Single axon terminal from topographic nucleus isthmi
Below is a drawing of an axon terminal in the turtle tectum that
arises from a cholinergic neuron in the topographic nucleus isthmi
(=parabigeminal nucleus in mammals) in a turtle. The over 3500
terminal boutons shown are distributed in the superficial and
intermediate layers of the ipsilateral tectum. The boutons are
all restricted to a very small portion of the area of the tectum
(see inset).
By contrast, the non-topographic rostral nucleus isthmi synapses
diffusely over a much larger area of the tectum (not shown). See
Sereno and Ulinski (1987) for (many more!) details.
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