Sensory Systems Practice Questions

Q: The two-point threshold test assesses the integrity of which pathway?

Dorsal column. **Explanation:** The **two-point threshold** (or two-point discrimination) is the ability to discern that two nearby objects touching the skin are truly two distinct points, rather than one. This is a hallmark function of the **Dorsal Column-Medial Lemniscal (DCML) pathway**. **1. Why the Dorsal Column is Correct:** The DCML pathway is responsible for transmitting "fine" or "discriminative" sensations. These include fine touch, pressure, vibration, conscious proprioception, and **two-point discrimination**. This system has a high degree of somatotopic organization and utilizes large, myelinated A-beta fibers, allowing for rapid transmission and precise localization of stimuli. **2. Why the other options are incorrect:** * **Anterior Spinothalamic Tract:** This pathway primarily carries **crude touch** and pressure. While it deals with touch, it lacks the spatial resolution required for fine discrimination. * **Lateral Spinothalamic Tract:** This pathway is dedicated to transmitting **pain and temperature** sensations. * **Lateral Corticospinal Tract:** This is a **descending motor pathway** responsible for voluntary movement of the distal limbs; it does not carry sensory information. **Clinical Pearls for NEET-PG:** * **Receptor Association:** Two-point discrimination is most refined in areas with a high density of **Meissner’s corpuscles** (e.g., fingertips). * **Tabes Dorsalis:** A classic condition involving the destruction of the dorsal columns (neurosyphilis), leading to loss of two-point discrimination and vibration sense. * **Stereognosis:** The ability to identify an object by touch (also a DCML function) requires intact two-point discrimination. * **Rule of Thumb:** If the sensation requires "precision" or "localization," think **Dorsal Column**. If it is "protective" (pain/heat), think **Lateral Spinothalamic**.

Q: In mammals, horizontal acceleration is detected by which structure?

Utricle. **Explanation:** The vestibular apparatus in the inner ear is responsible for maintaining equilibrium and detecting motion. It is divided into the **otolith organs** (utricle and saccule) and the **semicircular canals**. 1. **Why Utricle is Correct:** The utricle contains a sensory epithelium called the **macula**, which is oriented **horizontally** when the head is upright. Because of this orientation, the hair cells are maximally stimulated by **horizontal linear acceleration** (e.g., moving forward in a car) and head tilting in the frontal/sagittal planes. 2. **Why Saccule is Incorrect:** The macula of the saccule is oriented **vertically**. Therefore, it primarily detects **vertical linear acceleration** (e.g., moving in an elevator) and the force of gravity. 3. **Why Cupula/Ampulla are Incorrect:** These structures are part of the semicircular canals. The **ampulla** is the dilated end of the canal containing the sensory hair cells, and the **cupula** is the gelatinous mass overlying them. These structures detect **angular (rotational) acceleration**, not linear acceleration. **High-Yield Clinical Pearls for NEET-PG:** * **Otoliths (Statoconia):** These are calcium carbonate crystals that provide mass to the otolithic membrane, making it sensitive to gravity and inertia. * **Benign Paroxysmal Positional Vertigo (BPPV):** Caused when otoliths from the utricle dislodge and enter the semicircular canals (most commonly the posterior canal). * **Striola:** A central line in the macula; hair cells are arranged in opposing directions on either side of the striola, allowing the brain to detect movement in multiple directions. * **Summary Rule:** * **Utricle:** Horizontal acceleration. * **Saccule:** Vertical acceleration. * **Semicircular Canals:** Angular acceleration.

Q: Stimulation of which nerve leads to an elevated mood?

Olfactory nerve. The correct answer is **B. Olfactory nerve**. ### **Explanation** The olfactory system is unique among sensory systems because it has a direct anatomical connection to the **limbic system** (the emotional center of the brain) without an obligatory relay in the thalamus. Olfactory neurons project to the olfactory bulb, which then sends signals to the **amygdala** and the **hippocampus**. These structures are responsible for processing emotions, memory, and mood. This direct link explains why certain scents can instantly trigger vivid memories or alter emotional states. Aromatherapy and the use of specific scents to alleviate depression or anxiety are based on this physiological pathway. ### **Analysis of Incorrect Options** * **A. Optic nerve (CN II):** Primarily involved in vision. While visual stimuli can influence mood, the primary pathway is directed to the lateral geniculate nucleus (LGN) and the visual cortex, not directly to the emotional centers. * **C. Trochlear nerve (CN IV):** A pure motor nerve that innervates the superior oblique muscle of the eye. It has no sensory or emotional processing functions. * **D. Trigeminal nerve (CN V):** Primarily responsible for facial sensation and motor functions (mastication). While it carries "common chemical sense" (e.g., the sting of ammonia), it is not associated with mood elevation. ### **NEET-PG High-Yield Pearls** * **Direct Pathway:** Olfaction is the only sense that bypasses the thalamus to reach the primary sensory cortex. * **Anatomy:** The primary olfactory cortex includes the piriform cortex, amygdala, and entorhinal cortex. * **Clinical Link:** Anosmia (loss of smell) is frequently associated with an increased risk of developing clinical depression. * **Regeneration:** Olfactory receptor neurons are one of the few neurons in the adult human body that undergo continuous replacement throughout life.

Q: A 22-year-old man presents with increasing difficulty reading the newspaper. His vision problem most likely results from an inability to contract which of the following?

Ciliary body. ### Explanation The clinical presentation describes a failure of **accommodation**, the process by which the eye increases its refractive power to focus on near objects (like a newspaper). **1. Why the Ciliary Body is Correct:** Accommodation is mediated by the **parasympathetic fibers** of the Oculomotor nerve (CN III). When focusing on a near object, the **ciliary muscle contracts**. This contraction reduces the tension on the **suspensory ligaments (zonules of Zinn)**. With the tension released, the natural elasticity of the lens allows it to become more spherical (convex), thereby increasing its dioptric power to focus light from near objects onto the retina. An inability to contract the ciliary body prevents this rounding of the lens, leading to blurred near vision. **2. Why the Other Options are Incorrect:** * **Iris:** The iris controls the diameter of the pupil (miosis/mydriasis) to regulate light entry. While miosis occurs during the accommodation reflex to increase depth of field, it is not the primary mechanism for changing focal length. * **Suspensory Ligaments:** These are passive connective tissue strands. They do not "contract"; they are either pulled taut (when the ciliary muscle relaxes) or become slack (when the ciliary muscle contracts). * **Extraocular Muscles:** These muscles (e.g., medial rectus) are responsible for eye movements and convergence. While convergence is part of the "Near Triad," the actual change in refractive power is intraocular. **3. NEET-PG High-Yield Pearls:** * **The Near Triad:** 1. Pupillary constriction (Miosis), 2. Convergence of eyeballs, 3. Contraction of ciliary muscle (Accommodation). * **Presbyopia:** An age-related loss of accommodation due to decreased lens elasticity, not ciliary muscle failure. * **Drug Action:** Atropine (muscarinic antagonist) causes **cycloplegia** (paralysis of the ciliary muscle), resulting in a loss of accommodation.

Q: Which of the following is a phasic receptor?

Meissner's Corpuscle. ### Explanation The classification of sensory receptors into **Phasic** and **Tonic** is based on their adaptation rate to a constant stimulus. **1. Why Meissner’s Corpuscle is the Correct Answer:** Meissner’s corpuscles are **Rapidly Adapting (Phasic)** receptors. They respond vigorously at the onset and offset of a stimulus but remain silent during a sustained, constant pressure. This characteristic makes them specialized for detecting **fine touch, low-frequency vibration (flutter), and moving touch** (e.g., feeling the texture of a surface as your finger slides over it). **2. Analysis of Incorrect Options:** * **Ruffini’s Ending (Option A):** These are **Slowly Adapting (Tonic)** receptors. they respond to skin stretch and joint deformation, providing continuous information about the state of the body. * **Merkel’s Disc (Option B):** These are **Slowly Adapting (Tonic)** receptors located in the basal layer of the epidermis. They detect steady pressure and static features like shapes and edges. * **Krause’s End Bulb (Option D):** Traditionally associated with cold thermoreception, these are generally considered **Slowly Adapting** receptors found in conjunctiva and mucous membranes. **3. High-Yield Clinical Pearls for NEET-PG:** * **The "M" Rule:** Both **M**eissner and **M**erkel are found in the superficial layers (dermal papillae/epidermis), but **M**eissner is **M**oving/Phasic, while **M**erkel is Static/Tonic. * **Pacinian Corpuscle:** The most rapidly adapting receptor of all; it detects **high-frequency vibration**. * **Receptive Fields:** Meissner and Merkel have **small** receptive fields (precise localization), whereas Pacinian and Ruffini have **large** receptive fields (diffuse localization). * **Summary Table:** * **Phasic (Rapid):** Meissner (Flutter), Pacinian (Vibration). * **Tonic (Slow):** Merkel (Pressure), Ruffini (Stretch).

Q: Transducin is required for what sensory process?

Vision. **Explanation:** **Transducin** is a specialized G-protein (specifically $G_t$) essential for the process of **phototransduction** in the retina. When light hits the photoreceptors (rods and cones), it activates the pigment rhodopsin. Activated rhodopsin then activates **Transducin**, which in turn stimulates the enzyme **Phosphodiesterase (PDE)**. PDE breaks down cyclic GMP (cGMP), leading to the closure of sodium channels, hyperpolarization of the photoreceptor, and the eventual transmission of a visual signal to the brain. **Why other options are incorrect:** * **Smell (Olfaction):** This process utilizes a different G-protein called **$G_{olf}$**. Activation leads to the stimulation of Adenylyl Cyclase and an increase in cAMP, not Transducin. * **Hearing and Balance:** Both these senses rely on **mechanoreceptors** (hair cells in the cochlea and vestibular apparatus). Signal transduction here is mediated by the mechanical opening of potassium channels via tip links, not by G-protein coupled receptors like Transducin. **High-Yield Clinical Pearls for NEET-PG:** * **Hyperpolarization:** Remember that photoreceptors are unique because they **hyperpolarize** (become more negative) in response to a stimulus (light), whereas most other sensory receptors depolarize. * **Dark Current:** In the dark, cGMP levels are high, keeping sodium channels open; this state is known as the "dark current." * **Vitamin A:** Retinal, a component of rhodopsin, is derived from Vitamin A. Deficiency leads to Nyctalopia (night blindness) due to impaired rod function.

Q: Which of the following is true about color blindness?

Female only. ### Explanation The correct answer is **B. Hereditary**, although the provided key indicates "Female only." In standard medical physiology and genetics, color blindness is primarily a **hereditary** condition. **1. Why "Hereditary" is the correct concept:** Congenital color blindness is most commonly an **X-linked recessive** disorder. It occurs due to mutations in the genes responsible for producing photopigments in the cones (specifically the OPN1LW and OPN1MW genes on the X chromosome). Because it is genetic, it is present from birth and remains stable throughout life. **2. Analysis of Options:** * **A. Age-related:** While conditions like cataracts or macular degeneration can affect color perception, true "color blindness" (deficiency in cone pigments) is congenital, not a result of the aging process. * **C. Males only:** While significantly more common in males (approx. 8%) due to the X-linked inheritance pattern, it is **not exclusive** to them. * **D. Female only:** This is medically incorrect. Females can be color blind if they inherit two defective X chromosomes (one from a carrier/affected mother and one from an affected father), though the prevalence is low (approx. 0.5%). **3. NEET-PG High-Yield Pearls:** * **Inheritance:** Most common type is **Red-Green color blindness**, inherited as X-linked recessive. * **Trichromatic Theory:** Normal vision uses three cones (S-Blue, M-Green, L-Red). * **Terminology:** * *Protanopia:* Absence of red receptors. * *Deuteranopia:* Absence of green receptors (Most common). * *Tritanopia:* Absence of blue receptors (Rare, autosomal inheritance). * **Testing:** **Ishihara Charts** are the gold standard for screening; **Nagel’s Anomaloscope** is used for definitive diagnosis. *Note: If a specific exam source marks "Female only" as correct, it is likely a technical error in the question bank, as medical science confirms it is a male-predominant hereditary condition.*

Q: Which of the following statements regarding the movements of the cilia in the inner ear is incorrect?

Cilia movement occurs when the perilymph moves.. ### Explanation The sensory hair cells of the inner ear are located within the **membranous labyrinth**, which is filled with **endolymph**. The movement of cilia is governed by the dynamics of this endolymph, not the perilymph. **1. Why Option C is Incorrect (The Correct Answer):** The cilia (stereocilia and kinocilia) of the vestibular hair cells are embedded in the cupula (semicircular canals) or the otolithic membrane (utricle/saccule). These structures are bathed in **endolymph**. While perilymph surrounds the membranous labyrinth, it does not come into direct contact with the cilia. Therefore, cilia movement is triggered by the displacement of endolymph, not perilymph. **2. Analysis of Other Options:** * **Option A:** Head rotation causes the bony labyrinth to move. Due to inertia, the endolymph lags behind, creating relative fluid motion that bends the cilia. * **Option B:** When a moving person stops suddenly, the momentum of the endolymph causes it to continue moving briefly (post-rotatory nystagmus principle), which deflects the cilia. * **Option D:** Inertia is the primary physical principle behind vestibular function. The "lag" of the endolymph relative to the head's movement is what provides the mechanical force to bend the cilia. **High-Yield NEET-PG Pearls:** * **Endolymph vs. Perilymph:** Endolymph is unique because it is high in **Potassium ($K^+$)** and low in Sodium ($Na^+$), resembling intracellular fluid. Perilymph resembles ECF (high $Na^+$). * **Tip Links:** Mechanical gated $K^+$ channels are located at the tips of stereocilia. Bending **towards** the kinocilium causes depolarization; bending **away** causes hyperpolarization. * **Scarpa’s Ganglion:** Contains the cell bodies of the vestibular nerve fibers that innervate these hair cells.

Question 1

The two-point threshold test assesses the integrity of which pathway?

Accepted Answer

Dorsal column

Answer

Anterior spinothalamic tract

Answer

Lateral corticospinal tract

Answer

Lateral spinothalamic tract

Question 2

In mammals, horizontal acceleration is detected by which structure?

Accepted Answer

Utricle

Answer

Saccule

Answer

Cupula of semicircular canal

Answer

Ampulla of semicircular canal

Question 3

Which of the following physiologic responses occurs as the pitch of a sound is increased?

Accepted Answer

The location of maximal basilar membrane displacement moves toward the base of the cochlea

Answer

The frequency of action potentials in auditory nerve fibers increases

Answer

Units in the auditory nerve become responsive to a wider range of sound frequencies

Answer

A greater number of hair cells become activated

Question 4

Stimulation of which nerve leads to an elevated mood?

Accepted Answer

Olfactory nerve

Answer

Optic nerve

Answer

Trochlear nerve

Answer

Trigeminal nerve

Question 5

A 22-year-old man presents with increasing difficulty reading the newspaper. His vision problem most likely results from an inability to contract which of the following?

Accepted Answer

Ciliary body

Answer

Iris

Answer

Suspensory ligaments

Answer

Extraocular muscles

Question 6

Which of the following is a phasic receptor?

Accepted Answer

Meissner's Corpuscle

Answer

Ruffini's Ending

Answer

Merkel's Disc

Answer

Krause's End Bulb

Question 7

Transducin is required for what sensory process?

Accepted Answer

Vision

Answer

Smell

Answer

Hearing

Answer

Balance

Question 8

Which of the following is true about color blindness?

Accepted Answer

Female only

Answer

Age related

Answer

Hereditary

Answer

Males only

Question 9

If a single spinal nerve is cut, the area of tactile loss is always greater than the area of loss of painful sensations, because

Accepted Answer

The degree of overlap of fibres carrying tactile sensation is much less

Answer

Tactile information is carried by myelinated fast conducting fibres

Answer

Tactile receptors adapt quickly

Answer

In the primary sensory cortex, tactile sensation is represented on a larger area

Question 10

Which of the following statements regarding the movements of the cilia in the inner ear is incorrect?

Accepted Answer

Cilia movement occurs when the perilymph moves.

Answer

Cilia movement occurs when the head is rotated.

Answer

Cilia movement occurs when a moving person suddenly stops.

Answer

Cilia movement is guided by the inertia of the endolymph.

Sensory Systems — MCQs

Sensory Systems — MCQs

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