Sensory Systems Practice Questions

Q: Vibration sense is carried by which of the following structures?

Pacinian corpuscles. **Explanation:** The correct answer is **Pacinian corpuscles**. Vibration sense (pallesthesia) is mediated by specialized mechanoreceptors that are sensitive to high-frequency mechanical stimuli. **Pacinian corpuscles** are rapidly adapting (RA II) receptors located deep in the dermis and subcutaneous tissue. They have a large receptive field and are specifically tuned to detect high-frequency vibrations (ranging from 60–400 Hz, with peak sensitivity around 250 Hz). When a vibratory stimulus is applied, the concentric lamellae of the Pacinian corpuscle deform, triggering an action potential in the sensory nerve fiber. **Analysis of Incorrect Options:** * **Meckel’s disks:** These are slowly adapting (SA I) receptors located in the basal layer of the epidermis. They are responsible for detecting static touch, pressure, and vertical indentation (e.g., feeling the edges of an object). * **Ruffini corpuscle end-organs:** These are slowly adapting (SA II) receptors found in the deep dermis. They respond primarily to skin stretch and joint rotation. * **Free nerve endings:** These are non-specialized endings that primarily mediate pain (nociception) and temperature (thermoreception). **Clinical Pearls for NEET-PG:** * **Pathway:** Vibration sense is carried via the **Dorsal Column-Medial Lemniscal (DCML) pathway**. * **Clinical Testing:** Vibration is often the first sense lost in peripheral neuropathies (e.g., Diabetic neuropathy) and is tested using a **128 Hz tuning fork** over bony prominences. * **Meissner’s Corpuscles:** These also detect vibration, but at much lower frequencies (30–40 Hz), often described as "flutter." * **Rule of Thumb:** If the question specifies "high-frequency vibration," the answer is always Pacinian corpuscles.

Q: Fast pain has a conduction velocity of _____ m/sec?

15. **Explanation:** Pain is transmitted to the central nervous system via two distinct pathways involving different nerve fiber types. The correct answer is **15 m/sec**, which falls within the characteristic range for **Aδ (A-delta) fibers**. 1. **Why 15 m/sec is correct:** Fast pain (also known as "pricking" or "acute" pain) is carried by **Aδ fibers**. These are thinly myelinated fibers with a diameter of 2–5 μm. Their conduction velocity typically ranges from **6 to 30 m/sec**. Therefore, 15 m/sec is the most accurate representative value among the choices. 2. **Analysis of incorrect options:** * **1 m/sec (Option A):** This is the velocity for **C fibers**, which transmit **slow pain** (dull, aching, or burning). These fibers are small and unmyelinated (0.5–2 m/sec). * **5 m/sec (Option B):** This is too slow for Aδ fibers and too fast for typical C fibers; it does not represent the standard "fast pain" velocity. * **50 m/sec (Option D):** This velocity is characteristic of **Aβ (A-beta) fibers**, which carry non-noxious stimuli like touch and pressure. **High-Yield NEET-PG Pearls:** * **Double Pain Sensation:** When you stub your toe, the initial sharp sting is Fast Pain (Aδ), followed seconds later by a dull ache, which is Slow Pain (C fibers). * **Neurotransmitter:** Fast pain uses **Glutamate** (fast-acting), while slow pain uses **Substance P** (slow-releasing). * **Termination:** Fast pain fibers terminate mainly in **Laminae I and V** of the dorsal horn; slow pain fibers terminate in **Laminae II and III (Substantia Gelatinosa)**. * **Lateral vs. Medial:** Fast pain travels via the **Neospinothalamic tract**, whereas slow pain travels via the **Paleospinothalamic tract**.

Q: Which of the following structures contains endolymph?

Scala media. The inner ear consists of a bony labyrinth containing a membranous labyrinth. Understanding the fluid distribution within these compartments is a high-yield topic for NEET-PG. ### **Explanation of the Correct Answer** The **Scala Media** (also known as the cochlear duct) is the middle compartment of the cochlea and is part of the **membranous labyrinth**. It is filled with **endolymph**, a unique extracellular fluid that is high in Potassium ($K^+$) and low in Sodium ($Na^+$), resembling intracellular fluid. This high potassium concentration is essential for the depolarization of hair cells during auditory transduction. ### **Analysis of Incorrect Options** * **Scala Vestibuli (D) and Scala Tympani (C):** These are parts of the **bony labyrinth**. They are filled with **perilymph**, which is high in Sodium ($Na^+$) and low in Potassium ($K^+$), similar to cerebrospinal fluid (CSF). The Scala vestibuli is separated from the scala media by Reissner’s membrane, while the Scala tympani is separated by the Basilar membrane. * **Helicotrema (A):** This is the narrow opening at the apex of the cochlea where the Scala vestibuli and Scala tympani meet. Since it connects two perilymph-filled spaces, it contains **perilymph**, not endolymph. ### **High-Yield Clinical Pearls** * **Source of Endolymph:** It is secreted by the **Stria Vascularis** located in the lateral wall of the scala media. * **Endocochlear Potential:** The scala media has a positive potential of **+80 mV** relative to the perilymph, providing the driving force for sound transduction. * **Meniere’s Disease:** Caused by the "endolymphatic hydrops" (excess accumulation of endolymph), leading to the triad of vertigo, sensorineural hearing loss, and tinnitus.

Q: Which of the following does NOT present in the auditory pathway?

Medial lemniscus. The auditory pathway follows a specific sequence of relay stations often remembered by the mnemonic **E. COLIM** (Eighth nerve, Cochlear nuclei, Superior Olivary complex, Lateral lemniscus, Inferior colliculus, Medial geniculate body). ### Why Medial Lemniscus is the Correct Answer: The **Medial Lemniscus** is a major ascending pathway for the **Dorsal Column-Medial Lemniscal System (DCML)**. It carries sensory information related to fine touch, conscious proprioception, and vibration from the body to the thalamus (VPL nucleus). It is **not** involved in the transmission of auditory signals. The corresponding structure in the auditory system is the **Lateral Lemniscus**. ### Explanation of Incorrect Options: * **Superior Olivary Nucleus (A):** Located in the pons, this is the first site where auditory information from both ears converges. It plays a critical role in sound localization by detecting time and intensity differences. * **Medial Geniculate Body (C):** This is the "thalamic relay station" for hearing. All auditory fibers synapse here before projecting to the primary auditory cortex (Heschl’s gyrus). * **Trapezoid Body (D):** This consists of decussating fibers from the ventral cochlear nuclei. It is a vital part of the auditory pathway where fibers cross to the contralateral superior olivary nucleus. ### High-Yield NEET-PG Pearls: * **Lateral Lemniscus = Listening:** Always associate the *Lateral* lemniscus with the auditory system and the *Medial* lemniscus with somatosensory (touch) systems. * **MGB vs. LGB:** **M**edial Geniculate Body is for **M**usic (Hearing); **L**ateral Geniculate Body is for **L**ight (Vision). * **Primary Auditory Cortex:** Located in the superior temporal gyrus (Brodmann areas 41 and 42).

Q: What is the neurotransmitter employed by rods and cones?

Glutamate. **Explanation:** The correct answer is **Glutamate**. In the retina, photoreceptors (rods and cones) are specialized neuroepithelial cells that maintain a constant release of the excitatory neurotransmitter **glutamate** in the dark. **Why Glutamate is Correct:** Photoreceptors exhibit a unique physiological behavior called the "dark current." In the absence of light, rods and cones are relatively depolarized (approx. -40 mV), leading to the continuous release of glutamate onto bipolar cells. When light strikes the retina, it triggers a G-protein coupled cascade (involving transducin and phosphodiesterase) that closes sodium channels, causing **hyperpolarization**. This hyperpolarization *decreases* the release of glutamate. Thus, the signal for light is actually a reduction in glutamate secretion. **Analysis of Incorrect Options:** * **A. Dopamine:** In the retina, dopamine is primarily secreted by **amacrine cells** and interplexiform cells. it plays a role in light adaptation and circadian rhythms, but it is not the primary transmitter for photoreceptors. * **B. Serotonin:** While found in some invertebrate visual systems, it is not the neurotransmitter for mammalian rods and cones. * **D. Nitric Oxide:** This acts as a retrograde gaseous signaling molecule in various parts of the CNS but does not serve as the primary neurotransmitter for the first synapse in the visual pathway. **High-Yield NEET-PG Pearls:** * **The Visual Paradox:** Photoreceptors are the only sensory receptors that **hyperpolarize** in response to an adequate stimulus (light). * **Bipolar Cells:** Glutamate has different effects depending on the receptor: it inhibits **On-center** bipolar cells (via mGluR6 receptors) and excites **Off-center** bipolar cells (via AMPA/Kainate receptors). * **Vitamin A:** Retinal, a derivative of Vitamin A, is the prosthetic group of rhodopsin; its deficiency leads to Nyctalopia (night blindness).

Q: Which is the last discovered taste sensation?

Umami. **Explanation:** The correct answer is **Umami**. For decades, the tongue was believed to perceive only four primary tastes. However, Umami was officially recognized as the fifth primary taste sensation in the late 20th century after the identification of specific G-protein coupled receptors (mGluR4 and T1R1/T1R3) on the tongue. **Why Umami is correct:** Umami (a Japanese word meaning "savory" or "delicious") is triggered by **L-glutamate** and certain nucleotides like inosinate and guanylate. It is the last discovered sensation because it was only scientifically validated as a distinct primary taste (with its own dedicated receptors) long after the traditional four were established. It is commonly associated with protein-rich foods like meat, cheese, and MSG (Monosodium Glutamate). **Why other options are incorrect:** * **Sweet, Sour, and Bitter:** These are the "classical" taste sensations known since antiquity. * **Sweet** (triggered by sugars/glycols) and **Bitter** (triggered by alkaloids/long-chain organics) utilize G-protein coupled receptors. * **Sour** (triggered by H+ ions) and **Salty** (triggered by Na+ ions) primarily utilize ion channels. **High-Yield Facts for NEET-PG:** * **Receptor Types:** Sweet, Bitter, and Umami use **G-protein coupled receptors (GPCRs)**; Salty and Sour use **Ion channels**. * **Signal Transduction:** For GPCR-linked tastes, the specific G-protein involved is called **Gustducin**. * **Innervation:** The anterior 2/3 of the tongue is supplied by the **Chorda Tympani (CN VII)**; the posterior 1/3 by the **Glossopharyngeal nerve (CN IX)**; and the epiglottis/pharynx by the **Vagus nerve (CN X)**. * **Ageusia:** The clinical term for loss of taste sensation.

Question 1

Vibration sense is carried by which of the following structures?

Accepted Answer

Pacinian corpuscles

Answer

Meckel's disks

Answer

Ruffini corpuscle end-organs

Answer

Free nerve endings

Question 2

Fast pain has a conduction velocity of _____ m/sec?

Accepted Answer

15

Answer

1

Answer

5

Answer

50

Question 3

Which of the following structures contains endolymph?

Accepted Answer

Scala media

Answer

Helicotrema

Answer

Scala tympani

Answer

Scala vestibuli

Question 4

Which of the following does NOT present in the auditory pathway?

Accepted Answer

Medial lemniscus

Answer

Superior olivary nucleus

Answer

Medial geniculate body

Answer

Trapezoid body

Question 5

What is the consequence of removing one side of the auditory cortex?

Accepted Answer

Decreased sound localization

Answer

Total hearing loss

Answer

Mild decrease in hearing

Answer

Decreased sound interpretation

Question 6

When stereocilia of an auditory hair cell are deflected in the appropriate direction, potassium channels open in the apical membrane of the cell and?

Accepted Answer

Potassium ions flow into the cell, depolarizing the cell.

Answer

Potassium ions flow out of the cell, hyperpolarizing the cell.

Answer

Potassium ions flow out of the cell, depolarizing the cell.

Answer

Potassium ions flow into the cell, hyperpolarizing the cell.

Question 7

What is the neurotransmitter employed by rods and cones?

Accepted Answer

Glutamate

Answer

Dopamine

Answer

Serotonin

Answer

Nitric oxide

Question 8

Direction of sound is differentiated by which structure?

Accepted Answer

Inferior colliculus

Answer

Auditory cortex

Answer

Medial geniculate body

Answer

Lateral geniculate body

Question 9

Which is the last discovered taste sensation?

Accepted Answer

Umami

Answer

Sweet

Answer

Sour

Answer

Bitter

Question 10

Which of the following is TRUE regarding the sense of smell EXCEPT?

Accepted Answer

Affects a larger area

Answer

Rapidly adapting

Answer

The olfactory receptor cell is a bipolar neuron

Answer

The threshold of smell is low

Sensory Systems — MCQs

Sensory Systems — MCQs

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