Olfaction & Taste part 1

Summary

The human olfactory system, responsible for the sense of smell, operates through complex interactions within the nasal cavity. The olfactory epithelium, containing specialized cells like supporting, stem, and olfactory neurons, detects odor molecules. These neurons transmit signals to the olfactory bulb, a structure that processes smells and sends them to the brain's temporal lobe for perception. With about 350 different types of odor receptors, each olfactory neuron expresses only one type, enabling the detection of a vast array of smells. The system is sensitive, capable of detecting even harmful substances at incredibly low levels.

Takeaways

• 😀 The olfactory organ, located in the nasal cavity, functions to receive and interpret odor molecules.
• 😀 The olfactory epithelium, located on the roof of the nasal cavity, binds and recognizes odor molecules.
• 😀 The olfactory epithelium connects to the olfactory bulb, which is part of the olfactory nerve (cranial nerve I).
• 😀 The olfactory nerve is the first cranial nerve and originates at the base of the most anterior part of the brain.
• 😀 The olfactory bulb contains numerous glomeruli, where the axons of olfactory neurons synapse with secondary nerve cells.
• 😀 There are three types of cells in the olfactory epithelium: supporting cells, basal stem cells, and olfactory neurons.
• 😀 Olfactory neurons are replaced periodically (every 1–2 months) by basal stem cells due to constant exposure to odor molecules.
• 😀 Each olfactory neuron expresses only one type of odor receptor protein, which binds to specific odor molecules.
• 😀 There are around 350 types of odor receptor proteins, and a neuron that expresses the same receptor type synapses in the same glomerulus.
• 😀 The brain interprets smells based on a combination of activated odor receptor proteins, with each type contributing to the overall perception.
• 😀 The human nose can detect up to 10,000 distinct odors, despite having only 350 receptor types.
• 😀 The olfactory system is highly sensitive, capable of detecting even very low concentrations of harmful odor molecules, such as methyl mercaptan.

Q & A

What is the role of the olfactory organ?

The olfactory organ, or sense of smell, functions to receive and interpret odor molecules, allowing us to perceive different smells.

Where is the olfactory epithelium located?

The olfactory epithelium is located on the roof of the nasal cavity, in a groove called the olfactory orange or olfactory dress.

What is the connection between the olfactory epithelium and the olfactory bulb?

The olfactory epithelium is continuous with the olfactory bulb via the axons of olfactory neurons that pass through the pores in the sieve bone.

How does the olfactory bulb contribute to the sense of smell?

The olfactory bulb, which is the end of the olfactory nerve (cranial nerve I), processes odor information by synapsing with secondary nerve cells and transmitting impulses to the brain's odor perception center.

What are the three types of cells in the olfactory epithelium?

The three types of cells in the olfactory epithelium are supporting cells, basal cells (stem cells), and olfactory neurons.

What is the function of basal cells in the olfactory epithelium?

Basal cells, or stem cells, function to divide and replace damaged olfactory neurons, which are exposed to odor molecules and can easily be damaged.

What type of neurons are olfactory neurons, and what is their structure?

Olfactory neurons are bipolar neurons, meaning they have one dendrite and one axon. The axon penetrates the sieve bone and connects with nerve cells in the olfactory bulb.

How do olfactory neurons detect odors?

Olfactory neurons have receptors on their dendrite tips that bind to odor molecules. This binding causes depolarization of the neuron, transmitting an impulse through the axon to the olfactory bulb.

What is the role of glomeruli in the olfactory bulb?

Glomeruli are structures in the olfactory bulb where the axons of olfactory neurons synapse with secondary nerve cells. They play a key role in processing odor information and transmitting it to the brain.

How many types of odor receptor proteins exist in humans, and how does this affect odor perception?

Humans have around 350 types of odor receptor proteins. Each olfactory neuron expresses only one type of receptor protein, and the brain perceives odors based on the combination and activation of these receptors.