Sensory Systems — MCQs
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Cold water is not used for ear cleaning because
The mechanoreceptors in joints and ligaments are:
Which of the following principles forms the basis of stroboscopy?
Which one of the following is not true about rods?
Fine touch and rapidly adapting receptor is
Stapedial reflex is mediated by-
Motor protein in organ of Corti -
The only neurons in retina showing action potentials are
Function of Merkel's cells is:
The blobs of the visual cortex are associated with:
Sensory Systems Indian Medical PG Practice Questions and MCQs
Question 351: Cold water is not used for ear cleaning because
- A. Damage to tympanic membrane
- B. It will cause infection
- C. Caloric stimulation caused by cold water (Correct Answer)
- D. It will make the wax hard
Explanation: ***Caloric stimulation caused by cold water*** - Irrigating the ear canal with **cold water** causes significant **caloric stimulation** of the vestibular system. - This can induce **vertigo**, **nausea**, and **vomiting** due to the temperature difference stimulating the semicircular canals. *Damage to tympanic membrane* - While excessive pressure from irrigation can potentially damage the **tympanic membrane**, the temperature of the water itself is not the primary factor for this risk. - Damage is more related to the **force of irrigation** and pre-existing membrane integrity, not cold temperature. *It will cause infection* - The temperature of the water used for irrigation does not directly determine the risk of infection. - **Infection risk** is primarily associated with using unsterile water or introducing bacteria into a compromised ear canal, regardless of water temperature. *It will make the wax hard* - Earwax, or **cerumen**, is softened by water irrigation, not hardened. - **Warm water** is typically preferred because it aids in softening the wax more effectively and comfortably than cold water.
Question 352: The mechanoreceptors in joints and ligaments are:
- A. Adapt differentially for different stresses
- B. Slow adapting (Correct Answer)
- C. Fast adapting
- D. Non adapting
Explanation: ***Slow adapting*** - **Mechanoreceptors** in joints and ligaments, such as **Ruffini endings** and **Golgi-type endings**, are primarily **slowly adapting**. - This characteristic allows them to provide continuous information about **joint position** and **pressure** over extended periods. *Adapt differentially for different stresses* - While different mechanoreceptors respond to different types of stimuli (e.g., pressure, stretch), this option describes varying responses rather than the fundamental **adaptation rate**. - The primary characteristic being asked for is how their firing rate changes over time in response to a constant stimulus. *Fast adapting* - **Fast-adapting mechanoreceptors**, like **Pacinian corpuscles** and **Meissner's corpuscles**, respond strongly at the onset and offset of a stimulus. - They are more involved in sensing **vibration** and **changes in pressure** rather than sustained joint position. *Non adapting* - All biological sensory receptors exhibit some degree of **adaptation** to a constant stimulus, meaning their firing rate changes over time. - A truly **non-adapting** receptor would fire at a constant rate indefinitely for a given stimulus, which is not characteristic of mechanoreceptors.
Question 353: Which of the following principles forms the basis of stroboscopy?
- A. Talbot's law (Correct Answer)
- B. Weber's law
- C. Fechner's law
- D. Stevens' law
Explanation: ***Talbot's law*** - **Stroboscopy** is based on the principle of **flicker fusion** and **temporal integration** described by Talbot's law. - **Talbot's law** states that when light flashes at a frequency above the critical fusion frequency, the eye perceives the average brightness as if the light were continuous. - In stroboscopy, light flashes at a frequency slightly different from the vocal fold vibration frequency, creating the **stroboscopic effect** - an optical illusion of slow-motion or stopped motion that allows detailed visualization of vocal fold movement. - The principle of **temporal integration and flicker fusion** is fundamental to how the stroboscopic illusion works. *Fechner's law* - **Fechner's law** describes the logarithmic relationship between physical stimulus intensity and perceived sensation (S = k log I). - This psychophysical principle relates to how we perceive changes in stimulus magnitude, not to the creation of apparent motion through flickering light. - It does not explain the stroboscopic effect used in laryngeal examination. *Weber's law* - **Weber's law** describes the just noticeable difference (JND) between two stimuli being proportional to the magnitude of the original stimulus. - This principle relates to discrimination thresholds in sensory perception, not to visual illusions of motion. - It is not relevant to the mechanism of stroboscopy. *Stevens' law* - **Stevens' law** proposes a power-law relationship between physical stimulus magnitude and perceived intensity. - While it is an important psychophysical principle, it does not explain the temporal integration and flicker fusion that underpin stroboscopy. - It is an alternative to Fechner's law for describing stimulus-sensation relationships but is not the basis of the stroboscopic effect.
Question 354: Which one of the following is not true about rods?
- A. Pigment is rhodopsin
- B. Useful for the color vision (Correct Answer)
- C. More sensitive to light than cones
- D. Least number is present in fovea centralis
Explanation: ***Useful for the color vision*** - **Rods** are primarily responsible for **scotopic (low-light) vision** and **achromatic (black and white) vision**. - They lack the ability to differentiate between different wavelengths of light, thus contributing minimally to **color perception**. *Pigment is rhodopsin* - **Rhodopsin** is indeed the primary **photopigment** found in rod cells. - This pigment is highly sensitive to light, allowing rods to detect light even in **dim conditions**. *More sensitive to light than cones* - **Rods** are significantly more sensitive to light than cones, enabling vision in **low-light environments**. - This high sensitivity is due to their large number and the presence of **rhodopsin**, which is readily bleached by small amounts of light. *Least number is present in fovea centralis* - The **fovea centralis**, responsible for sharp central and color vision, is almost entirely composed of **cones**. - **Rods** are virtually absent in the fovea, increasing in density towards the periphery of the retina.
Question 355: Fine touch and rapidly adapting receptor is
- A. Ruffini's nerve ending
- B. Pacinian corpuscle
- C. Meissners corpuscle (Correct Answer)
- D. Merkel's disc
Explanation: ***Meissners corpuscles*** - They are responsible for **discriminative touch** and ability to differentiate between two points close together. - These receptors are **rapidly adapting**, meaning they respond strongly to initial stimulation but quickly cease firing if the stimulus is constant. *Ruffini's nerve ending* - These are **slowly adapting receptors** sensitive to **stretch** and sustained pressure. - They provide information about **proprioception** and the shape of objects. *Pacinian corpuscle* - Pacinian corpuscles are **rapidly adapting mechanoreceptors** sensitive to **vibration** and deep pressure. - They have a large receptive field and are less involved in fine touch discrimination. *Merkel's disc* - Merkel's discs are **slowly adapting mechanoreceptors** responsible for sensing sustained touch and **pressure**. - They contribute to the perception of **texture** and edges, having a small receptive field.
Question 356: Stapedial reflex is mediated by-
- A. VII and VIII nerves (Correct Answer)
- B. V and VIII nerves
- C. V and VII nerves
- D. VII and VI nerves
Explanation: ***VII and VIII nerves*** - The **afferent limb** of the stapedial reflex arc is carried by the **vestibulocochlear nerve (CN VIII)**, which detects the loud sound. - The **efferent limb** of the reflex, which causes contraction of the stapedius muscle, is mediated by the **facial nerve (CN VII)**. *V and VIII nerves* - The **trigeminal nerve (CN V)** is involved in sensation from the face and muscles of mastication, not directly in the stapedial reflex. - While **CN VIII** correctly represents the afferent pathway, **CN V** is not the efferent pathway for this reflex. *V and VII nerves* - This combination incorrectly identifies **CN V** as the afferent pathway for sound detection. - **CN VII** is correctly identified as the efferent pathway, but **CN V** is not involved in the sensory input for the stapedial reflex. *VII and VI nerves* - This option incorrectly identifies the **abducens nerve (CN VI)**, which controls the lateral rectus muscle of the eye, as part of the stapedial reflex. - Although **CN VII** is correctly identified as the efferent pathway, the afferent pathway (CN VIII) is missing and replaced by an irrelevant nerve (CN VI).
Question 357: Motor protein in organ of Corti -
- A. Kinesin
- B. Myosin (Correct Answer)
- C. Albumin
- D. Dynein
Explanation: **Myosin** - **Myosin I** and **Myosin VIIa** are key motor proteins found in the **hair cells** of the organ of Corti. - They play crucial roles in **stereocilia bundle stiffness** and the **adaptation** process of mechanotransduction, which is essential for hearing. *Kinesin* - **Kinesin** is primarily involved in **anterograde axonal transport** of vesicles and organelles along microtubules in neurons. - It is not the primary motor protein responsible for the unique mechanical properties of hair cells in the organ of Corti. *Albumin* - **Albumin** is a major **plasma protein** primarily involved in maintaining **osmotic pressure** and transporting various substances in the bloodstream. - It is not a motor protein and does not have a direct role in the mechanical function of the organ of Corti. *Dynein* - **Dynein** is a microtubule-associated motor protein responsible for **retrograde axonal transport** and the movement of cilia and flagella. - While important for intracellular transport in many cells, it is not the primary motor protein driving the mechanical processes within the hair cells of the organ of Corti.
Question 358: The only neurons in retina showing action potentials are
- A. Bipolar cells
- B. Amacrine cells
- C. Ganglion cells (Correct Answer)
- D. Rods and cones
Explanation: ***Ganglion cells*** - **Ganglion cells are the only retinal neurons that generate action potentials** to transmit visual information to the brain via the optic nerve. - All other retinal neurons produce graded potentials, which are local changes in membrane potential that do not propagate over long distances. *Bipolar cells* - **Bipolar cells operate via graded potentials**, not action potentials. - They receive input from photoreceptors and horizontal cells, and transmit signals to ganglion cells and amacrine cells. *Amacrine cells* - **Amacrine cells primarily use graded potentials** to modulate the activity of bipolar and ganglion cells. - They are involved in complex processing within the inner plexiform layer of the retina. *Rods and cones* - **Rods and cones (photoreceptors) respond to light with graded potentials** (hyperpolarization). - They are responsible for transducing light into electrical signals, but they do not generate action potentials.
Question 359: Function of Merkel's cells is:
- A. Tactile sensation (Correct Answer)
- B. Chemoreceptor
- C. Proprioception
- D. Temperature sensation
Explanation: ***Tactile sensation*** - **Merkel cells** are specialized epidermal cells located in the **stratum basale** that function as **mechanoreceptors**. - They are crucial for **light touch** and the discrimination of shapes and textures, making them essential for tactile sensation. *Chemoreceptor* - **Chemoreceptors** detect changes in chemical concentrations, such as taste, smell, or blood gas levels. - Merkel cells are not involved in chemical sensing; their primary role is in perceiving mechanical stimuli. *Proprioception* - **Proprioception** refers to the sense of the relative position of one's own body parts and the strength of effort being used in movement (body position sense). - This function is primarily mediated by receptors in muscles, tendons, and joints, not Merkel cells in the skin. *Temperature sensation* - **Temperature sensation** (thermoreception) is mediated by specialized thermoreceptors such as cold receptors (responding to temperatures below skin temperature) and warm receptors (responding to temperatures above skin temperature). - Merkel cells are mechanoreceptors that respond to mechanical deformation, not thermal stimuli, and do not play a role in temperature detection.
Question 360: The blobs of the visual cortex are associated with:
- A. Ocular dominance
- B. Color processing (Correct Answer)
- C. Saccadic eye movements
- D. Orientation
Explanation: ***Color processing*** - **Blobs** are cytochrome oxidase-rich regions within the **primary visual cortex (V1)**, specifically located in layers II and III. - They are primarily involved in the processing of **color information**, exhibiting selectivity for different wavelengths of light. *Ocular dominance* - **Ocular dominance columns** are organized bands of neurons in V1 that preferentially respond to input from either the left or the right eye. - While related to visual processing, ocular dominance is distinct from the function of the blobs. *Saccadic eye movements* - **Saccadic eye movements** are rapid, ballistic movements of the eyes that allow us to quickly shift our gaze from one point to another. - These movements are primarily controlled by brainstem and cortical areas separate from the blobs, such as the **frontal eye fields** and **superior colliculus**. *Orientation* - **Orientation columns** in V1 are groups of neurons that preferentially respond to visual stimuli with specific orientations (e.g., horizontal, vertical, diagonal). - This function is performed by neurons in the **interblob regions**, which are distinct from the blobs themselves.
Practice by Chapter
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Auditory System
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