Physiology · MU Sofia

91. Olfactory sensory system

Covers the olfactory system from the nasal epithelium to the cortex: the three epithelial cell types, the olfactory nerve and bulb with glomeruli, and the cAMP-based steps of odorant transduction. It then traces the pathway through mitral cells and the olfactory tract, notes inhibitory granule and periglomerular cells, and lists the olfactory cortex components and their wider connections. Closes with recap questions on transduction, the pathway, and olfactory dysfunction.

Inside: 1 section · 5 labelled pictures · 28 flashcards · 6 min

Topic 90 of 104 in the MU Sofia syllabus for Physiology (Medicine, Year 2). The free AceMed note covers it in 1 section, about 804 words (6 min of reading), with 28 flashcards.

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  1. Olfactory sensory system.

Olfactory sensory system.

The olfactory system is responsible for our sense of smell. It detects and processes odorants, chemical compounds in the air that we perceive as smells.

Structures of the Olfactory System

  • Nasal Cavity: Air containing odorants enters the nasal cavity, passing over the olfactory epithelium.
  • Olfactory Epithelium: Located in the upper region of the nasal cavity, the olfactory epithelium contains specialized olfactory receptor cells that detect odorants.

Olfactory epithelium consists of 3 cell types:

• Supporting cells, they are columnar epithelial cells lined with microvilli.

• Basal cells, they are located at the base of the olfactory epithelium and are undifferentiated stem cells that become olfactory receptors.

Via continues mitosis, there is a continues neurogenesis of olfactory receptors

• Olfactory receptor cells, these are the primary afferent neurons. On these receptors odorant molecules bind on the cilia. The axons of the receptors extend past the cribriform plate to reach the olfactory bulb.

  • Olfactory Receptor Cells: These cells are bipolar neurons with cilia that extend into the mucus layer of the nasal cavity. Odorant molecules bind to receptors on these cilia, initiating the process of olfactory transduction.
  • Olfactory Nerve (CN I): The axons of the olfactory receptor cells form the olfactory nerve, which transmits signals to the olfactory bulb. Olfactory axons are unmyelinated and among the slowest fibers in the nervous system.
  • Olfactory Bulb: Located in the forebrain, the olfactory bulb receives input from the olfactory nerve. It contains glomeruli, spherical structures where the axons of olfactory receptor cells synapse with the dendrites of mitral cells, the second-order neurons in the olfactory pathway.
  • Olfactory Tract: The axons of the mitral cells form the olfactory tract, which projects to various brain regions, including the olfactory cortex.
  • Olfactory Cortex: Located in the temporal lobe, the olfactory cortex is responsible for processing and interpreting olfactory information. It includes the piriform cortex, amygdala, olfactory tubercle, and parahippocampal gyrus.

Olfactory Transduction

Olfactory transduction is the process of converting chemical signals from odorants into electrical signals that can be transmitted to the brain. It occurs in the following steps:

  1. 1. Odorant Binding: Odorant molecules diffuse through the mucus layer of the nasal cavity and bind to specific olfactory receptor proteins on the cilia of olfactory receptor cells.
  2. 2. G-Protein Activation: The binding of odorants to their receptors activates G-proteins (Golf), which are coupled to the receptors.

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