Olfaction and taste Flashcards
What do olfaction and taste have in common?
- they are both chemosenses
- tastants or ordorants
- they are both involved in perception of food
- extremely important in eating
Describe the taste pathway
- senses from the tongue and pharynx travel through the geniculate, petrosal and nodose ganglion
- these are psuedounipolar and they travel to the solitary nuclear complex in the medulla
- then they travel ot the ventral posterior medial nucleus
- this is the part of the thalamus that mediates taste
- then these travel to the poscentral gyrus and the insula
Is the taste pathway contalateral or ipsilateral?
ipsilateral
- all taste sense stay on the same side
What nerve innervates the anterior 2/3 of the tongue for taste and which one does the psoterior 1/3
- chorda tympani innervates anterior 2/3 of tongue and conveys sweet, salty, umami, and sour information to the brain
- Glossopharyngeal nerve innervates posterior 1/3 of tongue and conveys bitter information to the brain
Where are the taste receptors located?
They are located on microvilli or receptor cells
- Fluids on the tongue enter the taste bud through the taste pore.
- Microvilli on the receptor cells contain taste receptors which are stimulated by molecules in the saliva.
- The receptor neurons release transmitter onto the afferent nerve fibers.
- Taste cells each have one of five different receptors: salty, sweet, bitter, sour and umami. GPCRs are important for sweet, bitter and umami.
- Many aspects of flavor derive from olfaction.
Three cranial nerves are primarily responsible for conveying taste information from the tongue and epiglottis to the brainstem. What are they?
- 1) The chorda tympani branch of the facial nerve innervates the anterior two-thirds of the tongue.
- The neuronal cell bodies which give rise to the chorda tympani are found in the geniculate ganglion.
- 2) The glossopharyngeal nerve innervates the posterior one-third of the tongue.
- The neuronal cell bodies that give rise to these axons are located in the petrosal ganglion.
- 3) A few fibers from the vagus convey taste information from the pharynx to the solitary nucleus.
- These cell bodies are located in the nodose ganglion.
Although different cranial nerves carry taste information to the brain, they all terminate in the_____?
- rostral portion of the nucleus of the solitary tract (gustatory nucleus) which is found in the medulla.
- The solitary tract consists of the portions of the axons from the ganglion cells which have entered the brainstem.
- once the afferent axons have entered the brainstem they are considered the solitary tact
Why is the solitary nucleus of gustation a little different?
Because the solitary nucleus surrounds the solitary tract
Explain the taste pathway in the brainstem after the neurons enter the solitary nucleus
- Neurons in the gustatory nucleus (solitary nucleus) have axons which ascend in the central tegmental tract to the ventral posteromedial (VPM) nucleus of the thalamus (VPM).
- Axons from neurons in the taste portion of VPM (parvocellular region) project to the insula and the postcentral gyrus.
- Note that the taste system ascends to the cortex on the ipsilateral side.
What projection in olfactory system is mostly involved in feeding behavior?
- really wanting to eat
- if youre kind of hungry and then you smell something really good you become very motivated to eat
- deep nuclues in temporal lobe in brain
Amygdala
- projects to the hypothalamus
Which projection is responsible for fine discrimination of smell
- his example of people being hired to be perfume specialists
Piriform cortex
- projects to the dorsomedial nucleus of the thalamus
- then this projects to orbitofrontal cerebral cortex (close to the orbit)
Why is the olfactory system unusual?
- because the second neuron is already in the telencephalon
- it has short axons
- small
- seperated
- unmylenated (so they are gray)
- hardest cranial nerve to see
- very vulnerable
Where are the olfactory receptors located?
Cilia at the end of dendritic knobs
What are the type of neuron are olfactory receptors?
Bipolar
What are interesting of basal cells of the olfactory system?
- they can give rise to new neurons in adults
- they are stem cells
What is the purpose of convergence in regards to olfaction?
- Thousands of olfactory nerve axons convered onto a few mitral cell dendrites (in glomeruli)
- Olfactory receptor cells with the same olfactory receptors convered on the same mitral cells
Whats weird about granule cells in olfaction?
Dont have axons
Does the olfactory tract terminate in the thalamus?
NO!
- the olfactory tract contains axons from the mitral cells and the anterior olfactory nucleus
What is the anterior perforated substance a marker for?
Its a marker for olfactory cortex
What is the cell type in the olfactory bulb? And where do they send their axons?
- Mitral cells
- the mitral cell axons head down the olfactory tract adn the anterior perforated substance (olfactory tubercle) recieves info from these mitral cells
Where is the piriform cortex located and what is it involved in?
- It is located at number 3
- it sends info to DM nuclues of orbitofrontal cortex involved in fine discrimination of odors
Where is the entorhinal cortex located and what what is it invovled in?
Entorhinal cortex is involved in associations between odors and memories
- temporal lobe number 3
Label these parts of the brain
