Question

The stimulation for olfaction involves odorant molecules a. bending the cilia of olfactory sensory receptor cells. b. binding to protein receptors of olfactory sensory receptor cells. c. entering the cytoplasm of olfactory sensory receptor cells. d. opening \(\mathrm{K}^{+}\) channels of olfactory sensory receptor cells. e. binding to cells located in the olfactory bulbs.

Short answer

b. binding to protein receptors of olfactory sensory receptor cells.

Step-by-step solution

Understanding Olfaction

Olfaction refers to the process of smelling. Central to this is the receptor cells of the olfactory system, particularly in the nose. These cells have hair-like structures called cilia extending from them, which are coated with a thin fluid layer. Odorants, or molecules with a smell, are airborne particles that dissolve in this fluid when we breathe in, and can then interact with the cilia.

Role of Odorant Molecules

Once an odorant molecule is dissolved in the fluid layer, it binds to specific olfactory receptors on the cilia. This binding process activates these receptors and begins a signal transduction pathway, causing an electrical signal to be sent to the brain. This signal is then interpreted as a specific smell.

Answering the Question

The role of odorant molecules in the process of olfaction, as we understand it, is binding to protein receptors of the olfactory sensory receptor cells, which then generates an electrical signal that the brain interprets as a smell. This mechanism does not involve odorant molecules bending the cilia, entering the cytoplasm of these cells, opening potassium channels, or interacting directly with cells in the olfactory bulbs. Therefore, the correct answer is b. binding to protein receptors of olfactory sensory receptor cells.

Key concepts

Olfactory Sensory Receptor Cells

Olfactory sensory receptor cells are specialized neurons located in the nasal cavity. They play a key role in our ability to detect and recognize different smells.
These cells are unique because they are exposed directly to the external environment. This makes them particularly important for detecting airborne chemicals known as odorants.
Each olfactory sensory receptor cell is topped with hair-like structures called cilia. These cilia extend into a mucus-covered layer in the nasal epithelium. The main task of these receptor cells is to detect odorant molecules, initiating the process of olfaction.
The vast diversity of these olfactory receptors allows us to perceive a wide array of scents by responding to different chemical compounds.

Odorant Molecules

Odorant molecules are small, volatile compounds that we identify as distinct smells. For us to perceive these molecules, they must first be airborne, allowing them to enter the nasal passage.
Once within the nasal cavity, these odorant molecules dissolve in the mucus lining the olfactory sensory receptor cells. This mucus serves as a medium through which the odorants can interact with the olfactory receptors.
Upon dissolution, odorant molecules bind to specific sites on these receptor proteins. This is the first crucial step in the detection process that allows us to perceive odors. Each molecule has a unique structure, which means that different receptors are activated by different odors, contributing to the sense of smell's complexity and versatility.

Protein Receptors

Protein receptors are integral components of the olfactory sensory receptor cells. They are specialized proteins located on the cilia of these cells and are crucial for detecting odorants.
Each olfactory receptor protein is tailored to bind to specific types of odorant molecules. This unique fit between the molecule and receptor allows for the precise identification of various smells.
When an odorant molecule successfully binds to a protein receptor, it triggers a cascade of events inside the olfactory cell. These events ultimately result in the conversion of a chemical signal (odorant-receptor binding) into an electrical signal that the brain can interpret.

• The diversity of olfactory receptors can correspond to a multitude of distinct smells.
• The binding specificity ensures precise detection of odorant signals.

Signal Transduction Pathway

The signal transduction pathway is the journey that begins once an odorant molecule binds to a protein receptor on the olfactory sensory receptor cells. This pathway is essential for converting chemical signals into electrical impulses that the brain can interpret as smells.
Upon binding, the interaction between the odorant and receptor activates a G-protein inside the olfactory cell. This activation leads to a series of biochemical reactions, often involving the production of a second messenger molecule. This molecule amplifies the original signal, resulting in the opening of ion channels.
The opening of these channels allows certain ions to flow into the cell, generating an electrical impulse. This impulse travels along the olfactory nerve to the brain, where it is processed and perceived as a specific scent.
This entire process is remarkably fast, allowing us to recognize smells in real-time, such as when detecting the aroma of fresh coffee or the scent of blooming flowers.