Nose and Tongue

Question 1

Chemoreceptors

Answer 1

Receptors for smell/taste. They respond to chemicals in a solution

Question 2

Olfactory Epithelium

Answer 2

The organ of smell located in the roof of the nasal cavity to avoid damage

Question 3

Olfactory sensory neurons

Answer 3

Bipolar neurons with a thin apical dendrite that terminates in a knot with several olfactory cilia

Question 4

Olfactory cilia

Answer 4

Long, largely non-motile cilia covered in mucous, which is the solvent for odorants

Question 5

Physiology of smell

Answer 5

An odorant must be in a gaseous state and dissolves in the fluid coating the olfactory epithelium that stimulates the olfactory receptors to smell it

Question 6

Anosmia

Answer 6

Temporary/permanent loss of the sense of smell, often caused by head injuries, localized inflammation or neurological disorders

Question 7

Olfactory neurons

Answer 7

• Relatively exposed to the outside world
• The life span of 30-60 days before they’re replaced by new neurons from olfactory stem cells (basal cells of the olfactory epithelium)
• They’re pain and temperature receptors in the nose which respond to irritants or can smell hot/cold

Question 8

Olfactory transduction

Answer 8

Axons of the olfactory sensory neurons synapse with the mitral cells in the olfactory bulbs
- An odorant binds to the olfactory receptor, a G protein and the secondary messenger of the cyclic AMP
- Prolonged stimulation decreases sensitivity (olfactory adaptation) ie people cant smell a certain odour after being exposed to it for a while

Question 9

Mitral cells

Answer 9

Second-order neurons that amplify, refine and relay signals
- Send impulses down the olfactory tracts to the frontal lobe, thalamus, hypothalamus, amygdaloid body and other members of the limbic system

Question 10

Cyclic AMP (cAMP)

Answer 10

It opens ion channels to depolarize the cell and cause impulse transmission. This allows a small number of odorant molecules to create a large number of effector molecules = action potential

Question 11

Taste buds

Answer 11

• Sensory receptor organs for taste
• Found in the mouth with the majority located within the papillae of the tongue
• Papillae: Not for tasting but to help the tongue grip and push food around
• Consists of 50-100 flask shaped epithelial cells

Question 12

Gustatory epithelial cells

Answer 12

Taste receptor cells that have microvilli (gustatory hairs) to project into taste pores
- Sensory dendrites coiled around these cells send taste signals to the brain

Question 13

Basal epithelial cells

Answer 13

Stem cells that divide every 7-10 days to replace damaged gustatory cells

Question 14

Physiology of taste

Answer 14

• Chemoreceptors for tasting are found on the epithelial cells
• A chemical must be dissolved in saliva, move into the taste pore or contact a receptor/ion channel on the surface of an epithelial gustatory cell to be tasted
• This causes the release of neurotransmitters to the dendrites of a sensory neuron, sending an action potential along one of the three cranial nerves

Question 15

Taste sensation

Answer 15

• Sweet: sugars, alcohol, acids
• Sour: hydrogen ions in solutions
• Salty: metal ions, NaCl tastes the saltiest
• Bitter: alkaloids like nicotine, caffeine and non-alkaloids like aspirin
• Umami: amino acids glutamate and aspartate that are found in savoury foods like meat, cheese

Question 16

Gustatory pathway

Answer 16

• Tastants interact with the gustatory epithelial cell membrane
• Neurotransmitters are released = graded potential depolarization in the dendrites of a sensory neuron which could generate an action potential
• There are different thresholds for activation with bitter receptors being the most sensitive

Question 17

Taste and cranial nerves

Answer 17

Taste can trigger digestion reflexes like saliva in the mouth and gastric juice in the stomach
- Taste disorders are less common than smell because the receptors are served by three different cranial nerves

Question 18

Influence of sensations

Answer 18

Taste is influenced by
- Smell ( if the nose is blocked, food tastes bland)
- Stimulation of thermo (hot foods taste better than warm foods) mechano, and nociceptors (spicy foods excite the nociceptors in the mouth)