SECTION I - LITERATURE REVIEW
The literature is reviewed with special reference to
knowledge of cutaneous afferent fibres and their representation in spinocervical tract fibres in the lumbar spinal
cord of the cat. Attention is drawn to the paucity of
information about forelimb afferents and their representation in the cervical spinal cord. The control of
transmission through ascending sensory pathways and in
particular the spinocervical tract is discussed. Finally
relevant work on the somatosensory cortex and corticofugal
inhibition is reviewed and comment is made on the influence
of anaesthetics on our knowledge of sensory mechanisms.
SECTION II - RECEPTIVE FIELDS AND CONDUCTION VELOCITIES
OF IDENTIFIED SPINOCERVICAL TRACT AXONS IN THE CERVICAL
Recordings were made with micro-electrodes from single
axons in the dorsolateral funiculus of the cervical spinal
cord of decerebrate cats. Some of these axons could be
designated on electrophysiological criteria as belonging to
the spinocervical tract. Such axons conveyed tactile
information qualitatively similar to that found by other
workers in the lumbar cord. Quantitatively SCT axons with
receptive fields in the forelimb were most common and were
more frequently activated only by hair movement. Axonal
conduction velocities were analysed in relation to the
site and type of their afferent input.
SECTION III - HOMOSEGMENTAL AND HETEROSEGMENTAL INHIBITION
OF TRANSMISSION THROUGH THE SPINOCERVICAL TRACT IN
Discharges evoked in SCT axons by electrical and
natural stimulation were tested for inhibition from other
cutaneous nerves both by electrical and natural stimulation.
Inhibition was most easily elicited from the homologous
limb and least easily from the heterologous contralateral
limb. Conditioning curves of segmental inhibition were
plotted and were consistent with a pre-synaptic mechanism.
In two spinalized decerebrate cats, only homosegmental
inhibition was found.
SECTION IV -
IPSI- AND CONTRALATERAL CORTICOFUGAL INHIBITION
OF TRANSMISSION THROUGH THE SPINOCERVICAL TRACT.
Chloralose anaesthetised curarised cats were used to
demonstrate corticofugal inhibition of spinocervical tract
cells which were excited by electrical stimulation of the
superficial radialX^nerve . Surf ace , sprung ball ,stimulating
electrodes were u^ed to make a grid map of the cortical
surface for areas of maximum inhibitory effect and glass
micro-electrodes were used to stimulate the depth of the
cortex. For both types of stimulation cathodal currents
were most effective. Those areas of cortex eliciting most
inhibition at a given current strength corresponded with
the contralateral forelimb sensory receiving areas S.I and
S.II. Weaker inhibition was elicited from the ipsilateral
cortex. Conditioning curves of corticofugal inhibition
SECTION V - CONCLUSION AND GENERAL DISCUSSION OF THE
FUNCTION OF THE SPINOCERVICAL TRACT.
The results of the previous sections are discussed in
relation to present knowledge of the ascending sensory
pathways and the problems they raise. Theories concerning
the function of the spinocervical tract are discussed and
it is postulated that the spinocervical tract may be
concerned in the control of certain types of movement.