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Synaptic Transmission: Visceral Efferent Endings<br />
NEUROPHYSIOLOGY<br />
Visceral Efferent Endings<br />
A. Smooth muscle<br />
Smooth muscle cells (cut)<br />
Schwann cell cap enclosing<br />
nerve axons<br />
Mucous cells<br />
Schwann cell<br />
cap enclosing<br />
nerve axons<br />
B. Gland (submandibular)<br />
Sympathetic terminal<br />
ending<br />
Varicosity<br />
Schwann<br />
cell cap<br />
⎧<br />
⎪⎪⎨⎪⎪⎩<br />
⎧<br />
⎪⎪⎨⎪⎪⎩<br />
⎧<br />
⎪⎪⎨⎪⎪⎩<br />
Axon<br />
C. <strong>Neuro</strong>secretory<br />
(posterior pituitary)<br />
Pituicyte processes<br />
Axon<br />
Schwann cell cap<br />
Smooth muscle cells<br />
Varicosities<br />
Terminal endings<br />
Serous cells<br />
Parasympathetic<br />
terminal ending<br />
Schwann cell<br />
cap enclosing<br />
nerve axons<br />
Varicosity<br />
Capillary<br />
Endothelium<br />
Mast cell<br />
Fibroblast<br />
<strong>Neuro</strong>secretory<br />
vesicles<br />
Collagen space<br />
Basement membrane<br />
©<br />
FIGURE 2.6<br />
VISCERAL EFFERENT ENDINGS •<br />
<strong>Neuro</strong>nal efferent endings on smooth muscle (A) and glands (B<br />
and C) exhibit unique endings unlike the presynaptic and postsynaptic<br />
terminals observed in neuronal and neuromuscular junction<br />
synapses. Rather, neurotransmitter substances are released<br />
into interstitial spaces (A and B) or into the bloodstream (C, neurosecretion)<br />
from expanded nerve terminal endings. This arrangement<br />
allows for the stimulation of numerous target cells over a<br />
wide area. Not all smooth muscle cells are innervated. They are<br />
connected to adjacent cells by gap junctions and can therefore<br />
contract together with the innervated cells.<br />
57
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