Mod7-Obj1: Receptors and neural pathways of olfaction and gustation

Question 1

The chemical senses: smell and taste

Answer 1

Smell (olfaction)
taste (gustation)
-smell receptors excited by airborne chemicals dissolved in nasal fluids
-taste receptors excited by food chemicals dissolved in saliva

Question 2

Olfaction (smell)

Answer 2

Sense of smell is provided by olfactory organs

• Located in the nasal cavity on either side of the nasal septum
• Olfactory receptor cells located in olfactory epithelium have cilia to increase receptive surface area and increase chance of capturing odorant

Question 3

Physiology of smell

Answer 3

Odorant must be volatile (gaseous)

• Must reach olfactory epithelium and dissolve in fluid
• Odorant then bind to receptors on ciliated epithelium
• Open gated channel on receptor
• generate an action potential
• Olfactory sensory neurons have been activated
• Action potential travels to brain for interpretation

Question 4

Olfactory pathway

Answer 4

Olfactory sensory neurons form CN II

• Olfactory neurons synapse with 2nd order neurons in olfactory bulb
• Impulses travel from bulb via olfactory tracts to olfactory cortex of temporal lobe

Question 5

2 Olfactory pathways

Answer 5

1. ) To frontal lobe: smell consciously interpreted and identified
2. ) Some information travels to hypothalamus and other regions of limbic system: emotional responses to odour elicited

Question 6

Gustation (taste)

Answer 6

The sense of taste is provided by the receptor organ in taste buds located mostly on tongue

Question 7

Gustatory receptors

Answer 7

Gustation receptors are located with the taste buds and bear cilia

Question 8

Taste buds: Sense of taste

Answer 8

• Widely distributed across the tongue
• Soft palate
• Cheeks
• Pharynx
• Epiglottis

Question 9

Physiology of taste

Answer 9

Food chemical must be dissolved in saliva

• Chemical must diffuse into the taste pore
• Food chemical must contact the gustatory hairs

Question 10

Gustatory pathway

Answer 10

• Facial (VII) and Glossopharyngeal (IX) nerves carry impulses from taste buds to medulla oblongata
• Impulses then travel to the thalamus and from there fibres branch to
• gustatory cortex in the insula
• Hypothalamus and limbic system
• Vagus nerve (X) transmits from epiglottis and lower pharynx

Question 11

Sweet

Answer 11

sugars, saccharin,

alcohol, some amino acids, some lead salts

Question 12

Sour

Answer 12

hydrogen ions in solution

Question 13

Salty

Answer 13

Metal ions (inorganic salts)

Question 14

Bitter

Answer 14

alkaloids such as quinine and nicotine; asparin

Question 15

Umami

Answer 15

Amino acids glutamate and aspartate

Question 16

Role of taste

Answer 16

Triggers reflexes involved in digestion

• Increase secretion of saliva into mouth
• Increase secretion of gastric juice into stomach
• May initiate protective reactions (gagging and reflex vomiting)

Question 17

Influence of other sensations on taste

Answer 17

Combined effect when interpreted in the cerebral cortex

• Much of what we taste is smelled
• Thermoreceptors, mechanorecptos, noiciceptors in mouth also influence taste
• Temperature and texture enhance or detract from taste