Smell (olfaction) Flashcards
What is the primary function of chemoreceptors?
a. To generate signals when they bind to chemicals in the external environment
b. To generate signals when they bind to chemicals in the internal environment
c. To generate signals when they bind to light
d. To generate signals when they bind to sound waves
a. To generate signals when they bind to chemicals in the external environment
Which of the following senses is thought to be one of the oldest, evolutionarily conserved senses?
a. Vision
b. Hearing
c. Chemosensation
d. Touch
c. Chemosensation
Which of the following statements about olfaction is true?
a. It provides information about ingested substances.
b. It provides information about airborne molecules.
c. It is not important for lower organisms.
d. It is not important for higher organisms.
b. It provides information about airborne molecules.
What is the function of the olfactory epithelium?
a. To produce mucus
b. To house the olfactory receptor neurons
c. To filter air
d. To connect the olfactory bulb to the brain
b. To house the olfactory receptor neurons
Where are the odorant receptors located in olfactory receptor neurons?
a. In the soma
b. In the cilia
c. In the axon terminals
d. In the dendrites
b. In the cilia
How many odorant receptor genes does each olfactory receptor neuron express?
a. One
b. Two
c. Three
d. All of them
a. One
What is the role of cyclic nucleotide-gated ion channels in odorant transduction?
a. They bind to odorant molecules
b. They convert the signal from GPCRs to an electrical signal
c. They amplify the electrical signal
d. They transmit the signal to the olfactory bulb
b. They convert the signal from GPCRs to an electrical signal
How are odorants encoded in the olfactory system?
a. Through a labeled-line coding system
b. Through an across-fiber pattern coding system
c. Through a temporal coding system
d. Through a rate coding system
b. Through an across-fiber pattern coding system
Which structure receives direct projections from the olfactory receptor neurons?
a. The thalamus
b. The piriform cortex
c. The olfactory bulb
d. The accessory olfactory nuclei
c. The olfactory bulb
What is the primary target of the lateral olfactory tract in humans?
a. The thalamus
b. The piriform cortex
c. The olfactory bulb
d. The accessory olfactory nuclei
b. The piriform cortex
Briefly describe the structure of the olfactory receptor neurons.
Olfactory receptor neurons are bipolar cells with a basal lateral domain that sends a process to the olfactory bulb. They are unmyelinated sensory afferent neurons with specialized cilia embedded within a mucus layer.
What is the role of the glomeruli in the olfactory bulb?
The glomeruli are regions in the olfactory bulb where synaptic connections are made between the olfactory receptor neurons and the mitral cells. Olfactory receptor neurons expressing the same receptor project to the same bilateral glomeruli.
Explain the concept of across-fiber pattern coding in the olfactory system
Across-fiber pattern coding refers to the idea that individual olfactory receptor neurons are sensitive to a subset of odorants, and the discrimination of a particular odor is achieved by the central neurons reading the different patterns of action potentials carried by many sensory neurons.
Describe the molecular mechanisms involved in odorant transduction in olfactory receptor neurons, including the roles of different molecules and the overall process of signal transduction.
The molecular mechanisms involved in odorant transduction in olfactory receptor neurons involve several key components and processes. First, the odorant-sensitive G protein-coupled receptors (GPCRs) are expressed in the cilia of the olfactory receptor neurons. These GPCRs serve as chemoreceptors and bind to specific odorant molecules.
When an odorant binds to its respective GPCR, it triggers a signaling cascade. The activated GPCR then activates a G protein, which in turn activates an enzyme called adenylyl cyclase III (ACIII). ACIII catalyzes the conversion of ATP to cyclic AMP (cAMP), leading to an increase in intracellular cAMP levels.
The elevated levels of cAMP then open cyclic nucleotide-gated ion channels, allowing the influx of cations, primarily Na+ and Ca2+, into the olfactory receptor neuron. This influx of positively charged ions causes a depolarization of the cell membrane, generating an electrical signal in the form of an action potential.
The action potential generated in the olfactory receptor neuron is then propagated along the axon and transmitted to the olfactory bulb, where it synapses with mitral and tufted cells.
It’s important to note that the olfactory transduction process involves a passive depolarization mechanism, in contrast to the active depolarization mechanisms seen in other sensory systems like vision and hearing.
Additionally, each olfactory receptor neuron expresses only one type of odorant receptor gene, allowing it to respond to a specific range of odorants. The discrimination of complex odors is achieved through an across-fiber pattern coding mechanism, where different combinations of olfactory receptor neurons are activated by different odorants, creating unique patterns of activity that are interpreted by higher brain centers.
Overall, the molecular mechanisms of odorant transduction in olfactory receptor neurons involve a sophisticated interplay between odorant-binding GPCRs, second messenger systems, ion channels, and electrical signaling, ultimately allowing for the detection and discrimination of a vast array of odorants.
