Chemosensation

Question 1

Aguesia

Dysguesia

Answer 1

aguesia: loss of sense of taste
Dysguesia: altered perception of taste (often persistent bad or salty taste)

Question 2

anosmia

Answer 2

loss of sense of smell

Question 3

hyposmia

Answer 3

diminished sense of smell

Question 4

dysosmia

Answer 4

altered or distored sense of smell

Question 5

parosmia

Answer 5

altered preception of smell in presence of an odor usually unpleasant

Question 6

phantosmia

Answer 6

perception of smell without an odor present

Question 7

Basic tastes and taste receptors

Answer 7

sour: ion channel (pH)
salty: ion
sweet: GPCR (carbs)
bitter: GPCR
umami (savory): GPCR (indicates presence of glutamate from animal origin–proteins)

Question 8

Chemosensory systems

Answer 8

taste
smell
chemesthesis (trigeminal)

Question 9

“Taste” sensation

Answer 9

stimulation of 3 sensory systems:

1. olfaction
2. gustation
3. chemesthesis (detection of irritant chemicals by trigeminal nerve endings–capsaicin, CO2)

-use taste buds in tongue/palate

Question 10

Olfactory receptor neuron location

Answer 10

-neuroepithleium lining the roof of the nasal cavity

Question 11

Smell:
receptor cell
cranial nerve
primary sensory nucleus

Answer 11

receptor cell: ciliated, bipolar neuron
cranial nerve: I
primary sensory nucleus: olfactory bulb

Question 12

Taste:
receptor cell
cranial nerve
primary sensory nucleus

Answer 12

receptor cell: modified epithelial cell (synapses onto nerve fiber from cranial ganglion cell)
cranial nerve: VII, IX, X
primary sensory nucleus: nucleus of the solitary tract

Question 13

Chesthesis
receptor cell
cranial nerve
primary sensory nucleus

Answer 13

receptor cell: free nerve ending of cranial ganglion cell
cranial nerve: V
primary sensory nucleus: spinal trigeminal nucleus

Question 14

Taste receptor cells

Answer 14

-Found in taste buds (tongue, soft palate, oropharynx, epiglottis)
-Lingual taste buds on taste papillae.
fungiform papillae (anterior tongue)
foliate papillae (sides)
circumvallate papillae (posterior part of tongue)

Filiform papillae are non-taste papillae and serve as tactile organs

Chorda tympani of facial n innervates fungiform pap in anterior 2/3 of tongue, glossopharyngeal inn circumvallate

taste buds in soft palate: sup petrosal br of facial n
Oropharynx and epiglottis buds: vagus

each taste bud has 50-100 cells, only some express receptor proteins; limited lifespan/replaced.; tast cells make functional contact with VII, IX, X fibers

Question 15

Excitation of taste cells

Answer 15

• Tastants reach elongate receptor cells through taste pore
• depol leads to transmitter release from basal portion of cell.
• ATP acts on P2X receptors
• individual taste receptor cells are sensitive mostly to one class of taste stimuli.
• CNS extracts info from POPULATION of cells.

Question 16

Where are taste receptors expressed?

Answer 16

in many cells of the body:

airways (nasal cavity, trachea, bronchi) use bitter recep to detect and respond to bacterial signaling molecules.

Question 17

Central taste pathways

Answer 17

• afferents from tongue run in facial (VII), glossophar (IX), and vagus (X) nerves
• enter CNS, synapse on second order neurons in the rostral area of ipsilateral nucleus of solitary tract (NST)
• second order cells of NST send axons bilaterally to medial part of ventrobasal thalamus
• thalamic neurons–>insular cortex
• secondary gustatory cortex (orbitofrontal face–integration of taste and flavor) receives projections from primary gustatory area located on anterior insula and from olfactory areas of insula
• NST also relays taste info to hypothalamus and amygdala for reg of food intake and visceral rxns to foods.
• Also: NST projects to brainstem for gagging (nuc ambiguus), swallowing (nuc ambig, hypoglossal nuc), and salivation (sup and inf, salivatory nuc)

Question 18

Olfactory neuroepithelium

Answer 18

covered with mucus

• olfac neurons extend cilia into mucus (cilia=large surface area)
• odorants dissolve in mucus and interact with olfactory receptor proteins
• cilia conver chem to elec info.
• Olfactory neurons=bipolar
• olfactory neurons are exposed to external environ
• olfactory neurons are the only neurons that are continuously undergoing neurogenesis and replacement (vulnerable to mitotic inhibitors like in cancer tx)

Question 19

Olfactory transduction

Answer 19

• olfactory receptor protein on olfac cilia.
• GPCR
• subfamilies of recep may bind distinct structural classes of odor stimuli
• Odorant binds to receptor protein, associated G-prot activates adenylyl cyclase generating cAMP
• cAMP opens gated ion channel (Ca, Na enter)
• Ca opens Ca gated Cl channel (outflow of Cl, depolarizing cell)–> AP.

-Kidney and lung also have functionng olfac receptors

Question 20

Olfactory bulb

Answer 20

• signals from olfactory neurons are processed in olfactory bulb.
• Axons of olfactory neurons penetrate ethmoid bone (cribriform plate) and converge on glomeruli on outer layer of olfac bulb (thousands of axons in each glomeruli from a single olfac neruon make excitatory synapses)
• olfactory receptor neurons expressing the same olfactory receptor protein project axons to the same glomerulus
• *Primary principle of encoding odor quality is through a odor-related map of glomeruli in the olfactory bulb (whereas in olfactory epithelium, receptor cells w/ common receptor are scattered)
• But each odorant can stimulate mult. receptors–>mult glomeruli
• Odor identific: recogonition of PATTERN of activity across all glomeruli

Question 21

Central olfactory pathways

Answer 21

Output of olfactory bulb do NOT travel thru thalamus before reaching cortex.

-Bulb–>tract–>olfactory cortex and amygdala.

Cortex: lateral olfactory gyrus and part of uncus
Olfactory cortex: piriform cortex, accessory olfactory nucleus, and olfactory tubercle.

Olfactory tract projects to:

• Piriform cortex projects to the orbitofrontal cortex (assoc area for olfactory and taste info–conscious perception), directly and indir via MD nucleus of thalamus
• Amygdala and olfactory tubercle are interconnected with the hypothalamus (visceral rxns and homeostasis)
• entorhinal cortex feeds into hippocampus (player in storage and retrieval of memory)