Sensory Systems — MCQs

Sensory Systems Indian Medical PG Practice Questions and MCQs

Question 401: Haarscheiben Cells in epidermis are responsible for

A. Pressure
B. Touch (Correct Answer)
C. Proprioception
D. Temperature

Explanation: ***Touch*** - **Haarscheiben cells**, also known as **Merkel cells**, are specialized epidermal cells associated with nerve endings. - They are primarily responsible for sensing **light touch** and **discriminative touch**, playing a crucial role in tactile sensation. *Pressure* - While Merkel cells contribute to touch sensation, the primary receptors for **deep pressure** and vibration are **Pacinian corpuscles**, located deeper in the dermis and hypodermis. - Light pressure can be detected by other mechanoreceptors such as **Meissner's corpuscles**. *Proprioception* - **Proprioception** refers to the sense of body position and movement. - Receptors for proprioception are mainly located in **muscles, tendons, and joints** (e.g., muscle spindles, Golgi tendon organs), not primarily in the epidermis. *Temperature* - **Temperature sensation** is mediated by **thermoreceptors**, which are free nerve endings in the skin. - These receptors (e.g., Krause end bulbs for cold, Ruffini endings for warmth) are distinct from Haarscheiben/Merkel cells.

Question 402: Visual cycle refers to

A. Day vision and colour vision
B. Photodecomposition and regeneration of visual pigments (Correct Answer)
C. Alternate distance and near fixation
D. Cycle of night vision and colour vision

Explanation: **Photodecomposition and regeneration of visual pigments** * The visual cycle describes the continuous process of **photodecomposition** (bleaching) of rhodopsin in response to light and its subsequent **regeneration** to a light-sensitive state. * This cycle is essential for maintaining the eye's ability to detect light and adapt to varying light intensities. *Day vision and colour vision* * Day vision (photopic vision) and color vision are functions of the **cones** in the retina. * While dependent on photopigment activity, these terms refer to specific *types* of vision, not the underlying biochemical cycle. *Alternate distance and near fixation* * This describes the process of **accommodation**, which is the eye’s ability to change focus from distant to near objects. * Accommodation is controlled by the ciliary muscle and lens, and is distinct from the molecular processes of the visual cycle. *Cycle of night vision and colour vision* * Night vision (scotopic vision) is primarily mediated by **rods**, and color vision by cones. * While both involve visual pigments, the "visual cycle" specifically refers to the *biochemical pathway* of pigment breakdown and regeneration, not a cycle that alternates between these two types of vision.

Question 403: Vibration sense is detected by ?

A. Superficial receptors
B. Free nerve endings
C. Nociceptors
D. Deep receptors (Correct Answer)

Explanation: ***Deep receptors*** - **Vibration sense** is primarily mediated by **Pacinian corpuscles** and **Meissner's corpuscles**, which are considered deep receptors. - **Pacinian corpuscles** are located in the **deep dermis** and **subcutaneous tissue** and are highly sensitive to **high-frequency vibration** (200-300 Hz). - **Meissner's corpuscles** in dermal papillae detect **lower frequency vibration** and are rapidly adapting mechanoreceptors. *Superficial receptors* - **Superficial receptors** like **Merkel cells** primarily detect **sustained touch** and **pressure**, providing information about texture. - While they contribute to tactile sensation, they are **slowly adapting** and not specialized for rapidly oscillating stimuli like vibration. *Free nerve endings* - **Free nerve endings** are unmyelinated or lightly myelinated nerve terminals that detect **pain**, **temperature**, and **crude touch**. - They are not specialized mechanoreceptors and lack the structural organization needed to transduce vibratory stimuli. *Nociceptors* - **Nociceptors** are specialized sensory receptors that detect **noxious (harmful) stimuli** and mediate the sensation of **pain**. - They respond to extreme temperatures, intense mechanical stress, or chemical irritants, not to non-painful vibration.

Question 404: Which of the following receptors is responsible for measuring the intensity of a steady pressure on the skin surface?

A. Pacinian corpuscle
B. Merkel's disk (Correct Answer)
C. Ruffini ending
D. Meissner's corpuscle

Explanation: ***Merkel's disk*** - **Merkel's disks** are **slowly adapting Type I (SA I) mechanoreceptors** located at the epidermal-dermal junction. - They are specifically responsible for detecting **sustained pressure intensity** and provide continuous information about the magnitude of steady indentation on the skin. - They have high spatial resolution and are essential for **measuring the intensity of constant pressure** and fine tactile discrimination. *Ruffini ending* - **Ruffini endings** are **slowly adapting Type II (SA II) mechanoreceptors** located in the dermis and subcutaneous tissue. - Their primary function is detecting **skin stretch** and joint position, not measuring pressure intensity on the skin surface. - While they respond to sustained stimuli, they are stretch receptors rather than pressure-intensity detectors. *Pacinian corpuscle* - **Pacinian corpuscles** are **rapidly adapting mechanoreceptors** responsible for detecting **vibration** and rapid changes in deep pressure. - They respond to dynamic pressure changes, not sustained, steady pressure. *Meissner's corpuscle* - **Meissner's corpuscles** are **rapidly adapting mechanoreceptors** located in the dermal papillae. - They detect **light touch**, **texture**, and **low-frequency vibration** (flutter). - They are designed for detecting changes in touch and movement, not steady pressure intensity.

Question 405: Vibrations are felt by?

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

Explanation: ***Pacinian corpuscle*** - **Pacinian corpuscles** are rapidly adapting mechanoreceptors located deep in the dermis and subcutaneous tissue. - They are highly sensitive to **vibrations** and deep pressure, detecting rapid changes in mechanical stimuli. *Merkel's disc* - **Merkel's discs** are slowly adapting mechanoreceptors found in the basal epidermis. - They are primarily responsible for sensing **light touch**, pressure, and texture discrimination, not vibrations. *Ruffini's end organ* - **Ruffini's end organs** (or corpuscles) are slowly adapting mechanoreceptors located in the dermis and subcutaneous tissue. - They detect **skin stretch**, sustained pressure, and proprioception, contributing to the sense of position and continuous touch. *Meissner's corpuscle* - **Meissner's corpuscles** are rapidly adapting mechanoreceptors located in the dermal papillae, close to the skin surface. - They are responsible for sensing **light touch** and low-frequency vibrations (flutter), but the Pacinian corpuscles are more specialized for higher-frequency vibrations.

Question 406: Whispering produces a sound of:

A. 30-40db
B. 40-50db
C. 50-60db
D. 20-30db (Correct Answer)

Explanation: ***20-30db*** - Whispering is a very soft sound, falling within the lower range of human hearing and typically measuring **20-30 decibels (dB)**. - This low decibel level is why whispers are often used for private communication or when attempting to **avoid disturbing others**. *30-40db* - This range usually corresponds to sounds slightly louder than a whisper, such as a **quiet library**, **soft background music**, or the **rustling of leaves**. - While relatively low, it is still distinctively louder than the typical decibel level produced by whispering. *40-50db* - Sounds in this range are comparable to a **quiet office environment**, **moderate rainfall**, or **light traffic**. - These are clearly audible and significantly louder than a whispered voice. *50-60db* - This decibel level is associated with sounds like a **normal conversation at 3-5 feet**, a **dishwasher**, or **background restaurant noise**. - Such sounds are far too loud to be considered a whisper and would be easily heard by others.

Question 407: The parvocellular pathway from lateral geniculate nucleus to visual cortex is most sensitive for the stimulus of

A. Fine spatial detail (Correct Answer)
B. Saccadic eye movements
C. Luminance contrast
D. Temporal frequency

Explanation: ***Fine spatial detail*** - The **parvocellular pathway** is specialized for processing **high-acuity vision**, including color and fine spatial resolution. - Its neurons have **small receptive fields** and respond best to detailed patterns and stationary objects. *Saccadic eye movements* - **Saccadic eye movements** are rapid eye movements controlled by various brain regions, but their generation and control are not directly the primary function of the parvocellular pathway. - These movements are involved in scanning the visual field to bring objects of interest onto the fovea, which is then analyzed by the parvocellular pathway. *Luminance contrast* - While the parvocellular pathway does respond to contrast, the **magnocellular pathway** is more specialized for detecting rapid changes in **luminance contrast** and motion. - The magnocellular pathway has larger receptive fields and processes information about movement and depth. *Temporal frequency* - **Temporal frequency**, or the rate of flicker or motion, is primarily processed by the **magnocellular pathway**. - This pathway is optimized for detecting movement and rapid changes in the visual scene, rather than fine spatial details.

Question 408: Most recently identified taste sensation is?

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

Explanation: ***Umami*** - **Umami** is the most recently identified **fifth basic taste**, often described as a savory or meaty taste. - Its discovery and recognition as a distinct taste sensation occurred in the **early 20th century** by Kikunae Ikeda, who isolated glutamate from kombu. *Sour* - The sensation of **sourness** is one of the traditionally recognized basic tastes, identified much earlier than umami. - It is typically associated with **acids**, such as those found in lemons or vinegar. *Bitter* - **Bitterness** is another long-standing basic taste that serves an important protective function, often signaling potential toxins. - It is one of the earliest tastes understood and recognized, with receptors for a wide range of bitter compounds. *Sweet* - **Sweetness** is a fundamental and ancient taste, universally recognized as pleasurable and indicating energy-rich foods. - The perception of sweet taste, primarily from sugars, has been understood for centuries.

Question 409: Sound intensity of whispering is:

A. 30 dB (Correct Answer)
B. 90 dB
C. 120 dB
D. 2 dB

Explanation: ***30 dB*** - The **sound intensity** of whispering is approximately **30 decibels (dB)**, which is a quiet but clearly audible sound level. - This level is often used as a reference point for very low-level ambient noise. - Whispering typically ranges from **20-30 dB**, making 30 dB the upper end of the normal whispering range. *90 dB* - **90 dB** represents a significantly louder sound, comparable to that of a **lawnmower** or **jackhammer** from a distance, and is much louder than a whisper. - Prolonged exposure to sound levels at or above **85 dB** can cause hearing damage. *120 dB* - **120 dB** is an extremely loud and potentially damaging sound level, similar to a **rock concert** or **jet engine at takeoff**. - Exposure to such high intensity can cause immediate pain and permanent hearing loss. *2 dB* - **2 dB** is an extraordinarily low sound intensity, barely audible, and would be perceived as almost **complete silence**. - This level is significantly quieter than a whisper and would typically be below the threshold of normal hearing in most environments.

Question 410: The rod receptor potential differs from other sensory receptors in that it shows

A. Hyperpolarization (Correct Answer)
B. Increased conductance of sodium
C. Increased conductance of calcium
D. Depolarization

Explanation: ***Hyperpolarization*** - Rod photoreceptors are **unique among sensory receptors** because they **hyperpolarize** (rather than depolarize) in response to their adequate stimulus (light). - Light causes closure of **cGMP-gated sodium channels**, reducing sodium influx and causing membrane hyperpolarization. - This hyperpolarization **decreases** neurotransmitter (glutamate) release from the rod cell. - This is the **opposite** of most sensory receptors, which depolarize when stimulated. *Increased conductance of sodium* - In **darkness** (not light), rod cells maintain a high sodium conductance through open cGMP-gated channels, producing the "dark current." - **Light exposure decreases** (not increases) sodium conductance by causing channel closure. - This option represents what happens in the unstimulated (dark) state, not the light response. *Increased conductance of calcium* - Similar to sodium, **calcium ions** also flow through cGMP-gated channels that are open in darkness. - Light causes these channels to **close**, resulting in **decreased** calcium conductance. - This option incorrectly suggests an increase when the actual response is a decrease. *Depolarization* - **Most sensory receptors** (mechanoreceptors, chemoreceptors, thermoreceptors) respond to stimuli by **depolarizing**, which increases neurotransmitter release. - Rod photoreceptors are **depolarized in darkness** and **hyperpolarize when stimulated by light**. - This makes hyperpolarization the distinguishing feature of rod receptor potentials.

Practice by Chapter

General Sensory Physiology

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Somatosensation

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Pain Physiology

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Vision and Optics

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Retinal Physiology

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Visual Pathways and Processing

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Auditory System

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Vestibular System

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Taste and Smell

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Sensory Integration

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