1. ANATOMY AND PHYSIOLOGY OF THE CENTRAL NERVOUS SYSTEM
57
ing phase of the action potential. A maximum height of 11 mV was
recorded for the 3-7 msec hyperpolarization with a 13-msec spike
duration. Excitatory postsynaptic potentials were illicited by subliminal
afferent volleys. This monosynaptic stimulation resulted in complex
synaptic potentials with durations up to 40 msec, indicating the presence
of a polysynaptic (interneuron) linkage with a 'reverberating circuit to
account for the prolonged synaptic potential of the reticular cell. Thus,
a variety of polysynaptic pathways converge on reticulomotor cells.
The polysynaptic input was studied by initiating simultaneous stimulation to the left and right ophthalmic and left and right hyomandibular
nerves. The response of the reticulomotor cells to these inputs differed
in latency, distinctness in rising phase of the excitatory postsynaptic
potential, and amount of late activity induced within the cell by afferent
stimulation. Antidromic stimulation of reticulomotor cells could be
affected by stimulating the reticulomotor axons within the spinal cord.
The conduction velocity of reticulomotor fibers was calculated at 25-66
meters/sec by recording the transmission rates of known lengths of this
axon (Restieaux and Satchell, 1958).
The majority of reticulomotor cells produced more than one action
potential in response to a single stimulus. The latencies of these responses
were usually 7-14 msec, but longer latencies ( u p to 50 msec) were
observed. Many units produced action potentials as much as two or
three times to a single stimulus resulting in repetitive discharges and the
production of long spike trains. Increasing stimulus strength above threshold increased the number of spikes in a repetitively discharging unit
and shortened the latency of the first spike. This indicated that nerve
fibers of different thresholds exist in the peripheral nerve being stimulated for the afferent input to the neurons so that increased stimulus
strength resulted in increased afferent input to the neurons by the
recruitment of axons of higher threshold. This increased afferent activity
acting upon internuncial neurons relays information to the reticulomotor
cells until the synaptic potential reaches sufficient amplitude to initiate
a spike. Action potentials could be evoked by the summation of two
independent afferent stimuli neither of which could independently trigger
an action potential. The summation of response of the two afferent
volleys, either of which could produce a spike independently, resulted
in the initiation of a spike earlier in latency than either could produce
alone. Units were capable of discharging two or three times to a maximal stimulus applied to a single afferent channel, but discharged only
once to a liminal stimulus applied to a single afferent channel. These
data demonstrate that the multiple synaptic input can be summed when
liminal afferent volleys are presented over separate channels. Again, as
57
ing phase of the action potential. A maximum height of 11 mV was
recorded for the 3-7 msec hyperpolarization with a 13-msec spike
duration. Excitatory postsynaptic potentials were illicited by subliminal
afferent volleys. This monosynaptic stimulation resulted in complex
synaptic potentials with durations up to 40 msec, indicating the presence
of a polysynaptic (interneuron) linkage with a 'reverberating circuit to
account for the prolonged synaptic potential of the reticular cell. Thus,
a variety of polysynaptic pathways converge on reticulomotor cells.
The polysynaptic input was studied by initiating simultaneous stimulation to the left and right ophthalmic and left and right hyomandibular
nerves. The response of the reticulomotor cells to these inputs differed
in latency, distinctness in rising phase of the excitatory postsynaptic
potential, and amount of late activity induced within the cell by afferent
stimulation. Antidromic stimulation of reticulomotor cells could be
affected by stimulating the reticulomotor axons within the spinal cord.
The conduction velocity of reticulomotor fibers was calculated at 25-66
meters/sec by recording the transmission rates of known lengths of this
axon (Restieaux and Satchell, 1958).
The majority of reticulomotor cells produced more than one action
potential in response to a single stimulus. The latencies of these responses
were usually 7-14 msec, but longer latencies ( u p to 50 msec) were
observed. Many units produced action potentials as much as two or
three times to a single stimulus resulting in repetitive discharges and the
production of long spike trains. Increasing stimulus strength above threshold increased the number of spikes in a repetitively discharging unit
and shortened the latency of the first spike. This indicated that nerve
fibers of different thresholds exist in the peripheral nerve being stimulated for the afferent input to the neurons so that increased stimulus
strength resulted in increased afferent input to the neurons by the
recruitment of axons of higher threshold. This increased afferent activity
acting upon internuncial neurons relays information to the reticulomotor
cells until the synaptic potential reaches sufficient amplitude to initiate
a spike. Action potentials could be evoked by the summation of two
independent afferent stimuli neither of which could independently trigger
an action potential. The summation of response of the two afferent
volleys, either of which could produce a spike independently, resulted
in the initiation of a spike earlier in latency than either could produce
alone. Units were capable of discharging two or three times to a maximal stimulus applied to a single afferent channel, but discharged only
once to a liminal stimulus applied to a single afferent channel. These
data demonstrate that the multiple synaptic input can be summed when
liminal afferent volleys are presented over separate channels. Again, as