Chapter 7 - Excitation of skeletal muscle:
Neuromuscular transmission and excitation-
contraction coupling
Transmission of impulses from nerve endings to
skeletal muscle fibers: the neuromuscular junction
Skeletal muscle fibers are innervated by
nerve fibers that originate from large
motoneurons in the anterior horns of the
spinal cord. Each nerve ending makes a
junction, called the neuromuscular junction,
with the muscle fiber near its midpoint.
Figure 2C shows the junction between a
single axon terminal and the muscle fiber
membrane. The invaginated membrane is
called the synaptic gutter/trough, and the
space between the terminal and the fiber
membrane is called the synaptic space/cleft.
Sub neural clefts greatly increase the
surface area at which the synaptic
transmitter can act.
Source: Hall, J., 2020. Guyton And
Hall Textbook Of Medical Physiology.
13th ed.
Acetylcholine is synthesized in
the cytoplasm of the terminal,
but it is temporarily stored in
synaptic vesicles. In the synaptic
space are large quantities of
acetylcholinesterase, which
destroys acetylcholine a few
milliseconds after it has been
released from the vesicles.
On the inside surface of the
neural membrane are linear
dense bars. To each side of each
dense bar are protein particles
that penetrate the neural
membrane; these are voltage-
Source: Hall, J., 2020. Guyton And activated Ca++ channels. When an action
Hall Textbook Of Medical Physiology. potential spreads over the terminal, these
13th ed.
channels open and activate Ca++-calmodulin
dependent protein kinase, which, in turn, phosphorylates synapsin proteins that
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