Sensory Systems — MCQs

Sensory Systems Indian Medical PG Practice Questions and MCQs

Question 371: Fine touch is detected by

A. Pacinian corpuscle
B. Merkel's disc (Correct Answer)
C. Ruffini's nerve ending
D. Krause's end bulb

Explanation: ***Merkel's disc*** - **Merkel's discs** are specialized cells located in the **basal layer of the epidermis** that are responsible for detecting sustained pressure and light/fine touch. - They are **slowly adapting mechanoreceptors**, meaning they continue to fire as long as the stimulus is present, providing detailed information about touch. *Pacinian corpuscle* - **Pacinian corpuscles** are **rapidly adapting mechanoreceptors** located deeper in the dermis and subcutaneous tissue. - They are primarily involved in detecting **vibration** and **deep pressure**, not fine touch. *Ruffini's nerve ending* - **Ruffini's corpuscles** are **slowly adapting mechanoreceptors** found in the deep dermis, subcutaneous tissue, and joint capsules. - They respond to **stretch** and **sustained pressure**, contributing to our sense of joint position and skin stretch. *Krausse's bulb* - **Krause's end bulbs** (or Krause's corpuscles) are believed to be **thermoreceptors** that detect **cold sensation**. - They are found in mucous membranes (e.g., mouth, conjunctiva) and some skin areas, not primarily involved in fine touch.

Question 372: What is the typical sound level of normal conversation heard at 1 meter distance?

A. 130 dB
B. 90 dB
C. 60 dB (Correct Answer)
D. 30 dB
E. 45 dB

Explanation: ***60 dB*** - Normal conversation at **1 meter distance** typically measures around **60 decibels (dB)**, which is the standard reference level for comfortable speech communication. - This level allows for clear speech intelligibility without strain and is considered the optimal range for **everyday conversation** in most environments. *30 dB* - This sound level is too quiet for normal conversation, representing **whisper-level** sounds or a quiet library environment. - At **30 dB**, speech would be inaudible or require extreme proximity, making normal conversation impossible at the specified distance. *45 dB* - This level is still too quiet for typical conversation at 1 meter, representing **soft speech** or a quiet office environment. - While audible, **45 dB** would require raised voice for comfortable communication at 1 meter distance and does not represent normal conversational volume. *90 dB* - This level is significantly too loud for normal conversation, equivalent to **shouting** or **loud machinery** noise. - Prolonged exposure to **90 dB** can cause hearing damage and represents a sound level that would be uncomfortable for casual conversation. *130 dB* - This sound level reaches the **pain threshold** for human hearing and can cause immediate hearing damage. - **130 dB** represents sounds like jet engines at takeoff or pneumatic drills, making any form of conversation physically painful and dangerous.

Question 373: Which statement concerning sensory neurons or their functional properties is true?

A. Continuous subthreshold stimulation of a pool of sensory neurons results in disfacilitation of those neurons
B. In spatial summation, increasing signal strength is transmitted by using progressively greater numbers of sensory fibers (Correct Answer)
C. Increased stimulus intensity is signaled by a progressive decrease in the receptor potential
D. All sensory fibers are unmyelinated

Explanation: ***In spatial summation, increasing signal strength is transmitted by using progressively greater numbers of sensory fibers*** - **Spatial summation** occurs when multiple presynaptic neurons fire simultaneously to a single postsynaptic neuron, causing their excitatory postsynaptic potentials (EPSPs) to summate and potentially reach the threshold for an action potential. - In the context of sensory fibers, a stronger stimulus can activate a larger number of receptor cells and their associated sensory neurons, leading to a greater number of active fibers transmitting signals to the central nervous system. *Continuous subthreshold stimulation of a pool of sensory neurons results in disfacilitation of those neurons* - Continuous **subthreshold stimulation** typically leads to **facilitation**, not disfacilitation, meaning the neurons become more excitable and closer to firing an action potential. - **Disfacilitation** or **habituation** might occur with prolonged, constant stimulation, but the immediate effect of subthreshold stimulation is often increased excitability due to accumulation of neurotransmitters or changes in membrane potential. *Increased stimulus intensity is signaled by a progressive decrease in the receptor potential* - Increased **stimulus intensity** is signaled by a progressive **increase** in the **receptor potential**, which in turn leads to a higher frequency of action potentials. - The **receptor potential** is a graded potential, meaning its amplitude is proportional to the strength of the stimulus. *All sensory fibers are unmyelinated* - Many sensory fibers, particularly those responsible for rapid transmission of information such as **proprioception** and **discriminative touch**, are **myelinated**, which increases the speed of nerve impulse conduction. - While some sensory fibers (e.g., C fibers for slow pain and temperature) are **unmyelinated**, it is not true for **all** sensory fibers.

Question 374: Cochlear microphonic potentials are primarily produced by

A. Inner hair cells
B. Produced by outer hair cells (Correct Answer)
C. Supporting cells of the organ of Corti
D. Spiral ganglion neurons

Explanation: ***Outer hair cells*** - **Cochlear microphonic potentials** are primarily generated by the activity of **outer hair cells** in response to sound stimulation. - These potentials represent the **AC receptor potential** of the hair cells, directly reflecting the mechanical vibrations of the basilar membrane. - Outer hair cells have electromotile properties and their depolarization/hyperpolarization generates the cochlear microphonic. *Inner hair cells primarily transmit auditory signals* - **Inner hair cells** are primarily responsible for transmitting **auditory signals** to the brain via the auditory nerve (95% of afferent nerve fibers). - While inner hair cells also generate receptor potentials, the predominant contribution to the **cochlear microphonic potential** is from the **outer hair cells**. - Inner hair cells function mainly in sensory transduction rather than amplification. *Electrodes near the round window provide stronger signals* - This is true for **measurement** of cochlear microphonics, but doesn't describe what produces them. - Round window placement offers stronger signals for recording cochlear potentials due to proximity to the source. *Surface electrodes can measure it with reduced sensitivity* - This describes a **measurement technique**, not the cellular source of production. - While detection is possible, the signal is heavily attenuated through temporal bone and tissues.

Question 375: At what decibel level does auditory fatigue occur?

A. 80 dB
B. 90 dB (Correct Answer)
C. 50 dB
D. 60 dB

Explanation: ***90 dB*** - Auditory fatigue, a temporary shift in hearing threshold, typically begins with prolonged exposure to sound levels around **90 dB**. - This level is considered the lower limit for continuous exposure that can lead to **temporary threshold shift (TTS)**, a precursor to permanent damage if exposure continues. *80 dB* - While prolonged exposure to 80 dB can be irritating or cause a sense of discomfort, it is generally considered the threshold for initiating noise-induced hearing damage over a very long period, rather than the immediate onset of **auditory fatigue**. - The risk of **auditory fatigue** and **temporary threshold shift** is significantly lower at 80 dB compared to 90 dB, especially for shorter exposures. *50 dB* - Sound levels at 50 dB are comparable to a quiet conversation or a refrigerator hum and are well below the threshold for experiencing **auditory fatigue** or hearing damage. - Exposure to 50 dB is generally considered safe and comfortable, with no significant impact on **auditory thresholds**. *60 dB* - 60 dB is a common sound level for normal conversation and is not associated with the onset of **auditory fatigue** or risk of hearing damage. - At this level, the **auditory system** is not under significant stress that would cause a temporary change in hearing acuity.

Question 376: What is the function of the tip of the hair cell in utricle?

A. Vision
B. Receptor membrane Depolarization (Correct Answer)
C. Hearing
D. Formation of perilymph

Explanation: ***Receptor membrane Depolarization*** - The **utricle** is part of the vestibular system, containing hair cells with stereocilia that bend in response to head movements, specifically **horizontal linear acceleration** and **static head tilt**. - This bending creates tension in tip links, opening **potassium channels** at the hair cell tips, leading to an influx of K+ ions and subsequent **depolarization** of the receptor membrane. *Vision* - Vision is the sense of sight, which is the function of the **eyes** and the visual processing centers in the brain, not the inner ear structures like the utricle. - The **photoreceptor cells** (rods and cones) in the retina are responsible for transducing light into electrical signals. *Hearing* - Hearing is the function of the **cochlea**, another part of the inner ear, where sound vibrations are converted into electrical signals by hair cells. - The utricle is primarily involved in **balance and spatial orientation**, not auditory perception. *Formation of perilymph* - Perilymph is a fluid found in the **scala tympani** and **scala vestibuli** of the cochlea, important for the mechanics of hearing, but its formation is not directly a function of the hair cell tips. - Perilymph is similar in composition to cerebrospinal fluid and is secreted by cells within the bony labyrinth.

Question 377: Which of the following best describes the electrical response of the rods to light?

A. Depolarization
B. Hyperpolarization (Correct Answer)
C. Action potential
D. Capacitive discharge

Explanation: ***Hyperpolarization*** - Light causes **rhodopsin** to activate a G-protein cascade, leading to the closure of **cGMP-gated Na+ channels**. - This closure reduces the influx of positive ions (Na+), resulting in the cell becoming **more negative** (hyperpolarized). *Depolarization* - **Depolarization** occurs in the dark due to the continuous influx of Na+ ions through open cGMP-gated channels. - This is the "dark current" which is interrupted by light, leading to hyperpolarization, not depolarization. *Action potential* - **Rods and cones** do not generate action potentials; they produce graded potentials in response to light. - Action potentials are generated by **ganglion cells** further down the visual pathway. *Capacitive discharge* - **Capacitive discharge** is a term related to electrical components and does not describe the physiological electrical response of photoreceptor cells. - This term is irrelevant to the **neurobiological process** of phototransduction.

Question 378: According to Weber-Fechner's law, the perceived intensity of a stimulus is proportional to:

A. Number of neurons stimulated
B. Number of receptors stimulated
C. Amplitude of action potential
D. Logarithm of stimulus intensity (Correct Answer)

Explanation: ***Logarithm of stimulus intensity*** - **Weber-Fechner's Law** states that the perceived intensity of a sensation (**psychological magnitude**) is directly proportional to the logarithm of the physical stimulus intensity. - This law describes how the **just noticeable difference (JND)** between two stimuli is proportional to the magnitude of the original stimulus, meaning that as a stimulus gets stronger, an even greater change is needed for it to be noticed. *Number of neurons stimulated* - While the number of neurons stimulated can correlate with stimulus intensity, Weber-Fechner's law specifically quantifies the **perceived intensity** in relation to the **stimulus magnitude**, not directly the neural count. - The activation of more neurons typically leads to a stronger signal, but the mathematical relationship described by the law is different. *Number of receptors stimulated* - The number of receptors stimulated contributes to the overall signal received by the nervous system, but it is an earlier step in the sensory pathway. - Weber-Fechner's law describes the **psychophysical relationship** at a higher level of processing, not simply the initial receptor activation. *Amplitude of action potential* - The **amplitude of action potentials** is generally **all-or-none** and does not vary with stimulus intensity; rather, the *frequency* of action potentials increases with stronger stimuli. - Therefore, the amplitude of a single action potential does not directly reflect the perceived intensity according to Weber-Fechner's law.

Question 379: What are the primary receptor cells of hearing?

A. Tectorial membrane
B. Supporting cell
C. Tunnel of Corti
D. Hair cell (Correct Answer)

Explanation: ***Hair cell*** - **Hair cells** are the specialized receptor cells located in the **organ of Corti** within the inner ear. - They transduce mechanical vibrations caused by sound waves into electrical signals that the brain interprets as sound. *Tectorial membrane* - The **tectorial membrane** is an extracellular matrix that overlies the **organ of Corti** and is involved in stimulating the stereocilia of hair cells. - It is not a receptor cell itself but rather a crucial component in the mechanical transduction process. *Supporting cell* - **Supporting cells** (e.g., pillar cells, Deiters' cells) provide structural and metabolic support to the **hair cells** in the organ of Corti. - They do not directly detect sound vibrations or convert them into electrical signals. *Tunnel of corti* - The **tunnel of Corti** is a fluid-filled space within the **organ of Corti**, formed by the pillar cells. - It serves as a structural landmark and separates the inner and outer hair cells but does not contain receptor cells for hearing.

Question 380: Which structure in the inner ear is responsible for converting sound waves into electrical signals that can be interpreted by the brain?

A. Semicircular canals
B. Vestibule
C. Organ of Corti (Correct Answer)
D. Tympanic membrane

Explanation: ***Organ of Corti*** - The **organ of Corti** is located on the **basilar membrane** within the **cochlea** of the inner ear and is the primary structure responsible for **auditory transduction**. - It contains specialized **hair cells** (inner and outer) that convert mechanical vibrations from sound waves into **electrical signals** through **mechanotransduction**. - When sound waves cause the basilar membrane to vibrate, the hair cells' stereocilia bend, opening **mechanically-gated ion channels** and generating **receptor potentials** that trigger action potentials in the **auditory nerve (cranial nerve VIII)**. *Semicircular canals* - These are part of the **vestibular system** responsible for detecting **rotational movements** and maintaining **balance**, not for hearing. - They contain **ampullae with cristae** that detect angular acceleration but do not convert sound waves into electrical signals. *Vestibule* - The vestibule contains the **utricle and saccule**, which are part of the **vestibular system** responsible for detecting **linear acceleration** and **head position** relative to gravity. - These structures are involved in **balance and spatial orientation**, not in the conversion of sound waves. *Tympanic membrane* - The **tympanic membrane (eardrum)** is located in the **middle ear**, not the inner ear. - While it vibrates in response to sound waves and transmits these vibrations to the **ossicles**, it does not convert sound into electrical signals—it only serves as a mechanical transducer.

Practice by Chapter

General Sensory Physiology

Practice Questions

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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