Abstract
SECTION I: THE PREVIOUS LITERATURE. The literature
relevant to the subject of the thesis is reviewed. The
review is limited to reports on cutaneous receptors,
their afferent nerve fibres and those spinal cord mechanisms which are of general importance for sensory mechanisms. For the most part, the literature reviewed is
of experiments on cats, the species used most for neuronhysiological experiments. The importance of adequate
stimulation of identified receptors is stressed.
SECTION II: CUTANEOUS AFFERENT FIBRE COLLATERALS IN THE
DORSAL COLUMNS. Microelectrode recordings were made from
cutaneous afferent fibre collaterals, in the lumbar dorsal
column, which were antidromically excited from C 2. The
types of cutaneous afferent unit having axon collaterals
which ascend the dorsal columns to the dorsal column nuclei
were identified. All dorsal column collaterals had slower
conduction velocities than corresponding peripheral axons
and the degree of slowing was determined by the class of
unit. The differential slowing was confirmed by recording
compound action potentials from various parts of dorsal
column - peripheral nerve pathways.
SECTION III: THE SPINOCERVICAL TRACT: TYPES OF UNIT AND
THEIR STIMULUS—RESPONSE PROPERTIES. Microelectrode
recordings were made from axons of the spinocervical
tract, In anaesthetized, unanaesthetized decerebrate
and unanaesthetized spinal cats. The properties of the
units depended on the type of preparation used. Differences
between decerebrate and spinal cats were assumed to be due
to a descending neuronal system active in the decerebrate
animal. The Btimulus-response relationship to hair movement was described by a Power function, for those units
sensitive to hair movement. All spinocervical tract units
responded to high skin temperatures (above about 40°C)
with an increased frequency of discharge. Several types
of primary cutaneous afferent unit which excite the spinocervical tract were identified.
SECTION IV: MODALITY CODING IN THE SPINOCERVICAL TRACT,
Examination of individual spinocervical tract cell discharges
evoked by different forms of natural stimulation revealed
differences characteristic for the stimulus type. It was
concluded that the modality of a stimulus, as well as its
intensity, can be coded in the discharge of a single spinocervical tract cell.
SECTION V: CONTROL OF THE 8PIN0CERVICAL TRACT IN DECEREBRATE
'REPARATIONS. By means of a reversible cold block of the
spinal cord, individual spinocervical tract units were
examined in the decerebrate and in the spinal state, and
the actions of the descending neuronal system were studied.
The equivalence of unit types in the two preparations was
established. The descending system acts to inhibit certain of the excitatory inputs to individual
spinocervical tract cells, while at the same time it
prevents many inhibitory actions on the cells,
SECTION VI: GENERAL DISCUSSI0N. The properties of the
two ascending pathways studied are compared. Some problems
raised by the present work, and the possible functions of
the spinocervical system, are discussed.
