UPPER MOTOR NEURON SYSTEM HYPOTONIA
upper motor neuron system is more a functional concept than an anatomical
structure. The term refers to all the neurons in the brain (Figure 103.1),
cerebellum (Figure 103.1), and brainstem (Figure 103.1) that directly
or indirectly convey information to the motor neurons in the brainstem
and in the anterior horns of the spinal cord (lower motor neurons). The
term upper motor neuron system includes the axons of these neurons. These
axons travel through the brain and brainstem to make contact with the
motor neurons in the brainstem and through the brain, brainstem, and spinal
cord (Figure 103.1) to make contact with the motor neurons in the anterior
horn of the spinal cord.
Figure 103.1.— Schematic representation of the upper motor neuron system and the muscle motor-sensory unit. : motor cortex; : basal ganglia; : cerebellum; : red nucleus; : reticular formation; : lateral vestibular nucleus; : axons from extrapyramidal neurons; : intertesial neurons; : alpha motor neuron; [10: gamma motor neuron; : dorsal ganglion cell; (A) brain; (B) cerebellum; (C) brainstem; (D) spinal cord.