20.6 Smell and Taste Flashcards
What is chemoreception?
Ability to recognise and respond to environmental and internal chemicals (hormones and neurotransmitters)
It is the oldest form of sensory transduction (find nutrients, attract a mate) q
What types of chemoreceptors are present in the human body?
Olfaction
Taste
Chemosensory irritants (skin and mucous membranes)
Carotid bodies (O2, CO2 and H+)
Which structure in the body is responsible for transducing smell?
Olfactory epithelium in the nasal cavity
where are the chemoreceptors of the olfactory system found?
In the nasal mucosa
Which structures in the nasal cavity direct air upwards towards the olfactory mucosa?
Turbinates
What are the three different types of cell in the olfactory epithelium?
-Olfactory receptors/sensory neurons (site of chemoreceptors)
-Basal cells (stem cells)
-Supporting cells
Describe the structure of an olfactory receptor
True neuron with apical, thin cilium dendrite forming specialised cilia that carry odorant receptors
Unmyelinated and penetrate the cribiform plate to contact olfactory bulb
Where do the afferent olfactory neurons go?
Travel to olfactory bulb via the cribriform plate
What is the olfactory bulb?
Primary target of the olfactory receptor neurons located superior to the cribiform plate
Describe the structure of the olfactory bulb. What is found in each layer?
Outer olfactory neuron layer (axons of ORN)
Glomerular layer (organised into glomeruli for informaiton transfer)
External plexiform layer (synpase layer)
Mitral cell layer (MCL) (cell bodies of mitral cells)
Granule cell layer (cell bodies of granule cells)
Which cells are the source of output from the olfactory bulb? Where do they project?
Mitral cells project to the olfactory cortex WITHOUT A THALAMIC relay
(granule cells have no axons)
Which tract do mitral cells project into?
Olfactory tract
Where do the olfactory neurons synapase in the olfactory bulb?
Glomerulus with mitral cells (second order)
How does the olfactory system differ from other sensory systems in its targets?
other sensory systems first pass information to the thalamus before projecting to the cerebral cortex
olfactory system is more DIRECT
Where does the medial olfactory tract project to?
Projects via anterior commissure to contralateral olfactory structures and septal nuclei
What structure is highlighted?
Olfactory bulb
What structure is highlighted?
Olfactory tract
Where does the lateral olfactory tract target?
Hypothalamus
Primary olfactory cortex (enterohinal cortex, amygdala, hippocampus).
Orbitofrontal cortex via medial dorsal nucleus of the thalamus
What structure is highlighted?
Amygdala - associated with the emotion of fear
What structures are found on the tongue which help us taste?
Pappilae (bumps) shaped light mushrooms, ridges and pimples which each contain hundreds of taste buds, and each taste buds have numerous taste receptor cells
Describe the structure of taste buds?
Taste bud contain basal cells and taste receptor cells which are each innervated by afferents specific for that taste
Which cranial nerves carry gustatory information from the tongue? Which parts of the tongue?
Facial (VII) does anterior 2/3
Glossopharyngeal does posterior 1/3
Where do the facial and glossopharyngeal nerves project to?
Nucleus of the solitary tract in the medulla
Where do second order neurons go from the nucleus of the solitary tract?
VPM nucleus of the THALAMUS and then to the (primary gustatory cortex) orbitofrontal cortex and insula
Orbitofrontal cortex projects to the hypothalamus as feeding centre for salivation
