Sensory Systems — MCQs

Q: Which site contains endolymph?

Scala media. ***Scala media*** - The **scala media** (also known as the cochlear duct) is the only cochlear compartment filled with **endolymph**. - **Endolymph** is a unique fluid with a high **potassium concentration** and a low sodium concentration, essential for the transduction of sound. *Scala vestibuli* - The **scala vestibuli** contains **perilymph**, which has a high sodium and low potassium concentration, similar to extracellular fluid. - It is separated from the scala media by Reissner's membrane. *Helicotrema* - The **helicotrema** is the apex of the cochlea where the scala vestibuli and scala tympani communicate, allowing the **perilymph** to flow between them. - It does not contain endolymph and is not a separate compartment for fluid storage. *Organ of Corti* - The **Organ of Corti** is the sensory organ of hearing, located within the **scala media** and bathed in endolymph. - While it is surrounded by endolymph, the Organ of Corti itself is a collection of cells and not a fluid-filled space.

Q: Initiation of visual impulse is associated with which of the following?

Photoisomerization of 11-cis-retinal. ***Photoisomerization of 11-cis-retinal*** - The initiation of a visual impulse begins with the **photoisomerization of 11-cis-retinal** to **all-trans-retinal** upon absorption of light by rhodopsin. - This is the **primary photochemical event** that triggers the entire phototransduction cascade. - The conformational change in retinal subsequently causes a conformational change in the associated **opsin protein**, activating the **rhodopsin molecule** (visual purple) and initiating signal transduction through the G-protein cascade. - This process is also known as **photoactivation** or the first step in **bleaching of rhodopsin**. *Condensation of opsin with vitamin A aldehyde* - **Condensation of opsin with 11-cis-retinal** (vitamin A aldehyde derivative) occurs in the **dark** to form rhodopsin (visual purple). - This process represents the **regeneration of the photopigment**, not the light-triggered initiation of the visual impulse. - This is the reverse process that restores rhodopsin after bleaching. *NADP* - **NADP (nicotinamide adenine dinucleotide phosphate)** is primarily involved in **anabolic reactions** and oxidative stress response, acting as a cofactor in various metabolic pathways. - It is **not directly involved in the phototransduction cascade** that initiates a visual impulse. *NAD* - **NAD (nicotinamide adenine dinucleotide)** is a coenzyme crucial for **catabolic reactions** and energy metabolism, particularly in glycolysis and the citric acid cycle. - Similar to NADP, it plays **no direct role in the primary photochemistry** or signal transduction mechanisms that initiate a visual impulse.

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General Sensory Physiology

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Somatosensation

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Vision and Optics

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Visual Pathways and Processing

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Taste and Smell

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Sensory Integration

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