Exam 2: 5.2

Question 1

Understand the role of the thalamus in the sensory system

Answer 1

• It’s responsible for receiving, processing, and relaying sensory signals to the correct cortical areas for interpretation.

Question 2

Differentiate between encapsulated and unencapsulated sensory receptors

Answer 2

Encapsulated- Nerve endings that are fevered in connective tissue (pacinian Corpuscle)
- detect pressure vibration, stretch , and proprioception

• tactile corpuscles: light touch
  lamellar corpuscles: deeper/constant pressure due to further location in dermis

Nonencapsulated- Free nerve endings that are not surrounded by conncective tissye receive signals(hair follicles)

slow-adapting due to lack of mylination

Question 3

Describe the physiology of temperature, pain, and itch detection

Answer 3

Temperature:
detected by free nerve endings in the dermis
there are more cold than warm receptors

Pain:
Pain (nociception):

Activated by mechanical, chemical, or thermal damage.

Pathways:

Reflexive protective: Spinal and subcortical → withdrawal reflex + autonomic reaction.

Conscious sensation: Slower; reaches cortex → localizes pain, links emotional rxn

fast pain: myleinated c fibers
slow pain: unmylinated a fibers

Itch:
Transmitted by subtype of C fibers.

Pain and itch inhibit each other — scratching (pain) blocks itch transmission.

Question 4

Explain signal transduction in the olfactory neuron

Answer 4

Odorant binds to olfactory receptor (GPCR) → activates GPCR protein → adenylyl cyclase → cAMP increases.

cAMP opens cation channels → Na⁺ and Ca²⁺ influx → depolarization.

Ca²⁺ used as 2nd messenger to opens Cl⁻ channels, causing Cl⁻ efflux ( not enough soidum in mucus to depolarize cell so relies on cl- channels) → further depolarization.

depolarization causes : Action potential travels along cranial nerve Ito the olfactory bulb.

Question 5

Explain how the olfactory system is unique among the senses

Answer 5

Bypasses the thalamus ( signals go directly from the olfactory bulb to the cerebrum cortex)

the only CNS neuron that has constant turnover of cells as it is exposed to the outside world

Question 6

Describe how the zones of the nose allow for differing sensitivities of the glomerulus (and how its sensitivities are encoded).

Answer 6

Receptor Activation:
The olfactory epthelium has 4 zones and within each zone the odourant will activate and bind different OSN on the olfactory epethilium

Olfactory Bulb:
The specific pattern of neurons activated in the epthelium will plug into/light up a specific pattern of glomeruli on the olfactory bulb that is unique to the odourant. At the specfic glomerili the OSN will synapse with the mitral and tufted cells releasing glutamate at the synapse.

Leaving the olfactory bulb:
The mitral and tufted cells that receive input from the OSN at the glomeruli will fire a patter of APs that is sent to the olfactory cortex via the olfactory tract.

Question 7

Describe the locations in the brain where the olfactory bulb projects, noting significance

Answer 7

Primary olfactory cortex (piriform cortex): Conscious odor perception.

Amygdala: Emotional response to odors.

Hippocampus: Odor-related memories.

Orbitofrontal cortex: Odor identification and discrimination.
→ These projections explain why smell strongly triggers emotion and memory.

Question 8

Describe the anatomy, molecular mechanism of signal transduction (afferent pathway), and sensory processing in the CNS (integration center) for taste

Answer 8

Anatomy:

Taste buds on tongue papillae → contain 50–100 gustatory cells (non-neural receptors).

Each cell is sensitive to one taste (sweet, salty, sour, bitter, umami).

Transduction mechanisms:

TYPE II CELLS–> Sweet, umami, bitter: sweet, umami, biiter substance binds to receptor→ activate G-protein → ↑ cAMP or IP₃ → depolarization → block of K+ or IP3 cause ca2+ channel opening –> ATP release as neurotransmitter.

TYPE I CELLS–> Salty: Na⁺ enters directly through Na+ channels → depolarization opens up Ca2+ channels → influx of calcium triggers ATP release.

TYPE III CELLS–> Sour: H⁺ enters via sour foods–> blocks K⁺ channels → depolarization causes opening of CA@+ channels → influx of calcium elicits serotonin release.–> sretonin release regulates taste perception by shutting down ATP release by othe rcells

CNS processing:
Afferent pathway: Cranial nerves sends signals to thalamus → gustatory cortex (insula) where taste is processed .
Thalamus relays info to insula for conscious perception.

Integration with smell and texture creates full flavor perception.