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 cells5-18 Taste cellsBasal cells Life span : ~10 days Rapid adaptation (1 min)

SweetSaltySourBitterUmami.

Basic taste sensations

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

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 extractsAging 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

The end