Sensory Systems Practice Questions

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

Opening of Na+ channels. ***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.

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

Bitter. ***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.

Q: Warmth sensation is sensed by

Ruffini end organ. ***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.

Q: Rods and cones differ in all, except

Signal transduction. ***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).

Q: All of the following are carried by the dorsal column except?

Pain. ***Pain*** - Pain and temperature sensations are transmitted via the **spinothalamic tracts**, specifically the **lateral spinothalamic tract**, not the dorsal column. - The spinothalamic tracts decussate (cross) at the level of entry into the spinal cord, ascending contralaterally. *Vibration* - **Vibration sense** is a key modality carried by the dorsal column, along with proprioception and fine touch. - It involves receptors like **Pacinian corpuscles** and is crucial for detecting rapid changes in pressure and texture. *Touch* - **Fine discriminative touch** (two-point discrimination, precise localization, and tactile discrimination) is a primary function of the dorsal column-medial lemniscus pathway. - The dorsal column specifically carries fine touch, while crude touch has dual representation through both the dorsal column and the anterior spinothalamic tract. *Proprioception* - **Proprioception**, the sense of body position and movement, is heavily reliant on the dorsal column pathway. - Information from muscle spindles and Golgi tendon organs ascends through this pathway to the cerebral cortex for conscious awareness of limb position.

Q: The receptors of joint capsule and ligaments are

Slow adapting. ***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.

Q: Haarscheiben Cells in epidermis are responsible for

Touch. ***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.

Q: Visual cycle refers to

Photodecomposition and regeneration of visual pigments. **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.

Q: Vibration sense is detected by ?

Deep receptors. ***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.

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

Merkel's disk. ***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 1

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

Accepted Answer

Opening of Na+ channels

Answer

Activation of transducin

Answer

Structural changes in rhodopsin

Answer

Decreased intracellular cGMP

Question 2

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

Accepted Answer

Bitter

Answer

Sour

Answer

Sweet

Answer

Salty

Question 3

Warmth sensation is sensed by

Accepted Answer

Ruffini end organ

Answer

Meissner's corpuscle

Answer

Pacinian corpuscle

Answer

Krauses end bulb

Question 4

Rods and cones differ in all, except

Accepted Answer

Signal transduction

Answer

Wavelength

Answer

Acuity

Answer

Light sensitivity

Question 5

All of the following are carried by the dorsal column except?

Accepted Answer

Pain

Answer

Vibration

Answer

Touch

Answer

Proprioception

Question 6

The receptors of joint capsule and ligaments are

Accepted Answer

Slow adapting

Answer

Rapidly adapting

Answer

Non adapting

Answer

Fast adapting

Question 7

Haarscheiben Cells in epidermis are responsible for

Accepted Answer

Touch

Answer

Pressure

Answer

Proprioception

Answer

Temperature

Question 8

Visual cycle refers to

Accepted Answer

Photodecomposition and regeneration of visual pigments

Answer

Day vision and colour vision

Answer

Alternate distance and near fixation

Answer

Cycle of night vision and colour vision

Question 9

Vibration sense is detected by ?

Accepted Answer

Deep receptors

Answer

Superficial receptors

Answer

Free nerve endings

Answer

Nociceptors

Question 10

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

Accepted Answer

Merkel's disk

Answer

Pacinian corpuscle

Answer

Ruffini ending

Answer

Meissner's corpuscle

Sensory Systems — MCQs

Sensory Systems — MCQs

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