86
TOSHIAKI J. HARA
the fibrils are grouped together in clusters instead of forming individual
cilia and are enveloped by a single limiting membrane. Further, Wilson
and Westerman ( 1967) discovered a conspicuous well-differentiated new
cell type, the foliaceous cell, which has not been previously described in
olfactory mucosa. These foliaceous cells, enclosing prominent leaflike
organelles, communicate with the external environment through a small
stoma. Their complicated morphology together with their close association with the multifilamentous cilia and the myelinated nerve fibers observed in the stroma suggest that they may be receptor cells; however,
further work will be required to provide additional information on their
role and neural connection.
It is not clear which part of the receptor cell is involved in the initial
events of olfactory stimulation. However, it is reasonable to assume that
the receptor site lies on the membranes of the olfactory cilia since these
are the first points of contact with odorous molecules; moreover, the olfactory knob does not protrude beyond the limiting surface of the mucosa
as in other vertebrates. If this is the point of excitation, number, length,
and motility of the cilia would be signscant in enlarging the active receptor area and increasing the chance of contact between cilia and molecules. The theory that the olfactory cilia are the locus where electrical
excitation in the olfactory organ is initiated by contact with odorous
substances has been suggested by Reese (1965), who investigated the
fine specialization of olfactory epithelium of the frog. Motile olfactory
cilia were first described in Stenesthes by Hopkins (1926). However, the
motility of the olfactory cilia in Cyprinus, Esox, and Lampetru has
recently been observed ( Vinnikov, 1965; Kleerekoper, 1969). Jagodowski
(1901) found only one extremely long, thick cilium on each of the olfactory receptor cells of pike; and Bannister (1965) described a receptor
cell with only one rod-shaped process in the minnow. Further works will
be needed to determine whether any simple relation exists between the
characteristics of the cilia and sensitivity to odors.
The supporting cells are polygonal columnar epithelial cells which lie
between the receptor cells. They bear a small number of irregular microvilli and have prominent oval nuclei situated basally. The cytoplasm
immediately beneath the limiting surface is relatively scant with numerous
electron-dense vesicles. In the deeper parts of the cells an endoplasmic
reticulum and mitochondria are present as much as the receptor cells.
Although the significance of the supporting cells in olfactory perception
is not understood, it is likely that they have a significance beyond mere
mechanical support.
In addition to the olfactory cells mentioned above, free nerve endings
of the trigeminal nerve occur in the epithelium (Jagodowski, 1901). Al-
TOSHIAKI J. HARA
the fibrils are grouped together in clusters instead of forming individual
cilia and are enveloped by a single limiting membrane. Further, Wilson
and Westerman ( 1967) discovered a conspicuous well-differentiated new
cell type, the foliaceous cell, which has not been previously described in
olfactory mucosa. These foliaceous cells, enclosing prominent leaflike
organelles, communicate with the external environment through a small
stoma. Their complicated morphology together with their close association with the multifilamentous cilia and the myelinated nerve fibers observed in the stroma suggest that they may be receptor cells; however,
further work will be required to provide additional information on their
role and neural connection.
It is not clear which part of the receptor cell is involved in the initial
events of olfactory stimulation. However, it is reasonable to assume that
the receptor site lies on the membranes of the olfactory cilia since these
are the first points of contact with odorous molecules; moreover, the olfactory knob does not protrude beyond the limiting surface of the mucosa
as in other vertebrates. If this is the point of excitation, number, length,
and motility of the cilia would be signscant in enlarging the active receptor area and increasing the chance of contact between cilia and molecules. The theory that the olfactory cilia are the locus where electrical
excitation in the olfactory organ is initiated by contact with odorous
substances has been suggested by Reese (1965), who investigated the
fine specialization of olfactory epithelium of the frog. Motile olfactory
cilia were first described in Stenesthes by Hopkins (1926). However, the
motility of the olfactory cilia in Cyprinus, Esox, and Lampetru has
recently been observed ( Vinnikov, 1965; Kleerekoper, 1969). Jagodowski
(1901) found only one extremely long, thick cilium on each of the olfactory receptor cells of pike; and Bannister (1965) described a receptor
cell with only one rod-shaped process in the minnow. Further works will
be needed to determine whether any simple relation exists between the
characteristics of the cilia and sensitivity to odors.
The supporting cells are polygonal columnar epithelial cells which lie
between the receptor cells. They bear a small number of irregular microvilli and have prominent oval nuclei situated basally. The cytoplasm
immediately beneath the limiting surface is relatively scant with numerous
electron-dense vesicles. In the deeper parts of the cells an endoplasmic
reticulum and mitochondria are present as much as the receptor cells.
Although the significance of the supporting cells in olfactory perception
is not understood, it is likely that they have a significance beyond mere
mechanical support.
In addition to the olfactory cells mentioned above, free nerve endings
of the trigeminal nerve occur in the epithelium (Jagodowski, 1901). Al-