F - CLINICAL ASPECTS OF SPINAL CORD INJURIES
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B. Stage of reflex return—reflex automatism of the isolated cord
Once the stage of spinal shock subsides and the synaptic relays are released from the
resistance imposed upon them through the process of spinal shock, afferent impulses
arising from peripheral stations of the nervous system in skin, tendons, muscles, ligaments,
joints, and viscera begin to elicit their excitatory influence on the neural elements within
the isolated cord. Conversely, the cord reacts, now unrestrained from supraspinal
inhibitory influences, with complex efferent responses (Mass Response). The reflex
automatism of the isolated cord thus established, is characterized by hyperreflexia,
rigidity and spasticity of the muscles.
In recent years, the excitatory and inhibitory function of synapses, which act as
devices for the transmission of information from one neuron to another by a chemical
transmitter mechanism, has been the subject of intensive research by cell physiologists,
and electron microscopy has contributed much information on the monosynaptic and
polysynaptic connections of the spinal cord, pre-eminently through the work of Eccles
and his school (Eccles & Lundberg, 1959; Eccles, 1964; Lundberg, 1964; Granit, 1966;
Eccles & Schade, 1964). Synapse, a term originally proposed by Sherrington (1897),
now embraces the presynaptic terminal with its synaptic vesicles, synaptic cleft and the
subsynaptic membrane with its special receptive and reactive mechanism. Moreover,
the important part which peripheral receptor organs, such as Golgi's tendon organ and
especially the muscle spindle, play in the complex mechanism of the spinal cord has also
come to light. Although Sherrington (1897) recognized the muscle spindle as a sensory
organ, the detailed organization of this encapsulated organ in nuclear-chain and nuclear-
bag fibres and their innervation by group I and II sensory and gamma I and II motor
nerve fibres has only recently been elaborated. Cooper & Daniel (1956), Boyd
et al.
(1964) and Rushworth (1960, 1964) found the muscle spindle contribution to the afferent
influx dominant in the majority of clinical states of either rigidity or spasticity of the
skeletal muscles in the paralysed limbs. Whitteridge (1966), Rushworth (1966) and Phil
lips (1970) have given excellent reviews on this problem. In this connection, it may be
remembered that it was the realization of the importance of afferent impulses on motor
reflex response in the treatment of spasticity and rigidity which many years ago led
Foerster (1911) to introduce the posterior rhizotomy in the treatment of spastic con
ditions.
As a rule, reflex return is in headward direction. The reflexes appearing first in the
spinal man are anal and bulbo-cavernosus reflexes and responses to plantar stimulation
such as plantar and/or dorsiflexion of the toes and the ipsilateral flexor reflex of the leg.
Actually, the ipsilateral flexor reflex of the leg may be elicitable before a significant
reflex response of the toes or tibialis anterior or return of the knee and ankle jerks is
noticeable (Fig. 105). At first, a strong stimulus or summation of several stimuli to the
sole of the foot is necessary to elicit any reflex response of muscles of the leg and there
is fatigue in their reflex-responses. Moreover, there are differences in onset and inten
sity of reflex recovery between the two sides of the lower and (in cervical lesions)
upper limbs indicating a difference in the intensity of spinal shock within the two halves
of the isolated cord. In later stages of reflex automatism, the receptive field increases
