Biomedical Engineering Reference
In-Depth Information
Neuromuscular
junction
Motor
neurons
Spinal cord
Muscle fibers (cells)
FIGURE A.2
Motor unit showing two motor neurons supplying the muscle fibers.
Myelin sheath
surrounding axon
of motor neuron
Axon
terminal
Neuromuscular
junction
Nuclei of muscle
fiber (cell)
Sarcolemma
Mitochondria
Sarcoplasm
Myofibrils of
muscle fiber
(b) Diagram bassed on photomicrograph
FIGURE A.3
Neuromuscular junction (NMJ).
strength of a contraction is varied in part by adjusting the number of motor units
that are activated.
Neuromuscular junction (NMJ) is where a synapse takes place between a motor
neuron and a skeletal muscle fiber (fig. A.3). This is done by releasing chemicals
called neurotransmitters at this junction. Axon terminals are clusters of bulb-shaped
structures where axons end at the muscle fiber junction. The region of muscle fiber
membrane where the axon terminal ends is called the motor end plate and has
special features. Neuromuscular junction refers to the axon terminal of the motor
neuron as well as the motor end plate of the muscle fiber. The distal end of an
axon terminal contains many membrane-enclosed sacs called synaptic vesicles.
Inside each synaptic vesicle are thousands of neurotransmitter molecules. Acetyl-
choline (ACh) is the one neurotransmitter found in the NMJ of the motor neuron
synaptic vesicle.
