Olfactory

Olfactory System

The olfactory system is the sensory system used for smelling (olfaction). Most mammals and reptiles have a main olfactory system and an accessory olfactory system. The main olfactory system detects airborne substances, while the accessory system senses fluid-phase stimuli.

Structure

The main components of the olfactory system are: the olfactory epithelium, the olfactory bulb, and the olfactory cortex. The olfactory neurons in the epithelium detect smell, and their axons form the olfactory nerve which passes the information about the smell to the olfactory bulb. The olfactory bulb then transmits the signals to the olfactory cortex, which interprets the smell.

Olfactory Epithelium

The olfactory epithelium is a specialized epithelial tissue inside the nasal cavity that is involved in smell. It is a part of the olfactory system. In humans, it measures about 1 square centimeter (on each side) and lies on the roof of the nasal cavity about 7 cm above and behind the nostrils.

Olfactory Bulb

The olfactory bulb is a neural structure of the vertebrate forebrain involved in olfaction, the perception of odors. It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex and the hippocampus where it can be associated with emotions, memory and learning.

Olfactory Cortex

The olfactory cortex is a part of the cerebral cortex that is involved in the sense of smell. It is a component of the rhinencephalon. It includes the piriform cortex, the entorhinal cortex, the olfactory tubercle, the amygdala, the anterior olfactory nucleus, the lateral olfactory tract, and the anterior perforated substance.

Function

The olfactory system starts functioning when odor molecules bind to specific sites on the olfactory receptors. These receptors are activated and send signals to the olfactory bulb, which processes the data and then passes it on to the olfactory cortex. The olfactory cortex then interprets the smell.

Clinical significance

Dysfunction of the olfactory system can lead to conditions such as anosmia, hyposmia, and hyperosmia. Anosmia is the inability to perceive odor or a lack of functioning olfaction. Hyposmia is a reduced ability to smell and to detect odors. Hyperosmia is an increased ability to smell and a heightened sense of smell.

See also

• Olfaction
• Olfactory receptor
• Olfactory nerve
• Olfactory bulb
• Olfactory epithelium
• Olfactory cortex

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