Taste and Smell Chemoreception

Chemoreceptors Receptors for taste and smell Respond to many of the same stimuli Chemicals in solution Receptors for Taste and Smell Compliment each other

Page 150 of notes #1-3 Vagus nerve

Circumvallate Papillae

Sweet Receptors respond to substances like Sugar, Saccharine, and some Amino Acids (Energy-Rich Substances) *The common factor is the hydroxyl group (-OH) attached to these substances Sour Receptors respond to hydrogen (H+) ions, or the acidity of the solution Bitter Receptors respond to alkaloids (bases) *Common factor is the hydroxide (OH-) ions *Since many natural poisons and spoiled foods are bitter, our dislike for bitterness is protective. Salty Receptors respond to metal ions (+) in soln (Electrolytes)

Spicy foods actually excite the pain receptors in the mouth Taste Buds Specific receptors for the sense of taste *~10,000 taste buds *mostly on tongue *some on soft palate and inner surface of cheek Spicy foods actually excite the pain receptors in the mouth

*Surround gustatory cells Supporting Cells *Surround gustatory cells Microvilli- Gustatory Hairs *Protrude through taste pore Cranial Nerve Fibers Taste Pore Connective Tissue Gustatory Cells *Respond to chemicals in saliva

Taste Disorders Hypogeusia: A reduced ability to taste things (to taste sweet, sour, bitter, or salty substances). Ageusia: An inability to taste sweet, sour, bitter, or salty substances. Dysgeusia: A condition in which a foul, salty, rancid, or metallic taste sensation will persist in the mouth

Causes of Taste Disorders Some people are born with taste disorders but most develop after an injury or illness. Upper respiratory and middle ear infections Radiation therapy for cancers of the head and neck Exposure to certain chemicals, such as insecticides and some medications, including some common antibiotics and antihistamines Head injury Some surgeries to the ENT (e.g., third molar—wisdom tooth—extraction and middle ear surgery) Poor oral hygiene and dental problems http://www.nidcd.nih.gov/health/smelltaste/pages/taste.aspx

Sense-Sational Facts We have almost 10,000 taste buds inside our mouths; even on the roofs of our mouths. Insects have the most highly developed sense of taste. They have taste organs on their feet, antennae, and mouthparts. Fish can taste with their fins and tail as well as their mouth. In general, girls have more taste buds than boys. Taste is the weakest of the five senses.

Olfactory Bulb *Size of a postage stamp *Found on roof of nasal cavity

Fibers of Olfactory Tract Olfactory Bulb Cribriform Plate of the Ethmoid Bone Olfactory Nerve Fibers Olfactory Neurons (Receptor Cells) Supporting Cells *epithelium Olfactory Hairs *long cilia *protrude from nasal epithelium *continually bathed by mucus to dissolve chemicals

Olfactory Bulb Fibers of Olfactory Tract Cribriform Plate of the Ethmoid Bone Olfactory Nerve Fibers Olfactory Neurons (Receptor Cells) Supporting Cells *epithelium Olfactory Hairs *long cilia *protrude from nasal epthelium *continually bathed by mucus to dissolve chemicals

Olfactory Disorders : -osmias Most result from head injuries Some result from nasal inflammation (cold, allergy, smoking) Aging

Anosmia - Inability to detect odors Hyposmia - Decreased ability to detect odors Dysosmia - Distorted identification of smell Parosmia - Altered perception of smell in the presence of an odor, usually unpleasant Phantosmia – Perception of smell without an odor present Agnosmia - Inability to classify or contrast odors, although able to detect odors http://emedicine.medscape.com/article/861242-overview

1/3 of all disorders are caused by a Zn deficiency Cure is almost instant once the right form of Zn is prescribed.

Some brain disorders can destroy the sense of smell – or minimize it. Olfactory auras (hallucinations) are experienced by epileptics just before a seizure