Neurology · MU Sofia

13. Olfaction and taste: anatomy, physiology, examination, syndromes

Covers the olfactory pathway from nasal receptors through the cribriform plate to the temporal cortex, and how smell relates to flavour and the limbic system. It sets out how to test each nostril with familiar odours while avoiding irritants, then classifies smell disorders from anosmia to phantosmia. Taste is handled next: nerve supply by tongue region, the route to the insula, the five modalities, side-by-side testing and taste disorders, ending with clinical correlations for facial and glossopharyngeal lesions and early smell loss in neurodegenerative disease.

Inside: 1 section · 1 labelled picture · 1 table · 16 flashcards · 2 min

Topic 13 of 88 in the MU Sofia syllabus for Neurology (Medicine, Year 4). The free AceMed note covers it in 1 section, about 308 words (2 min of reading), with 16 flashcards.

In this note

  1. Olfaction and taste - anatomy, physiology, examination, syndromes

Olfaction and taste - anatomy, physiology, examination, syndromes

Olfaction (Smell) → special sensory

Anatomy

Olfactory Pathway (CN I)

1.Olfactory receptors in the nasal mucosa (roof of nasal cavity)

2.Olfactory nerve fibers pass through the cribriform plate of the ethmoid bone

3.Olfactory bulb

4.Olfactory tract

5.Primary olfactory cortex (temporal lobe)

Physiology

  • Perception and identification of odors
  • Contributes significantly to flavor perception
  • Closely connected to the limbic system (memory and emotions)

Examination

  • Test each nostril separately: Eyes closed. One nostril occluded. Present familiar non-irritating odors (coffee, vanilla, soap). Avoid irritants (ammonia), which stimulate CN V rather than CN I.

Olfactory Syndromes

1.Anosmia: Complete loss of smell.

  • Causes:Upper respiratory infections. Head trauma (cribriform plate injury). Tumors. Neurodegenerative diseases (e.g., Parkinson disease)

2.Hyposmia: Decreased sense of smell.

3.Hyperosmia: Increased sensitivity to odors.

4.Parosmia: Distorted perception of odors.

5.Phantosmia: Perception of odors without a stimulus (olfactory hallucinations).

Taste (Gustation)

Anatomy: Taste receptors are located in the taste buds of the tongue, palate, and pharynx.

Cranial Nerves Involved

Pathway

Taste receptors → CN VII/IX/X → Brainstem (nucleus tractus solitarius) → Thalamus → Gustatory cortex (insula)

Physiology

  • Primary Taste Modalities: Sweet. Salty. Sour. Bitter. Umami
  • Functions: Food recognition. Protective detection of harmful substances. Regulation of appetite
  • Examination of Taste
  • Test each side of the tongue separately.
  • Apply solutions representing: Sweet (sugar). Salty (salt). Sour (lemon). Bitter (quinine/coffee)
  • Patient identifies the taste with eyes closed.

Taste Disorders

1.Ageusia: Complete loss of taste.

2.Hypogeusia: Reduced taste sensation.

3.Hypergeusia: Increased taste sensitivity.

4.Dysgeusia: Distorted or unpleasant taste sensation.

Causes of Taste Disorders: Facial nerve lesions (CN VII). Glossopharyngeal nerve lesions (CN IX). Oral infections. Zinc deficiency. Medications. Smoking

Clinical Correlations

Facial Nerve (CN VII) Lesion

  • Loss of taste from anterior 2/3 of tongue
  • May be associated with facial weakness

Glossopharyngeal Nerve (CN IX) Lesion

  • Loss of taste from posterior 1/3 of tongue
  • Reduced gag reflex

Neurodegenerative Diseases

  • Early anosmia may occur in: Parkinson Disease. Alzheimer Disease

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