Sensory Systems Practice Questions

Q: Horner syndrome causes all of the following except:

Mydriasis. **Explanation:** Horner syndrome is a clinical condition resulting from the interruption of the **sympathetic nerve supply** to the eye. To answer this question, one must understand that the sympathetic system is responsible for "fight or flight" responses, including pupil dilation. **1. Why Mydriasis is the Correct Answer:** Sympathetic fibers innervate the **dilator pupillae** muscle. In Horner syndrome, the loss of sympathetic tone leads to the unopposed action of the parasympathetic system (via the oculomotor nerve), resulting in **miosis** (constricted pupil), not mydriasis (dilated pupil). Therefore, mydriasis is the "except" in this list. **2. Analysis of Incorrect Options:** * **Enophthalmos (A):** The loss of sympathetic supply to the **orbitalis muscle** (Müller’s muscle) causes the eye to appear slightly sunken. * **Anhidrosis (C):** Sympathetic fibers control sweat glands. A lesion (especially pre-ganglionic) leads to a loss of sweating on the affected side of the face. * **Narrowed palpebral fissure (D):** This is caused by **partial ptosis**. The superior tarsal muscle (involuntary) is sympathetically innervated; its paralysis causes the upper eyelid to droop slightly, narrowing the fissure. **High-Yield Clinical Pearls for NEET-PG:** * **The Classic Triad:** Ptosis, Miosis, and Anhidrosis. * **Apparent Enophthalmos:** It is often described as "apparent" because the narrowing of the palpebral fissure creates the illusion of a sunken eyeball. * **Cocaine Test:** In a normal eye, cocaine drops cause mydriasis. In Horner syndrome, the pupil **fails to dilate** because there is no norepinephrine in the synaptic cleft for cocaine to act upon. * **Common Causes:** Pancoast tumor (at the lung apex), carotid artery dissection, or syringomyelia.

Q: Impulses generated in the taste buds of the tongue reach the cerebral cortex via which structure?

Thalamus. **Explanation:** The correct answer is **Thalamus**. In the sensory pathway for gustation (taste), the thalamus acts as the essential relay station before information reaches the primary gustatory cortex. **The Pathway:** 1. **First-order neurons:** Taste impulses from the tongue are carried by the Facial (CN VII), Glossopharyngeal (CN IX), and Vagus (CN X) nerves. 2. **Second-order neurons:** These fibers synapse in the **Nucleus Tractus Solitarius (NTS)** in the medulla. Axons from the NTS ascend via the central tegmental tract. 3. **Third-order neurons:** These are located in the **Ventral Posteromedial (VPM) nucleus of the Thalamus**. From here, impulses are projected to the gustatory cortex (Insula and frontal operculum). **Why other options are incorrect:** * **Internal capsule:** While taste fibers pass through the posterior limb of the internal capsule to reach the cortex, it is a white matter tract (conduit), not the relay structure where the synapse occurs. * **Cervical spinal nerve:** These carry general somatic sensation from the neck and back of the head, not special visceral afferents like taste. * **Trigeminal nerve:** This nerve carries general sensations (touch, pain, temperature) from the anterior 2/3rd of the tongue via the lingual nerve, but it does not carry taste impulses. **High-Yield NEET-PG Pearls:** * **VPM Nucleus:** Remember the mnemonic **"VPM = Very Polar Mouth"** (relays sensory/taste from the face/mouth). In contrast, the **VPL** relays sensations from the **L**imbs/body. * **Ageusia:** Loss of taste sensation. * **NTS:** Known as the "sensory nucleus" for all visceral afferents (Taste, Baroreceptors, Chemoreceptors).

Q: Stereognosis will be lost in a lesion of which pathway?

Fasciculus cuneatus. **Explanation:** **Stereognosis** is the ability to identify an object by touch and manipulation without visual input. This is a complex cortical sensation that requires intact **fine touch, pressure, and proprioception**—all of which are carried by the **Dorsal Column-Medial Lemniscal (DCML) pathway**. 1. **Why Fasciculus Cuneatus is correct:** The DCML pathway is divided into the Fasciculus Gracilis (medial) and Fasciculus Cuneatus (lateral). The **Fasciculus Cuneatus** carries sensory information from the **upper limbs and upper trunk (above T6)**. Since stereognosis is clinically tested using the hands (e.g., identifying a key or coin), a lesion in the Fasciculus Cuneatus specifically results in the loss of this ability in the upper extremities. 2. **Why other options are incorrect:** * **Fasciculus Gracilis:** While also part of the DCML, it carries sensations from the **lower limbs (below T6)**. While a lesion here would affect fine touch in the legs, stereognosis is not typically tested or functional in the lower limbs. * **Anterior Spinothalamic Tract:** This pathway carries **crude touch and pressure**. * **Lateral Spinothalamic Tract:** This pathway carries **pain and temperature** sensations. **Clinical Pearls for NEET-PG:** * **Astereognosis** is often a sign of a lesion in the **Parietal Lobe** (specifically the somatosensory association cortex) or the dorsal columns. * **Rule of Thumb:** Gracilis is "G" for Ground (legs); Cuneatus is for the arms. * **DCML vs. Spinothalamic:** DCML fibers decussate in the **medulla** (internal arcuate fibers), whereas Spinothalamic fibers decussate at the **spinal cord level** (anterior white commissure). * **Tabes Dorsalis:** A classic condition involving the destruction of dorsal columns, leading to loss of vibration, position sense, and two-point discrimination.

Q: Which lobe of the cerebrum contains the auditory cortex?

Temporal lobe. **Explanation:** The **Temporal lobe** is the primary site for auditory processing. The **Primary Auditory Cortex (Brodmann areas 41 and 42)** is located on the superior temporal gyrus, specifically within the **Heschl’s gyri**. It receives sensory input from the cochlea via the medial geniculate nucleus (MGN) of the thalamus. **Analysis of Options:** * **Temporal Lobe (Correct):** Responsible for hearing, memory (hippocampus), and language comprehension (Wernicke’s area). * **Parietal Lobe:** Primarily involved in **somatosensory processing** (postcentral gyrus, areas 1, 2, 3) and spatial awareness. * **Frontal Lobe:** Responsible for **motor control** (precentral gyrus), executive functions, and motor speech (Broca’s area). * **Occipital Lobe:** Dedicated to **visual processing** (Primary visual cortex, area 17). **High-Yield Clinical Pearls for NEET-PG:** * **Tonotopic Organization:** The auditory cortex is organized by sound frequency; high frequencies are processed posteromedially, while low frequencies are processed anterolaterally. * **Wernicke’s Area:** Located in the posterior part of the superior temporal gyrus (usually in the left hemisphere). Damage leads to **Sensory/Receptive Aphasia** (fluent but meaningless speech). * **Meyer’s Loop:** Part of the visual pathway that passes through the temporal lobe; a lesion here causes **Superior Quadrantanopia** ("pie in the sky" defect). * **Mnemonic:** "The **T**emporal lobe is near the **T**ips of the ears."

Q: Absence of taste sensation is termed as:

Ageusia. ### Explanation The correct answer is **B. Ageusia**. **Understanding the Concept:** Taste sensation (gustation) is mediated by taste buds located on the tongue, soft palate, and epiglottis. In medical terminology, the suffix **"-geusia"** refers to the sense of taste. The prefix **"a-"** denotes a total absence or lack thereof. Therefore, **Ageusia** is defined as the complete loss of taste functions. True ageusia is relatively rare and is often confused with anosmia (loss of smell), as flavor perception relies heavily on olfactory input. **Analysis of Incorrect Options:** * **A. Hypogeusia:** Refers to a **reduced** or diminished ability to taste. It is a quantitative decrease rather than a total absence. * **C. Dysgeusia:** Refers to a **distortion** or perversion of taste. Patients often complain of a persistent metallic, salty, or rancid taste in the mouth. * **D. Partial ageusia:** Refers to the loss of taste for **specific** modalities (e.g., unable to taste bitter but can taste sweet) or loss in a specific area of the tongue. **Clinical Pearls for NEET-PG:** * **Nerve Supply:** Remember the "2/3 and 1/3" rule. Anterior 2/3 of the tongue is supplied by the **Chorda tympani** (branch of Facial nerve, CN VII); Posterior 1/3 is supplied by the **Glossopharyngeal nerve** (CN IX). * **Zinc Deficiency:** A classic high-yield cause of hypogeusia/ageusia is **Zinc deficiency**. * **Drug-induced:** Drugs like **Captopril** (ACE inhibitor) and **Penicillamine** are frequently associated with taste disturbances (Dysgeusia). * **Pathway:** Taste fibers terminate in the **Nucleus Tractus Solitarius (NTS)** in the medulla.

Q: Which body part is represented superiorly and medially within the postcentral gyrus?

Lower limb. ### Explanation The **postcentral gyrus** of the parietal lobe houses the **Primary Somatosensory Cortex (Brodmann areas 3, 1, and 2)**. The spatial distribution of body parts in this area follows a specific pattern known as the **Sensory Homunculus**. **1. Why the Lower Limb is Correct:** The sensory homunculus is an "upside-down" representation of the body. The **lower limb (leg and foot)** and the **perineum** are represented on the **medial surface** of the hemisphere and the most **superior (dorsal)** aspect of the postcentral gyrus. These areas are supplied by the **Anterior Cerebral Artery (ACA)**. **2. Analysis of Incorrect Options:** * **A. Upper Limb:** The hand and arm are represented on the **superolateral** aspect of the postcentral gyrus. The hand, particularly the thumb and fingers, occupies a disproportionately large area due to high receptor density. * **C. Abdomen:** The trunk and abdomen are located on the upper part of the **lateral surface**, inferior to the lower limb representation but superior to the upper limb. * **D. Genitalia:** While genitalia are also represented medially, they are located most inferiorly on the medial wall, often below the representation of the toes. In the context of "superior and medial," the lower limb is the primary landmark. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Blood Supply:** A stroke involving the **Anterior Cerebral Artery (ACA)** leads to sensory and motor deficits primarily in the **contralateral lower limb**. In contrast, a **Middle Cerebral Artery (MCA)** stroke affects the face and upper limb. * **Disproportionate Representation:** The size of the cortical area is not proportional to the size of the body part, but to the **density of sensory receptors** (e.g., the lips and hands have the largest representation). * **Sequence (Medial to Lateral):** Toes → Foot → Leg → Hip → Trunk → Upper Limb → Face → Intra-abdominal.

Q: What is the function of utricle and saccule?

Linear acceleration. ***Linear acceleration***- The **utricle** and **saccule** are the two **otolithic organs** of the inner ear responsible for detecting mechanical forces related to **linear motion** (acceleration, deceleration) and the pull of gravity.- The **utricle** senses horizontal linear acceleration (e.g., walking), while the **saccule** senses vertical linear acceleration (e.g., riding an elevator).*Hearing high-frequency sounds*- Sound detection (hearing) is carried out by the **cochlea** and its associated structures, primarily the hair cells in the **Organ of Corti**.- High frequencies stimulate hair cells located near the **base** of the **basilar membrane** but this is unrelated to the vestibular functions of the utricle and saccule.*Angular acceleration*- Rotational movements of the head, or **angular acceleration**, are detected solely by the three **semicircular canals**.- The canals use the movement of endolymph to displace the **cupula** within the **ampullae**, stimulating the enclosed hair cells.*Hearing low-frequency sounds*- The **cochlea** is the auditory apparatus; the utricle and saccule are part of the **vestibular system** responsible for balance and spatial orientation.- Low frequencies primarily stimulate hair cells located near the **apex** of the **basilar membrane** (apex is furthest from the oval window).

Question 1

Somatosensory area I has the largest representation for which body part?

Accepted Answer

Arm

Answer

Leg

Answer

Back

Answer

Head

Question 2

Horner syndrome causes all of the following except:

Accepted Answer

Mydriasis

Answer

Enophthalmos

Answer

Anhidrosis

Answer

Narrowed palpebral fissure

Question 3

Stereoanesthesia is due to a lesion of which of the following?

Accepted Answer

Cerebral cortex

Answer

Nucleus Gracilis

Answer

Nucleus cuneatus

Answer

Spinothalamic tract

Question 4

Impulses generated in the taste buds of the tongue reach the cerebral cortex via which structure?

Accepted Answer

Thalamus

Answer

Internal capsule

Answer

Cervical spinal nerve

Answer

Trigeminal nerve

Question 5

Stereognosis will be lost in a lesion of which pathway?

Accepted Answer

Fasciculus cuneatus

Answer

Fasciculus gracilis

Answer

Anterior spinothalamic tract

Answer

Lateral spinothalamic tract

Question 6

Which lobe of the cerebrum contains the auditory cortex?

Accepted Answer

Temporal lobe

Answer

Parietal lobe

Answer

Frontal lobe

Answer

Occipital lobe

Question 7

Absence of taste sensation is termed as:

Accepted Answer

Ageusia

Answer

Hypogeusia

Answer

Dysgeusia

Answer

Partial ageusia

Question 8

Which body part is represented superiorly and medially within the postcentral gyrus?

Accepted Answer

Lower limb

Answer

Upper limb

Answer

Abdomen

Answer

Genitalia

Question 9

Bilateral destruction of the auditory cortex in humans causes what type of hearing impairment?

Accepted Answer

Deficiency in the interpretation of sounds

Answer

Almost total deafness

Answer

Hearing defect for higher frequency sounds

Answer

Inability for the orientation of sounds

Question 10

What is the function of utricle and saccule?

Accepted Answer

Linear acceleration

Answer

Hearing high-frequency sounds

Answer

Hearing low-frequency sounds

Answer

Angular acceleration

Sensory Systems — MCQs

Sensory Systems — MCQs

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