Module D-13 Flashcards
Where are Gustatory functions active?
In tongue and associated parts of the oral cavity like epiglottis
which are the 5 taste qualities?
Salty Sweet Bitter Sour Umami
Umami is the taste of __________
Monosodium Glutamate (MSG)
Describe the transduction process of taste
1) apical pole of the taste receptor cells, which is oriented towards the taste pore, is the site of signal transduction. 2)Their basal pole is the site of release of transmitter substances, which activate the afferent fibers forming different cranial nerves
3) taste receptor cells have NO AXONS
what are the cell types found in the taste bud?
1) Taste receptor cell
2) Basal cell
3) axon of afferent fibers
Function of Basal cells
can undergo cell division and form the precursors for the development of new taste receptor cells
What mechanism is used to transduce signal for SALTY and SOUR?
Ionotropic
What mechanism is used to transduce signal for SWEET and BITTER?
Metabotropic
Describe the ionotropic transduction of salty taste
1) Sodium ions enter amiloride sensitive sodium channels. 2) Inward current of positively charged ions
3) Depolarization of the taste receptor cell
4) Opens voltage-gated calcium channels
5) Release of transmitter from the synaptic vesicles at the
base of the receptor cell.
Describe the ionotropic transduction of SOUR taste
1) Hydrogen ions (protons), which can work in two ways.
a) enter amiloride sensitive sodium channels, or
b) can block potassium channels, which would be
open at rest.
2) This causes a depolarization of the taste receptor cell by:
a) Either the inward current of positively charged
sodium ions, or
b) the blockage of outward current of positively
charged potassium ions
3) opens voltage-gated calcium channels
4)Transmitter release
Describe the Metabotropic transduction of SWEET taste
1) A molecule with sweet taste qualities binds to its
metabotropic receptor
2) G Protein is released which activates Adenylyl cyclase
3) The enzyme Adenylyl cyclase induces synthesis of the second messenger cyclic AMP (cAMP).
4)cAMP causes the closure of potassium channels, reduces the outward current of positive charges
5) Leads to a depolarization of the cell,
6) the opening of voltage-gated calcium channels
7) increase in intracellular calcium causes transmitter release onto afferents
Describe the Metabotropic transduction of bitter taste
1) A molecule with bitter taste qualities binding to its receptor , G protein is released
2) Activates the enzyme phospholipase C
3) starts the inositol tris phosphate cascade
4) PIP2 -> IP3
5) increase in the concentration of intracellular Calcium. 6)This allows an inward current of sodium ions through a channel specific to taste receptor cells
7) increase in intracellular calcium causes transmitter release onto afferents
8) there is also additional blockage of K+ channels
What is one main difference btw gustatory pathway and the other sensory pathways?
Gustatory stay ipsilateral,ie, dont cross midline
Which nerve carries sensory information for anterior 2/3rds of tongue?
CN VII (facial nerve)
Which nerve carries sensory information for posterior 1/3rds of tongue?
CN IX (Glossopharyngeal)
Which 3 nerves carry gustatory information?
CN VII, IX and X
Which nerve carries sensory information for most posterior part of tongue?
CN X vagus
Which gustatory sensory info does facial nerve carry?
sweet, salty & sour
Which gustatory sensory info does glossopharyngeal nerve carry?
sour and bitter
What type of neurons are primary afferent neurons of the gustatory pathways?
Pseudounipolar neurons
Where are cell bodies for primary afferent neurons of the gustatory pathways located?
1) Geniculate ganglion of the facial nerve
2) Inferior ganglion of the glossopharyngeal
3) Inferior ganglion of the vagus nerve
Describe the gustatory pathway.
1) Afferent fibers originating in the tongue enter the brainstem at the pontomedullary junction or below.
2)They synapse in the nucleus of the solitary tract (also called solitary nucleus).
3) Fibers of the second order neurons don’t cross the midline and ascend, to form synapses in the ipsilateral ventral posterior medial (VPM) nucleus of the thalamus.
4) Fibers of the third order neurons located in the thalamus synapse in the primary gustatory cortex, which is located in the insular lobe and the lower parts of the
postcentral gyrus.
Which cells are the Olfactory Transducers?
Olfactory receptor neuron NOT receptor cells
What are the cell types in the olfactory epithelium?
1) supporting cell
2) olfactory receptor neuron
3) basal cell
Describe the structure of the olfactory receptor neuron.
cilia on apical end embedded in mucus with afferent fibers are covered in bundles by olfactory ensheathing cells
What is olfactory ensheathing cell?
cover afferent fiber bundles; are neither Schwann cells, nor oligodendrocytes
What is the turnover time for Olfactory sensory receptor neurons?
replaced every 60 days by the basal cell
What receptor mechanism is used for signal transduction in the olfactory receptor neurons?
Metabotropic
Describe the olfactory pathway.
1) An odorant molecule in the olfactory mucosa activates an odorant receptor embedded in the membrane of the cilia of an olfactory receptor neuron.
2) dislocation of the alpha subunit of a G protein (GTP binding protein).
3) stimulates the enzyme adenylyl cyclase
(adenylate cyclase)
4)Enzymatic activity of adenylyl cyclase increases the second messenger cyclic AMP
5) cAMP opens cation channels.
6) Inward current of cations (Ca2+ and Na+)
causes depolarization of the olfactory receptor neuron, a graded receptor potential.
7) When the graded receptor potential reaches threshold, action potentials are generated within the cell body of the olfactory receptor neuron, which are further propagated along its axon.
8)The axons of all olfactory receptor neurons together form the first cranial nerve,
the olfactory nerve (CN I).
How many odorant receptor proteins does each olfactory receptor neuron express?
one
describe the response to odorant molecules
Odorant molecule stimulates receptor neuron 1 maximally, receptor neuron 2 less, and receptor neuron 3 even less (the graded receptor potential does not even reach threshold).
The signals of all receptor neurons are conducted along their axons, which pass
through the holes in the cribriform plate and synapse in the glomeruli of the
olfactory bulb.
Each glomerulus receives input only from olfactory receptor neurons of the_____ type, expressing the same _____________
same; odorant receptor protein
what is the vertical information flow through olfactory bulb?
starting with the olfactory receptor neurons and ending with the output of the olfactory bulb
what is the horizontal information flow through olfactory bulb?
The elements of the horizontal information flow
are inhibitory interneurons.
What is the purpose of horizontal information flow?
segregating the tens of thousands of different odorants into different
categories, by comparing the levels of excitation of different types of receptor
neurons and their associated glomeruli.
What are the output neurons of the olfactory bulb?
Mitral or tufted cell
What are the inhibitory interneurons called?
Periglomerular cell
What makes the olfactory pathway different from the other sensory pathways?
It goes to cortex first Then the Thalamus
doesn’t go through the thalamocortical projections
Describe the olfactory pathway
Axons of the tufted cells and the mitral cells, of the olfactory bulb, run through the lateral olfactory tract and synapse in the olfactory cortex
Which are the olfactory cortex areas and where are they located?
piriform cortex, the periamygdaloid cortex and entorhinal cortex, which are all located in the temporal lobe, around the region of
the uncus
Where is the Vomeronasal organ located?
In the vomer bone at each side of the nasal septum
What type of neurons are found in the vomeronasal organ?
bipolar receptor neurons
What is the function of the vomeronasal organ in mammals?
pheromone communication
What is Hypoaguesea?
decreased taste function
Causes of Hypoaguesea
due to local pathology of the oral cavity, secondary to salivary gland dysfunction, leading to taste bud destruction
Define Ageusea
loss of taste function
Causes of Aguesea
usually due to a lesion of the chorda tympani
of CN VII facial nerve (Bell’s palsy), which often occurs unilaterally, and causes ipsilateral loss of taste from the anterior two thirds of the tongue
Syndrome that may also cause ipsilateral aguesea
Wallenberg’s syndrome (lateral medullary syndrome)
why does Wallenberg’s syndrome (lateral medullary syndrome) cause aguesea
due to infarction of the lateral
medulla, after occlusion of the posterior inferior cerebellar artery (PICA)
What is Hyposmia?
decreased smell function
What is Anosmia
Loss of smell function
Cause of Anosmia
compression of the olfactory tract by tumors, especially meningeomas
What causes Olfactory hallucinations?
Partial epileptic seizures originating in the vicinity of the uncus
