Download Muscles and Muscle Tissue

Muscles and Muscle Tissue
Muscle Types
• Skeletal - voluntary, striated
(fast, short contractibility)
• Cardiac - involuntary, striated
(fast, rapid recovery)
• Smooth- involuntary, nonstriated, visceral
(slow, sustained contractibility)
Muscle Functions
•
•
•
•
Producing movement
Maintaining posture
Stabilizing joints
Generating heat
Functional properties of Muscle
•
•
•
•
Excitable (irritable)
Contractile
Extensible
Elastic
Anatomy of Skeletal Muscle
• A single skeletal muscle, such as the
triceps muscle, is attached at its origin
to a large area of bone; in this case, the
humerus
At its other end, the insertion, it
tapers into a glistening white
tendon which, in this case, is
attached to the ulna, one of
the bones of the lower arm.
• Each skeletal muscle is an
organ.
• Each muscle fiber is a cell.
• Each muscle is surrounded by
CT.
• Muscles contain nerve fibers
and blood vessels.
• Tendons are extensions of CT
beyond muscle cells that attaches
muscle to bone or to other
muscle.
Other muscle injuries
• Muscle strain = pull = tear
• Charlie horse (muscle tear and/or contusion usually due
to impact I.e. helmet to quadracep)
Microscopic Anatomy
• Each muscle fiber – long cell with many
nuclei just below the PM (sarcolemma)
• Sarcolemma- wraps each muscle fiber.
Microscopic Anatomy
• The sarcoplasm of
the muscle fiber is
similar to the
cytoplasm of other
cells.
It also has a higher
content of
myoglobinan oxygen-binding
pigment.
• Myofibrils- the
contractile proteins
(actin and myosin) that
make up muscle fibers.
• Sarcoplasmic
reticulum- surrounds
each myofibril. It
regulates intracellular
levels of ionic calcium.
• T-tubules- where the
interior of the cell
meets with the
sarcolemma. It
conducts impulses to
every sarcomere.
A. Sarcomere- region
between two
successive Z lines.
B. A bands- thick
(myosin) filaments
C. I bands- thin
(actin) filaments
D. Z line- intersection
between
sarcomeres.
Two types of proteins involved:
A. Contractile proteins – actin and
myosin do the contracting.
Myosin – Thick. Shaped like golf clubs
twisted together.
Actin – Thin. Looks like a twisted helix.
Has a myosin binding site.
B. Regulatory proteins – troponin and
tropomyosin.
Found on the actin myofiber. Help switch
contractions on and off.
Contraction of a Skeletal Muscle
Fiber
Sarcomeres shorten because
filaments in each sarcomere slide
together.
This makes the myofibrils shorten,
making the fiber shorten, and
finally the whole muscle shortens.
Sliding Filament Theory of Contraction – what
happens when a muscle contracts
A. Troponin blocks the binding site for the
myosin head.
B. A nerve impulse causes Ca++ to enter the
cytoplasm.
C. Ca++ moves troponin aside.
D. The myosin head can attach to the binding
site.
E. The myosin head bends and pulls the actin
– this is the power stroke.
F. ATP provides energy to release the myosin
head from the binding site.
G. This re-cocks the myosin head, making it
ready for its next attachment and power
stroke sequence
Energy for contraction
• Movement of myosin requires ATP.
• Each stroke shortens muscle 1%
• When a muscle contracts, it shortens
about 35%
• Therefore, many attachments form and
break with each contraction.
• Takes lots of ATP.
Neuromuscular Junction – nerve
impulse triggers muscle contraction
A. Where the axon terminal (end of
nerve) and the sarcolemma meet.
Called a motor end plate.
B. When a nerve impulse reaches
the axon terminal, the muscle cell
allow the entry of calcium.
C. The calcium causes acetylcholine
to diffuse across the membrane
and attach to the ACh receptors on
the sarcolemma.
Generation of an Action
Potential
A. The outside of the sarcolemma has Na+ ions.
B. The inside of the sarcolemma has K+ ions.
C. When ACh attaches to the sarcolemma, it causes Na+
ions to rush in.
D. If the effect is great enough, than an action potential will
occur across the sarcolemma. If not, then is will stop
right there. This is called the all-or-none response.
E. After the action potential propagates across the entire
membrane, the membrane repolarizes to its original
state.
Muscle Responses- Terms To
Learn
A. Tetanus- smooth, continuous contraction
without relaxation.
B. Muscle Tone- muscles are in a slightly
contracted state.
Isotonic and Isometric
Contractions
Isotonic
Isometric
The tension continues to
Changes in length to
increase but the
move the load.
muscle neither
Ex. Picking up a book, shortens or lengthens.
Your calf muscle when Ex. Muscles that hold your
posture or hold joints.
you walk up a hill.
Examples of Isotonic and
Isometric Contractions
Throwing is
a Isotonic
Contraction
Squeezing is
a Isometric
Contraction
Lifting up a heavy object
uses both contractions in
your leg muscles.
Muscle Metabolism Making ATP
for Energy
1. Direct Phosphorylation of ADP by
Creatine Phosphate- Uses stored creatine
phosphate and ADP to make creatine and ATP.
Altogether, they provide max. power for 15-20 seconds.
2. Aerobic Respiration-
occurs in the
mitochondria. Yields 36 ATP. Glucose+Oxygen>Carbon
Dioxide+Water+ATP
3. Anaerobic Glycolysis and Lactic Acid
Formation- Glucose>Pyruvic Acid>Lactic Acid
Muscle Fatigue and Oxygen
Debt
Muscle Fatigue- the state of physiological inability to
contract. When you lack ATP, you are in a phase of
continuous contractions because the cross bridges
cannot detach from the binding site.
Other Causes- Excessive accumulation of
lactic acid and ionic imbalances.
Oxygen Debt- Extra amount of oxygen that
must be replenished.
Force of muscle contractions
1. # of muscle fibers contracting- the more the
greater
2. Size of the muscle- the bulkier the more tension
and strength it can produce
3. Degree of muscle stretch- the optimal resting
length is when a muscle is slightly stretched and
the actin and myosin filaments barely overlap.
This allows sliding across the entire length of the
action filaments.
Muscle Fiber Types
A. Red slow-twitch fibers
Lots of mitochondria, lots of oxygen, long
endurance, low power, reddish color.
B. Intermediate fast-twitch fibers
Contract quickly like fast-twitch fibers but are
oxygen dependent like slow-twitch fibers.
C. White fast-twitch fibers
Few mitochondria, contracts quickly, fatigable, high
power, and high glycogen reserves.
Pic of different fiber types.
Can you guess this
guy’s fiber type?
Slow-twitch Fibers
How about this guy?
Fast- Twitch Fibers
A nice analogy can be used to explain the
various actions of these two fiber types.
Chickens, like us, have both fast and slowtwitch fibres:
their darker (red) meat is composed of
slow-twitch fibers
the white meat of fast-twitch fibers
.
Chickens use their legs (red meat) for walking
and standing for large periods of time, while
their wings (white meat) are used for brief
bursts of activity.
Human muscles contain a genetically
determined mixture of both slow and
fast fiber types.
On average, we have about 50 percent
slow twitch and 50 percent fast twitch
fibers in most of the muscles used for
movement.
Our muscle fiber type may influence
what sports we are naturally good at or
whether we are fast or strong.
Olympic athletes tend to fall into
sports that match their genetic
makeup. Olympic sprinters have been
shown to possess about 80 percent fast
twitch fibers, while those who excel in
marathons tend to have 80 percent
slow twitch fibers.
Effects of Exercise on
Muscles
• Regular aerobic exercise
efficiency, endurance, and
strength of skeletal muscles.
• Resistance exercises
– skeletal muscle hypertrophy.
• Immobilization
– muscles weakness and muscle atrophy.
• Cross-training provides the best health
program because it alternates between
aerobic and anaerobic exercises.
Smooth Muscles
Small spindle-shaped cells, each with
one centrally located nucleus.
• Located in the walls of hollow organs.
• Ex. Digestive, urinary, and
reproductive tracts.
• Movements slow and synchronized
Smooth Muscle
• Two different types of sheets are usually
present
– Longitudinal Layer- runs parallel to the long
axis of the organ. Shortens the organ.
– Circular Layer- run around the
circumference. Elongates the organ.
• Peristalsis- the alternation between these
two opposing layers mix substances in the
lumen (cavity) and pushes them through the
organ pathway.
Smooth Muscle Examples
The smooth muscles help dilate the eyes
The smooth muscles
help line the
respiratory tracts
Developmental Aspects of
Muscles
• Women’s muscles=36% of total body
weight
• Men’s muscles=42% of total body weight.
• Skeletal muscles become fibrous and
atrophy as we age.