Sensory Systems — MCQs

Sensory Systems Indian Medical PG Practice Questions and MCQs

Question 391: Red cones in fovea have peak sensitivity at which wavelength?

A. 560nm (Correct Answer)
B. 520nm
C. 460nm
D. 480nm

Explanation: ***560nm*** - Red cones (also known as **L-cones** for long wavelength) are most sensitive to light with a wavelength around **560 nanometers (nm)**, which corresponds to the reddish-yellow part of the visible spectrum. - This peak sensitivity allows them to detect red and distinguish it from other colors when combined with signals from other cone types. *520nm* - This wavelength represents the approximate peak sensitivity for **green cones** (M-cones, for medium wavelength), which are responsible for detecting green hues. - While red cones have some sensitivity at 520nm, it is not their peak or primary wavelength of maximal response. *460nm* - This wavelength is close to the peak sensitivity of **blue cones** (S-cones, for short wavelength), which are responsible for detecting blue and violet light. - Red cones have very limited or no significant sensitivity at such short wavelengths. *480nm* - This wavelength falls in the blue-green region of the spectrum, where both blue and green cones show significant sensitivity. - It is not the peak sensitivity for red cones, which are predominantly responsive to longer wavelengths.

Question 392: Sensory organ for responding to texture is:

A. Pacinian corpuscles
B. Ruffini corpuscles
C. Merkel cells
D. Meissner corpuscles (Correct Answer)

Explanation: ***Meissner corpuscles*** - These are **mechanoreceptors** located in the **dermal papillae** of glabrous (hairless) skin, particularly abundant in fingertips, palms, and soles. - They are responsible for detecting **light touch**, discrimination of two points, and are crucial for sensing **texture** and fine tactile discrimination. *Pacinian corpuscles* - These are large **mechanoreceptors** located deeper in the dermis and subcutaneous tissue. - They detect **vibration** and **pressure**, rather than texture or sustained light touch. *Ruffini corpuscles* - These are **mechanoreceptors** found in the deep layers of the dermis and joint capsules. - They are primarily responsible for detecting **skin stretch** and **sustained pressure**. *Merkel cells* - These are **mechanoreceptors** located in the **basal layer of the epidermis**. - They are involved in sensing **sustained pressure** and **light touch**, contributing to static tactile discrimination, but Meissner corpuscles are more specialized for texture.

Question 393: Endolymph in the ear is equivalent to

A. ICF (Correct Answer)
B. CSF
C. Lymph
D. Blood

Explanation: ***ICF*** - **Endolymph** is characterized by a **high potassium concentration** and a **low sodium concentration**, mirroring the ionic composition of intracellular fluid (**ICF**). - This unique ionic composition is crucial for the generation of the **endocochlear potential**, which drives the transduction of sound and head movements into electrical signals. *CSF* - **Cerebrospinal fluid (CSF)** has a relatively **high sodium concentration** and a **low potassium concentration**, more closely resembling extracellular fluid. - Its primary role is to cushion the brain and spinal cord, and it is found in the subarachnoid space and ventricles, not the inner ear. *Lymph* - **Lymph** is essentially filtered blood plasma and thus has an ionic composition similar to **extracellular fluid**, with **high sodium** and **low potassium**. - It circulates throughout the lymphatic system and plays a role in immunity and fluid balance, distinctly different from endolymph's function. *Blood* - **Blood plasma** also has a **high sodium concentration** and a **low potassium concentration**, typical of extracellular fluid. - Its primary functions include transport of oxygen, nutrients, hormones, and waste products, and it does not directly come into contact with the structures of the inner ear.

Question 394: Weber-Fechner law is related with:

A. Amplitude
B. Surface area
C. Number of sensory fibre involvement
D. Stimulus discrimination (Correct Answer)

Explanation: ***Stimulus discrimination*** - The **Weber-Fechner Law** describes the relationship between the **physical magnitude of a stimulus** and the **perceived intensity** of that stimulus. - It posits that the **just noticeable difference (JND)** between two stimuli is a constant proportion of the original stimulus, which is critical for **sensory discrimination**. *Amplitude* - While amplitude is a characteristic of some stimuli (e.g., sound waves), the Weber-Fechner Law is not exclusively about amplitude. - It refers to the **overall intensity** of a stimulus in relation to its perception, not just its amplitude. *Surface area* - **Surface area** might be relevant in terms of the body area stimulated (e.g., touch), but it is not directly related to the core principle of proportional change in stimulus intensity as described by the Weber-Fechner Law. - The law focuses on the **relative change in intensity** needed to perceive a difference, regardless of the absolute surface area involved. *Number of sensory fibre involvement* - The **number of sensory fibers** involved is related to the **encoding and transmission of sensory information**, but the Weber-Fechner Law describes the **psychophysical relationship** between the physical stimulus and its perception. - It's a **higher-level psychophysical law**, not a physiological description of nerve fiber recruitment.

Question 395: Exposure to 90 dB and 4000 Hz noise for a short duration results in -

A. Auditory fatigue
B. Permanent hearing loss
C. Rupture of tympanic membrane
D. Temporary hearing loss (Correct Answer)

Explanation: ***Temporary hearing loss*** - Exposure to **90 dB** for about 8 hours can lead to noise-induced hearing loss, but prolonged exposure above 85 dB for several hours is usually required for **permanent damage**. - Moderate noise exposure (below the threshold for permanent damage) typically causes a **temporary threshold shift** or **auditory fatigue**, from which the ear can recover. *Auditory fatigue* - While auditory fatigue is a component of noise exposure, the intensity and frequency mentioned (**90 dB, 4000 Hz**) are more specifically associated with a measurable **temporary hearing loss** rather than just fatigue. - Auditory fatigue is generally a precursor to temporary hearing loss, but the term **temporary hearing loss** better encapsulates the measurable shift in hearing threshold. *Permanent hearing loss* - **Permanent hearing loss** typically results from **chronic exposure to high-intensity noise** (e.g., >85 dB for many years) or very intense, short bursts of sound. - A single exposure to **90 dB** at 4000 Hz for a relatively short duration (implied if not specified as chronic) is more likely to cause temporary rather than permanent damage. *Rupture of tympanic membrane* - **Tympanic membrane rupture** usually requires a **sudden, very high-intensity sound pressure** (e.g., an explosion or blast injury), typically in the range of **160-190 dB** or higher. - **90 dB** is below the threshold for causing direct mechanical damage like a tympanic membrane rupture, although it is sufficient to cause sensorineural hearing damage.

Question 396: Which of the following events does NOT occur in rods in response to light

A. Opening of Na+ channels (Correct Answer)
B. Activation of transducin
C. Structural changes in rhodopsin
D. Decreased intracellular cGMP

Explanation: ***Opening of Na+ channels*** - In response to light, **rods hyperpolarize** due to the **closure of Na+ channels**, which reduces the influx of positive ions. - The opening of Na+ channels would lead to depolarization, which is the opposite of what occurs during light detection in rods. *Activation of transducin* - Light causes **conformational changes in rhodopsin**, which in turn activates the G-protein **transducin**. - Activated transducin then goes on to activate **phosphodiesterase (PDE)** as part of the phototransduction cascade. *Structural changes in rhodopsin* - When light strikes the rhodopsin molecule, the **11-cis-retinal chromophore** isomerizes to **all-trans-retinal**. - This **conformational change** in rhodopsin is the initial step that triggers the entire phototransduction pathway. *Decreased intracellular cGMP* - Activated **phosphodiesterase (PDE)**, stimulated by transducin, hydrolyzes **cGMP to GMP**. - The reduction in **cGMP levels** leads to the closure of cGMP-gated Na+ channels, causing hyperpolarization.

Question 397: Which taste sensation is the most sensitive (i.e., has the lowest stimulation threshold)?

A. Sour
B. Sweet
C. Salty
D. Bitter (Correct Answer)

Explanation: ***Bitter*** - The sensation of **bitterness** serves as a protective mechanism, as many naturally occurring **toxins and poisons** are bitter. - Due to this crucial role, the **taste receptors for bitter compounds** are exceptionally sensitive, allowing detection at **very low concentrations** (threshold as low as 0.000008 M for quinine). - **Bitter taste has the lowest threshold** among all taste sensations, making it the most sensitive. *Sour* - **Sour taste** is typically triggered by **acids** (hydrogen ions) and is often associated with unripe or spoiled foods. - While important for detecting acidity, its **threshold is significantly higher** than that for bitter taste. *Sweet* - **Sweet taste** is primarily associated with **energy-rich compounds** like sugars, signaling a caloric source. - The sensitivity for sweet taste is **much lower than bitter**, with a threshold around 0.01 M for sucrose. *Salty* - **Salty taste** is primarily due to the presence of **sodium ions** and is essential for maintaining electrolyte balance. - The threshold for salty taste is **higher than bitter**, with moderate sensitivity at around 0.01 M for NaCl.

Question 398: Warmth sensation is sensed by

A. Meissner's corpuscle
B. Ruffini end organ (Correct Answer)
C. Pacinian corpuscle
D. Krauses end bulb

Explanation: ***Ruffini end organ*** *(Classical teaching - historically associated with warmth)* - **Ruffini corpuscles** are slow-adapting mechanoreceptors (Type II) located deep in the dermis and subcutaneous tissue. - **Classically taught** as receptors for warmth sensation, though their primary function is sensing **skin stretch, sustained pressure, and joint position**. - **Modern understanding:** Warmth is primarily sensed by **free nerve endings** with **TRPV3 and TRPV4 ion channels** (activated at 30-43°C), not by specialized encapsulated receptors. - This question tests classical receptor classification commonly found in traditional physiology curricula. *Meissner's corpuscle* - **Meissner's corpuscles** are rapidly adapting mechanoreceptors (Type I) located in dermal papillae. - Specialized for detecting **light touch and low-frequency vibration** (flutter), not temperature. *Pacinian corpuscle* - **Pacinian corpuscles** are rapidly adapting mechanoreceptors found deep in dermis and subcutaneous tissue. - Highly sensitive to **high-frequency vibration and deep pressure**, not temperature. *Krauses end bulb* - **Krause's end bulbs** were historically thought to be cold receptors, but their function remains unclear. - **Modern understanding:** Cold sensation is mediated by **free nerve endings** with **TRPM8 ion channels** (activated at 8-28°C), not by this corpuscle.

Question 399: Rods and cones differ in all, except

A. Signal transduction (Correct Answer)
B. Wavelength
C. Acuity
D. Light sensitivity

Explanation: ***Signal transduction*** - Both rods and cones utilize the same basic **G-protein coupled receptor cascade** for signal transduction, involving **rhodopsin/photopsin**, **transducin**, and **cGMP phosphodiesterase**. - The fundamental molecular mechanism of converting light into an electrical signal is shared between these photoreceptor types. *Wavelength* - **Rods** are largely monochromatic, primarily sensitive to **blue-green light** (around 500nm), making them responsible for **scotopic (low-light)** vision. - **Cones** are responsible for **photopic (daylight)** and **color vision**, with three types (red, green, blue) possessing different opsins sensitive to various wavelengths. *Acuity* - **Cones** are responsible for **high visual acuity** due to their concentrated distribution in the **fovea** and their "private line" connections to ganglion cells. - **Rods** have **low visual acuity** because many rods converge onto a single ganglion cell, leading to spatial summation rather than discrete detailed information. *Light sensitivity* - **Rods** are much more sensitive to light and operate in **dim illumination**, allowing for vision in low light conditions (scotopic vision). - **Cones** require **bright illumination** to function and are responsible for vision in daylight conditions (photopic vision).

Question 400: The receptors of joint capsule and ligaments are

A. Rapidly adapting
B. Non adapting
C. Fast adapting
D. Slow adapting (Correct Answer)

Explanation: ***Slow adapting*** - Receptors in the **joint capsule** and **ligaments** are primarily **slowly adapting mechanoreceptors**. - They provide continuous information about **joint position**, **movement**, and **stretch**, essential for proprioception and posture. *Rapidly adapting* - **Rapidly adapting receptors** (e.g., Pacinian corpuscles) detect changes in stimuli, such as **vibration** or **sudden movement**, but quickly cease firing. - While present in some joint structures, they are not the primary type for sustained positional feedback in the capsule and ligaments. *Non adapting* - The term **"non-adapting"** is generally not used in the context of sensory receptors. - Most biological receptors exhibit some degree of adaptation, even if it's very slow. *Fast adapting* - **Fast adapting receptors** are synonymous with rapidly adapting receptors. - They respond to the onset and offset of a stimulus but not to its sustained presence, making them less suited for sensing static joint position.

Practice by Chapter

General Sensory Physiology

Practice Questions

Somatosensation

Practice Questions

Pain Physiology

Practice Questions

Vision and Optics

Practice Questions

Retinal Physiology

Practice Questions

Visual Pathways and Processing

Practice Questions

Auditory System

Practice Questions

Vestibular System

Practice Questions

Taste and Smell

Practice Questions

Sensory Integration

Practice Questions

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