Sensory Systems Practice Questions

Q: Identify the skin receptor shown in the image:

Pacinian corpuscle. ***Pacinian corpuscle*** - These are **large, encapsulated mechanoreceptors** characterized by a distinctive 'onion-like' appearance due to multiple concentric lamellae of connective tissue. - Located deep in the dermis and subcutaneous tissue, they are specifically adapted to detect **high-frequency vibration** and deep pressure. *Merkel disc* - These are non-encapsulated receptors located in the **stratum basale** of the epidermis. - They function primarily as **slowly adapting** receptors responsible for sensing **fine touch** and texture. *Ruffini ending* - These appear as spindle-shaped receptors located deep within the dermis and joint capsules. - They are **slowly adapting** mechanoreceptors that detect **skin stretch** and sustained pressure. *Meissner corpuscle* - These are encapsulated receptors located in the **dermal papillae** of glabrous (hairless) skin. - They are **rapidly adapting** receptors that specialize in detecting **low-frequency vibration** and light touch.

Q: Which sensory receptor generates a hyperpolarizing receptor potential upon stimulation?

Visual receptor (rods/cones). ***Visual receptor (rods/cones)*** - Unlike most sensory receptors that depolarize, light absorption by **photopigments** in photoreceptors activates a G-protein cascade (transducin) that closes **cGMP-gated sodium channels**. - This closure leads to a **reduction in cation influx** (sodium and calcium currents), resulting in **hyperpolarization** of the receptor membrane and a subsequent decrease in glutamate release. *Gustatory receptor* - Most taste receptors, such as those for **sweet, bitter, and umami**, utilize G-protein coupled receptors that trigger intracellular signaling cascades leading to **depolarization**. - Depolarization promotes the opening of voltage-gated calcium channels, triggering the release of neurotransmitters to sensory afferents. *Olfactory receptor* - Binding of odorants to G-protein coupled receptors (Golf) activates **adenylyl cyclase**, increasing cyclic AMP (cAMP) levels. - Increased cAMP opens cyclic-nucleotide-gated channels, allowing **influx of sodium and calcium**, which results in **depolarization** of the olfactory receptor neuron. *Auditory receptor* - Hair cells in the cochlea depolarize when stereocilia are bent toward the tallest stereocilium, causing **mechanically-gated ion channels** to open. - This cation influx (predominantly **potassium**) leads to **depolarization** of the hair cell membrane.

Q: Which of the following is NOT a primary color?

Yellow. In ophthalmology and visual physiology, the concept of primary colors is based on the **Trichromatic Theory (Young-Helmholtz Theory)**. This theory states that the human retina contains three types of photoreceptor cones, each sensitive to a specific wavelength of light. ### **Explanation of the Correct Answer** **D. Yellow** is the correct answer because it is **not** a primary color in the additive color system (light). In visual physiology, yellow is a secondary color produced by the simultaneous stimulation of Red and Green cones. While yellow is a primary color in the *subtractive* system (pigments/paints), medical exams focus on the *additive* system of light perception. ### **Analysis of Incorrect Options** The primary colors of light are: * **A. Blue:** S-cones (Short-wavelength sensitive), peak absorption at ~420 nm. * **B. Green:** M-cones (Medium-wavelength sensitive), peak absorption at ~530 nm. * **C. Red:** L-cones (Long-wavelength sensitive), peak absorption at ~560 nm. These three colors can be combined in various proportions to create the entire visible spectrum. ### **Clinical Pearls for NEET-PG** * **Photopigments:** Cones contain **Photopsin**, while rods contain **Rhodopsin** (sensitive to scotopic/low-light vision). * **Color Blindness:** * **Protanopia:** Absence of Red cones. * **Deuteranopia:** Absence of Green cones (Most common type of color blindness). * **Tritanopia:** Absence of Blue cones (Rare). * **Testing:** The **Ishihara Chart** is the most common screening tool, but it primarily detects red-green deficiencies. The **Farnsworth-Munsell 100 Hue Test** is the gold standard for detailed assessment. * **Location:** The highest concentration of cones is in the **fovea centralis**, which is responsible for maximum visual acuity and color vision.

Q: The minimum separable distance for the two-point threshold test is greatest at which location?

Back of scapula. **Explanation:** The **two-point threshold** is the minimum distance at which two distinct tactile stimuli can be perceived as separate. This distance is inversely proportional to the density of mechanoreceptors (specifically Meissner’s corpuscles and Merkel discs) and the size of their receptive fields. **1. Why the Back of the Scapula is Correct:** The back has the **lowest density of sensory receptors** and the **largest receptive fields**. In this region, a single sensory neuron covers a wide area of skin. If two points fall within the same large receptive field, they are perceived as a single touch. Consequently, the minimum separable distance is greatest here (approx. 40–70 mm). **2. Analysis of Incorrect Options:** * **Lips (Option A):** These have the highest density of receptors and the smallest receptive fields, resulting in the lowest (finest) two-point threshold (approx. 2–3 mm). * **Palm of hand (Option B):** Highly sensitive with a high receptor density, though slightly less sensitive than the fingertips or lips. * **Dorsum of hand (Option D):** While less sensitive than the palm, it still possesses a much higher receptor density than the trunk or back. **3. NEET-PG High-Yield Pearls:** * **Cortical Representation:** The two-point threshold correlates directly with the **Sensory Homunculus** in the postcentral gyrus (Brodmann areas 3, 1, 2). Areas with the smallest thresholds (lips, fingertips) have the largest representation in the cerebral cortex. * **Lateral Inhibition:** This physiological process sharpens the perception of two distinct points by inhibiting neighboring neurons, enhancing contrast. * **Order of Sensitivity (Highest to Lowest):** Fingertips/Lips > Palms > Forehead > Dorsum of hand > Back/Thigh.

Q: Otoconia is related to which bodily function?

Balance. **Explanation:** **Otoconia** (also known as statoconia or "ear stones") are microscopic crystals of **calcium carbonate** located within the gelatinous otolithic membrane of the **Utricle and Saccule** (the otolith organs) in the inner ear. 1. **Why Balance is Correct:** The otolith organs are responsible for sensing **linear acceleration** and **static head tilt** (gravity). When the head moves, the weight of the otoconia causes the otolithic membrane to shift, bending the underlying hair cells and sending signals to the brain regarding the body's position in space. Thus, they are fundamental to the vestibular system and the maintenance of equilibrium. 2. **Why Other Options are Incorrect:** * **Hearing:** This is the function of the **Organ of Corti** located within the cochlea. While the cochlea is part of the inner ear, it does not contain otoconia. * **Smell:** This is mediated by the olfactory epithelium and the Olfactory nerve (CN I) in the nasal cavity. * **Taste:** This is mediated by taste buds on the tongue and transmitted via the Facial (CN VII), Glossopharyngeal (CN IX), and Vagus (CN X) nerves. **Clinical Pearls for NEET-PG:** * **BPPV (Benign Paroxysmal Positional Vertigo):** This common condition occurs when otoconia become dislodged from the utricle and migrate into the **Semicircular Canals** (most commonly the **Posterior Canal**). * **Diagnosis & Treatment:** BPPV is diagnosed using the **Dix-Hallpike Maneuver** and treated using canalith repositioning procedures like the **Epley Maneuver**. * **Composition:** Otoconia are primarily composed of **calcium carbonate (calcite)** and a protein matrix (otolin).

Q: Proprioception is carried by which nerve fibers?

Fasciculus cuneatus and fasciculus gracilis. ### Explanation **Correct Option: A (Fasciculus cuneatus and fasciculus gracilis)** Proprioception (position sense), along with fine touch, vibration, and two-point discrimination, is carried by the **Dorsal Column-Medial Lemniscal (DCML) pathway**. This pathway consists of the **Fasciculus Gracilis** (carrying fibers from the lower limbs/T6 and below) and the **Fasciculus Cuneatus** (carrying fibers from the upper limbs/above T6). These first-order neurons ascend ipsilaterally in the spinal cord and synapse in the medulla (nucleus gracilis and cuneatus). **Analysis of Incorrect Options:** * **B. Anterior spinothalamic tract:** This pathway primarily carries **crude touch** and pressure. * **C. Lateral spinothalamic tract:** This pathway is responsible for transmitting **pain and temperature** sensations. * **D. Spinocerebellar tract:** While this tract carries *unconscious* proprioception to the cerebellum for coordination, the term "proprioception" in a clinical or sensory examination context typically refers to **conscious proprioception**, which is the hallmark of the DCML system. **High-Yield NEET-PG Pearls:** * **Fiber Type:** Proprioceptive information is carried by the fastest-conducting, heavily myelinated fibers (**Type Aα or Ia and Ib**). * **Tabes Dorsalis:** A late stage of syphilis that selectively damages the dorsal columns, leading to "sensory ataxia" and a positive **Romberg’s sign**. * **Rule of 6:** Fasciculus **G**racilis is **G**round-level (lower limbs/medial), while Fasciculus Cuneatus is superior (upper limbs/lateral). * **Decussation:** The DCML pathway crosses (decussates) in the **medulla** as internal arcuate fibers, whereas the spinothalamic tracts cross at the level of entry in the spinal cord.

Q: What is the most common loss of sense in individuals over 70 years of age?

Vibration sense. **Explanation:** The correct answer is **Vibration sense (Option B)**. Aging is associated with a progressive decline in sensory functions due to the degeneration of peripheral nerves, sensory receptors, and central processing pathways. Among the somatosensory modalities, **vibration sense** is the most commonly and earliest affected in individuals over 70 years of age. This loss is primarily attributed to the degeneration of **Pacinian corpuscles** (rapidly adapting mechanoreceptors) and a decrease in the number of large-diameter myelinated fibers in the **dorsal columns** of the spinal cord. This clinical finding is most pronounced in the lower extremities, particularly at the great toe and ankles. **Analysis of Incorrect Options:** * **Proprioception (Option A):** While proprioception (position sense) does decline with age and contributes to falls in the elderly, it is generally better preserved than vibration sense. * **Touch and Pressure (Options C & D):** These sensations are mediated by various receptors (Meissner’s corpuscles, Merkel discs, etc.). While their thresholds increase slightly with age, they remain relatively intact compared to the significant loss seen in high-frequency vibratory perception. **High-Yield Facts for NEET-PG:** * **Receptor Match:** Vibration is sensed by **Pacinian corpuscles** (high frequency) and **Meissner’s corpuscles** (low frequency). * **Pathway:** Both vibration and proprioception travel via the **Dorsal Column-Medial Lemniscal (DCML) pathway**. * **Clinical Pearl:** When examining an elderly patient, a mild loss of vibration sense at the ankles can be a "normal" finding of aging, but a loss of position sense is usually pathological. * **Differential:** If vibration loss is disproportionate or occurs in younger patients, consider **Vitamin B12 deficiency** (Subacute Combined Degeneration) or **Diabetes Mellitus**.

Q: True about colour blindness?

Defect in 1 or more prime colours. **Explanation:** Color blindness (color vision deficiency) is the inability to perceive differences between some of the colors that others can distinguish. It results from the absence or dysfunction of one or more of the three types of cone photoreceptors (Long/Red, Medium/Green, Short/Blue) in the retina. **Why Option D is Correct:** The Young-Helmholtz theory states that there are three primary colors (Red, Green, and Blue). Color blindness occurs when there is a **defect in one or more of these primary colors**. This can range from a slight deficiency in one pigment (anomalous trichromacy) to a total absence of one (dichromacy) or all three (achromatopsia). **Analysis of Incorrect Options:** * **Option A:** Most common forms of color blindness (Red-Green) are **X-linked recessive**, not autosomal dominant. This explains why it is significantly more common in males (~8%) than females (0.5%). * **Option B:** **Deuteranomaly** (a type of red-green deficiency) is the most common disorder. **Tritanopia** (blue-yellow deficiency) is extremely rare and is inherited as an autosomal dominant trait. * **Option C:** Trichromats have all three cone types and **can** appreciate blue. *Anomalous trichromats* have all three cones but one is shifted in sensitivity, while *Dichromats* (specifically Tritanopes) are the ones unable to appreciate blue. **High-Yield Clinical Pearls for NEET-PG:** * **Ishihara Charts:** The most common screening test for Red-Green color blindness. * **Edridge-Green Lantern Test:** Used to assess functional color vision for occupations like the Merchant Navy or Railways. * **Protanopia:** "Red-blindness" (missing L-cones). * **Deuteranopia:** "Green-blindness" (missing M-cones). * **Tritanopia:** "Blue-blindness" (missing S-cones).

Q: Tritanopes have defective assessment of which color?

Blue. **Explanation:** Color vision is mediated by three types of photopsins (cone pigments) in the retina, each sensitive to specific wavelengths. Defects in these pigments lead to specific types of color blindness, categorized based on the Greek prefixes for 1, 2, and 3. **1. Why Blue is Correct:** **Tritanopia** is a rare form of dichromacy caused by the absence or deficiency of **S-cones** (Short-wavelength sensitive cones). These cones are responsible for detecting the **blue** end of the spectrum. Therefore, tritanopes have a defective assessment of blue and often confuse it with green, while yellow may be perceived as pink. **2. Analysis of Incorrect Options:** * **A. Red:** Defect in red color perception is known as **Protanopia** (absence of L-cones) or Protanomaly (weakness). Red is the "first" color (Protos). * **C. Green:** Defect in green color perception is known as **Deuteranopia** (absence of M-cones) or Deuteranomaly (weakness). This is the most common type of color vision deficiency. * **D. Yellow:** Yellow is a secondary color perceived through the stimulation of both red and green cones. There is no primary "yellow-cone" deficiency named in this classification. **3. High-Yield Facts for NEET-PG:** * **Genetics:** Protanopia and Deuteranopia are **X-linked recessive** (more common in males). Tritanopia is **Autosomal Dominant** (equally affects males and females) and is linked to Chromosome 7. * **Ishihara Charts:** The most common screening tool for red-green defects. * **Hardy-Rand-Rittler (HRR) Plates:** Better for detecting blue-yellow (Tritan) defects. * **Mnemonic:** **P**rotan (1st - Red), **D**euteran (2nd - Green), **T**ritan (3rd - Blue). Remember: **"RGB = 123"**.

Q: Which of the following is NOT characteristic of visceral pain?

Very rapid adaptation. **Explanation:** Visceral pain is the sensation arising from internal organs (viscera). Understanding its physiological properties is crucial for clinical diagnosis. **Why "Very rapid adaptation" is the correct answer:** Pain receptors (nociceptors) are **non-adaptive** or very slowly adapting. This is a protective physiological mechanism; if pain receptors adapted quickly, the body would cease to perceive ongoing tissue damage, leading to neglect of serious injuries or pathologies. Therefore, visceral pain—like all nociception—does not show rapid adaptation. **Analysis of Incorrect Options:** * **A & B. Poor localization and Diffuse nature:** These are hallmark characteristics of visceral pain. Because the density of sensory receptors in viscera is low and the afferent fibers (mostly Type C) converge with somatic fibers in the spinal cord (Dermatomal rule), the brain cannot precisely pinpoint the source. * **C. High threshold:** Visceral nociceptors generally have a high threshold for stimulation. They do not respond to cutting or burning (which affect the skin) but are triggered by specific stimuli like distension of a hollow viscus, ischemia, chemical irritation, or smooth muscle spasms. **NEET-PG High-Yield Pearls:** 1. **Fiber Types:** Visceral pain is primarily transmitted by **unmyelinated Type C fibers**, leading to "slow pain" (dull, aching, or burning). 2. **Referred Pain:** This occurs due to the **Convergence-Projection Theory**, where visceral and somatic afferents synapse on the same second-order neurons in the dorsal horn. 3. **Autonomic Association:** Visceral pain is frequently accompanied by autonomic responses like nausea, vomiting, sweating, and changes in blood pressure.

Question 1

Identify the skin receptor shown in the
image:

Accepted Answer

Pacinian corpuscle

Answer

Merkel disc

Answer

Ruffini ending

Answer

Meissner corpuscle

Question 2

Which sensory receptor generates a hyperpolarizing receptor potential upon stimulation?

Accepted Answer

Visual receptor (rods/cones)

Answer

Gustatory receptor

Answer

Olfactory receptor

Answer

Auditory receptor

Question 3

Which of the following is NOT a primary color?

Accepted Answer

Yellow

Answer

Blue

Answer

Green

Answer

Red

Question 4

The minimum separable distance for the two-point threshold test is greatest at which location?

Accepted Answer

Back of scapula

Answer

Lips

Answer

Palm of hand

Answer

Dorsum of hand

Question 5

Otoconia is related to which bodily function?

Accepted Answer

Balance

Answer

Hearing

Answer

Smell

Answer

Taste

Question 6

Proprioception is carried by which nerve fibers?

Accepted Answer

Fasciculus cuneatus and fasciculus gracilis

Answer

Anterior spinothalamic tract

Answer

Lateral spinothalamic tract

Answer

Spinocerebellar tract

Question 7

What is the most common loss of sense in individuals over 70 years of age?

Accepted Answer

Vibration sense

Answer

Proprioception

Answer

Touch sensation

Answer

Pressure sense

Question 8

True about colour blindness?

Accepted Answer

Defect in 1 or more prime colours

Answer

Autosomal dominant inheritance

Answer

Tritanopia is the commonest disorder

Answer

Trichromats are unable to appreciate blue colour

Question 9

Tritanopes have defective assessment of which color?

Accepted Answer

Blue

Answer

Red

Answer

Green

Answer

Yellow

Question 10

Which of the following is NOT characteristic of visceral pain?

Accepted Answer

Very rapid adaptation

Answer

Poor localization

Answer

Diffuse in nature

Answer

High threshold

Sensory Systems — MCQs

Sensory Systems — MCQs

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