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Muscular System

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by

Pamela Stephens

on 27 February 2014

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Transcript of Muscular System

Several bacteria, viruses, and parasites can infect muscles
Poliomyelitis
is a
viral

infection of motor nerves
that ranges from mild to life threatening





Trichinosis

parasite that invades muscles
after eating infected
pork
Influenza

viral
infection that causes muscle pain and stiffness

Muscular System
Functions of Skeletal Muscle
Movement
Groups of muscles work together to produce movement
Prime mover
—muscle whose contraction is mainly responsible for producing a given movement
Synergist
—muscle whose contractions help the prime mover produce a given movement
Antagonist
—muscle whose actions oppose the action of a prime mover in any given movement (they relax as prime mover/synergist contract)
Joint Stabilization
Stabilize joints with their
TENDONS
Rigor Mortis
Latin phrase meaning “
stiffness of death

Refers to the stiffness of skeletal muscles sometimes observed shortly after death
Cause?
At time of death,
stimulation
of muscle cells
ceases
Muscle fibers that were
mid-contraction
(myocin-actin cross-bridges still intact)
can’t obtain the ATP necessary to release the cross-bridge
Actin and myosin fibers will remain linked until the muscles themselves start to decompose -- body will then "relax"
Rigor mortis can be used to help
estimate time of death
Effects of Exercise on Skeletal Muscles
Exercise, if regular and properly practiced,
improves muscle tone and posture
, results in
more efficient heart and lung functioning
, and
reduces fatigue
Muscles undergo changes related to the amount of work they normally do
Prolonged inactivity causes
disuse atrophy
(a shrink in mass)
Regular exercise increases muscle size, called
hypertrophy

Microscopic Structure of Skeletal Muscle
Basic functional (contractile) unit called a
sarcomere
Sarcomeres separated from each other by dark bands called
Z lines
Sliding filament model
explains mechanism of contraction
Thick and thin
myofilaments
slide past each other as a muscle contracts
Contraction requires
calcium
, energy-rich
ATP
molecules, and
acetylcholine
(neurotransmitter that relays message from nerve to muscle fiber)

Types of Muscle Tissue
Skeletal Muscle
(AKA striated, voluntary)
"
red meat
" attached to bones
40-50% of body weight
multiple nuclei, crosswise stripes/striations
voluntary
control
Cardiac Muscle
composes bulk of
heart
single nucleus, crosswise stripes/striations
cells branch and recombine -- allows heart to contract efficiently as a unit
dark bands --
intercalated disks
-- allows heart to contract efficiently as a unit
involuntary
control
Smooth Muscle
(AKA visceral, nonstriated, involuntary)
Found in
walls of hollow internal organs
(viscera) such as digestive tract, blood vessels, and ureters; attaches to hair follicles in skin
single nucleus, no crosswise stripes/striations, cells tapered at each end
involuntary
control
Motor Unit
Stimulation
of a muscle by a nerve impulse is required before a muscle can shorten and produce movement
Motor neuron
-- the specialized
nerve
that transmits an impulse to a muscle, causing contraction
Neuromuscular junction
-- the specialized point of contact between a nerve ending and the muscle fiber it innervates
Motor unit
-- the combination of a motor neuron with the muscle cell or cells it innervates
Fine control
: fingers, eyes
< 150 muscle fibers per motor neuron
Less precise control
: hips, legs
> 150 muscle fibers per motor neuron


Myasthenia gravis
Autoimmune
muscle disease characterized by
weakness
and
chronic fatigue
Begins in the face and throat
Progresses to rest of the body, causes
immobility
in all four limbs and eventual
respiratory

failure
because of weakness in respiratory muscles
Immune system attacks muscle cells at the neuromuscular junction
Nerve impulses from motor neuron are unable to fully stimulate the affected muscle

Types of Skeletal Muscle Contraction
Tetanic contractions
Sustained and steady
muscular contractions caused by a series of stimuli bombarding a muscle in rapid succession
Tetanus
– sustained contraction
Isotonic contractions
Contraction of a muscle that
produces movement
at a joint
The
muscle changes length
, causing the insertion end of the muscle to move relative to the point of origin
Most types of body movements such as
walking
,
breathing
, and
running
are caused by isotonic contractions
Isometric contractions
Muscle contractions that
do not produce movement
The muscle as a whole
does not shorten
Although no movement occurs during isometric contractions,
tension
within the muscle
increases
Repeated isometric contractions make muscles
grow larger and stronger
Ex.
pushing against a wall
or other immovable object

Occupational Health Problems
All muscle cells specialize in
contraction
(shortening)
Muscle cells shorten by converting
chemical energy
(obtained from food) into
mechanical energy
, which causes movement

Structure of Skeletal Muscle
Each skeletal muscle is an
organ
composed mainly of skeletal muscle
cells
and connective
tissue
Consists of hundreds to thousands of muscle cells (
fibers
)
Covered by
epimysium
(connective tissue that binds muscles into functional groups)
Blood vessels & nerve fibers
Fascicle
: portion of muscle (bundle of muscle cells surrounded by
perimysium
)

Muscles attach to bone by
tendons
—strong cords of fibrous connective tissue
Bursae
—small synovial-lined sacs containing a small amount of
synovial fluid
located between some tendons and underlying bones
makes it easier for a tendon to slide over a bone when the muscle shortens

Microscopic structure
Contractile cells called
fibers
—grouped into bundles
Myofibril
: complex
organelle
composed of bundles of
myofilaments
Fibers contain
thick
myofilaments (containing the protein
myosin
) and
thin
myofilaments (composed of the protein
actin
)
Surrounded by
endomysium
(connective tissue)

Posture
A specialized type of muscle contraction, called
tonic contraction
, enables us to maintain body position
Only a few of a muscle’s fibers shorten at one time, so
muscle as a whole does not shorten
Produce
no movement
of body parts
Counteracts
the pull of
gravity
Balances the
distribution of weight
to put the least strain on muscles, tendons, ligaments, and bones
Poor posture causes
fatigue
and may lead to
deformity
Heat production
Survival depends on the body’s ability to maintain a
constant
body temperature
Fever
—an elevated body temperature—often a sign of illness
Hypothermia
—a reduced body temperature
Contraction
of muscle fibers produces most of the heat required to maintain normal body temperature (3/4 of energy produced by
ATP
escapes as heat)

Muscle Metabolism
Energy
for contraction --
ATP
,
glucose
, &
glycogen
(storage form of glucose in animals)
made during
cellular respiration
in cytoplasm & mitochondrion

Muscle Fatigue
Glucose from blood & reserve glycogen are exhausted
Lactic acid
buildup -- contributes to muscle
soreness
ATP cannot keep pace
Reduced
strength of muscle contraction
Caused by repeated muscle stimulation without
adequate periods of rest
Depletes

cellular ATP
stores and
Blood supply
unable to replenish oxygen and nutrients

Oxygen Debt
the
metabolic effort
required to
burn excess lactic acid
that may accumulate during prolonged periods of exercise
the body is attempting to
return the cells’ energy and oxygen
reserves to
pre-exercise levels
(this is why we
breathe hard
after exercising)

Mitochondrion
Anaerobic Rxn
Aerobic Rxns
sore muscles!
make bread & alcohol
AKA cellular respiration
Muscle Stimulus
A muscle will contract only if an applied stimulus reaches a certain level of intensity
Threshold stimulus
-- the minimal level of stimulation required to cause a muscle fiber to contract
Once stimulated by a threshold stimulus, a muscle fiber will contract completely, a response called
all or none
Different muscle fibers in a muscle are controlled by different motor units having different threshold–stimulus levels
Although
individual muscle fibers always respond all or none
to a threshold stimulus, the
muscle as a whole does not
You can pick up a 2 L soda or a 20 kg weight because different numbers of motor units can be activated

Endurance training
(AKA aerobic training) is exercise that increases a muscle’s ability to sustain moderate exercise over a long period
Ex. running, bicycling, other primarily isotonic movements
Allows more efficient delivery of oxygen and nutrients to a muscle via increased blood flow –
increases the number of blood vessels in a muscle
Increases number of mitochondria
in muscle fibers
Does not usually result in muscle hypertrophy
Strength training
is exercise involving contraction of muscles against heavy resistance
Ex. isometric exercises, weight lifting
Increases the numbers of myofilaments
in each muscle fiber, and as a result, the
total mass of the muscle increases
Does not increase the number of muscle fibers

Contusion

bruise
– involves local internal bleeding and inflammation
Strain
—injury from
overexertion
or
trauma
; involves
stretching
or
tearing
of muscle fibers
Often accompanied by
myalgia
(muscle pain)
May result in inflammation of muscle (
myositis
) or of muscle and tendon (
fibromyositis
) [ex. charley horse]
If injury is near a joint and involves ligament damage, it may be called a
sprain
Cramps
are painful muscle
spasms
(involuntary twitches)
Can result from mild myositis or fibromyositis
Can be a symptom of
irritation
or
ion or water imbalance
Crush injuries
result from
severe muscle trauma
and may release cell contents that ultimately cause
kidney failure
Stress-induced muscle tension
can cause
headaches
and
back pain
Treatments include
massage, biofeedback, relaxation training

Muscle injury
Severe strain of muscle,
causing a tearing in half
of muscle
Infections
Muscular dystrophy
Group of
genetic disorders
characterized by
muscle atrophy
Duchenne (pseudohypertrophic) muscular dystrophy
is the most common type
Atrophy of muscles is masked by excessive
replacement of muscle by fat and fibrous tissue
Characterized by rapid progression of
weakness and atrophy
, resulting in
death by age 21
X-linked inherited
disease, affecting mostly
boys
Gene that codes for protein called dystrophin missing from X chromosome –
muscle cells become too weak
to hold together during muscle contraction
Gene therapy
is being tested with the hope that the gene for dystrophin can be replaced by cells from a healthy donor

Development of the Muscular System
Muscles & their respective nerves develop early in pregnancy – mothers can feel fetus by
16th week
of pregnancy
Initially after birth, movements are all
gross reflexes
– nervous system must mature before the baby can control muscles
Gross movements precede fine ones
Develop
cephalic to caudal
(head to tail/butt)
Peak
development by
midadolescence
(can be furthered with athletic training)

Effects of Aging on the Muscular System
Muscles undergo a great amount of
atrophy
Gradual
decrease
in number of
muscle fibers
and their individual bulk
Fibrous tissue replaces muscle tissue
Decrease in muscular strength and endurance
Diminished storage of glycogen may cause loss energy reserve --
fatigue
A 70-year-old man has
50%
the strength of a 30-year-old man
Frail older people can rebuild muscle mass and dramatically increase strength by
“pumping iron”

Muscular System Therapies
Massage
– health care professional must be able to locate the appropriate skeletal muscles on individuals of all different physiques – used to
relieve stress & pain
Electrical Stimulation
– achieve their effect through
nerve stimulation
– used to
increase ROM, increase muscle strength, reeducate muscles, improve muscle tone, enhance function, control pain, accelerate wound healing, reduce muscle spasms

Enhancing Muscle Strength
Strength training

Most obvious and effective way to
increase muscle strength
Maximal
amount of muscular strength is determined primarily by
genetics
Chemical enhancements
Vitamin supplements

Overused by athletes in 20th century – leads to
hypervitaminosis
and possible serious consequences
Anabolic steroids

Usually synthetic derivatives of
testosterone
(male hormone)
Prolonged use can cause
serious to life-threatening
hormonal imbalances
Banned
from most organized sports

Intramuscular Injections
If amount to be injected is
2 mL or less
, the
deltoid
muscle is often selected
If amount to be injected is
2-3 mL
, the
gluteal
area is often used
Nerves and blood vessels must be
avoided
Individuals may be instructed on
self-injection
techniques – ex. insulin shots for diabetics, hormone shots for infertility

Occupational health

study of health matters related to
work
or the
workplace
Many problems caused by
repetitive motions
of wrists or other joints
Tenosynovitis

inflammation of a tendon sheath – ex.
carpal tunnel syndrome
– treat with anti-inflammatory agents or surgery
Bursitis

inflammation of a bursa – ex. carpet layers, roofers – treat with anti-inflammatory agents
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