Olfactory receptor neuron
The olfactory mucosa and the olfactory epithelium in mammals ( olfactory region ) contains the sensory cells of the olfactory sense. It is that mucosa, with the nasal cavity is lined at the top. The chemo receptors ( ORs ) of the olfactory cells are responsible for ensuring that we can take and differentiate a variety of odors.
For other animal strains, the olfactory cells can sit at completely different parts of the body - as in insects and numerous aquatic animals at the probes.
Structure of the olfactory mucosa
The olfactory mucosa is on the left and right side of the roof of the upper nasal cavity. It has a brown color and an area of about human 2 x 5 cm. The olfactory mucosa is built up from the olfactory cells, supporting and microvilli cells, and is supplemented by basal cells and serous glands.
The olfactory receptor cells can renew if necessary (for damage or similar) from differentiated basal cells (stem cells), while the old, dysfunctional olfactory cells perish by apoptosis. It is this amazing, ongoing regeneration has led to the realization that it is based on neural stem cells, the existence of which nothing was known a long time.
In the epithelium of the olfactory mucosa about 10-30 million olfactory sensory cells ( olfactory receptor cells ) are embedded in humans. A dog has about 250 million olfactory cells, an eel nearly a billion. From each of these cells protrude 5-20 hairs ( cilia ) with special smell receptors also in the mucous membrane, whose thin coating is called mucus. The receptors respond to the arriving there with the breath odor molecules.
Of them, there are about 350 different species, each of which responds only to a specific odorant molecule group that must fit into the lock like a key. The molecular groups differ both in form and through its electricity. The combination of the aforementioned receptors results in an odor mixture can have several thousand variants.
The olfactory cells of the outgoing nerve fibers ( axons) are bundled by the thousands, to allow filtering and preprocessing. This Axonbündel then follow through fine openings of the ethmoid bone ( cribriform plate ) to the olfactory bulb ( olfactory bulb ), which is to be regarded as upstream part of the brain. The entire olfactory nerve is called in science olfactory nerve.
Excitation of the olfactory cells
The carriers of the odors are molecules of each gas, but contained in the air usually only in low concentration. The odor molecules enter through the nose or mouth into the upper nasal cavity to the olfactory mucosa, where they are released and chemically can trigger emotions in the olfactory cells. These cells (primary sensory cells ) react to the incoming molecules about their small cytoplasmic extensions ( olfactory cilia ), in which membranes are the olfactory receptors.
When the receptors are stimulated by odor molecules, produced at a sufficiently high concentration of the molecules, an action potential at the axon hillock of the olfactory cell. The electrical pulses are summarized by integrating nerve fibers and forwarded to the olfactory bulb.
Olfactory cells and " suppressor"
The molecular processes in the olfactory sensory neurons via G- protein -coupled receptors. Open CNG ion channels via ACIII → cAMP → increase Ca2 influx → depolarization. As a result of these operations, the cells were able to adapt within a few minutes, that is, to adapt to strong stimuli.
Furthermore, the mucus contains some enzymes ( CYP450 ), which may disable annoying molecules in the olfactory sensation, as well as transport proteins, which provide a better transport of odor molecules through the mucus to the cilia
Olfactory bulb and forwarding of stimuli
In the olfactory bulb, the first and only synaptic connectivity of olfaction takes place before the information reaches the appropriate brain centers. Filter So-called mitral cells and enhance the sensory stimulus by integrating a number of olfactory cells, which have in common that they are excited by the same odor molecules. Thus, each mitral cell represents a certain smell.
From the olfactory bulb from the nerve cords run ( axons) in the olfactory tract, which now divides in two: into a medial branch ( medial olfactory stria ) and a lateral line ( olfactory stria lateralis). The medial strand reaches the septal area and olfactory tubercle, this information remains unconscious. The lateral strand leads to the cortex praepiriformis ( primary olfactory cortex ), the entorhinal cortex and the cortical nucleus of the amygdala. There are still connections to the hypothalamus and (partly after interconnection in the mediodorsal nucleus of the thalamus ) to the orbito -frontal association cortex ( the seat of the personality).
The olfactory function protects the respiratory organs and the whole organism from harmful influences, such as toxic (usually foul-smelling ) gases (caution: Carbon monoxide is odorless ). Pleasant smells trigger Sekretionsreflexe, such as " the mouth water " " a running" in smell of delicious food. Unpleasant odors, however, can cause nausea. Thus, there is a close relationship between odor perception and the unconscious working part of the nervous system ( autonomic nervous system ). So could show, for example, McClintock and Russell that the synchronization of the menstrual cycle of women living in community is based on odor perception.