LAB EXERCISE 17 OLFACTION & TASTE

Chemical Senses Taste (gustatory) and smell (olfaction) They are interpreted by cerebral cortex and limbic system. Their chemoreceptors respond to chemicals in aqueous solution Taste Taste receptors are excited by food chemicals dissolved in saliva

Chemical Senses Smell Smell receptors are excited by air-borne chemicals that dissolve in the fluids coating the nasal membrane million receptors Difficult to research because one smell can involve up to 10,000 odors

The Special Senses Learning Outcomes 17-1 Describe the sensory organs of smell, trace the olfactory pathways to their destinations in the brain, and explain the physiological basis of olfactory discrimination.

Smell (Olfaction) Olfactory Organs Located in nasal cavity on either side of nasal septum Made up of two layers Olfactory epithelium Lamina propria

Olfaction (Smell) 9/21/2018 The olfactory epithelium consists of different types of neurons and olfactory glands that are innervated by the facial nerve. Olfactory glands (Bowman’s) Produce mucous which aid in dissolving odorants so transduction can occur. Basal cells = stem cells Replace receptors monthly Olfactory receptors First order neurons with cilia or olfactory hairs that convert stimulus energy into a graded potential Supporting cells Columnar epithelium that provide nourishment, support and insulation. They also detoxify chemicals Cilia – Increases surface area and captures chemicals. immobile Copyright 2005 Brainy Betty, Inc.

Olfactory Pathway **Cilia pick up the chemicals and move them through the axons from olfactory receptors  First Order Neurons **The 40 or so first order neurons form the right and left olfactory nerves. --Cranial nerve I

Olfactory Pathway They pass through foramina in the cribiform plate and synapse in the olfactory bulb where they become second order neurons  Mitral Cells **The glomeruli represent a single aspect of smell. >They also release GABA to inhibit mitral cells so that only highly excitable smells activate the mitral cells. **These neurons form the olfactory tract.

Olfactory Pathway Second-order neurons then move to one of three integration centers by communication of interneurons. **The only sensory information that reaches the cortex directly without first synapsing in thalamus Primary olfactory cortex of temporal lobe Conscious awareness of smell begins 2. The hypothalamus 3. The limbic system Where memory dictates what we will do with the smell Hippocampus (Past) Amygdala (Reaction) anger, happy, sad etc.

Physiology & Adaptation Genetic evidence suggests there are hundreds of primary scents and an ability to recognize 10,000 scents. Adaptation to odors occurs quickly, and the threshold of smell is low: only a few molecules of certain substances need be present in air to be smelled. Hyposmia A reduced ability to smell, affects half of those over age 65 and 75% of those over 80. It can be caused by neurological changes, drugs, or the effects of smoking .

Upper Nasal Meatus Middle Nasal Meatus Inferior Nasal Meatus Superior Nasal Concha Middle Nasal Concha Inferior Nasal Concha Olfactory Tract Olfactory Bulb

The Special Senses Learning Outcomes 17-2 Describe the sensory organs of taste, trace the gustatory pathways to their destinations in the brain, and explain the physiological basis of gustatory discrimination.

Taste (Gustation) Taste Provides information about the foods and liquids consumed Taste Receptors (Gustatory Receptors) Are distributed on Tongue Soft palate Pharynx Larynx Inside cheeks

Taste (Gustation) Taste receptors are clustered into taste buds Associated with epithelial projections (lingual papillae) on superior surface of tongue

Taste (Gustation) Three Types of Lingual Papillae Filiform papillae Provide friction Do not contain taste buds Fungiform papillae Contain five taste buds each Circumvallate papillae For V-shape Contain 100 taste buds each

Taste (Gustation) Contain: Basal cells Stem cells Gustatory cells Extend taste hairs through taste pore Survive only 10 days before replacement

Taste (Gustation) Gustatory Discrimination Four primary taste sensations Sweet Salty Sour Bitter

Taste (Gustation) Additional Human Taste Sensations Umami Characteristic of beef/chicken broths and Parmesan cheese Receptors sensitive to amino acids, small peptides, and nucleotides Water Detected by water receptors in the pharynx Affects hypothalamus and ADH secretion

Gustatory Pathway 1. In order to be tasted, a chemical: Must be dissolved in saliva Must contact gustatory hairs in the taste bud

Gustatory Pathway 2. Binding of the food chemical (taste) Depolarizes the taste cell membrane, causing release of neurotransmitter Initiates a generator potential that elicits an action potential

Gustatory Pathway Gustatory fibers found in following cranial nerves *Facial (7) Serves anterior 2/3 of tongue Glossopharyngeal (IX) Serves posterior 1/3 of tongue Vagus Serves palate & epiglottis

Gustatory Pathway The first order neurons travel to the solitary nucleus of the medulla

Gustatory Pathway The second order neuron crosses over at medial lemniscus with other somatic sensory information and is relayed to thalamus

Gustatory Pathway After synapsing in the thalamus, it becomes a third order neuron. Joins with somatic sensory neurons carrying information on touch, pressure & proprioreception ** Also recieves information from the limbic system

Gustatory Pathway The impulse is then routed to appropriate area of the gustatory cortex of the insula. **

Gustatory Receptors and Pathways Central processing of gustatory sensations Conscious perception of taste occurs at the primary sensory cortex Taste sensation is analyzed with taste-related sensations “Peppery” or “burning hot” from afferents in Trigeminal nerve (V) Complete adaptation in 1 to 5 minutes Adaptation quickly reduces sensitivity to new tastes

Taste (Gustation) Taste Sensitivity “Tastes” are a combination of the five taste sensations plus olfaction. (80% smell) Exhibits significant individual differences Some conditions are inherited For example, phenylthiocarbamide (PTC) 70% of Caucasians taste it but 30% do not

Taste (Gustation) Taste Sensitivity Other Factors also influence taste Thermoreceptors, Mechanoreceptors, Nociceptors Texture enhance or detract from taste Number of taste buds Begins declining rapidly by age 50