CNS 7- Olfaction and taste

7.0 Describe the anatomy of the gustatory system:

The gustatory system includes taste buds containing taste receptor cells, located on the tongue within papillae. These cells detect tastants and send signals via cranial nerves to the brainstem and then to the gustatory cortex in the parietal lobe.

7.1 Describe gustatory sensory neurons and receptors:

Gustatory sensory neurons receive input from taste receptor cells located in taste buds. Taste receptor cells express approximately 40–45 taste receptor genes that detect five taste modalities. These signals travel to the brainstem for initial processing.

7.2 Describe the anatomy of the olfactory system:

The olfactory system consists of the olfactory epithelium in the nasal cavity, containing olfactory sensory neurons whose axons pass through the cribriform plate foramina to reach the olfactory bulbs. The bulbs (part of the limbic system) send processed signals via the olfactory tract to central brain regions.

7.3 Describe olfactory sensory neurons and receptors:

Olfactory sensory neurons are bipolar neurons in the olfactory epithelium that extend cilia into the mucus layer to detect odorants. Humans have approximately 396 functional olfactory receptor genes. Odor perception is generated by composite activation patterns across multiple receptors.

7.4 Describe the vomeronasal organ and pheromone reception:

The vomeronasal organ (VNO) is associated with pheromone detection and uses a small set of specialized pheromone receptors (~3 in humans). Its role is in detecting social/pheromonal chemical cues.

What is the functional role of taste buds?

To house taste receptor cells that detect dissolved tastants.

What does the presence of microvilli on taste receptor cells indicate?

They increase the surface area for tastant binding in saliva.

Why is the taste pathway considered a cranial nerve–mediated system?

Gustatory signals travel via facial, glossopharyngeal, and vagus nerves to the brainstem.

Why is the parietal lobe involved in taste?

It contains the primary gustatory cortex, which interprets taste quality and intensity.

What does the slide imply about taste being a multi-step sensory process?

It requires peripheral receptor activation, brainstem relay, and cortical integration.

Why does the olfactory epithelium require constant regeneration?

Olfactory neurons are directly exposed to the environment and can be damaged, requiring replacement by basal stem cells.

What is the functional purpose of olfactory cilia?

To interact with odorant molecules dissolved in mucus where receptors are located.

Why must olfactory axons pass through the cribriform plate foramina?

To reach the olfactory bulb for synaptic processing.

What does the slide’s depiction of OSNs suggest about receptor organization?

Each OSN expresses only one type of olfactory receptor gene.

What structural feature of the olfactory epithelium contributes to odor sensitivity?

Its large surface area and dense packing of receptor neurons.

What is the significance of olfactory bulbs being part of the limbic system?

Odors strongly influence emotion and memory due to direct limbic connections.

What does the depiction of the olfactory tract illustrate about signal flow?

Signals from the bulb are carried directly to cortical and limbic targets without thalamic relay.

What does the presence of glomeruli in the bulb imply about odor coding?

OSNs expressing the same receptor converge onto the same glomerulus, creating a spatial odor map.

Why does composite activity across multiple olfactory receptors create odor perception?

Each odorant activates a unique combination of receptors, producing a pattern interpreted as a specific smell.

What does the table indicate about the diversity of DRG sensory neurons?

They include thermal, mechanical, chemical, and nociceptive subtypes with distinct receptor families.

Why are Piezo channels notable in sensory physiology?

They serve as the primary mechanotransducers in both somatic and visceral mechanosensation.

What does the variability in receptor gene numbers show across senses?

Smell has the most receptor diversity (~396 genes), while systems like photoreception use far fewer genes.

What does the presence of ~24 DRG thermo/noci neuron subtypes suggest?

That pain and temperature perception rely on highly specialized neuron classes.

Why is the number of taste receptors (~40–45) relatively low compared to olfactory receptors?

Taste encodes fewer basic modalities, while olfaction discriminates thousands of odorants.

What is the significance of the vomeronasal organ having only ~3 pheromone receptors?

Humans likely have limited pheromone-based communication.

What functional role does the VNO play in animals with robust pheromone systems?

Detects social cues like mating status, territory, and aggression.

Why is the VNO considered distinct from the main olfactory system?

It uses different receptors and projects to different brain regions associated with social behavior.

What does the repeated appearance of “Olfaction and taste” images indicate?

The two systems share similar basic organization

Why is the anatomical localization of the olfactory system important?

Its location at the nasal roof allows direct detection of airborne chemical stimuli.

What does the projection diagram of the olfactory tract emphasize about cortical targets?

Olfaction reaches primary olfactory cortex, amygdala, and hippocampal regions early.

Why does the slide highlight “Primary Sensory Areas”?

To show that each sense has a dedicated cortical region specialized for processing that sensory modality.

How do taste signals pass through the nervous system, and what brain areas do they reach?

Taste receptor cells activate gustatory sensory neurons, which project to the brainstem and then to the gustatory cortex in the parietal lobe.

How do odor signals pass through the nervous system, and what brain areas do they reach?

Odorants activate olfactory sensory neurons in the olfactory epithelium; their axons pass through the cribriform plate to the olfactory bulbs (part of the limbic system), and processed signals travel via the olfactory tract to central brain regions.

What is the structure of taste buds?

Taste buds are clusters of elongated taste receptor cells arranged around a central taste pore where microvilli extend into saliva to detect tastants.

How do taste receptors function?

Taste receptor cells bind tastants with specialized taste receptor proteins (~40–45 genes), initiating transduction that activates gustatory sensory neurons sending signals to the brainstem.

What channels are involved in taste transduction?

Taste receptor cells use families of taste receptors, each corresponding to specific taste modalities, which trigger intracellular signaling that ultimately depolarizes the cell and activates gustatory neurons.

What do olfactory sensory neurons contact and act on?

Olfactory sensory neurons extend cilia into the mucus of the olfactory epithelium to detect odorants; their axons pass through the cribriform plate foramina and synapse in the olfactory bulb, where composite receptor activity produces odor perception.