Biochemistry - Vision, Gustation, and Olfaction

Electromagnetic energy (light photons)

What type of stimulus is involved in vision?

CN I (Olfactory nerve)

Which cranial nerve is primarily responsible for olfaction?

Cerebral cortex (after thalamic relay)

Where does cortical perception of sensory stimuli occur?

Special visceral afferents

Which division of the sensory nervous system detects odor and taste?

Signal transduction (via specialized receptors)

What initial process converts sensory stimuli to electrical impulses?

True

T/F: The retina converts light to electrical signals before it reaches the cortex.

False

T/F: Special somatic senses include taste and smell.

True

T/F: Conscious awareness of stimuli only occurs after cortical integration.

False

T/F: Vision does not involve memory integration.

False

T/F: The thalamus plays no role in sensory signal routing.

Endothelium (posterior corneal epithelium)

Which layer of the cornea maintains deturgescence?

Keratan sulfate

What glycosaminoglycan is made of N-acetylglucosamine and galactose?

Destructive interference

What phenomenon helps reduce light scattering in the stroma?

Soluble VEGF receptor-3 (sVEGFR-3)

Which molecule blocks lymphangiogenesis in the cornea?

ALDH1A1 and ALDH3A1 with glutathione system

What enzyme system protects the cornea from oxidative damage?

False

T/F: The cornea is the most vascularized part of the eye.

True

T/F: Corneal transparency depends on uniform collagen fibrils.

False

T/F: Bowman’s membrane is cellular and highly regenerative.

True

T/F: Oxidative stress in the cornea is countered by ALDH enzymes.

False

T/F: Stromal deturgescence leads to corneal edema.

Crystallins (a, B, y)

What are the major proteins responsible for lens transparency?

Presbyopia

What age-related condition affects lens accommodation?

Anaerobic glycolysis

What metabolic pathway dominates ATP production in the lens?

Organelles

What cellular structure is lost in mature lens fibers?

Sorbitol

What sugar alcohol accumulates in diabetic cataracts?

False

T/F: The lens relies on blood vessels for nutrients.

False

T/F: Presbyopia is caused by increased lens elasticity.

True

T/F: Cataracts can result from oxidative protein damage.

True

T/F: Crystallins act as chaperones in lens protein maintenance.

False

T/F: Phacoemulsification is a medical therapy for glaucoma.

Rods

Which cells in the retina detect dim light?

Fovea

What area of the retina contains mostly cones?

Rhodopsin

What is the main pigment found in rods?

Cones

Which photoreceptor contributes more to visual acuity?

Erythrolabe (red opsin)

What visual pigment is found in cones sensitive to red light?

False

T/F: Rods are more responsive to bright light than cones.

True

T/F: Cones respond faster than rods.

False

T/F: Visual pigments are located in the inner segment of photoreceptors.

True

T/F: Rhodopsin contains 11-cis-retinal.

True

T/F: All cones respond equally to produce white light.

Night blindness

What is the earliest sign of Vitamin A deficiency?

Ito cells in the liver

Where is the majority of Vitamin A stored?

Retinol-binding protein (RBP)

What protein transports retinol in the blood?

Bitot spots

What epithelial manifestation is associated with Vitamin A deficiency?

Retinoic acid

Which vitamin A derivative supports epithelial cell turnover?

False

T/F: Vitamin A is synthesized de novo in the human body.

True

T/F: Rhodopsin synthesis depends on Vitamin A availability.

False

T/F: Xerophthalmia affects vision through retinal photoreceptor damage.

True

T/F: Vitamin A helps prevent superinfection in measles.

True

T/F: Liver is the major site of Vitamin A metabolism and storage.

Metarhodopsin II

What is the activated form of rhodopsin in light?

Transducin

What G-protein is activated during phototransduction?

Phosphodiesterase (PDE)

What enzyme hydrolyzes cGMP in phototransduction?

Closure of Na+/Ca2+ channels → hyperpolarization

What is the result of cGMP hydrolysis on ion channels?

Hyperpolarization

What unique event happens to photoreceptors in response to light?

False

T/F: Light activation of rhodopsin causes depolarization.

True

T/F: Transducin binds GDP in its inactive state.

True

T/F: In darkness, glutamate is released continuously.

False

T/F: Metarhodopsin II causes cGMP levels to rise.

False

T/F: Photoreceptors release glutamate in the presence of light.

G-protein-coupled receptors (GPCRs)

What type of receptors detect odorants?

Ca2+

Which ion influx is primarily involved in olfactory depolarization?

Adenylyl cyclase

What enzyme synthesizes cAMP in olfactory transduction?

Glomeruli in the olfactory bulb

What structure allows combinatorial odor detection?

CN I (Olfactory nerve)

What cranial nerve transmits olfactory signals?

False

T/F: Each olfactory receptor binds to one unique odorant.

True

T/F: Olfaction is mediated by chemical stimuli.

True

T/F: Odor discrimination relies on cortical interpretation.

False

T/F: The olfactory bulb is bypassed in odor transmission.

True

T/F: Odorant binding increases intracellular cAMP.

T1R1 + T1R3 receptors

Which taste buds detect umami?

CN VII (Facial nerve)

What cranial nerve carries taste from the anterior 2/3 of the tongue?

IP3 (Inositol triphosphate)

Which second messenger is involved in bitter and sweet taste transduction?

Proton-sensitive channels

Which type of ion channel is involved in detecting sour taste?

Na+

What is the main ion responsible for salty taste perception?

False

T/F: Salty taste transduction is mediated by G-proteins.

True

T/F: Gustation and olfaction are interdependent in flavor detection.

True

T/F: Umami receptors detect L-glutamate.

True

T/F: Bitter tastes are detected by T2R receptors.

False

T/F: Sweet and umami taste use identical receptor dimers.

CD36

What taste receptor detects dietary fatty acids?

GPR120

What is the other main fat sensor in taste cells?

DAG (Diacylglycerol)

Fat taste transduction is proposed to involve which intracellular molecule?

TRPM5

Fatty acid stimulation modulates what kind of ion channels?

Umami

What taste is potentiated by fat intake?

False

T/F: Fat has no recognized taste modality.

True

T/F: CD36 functions as a fatty acid transporter and taste sensor.

False

T/F: Fatty acids activate only sodium channels.

True

T/F: Fat ingestion influences appetite regulation.

False

T/F: GPR120 activation triggers aversive taste responses.