insuli ventropostero-medial nucleus of thalamu:
cranial nerve (VII, IX, orX) taste bud d: dark cell i: intermediate cell I: light cell t: taste pore b: basal cell taste bud
apical membrane out
apical membrane out
^ adenylate cyclase " taste" receptor • "sweet" raste Na+channel basolateral Ca2+ membrane
Na+/lC ATPase pump Ca+ channel
The sense of smell is mediated by the olfactory system. This is the detection of airborne chemicals by specialized receptors in the olfactory mucosa. Animals that rely heavily on olfaction for survival and reproduction are termed macrosmatic, while humans, who do not, are microsmatic. Nevertheless, humans are able to detect many different airborne chemicals at low concentrations. Olfaction and taste work together to achieve the sensation referred to as taste; if for any reason olfaction is impaired, the patient complains that food cannot be properly tasted. In contrast to the taste system, which distinguishes relatively few modalities of sour, sweet, bitter, and salt, the olfactory system can distinguish very many different odorants, which contribute to the subtle modality of smell.
The olfactory system is completely neural, since the receptors are modified neurons that transduce and transmit olfactory inputs to the brain via the olfactory bulb, the lateral olfactory tract, and from there to the olfactory cortex. The olfactory system is unique among the senses, in that receptors project directly to cortex; the other senses relay through the thalamus. The olfactory bulb is part of the forebrain, situated on its ventral surface in the olfactory sulcus, and attached to it by the olfactory tract. The olfactory tract consists mainly of fibers of the anterior olfactory nucleus, the lateral olfactory tract, and the anterior limb of the anterior commissure. This tract carries many centrifugal fibers from the brain to the olfactory bulb.
The lateral olfactory tract (LOT), which transmits olfactory inputs to the brain, gives off collaterals to the limbic system, to the olfactory cortex, and to the anterior olfactory nucleus. The anterior olfactory nucleus projects mainly to both the olfactory bulbs and to its contralateral partner. The axons of the LOT travel caudally as the lateral olfactory stria; these synapse in the piriform cortex, a major component of the olfactory cortex, and the olfactory tubercle. The LOT projects further caudally to the anterior cortical amygdaloid nucleus, the lateral entorhi-nal cortex and the periamygdaloid cortex, which is part of the piriform cortex that overlies the amygdala.
The main areas of the olfactory cortex are the anterior cortical amygdaloid nucleus, anterior olfactory nucleus, lateral entorhinal cortex, periamygdaloid nucleus, piriform cortex, and olfactory tubercle. All these areas have reciprocal intrinsic connections. The main intrinsic connections stem from the anterior olfactory nucleus, lateral entorhinal cortex, and piriform cortex. The olfactory cortex is phylogenetically identified as paleocortex, because most of it contains three cell layers, while neocortex has six layers of cells.
The olfactory cortex projects to several other extrinsic areas. These are the olfactory bulb, which receives fibers from all areas of the olfactory cortex except the olfactory tubercle; to the hippocampus from the lateral entorhinal cortex, and to the lateral hypothalamus, mainly from the piriform cortex and anterior olfactory nucleus. The connections to the hippocampus mediate olfactory contribution to memory and learning. The connections to the hypothalamus mediate feeding behavior and perhaps emotional responses such as food-evoked rage responses.
corpus callosurn olfactory bulb olfactory tract rhinal fissure corpus callosurn
medial aspect of cerebral hemisphere olfactory sulcus olfactory_ bulb olfactory_ tract olfactory sulcus olfactory_ bulb olfactory_ tract lateral olfactory_ stria olfactory tubercle-
entorhinal cortex overlying cortex cut away on this side lateral olfactory_ stria olfactory tubercle-
efferent projections of olfactory bulb orbital gyri anterior olfactory nucleus lateral olfactory "tract amygdala periamygdaloid cortex piriform cortex entorhinal cortex overlying cortex cut away on this side centrifugal fibers olfactory mucosa olfactory bulb centrifugal fibers centrifugal fibers olfactory mucosa olfactory bulb centrifugal fibers
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