| olfactory placodes | Paired ectodermal placode's which come to lie in the bottom of the olfactory pits as the pits are deepened by the growth of the surrounding medial and lateral nasal processes. Synonym: nasal placodes. (05 Mar 2000) |
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| olfactory pyramid | A small area of gray matter situated between the roots of the olfactory tracts; it is continuous caudally with the anterior perforated substance. (05 Mar 2000) |
| olfactory receptor cells | Very slender nerve cell's, with large nuclei and surmounted by six to eight long, sensitive cilia in the olfactory epithelium at the roof of the nose; they are the receptors for smell. Synonym: olfactory cells, Schultze's cells. (05 Mar 2000) |
| olfactory receptor neurons | Neurons in the olfactory epithelium with proteins (receptors, odourant) that bind, and thus detect, odourants. Olfactory receptor neurons are bipolar. They send to the surface of the epithelium apical dendrites with non-motile cilia from which project odourant receptor molecules. Their unmyelinated axons synapse in the olfactory bulb of the brain. Unlike other neurons, they can be generated from precursor cells in adults. (12 Dec 1998) |
| olfactory region of tunica mucosa of nose | The specialised olfactory receptive area that includes the upper one-third of the nasal septum and the lateral wall above the superior concha; it is lined with olfactory mucosa. Synonym: regio olfactoria tunicae mucosae nasi, olfactory region of tunica mucosa of nose, Schultze's membrane. (05 Mar 2000) |
| olfactory roots | Three distinct fibre bands (stria medialis, stria intermedia, stria lateralis) that caudally extend the olfactory tract beyond its attachment to the olfactory trigone. The medial stria curves dorsally into the tenia tecta; the intermediate, often barely visible, extends straight back and terminates in the olfactory tubercle; the lateral olfactory stria, the largest of the three, passes along the lateral side of the olfactory tubercle, curving laterally as far as the limen insulae, then sharply medially to reach the uncus of the parahippocampal gyrus where it terminates in the plexiform layer of the olfactory cortex. See: medial longitudinal stria. Synonym: striae olfactoriae, olfactory roots. (05 Mar 2000) |
| olfactory striae | Three distinct fibre bands (stria medialis, stria intermedia, stria lateralis) that caudally extend the olfactory tract beyond its attachment to the olfactory trigone. The medial stria curves dorsally into the tenia tecta; the intermediate, often barely visible, extends straight back and terminates in the olfactory tubercle; the lateral olfactory stria, the largest of the three, passes along the lateral side of the olfactory tubercle, curving laterally as far as the limen insulae, then sharply medially to reach the uncus of the parahippocampal gyrus where it terminates in the plexiform layer of the olfactory cortex. See: medial longitudinal stria. Synonym: striae olfactoriae, olfactory roots. (05 Mar 2000) |
| olfactory sulcus | The sagittal sulcus on the inferior or orbital surface of each frontal lobe of the cerebrum, demarcating the straight gyrus from the orbital gyri, and covered on the orbital surface by the olfactory bulb and tract. Synonym: sulcus olfactorius, olfactory groove. (05 Mar 2000) |
| olfactory sulcus of nasal cavity | The narrow groove in the nasal cavity above the agger nasi that leads from the atrium to the olfactory area. Synonym: sulcus olfactorius cavum nasi. (05 Mar 2000) |
| olfactory tract | A nervelike, white band composed primarily of nerve fibres originating from the mitral cells and tufted cells of the olfactory bulb but also containing the scattered cells of the anterior olfactory nucleus. The tract is closely applied to the ventral surface of the frontal lobe, and attaches itself to the base of the cerebral hemisphere at the olfactory trigone, beyond which it extends in the form of the olfactory striae which distribute their fibres to the olfactory tubercle and, in largest number, to the olfactory cortex on and around the uncus of the parahippocampal gyrus. See: olfactory nerves. Synonym: tractus olfactorius, olfactory peduncle. (05 Mar 2000) |
| olfactory trigone | A grayish triangular area corresponding to the attachment of the olfactory peduncle ("olfactory nerve" or olfactory tract) to the base of the brain, at the anterior border of the anterior perforated substance. Synonym: trigonum olfactorium. (05 Mar 2000) |
| olfactory tubercle | A small, oval area at the base of the cerebral hemisphere, between the diverging medial and lateral olfactory striae, in the anteromedial part of the anterior perforated substance; it is formed by a small area of allocortex characterised by the presence of the islands of Calleja. Corresponding to a much more prominent structure in nonprimate mammals (especially rodents and insectivores), the olfactory tubercle receives fibres from the olfactory bulb by way of the intermediate olfactory stria; it has efferent connections with the hypothalamus and the mediodorsal nucleus of the thalamus. Synonym: tuberculum olfactorium. (05 Mar 2000) |
| A layer | <molecular biology> Right handed double helical DNA with approximately 11 residues per turn. Planes of base pairs in the helix are tilted 20 deg away from perpendicular to the axis of the helix. Formed from B DNA by dehydration. (18 Nov 1997) |
| ameloblastic layer | The internal layer of the enamel organ. Synonym: enamel layer. (05 Mar 2000) |
| anterior elastic layer | A transparent homogeneous acellular layer, 6 to 9 um thick, lying between the basal lamina of the outer layer of stratified epithelium and the substantia propria of the cornea; considered to be a basement membrane. Synonym: lamina limitans anterior corneae, anterior elastic layer, Bowman's membrane, lamina elastica anterior, limiting layers of cornea. (05 Mar 2000) |