CHAPTER 21
PATHOPHYSIOLOGY OF THE MOTOR
SYSTEM
The loss of voluntary function of the skeletal muscles is one of the main symptoms of
transverse spinal cord lesions. The paralysis of the muscles at segmental level of the
lesion differs fundamentally from the motor paralysis below the level of the transverse
lesion.
Motor paralysis at segmental level
The muscles innervated by the affected segment or segments at the level of the lesion
show the classical signs of a flaccid paralysis of lower motor neuron type as a result of the
destruction of their anterior horn cells and anterior roots. There is loss of reflex function
and tone of the muscles and their electrical excitability undergoes changes (degenerative
reaction, RD), and the electromyogram reveals a curve characteristic for a lower motor
neuron lesion. Moreover, there are alterations of their blood supply and trophic condition
resulting in muscular atrophy. These changes are found at any level including conus and
cauda equina.
Motor paralysis below the level of the lesion
In contrast, the motor paralysis below the level of the transection is of upper motor
neuron type provided that the segments below the transverse lesions are intact. Although
the motor paralysis as the immediate effect of the sudden onset of a transverse lesion is at
first also of flaccid type with areflexia (stage of spinal shock), in due course muscle tone
and reflex function of the muscles will return (stage of reflex automatism) and the
motor paralysis is of spastic type. However, the paralysis of the skeletal muscles below
the level of the transverse spinal cord lesion will also be of lower motor neuron type if
in addition to the cord damage in the transverse plane destruction of the cord in the
vertical plane has occurred. This will also affect the reflex function of the isolated cord
resulting in hypo- or areflexia of skeletal muscles.
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