FREEMAN, W. J. 
At the level of the spinal cord, there is a highly complex set of 
structures concerned with shivering, including the terminal fibers 
of sensory nerves, the interneurons and their dendritic systems, 
recurrent collaterals, the afferent fibers from sensory organs in 
muscle, and so forth. All of these structures comprising the basic 
apparatus of the segmental spinal reflexes are unquestionably in- 
volved in shivering. They are equally unquestionably involved in all 
other types of directed muscular activity, and yet they are not 
sufficient for either. The particular contributionof these structures 
appears to be the adaptation of an overall pattern of body activity 
to local conditions encountered in the trunk and extremities. Specif- 
ically, the frequency of tremor of any given muscle or muscle group 
is determined at the spinal level. The question of whether or not 
shivering will occur, and if so, with what severity, is decided else- 
where. 
There is a great deal that ought to be known about higher struc- 
tures in relation to shivering, which we do not yet know. Perhaps 
Dr. Stuart will tell us something along that line. Proprioceptive 
activity is associated with the ascending discharges in the spino- 
cerebellar tracts, terminal fibers of which are broadly distributed 
over the cerebellar cortex. There are indications that cutaneous 
sensory activity may also reach the cerebellum. The spino-thalamic 
tracts subserving thermal sensation pass laterally and ventrally 
through the medulla over the lateral reticular nucleus, and they 
give off collaterals to it. Virtually the entire efferent discharge of 
this nucleus is distributed to the cerebellum. It is now known that 
electrical potentials related toavariety of afferent stimuli including 
visual, tactile, and auditory stimuli reach the cerebellum, and it 
seems likely, although the direct evidence is lacking, that thermal 
stimuli can induce cerebellar responses. In this case, the cerebellum 
can be regarded as a site for the mixing of cutaneous and proprio- 
ceptive discharges to produce a new pattern which is specific for 
these two types of input. Dr. Kawamura has shown in this symposium 
that an increase in proprioceptive activity associated with increased 
muscle tonus is a prelude to shivering. Obviously, cutaneous cooling 
is an essential element. When proprioceptive and cold receptor 
activity are mixed, as they may well be in the cerebellum, the 
groundwork is laid for an appropriate response peculiar to this 
unique combination of sensory input. Clearly the cerebellum is not 
specific for shivering, but it plays a significant role, since shivering 
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