Physiology of Smell

Structure of the olfactory system

Olfactory epithelium

Olfactory neurons are short- lived (30-60 days) Replaced from the basal stem cells Are bipolar nerve cells 5-20 cilia protrude from dendrite into the layer of mucus Cilia have specific receptors for odorants (1000 types) Receptors have: Low threshold (methylmercaptan) Rapid adaptation (localized and central), 50% in first second

Mucus is secreted by: Supporting cells Bowmannś glands Mucus provide appropriate molecular and ionic environment for odor detection Mucus contain odorant- binding proteins (OBP)

(Mitral cells)

Olfactory signal transmission: through thalamus to orbitofrontal cortex: Perception & Discrimination of odors to amygdala and hypothalamus: Emotional & Motivational aspects of smell Bahavioral effects

Rapid adaptation, 50% in first second Localized Inactivation or desensitization Central

Physiology of Taste

Anatomy of a taste bud Adults have 3000 to 10,000 taste buds Each taste bud contain: 40 Supporting cells 5-18 Taste cells Basal cells Life span : ~10 days Rapid adaptation (1 min)

Basic taste sensations Sweet Salty Sour Bitter Umami.

Sour Proportional to pH Lateral surface of tongue (Posterior) Salty Cations and anions of ionized salts Metal ions Lateral surface of tongue (Anterior)

Sweet Organic compounds, sugars, glycols, amino acids Inorganic salts of lead Anterior surface of tongue

Long chain organic substances contain nitrogen Alkaloids Bitter Long chain organic substances contain nitrogen Alkaloids Quinine Caffeine Strychnine Nicotine Taste threshold lowest for bitter substances Caudal surface of tongue

Umami Meaning delicious Glutamate, monosodium glutamate (MSG) Is the dominant taste of: Meat extracts Aging cheese

Abnormality of olfaction & taste Hyposemia (diminished sense of smell) Anosemia (complete lack of olfactory sensation) Causes: Infections Head trauma Particular diseases (Parkinson) Ageusia (taste blindness) Hypogeusia (diminished taste sensitivity) Dysgeusia (disturbed sense of taste) Captopril and penicillamine, which contain sulfhydryl groups, cause temporary loss of taste sensation

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