Chemical Senses

Question 1

Functions of the Chemical Senses:

Answer 1

• Locate food
• Assess food safety
• Derive pleasure from eating

Question 2

Components of the Olfactory System:

Answer 2

• Olfactory epithelium
  
  • Olfactory neurons
  • Basal stem cells
  • Supporting cells
  • Bowman’s glands
• Odorant Receptors
• Olfactory Bulbs
• Olfactory Cortex

Question 3

Olfactory Epithelium:

Properties

Answer 3

• 5 cm² area in the superior part of the nasal mucosa
• pseudostratified epithelium

Question 4

Describe the olfactory neurons:

Answer 4

• Unique among sensory systems in that they are regularly replaced (lifespan is 30-60 days) and can regenerate after injury
• Bipolar
• Cilia within mucosa

Question 5

Basal stem cells:

Answer 5

Give rise to new neurons

Question 6

Supporting cells & Bowman’s glands:

Answer 6

Secrete mucus

Question 7

Desribe how oderant receptors function:

Answer 7

• G-protein-coupled receptors (1000 different types) located on olfactory neuron cilia
• 1 type of odorant receptor per neuron
• Ligand (odorant) binds to receptor in a “pocket” formed by a combination of the 7 transmembrane regions
• Highly variable amino acid sequence in transmembrane regions ⇒ a possible mechanism for recognition of so many different ligands (odorants)
• Odorant binding ⇒ depolarization

Question 8

Olfactory Bulb:

Answer 8

• Olfactory neurons project through cribriform plate ⇒ olfactory bulbs where they synapse onto glomeruli
• Within each glomerulus are:
  
  • Mitral cells
  • Tufted relay cells
  • Periglomerular interneurons

Question 9

Olfactory Bulb:

Convergence, Spatial Map, Processing

Answer 9

• Convergence – Within each glomerulus of the olfactory bulb, several thousand olfactory neurons synapse onto 25-50 relay cells.
• Spatial Map – each glomerulus receives input from only 1 type of receptor. Different odorant receptors ⇒ different glomeruli
• Processing – higher level processing of the sense of smell occurring within the olfactory bulb

Question 10

**Olfactory Cortex:
Olfactory tract **

Answer 10

consists of axons of mitral and tufted cells from olfactory bulb

Question 11

Olfactory Tract:

Anterior commissure

Answer 11

• projections to contralateral olfactory bulb
• All other projections are ipsilateral

Question 12

Where does the olfactory tract project to?

Answer 12

• Olfactory tract projects DIRECTLY to cortex

Other Projections:

• Thalamus:
  
  • directing one’s attention to a particular stimulus
  • perception and discrimination of odors
• Amygdala and hippocampus:
  
  • emotional and motivational aspects of smell
• Hypothalamus:
  
  • mediate the physiological aspects of smell

Question 13

Taste Sensation:

Answer 13

• Taste = gustatory sensation
• Flavor = gustatory sense + olfactory sense + general sensation

Question 14

Taste Buds:

Answer 14

• Taste Receptors – epithelial cells
• Basal cells – stem cells
• 100’s of taste cells per taste bud
• Microvilli extend into taste pore
• Sensory neurons contact taste receptors

Question 15

• *Taste Sensation:**
• *Taste Qualities**

Answer 15

• Bitter
• Salty
• Sour
• Sweet
• Umami

Question 16

Taste Pathway:

Answer 16

• Tongue (Anterior 2/3^rds) ⇒ Facial n. (CN VII) ⇒ Chorda tympani ⇒ Geniculate ganglion ⇒ Rostral Nucleus Solitarius
• Tongue (Posterior 1/3^rd) & Pharynx ⇒ Glossopharyngeal n. (CN IX) ⇒ Petrosal ganglion ⇒ Rostral Nucleus Solitarius
• Palate ⇒ Facial n. (CN VII) ⇒ Greater petrosal n. ⇒ Geniculate ganglion ⇒ Rostral Nucleus Solitarius
• Epiglottis & Esophagus ⇒ Epigolttis: Vagus n. (CN X); Esophagus: Superior laryngeal n. – internal laryngeal branch ⇒ Nodose ganglion ⇒ Rostral Nucleus Solitarius