Sensory Systems Practice Questions

Q: Taste sensation is carried by all nerves except:

Trigeminal nerve. **Explanation:** The sensation of taste (gustation) is mediated by specialized chemoreceptors located in taste buds. These are innervated by three specific cranial nerves (CN VII, IX, and X). The **Trigeminal nerve (CN V)** is the correct answer because it does **not** carry special visceral afferent (taste) fibers; instead, it provides general somatic afference (touch, pain, and temperature) to the anterior two-thirds of the tongue via its lingual branch. **Analysis of Options:** * **Facial Nerve (CN VII):** Carries taste from the **anterior 2/3rd** of the tongue via the **chorda tympani** nerve. * **Glossopharyngeal Nerve (CN IX):** Carries taste from the **posterior 1/3rd** of the tongue (including the circumvallate papillae). * **Vagus Nerve (CN X):** Carries taste from the **extreme posterior part** of the tongue, the epiglottis, and the pharynx via the internal laryngeal nerve. * **Trigeminal Nerve (CN V):** While the lingual nerve (a branch of V3) physically carries the chorda tympani fibers to the tongue, the taste fibers themselves originate from the facial nerve, not the trigeminal. **High-Yield Clinical Pearls for NEET-PG:** * **Nucleus Tractus Solitarius (NTS):** All taste fibers from CN VII, IX, and X terminate in the gustatory portion (rostral part) of the NTS in the medulla. * **Ageusia:** Loss of taste sensation. * **Papillae:** Taste buds are found on fungiform, circumvallate, and foliate papillae. **Filiform papillae** are the most numerous but contain **no taste buds** (only tactile receptors). * **Pathway:** NTS → Thalamus (VPM nucleus) → Primary Gustatory Cortex (Insula and frontal operculum).

Q: What stimulates the macula?

All of the above. The **maculae** are the sensory receptors located within the **utricle and saccule** of the inner ear. They are responsible for detecting **static equilibrium** and **linear acceleration**. ### **Explanation of the Correct Answer** The maculae consist of hair cells embedded in a gelatinous **otolithic membrane**, which contains calcium carbonate crystals called **otoconia**. * **Gravity & Head Position (Static Equilibrium):** When the head tilts, gravity pulls on the heavy otoconia. This shifts the otolithic membrane, bending the hair cell stereocilia and signaling the brain about the head's orientation relative to the vertical axis. * **Linear Acceleration (Dynamic Equilibrium):** When the body moves in a straight line (e.g., a car accelerating or an elevator rising), the inertia of the otoconia causes the membrane to lag behind the sensory epithelium. This displacement stimulates the hair cells. Since the macula responds to gravitational pull, changes in head tilt, and straight-line movement, **Option D (All of the above)** is correct. ### **Why other options are not "the only" answer** Options A, B, and C are all individual components of macular function. Selecting only one would be incomplete, as the vestibular system integrates all three stimuli to maintain balance and posture. ### **High-Yield Clinical Pearls for NEET-PG** * **Utricle vs. Saccule:** The Utricle detects **horizontal** acceleration (e.g., driving a car), while the Saccule detects **vertical** acceleration (e.g., riding an elevator). * **Semicircular Canals:** These detect **angular (rotational) acceleration**, not linear. Their sensory organ is the **Crista Ampullaris**. * **BPPV (Benign Paroxysmal Positional Vertigo):** This occurs when otoconia from the macula dislodge and enter the semicircular canals, causing brief episodes of vertigo. * **Striola:** The central landmark of the macula where hair cells change their orientation.

Q: Auditory receptors are found in which structure?

Organ of Corti. **Explanation:** The **Organ of Corti** is the correct answer because it is the specialized sensory organ of hearing located within the cochlea of the inner ear. It sits on the basilar membrane and contains **hair cells** (inner and outer), which are the actual auditory receptors. These receptors convert mechanical sound vibrations (fluid waves) into electrical nerve impulses via the vestibulocochlear nerve (CN VIII). **Analysis of Incorrect Options:** * **A. Semicircular canals:** These are part of the vestibular system, not the auditory system. They contain receptors (crista ampullaris) that detect **rotational acceleration** and maintain dynamic equilibrium. * **C. Ear ossicles:** These are three tiny bones (Malleus, Incus, Stapes) in the middle ear. Their function is mechanical—they **amplify and conduct** sound vibrations from the tympanic membrane to the oval window; they do not contain receptors. * **D. Tympanic membrane:** Also known as the eardrum, this structure marks the boundary between the outer and middle ear. It vibrates in response to sound waves but serves as a **transmitter**, not a sensory receptor site. **High-Yield NEET-PG Pearls:** * **Endolymph vs. Perilymph:** The Organ of Corti is bathed in **endolymph**, which is unique for being high in Potassium ($K^+$) and low in Sodium ($Na^+$). * **Tonotopic Organization:** The **base** of the cochlea (near the oval window) detects high-frequency sounds, while the **apex** (helicotrema) detects low-frequency sounds. * **Clinical Correlation:** Damage to the hair cells in the Organ of Corti (due to loud noise or ototoxic drugs like aminoglycosides) results in **sensorineural hearing loss**.

Q: Hot water bottles relieve pain from abdominal spasms by which mechanism?

Stimulation of touch receptors. ### Explanation The relief of pain via hot water bottles is a classic clinical application of the **Gate Control Theory of Pain**, proposed by Melzack and Wall. **Why Option A is Correct:** When a hot water bottle is applied to the skin, it provides thermal and tactile stimuli. These stimuli activate large-diameter, myelinated **A-beta (Aβ) sensory fibers** (responsible for touch and pressure). These fibers enter the dorsal horn of the spinal cord and stimulate inhibitory interneurons (specifically in the *substantia gelatinosa*). These interneurons release enkephalins, which inhibit the transmission of pain signals from small, unmyelinated **C-fibers** (carrying dull, aching pain from spasms) to the second-order projection neurons. Essentially, the "gate" for pain is closed by the stimulation of non-nociceptive touch/tactile receptors. **Analysis of Incorrect Options:** * **B. Stimulation of cholinergic fibers:** Cholinergic fibers are primarily involved in the parasympathetic nervous system and neuromuscular junctions; they do not mediate the immediate sensory modulation of pain in the dorsal horn. * **C & D. Inhibition of receptors:** The mechanism is based on the **activation** of specific receptors (thermoreceptors and mechanoreceptors) to override pain, rather than the inhibition of cold or heat receptors themselves. **High-Yield Clinical Pearls for NEET-PG:** * **Gate Control Theory:** Large Aβ fibers "close" the gate; small C and Aδ fibers "open" the gate. * **Transcutaneous Electrical Nerve Stimulation (TENS):** Works on the same principle as the hot water bottle—stimulating Aβ fibers to suppress chronic pain. * **Substantia Gelatinosa (Lamina II):** The anatomical site in the dorsal horn where this "gating" occurs. * **Counter-irritation:** Rubbing a bumped knee or using liniments are other examples of Aβ fiber stimulation relieving pain.

Q: When light strikes the eye, there is an increase in which of the following?

The activity of transducin. ### Explanation The visual transduction cascade is a unique process where light stimulation leads to the **hyperpolarization** of photoreceptors (rods and cones), rather than depolarization. **1. Why Option A is Correct:** When light (photons) strikes the retina, it is absorbed by rhodopsin, converting 11-cis retinal to all-trans retinal. This activates **metarhodopsin II**, which in turn activates a G-protein called **transducin**. Transducin then activates cGMP-phosphodiesterase (PDE), which breaks down cGMP. The decrease in cGMP levels causes the closure of Na⁺ channels, leading to hyperpolarization. **2. Why the Other Options are Incorrect:** * **Option B:** Because light causes hyperpolarization, it leads to a **decrease** in the release of the neurotransmitter (glutamate) from the synaptic terminals of photoreceptors. Photoreceptors release the most transmitter in the dark. * **Option C:** While 11-cis retinal is converted to all-trans retinal, the all-trans retinal is rapidly shuttled out of the photoreceptor to the **Retinal Pigment Epithelium (RPE)** for regeneration. Therefore, its concentration within the photoreceptor does not "increase" in a sustained manner during active signaling; rather, it is consumed. * **Option D:** The closure of cyclic nucleotide-gated channels (which are permeable to both Na⁺ and Ca²⁺) leads to a **decrease** in intracellular calcium concentration during light exposure. ### High-Yield NEET-PG Pearls * **Dark Current:** In the dark, photoreceptors are depolarized (~ -40 mV) due to constant Na⁺ influx. Light "shuts off" this current. * **Vitamin A:** It is the precursor for 11-cis retinal. Deficiency leads to Nyctalopia (night blindness). * **RPE Function:** The Retinal Pigment Epithelium is essential for the reisomerization of all-trans retinal back to 11-cis retinal (the visual cycle). * **Second Messenger:** In phototransduction, the second messenger is **cGMP**, not cAMP.

Q: The visual center is present in which lobe of the brain?

Occipital lobe. **Explanation:** The primary visual center is located in the **Occipital lobe**, specifically in the area surrounding the calcarine sulcus. This region is designated as **Brodmann area 17** (Primary Visual Cortex or V1). It receives sensory input from the lateral geniculate nucleus (LGN) of the thalamus via optic radiations. Surrounding this are Brodmann areas 18 and 19 (Visual Association Areas), which are responsible for interpreting visual stimuli, such as recognizing objects and perceiving movement. **Analysis of Incorrect Options:** * **Parietal lobe:** Primarily houses the **Somatosensory cortex** (Brodmann areas 3, 1, 2). It is involved in processing tactile sensation, proprioception, and spatial awareness (the "where" pathway of vision). * **Frontal lobe:** Contains the **Motor cortex** and is responsible for executive functions, personality, and voluntary motor control. It also houses the **Frontal Eye Field (Area 8)**, which controls voluntary conjugate eye movements, but not visual perception. * **Temporal lobe:** Contains the **Primary Auditory cortex** (Areas 41, 42) and is involved in memory (hippocampus) and language comprehension (Wernicke’s area). It also processes the "what" pathway (object recognition) of vision. **High-Yield Clinical Pearls for NEET-PG:** * **Macular Sparing:** A lesion of the occipital cortex (e.g., PCA stroke) often results in contralateral homonymous hemianopia with macular sparing due to the dual blood supply (PCA and MCA) to the occipital pole. * **Meyer’s Loop:** Fibers of the optic radiation that pass through the **Temporal lobe**; a lesion here causes "pie in the sky" (superior quadrantanopia). * **Baum’s Loop:** Fibers passing through the **Parietal lobe**; a lesion here causes "pie on the floor" (inferior quadrantanopia).

Q: Perception of white light is due to:

Stimulation of red, blue and green cones equally. ### Explanation **Core Concept: The Young-Helmholtz Trichromatic Theory** The perception of color is based on the **Trichromatic Theory**, which states that the human retina contains three types of cone photoreceptors, each sensitive to a specific range of wavelengths: **S-cones (Blue)**, **M-cones (Green)**, and **L-cones (Red)**. The sensation of **white light** is a result of the simultaneous and **equal stimulation** of all three types of cones. When the brain receives balanced signals from the red, green, and blue cones, it interprets the combined input as white. This is an additive process; conversely, the absence of any cone stimulation results in the perception of black. **Analysis of Options:** * **Option D (Correct):** Equal stimulation of all three cone types (Red, Blue, and Green) is the physiological requirement for the perception of white light. * **Options A, B, and C (Incorrect):** If one cone type is stimulated significantly more than the others, the brain perceives a specific hue rather than white. For example, predominant stimulation of L-cones results in the perception of red, M-cones in green, and S-cones in blue. **High-Yield Clinical Pearls for NEET-PG:** * **Photopigments:** Cones contain **Photopsins** (Iodopsin), while rods contain **Rhodopsin**. * **Color Blindness:** The most common type is **Red-Green color blindness**, which is an **X-linked recessive** condition. It is most frequently due to the absence of red (Protanopia) or green (Deuteranopia) cones. * **Ishihara Charts:** These are the gold standard clinical tool used to screen for color vision deficiencies. * **Fovea Centralis:** This area of the retina contains the highest concentration of cones and lacks rods, making it the point of highest visual acuity and color perception.

Question 1

Taste sensation is carried by all nerves except:

Accepted Answer

Trigeminal nerve

Answer

Facial nerve

Answer

Vagus nerve

Answer

Glossopharyngeal nerve

Question 2

What stimulates the macula?

Accepted Answer

All of the above

Answer

Gravity

Answer

Head position change

Answer

Linear acceleration

Question 3

Auditory receptors are found in which structure?

Accepted Answer

Organ of Corti

Answer

Semicircular canal

Answer

Ear ossicles

Answer

Tympanic membrane

Question 4

A 50-year-old woman undergoes a neurologic exam that indicates loss of pain and temperature sensitivity, vibratory sense, and proprioception in the left side of the body. These symptoms could be explained by:

Accepted Answer

A tumor affecting the right postcentral gyrus

Answer

A tumor on the right medial lemniscal pathway in the spinal cord

Answer

A tumor on the left medial lemniscal pathway in the spinal cord

Answer

A large tumor in the right ventrolateral spinal cord

Question 5

In dark adaptation, what occurs?

Accepted Answer

No change in the dioptric power of the eye

Answer

Breakdown of rhodopsin

Answer

Increased threshold for vision

Answer

No role for cones

Question 6

Hot water bottles relieve pain from abdominal spasms by which mechanism?

Accepted Answer

Stimulation of touch receptors

Answer

Stimulation of cholinergic fibers

Answer

Inhibition of cold receptors

Answer

Inhibition of heat receptors

Question 7

When light strikes the eye, there is an increase in which of the following?

Accepted Answer

The activity of transducin

Answer

The amount of transmitter released from the photoreceptors

Answer

The concentration of all-trans retinal within the photoreceptors

Answer

The concentration of calcium within the photoreceptors

Question 8

Which of the following sensations is most affected by cortical lesions?

Accepted Answer

Proprioception

Answer

Temperature

Answer

Itch

Answer

Pain

Question 9

The visual center is present in which lobe of the brain?

Accepted Answer

Occipital lobe

Answer

Parietal lobe

Answer

Frontal lobe

Answer

Temporal lobe

Question 10

Perception of white light is due to:

Accepted Answer

Stimulation of red, blue and green cones equally

Answer

Stimulation of red cones more than blue or green

Answer

Stimulation of blue cones more than red or green

Answer

Stimulation of green cones more than blue or red

Sensory Systems — MCQs

Sensory Systems — MCQs

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