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In contrast, a permanent loss of smell may be caused by death of olfactory receptor neurons in the nose or by brain injury in which there is damage to the olfactory nerve or damage to brain areas that process smell (see olfactory system). The lack of the sense of smell at birth, usually due to genetic factors, is referred to as congenital anosmia.
The cause of congenital anosmia is not fully understood, but it is often linked to the underdevelopment or absence of the olfactory bulbs and tracts. [9] Diagnosis typically involves clinical evaluation, smell tests, and imaging studies to identify any structural abnormalities in the olfactory system. [10]
The specialized olfactory receptor neurons of the olfactory nerve are located in the olfactory mucosa of the upper parts of the nasal cavity.The olfactory nerves consist of a collection of many sensory nerve fibers that extend from the olfactory epithelium to the olfactory bulb, passing through the many openings of the cribriform plate, a sieve-like structure of the ethmoid bone.
Hyperosmia is an increased olfactory acuity (heightened sense of smell), usually caused by a lower threshold for odor. [1] This perceptual disorder arises when there is an abnormally increased signal at any point between the olfactory receptors and the olfactory cortex.
The underlying cause is due to the defective migration of GNRH neurons from olfactory placode to hypothalamus, leading to congenital GNRH deficiency. This leads to olfactory problems such as anosmia, optic defects like color blindness, and results in hypothalmic deficiencies associated with low levels of LH, affecting sex hormone testosterone in males or estrogen and progesterone in females.
The Lady and the Unicorn, a Flemish tapestry depicting the sense of smell, 1484–1500. Musée national du Moyen Âge, Paris.. Early scientific study of the sense of smell includes the extensive doctoral dissertation of Eleanor Gamble, published in 1898, which compared olfactory to other stimulus modalities, and implied that smell had a lower intensity discrimination.
Sensory processing disorder is present in many people with dyspraxia, autism spectrum disorder, and attention deficit hyperactivity disorder (ADHD). Individuals with SPD may inadequately process visual , auditory , olfactory (smell), gustatory (taste), tactile (touch), vestibular (balance), proprioception (body awareness), and interoception ...
Olfactory receptor neuron axons project through the cribriform plate to the olfactory bulb. The olfactory bulb is a structure at the base of the frontal lobe. It comprises neurons, nerve fibers, interneurons, microglia, astrocytes, and blood vessels. It is made up of 6 layers: olfactory nerve layer, glomerular layer, external plexiform layer ...