Muscle System Flashcards
Functions of the muscular system
- Movement
- Tone
- Protection
- Control of Openings
- Body Temperature
Functions of the muscular system- movement
As muscle
contracts, it
pulls bones.
Functions of the muscular system-tone
Even when not
moving, some muscle
units are always
contracted.
Functions of the muscular system- protection
Abdominal organs
are only
protected by
muscle.
Functions of the muscular system- control of opening
Sphincters guard the
openings of the
digestive and urinary
systems.
Functions of the muscular system- body temperature
Muscle contractions
generate heat.
Muscles
- Muscle is made of a hierarchy of elongated
bundles.
▪ Fascicles are the largest bundles and can be
seen with the naked eye. - Each layer of bundles is covered with a
type of fascia
Fascia
(Def) connective tissue that
separates it from other tissues
- All layers of fascia
combine to form tendons
or aponeuroses.
▫ Tendons are
cylindrical and
attach to bones.
▫ Aponeuroses are flat
and attach to bones
or other muscles.
Tendon
(Def) are cylindrical and
attach to bones.
- A ruptured tendon will detach a muscle from one of its bones, rendering it unusable.
(the entire organ) is covered with
Epimysium
Muscle
(groups of skeletal muscle fibers) are covered with Perimysium
Fascicles
(highly specialized muscle cells) are covered with
Endomysium
Muscle fibers
(muscle cell threads made of myofilaments: actin &
myosin) are covered with Sarcoplasmic Reticulum
Myofibrils
Organization of skeletal muscles
Muscle- belly
|
Fascicle- a bundle of muscle fibers
|
Muscle fiber- muscle cell
|
Sarcomere- units of myofibrils responsible for the striated appearance
|
Myofibrils- structures that make up a muscle fiber
|
Myofilament- protein filaments that make up a sarcomere
- myosin- thick filaments
- actin- thin filaments
Skeletal muscle fibers
▫ Very long (up to 30cm).
▫ Multinucleate: Multiple nuclei per cell.
▫ Amitotic: Unable to divide
Special structures within muscle fibers include
- Sarcolemma
- M itochondria
- Sarcoplasmic reticulum
- Myofibrils
Sarcolemma
Cell membrane;
contain t-
tubules that
penetrate
through the
center of the
cell.
Mitochondria
Generate ATP.
Sarcoplasmic
Reticulum
Type of smooth
ER that stores
calcium ions
that trigger
contraction.
Myofibrils
Rod-shaped
organelles with
contractile proteins
called actin and
myosin.
sarcomere
- is the contractile unit of
myofibrils, with two types of protein
filaments:
▫ Actin, which are thinner and lighter.
▫ Myosin, which are thicker and darker.
Myosin and actin
- Myosin and actin
overlap somewhat
in the sarcomere - Myosin filaments
have heads
(extensions) that
can ‘grab’ onto
actin forming a
crossbridge - During muscle contraction, “heads” on the
myosin filaments attach to actin filaments,
pulling them inwards. - When this happens across
the entire muscle, it
contracts and shortens,
forming a muscle belly. - Myosin will only pull actin in the presence
of ATP.
▫ Constant energy input is required for
movement.
Sliding Filament
a muscle
contracts when the thin filament in the
muscle fiber slides over the thick filament
- Activated by ATP and calcium (Ca+) ions
The Sliding Filament Theory of Muscle Contraction
1) An influx of Ca2+ causes thick myosin filaments to form
crossbridges with the thin actin filament by exposing the
binding site on actin
2) The crossbridges change shape as it pulls
on filaments which slides towards the center
of the sacromere in the power stroke
- The distance between the Z line decreases,
shortening the muscle.
3) The crossbridges detach from the actin filament when ATP bonds to myosin head.
4) The myosin head gets ready to bond to actin again
using ATP energy
- The cycle is repeated on another site of actin filament using the
stored ATP energy
Rigor mortis
- is the stiffening of muscles
after death due to the lack of ATP production. - Lasts 1-4 days, until muscle fibers break
down.
Neuromuscular Coordination
Muscle tissue is not able
to contract without the
support of one or more
nerves
• The collective
relationship between the
muscular and nervous
systems is called the
neuromuscular system
motor neuron
the type of nerve cell that
stimulates a muscle.
• This occurs across a
neuromuscular junction
Transmission of Nerve Impulse to Muscle
-Step 1: Nerve releases a
neurotransmitter (acetylcholine)
-Step 2: Neurotransmitter causes the
muscle cell membrane gates to open
-Step 3: Ions (Na+ & K+) exchange places
causing the sarcoplasmic reticulum to
release Ca2+
-Step 4: This release of Ca+ starts the
muscle contraction as the actin filaments
slide past the myosin filaments
steps of Muscle Contraction
▪ A signal is received from a motor neuron.
▪ Signal is sent to every myofibril in the
muscle fiber simultaneously through t-
tubules.
▪ The sarcoplasmic reticulum releases
calcium ions (Ca2+).
▪ The calcium influx stimulates the myosin
filaments to attach to the actin
filaments.
▪ Myosin attaches to ATP, releasing actin.
Skeletal muscles
must be
stimulated by a
nerve (motor
neuron) to
contract
twitch
is a single contraction
relaxation cycle of
a motor unit.
Motor units
are
motor neurons
and all their
associated
muscle fibers.
Summation
occurs when two twitches combine
into a more powerful movement.
▫ Second stimulus is received before the
motor unit completes relaxation.
Tetanus
occurs when the frequency of
stimulation is so high that the relaxation
phase disappears.
▫ Maximum muscle tension.
ATP
is broken down into ADP to provide an energy source for muscle contraction.
▫ ATP is unstable, so cells only have enough available to last a few seconds.
Creatine phosphate
can be broken down to
release high energy
phosphates,
recharging ATP.
▫ Muscles store 8-10
seconds worth
Glycolysis
- Happens in the
cytosol. - Generates 2 ATP
per glucose
molecule. - Anaerobic: no
oxygen required.
Aerobic Respiration
- Happens in the
mitochondria. - Generates 34 ATP
per glucose
molecule. - Aerobic: oxygen is
required. - if oxygen is abundant
Lactic Acid Fermentation
- Happens in the
cytosol. - Allows glycolysis
to continue. - Anaerobic: no
oxygen needed - if oxygen is deficient
Glucose
▪ Glucose is
regenerated by
breaking down
glycogen, a
polysaccharide.
▫ Stored in the
liver and muscles.
Fatigue arises from two conditions that limit ATP
- Insufficient Oxygen
- Insufficient Glucose
Insufficient Glucose
- Glycogen storage is
completely used up. - Blood glucose levels
become too low. - “Hitting the wall”
Insufficient Oxygen
- Muscles must use
glycolysis and
lactic acid
fermentation. - Lactic acid
irritates muscles,
causing soreness. - “Out of breath”
Aerobic Exercise
- Improved oxygen
intake, lactate
clearance, and
glycogen storage. - Improved
endurance. - Jogging,
distance swimming
Anaerobic Exercise
- Muscle fiber size
increases. - Improved strength.
- Weightlifting,
sprinting
Fast Twitch
- Reach peak
tension quickly. - Densely packed
with myofibrils. - Fewer
mitochondria. - Produce more
force, but tire
quickly
Slow Twitch
- Reach peak tension more slowly.
- More mitochondria.
- Contains myoglobin
that stores
oxygen. - Produces less
force, but better
endurance.
Anabolic steroids
- mimic testosterone,
increasing protein
synthesis in muscle
fibers.
▪ Side effects:
▫ Increase in blood
cholesterol
▫ Acne ▫ High blood pressure ▫ Testicular atrophy ▫ Emergence of male
characteristics in women
Muscular
dystrophy
causes the
degeneration
and
atrophy of
muscle.
Muscle spasms
- are involuntary
contractions of
single muscles.
▫ Painful spasms are
called cramps
▪ Caused by overuse,
lack of electrolytes,
dehydration, etc.
Polio
a virus that
destroys motor
neurons, causing
paralysis.
Amyotrophic Lateral
Sclerosis (ALS)
is a genetic disease that
damages motor neurons,
causing gradual muscle
atrophy.
Fibromyalgia
causes pain
throughout the
muscle fascia
–
epimysium,
perimysium,
endomysium, and
tendons.
