Sensory Systems – Olfaction, Gustation & Intro to Vision

Question-and-Answer flashcards covering olfaction, gustation, and introductory vision topics including pathways, receptor mechanisms, cortical processing, phototransduction, and visual perception phenomena.

Which sense is the only one whose primary cortical area is reached before the thalamus?

Olfaction (smell).

What are the first-order neurons in the olfactory system called?

Olfactory receptor (olfactory sensory) neurons.

To which olfactory bulb structures do olfactory receptor axons first synapse?

Glomeruli.

Name the second-order neurons of the olfactory pathway.

Mitral cells of the olfactory bulb.

List three brain areas that receive direct projections from mitral cells.

Hypothalamus, amygdala, prepiriform (primary olfactory) cortex.

Which thalamic nucleus relays olfactory information to higher cortex?

Medial dorsal thalamus.

Where do taste and smell signals first converge to create flavor perception?

The insula (primary gustatory cortex).

Which cortical area integrating olfaction is crucial for decision-making?

Orbitofrontal cortex.

Taste is classified as what type of sensory modality?

A chemical sense.

What is the basic definition of 'taste' in gustation?

A substance that can be tasted touches the tongue, dissolves in saliva, and interacts with taste buds.

Where are taste buds located in relation to papillae?

Hidden in the grooves between papillae.

What structure allows dissolved chemicals to enter a taste bud?

The taste pore.

How many basic taste qualities are recognized, and what are they?

Five: salty, sour, sweet, bitter, and umami.

Which ion channel mediates salty taste transduction?

ENaC (Epithelial Sodium Channel).

What protein channel is responsible for sour taste detection?

PKD2L1.

Sweet taste cells express which two GPCR subunits?

T1R2 and T1R3.

Umami taste uses a metabotropic glutamate receptor and which GPCR dimer?

T1R1 + T1R3.

Which receptor family (numerous types) detects bitter substances?

T2Rs.

Which cranial nerve carries taste from the anterior two-thirds of the tongue?

Facial nerve (CN VII).

Which cranial nerve innervates taste buds on the posterior third of the tongue?

Glossopharyngeal nerve (CN IX).

Which cranial nerve conveys taste from the throat and epiglottis?

Vagus nerve (CN X).

Taste fibers from the tongue synapse in what key brainstem nucleus?

Nucleus of the Solitary Tract (NST).

Which thalamic nucleus relays gustatory information to cortex?

Ventral Posterior Medial (VPM) nucleus.

Name the two cortical regions considered primary gustatory cortex.

Anterior insula and frontal operculum.

What term describes the integrated perception produced by taste, smell, texture, and temperature?

Flavor.

Which cortical region first encodes the palatability of food?

The insula (gustatory cortex).

What experiment used DREADDs to demonstrate hard-wired valence of taste qualities?

The Spiradoline two-bottle preference test in mice.

How did mice with Rasl receptors in sweet cells respond to Spiradoline?

They showed a dose-dependent preference, treating it as sweet.

What was the response when Rasl receptors were expressed in bitter cells?

Mice displayed a dose-dependent aversion, even without actual bitter tastants.

Why is bitter taste aversion considered evolutionarily advantageous to be hardwired?

It helps avoid poisons without requiring dangerous learning experiences.

Which taste receptor population declines with age, partly explaining adult acceptance of bitter foods?

Bitter taste cells.

What is the main function of the iris in eye anatomy?

To regulate how much light enters the pupil by dilating or constricting.

Which eye structure changes shape to focus light on the retina?

The lens, adjusted by ciliary muscles.

What is the fovea?

A small pit in the retina providing the highest acuity at the center of gaze.

Why does the optic disc create a blind spot?

It contains only optic nerve axons and no photoreceptors.

List the five main retinal layers from back (outer) to front (inner).

Photoreceptor layer, bipolar cell layer, ganglion cell layer, optic nerve fiber layer, inner limiting membrane (axons).

Which photoreceptor type is specialized for low-light, monochromatic vision?

Rods.

Which photoreceptors are concentrated in the fovea and enable color vision?

Cones.

Name the three cone classes and the wavelength they best detect.

S (blue, short λ), M (green, medium λ), L (red, long λ) cones.

What is the chromophore linked to opsins that starts phototransduction?

Retinal (a form of vitamin A).

In darkness, are photoreceptors depolarized or hyperpolarized?

Depolarized (~-35 mV).

Which molecule keeps Na+ channels open in dark photoreceptors?

Cyclic GMP (cGMP).

During light activation, which enzyme breaks down cGMP?

Phosphodiesterase (PDE) activated by Transducin.

What happens to glutamate release from photoreceptors when light is present?

It decreases (photoreceptors hyperpolarize).

What genetic condition results from missing or altered cone opsins, producing two instead of three cone types?

Dichromacy (color blindness).

Why are biological males more likely to be red-green color-blind?

Red and green opsin genes are on the X chromosome; males have only one X, so a mutation is expressed.

What retinal cells first generate true action potentials?

Ganglion cells.

How do on-center bipolar cells respond to glutamate from photoreceptors?

They are inhibited by it (via mGluR).

Describe the effect of light on on-center ganglion cell firing rate.

Light increases their firing because their upstream pathway is excited.

What is a center-surround receptive field and its functional advantage?

A field where the center and surrounding regions have opposite effects, enhancing edge detection and signal-to-noise.

Which interneuron type performs lateral inhibition in the retina?

Horizontal cells.

Why do optical illusions demonstrate that vision is a representation, not a direct recording?

Because the brain uses contextual cues and prior knowledge to interpret ambiguous or misleading stimuli.

What causes an afterimage of the complementary color after staring at a color patch?

Photoreceptor adaptation (fatigue) shifts balance toward the opponent color when looking at white.

Why don’t stationary images normally fade from view even when we fix our gaze?

Tiny involuntary eye movements called saccades continually refresh the retinal image.

How do televisions create the illusion of motion?

By rapidly presenting a sequence of still frames (e.g., 30 per second) that the brain blends into continuous movement.

What three subpixels form each pixel on an RGB screen?

Red, green, and blue subpixels.

Which part of the electromagnetic spectrum can humans see?

Approximately 400 nm (violet) to 700 nm (red).

What determines the perceived color of an object we view?

The wavelengths of light it reflects (not absorbs) that reach our eyes.

What dual nature do photons exhibit?

They behave as both particles and waves.

Which photoreceptor pigment is found in rods?

Rhodopsin.