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Reading Notes
Section 10.1
Pages 331-342
■ ____________ muscle cells are non-striated, have a __________ nucleus, and
are usually arranged in _____________ lines, forming sheets. They are under
________________ control and found in the walls of many _______________
organs.
■ Cardiac muscle is _____________ found in the ______________ and forms the
wall of this organ. Its cells are ______________, and each has a single
______________. Cardiac muscle cells are _____________ and branched, forming
a ______________, net-like structure. Cardiac muscle contraction is
________________.
■ _____________ muscles are tubular and striated. Skeletal muscle contraction is
___________________. These muscle cells are __________, and each has a
number of ______________ (multinucleated). They are usually referred to as
______________, rather than ______________.
To lengthen, a muscle must ____________ so that an opposing force can
___________ the muscle back to its full length. The arrangement of
_______________ pairs of muscles around a joint (in effect, a fulcrum) allows
them to act together to _______________ each other out and provides the force to
move a ______________ (in effect, a lever) in _________________ directions.
________________ muscle fibre consists of hundreds of thousands of cylindrical
sub-units called _________________. Each of these is made of even finer
_____________________, which contain _______________ structures responsible
for muscle contraction.
An _______________ (thin) myofilament consists of two strands of protein
molecules that are wrapped around each other, somewhat like two strands of
_____________ loosely wound together.
A myosin (______________) myofilament is also composed of two strands of
______________ wound around each other; however, a myosin myofilament is
about 10 times ______________ than an actin myofilament, and the myosin
strands have a different shape. One end of a myosin myofilament consists of a long
____________, while the other end consists of a _________________-headed
globular region, often called the “____________________.”
When a muscle fibre ______________, the heads of thousands of myosin
myofilaments move _____________. This moves them closer to their rod-like
“backbone” and a few nanometers in the direction of the __________. Because the
heads are _____________ (chemically bound) at this time to actin myofilaments,
the ____________ myofilaments are pulled along with the myosin heads as they
flex. As a result, the actin myofilaments _____________ past the myosin
myofilaments in the direction of the flex.
As one myosin ______________ after another flexes, the myosin, in effect,
“walks” in place, step by step, along the _______________.
Each step requires a molecule of ____________ to provide the energy that
repositions the _________________ head before each flex.
The ______________________ model of muscle contraction can be described as
follows:
■ Within each myofilament, the _______________ is anchored at one end, at a
position in striated muscle tissue called the ____________ line. Because it is
tethered like this, the movement of actin pulls its “_______________” (the Z line)
along with it.
■ As _____________ moves past ______________, it drags the Z line toward the
_________________.
■ The mechanism of muscle contraction depends on the structural arrangement of
__________________ of myosin myofilaments in relation to thousands of pairs
actin myofilaments. With one actin molecule being pulled __________________
in one direction, and the other actin molecule being pulled inward in the
_________________ direction, the two __________ of actin drag the
______________ lines towards each other as they slide past the
________________. As the Z lines are pulled _______________ together, the
plasma membranes to which they are attached move __________________ one
another, and the entire muscle fibre __________________.
Muscle cannot contract without ____________ ions. When the ________________
ion concentration in the sarcoplasm is low, ________________ inhibits myosin
binding, and the muscle is ________________.
When the calcium ion concentration is _____________, Ca++ binds to
_______________. This causes the troponintropomyosin complex to be shifted
away from the attachment sites for the ____________ heads on the
_________________. When this repositioning has occurred, the myosin heads
attach to actin and, using ATP energy, move the actin myofilament to shorten the
myofibril.
__________________ is a high-energy compound that builds up when a muscle is
resting. This compound cannot participate directly in muscle contraction; instead,
it can regenerate ______________. The chemical reaction occurs in the midst of
sliding filaments. Therefore, it is the ________________ way to make ATP
available to muscles.
Creatine phosphate provides enough _____________ for only about
________________ seconds of intense activity, and then it is spent.
___________________, such as creatine phosphate breakdown, supplies ATP
without consuming _________________. This allows the muscle to continue
activity in ________________ conditions.
Aerobic cellular respiration, completed in ___________________, usually
provides most of a muscle’s ___________. ________________ and ___________
are stored in muscle cells. Therefore, a muscle fibre can use ______________ from
glycogen and fatty acids from fats as fuel to produce _____________ when oxygen
is available.
When a muscle uses fermentation to supply its energy needs, it incurs an oxygen
_______________. _______________ is obvious when a person continues to
breathe heavily after exercising. Replenishing an oxygen deficit requires
replenishing _______________________ supplies and disposes of
_________________. Lactate can be changed back to ________________ and
metabolized completely in mitochondria; it can also be sent to the liver to
synthesize glycogen.