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CHAPTER 22
been, the modern concept of spinal shock is based on the work of Sherrington and his
school, which suggests that the transient reflex depression in the segments below the
spinal cord transection is the result of the sudden withdrawal of a predominantly facili
tating or excitatory influence of descending supraspinal tracts, resulting in a disruption
of transmission at the synapse and thus rendering the process of conduction impossible
or difficult. In recent years, thanks to the work of Eccles and his colleagues (1964), much
of the research was concerned with the mechanism of synaptic excitation and inhibition,
whereby the importance of the peripheral organs in the muscle system has been more
and more recognized in the process of transmission. It has been concluded that a
primary factor in the tendinous areflexia in spinal shock is the reduced discharge of
spindle receptors, produced by relaxation of intrafusal muscle fibres through the acute
deficit of the fusimotor control from the gamma-motor neurons. There are other factors
involved in the mechanism of spinal shock, and McCouch (1964) postulated three as
probably significant.
1
Loss of facilitation from descending tracts.
2 Persisting inhibition from below acting upon extensor reflexes. It has been shown
that if in a decerebrate animal a transection of the spinal cord is performed in the mid-
thoracic region, the extensor rigidity of the fore-limbs resulting from the decerebration
is intensified as a source of inhibition arising from the lumbar enlargement if the cord
has been removed from its effect upon extensor reflexes of the cervical and upper thoracic
spinal segments (Ruch, 1956). On the other hand, I found in the spinal man with cervical
lesion resulting in intractable spasticity of both lower and upper limbs that elimination of
the thoraco-lumbar portion of the spinal cord by intrathecal alcohol block decreased
rigidity and spasticity in the upper limbs.
3 Axonal degeneration of interneurons. Axonal degeneration is more severe where
the axon is cut near the cell body. This accords, according to McCouch, with the greater
severity of spinal shock from lesions at lower levels.
In the following various problems concerned with the reflex behaviour of the skeletal
muscles during the stage of spinal shock in man are discussed:
(i)
Spinal shock and traumatic shock
In spite of a certain superficial similarity, as far as fall of blood pressure (in high lesions)
is concerned, there are fundamental differences between spinal shock and traumatic
shock, and these two phenomena should not be confused. While in transections above the
sympathetic outflow (T5), especially cervical lesion, there is initially a marked fall of
blood pressure, this returns to normal very soon, while the reflex depression as a result
of the spinal shock remains unchanged for more or less long periods. Furthermore, in
distal cord lesions, spinal shock is severe while the blood pressure may remain normal
immediately after injury. If the traumatic shock results in fall of blood pressure, this is
readily restored by blood transfusion but this has no effect on the intensity of the spinal
shock. Moreover, it does not make any significant difference to the degree of reflex
depression due to spinal shock whether the anterior spinal artery is severed or not.
(Hunter & Royle, 1924).
