Chapter 6 - Contraction of skeletal muscle
Physiology anatomy of skeletal muscle
Each muscle fiber is usually
innervated by only one nerve
ending, located near the middle of
the fiber. The sarcolemma is a
thin membrane enclosing a
skeletal muscle fiber. At each end
of a muscle fiber, the surface
layer of the sarcolemma fuses
with a tendon fiber.
Myofibrils are composed of actin
and myosin filaments. The thick
filaments are myosin and the thin
filaments are actin. Myofibrils
contain different bands:
I Only actin Isotropic
band filaments to
s polarized
light
A Myosin Anisotroph
band filaments ic to
s and ends of polarized
actin light
filaments
The ends of an actin filament are
attached to a Z disk. From this disk, the
filaments extend in both directions to connect Source: Hall, J., 2020. Guyton And
Hall Textbook Of Medical Physiology.
to myosin filaments. The portion of the 13th ed.
myofibril that lies between two successive Z
disks is called a sarcomere. Titin filamentous molecules keep the myosin and actin
filaments in place, they act as a spring.
, General mechanisms of Source: Hall, J., 2020. Guyton And
Hall Textbook Of Medical Physiology.
muscle contraction 13th ed.
1. Action potential travels along a motor nerve to its endings on muscle fibers
2. The nerve secretes a small amount of acetylcholine
3. Acetylcholine opens acetylcholine-gated channels through protein molecules
floating in the membrane
4. Large quantities of sodium diffuse to the interior of the muscle fiber
membrane. This produces a local depolarization, which causes voltage-gated
channels to open, causing an action potential at the membrane.
5. The action potential travels along the muscle fiber membrane
6. The action potential depolarizes muscle membrane. The electricity of the
action potential in the sarcoplasm, the sarcoplasmic reticulum is activated to
release large quantities of calcium ions.
7. The calcium ions initiate a contraction between actin and myosin filaments
8. The calcium ions are pumped back into the SR by Ca++ membrane pump
and remains stored until a new action potential arrives
Molecular mechanism of muscle contraction
In the relaxed state, the ends of the actin
filaments extending from two sequential
Z disks barely overlap each other.
Conversely, in the contracted state,
these actin filaments have been pulled
inward among the myosin filaments up to
the ends of the myosin filaments. This
action is caused by forces generated by
interaction of cross-bridges from the
myosin filaments with the actin
filaments.
Myosin filaments are composed of
multiple myosin molecules. The molecule
is composed of two heavy chains and
four light chains. The two heavy chains
wrap spirally around each other to form a
double helix, which is called the tail of
the myosin molecule. One end of each of
Source: Hall, J., 2020. Guyton And
Hall Textbook Of Medical Physiology.
13th ed.
Physiology anatomy of skeletal muscle
Each muscle fiber is usually
innervated by only one nerve
ending, located near the middle of
the fiber. The sarcolemma is a
thin membrane enclosing a
skeletal muscle fiber. At each end
of a muscle fiber, the surface
layer of the sarcolemma fuses
with a tendon fiber.
Myofibrils are composed of actin
and myosin filaments. The thick
filaments are myosin and the thin
filaments are actin. Myofibrils
contain different bands:
I Only actin Isotropic
band filaments to
s polarized
light
A Myosin Anisotroph
band filaments ic to
s and ends of polarized
actin light
filaments
The ends of an actin filament are
attached to a Z disk. From this disk, the
filaments extend in both directions to connect Source: Hall, J., 2020. Guyton And
Hall Textbook Of Medical Physiology.
to myosin filaments. The portion of the 13th ed.
myofibril that lies between two successive Z
disks is called a sarcomere. Titin filamentous molecules keep the myosin and actin
filaments in place, they act as a spring.
, General mechanisms of Source: Hall, J., 2020. Guyton And
Hall Textbook Of Medical Physiology.
muscle contraction 13th ed.
1. Action potential travels along a motor nerve to its endings on muscle fibers
2. The nerve secretes a small amount of acetylcholine
3. Acetylcholine opens acetylcholine-gated channels through protein molecules
floating in the membrane
4. Large quantities of sodium diffuse to the interior of the muscle fiber
membrane. This produces a local depolarization, which causes voltage-gated
channels to open, causing an action potential at the membrane.
5. The action potential travels along the muscle fiber membrane
6. The action potential depolarizes muscle membrane. The electricity of the
action potential in the sarcoplasm, the sarcoplasmic reticulum is activated to
release large quantities of calcium ions.
7. The calcium ions initiate a contraction between actin and myosin filaments
8. The calcium ions are pumped back into the SR by Ca++ membrane pump
and remains stored until a new action potential arrives
Molecular mechanism of muscle contraction
In the relaxed state, the ends of the actin
filaments extending from two sequential
Z disks barely overlap each other.
Conversely, in the contracted state,
these actin filaments have been pulled
inward among the myosin filaments up to
the ends of the myosin filaments. This
action is caused by forces generated by
interaction of cross-bridges from the
myosin filaments with the actin
filaments.
Myosin filaments are composed of
multiple myosin molecules. The molecule
is composed of two heavy chains and
four light chains. The two heavy chains
wrap spirally around each other to form a
double helix, which is called the tail of
the myosin molecule. One end of each of
Source: Hall, J., 2020. Guyton And
Hall Textbook Of Medical Physiology.
13th ed.
