate
- Muscle fiber membrane is specialized to form
this where nuclei and mitochondria are
abundant and the sarcolemma is extensively
folded
* together, a motor neuron and the muscle fibers it
controls constitute a motor unit
Synaptic Cleft
- A small gap that separates the membrane of the
neuron and the membrane of the muscle fiber
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BMLS II-E (2012) Human Anatomy and Physiology 4
STIMULUS FOR CONTRACTION
Acetylcholine
- Is the neurotransmitter that motor neurons use
to control skeletal muscle contraction
- It is synthesized in the cytoplasm of the motor
neuron and is stored in synaptic vesicle near the
distal end of its axon
- Acetylcholine diffuses rapidly across the
synaptic cleft, combines with Ach receptors on
the motor endplate, and stimulates the muscle
fiber, the response is muscle impulse
Muscle Impulse
- Is an electrical signal that is very much like a
nerve impulse
- It changes the muscle cell membrane in a way
that transmits the impulse in all directions along
and around the muscle cell into the T-tubules,
into the sarcoplasm and ultimately to the
sarcoplasmic reticulum and the cisternae.
EXCITATION CONTRACTION COUPLING
THE SLIDING FILAMENT
Model of Muscle Contraction
- when sarcomeres shorten, the thick and thin
filaments do not change length. They slide past
one another with the thin filaments moving
toward the center of the sarcomere form both
ends. As this occurs, the H zone and the I bands
narrow, the regions of overlap widen and Z lines
move closer together, shortening the sarcomere
Major events of muscle fiber contraction
- a nerve impulse travels down a motor neuron
axon
- the motor neuron terminal releases the
neurotransmitter acetylcholine (Ach)
- Ach binds to Ach receptors
- The sarcolemma is stimulated and a muscle
impulse travels over the surface of the muscle
fiber and deep into the fiber through the
transverse tubules
- The muscle impulse reaches the sarcoplasmic
reticulum and calcium channels open
- Calcium ion diffuse from the sarcoplasmic
reticulum into the sarcoplasm and bind to
troponin molecules
- Tropomyosin molecules move and expose
specific sites on actin
- Actin and myosin form linkages
- Thin (actin) filaments are pulled toward the
center of the sarcomere by myosin cross-
bridges
- The muscle fiber shortens and contracts
Cross-Bridge Cycling
- the force that shortens the sarcomeres comes
from cross-bridges pulling on the thin filaments.
A myosin cross bridge can attach to an actin
binding site and bend slightly, pulling on the
actin filament. Then the head can release,
straighten, combine with another binding site
further down the actin filament and pull again.
- Myosin cross-bridges contain the enzyme
ATPase, which catalyzes the breakdown of ATP
to ADP and phosphate
Relaxation
- When nerve impulses cease, two events relax
the muscle fiber.
- Acetylcholinesterase rapidly decomposes any
acetylcholine remaining in the synapse. This
enzyme prevents a single nerve impulse from
continuous stimulating a muscle fiber.
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BMLS II-E (2012) Human Anatomy and Physiology 5
Major events of muscle fiber relaxation
- Acetylcholinesterase decomposes acetylcholine
and the muscle fiber membrane is no longer
stimulated
- Calcium ions are actively transported into the
sarcoplasmic reticulum
- ATP breaks linkages between actin and myosin
fiaments without breakdown of the ATP itself
- Breakdown of ATP “cocks” the cross-bridges
- Troponin and tropomyosin molecules inhibit the
interaction between myosin and actin filaments
- Muscle fiber remains relaxed, yet ready until
stimulated again
ENERGY SOURCES FOR CONTRACTION
Creatine Phosphate
- The initial source of energy available to
regenerate ATP from ADP and phosphate
- Includes a high-energy phosphate bond
- Is 4 to 6 times more abundant in muscle fibers
than ATP
- Cannot directly supply energy to a cell
- It stores energy released from mitochondria
OXYGEN SUPPLY AND CELLULAR RESPIRATION
Anaerobic
- Early phase of cellular respiration, occurs in the
cytoplasm is anaerobic
- Only partially breaks down energy-supplying
glucose and releases only a few ATP molevules
Aerobic
- Complete breakdown of glucose occurs in the
mitochondria and is aerobic
- Includes the complex series of reactions of the
citric acid cycle and electron transport chain
Myoglobin
- A pigment and is synthesized in muscle cells and
imparts the reddish brown color of skeletal
muscle tissue.
- Can loosely bind oxygen and has greater
attraction for oxygen than does hemoglobin
- Can temporarily store oxygen in muscle tissue
which reduces a muscle’s requirement for a
continuous blood supply during contraction
OXYGEN DEBT
Lactic acid threshold
- Shift in metabolism
- Anaerobic threshold
OXYGEN DEBT
- When lactic acid accumulates, a person
develops an oxygen debt
- The amount of oxygen debt roughly equals the
amount of oxygen liver cells require to use the
accumulated lactic acid to produce glucose, plus
the amount the muscle cells require to
resynthesize ATP and creatine phosphate and
restore their original concentrations
MUSCLE FATIGUE
- A condition when a muscle exercised
persistently for a prolonged period may lose its
ability to contract
- Is most likely to arise from accumulation of
lactic acid in the muscle from anaerobic ATP
production
Cramped
- A sustained, painful, involuntary muscle
contraction
- Decreased electrolyte concentration, occurring
in the extracellular fluid surrounding the muscle
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BMLS II-E (2012) Human Anatomy and Physiology 6
fibers and their motor neurons trigger
uncontrolled stimulation of the muscle
MUSCULAR RESPONSES
Threshold Stimulus
- When an isolated muscle fiber is exposed to a
series of stimuli of increasing strength, the fiber
remains unresponsive until a certain strength of
stimulation called threshold stimulus is applied
- Once threshold is reached, an action potential is
generated, resulting in a muscle impulse that
spreads throughout the muscle fiber, releasing
enough calcium ions from the sarcoplasmic
reticulum to activate cross-bridges binding and
cause a contraction of that fiber
RECORDING OF A MUSCLE CONTRACTION
Twitch
- A contractile response of a single muscle fiber
to a muscle impulse
- Consists of a period of contraction, during
which the fiber pulls at its attachments,
followed by a period of relaxation, during which
the pulling force declines.
- These events can be recorded in a pattern
called a myogram
Latent Period
- A brief delay between the time of stimulation
and the beginning of contraction
- In human muscle may be less than 2
milliseconds
Summation
- The force of individual twitches combines by
the process of summation
Tenatic Contraction
- When the resulting forceful, sustained
contraction lacks even partial relaxation
Multiple Motor Unit Summation or Recruitment
- An increase in the number of activated motor
units
Sustained Contractions
- During sustained contractions, smaller motor
units which have smaller diameter axons are
recruited earlier. The larger motor units, which
include larger diameter axons, respond later
and more forcefully. The result is a sustained
contraction of increasing strength
Muscle tone (tonus)
- Even when a muscle appears to be at rest, a
certain degree of sustained contraction occurs
in its fiber. This is called muscle tone.
TYPES OF CONTRACTIONS
Isotonic – (equal force – change in length)
Concentric – shortening occurs
Eccentric Contraction
- Lengthening
- Occurs when the force a muscle generates is
less than that requires to move or lift an object.
- Even if such a contraction, cross-bridges are
working but not generating enough force to
shorten the muscle
Isometric – (equal length-change in force)
Fast and Slow-Twitch Muscle Fibers
Slow-twitch fibers (type I)
- Always oxidative and are therefore resistant to
fatigue
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BMLS II-E (2012) Human Anatomy and Physiology 7
- Often called red fiber because they contain the
red, oxygen-storing pigment myoglobin
Fast-twitch fibers (type II)
- May be primarily glycolytic (fatigable) or
primarily oxidative (fatigue resistant)
Fast-twitch glycolytic fibers (type IIa)
- Also called white fibers because they have less
myoglobin and have a poorer blood supply then
red fibers
Fast-twitch fatigue-resistant fibers (type IIb)
- Also called intermediate fibers
- These fibers have the fast-twitch speed
associated with white fibers combined with a
substantial oxidative capacity more
characteristic of red fibers
SMOOTH MUSCLES
- Smooth muscle contraction resembles skeletal
muscle contraction in a number of ways. Both
mechanisms reflect reactions of actin and
myosin; both are triggered by membrane
impulses and release of calcium ion; and both
use energy from ATP molecules
Calmodulin
- Binds to calcium ions released when its fiber are
stimulated, activating actin-myosin contraction
CARDIAC MUSCLE
- Appears only in the heart. It is composed of
striated cells joined end to end, forming fibers
that are interconnected in branching, three-
dimensional networks.
- The opposing ends of cardiac muscle cells are
connected by cross-bands called intercalated
disc. These bands are complex membrane
junctions. Not only do they help join cells and
transmit the force of contraction from cell to
cell, but the intercellular junctions of the fused
membranes of intercalated disc allow ions to
diffuse between the cells. This allow muscle
impulses to travel rapidly from cell to cell
SKELETAL MUSCLE ACTIONS
- Skeletal muscle generates a great variety of
body movements. The action of each muscle
mostly depends upon the kind of joint it is
associated with and the way the muscle is
attached on either side of that joint
Origin and Insertion
Origin – immovable end
Insertion – movable end
Interaction of Skeletal Muscles
Prime mover or Agonist
- Is the muscle primarily responsible for
producing an action
Synergists
- Muscles that contract and assist a prime mover
Antagonists
- These muscles can resist a prime mover’s action
and cause movement in the opposite direction
Muscular System
BMLS II-E (2012) Human Anatomy and Physiology 8
MAJOR SKELETAL MUSCLES
MUSCLES OF FACIAL EXPRESSION
Muscular System
BMLS II-E (2012) Human Anatomy and Physiology 9
MUSCLES MOVING THE HEAD
MUSCLES OF MASTICATION
Muscular System
BMLS II-E (2012) Human Anatomy and Physiology 10
HYOID MUSCLE
TONGUE MUSCLE
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BMLS II-E (2012) Human Anatomy and Physiology 11
MUSCLES OF SWALLOWING AND THE LARYNX
Muscular System
BMLS II-E (2012) Human Anatomy and Physiology 12
MUSCLES MOVING THE EYES
MUSCLES ACTING ON THE VERTEBRAL COLUMN
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BMLS II-E (2012) Human Anatomy and Physiology 13
MUSCLES ACTING ON THE VERTEBRAL COLUMN
Muscular System
BMLS II-E (2012) Human Anatomy and Physiology 14
MUSCLES OF THORAX
MUSCLES OF ABDOMINAL WALL
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BMLS II-E (2012) Human Anatomy and Physiology 15
MUSCLES OF THE PELVIC FLOOR AND PERINEUM
MUSCLES ACTING ON THE SCAPULA
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BMLS II-E (2012) Human Anatomy and Physiology 16
MUSCLES ACTING ON THE ARM
SUMMARY OF MUSCLE ACTIONS ON THE SHOULDER AND ARM
MUSCLES ACTING ON THE FOREARM
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BMLS II-E (2012) Human Anatomy and Physiology 17
MUSCLES ACTING ON THE FOREARM
MUSCLES OF THE FOREARM ACTING ON WRIST, HAND AND FINGERS
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BMLS II-E (2012) Human Anatomy and Physiology 18
MUSCLES OF THE FOREARM ACTING ON WRIST, HAND AND FINGERS
INSTRINSIC HAND MUSCLE
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BMLS II-E (2012) Human Anatomy and Physiology 19
INSTRINSIC HAND MUSCLE
MUSCLES ACTING ON THE THIGH
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BMLS II-E (2012) Human Anatomy and Physiology 20
SUMMARY OF MUSCLE ACTION ON THE HIP AND THIGH
MUSCLES OF THE THIGH
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BMLS II-E (2012) Human Anatomy and Physiology 21
MUSCLES OF THE LEG ACTING ON THE LEG, ANKLE AND FOOT
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BMLS II-E (2012) Human Anatomy and Physiology 22
INSTRINSIC MUSCLE OF THE FOOT
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BMLS II-E (2012) Human Anatomy and Physiology 23
DISEASES
Moebius Syndrome
- absence of the 6th and 7th cranial nerves which carry impulses from the brain to the muscles of the face, leads to an odd collection of symptoms
- 1st signs: difficulty sucking, excessive drooling and sometimes crossed eyes TENDINITIS and TENOSYNOVITIS
- A tendon or the connective tissue sheath of a tendon (tenosynovium) may become painfully inflamed and swollen following an injury or the repeated stress of athletic activity
- The tendons most commonly affected are those associated with the joint capsules of the shoulder, elbow, hip and knee and those involved with moving the wrist, hand, thigh and foot
COMPARTMENT SYNDROME
- A condition wherein an injury causes fluid, such as blood from an internal hemorrhage, to accumulate within a compartment, the pressure inside will rise. The increase pressure, in turn, may interfere with blood flow into the region, reducing the supply of oxygen and nutrients to the affected tissues
- Treatment may require immediate intervention by a surgical incision through the fascia (fasciotomy) to relieve the pressure and restore circulation
MUSCLE STRAIN
- A type of injury that is common to athletes, muscle fibers and connective tissues, can be tear if overstretched - Mild strain – only a few muscle fibers are injured, the fascia remains intact and little function id lost - Severe Strain – many muscle fibers as well as fascia tear, and muscle function may be lost completely
MYASTHENIA GRAVIS
- An autoimmune disorder, the immune system attacks part of the body, that part is the muscular system, particularly receptors for acetylcholine on muscle cells at neuromuscular junctions.
TERMINOLOGIES COMPARTMENT
- The space that contains a particular group of muscles, blood vessels, and nerves, all tightly enclosed by fascia. DYSTROPHIN
- Rod-shaped muscle proteins that are vital to muscle function - It accounts for only 0.002% of total muscle protein in skeletal muscle, but its absence causes the devastating
inherited disorder RIGOR MORTIS
- A condition wherein a few hours after death, the skeletal muscles partially contracts, fixing the joints - May continue for seventy-two hours or more - It results from an increase in membrane permeability to calcium ions which promotes cross-bridge attachment
and a decrease in availability of ATP in the muscle fibers