Skeletal muscles contract to produce movement in response to nerve signals. Rigor mortis is a temporary stiffening of muscles after death. The four factors influencing muscle contraction strength are joint angle, cross-sectional area, speed of movement, and muscle fiber type. Calcium ions play a key role in muscle excitation, contraction, and relaxation by binding to and unbinding from troponin. Cardiac muscle forms a syncytium of electrically coupled fibers for coordinated pumping, unlike skeletal muscle fibers which taper individually.

1. Q&A (Cont.)
Describe Rigor Mortis.
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Rigor Mortis is when the body stiffens and
becomes rigid after death. It is a short 50% Off
period of time where all the muscles in the PLUS days
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body contract but it is only a temporary
state.
Describe in detail the 4 factors that
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influence the strength of muscle
contractions.
The 4 factors that influence the strength
of muscle contractions are:
Joint angle: A joint between two bones
which results in a change in direction. 2013 Byron Nelson Blvd
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the cross section of a muscle Fax: 817.714.2013
perpendicular to its longitudinal FIT4LIFE@FITNESS.COM
dimension generally at it largest point. It is
used to describe muscle contraction
properties.
Speed of Movement: is how fast
Muscle Fiber Type: the structural cells of a
muscle

2. Things you should know…
Q&A Relate contractility and Extensibility to the Explain how the sliding filament theory allows
concept of agonist and antagonist discussed for the shortening of a muscle fiber.
Explain how skeletal muscles provide movement,
in chapter 10. The theory allows for the shortening of the
heat, and posture. Are all of these functions unique
to muscles? Explain your answer. Contractility is when a tissue can shorten and muscle fiber because it states that the Z-lines
contract witch make the A-band shorten. There
thicken. Muscle extensibility refers to the
The skeletal system works with the muscular is a myosin in the middle of the Z-lines and on
ability of a muscle group to lengthen. It
system to allow movement. Skeletal muscles cross each of the myosin there are little proteins that
relates to the concept of agonist and connect to them called actin that grab a hold to
joints and are attached to the bones on either side
antagonist because agonist produces an the fibers in the muscle and that allows for the
by tough cords called tendons. They contract, to
action and antagonist opposes theaction, muscle to shorten. The actin will continue to
produce movement, as a result of nerve signals
same when contractility shortens a tissue and grab the muscle fibers until there is eventually
sent from the brain and spinal cord. Skeletal
extensibility lengthens it. no more room on the myosin.
muscles produce heat (through the splitting of
Adenosine Triphosphate (ATP) during contraction.) What structures are unique to skeletal How does the treppe effect relate to the warm-
Skeletal muscles also provide the framework for muscle fibers? up exercises of athletes?
the body and protect the body’s internal organs.
Bone, tendon, myofibrils, mitochondria, thin The treppe effect is the gradual increase in
Skeletal muscles aid in helping muscles maintain muscular contraction following rapidly repeated
posture and produce movement. and thick filaments, sarcomere, actin and
stimulation, so whenever athletes warm up
myosin filaments.
they are gradually increasing how much they
The characteristics of excitability is shared by what
Which of the structures involved primarily in will be using their muscles and it allows for the
other system?
muscles to prepare themselves to get broken
contractility and which are in involved in
Excitability: the ability to respond to stimuli by the down and allow them to work out without
excitability?
hurting themselves.
production of electrical impulses. The nervous
system also sends messages throughout the body Contractility: muscles, tendons, and
to respond to stimuli. attachments.
Excitability: nerves, tendon, muscle fiber.

3. Q&A (Cont.)
Explain how the structure of the myofilaments At the ends of fibrils, special structures
is related to their function. anchor the terminal actin filaments to the
membrane. There also appear to be
Myofilament is the term for the chains of connections between the Z and M lines and
(primarily) actin and myosin that pack a the cell membrane.
muscle fiber. These are the force generating
structures. Seen in longitudinal section (with In easier words the structure of the
an electron microscope), a myofilament myofilament have gapes in them and which
shows several distict bands, each of which has allow for them to overlap and make a
been given a special letter. The lightest (least muscle shorter, they can also stretch out to
electron dense) band is known as the I band make a muscle longer.
and consists mostly of actin. The wide, dark
Using fiber types, design a muscle for a
band, known as the A band, is composed
marathon runner and a different muscle for
primarily of myosin. In the center of the I band
a 100-yard-dash Sprinter. Explain our
is an electron dense line, known as the Z-line.
choice.
In the middle of the A band is another dense
line known as the M line. In cross section, Type 1 muscle fibers would be ideal for a
under very high magnification, both A and I marathon runner, because they are more
bands can be seen to be hexagonal networks. efficient at usingoxygen, means they can
These networks are apparently ordered and handle extended muscle contractions over
fixed at the M- and Z-lines. . In the region a long period of time. Type 2 muscle fibers
where the A and I bands overlap (sometimes would be ideal for a sprinter. These muscle
known as the H band) the two hexagonal fibers use anaerobic metabolism to create
networks intermesh so that each myosin energy, so they are good at creating rapid
filament is surrounded by six actin filaments. bursts of energy. Because they fire more
These networks appear to be anchored to quickly than type 1 muscle fibers, they
(and through) the cell membrane in two ways. fatigueat much quicker pace.

4. Q&A (Cont.)
Calcium ions bons to troponin: the
What are the phases of a twitch troponin-tropopmyosin complex changes
contraction? What molecular events occur its position and exposes the active site on
during each of these phases. the actin myofilaments.
Latent phase: action potential is Contraction phase: Cross bridges between
propagated to the presynaptic terminal of actin and myosin form, move, release, and
motor neuron. This action potential causes reform many times. This results in the
sodium and potassium permeability of the shortening of the sacrometes. After cross-
presynaptic terminal to increase. bridge movement has occurred, ATP binds
Acetylcholine is released by exocytosis into to the myosin head. ATP breaks down into
the synaptic cleft and diffuses across it to ADP, and part of the energy is used to
bind to acetylcholine receptor molecules in release the cross bridge. This makes the
the postsynaptic membrane. This causes myosin head to move back to its resting
ligand-gated sodium ion channels to open, position where it becomes ready again to
and the membrane becomes more form a cross bridge. Part of the energy
permeable to sodium ions. Sodium ions from the ATP is stored in the head of the
diffuse into the muscle fiber, causing local myosin molecules and is used for the next
depolarization that exceeds threshold and cross-bridge formation and movement.
produces an action potential. One
Relaxation phase: Calcium ions are actively
presynaptic action potential produces one
transported into the sarcoplasmic
postsynaptic action potential in each
reticulum. The troponin-tropomyosin
muscle fiber. The depolarization that occurs
complexes inhibit cross-bridge formation.
in the T tubule in response to the action
The muscle fibers then lengthen passively.
potential causes voltage-gated Ca2+
channels of the membrane of the
sarcoplasmic reticulum becomes very
permeable to Ca2+ ions.

5. Q&A (Cont.) The cardiac muscle fiber does not taper Difference between fine and gross motor
like a skeletal muscle fiber, but instead, units- Fine or small motor units, for
Compare and contrast the role of Ca++ in
forms strong, electrically coupled example in the hand, only include a few
excitation, contraction, and relaxation of a
junctions with other fibers. This feature, muscle fibers which can produce precise
muscle cell.
along with the branching exhibited by movements of the fingers. Gross motor
The role of Ca++ in excitation is where it individual cells, allows cardiac fibers to units on the other hand do not produce
binds to troponin molecules in the thin form a continuous, electrically coupled precise movements, but they include
mass, called a syncytium. Band The more than a hundred muscle fibers each.
myofilaments then Tropomyosin
cardiac muscles form a continuous, (8, pg. 322)
molecules in the thin myofilaments shift,
contractile around the heart chambers
exposing actin’s active sites. Energized People who exercise seriously are
that conducts a single impulse which
myosin cross bridges of the thick helps make an efficient, coordinated sometimes told to work a muscle until
myofilaments bind to actin and use their pumping action. (pg. 330) they "feel the burn". In terms of how
energy to pull the thin myofilaments muscle is able to release energy, explain
toward the center of each sarcomere. Describe the anatomical arrangement of a what is going on in the muscle early in
motor unit. Contrast fine and gross motor the exercise and when the muscle is
This cycle repeats itself many times per
units "burning."
second, as long as adenosine
triphosphate is available. After impulse is Anatomical arrangement of a motor unit- During exercise muscles contract and
When entering the skeletal muscle, the swell and the burning during a workout
over, the SR begins actively pumping
single fiber of a somatic motor neuron will is caused by acidity from accumulation of
Ca++ back into sacs. As Ca++ is stripped divide into variable numbers of branches. lactic acid. Because muscles cannot
from troponin molecules in the think Those neuron branches will only terminate
receive all of the oxygen they need to
myofilaments, trpomyosin returns to its in a few muscle fibers while others may
convert food to energy, lactic acid begins
terminate in several fibers. Because of
position, blocking actin’s active sites. to build up in the muscles which results
this, impulse contradiction by another
Because the thick and thin myofilaments motor unit may only activate a hundred or in acidity which then causes the “burning
are no longer connected, the muscle fiber more fibers simultaneously. More precise feeling” in an intense workout. (17)
may return to its longer, resting length. movements that the muscle can produce
(Pg.316) is a result of the fewer number of fibers
supplied by a skeletal muscle’s individual
Explain the meaning of a "unit of combined motor units. (8, pg. 322)
cells" as it relates to cardiac Muscle. How
does the structure arrangement affect its
function?