Sensory Systems Practice Questions

Q: Proprioception is mediated by which of the following pathways?

Dorsal column. **Explanation:** The **Dorsal Column-Medial Lemniscal (DCML) pathway** is the primary sensory tract responsible for conveying "fine" sensations. It carries **conscious proprioception** (sense of position and movement), fine touch, pressure, vibration, and two-point discrimination. These fibers are large, myelinated, and have high conduction velocities. They ascend ipsilaterally in the spinal cord and decussate (cross over) in the medulla at the level of the internal arcuate fibers. **Analysis of Incorrect Options:** * **A. Lateral Spinothalamic Tract:** This pathway primarily carries sensations of **pain and temperature**. * **B. Ventral (Anterior) Spinothalamic Tract:** This pathway is responsible for **crude touch and pressure**. * **C. Corticospinal Tract:** This is a descending **motor pathway**, not a sensory pathway. It controls voluntary skilled movements of the limbs. **High-Yield Clinical Pearls for NEET-PG:** * **Tabes Dorsalis:** A late stage of neurosyphilis that specifically damages the dorsal columns, leading to loss of proprioception, a positive Romberg sign, and a "stamping gait." * **Unconscious Proprioception:** While conscious proprioception travels via the Dorsal Columns to the cortex, **unconscious proprioception** (required for coordination) is mediated by the **Spinocerebellar tracts** to the cerebellum. * **Brown-Séquard Syndrome:** In a spinal cord hemisection, proprioception and vibration are lost **ipsilaterally** (same side) because the dorsal columns do not decussate until they reach the brainstem.

Q: Damage to which of the following structures might produce hair cell loss?

Organ of Corti. **Explanation:** The **Organ of Corti** is the specialized sensory organ of hearing located within the cochlear duct (scala media). It contains the **hair cells** (inner and outer), which act as mechanoreceptors. These hair cells are the actual sensory transducers that convert mechanical sound vibrations into electrical nerve impulses. Therefore, direct damage to the Organ of Corti leads to the destruction of these hair cells, resulting in sensorineural hearing loss. **Analysis of Options:** * **Basilar Membrane (Option A):** This is the structural floor upon which the Organ of Corti rests. While its vibration is essential for stimulating hair cells, the membrane itself is a fibrous tissue layer, not the site where hair cells are located. * **Reissner’s Membrane (Option B):** Also known as the vestibular membrane, it separates the scala media from the scala vestibuli. It maintains the ionic gradient of endolymph but does not contain sensory receptors. * **Scala Tympani (Option D):** This is one of the perilymph-filled cavities of the cochlea. It is an extracellular space and does not contain the cellular architecture of the hair cells. **High-Yield NEET-PG Pearls:** * **Inner Hair Cells:** Responsible for 90-95% of auditory neurotransmission to the VIIIth cranial nerve. * **Outer Hair Cells:** Act as "cochlear amplifiers" by changing their length (electromotility) via the protein **Prestin**. * **Ototoxicity:** Drugs like Aminoglycosides and Cisplatin specifically target and destroy hair cells in the Organ of Corti. * **Endolymph:** The Organ of Corti is bathed in endolymph, which is unique for being high in **Potassium (K+)** and low in Sodium (Na+).

Q: Features of Horner's syndrome include all of the following except?

Exophthalmos. **Explanation:** Horner’s syndrome is caused by a lesion in the **sympathetic pathway** supplying the eye and face. This pathway is responsible for "fight or flight" responses; its interruption leads to a loss of sympathetic tone. **Why Exophthalmos is the correct answer:** Exophthalmos (protrusion of the eyeball) is not a feature of Horner’s syndrome. In fact, patients often exhibit **Enophthalmos** (the appearance of a sunken eyeball). This is a "pseudo-enophthalmos" caused by the narrowing of the palpebral fissure due to ptosis. True exophthalmos is typically associated with hyperthyroidism (Graves' disease) or orbital tumors. **Analysis of other options:** * **Miosis:** Sympathetic fibers normally innervate the *dilator pupillae* muscle. Their loss results in unopposed parasympathetic action on the *sphincter pupillae*, leading to a constricted pupil (miosis). * **Ptosis:** The sympathetic system supplies the **Müller’s muscle** (superior tarsal muscle), which helps maintain the elevation of the upper eyelid. Paralysis of this muscle causes partial drooping of the eyelid (partial ptosis). * **Anhydrosis:** Sympathetic fibers also supply the sweat glands of the face. Interruption of these fibers leads to a loss of sweating (anhydrosis) on the affected side. **High-Yield Clinical Pearls for NEET-PG:** * **The Triad:** The classic triad is Miosis, Partial Ptosis, and Anhydrosis. * **Ciliospinal Reflex:** This reflex (pupillary dilation in response to pain on the neck) is **absent** in Horner’s syndrome. * **Pancoast Tumor:** A common cause of Horner’s syndrome due to compression of the sympathetic chain by an apical lung carcinoma. * **Cocaine Test:** In Horner’s syndrome, the pupil **fails to dilate** after the administration of cocaine drops.

Q: Which of the following proteins is NOT found in the organ of Corti?

Microtubule associated protein 4. ### Explanation The **organ of Corti** is a highly specialized neuroepithelial structure within the cochlea, relying on a complex cytoskeleton to maintain its architectural integrity and facilitate mechanotransduction. **Why Option C is Correct:** **Microtubule-associated protein 4 (MAP4)** is primarily expressed in non-neuronal tissues and is involved in stabilizing microtubules in dividing cells. While MAPs are crucial for the structural stability of the organ of Corti, research indicates that **MAP2** (found in the cell bodies and dendrites) and **MAP1** are the predominant isoforms in the cochlea. MAP4 is notably absent or not a functional component of the hair cells or supporting cells in the organ of Corti. **Why the Other Options are Incorrect:** * **A. Myosin:** Various unconventional myosins (especially **Myosin VIIa, VI, and XVa**) are critical for the development and movement of stereocilia. Mutations in these proteins are classic causes of hereditary deafness (e.g., Usher Syndrome). * **B. Microtubule-associated protein 2 (MAP2):** This protein is present in the cytoplasm of the hair cells and the supporting cells (like Pillar cells), providing the rigid framework necessary to withstand mechanical vibrations. * **D. Fodrin:** Also known as non-erythroid spectrin, fodrin is located in the **cuticular plate** (the actin-rich apical surface) of hair cells. It helps anchor the stereocilia and maintains the structural tension of the hair cell apex. **High-Yield Facts for NEET-PG:** * **Prestin:** A motor protein found in the outer hair cells (OHCs) responsible for electromotility (cochlear amplifier). * **Tip Links:** Composed of **Cadherin 23** and **Protocadherin 15**; they open the mechano-electrical transduction (MET) channels. * **Actin:** The primary structural protein of stereocilia. Unlike the kinocilium (which has a 9+2 microtubule arrangement), stereocilia are actin-based microvilli.

Q: Which of the following is true about A-delta fibers?

Associated with fast pain. **Explanation:** Pain sensation is transmitted to the Central Nervous System (CNS) via two distinct types of primary afferent fibers: **A-delta (Aδ)** and **C fibers**. **Why Option B is correct:** A-delta fibers are responsible for **fast pain** (also known as first, sharp, or pricking pain). This is due to their structural characteristics: they are **thinly myelinated** and have a larger diameter compared to C fibers. Myelination allows for saltatory conduction, resulting in a relatively fast conduction velocity (approx. 6–30 m/s). This allows the body to perceive and react to a noxious stimulus almost instantaneously. **Why other options are incorrect:** * **Option A:** **Slow pain** (also known as second, dull, aching, or burning pain) is mediated by **C fibers**. These fibers are **unmyelinated** and have a very small diameter, leading to a much slower conduction velocity (approx. 0.5–2 m/s). * **Option C & D:** These are incorrect because A-delta and C fibers have distinct, non-overlapping roles in the temporal perception of pain. **High-Yield NEET-PG Pearls:** * **Neurotransmitter:** A-delta fibers primarily use **Glutamate** (fast action), while C fibers use **Substance P** (slow, prolonged action). * **Localization:** Fast pain (A-delta) is well-localized; slow pain (C fibers) is poorly localized. * **Rexed Laminae:** A-delta fibers terminate mainly in **Laminae I and V** of the dorsal horn; C fibers terminate in **Laminae II and III** (Substantia Gelatinosa). * **Neospinothalamic vs. Paleospinothalamic:** A-delta fibers constitute the Neospinothalamic tract, while C fibers constitute the Paleospinothalamic tract.

Q: Pain is carried by which type of nerve fibers?

C. **Explanation:** Pain sensation is transmitted from the periphery to the central nervous system via two specific types of primary afferent fibers: **Aδ (A-delta)** and **C fibers**. 1. **Why Option D is Correct:** **C fibers** are small-diameter, **unmyelinated** nerve fibers with slow conduction velocities (0.5–2 m/s). They are responsible for "slow pain"—the dull, aching, or burning sensation that is poorly localized and persists after the initial stimulus. Since Aδ is not an option here, C fibers are the correct choice for carrying pain. 2. **Why Other Options are Incorrect:** * **Aα (Alpha):** These are the largest, fastest myelinated fibers. They primarily carry **proprioception** (from muscle spindles and Golgi tendon organs) and somatic motor impulses. * **Aβ (Beta):** These are medium-sized myelinated fibers that carry sensations of **fine touch, pressure, and vibration**. According to the *Gate Control Theory*, stimulation of Aβ fibers can actually inhibit pain transmission in the spinal cord. * **B fibers:** These are small, myelinated **preganglionic autonomic** fibers. They do not carry sensory information like pain. **High-Yield Clinical Pearls for NEET-PG:** * **Fast vs. Slow Pain:** Fast pain (sharp, pricking) is carried by **Aδ fibers** (glutamate is the neurotransmitter). Slow pain (chronic, burning) is carried by **C fibers** (Substance P is the neurotransmitter). * **Erlanger-Gasser Classification:** Remember the order of sensitivity to local anesthetics: **Type C > Type B > Type A**. * **First to be blocked:** In a nerve block, B fibers (autonomic) are blocked first, followed by C and Aδ (pain/temp), then Aβ (touch), and finally Aα (motor).

Q: The otolithic organs are responsible for which sensory function?

Linear acceleration. **Explanation:** The vestibular apparatus of the inner ear consists of the semicircular canals and the **otolithic organs** (the **Utricle** and **Saccule**). **Why Linear Acceleration is Correct:** The otolithic organs contain a sensory epithelium called the **macula**. This macula is covered by a gelatinous otolithic membrane embedded with calcium carbonate crystals called **statoconia (otoliths)**. Because these crystals are denser than the surrounding endolymph, they have greater inertia. When the head moves linearly or tilts, gravity or acceleration causes the otoliths to shift, dragging the gelatinous layer and bending the hair cell stereocilia. * **Utricle:** Primarily detects **horizontal** linear acceleration (e.g., moving in a car). * **Saccule:** Primarily detects **vertical** linear acceleration (e.g., moving in an elevator). **Analysis of Incorrect Options:** * **A. Hearing:** This is the function of the **Organ of Corti** located within the cochlea. * **B. Rotatory nystagmus:** This is a clinical sign resulting from the stimulation of the semicircular canals (Vestibulo-ocular reflex), not a primary sensory function of the otoliths. * **D. Angular acceleration:** This is detected by the **Crista Ampullaris** located in the ampulla of the **Semicircular Canals**, which respond to rotational head movements. **High-Yield Clinical Pearls for NEET-PG:** * **BPPV (Benign Paroxysmal Positional Vertigo):** Caused when otoliths (canaliths) from the utricle displace into the semicircular canals (most commonly the posterior canal). * **Striola:** The central landmark in the macula; hair cells are oriented toward the striola in the utricle and away from it in the saccule. * **Scarpa’s Ganglion:** Contains the cell bodies of the vestibular nerve fibers.

Question 1

Proprioception is mediated by which of the following pathways?

Accepted Answer

Dorsal column

Answer

Lateral spinothalamic tract

Answer

Ventral spinothalamic tract

Answer

Corticospinal tract

Question 2

Amacrine cells secrete all except?

Accepted Answer

Acetylcholine

Answer

GABA

Answer

Adrenaline

Answer

Glycine

Question 3

Damage to which of the following structures might produce hair cell loss?

Accepted Answer

Organ of Corti

Answer

Basilar membrane

Answer

Reissner's membrane

Answer

Scala tympani

Question 4

Features of Horner's syndrome include all of the following except?

Accepted Answer

Exophthalmos

Answer

Miosis

Answer

Ptosis

Answer

Anhydrosis

Question 5

Repetitive stimulation increases pain sensation. What is the probable cause?

Accepted Answer

Hypersensitization

Answer

Decreased reflex time

Answer

Increase in the threshold of pain

Answer

Decreased receptor area

Question 6

Which of the following proteins is NOT found in the organ of Corti?

Accepted Answer

Microtubule associated protein 4

Answer

Myosin

Answer

Microtubule associated protein 2

Answer

Fodrin

Question 7

Which of the following is true about A-delta fibers?

Accepted Answer

Associated with fast pain

Answer

Associated with slow pain

Answer

Both

Answer

None

Question 8

Pain is carried by which type of nerve fibers?

Accepted Answer

C

Answer

Aa

Answer

Ab

Answer

B

Question 9

Which of the following systems does NOT contain neuroepithelium-type sensory receptors?

Accepted Answer

Auditory

Answer

Visual

Answer

Gustatory

Answer

Olfactory

Question 10

The otolithic organs are responsible for which sensory function?

Accepted Answer

Linear acceleration

Answer

Hearing

Answer

Rotatory nystagmus

Answer

Angular acceleration

Sensory Systems — MCQs

Sensory Systems — MCQs

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