The document summarizes key aspects of muscular physiology. It discusses how skeletal muscles uniquely provide the body with heat production, movement, and posture maintenance. It then explores various topics in more depth, including heat production, movement, posture, similarities with other systems, myofilament structure, the sliding filament theory, movement terms, muscle fiber types in marathon runners versus sprinters, cardiac muscle structure, rigor mortis, motor unit activation, stimulation frequency, muscle fiber length, contraction speed, contraction phases, molecular events of crossbridge cycling, and the concept of treppe during warm up.

1. Muscular
Physiology
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2. Skeletal Muscles Uniquely
Provide The Body With:
•Heat Production
•Movement
•Posture Maintenance
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3. Heat Production
• Because skeletal muscles release such a massive
amount of heat, even while doing no work, the
muscles are a great influence on body temperature
• When body temperature falls below the temperature
set by the hypothalamus of the brain, temperature
sensors send a message to the hypothalamus to
instruct the skeletal muscle to contract (explained on
the next slide), therefore releasing more heat, thus
bringing the body temperature back up to
homeostasis temperature
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4. Movement
• An impulse, which creates a temporary imbalance, is conducted
along the sarcolemma and inward along the T tubules. The
impulse in the tubule triggers the release of a flood of calcium
ions from the near-by sacs of the SR. In the sarcoplasm, the fluid in
the sarcolemma, which contains the sarcomere, the calcium ions
combine with troponin molecules in the thin filaments of the
myofibrils. The troponin normally holds tropomyosin strands in a
position that blocks the chemically active sites of actin molecules.
After active sites are exposed, myosin heads become energized
and bind to actin, which move the actin forward and backwards,
therefore contracting the muscle.
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5. Posture
• Because skeletal muscles are the muscles responsible
for movement for the body, the muscles are unique
in that they establish and maintain posture for the
human body by creating the upper and lower limits,
as well as the resting location, of most joints and
appendages.
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6. Similarities with
other Systems
• The concept of excitability is also shared with the nervous system,
which is the case because the nervous system, in most cases, is
the system responsible for controlling muscle movement.
• Contractility and extensibility is related to agonist and antagonist
in that the contractility of a muscle refers to it’s specific ability to
contact, or cause movement, which is connected to agonist, the
main muscle required for a specific movement. Antagonist refers
to extensibility because muscles cannot extend on their own, but
rather, they require muscles which cause the exact opposite
movement, therefore extending the muscle itself.
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7. Myofilament
• the term for the chains of actin and myosin that pack muscle fiber. These are
the force generating structures. When looking at the longitudinal section
through an electron microscope, a myofilament shows several distinct bands,
each of which has been given a special letter. The lightest (least electron
dense) band is known as the I-band and consists mostly of actin. The wide,
dark band, known as the A band, is composed primarily of myosin. In the
center of the I-band is an electron dense line, known as the Z-line. In the
middle of the A band is another dense line known as the M line. In cross
section, under very high magnification, both A and I bands can be seen to be
hexagonal networks. These networks are apparently ordered and fixed at the
M- and Z-lines. In the region where the A and I bands overlap (sometimes
known as the H band) the two hexagonal networks intermesh so that each
myosin filament is surrounded by six actin filaments. These networks appear
to be anchored to (and through) the cell membrane in two ways. At the ends
of fibrils, special structures anchor the terminal actin filaments to the
membrane. There also appear to be connections between the Z and M lines
and the cell membrane. In conclusion, the structure of the myofilament have
gapes in them and which allow for them to overlap and make a muscle
shorter, they can also stretch out to make a muscle longer.
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8. Sliding Filament
Theory
• The sliding filament theory allows for the
shortening of the muscle fiber because the Z-
lines contract which make the A-band shorten.
There are myosin in the middle of the Z-lines
and on each of the myosin there are little
proteins that connect to them called actin that
grab a hold to the fibers in the muscle and
that allows for the muscle to shorten. The
actin will continue to grab the muscle fibers
until there is eventually no more room on the
myosin.
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9. Movement Terms
•
Excitation: A neural synapse induces an action potential
in a muscle cell (fiber) that, in turn, results in calcium
ions to be released into the cytosol from the
sarcoplasmic reticulum when calcium channels open.
•
Contraction: Calcium ions are an intracellular signaling
molecule for muscle contraction. Calcium binds to
troponin-C to initiate contraction; this will continue
until excitation ceases.
•
Relaxation: removal of intracellular calcium allows the
muscle to relax.
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10. Marathon Runner
Type I muscle fibers are classified as “slow-
twitch”, meaning they develop force slowly and
relax at a similar pace with a longer “twitch” in
between. Why? Because..
-
It doesn’t utilize much energy from ATP.
-
It is more aerobic than anaerobic.
-
& it can function for longer periods of time
with repetitive contractions, because of
readily supply of oxygen.
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11. Sprinter
• Type II fibers are the “fast-twitch” explosive muscle fibers
associated with power and explosiveness in athletes.
“Inefficient and Fatigable” - characterizes high anaerobic power but
very low aerobic power which equates to shorter duration, but more
powerful contractions of the muscle as a whole.
The main difference between type 2a and 2b muscle fibers comes
from their “capacity for aerobic-oxidative energy supply.” Type 2a
muscle fibers have a more efficient meanings of aerobic metabolism
due to a higher number of surrounding capillaries that circulate blood
throughout the muscle which results in a higher resistance to fatigue.
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12. Units of Combined
Cells
• Cardiac muscles are the muscles of the
heart. Cardiac muscle cells make up the
myocardium portion of the heart wall. They
have an overlapping arrangement of light
and dark striations. It measures about
10-15 micrometers in diameter and 50-100
meters in length.
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13. Rigor Mortis
• A few hours after a person or animal dies,
the joints of the body stiffen and become
locked in place. This stiffening is called
rigor mortis. It is caused by the skeletal
muscles partially contracting. The muscles
are unable to relax, so the joints become
fixed in place.
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14. Motor Unit
Activation
• A motor unit consists of an alpha-motor neuron and the
muscle fibers it innervates. Depending on the size of the
motor unit, the alpha-motor neuron connects to
between 10 and 1,000 muscle fibers and sends a signal
to trigger simultaneous contraction of all the fibers in
that motor unit. This synchronized contraction allows
the muscle to make coordinated movements. For
movements requiring little force, such as picking up a
pencil, you recruit small motor units in your arm
muscles. For high-force movements, such as picking up
a brick, you will recruit large motor units in addition to
the small ones to execute the movement.
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15. Stimulation
Frequency
• A single stimulus of the muscle fiber from the nervous
system will produce a small amount of muscle force,
followed by a muscle relaxation as the fiber returns to
baseline. However, if the nervous system delivers
several stimuli before the fibers can fully relax, the
muscle fibers produce more force than they would in
response to a single stimulus. Continual nervous system
stimulation of the motor unit and muscle fibers yields
the maximal force possible of the given muscle fibers,
increasing the strength of the muscle contraction.
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16. Muscle Fiber Length
• Your muscles have thin and thick filaments, which are
organized into contractile units called sarcomeres.
Within each sarcomere, thick filament proteins slide and
bind to proteins in the thin filament during muscle
contraction. The sarcomeres have an optimal length at
which the number of possible binding sites between the
filaments is maximized. If your muscle fibers are shorter
or longer than this optimal length, they do not have as
much force-producing potential because there are fewer
available binding sites between the filaments. For
example, when your elbow is fully bent, the length of
your biceps muscle fibers is shorter and less capable of
producing force than when your elbow is extended.
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17. Contraction Speed
• Muscle contraction speed determines the force-
producing capacity of your muscle. For a concentric
muscle contraction in which the muscle fibers shorten,
your muscles' force-producing capacity decreases at
faster contraction speeds. Conversely, an eccentric
contraction in which the muscle lengthens produces
greater force at faster contraction speeds, and force-
production capacity is always greater in an eccentric
contraction compared to a concentric contraction. For
example, you may be capable of lowering a heavy
barbell to your chest during a chest press, but cannot
lift it off your chest. This is because the chest and
shoulder muscles eccentrically contract to lower the
weight and contract concentrically to lift the weight.
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18. Contraction Phases
• Latent Phase: Is the interval from the stimulus application until the
muscle begins to contract (shorten). Note that there is no traced
activity during this phase, but there are some electrical and
chemical changes taking place during this phase.
• Contraction Phase: This phase is when the muscle fibers shorten,
the tracings will show during this phase (a) peak(s).
• Relaxation Phase: This phase is represented by the downward
curve in your tracings, this is when the muscle is going back to its
original state of relaxation and the muscle will once again
lengthen.
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19. Molecular Events
1. During contraction, the myosin molecule forms a chemical bond with an
actin molecule on the thin filament (gripping the rope). This chemical bond is
the crossbridge. For clarity, only one cross-bridge is shown in the figure above
(focusing on one arm).
2. Initially, the crossbridge is extended (your arm extending) with adenosine
diphosphate (ADP) and inorganic phosphate (Pi) attached to the myosin.
3. As soon as the crossbridge is formed, the myosin head bends (your arm
shortening), thereby creating force and sliding the actin filament past the myosin
(pulling the rope). This process is called the power stroke. During the power
stroke, myosin releases the ADP and Pi.
4. Once ADP and Pi are released, a molecule of adenosine triphosphate (ATP)
binds to the myosin. When the ATP binds, the myosin releases the actin molecule
(letting go of the rope).
5. When the actin is released, the ATP molecule gets split into ADP and Pi by
the myosin. The energy from the ATP resets the myosin head to its original
position (re-extending your arm).
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20. Warm up by Treppe
• The concept or phenomenon of "Treppe" occurs when a
muscle contracts more forcefully after it has contracted
a few times than when it first contracts. This is due to
the fact that active muscles require decreasing degrees
of succeeding stimuli to elicit maximal contractions.
Returning to our example of the second set of squats
feeling easier than the first, during the first set there
was insufficient warm-up, and the second set felt easier
because the first set actually served as a warm-up. The
phenomenon in which the contraction strength of a
muscle increases, due to increased Ca2+ availability and
enzyme efficiency during the warm-up.
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21. Works Cited
• All information derived from source #1
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