Figure 130.1.— Schematic representation of the motor-sensory
unit system and the possible sites lesions producing hypotonia. AMN: alpha
motor neuron; RC: Renshaw cell; DGC: dorsal ganglion cell; EFMF: extrafusal
motor fiber; IFMF: intrafusal motor fiber; GMN: gamma motor neuron. Arrows
indicate direction of conduction. (5) alpha motor neuron; (6) nerve; (7)
myoneural junction; (8) muscle.
Figure 130.2.— Schematic representation of the upper motor neuron system [A] and lower motor unit structures [B] demonstrating possible sites of anatomical involvement that lead to generalized hypotonia. Simplified schematic representation of the lower motor system [C] following same numerical order as [B]. Generalized hypotonia may be due to an upper motor neuron lesion at the (1) brain, (2) brainstem, (3) rostral cervical spinal cord, or (5) cerebellum. Generalized hypotonia may result from damage to the lower motor neurons of the arms and the upper motor neuron fibers of the legs in the lower cervical spine area (4). Generalized hypotonia may be due to lower motor neuron lesions at the: (6) alpha motor neuron; (7) nerve; (8) presynaptic myoneural junction; (9) postsynaptic myoneural junction; and (10) muscle. LMN: lower or alpha motor neuron; MNJ: myoneural junction.