Sense Organs; Smell

Question 1

Smell

Answer 1

Taste and smell are chemical senses because they arise from interaction with molecules

Question 2

Olfaction

Answer 2

Olfaction is the sense of smell
The nose contains 10-100 million receptors for olfaction contained within a tiny area (5 cm2) called the olfactory epithelium.
The olfactory epithelium contains three types of cells:
1. Olfactory receptors
2. Supporting cells
3. Basal cells

Question 3

Olfactory receptors

Answer 3

Neurons attached to olfactory hairs. Respond to chemical stimulus of odorants by producing an action potential

Question 4

Supporting cells

Answer 4

Provide physical support, nourishment and help detoxify odorant chemicals

Question 5

Basal cells

Answer 5

Stem cells that continually divide to produce new olfactory receptors (live 1 month)

Question 6

Mucus

Answer 6

• Olfactory glands in the connective tissues supporting the olfactory epithelium produce mucus that is carried to the surface by ducts
• The secretion moistens the olfactory epithelium and helps to dissolve odorants
• Inflammation of the nasal mucosa inhibits olfaction (i.e. rhinitis)

Question 7

Smell sensation

Answer 7

• Sense of smell involves the Olfactory nerve (CNI) (unmyelinated –slower)
• Nerve axons extend through about 20 olfactory foramina in the cribriform plate of the ethmoid bone to the temporal lobe.
• Olfactory bulb  olfactory tract  olfactory area in the temporal lobe
• Some of the axons of the olfactory tract project into the limbic system (relation between smell and emotion).
• Sense of smell may also affect appetite and our moods
• The sense of smell in humans is less than many animals

Question 8

Smell sensation; Adaptation

Answer 8

• Like all the special sense, olfaction has a low threshold and only a few molecules need to be present for us to detect a smell
• Adaptation: Decreased sensitivity to odours occurs rapidly. Olfactory receptors adapt by 50% in first second. Odours seem 80% less powerful after a few minutes of exposure
• Prevents smelling bad odour e.g. working new a foul odour gets to the point where olfactory adaptation is 100%
• The aim of adaptation is to protect from danger – if the scent is not a danger it re-calibrates to be able to detect for other smells which might indicate harm

Question 9

Olfactory cells

Answer 9

The olfactory epithelium contains three types of cells:
1. Olfactory receptors
2. Supporting cells
3. Basal cells