Biomedical Engineering Reference
In-Depth Information
2.5
2
1.5
1
0.5
y = 0.0125x + 0.9418
y = 0.1024x + 0.2492
0
0
5
10
15
20
(a)
Saccade Magnitude (deg)
60
50
40
30
y = 2.664x
−
6.6
20
10
y = 1.1661x + 4.834
0
0
5
10
15
20
(b)
Saccade Magnitude (Degrees)
FIGURE 13.54
Agonist pulse magnitude (a) and duration (b) as functions of saccade magnitude.
normal characteristics. The antagonist onset delay varies from 3 ms to approximately 25 ms.
With a larger rebound burst, the onset delay is typically shorter for each type of saccade.
An inherent coordination error exists between the return to tonic firing levels in the
abducens and oculomotor motoneurons during the completion of a saccade. During an
abducting saccade, ipsilateral abducens motoneurons fire without inhibition and oculomo-
tor motoneurons are inhibited during the pulse phase. Because the IBN inhibits antagonist
motoneurons, resumption of tonic firing and PIRB activity in the motoneurons does
not begin until shortly after the ipsilateral IBNs cease firing. This same delay exists in the
abducens motoneurons for adducting saccades.
There are significantlymore internuclear neurons between the contralateral EBN and the TN
and the ipsilateral oculomotor motoneurons (antagonist neurons during an abducting saccade)
than the ipsilateral EBN and TN and ipsilateral abducens motoneurons (antagonist neurons
during an adducting saccade). Due to the greater number of internuclear neurons operating
during an abducting saccade, a longer time delay exists before the resumption of activity in
the oculomotor motoneurons after the pulse phase for abducting than adducting saccades.
