Sensory Systems — MCQs

Sensory Systems Indian Medical PG Practice Questions and MCQs

Question 461: Which part of the tongue is most sensitive to bitter taste?

A. Tip of the tongue.
B. Lateral border of the tongue.
C. Central portion of the tongue.
D. Posterior portion of the tongue. (Correct Answer)

Explanation: ***Posterior portion of the tongue*** - Traditionally, the **back of the tongue** has been described as more sensitive to **bitter tastes**, particularly on the **circumvallate papillae**. - This concept stems from the classical "tongue map" theory, which suggested regional taste specialization. - **Modern understanding:** While all taste sensations can be detected across the entire tongue, the posterior region does contain a high concentration of taste receptors, including those for bitter compounds, which may serve as a protective mechanism against potentially toxic substances. *Tip of the tongue* - Classically described as most sensitive to **sweet tastes**. - Contains taste buds capable of detecting all taste modalities, though historically associated with sweet taste detection. *Lateral border of the tongue* - Traditionally associated with **sour and salty taste** detection. - Contains fungiform and foliate papillae with taste buds that detect multiple taste qualities. *Central portion of the tongue* - Contains **fewer taste buds** compared to other regions. - Less specialized for taste reception; primarily involved in food manipulation. **Note:** Current research shows all taste modalities can be detected across the entire tongue, though subtle regional variations in receptor density may exist.

Question 462: The distance by which two touch stimuli must be separated to be perceived as two separate stimuli is greatest at which body part?

A. The lips
B. The palm of the hand
C. The back of scapula (Correct Answer)
D. The dorsum of the hand

Explanation: ***The back of scapula*** - The **two-point discrimination threshold** is greatest on body parts with **lower densities of innervation** and larger **receptive fields**, such as the back of the scapula. - This means a greater distance is required between two stimuli for them to be perceived as distinct, reflecting less tactile acuity. *The lips* - The lips have one of the **smallest two-point discrimination thresholds** due to a very high density of **Meissner's corpuscles** and other touch receptors, allowing for fine tactile discrimination. - They also have a disproportionately large representation in the **somatosensory cortex**. *The palm of the hand* - The palm of the hand also exhibits a relatively **low two-point discrimination threshold** because it is a primary site for tactile exploration and manipulation, requiring high tactile acuity. - It possesses a high density of **mechanoreceptors** and small **receptive fields**. *The dorsum of the hand* - While not as sensitive as the palm, the dorsum of the hand still has a **lower two-point discrimination threshold** compared to the back of the scapula. - It is involved in various tactile sensations and generally has more innervation than areas like the back.

Question 463: Which of the following helps in the detection of horizontal linear acceleration of the head?

A. Middle ear
B. Cochlea
C. Utricle (Correct Answer)
D. Endolymphatic sac

Explanation: ***Utricle*** - The **utricle** is one of the two otolith organs in the **vestibular system** responsible for detecting **linear acceleration** and **head tilts**. - Specifically, it senses **horizontal linear accelerations** and static head tilt relative to gravity, crucial for detecting horizontal movement. *Middle ear* - The **middle ear** is primarily involved in **transmitting sound waves** from the outer ear to the inner ear through the ossicles. - It plays no direct role in the detection of **head movement** or balance. *Cochlea* - The **cochlea** is part of the inner ear responsible for **hearing** and converting sound vibrations into electrical signals that are sent to the brain. - It is not involved in the detection of **head movement** or maintaining balance. *Endolymphatic sac* - The **endolymphatic sac** is involved in the **regulation of endolymph volume** and pressure within the inner ear's membranous labyrinth. - While important for inner ear homeostasis, it does not directly detect **head movements**.

Question 464: Which cells are primarily responsible for generating the 'a' wave in the electroretinogram (ERG)?

A. Ganglion cell
B. Bipolar cell
C. Photoreceptors (Correct Answer)
D. Retinal pigment epithelium

Explanation: ***Photoreceptors*** - The **a-wave** of the ERG represents the initial corneal-negative deflection, primarily reflecting the activity of the **photoreceptors** (rods and cones). - This wave is generated by the hyperpolarization of photoreceptor outer segments in response to light stimulation. - The a-wave appears within milliseconds of light stimulus and reflects the early hyperpolarization response. *Incorrect - Ganglion cell* - **Ganglion cells** transmit visual information to the brain via the optic nerve and contribute minimally to early ERG components. - Their activity is more closely reflected in later ERG components and the **pattern ERG (PERG)**, not the a-wave. *Incorrect - Bipolar cell* - **Bipolar cells** are responsible for generating the **b-wave** of the ERG, which is a corneal-positive deflection following the a-wave. - They transmit signals from photoreceptors to ganglion cells and represent the second major component of the ERG response. *Incorrect - Retinal pigment epithelium* - The **retinal pigment epithelium (RPE)** supports photoreceptor function and is primarily responsible for generating the **c-wave** of the ERG. - This slow, positive wave reflects changes in RPE membrane potential in response to light-induced alterations in subretinal potassium concentration.

Question 465: Which part of the retina is the most sensitive to light?

A. Peripheral retina (Correct Answer)
B. Macula lutea
C. Fovea centralis
D. Optic nerve head

Explanation: ***Peripheral retina*** - The **peripheral retina** contains a much higher concentration of **rods** compared to the central retina, making it highly sensitive to **low light levels** and responsible for **scotopic vision** (night vision). - **Peak rod density** occurs at approximately **20 degrees from the fovea** in the parafoveal/perifoveal region, with around 150,000 rods/mm². - The peripheral retina is far more sensitive to **detecting light and motion** in dimly lit environments compared to the cone-dominated central retina. - While visual acuity is lower in the periphery, its **light sensitivity** is superior. *Fovea centralis* - The **fovea centralis** is specialized for **high-acuity vision** and **color perception** due to its exclusive concentration of **cones** (rod-free zone). - It is **least sensitive to dim light** because it completely lacks rods and requires bright illumination for optimal function. - The fovea provides the sharpest vision but has the poorest light detection threshold. *Macula lutea* - The **macula lutea** is the larger oval region (about 5-6 mm diameter) surrounding the fovea, containing both rods and cones. - Its primary role is in **high-resolution central vision**, though it has better light sensitivity than the fovea due to the presence of rods in its outer regions. - Still predominantly cone-rich and less light-sensitive than the more peripheral retina. *Optic nerve head* - The **optic nerve head** (optic disc), also known as the **blind spot**, contains **no photoreceptor cells** (neither rods nor cones). - It is the exit point for retinal ganglion cell axons forming the optic nerve. - Therefore, it is completely **insensitive to light** and creates a physiological blind spot in the visual field.

Question 466: The colour vision is governed by all of the following colour-sensitive pigments except which of the following?

A. Transducin (Correct Answer)
B. Chloropsin
C. Cyanopsin
D. Porphyropsin

Explanation: ***Transducin*** - **Transducin** is a **G-protein** involved in the phototransduction cascade within photoreceptor cells, but it is **not a color-sensitive pigment** itself. - It acts as a signaling molecule in the visual cascade, activated when light strikes visual pigments like rhodopsin or cone opsins. - Unlike the actual pigments, transducin does not directly absorb light but rather transmits the signal downstream. *Porphyropsin* - **Porphyropsin** is a visual pigment found in the retina of **freshwater fish and amphibians**, containing retinal₂ (3,4-didehydroretinal) as its chromophore. - It is structurally similar to rhodopsin but has an **absorption maximum shifted toward longer wavelengths**, making it useful in aquatic environments. - While it is a **light-sensitive pigment**, it functions analogously to rhodopsin in dim-light vision. *Chloropsin* - **Chloropsin** (also known as **green opsin** or M-opsin) is one of the three **cone cell pigments** responsible for **color vision** in humans. - It is sensitive to **medium wavelength light (~530 nm)** in the green spectrum and plays a crucial role in color perception. - Along with cyanopsin (blue) and erythropsin (red), it enables trichromatic color vision. *Cyanopsin* - **Cyanopsin** (also known as **blue opsin** or S-opsin) is one of the three **cone cell pigments** responsible for **color vision** in humans. - It is sensitive to **short wavelength light (~420 nm)** in the blue spectrum and is essential for perceiving blue colors. - It works together with the other cone opsins to provide full color discrimination.

Question 467: Endolymph resembles which fluid in its ionic composition?

A. ICF (Correct Answer)
B. Plasma
C. Extracellular fluid (ECF)
D. Cerebrospinal fluid (CSF)

Explanation: ***ICF*** - **Endolymph** is unique among extracellular fluids because its ionic composition, particularly high **potassium (K+)** and low **sodium (Na+)** concentrations, resembles that of **intracellular fluid (ICF)**. - This unusual composition is crucial for the function of **hair cells** in the inner ear, allowing for proper **depolarization** upon mechanical stimulation. *Extracellular fluid (ECF)* - While endolymph is technically an extracellular fluid as it surrounds cells, its specific ionic composition does not resemble typical **ECF**, which is high in **sodium** and low in **potassium**. - This difference is a key characteristic that distinguishes endolymph from other bodily fluids. *Plasma* - **Plasma** is the liquid component of blood and has a high concentration of **sodium**, **chloride**, and proteins, which is very different from the high potassium content of endolymph. - Its primary role is transport of nutrients, waste, and blood cells throughout the body, not electrochemical transduction in the inner ear. *Cerebrospinal fluid (CSF)* - **CSF** has an ionic composition closer to that of typical **ECF**, being high in **sodium** and low in **potassium**, unlike endolymph. - While both endolymph and CSF are critical fluids in the nervous system, their specific roles and compositions are distinct.

Question 468: Which of the following statements about the fovea is true?

A. It contains only cones.
B. It contains only rods.
C. It has the lowest threshold for light.
D. It has maximum visual acuity. (Correct Answer)

Explanation: ***It has maximum visual acuity.*** - The fovea is the central part of the **macula** and is responsible for **sharp, detailed vision** due to a high concentration of cones and a specialized anatomical arrangement. - This region has a 1:1 ratio between **photoreceptors, bipolar cells, and ganglion cells**, and overlying retinal layers are displaced to allow light to strike the cones directly, optimizing visual acuity. *It has the lowest threshold for light.* - The **rods**, not the cones or fovea, are responsible for vision in **low-light conditions** because they are highly sensitive to dim light, contributing to the lowest light threshold. - The fovea, containing only cones, is primarily for **photopic (daylight) vision** and requires more light for stimulation compared to the rod-rich periphery. *It contains only cones.* - While overwhelmingly dominated by cones, the fovea does not exclusively contain only cones; there are a few residual rods at its margins, though the very center, the **foveola**, is rod-free. - Cones are responsible for **color vision** and high spatial resolution, which is why the fovea is central to sharp, color-sensitive vision. *It contains only rods.* - The fovea is entirely devoid of rods in its central part (foveola) and primarily consists of cones, with rods increasing in density in the **retinal periphery**. - Rods are responsible for **scotopic (night) vision** and detecting motion but lack the ability to resolve fine detail or color, which distinguishes them from cones.

Question 469: Which site contains endolymph?

A. Scala vestibuli
B. Scala media (Correct Answer)
C. Organ of Corti
D. Helicotrema

Explanation: ***Scala media*** - The **scala media** (also known as the cochlear duct) is the only cochlear compartment filled with **endolymph**. - **Endolymph** is a unique fluid with a high **potassium concentration** and a low sodium concentration, essential for the transduction of sound. *Scala vestibuli* - The **scala vestibuli** contains **perilymph**, which has a high sodium and low potassium concentration, similar to extracellular fluid. - It is separated from the scala media by Reissner's membrane. *Helicotrema* - The **helicotrema** is the apex of the cochlea where the scala vestibuli and scala tympani communicate, allowing the **perilymph** to flow between them. - It does not contain endolymph and is not a separate compartment for fluid storage. *Organ of Corti* - The **Organ of Corti** is the sensory organ of hearing, located within the **scala media** and bathed in endolymph. - While it is surrounded by endolymph, the Organ of Corti itself is a collection of cells and not a fluid-filled space.

Question 470: What is the typical decibel range for a whispered voice in a clinical setting?

A. 10 db
B. 20 - 30 db (Correct Answer)
C. 30 - 50 db
D. 60 db

Explanation: ***20 - 30 db*** - A **whispered voice** in a clinical or quiet setting typically falls within this decibel range, which is just above the threshold of normal hearing. - This level is used during the **whisper test** to assess hearing acuity in clinical examinations. *10 db* - This decibel level is extremely quiet, representing sounds like a very faint rustle or barely audible sound. - It is generally considered too low for a **whispered voice** used for clinical communication or testing. *30 - 50 db* - This range corresponds to a **soft conversational voice** or quiet room sounds. - It's louder than a typical **whispered voice** and represents the lower end of normal speech. *60 db* - This level is equivalent to the sound of a **normal conversation** at typical distance. - It is significantly louder than a **whispered voice** and would not be considered in that category.

Practice by Chapter

General Sensory Physiology

Practice Questions

Somatosensation

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Pain Physiology

Practice Questions

Vision and Optics

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Retinal Physiology

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Visual Pathways and Processing

Practice Questions

Auditory System

Practice Questions

Vestibular System

Practice Questions

Taste and Smell

Practice Questions

Sensory Integration

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