Download Muscles Part 1 Powerpoint

Muscles Part 1
By the end of this class you should
understand:
• The structure and function of whole muscle
• The sliding filament model of skeletal muscle
contraction
• The role of ions in the stimulation and
contraction of muscles
• The role of different energy sources in muscle
contraction
Muscles
• Muscle is a general term
for the tissues and organs
of the body that produce
force
– The organ is sometimes
referred to as whole muscle
• There are three types of
muscle tissue:
– Skeletal (voluntary)
– Cardiac (heart)
– Smooth (hollow organs)
Whole Muscle
• Whole muscle is an organ
composed of skeletal
muscle tissue wrapped in
areolar connective tissue
• Produces force when
stimulated by a voluntary
nerve fiber
– Under conscious control
– These are the muscles we
think of as muscles
Whole Muscle Anatomy
• A muscle has an origin and
an insertion
• Generally the more proximal
attachment point is the
origin and the distal
attachment point is the
insertion
– Example: Biceps have origin
at shoulder and insertion at
elbow
• Produce force by shortening
Whole Muscle Microanatomy
• The muscle organ is
composed of many cells
called muscle fibers which
are huge (each the size of
a human hair)
– Multinucleate due to being
many cells fused together
• These muscle fibers are
arranged into bundles
called fascicles
Muscle Fiber
• A muscle fiber is a single
cell composed of many
fused cells
• Most of the cell is filled
with huge organelles
called myofibrils
– Myo- is the latin root for
muscle
• The myofibril is made up
of many sarcomeres
Sarcomeres
• The sarcomeres are the
actual force-producing
organelles of the cell
– Composed essentially
entirely of protein
– This is why protein is
essential to the diet of any
athlete
– Also why animal meat is
full of protein
Muscle Stimulation
• Muscles receive signals from
motor neurons
– These signals are transmitted
by a neurotransmitter called
acetylcholine
– The signal is very brief so the
muscle relaxes as soon as the
signal is no longer being sent
by the brain
• These signals will be explored
in more detail next week
T Tubule
• The motor neuron’s signal reaches
the outside of the muscle fiber
and then is transmitted
throughout the entire fiber
through the T tubules
– The signal is made up of sodium and
potassium ions moving back and
forth across the cell membrane
– This is also known as an action
potential
– It moves much faster than diffusion
T Tubule and SR
• When a neurotransmitter is
released onto a muscle
fiber, the electrochemical
signal is transmitted
through the T tubules
through the entire fiber
• As the signal moves through
the T tubules, it stimulates
the sarcoplasmic reticulum
to release calcium
– Modified version of the
endoplasmic reticulum
Calcium?
• Calcium ions are being constantly pumped into the SR
– When the muscle is not being stimulated, all calcium ions are in the SR
– When the muscle is stimulated, calcium is released but is still being
pumped back into the SR
– This means once the signal ends the muscle will stop contracting
quickly
• This requires a lot of constant ATP expenditure
Sarcomere
• A sarcomere is made of two different kinds of protein
fibers
– Myosin filaments
– Actin filaments
• The myosin filaments have many myosin heads with two
features:
– They can attach to actin filaments
– They try to bend
Sliding Filament Model
• The myosin heads of the
myosin filament attach to the
actin filaments and attempt
to move them together
• There are two things that are
required for this:
– The actin can only be attached
to when it has a calcium ion
– The myosin head needs ATP to
detach after it bends
Sliding Filaments
• The actin filament has two
molecules called troponin
and tropomyosin
– Together they block the
myosin head from attaching
to the actin filament
• When a calcium ion
attaches to the troponin,
the tropomyosin is moved
out of the way
– The myosin head may now
attach to the actin filament
ATP Usage
• Clearly contracting our
muscles requires energy
• The actual use of the ATP is
to detach the myosin head
from the actin filament
– Once the myosin head is
detached it can reattach at a
new point and pull again
• Imagine if you had to stay in
place and help play tug-ofwar!
ATP Sources
• All muscle cells have some free
ATP when relaxed but this is
depleted almost immediately
during contraction
• Once the ATP supply is
depleted one of two things will
happen:
– More ATP must be produced
rapidly
– ATP will only be produced
slowly by the mitochondria and
the force produced will be less
Sources of ATP:
• Creatine Phosphate (anaerobic)
– Rapidly converted to an ATP, runs out after a few
more seconds
• Glycogen (anaerobic)
– Stored glucose in the muscle fiber
• Blood Glucose (aerobic)
– Only absorbed and metabolized slowly
• Fatty acids (aerobic)
– Stored in muscle, metabolized slowly
ATP Depletion
• Once the muscle’s main ATP supply is depleted,
the available force produced is much lower
– Fatigue
• If all ATP is depleted, the muscle may lack the ATP
supply to detach the myosin heads once the
nerve signal ends
– Cramp!
• Once the muscle is relaxed, blood glucose and O2
are used to restore the ATP supply
– Oxygen debt
Oxygen Debt
• If more energy is used than can
be produced aerobically,
anaerobic production of energy
can sustain activity
– Produces by products such as
lactic acid
• Lactic acid can be reabsorbed
and processed aerobically
using more oxygen
– This is why people pant and
become winded if they have
exerted themselves anaerobically
Rigor Mortis
• When a person dies, they are
initially limp
• Once all ATP has been depleted
from the cells, calcium begins to
diffuse into the muscles
– Calcium allows myosin head to
attach to actin filament
• Lack of ATP means the myosin
head cannot be detached
• Ultimately the entire body
becomes incredibly stiff and will
stay that way until the proteins
physically break down from
rotting (rigor mortis)
See you Wednesday!