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Flashcards in 8 Taste & Smell Deck (25):
1

What is the purpose of the chemosensory system?

Chemosensation is th eperception of chemicals. We detect chemicals through three different systems: taste, olfaction, and somatosensory. tase refers to the sensation arising from taste receptors and is used to evaluate the nutritious content of food and avoid ingestion of toxic substances.  Smell is the detections of volatile odorants through olfactory and somatosensory systems. Olfaction is the perception of odorants through activation of odorant receptors, and is mediated by cranial nerve I. Smell is important for social interactions and memory. Trigeminal somatosensory fibers of CN V detect thermal, mechanical, and chemical stimuli in the head and neck, and initiate protective respiratory reflexes for noxious chemicals.

2

What are the consequences of taste or smell dysfunction?

What are the consequences of taste or smell dysfunction?

Chemosensation is an integral aspect of how we interact with the environment and guides our behavior. Loss of these senses can lead to hazardous situations, such as food poisoning and the inability to detect fire or gas. The disruption of appetitive cues can lead to weight changes and nutritional deficiencies. People without taste often lose the desire to eat and may require medical intervention to restore their appetite.

3

What is the impact of taste or smell dysfunction on quality of life?

What is the impact of taste or smell dysfunction on quality of life?

There is a well-established relationship between olfaction, emotion, and memory, in which odorants can strongly evoke emotions related to the previous experiences associated with that odor. Odor-associated memories are long-lasting and salient. The loss of chemosensation impairs the ability to feel motivated and engage in pleasurable activities, and is correlated with lower perception of quality of life, changes in mood, and depression.

Social chemical cues play a role in determining our social behavior. It has been shown that odorants are reported to influence mate selection and cause females to synchronize their menstrual cycle, indicating a biological importance for olfactory cues. Smell dysfunction can lead to impaired social interactions and social isolation.

4

What is the relationship between taste, smell, and flavor?

What is the relationship between taste, smell, and flavor?

The flavor of our food is the combination of taste, smell, and the somatosensory-mediated sensations of temperature, texture, and pungency. Thus, patients presenting with taste complaints may often really suffer from olfactory dysfunction.

5

Describe the trigeminal (CN V) contribution to smell.

The trigeminal system mediates the perception of touch, pressure, temperature, and nociception (pain or irritation), and displays a limited spectrum of sensations compared to olfaction. The ophthalmic and maxillary branches of the trigeminal nerve innervate the nasal cavity. Most odorants can activate the trigeminal system, and individuals with impaired olfaction (CN I) may still be able to detect odors (often strong irritating odors such as gasoline or ammonia) through trigeminal sensations.

Describe the trigeminal (CN V) contribution to smell.

The trigeminal system mediates the perception of touch, pressure, temperature, and nociception (pain or irritation), and displays a limited spectrum of sensations compared to olfaction. The ophthalmic and maxillary branches of the trigeminal nerve innervate the nasal cavity. Most odorants can activate the trigeminal system, and individuals with impaired olfaction (CN I) may still be able to detect odors (often strong irritating odors such as gasoline or ammonia) through trigeminal sensations.

6

What are the five basic tastes?

What are the five basic tastes?

Taste is limited to a spectrum of five tastes: salty, sour, sweet, bitter, and umami. Umami is the detection of L-amino acids and is also described as savory. Sweet is indicative of energy-rich foods. The detection of salt allows us to control proper dietary electrolytic balance. Sour and bitter are used to warn against noxious/poisonous compounds.

7

Where are taste receptors located?

Where are taste receptors located?

Taste receptors are located on taste receptor cells. Taste buds are bundles of taste receptor cells. Taste receptors are also found on specialized chemosensory cells, ciliated cells, and smooth muscle cells in the airway and are thought to mediate the perception of irritants. Taste-sensing of food also occurs within the gastrointestinal tract as taste receptors are expressed by enteroendocrine cells.

8

Where are taste buds located?

Where are taste buds located?

Taste buds are located on a large portion of the tongue dorsum within small protrusions of epithelium called papillae. Taste buds are also found on the soft palate, larynx, pharynx, and epiglottis, and these taste buds are innervated by the vagus nerve (CN X).

9

Describe the four types of papillae.

Describe the four types of papillae.

The anterior two-thirds of the tongue contains fungiform papillae. Fungiform papillae contain 1 to 15 taste buds each and are innervated by the chorda tympani branch of the facial nerve (CN VII). There are approximately 750 fungiform papillae.

The posterior aspects of the tongue contain circumvallate and foliatepapillae and are innervated by the glossopharyngeal nerve (CN IX). Humans have 8 to 12 circumvallate papillae arranged in a V-shape on the dorsal tongue and a few foliate papillae on the lateral sides, each housing dozens of taste buds.

Filiform papillae are distributed throughout the tongue dorsum. They contribute to the mechanical distribution of chemicals on the tongue, and do not contain taste buds.

10

Describe the central processing of taste.

Describe the central processing of taste.

Taste receptor cells transmit taste information to neural fibers within the taste bud, which project from neurons located in the sensory ganglia of cranial nerves VII, IX, and X. The cranial nerves enter the central nervous system at the brainstem and converge to form the solitary tract. Afferent information enters the thalamus and proceeds to the gustatory cortex.

11

Where is olfactory epithelium found?

Where is olfactory epithelium found?

The olfactory epithelium is located in the superior and posterior aspect of the nasal cavity, including the nasal septum and superior and middle turbinates. The precise location of the olfactory epithelium varies between individuals.

12

Describe the cellular composition of the olfactory epithelium.

Describe the cellular composition of the olfactory epithelium.

The olfactory epithelium is a pseudostratified columnar epithelial tissue comprised of several cell types. Bipolar sensory neurons extend an apical dendrite to the epithelial surface from which cilia extend to detect odors. The basal pole extends into an axon, which crosses the cribriform plate and enters the olfactory bulb. The axons of the sensory neurons are ensheathed by olfactory ensheathing cells, which have received clinical interest for their ability to support axon growth.Basal cells produce new olfactory sensory neurons as the old neurons die or are damaged. Supporting or sustentacular cells regulate and maintain the mucus layer into which odorants dissolve. Flask-shapedmicrovillar cells have no known role, but can respond to odorants and may play a role in reception.

13

Where are olfactory receptors located?

Where are olfactory receptors located?

We are able to distinguish over 1,000 odorants through a large multigene family of receptors that detect specific chemical structures within odorant molecules. Olfactory receptors are located on the cilia of bipolar sensory neurons within the olfactory epithelium. Each sensory neuron expresses only one type of receptor.

14

Describe the central processing of olfactory stimuli.

Describe the central processing of olfactory stimuli.

Odorant molecules that enter the nasal cavity and diffuse through the mucus layer bind to specific odorant receptors depending on their chemical structure. Odor-evoked responses are conducted through the sensory neuron axons, which converge with axons expressing the same receptor type into circular structures called glomeruli in the olfactory bulb. Information about the odorant is encoded by the pattern of sensory neurons and the glomeruli they activate forming a chemotopic map. Second-order neurons (mitral and tufted cells) transmit the response through the olfactory tract to regions in the frontal lobe and dorsomedial temporal lobe. There is a structural overlap of olfactory-responsive regions and those related to emotion, memory, and motivation. These regions include the amygdala, entorhinal cortex, orbital cortex, striatum, hypothalamus, and hippocampus. The structural overlap is thought to contribute to the salience of olfactory memories and emotional responses.

15

What are the terms used to describe olfactory dysfunction?

What are the terms used to describe olfactory dysfunction?

Anosmia is the absence of olfactory function. Hyposmia describes reduced olfactory function. Dysosmias are changes in odor quality, including parosmia (altered perception of an odor) and phantosmia(perception of an odor when that odor is not present).

16

What are the terms used to describe taste dysfunction?

What are the terms used to describe taste dysfunction?

Ageusia is the absence of the ability to taste. Hypogeusia describes reduced taste perception. Dysgeusias are changes in taste quality, including parageusia (altered perception of tastant) and phantogeusia(taste detection in the absence of stimulus).

17

How are sensory dysfunctions classified?

How are sensory dysfunctions classified?

Disruption of the transmission of sensory information can occur at multiple levels from the peripheral elements to areas within the central nervous system.

  • Transport or conductive losses refer to conditions that interfere with access to receptor cells. Transport losses in taste can result from infections, oral inflammation, and dry mouth (xerostomia). Transport losses in olfaction can result from mucosal inflammation, structural obstructions, and alterations in nasal mucus.
  • Sensory losses refer to conditions that disrupt receptor cell function, including the loss of receptor cells due to injury. Olfactory neuron disruption can occur from head injury, sinonasal disease, respiratory tract infections, and chemical exposure. Taste receptor cell loss may be caused by medications, radiation therapy, infection, and endocrine disorders.
  • Neural losses refer to disruptions in the transmission of information upstream of receptor cells. For olfaction this includes injury to the olfactory bulb and cortex. Neural losses in taste can occur following damage to the chorda tympani, facial, vagus, and glossopharyngeal nerves as well as with brain injury.

18

What are the major causes of taste disorders?

What are the major causes of taste disorders?

Respiratory infections, head trauma, radiation therapy, medication side effects, chemical exposure, endocrine disorders, and poor oral hygiene. Isolated taste dysfunction is very rare, with a prevalence of 0.001% of the population.

19

What are the major causes of olfactory disorders?

What are the major causes of olfactory disorders?

Olfactory dysfunction occurs in 1% to 2% of the population. The prevalence of olfactory dysfunction increases with age with estimates of 24% to 40% in individuals over 50 years of age. Causes include upper respiratory infection, head trauma, sinonasal disease, medication, and chemical exposure.

20

What are key questions to ask during evaluation of the patient with a taste or smell problem?

What are key questions to ask during evaluation of the patient with a taste or smell problem?

Inquire about any prior history of dysfunction, including any upper respiratory infections, nasal obstruction, sinonasal disease, head trauma, or prior ear surgery. Ask if the onset was gradual of sudden, or if it fluctuates. Determine whether the loss is complete or partial, and if there are any distortions/hallucinations in taste or olfaction. Inquire about cognition, medication use, appetite, and changes in weight.

21

What should you look for on physical examination of a patient with a taste or smell problem?

What should you look for on physical examination of a patient with a taste or smell problem?

Nasal examination should assess for septal deviation, turbinate enlargement, allergic appearance of mucosa, or presence of nasal polyps or purulence. Mucus character and signs of epithelial irritation or inflammation should be assessed in the nasal cavity and oral cavity. Ear examination should assess the middle ear space to rule out disease affecting the chorda tympani.

22

How do you proceed with the workup for taste and/or smell dysfunction?

How do you proceed with the workup for taste and/or smell dysfunction?

Formal testing may include threshold and odorant identification tests for olfactory loss. MRI may be indicated to rule out central processes, and can demonstrate presence of sinus inflammation.

23

How do you assess olfactory function?

How do you assess olfactory function?

Patients often do not accurately report deficits in olfaction; therefore, it can be important to obtain a more objective measurement of olfactory function. Several standardized tests of olfactory function have been developed. The two most frequently used are the Smell Identification Test (SIT), an odor identification “scratch and sniff” test, and Sniffin Sticks, an odor identification, discrimination, and threshold assessment using odor-dispensing pens. Odor identification and discrimination tasks are generally thought to assess peripheral and central processing, while threshold testing reflects mainly peripheral processing. Direct measures of odor-evoked responses are not often used, but the ability of sensory neurons to respond can be measured using electroolfactograms (EOGs) and cortical responses can be assessed using electroencephalograms (EEGs) or imaging.

24

Will steroid administration help sense of smell?

Will steroid administration help sense of smell?

Steroid administration is frequently used to reduce inflammation and clear obstruction of the olfactory cleft. Rapid improvement of olfactory function is often observed, however, this is usually transient and permanent restoration of normal function is unlikely. Systemic administration is more effective then topical application, but extended administration of systemic steroids puts the patient at risk of side effects.

25

Will surgery help sense of smell?

Will surgery help sense of smell?

If the deficit is due to obstruction of the olfactory cleft, then restoring airflow with surgery will aid in recovery of olfactory function. Sinus surgery to decrease infection and/or inflammation often provides some degree of benefit, particularly in patients with nasal polyps. While improvement of olfactory function is possible, it is frequently transient and incomplete.

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