Receptor which itself is a dendrite of a nerve

Medicoman · May 28, 2018, 9:38am

1.Olfactory
2.Gustatory
3.Visual Hearing
4.Hearing

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Olfaction (sense of smell)

The smell receptors are distance receptor (teleceptors)
The smell pathway, is the only sense, have no relay in the thalamus and there is no neocortical projection area for olfaction.
The olfactory receptor are located in a specialized portion of the nasal mucosa, the yellow brown pigmented olfactory mucous membrane. The general lining of the olfactory area (mucosa) is pseudostratified columnar epithelium.
Olfactory mucous membrane is small in microsmatic animals such as human, covering an area of 5cm2 in the roof of the nasal cavity near the septum (cribriform plate)
There total 10.20 milion of lactory cells in human, which are surrounded by sustentacular (supporting) cells.
Each olfactory receptor is a neuron, each neuron (receptor) has a short, thick dendrite with an expanded end called an olfactory rod, from these each rod, 10-20 cilia project
Bowman’s glands are located just under the basal lamina of the olifactory mucous membrane, which secrete mucus.
From these receptor (neurons), emerge axon fibers, pierce the cribriform plate of the ethamoid bone and enter the olfactory bulbs. This axon fibers are 20 in numbers, and are 1st order neurons.
From Glomeruli (mitral cells and tuft cells) of olfactory bulb ◊ 2nd order neurons arises ◊ and forms the olfactory tract ◊ and ends as follows: in
(i) Medial olfactory stria ◊ cross opposite side and
(ii) Lateral olfactory stria ◊ terminates chiefly in
(a) Primary olfactory cortex ◊ consists of pro-pyriform area pyriform cortex and olfactory tubercle, olfactory cortex lies in the frontal lobe of brain and
(b) Amygdaloid complex
Olfactory tubercle may be related to abnormal olfactory perceptions in schizophrenia
Efferent fibers of the olfactory tubercle goes to limbic system ~ thus smell is associated with emotion and behaviors.
Efferent fibers from amygdala go to the hypothalamus ~ thus olfaction is associated with appetite and social behavior.
Note:
(i) Olfactory neurons (receptor) ◊ bipolar neurons.
(ii) To reach primary olfactory cortex, therefore only two neurons (1st order and 2nd order) are required, which is rather exceptional in sensory physiology.