Sensory Systems Practice Questions

Q: What is true about the fovea?

Contains only cones. The **fovea centralis** is a small, specialized depression located at the center of the **macula lutea** of the retina. It represents the area of highest visual acuity and color vision. ### **Explanation of the Correct Answer** * **Option B (Contains only cones):** The fovea is unique because it is entirely devoid of rods. It contains a high density of long, slender, and closely packed **cones**. To allow light to pass directly to these photoreceptors without interference, the other retinal layers (ganglion cells and bipolar cells) are displaced peripherally. This anatomical arrangement ensures the highest possible resolution and detailed central vision. ### **Why Other Options are Incorrect** * **Option A & D:** These are incorrect because **rods are completely absent** in the fovea centralis. Rod density actually peaks about 20 degrees away from the fovea and is responsible for peripheral and scotopic (low-light) vision. * **Option C:** The fovea is situated **lateral (temporal)** to the optic disc, not above it. The optic disc (the blind spot) is located medially/nasally relative to the fovea. ### **High-Yield NEET-PG Pearls** * **Visual Acuity:** The fovea is the point of maximum visual acuity because of the 1:1 ratio between cones, bipolar cells, and ganglion cells (no convergence). * **Blood Supply:** The central part of the fovea (foveola) is **avascular**, receiving its nourishment via diffusion from the underlying choriocapillaris. * **Macula Lutea:** It appears yellow due to the presence of carotenoid pigments (**Lutein and Zeaxanthin**), which act as antioxidants and filter harmful blue light. * **Clinical Correlation:** In **Central Retinal Artery Occlusion (CRAO)**, a "Cherry Red Spot" is seen at the fovea because the thin foveal retina allows the underlying red choroid to show through, contrasted against the surrounding pale, edematous retina.

Q: Auditory transmission is via which pathway?

Lateral Lemniscus. **Explanation:** The auditory pathway is a complex, multisynaptic circuit that transmits sound information from the cochlea to the auditory cortex. The correct answer is **Lateral Lemniscus** because it represents the primary ascending tract of the auditory system in the brainstem. **Why Lateral Lemniscus is Correct:** After sound is transduced in the cochlea, signals travel via the vestibulocochlear nerve (CN VIII) to the cochlear nuclei. From there, fibers cross the midline (trapezoid body) and ascend as the **Lateral Lemniscus**. This tract carries auditory information from the superior olivary complex to the inferior colliculus. A high-yield mnemonic for the auditory pathway is **ECOLI**: **E**ighth nerve, **C**ochlear nuclei, **O**livary complex (superior), **L**ateral lemniscus, **I**nferior colliculus. **Why Other Options are Incorrect:** * **Lateral Geniculate Body (LGB):** This is the relay station for the **visual pathway**, not auditory. (Mnemonic: **L** for **L**ight). * **Medial Lemniscus:** This tract carries **fine touch, vibration, and conscious proprioception** (DCML pathway) from the body to the thalamus. * **Pretectal Nucleus:** This structure is involved in the **pupillary light reflex** circuit, located in the midbrain. **High-Yield Clinical Pearls for NEET-PG:** * **Medial Geniculate Body (MGB):** This is the thalamic relay station for hearing (Mnemonic: **M** for **M**usic). * **Bilateral Representation:** Above the level of the cochlear nuclei, auditory information is represented bilaterally. Therefore, a unilateral lesion of the lateral lemniscus or auditory cortex does not cause complete deafness in one ear but rather results in difficulty localizing sound. * **Primary Auditory Cortex:** Located in the superior temporal gyrus (Brodmann areas 41, 42).

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

A alpha fibers. **Explanation:** Proprioception (the sense of body position and movement) requires the fastest possible transmission to the central nervous system to maintain balance and coordinate motor activity. This is achieved via **A-alpha (Aα) fibers**, which are the thickest and most heavily myelinated nerve fibers. **1. Why A-alpha is correct:** According to the Erlanger-Gasser classification, **A-alpha fibers** have the largest diameter (12–20 μm) and the fastest conduction velocity (70–120 m/s). They carry sensory information from **muscle spindles (Ia)** and **Golgi tendon organs (Ib)**, which are the primary receptors for proprioception. **2. Analysis of Incorrect Options:** * **A-beta (Aβ) fibers:** These are slightly smaller and slower than A-alpha. They primarily carry sensations of **fine touch, pressure, and vibration**. * **B fibers:** These are preganglionic autonomic fibers. They are small, myelinated, and have much slower conduction velocities than A-type fibers. * **C fibers:** These are the smallest, **unmyelinated** fibers. They carry "slow" pain (dull, aching), temperature, and crude touch. They have the slowest conduction velocity (0.5–2 m/s). **Clinical Pearls & High-Yield Facts:** * **Order of Susceptibility:** * **Hypoxia:** B > A > C (B fibers are most sensitive). * **Pressure:** A > B > C (A fibers are most sensitive; this is why your foot "falls asleep" when compressed). * **Local Anesthetics:** C > B > A (C fibers are most sensitive; pain is blocked before motor function). * **Fastest to Slowest:** Aα > Aβ > Aγ > Aδ > B > C. * **A-delta (Aδ) fibers** carry "fast" pain (sharp, localized) and cold temperature.

Q: Which function is controlled by the striate cortex of the brain?

Vision. **Explanation:** The **striate cortex**, also known as the **Primary Visual Cortex (Brodmann area 17)**, is located in the occipital lobe, specifically along the calcarine fissure. It is termed "striate" because it contains the **Gennari line**, a distinct white matter band visible to the naked eye, representing myelinated fibers from the lateral geniculate nucleus (LGN) of the thalamus. Its primary function is the initial processing of visual information, including orientation, motion, and edge detection. **Analysis of Options:** * **Vision (Correct):** The striate cortex receives sensory input directly from the LGN. Damage to this area results in cortical blindness or contralateral homonymous hemianopia with macular sparing. * **Speech:** Controlled primarily by **Broca’s area** (Brodmann 44, 45) in the frontal lobe for production and **Wernicke’s area** (Brodmann 22) in the temporal lobe for comprehension. * **Balance:** Primarily regulated by the **cerebellum** and the vestibular system (vestibular nuclei in the brainstem). * **Auditory processing:** Located in the **Primary Auditory Cortex** (Brodmann areas 41, 42), also known as Heschl’s gyri, in the superior temporal lobe. **High-Yield NEET-PG Pearls:** * **Blood Supply:** The primary visual cortex is supplied by the **posterior cerebral artery (PCA)**. * **Macular Sparing:** In PCA strokes, the macula is often spared because the occipital pole has a dual blood supply from both the PCA and the **middle cerebral artery (MCA)**. * **Visual Association Areas:** Brodmann areas 18 and 19 are the extrastriate (association) areas responsible for interpreting visual images.

Q: Which of the following nuclei is involved in both the light reflex and the accommodation reflex?

Edinger-Westphal nucleus. The **Edinger-Westphal (EW) nucleus** is the correct answer because it serves as the common **parasympathetic efferent (motor) limb** for both the light reflex and the accommodation reflex. ### Why the Edinger-Westphal Nucleus is Correct: * **Light Reflex:** When light hits the retina, signals reach the EW nucleus via the pretectal nucleus. The EW nucleus then sends preganglionic parasympathetic fibers (via CN III) to the ciliary ganglion, resulting in **pupillary constriction (miosis)**. * **Accommodation Reflex:** When focusing on a near object, the visual cortex sends signals to the EW nucleus. This triggers a triad of responses: **miosis** (via the sphincter pupillae), **lens thickening** (via the ciliary muscle), and **convergence** (via the medial rectus). Since the EW nucleus provides the parasympathetic outflow for pupillary constriction in both pathways, it is the shared anatomical component. ### Why Other Options are Incorrect: * **A. Pretectal Nucleus:** This is the afferent processing center specifically for the **light reflex** only. It is bypassed during the accommodation reflex. * **C. Suprachiasmatic Nucleus:** Located in the hypothalamus, this nucleus is the master regulator of **circadian rhythms** (the biological clock), not visual reflexes. * **D. Supraoptic Nucleus:** This hypothalamic nucleus is responsible for the synthesis of **ADH (Vasopressin)**; it has no role in ocular reflexes. ### High-Yield NEET-PG Pearls: * **Argyll Robertson Pupil:** Characterized by "Accommodation Present, Light reflex Absent" (ARP). It is classically associated with neurosyphilis and involves a lesion in the pretectal area. * **Pathway Tip:** The light reflex is **subcortical** (pretectal nucleus), while the accommodation reflex is **cortical** (requires the visual cortex). * **Ciliary Ganglion:** This is where the EW nucleus fibers synapse before reaching the eye.

Q: Which of the following supplies the dilator papillae?

Sympathetic fibres from the V cranial nerve. ### Explanation The **dilator pupillae** (radial muscle of the iris) is responsible for **mydriasis** (pupillary dilation). It is under the control of the **sympathetic nervous system**. **Why Option B is correct:** The sympathetic pathway for the eye is a three-neuron chain: 1. **First-order neurons:** Hypothalamus to the ciliospinal center of Budge (C8–T2). 2. **Second-order neurons:** Exit via the sympathetic chain to the **Superior Cervical Ganglion**. 3. **Third-order neurons (Postganglionic):** Travel along the internal carotid artery, enter the orbit, and join the **Ophthalmic division of the Trigeminal nerve (V1)**. They reach the dilator pupillae via the **long ciliary nerves**. Thus, while the fibers originate from the cervical ganglion, they are anatomically "supplied" to the muscle via the branches of the Vth cranial nerve. **Why other options are incorrect:** * **Option A & C:** The **Oculomotor nerve (III)** carries **parasympathetic** fibers originating from the **Edinger-Westphal nucleus**. These fibers synapse in the ciliary ganglion and supply the **sphincter pupillae** (causing miosis) and the ciliary muscle (accommodation), not the dilator pupillae. * **Option D:** While the fibers are indeed postganglionic sympathetic fibers from the superior cervical ganglion, Option B is a more specific anatomical description of how these fibers physically reach the iris (via the Vth nerve). **High-Yield Clinical Pearls for NEET-PG:** * **Horner’s Syndrome:** Caused by a lesion anywhere along the sympathetic pathway. Clinical triad: Ptosis (partial), Miosis, and Anhidrosis. * **Argyll Robertson Pupil:** "Prostitute's Pupil" (Accommodates but does not React to light). Seen in neurosyphilis; lesion is in the pretectal nucleus. * **Adie’s Tonic Pupil:** A dilated pupil with delayed response to light, caused by damage to the postganglionic parasympathetic fibers (ciliary ganglion).

Q: The dorsal column of the spinal cord does not carry fibers for which of the following sensations?

Pain. The sensory pathways of the spinal cord are divided into two major systems: the **Dorsal Column-Medial Lemniscal (DCML) system** and the **Anterolateral (Spinothalamic) system**. ### Why Pain is the Correct Answer **Pain** (along with temperature and crude touch) is carried by the **Anterolateral system**. These fibers (A-delta and C fibers) synapse in the dorsal horn, decussate (cross over) at the level of the spinal cord, and ascend in the lateral spinothalamic tract. Therefore, the dorsal column does not carry pain sensations. ### Why the Other Options are Incorrect The **Dorsal Column** (comprising the Fasciculus Gracilis and Fasciculus Cuneatus) is responsible for "fine" sensations. It carries: * **Vibration (Option A):** Detected by Pacinian corpuscles and transmitted via large myelinated A-beta fibers. * **Two-point discrimination (Option C):** The ability to discern that two nearby objects touching the skin are truly two distinct points. * **Stereognosis (Option D):** The ability to identify an object by touch without visual input. * **Proprioception:** Sense of position and movement. ### High-Yield NEET-PG Pearls * **Decussation:** DCML fibers decussate in the **medulla** (as internal arcuate fibers), whereas Spinothalamic fibers decussate at the **spinal cord level**. * **Tabes Dorsalis:** A late stage of syphilis that specifically affects the dorsal columns, leading to loss of vibration and position sense (sensory ataxia). * **Brown-Séquard Syndrome:** In a spinal cord hemisection, there is **ipsilateral** loss of DCML sensations (vibration/proprioception) and **contralateral** loss of pain and temperature. * **First Order Neurons:** For the DCML, the cell bodies are located in the **Dorsal Root Ganglion**.

Q: Which of the following is an example of extraspectral color?

Purple. ### Explanation **1. Why Purple is the Correct Answer:** The visible spectrum (VIBGYOR) consists of colors produced by a single wavelength of light, ranging from approximately 400 nm (violet) to 700 nm (red). **Extraspectral colors** are those that cannot be generated by a single wavelength; instead, they are perceived by the brain when the retina is stimulated by a combination of wavelengths from different ends of the spectrum. **Purple** (or magenta) is the classic example of an extraspectral color. It is perceived when the **S-cones** (short-wave/blue) and **L-cones** (long-wave/red) are stimulated simultaneously, without significant stimulation of the M-cones (green). Because there is no single "purple" wavelength in the electromagnetic spectrum, it is considered extraspectral. **2. Why the Other Options are Incorrect:** * **A. Red:** This is a spectral color corresponding to long wavelengths (approx. 625–740 nm). * **B. Green:** This is a spectral color corresponding to medium wavelengths (approx. 500–565 nm). * **C. Blue:** This is a spectral color corresponding to short wavelengths (approx. 450–485 nm). * *Note:* Violet is also a spectral color (the shortest visible wavelength), whereas Purple is the extraspectral mixture of red and blue. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Young-Helmholtz Theory (Trichromatic Theory):** Human color vision relies on three types of cone photopsies: S (Blue), M (Green), and L (Red). * **Ishihara Charts:** The gold standard for screening X-linked recessive color blindness (most commonly Red-Green deficiency). * **Complementary Colors:** Any two colors that, when mixed, create white light (e.g., Blue and Yellow). * **After-images:** Explained by the **Opponent Process Theory**, where fatigue in one color pathway (e.g., Red) leads to the perception of its opponent (e.g., Green) when looking at a neutral surface.

Question 1

Which of the following is true about the generator potential?

Accepted Answer

Its magnitude increases in direct proportion to the strength of the stimulus.

Answer

It is not graded.

Answer

It is an all-or-none phenomenon.

Answer

It is propagated.

Question 2

What is true about the fovea?

Accepted Answer

Contains only cones

Answer

Contains only rods

Answer

Situated above the optic disc

Answer

Contains both rods and cones

Question 3

Which part of the retina is primarily involved in the process of dark adaptation?

Accepted Answer

Both rods and cones

Answer

Rods

Answer

Cones

Answer

Pigment epithelium

Question 4

Auditory transmission is via which pathway?

Accepted Answer

Lateral Lemniscus

Answer

Lateral Geniculate body

Answer

Medial Lemniscus

Answer

Pretectal Nucleus

Question 5

Proprioception is carried by which type of nerve fibers?

Accepted Answer

A alpha fibers

Answer

A beta fibers

Answer

B fibers

Answer

C fibers

Question 6

Which function is controlled by the striate cortex of the brain?

Accepted Answer

Vision

Answer

Speech

Answer

Balance

Answer

Auditory processing

Question 7

Which of the following nuclei is involved in both the light reflex and the accommodation reflex?

Accepted Answer

Edinger-Westphal nucleus

Answer

Pretectal nucleus

Answer

Suprachiasmatic nucleus

Answer

Supraoptic nucleus

Question 8

Which of the following supplies the dilator papillae?

Accepted Answer

Sympathetic fibres from the V cranial nerve

Answer

Occulomotor (III) cranial nerve

Answer

Postganglionic parasympathetic fibers from Edinger Westphal nucleus

Answer

Postganglionic sympathetic fibers from cervical ganglion

Question 9

The dorsal column of the spinal cord does not carry fibers for which of the following sensations?

Accepted Answer

Pain

Answer

Vibration

Answer

Two point discrimination

Answer

Stereognosis

Question 10

Which of the following is an example of extraspectral color?

Accepted Answer

Purple

Answer

Red

Answer

Green

Answer

Blue

Sensory Systems — MCQs

Sensory Systems — MCQs

On this page

Practice by Chapter

Want unlimited practice?