1. Muscular Physiology Newsletter
Rigor Mortis
Rigor mortis is the process that your body goes through after you have died.
It is the latin phrase for “stiffness of death”(1). It is where your skeletal muscles
stiffen because the stimulation of muscle cells stop. And the muscle fibers might
have been in mid-action at the time of death. And this may be when the cross
bridges are still intact and your body needs ATP to release the cross bridges but
because the ATP is used up when you die, so the cross bridges become “stuck” in a
position (1). This leaves the muscles in a dead body stiff because there was no
more ATP to “turn off” the contraction.
4 Factors that Influence the Strength of
Muscle Contractions
The muscle is capable of many different things. That helps us do things such
as lifting weights, to shaking hands, and writing. Sometimes we need a lot of
strength and other times we don’t need a lot. Four factors that affect the strength
of muscle contractions are the number of cross bridges that can make contact, the
length of the fibers, and the frequency of the stimulation; summation and
recruitment (8.) The length influences the contraction because at a certain point it
is the strongest. And the length affects the cross bridges contact, if its too long the
cross bridges can’t reach, making contraction weak and if the muscle is too short, a
lot of cross bridges will be able to reach but it would get crowded and also make
contraction weak. (8.) The frequency of the stimulation impulses also affect the
contraction.

2. Phases of a Twitch Contraction
There are 3 phases of a twitch contraction called the latent period,
contraction phase, and relaxation phase. During the latent period the impulse
travels through the sarcolemma and T tubules into the SR where it triggers the
release of calcium ions (1). This calcium binding to troponin is what causes the
contraction to start, which is the contraction phase. After a few milliseconds the
contraction ceases and the relaxation phase begins.
How the Treppe effects relates to Athletes
The Treppe is a gradual, steplike increase in the strength of contraction. This
relates to the warm up of athletes because they use the principle of the staircase
phenomenon when they warm up. A muscle contracts more forcefully after it has
contracted a few times then when it first contracts (1). This allows the warm up of
the athletes to be more beneficial because it helps them get stronger and work
their muscles more.

3. Skeletal Muscle Fibers
One of the interesting things for Skeletal muscles is the a muscle organ is
composed of bundles of contractile muscle fibers held together by connective
tissue. Closer magnification of a fiber shows another fiber, myofibrils, in the
sarcoplasm, note sarcoplasm reticulum and t tubules forming a three part structure
called a triad. A unique feature of the skeletal muscle cell is the t tubules, which are
extensions of the plasma membrane, or sarcolemma, and the sarcoplasmic
reticulum (SR), which forms networks of tubular canals and sacs. A triad is a triplet
of adjacent tubules: a terminal sac of the sr, a t tubule, and another terminal sac of
the sr. (1)
First of there is four different type of Myofilaments which are myosin, actin,
tropomyosin, and troponin. The thin filaments are made of a combination of three
proteins. The way they work is that the myosin head is chemically attracted to the
actin molecules of the nearby thin filaments, so they angle the filaments. When
they bridge the gap between adjacent myofilaments, the myosin heads are usually
called cross bridges. (1)

4. Sliding Filament Theory
The sliding filament theory is a muscle contraction. It allows for the shortening of
muscle fibers because the myosin heads attach themselves to the thin filaments
and pull with a lot of force that moves the filament closer together, past them. This
shortens the entire myrofibril and muscle fiber. (1)
Ca++ in excitation, contraction, and
relaxation of a muscle cell
Extremely large protein complexes involved in the Ca2+-regulatory system of the
excitation-contraction-relaxation cycle have been identified in skeletal muscle, i.e.
clusters of the Ca2+-binding protein calsequestrin, apparent tetramers of Ca2+-
ATPase pump units and complexes between the transverse-tubular alpha1-
dihydropyridine receptor and ryanodine receptor Ca2+-release channel tetramers of
the sarcoplasmic reticulum. While receptor interactions appear to be crucial for
signal transduction during excitation-contraction coupling, avoidance of passive
disintegration of junctional complexes and stabilization of receptor interactions may
be mediated by disulfide-bonded clusters of triadin. Oligomerization of Ca2+-
release, Ca2+-sequestration and Ca2+-uptake complexes appear to be an intrinsic
property of these muscle membrane proteins. During chronic low-frequency
stimulation, the expression of triad receptors is decreased while conditioning has
only a marginal effect on Ca2+-binding proteins. In contrast, muscle stimulation
induces a switch from the fast-twitch Ca2+-ATPase to its slow-twitch/cardiac
isoform. These alterations in Ca2+-handling might reflect early functional
adaptations to electrical stimulation. Studying Ca2+-homeostasis in transformed
muscles is important regarding the evaluation of new clinical applications such as
dynamic cardiomyoplasty. Studies of Ca2+-handling in skeletal muscle fibers have
not only increased our understanding of muscle regulation, but have given
important insights into the molecular pathogenesis of malignant hyperthermia,
hypokalemic periodic paralysis and Brody disease. (1)

5. Work a Muscle Until you
"Feel the Burn"
When you work out you are essentially tearing your muscle (actin) and when your
body repairs your muscle it makes it bigger and stronger (more actin). During
excersise your muscles use up oxygen and tries to replenish it through anaerobic
respiration which results in the formation of lactic acid, which is what causes the
burning sensation. (1)
motor unit
Most mature extrafusal skeletal muscle fibers in mammals are innervated by only a
single α motor neuron. Since there are more muscle fibers by far than motor
neurons, individual motor axons branch within muscles to synapse on many
different fibers that are typically distributed over a relatively wide area within the
muscle, presumably to ensure that the contractile force of the motor unit is spread
evenly (Figure 16.4). In addition, this arrangement reduces the chance that
damage to one or a few α motor neurons will significantly alter a muscle's action.
Because an action potential generated by a motor neuron normally brings to
threshold all of the muscle fibers it contacts, a single α motor neuron and its
associated muscle fibers together constitute the smallest unit of force that can be
activated to produce movement. Sherrington was the first to recognize this
fundamental relationship between an α motor neuron and the muscle fibers it
innervates, for which he coined the term motor unit. (1)

6. Unit of Combined Cells
The cardiac muscle fiber does not taper like a skeletal muscle fiber. Cardiac
fibers to form a continuous, electrically coupled mass called a SYNCYTIUM “unit of
combined cells”. The Cardiac muscle forms a continuous, contractile band around
the heart chambers. It conducts a single impulse across a virtually continuous
sarcolemma. These features are necessary for an efficient, coordinated pumping
action. (1)

7. Skeletal Muscles Provide…
Skeletal Muscles provide movement, heat production, and posture. Skeletal muscle
contractions allow for the movement of the body as a whole. Skeletal muscle cells
are very active and numerous which allows for a huge amount of body heat
because each cell goes through the process of catabolism to make heat. The muscle
contractions also allow for people to stand, sit, and maintain posture throughout
the day doing various activities. (1)
Excitability, Contractility, and
Extensibility
Our body muscles are capable of many things. One of those things is the
ability to feel things or excitability which coincides with the nervous system because
the muscle cells can respond to nerve signals. Contractility is the muscle being able
to contract or shorten, While extensibility is the muscles being able to extend or
stretch.(1) These two things relate to agonist and antagonist because they are both
opposites and are the motions of what the agonist and antagonists do.