Sensory Systems Practice Questions

Q: Hot water bottle relieves pain of abdominal spasm by:

Stimulation of adrenergic fibers. **Explanation:** The relief of abdominal spasm by a hot water bottle is a classic physiological application of the **Gate Control Theory of Pain** and the **viscerosomatic reflex**. **Why Option A is correct:** When heat is applied to the skin of the abdomen, it stimulates thermal receptors. These impulses travel via sensory nerves to the spinal cord, where they trigger a reflex increase in **sympathetic (adrenergic) activity** to the underlying viscera. The stimulation of these adrenergic fibers leads to the release of norepinephrine, which acts on the smooth muscles of the gastrointestinal tract to cause **relaxation**. By relieving the muscle spasm (the source of the pain), the intensity of the pain signal is significantly reduced. **Why the other options are incorrect:** * **Option B:** Stimulation of cholinergic (parasympathetic) fibers would typically increase GI motility and contraction, potentially worsening an abdominal spasm rather than relieving it. * **Option C & D:** While heat does affect thermal receptors, the therapeutic effect on *spasm* is not merely the inhibition of cold or heat receptors. It is the active physiological response (adrenergic stimulation) triggered by the heat that leads to muscle relaxation. **High-Yield Clinical Pearls for NEET-PG:** * **Gate Control Theory:** Proposed by Melzack and Wall; suggests that non-painful input (like heat or touch) "closes the gate" to painful input in the spinal cord dorsal horn. * **Counter-irritation:** The process where one stimulus (heat) masks the perception of another (pain). * **Adrenergic receptors in Gut:** Primarily $\alpha_2$ and $\beta_2$ receptors mediate relaxation of the gut wall.

Q: A patient presented with normal eyesight and absence of direct and consensual light reflexes. Which of the following cranial nerves is suspected to be lesioned?

Occulomotor. ### Explanation The pupillary light reflex involves a complex neural pathway consisting of an **afferent limb** (sensory) and an **efferent limb** (motor). **1. Why Occulomotor (CN III) is Correct:** The question states the patient has **normal eyesight**, which implies the **Optic nerve (CN II)**—the afferent limb—is intact. The absence of both direct and consensual reflexes indicates a failure in the **efferent limb**. The Occulomotor nerve carries parasympathetic fibers from the Edinger-Westphal nucleus to the ciliary ganglion and eventually to the sphincter pupillae muscle. A lesion in CN III prevents pupillary constriction in response to light, regardless of which eye is stimulated. **2. Analysis of Incorrect Options:** * **Optic Nerve (CN II):** If the optic nerve were lesioned, the patient would have impaired vision (blindness) in that eye. Additionally, stimulating the blind eye would yield no response in either eye, but stimulating the *normal* eye would produce both direct and consensual responses. * **Trochlear (CN IV) & Abducent (CN VI):** These are purely motor nerves supplying the Superior Oblique and Lateral Rectus muscles, respectively. They have no role in the pupillary light reflex pathway. **3. Clinical Pearls for NEET-PG:** * **Afferent Limb:** Optic Nerve (CN II) → Pretectal Nucleus. * **Efferent Limb:** Occulomotor Nerve (CN III) → Sphincter Pupillae. * **Argyll Robertson Pupil:** Characterized by "Accommodation Reflex Present, Light Reflex Absent" (ARP/LRA). It is classically seen in neurosyphilis. * **Adie’s Tonic Pupil:** A post-ganglionic parasympathetic denervation resulting in a dilated pupil that reacts slowly to light but better to accommodation.

Q: Which of the following is not considered a primary color?

White. ### Explanation The correct answer is **White**. **1. Why White is the Correct Answer:** In human physiology, the concept of primary colors is based on the **Young-Helmholtz Trichromatic Theory**. This theory states that the retina contains three distinct types of cone photoreceptors, each maximally sensitive to a specific wavelength of light. White is not a primary color because it is a **polychromatic sensation** produced by the simultaneous and equal stimulation of all three types of cones (Red, Green, and Blue). It represents the presence of all visible wavelengths rather than a single primary input. **2. Analysis of Incorrect Options:** * **Red (Option C):** Corresponds to **L-cones** (Long-wavelength sensitive). These are stimulated by wavelengths around 560 nm. * **Green (Option A):** Corresponds to **M-cones** (Medium-wavelength sensitive). These are stimulated by wavelengths around 530 nm. * **Blue (Option B):** Corresponds to **S-cones** (Short-wavelength sensitive). These are stimulated by wavelengths around 430 nm. Together, these three are the **additive primary colors** of light. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Photopigments:** Cones contain **Photopsin** (Iodopsin), while rods contain **Rhodopsin**. * **Color Blindness:** The most common type is **Red-Green color blindness**, which is an X-linked recessive trait. * *Protanopia:* Absence of red cones. * *Deuteranopia:* Absence of green cones (most common). * *Tritanopia:* Absence of blue cones (rare). * **Ishihara Charts:** The gold standard clinical test used to screen for color vision deficiencies. * **Fovea Centralis:** The area of highest visual acuity, containing a high density of cones but **no rods**.

Q: A lesion in which area of the occipital cortex leads to cerebral achromatopsia?

Area V4. **Explanation:** The correct answer is **Area V4**. **1. Why Area V4 is correct:** In the visual hierarchy, the ventral stream (the "What" pathway) is responsible for object recognition and color perception. **Area V4**, located in the lingual and fusiform gyri of the occipital cortex, is the primary specialized center for **color processing**. A lesion here does not cause blindness but results in **Cerebral Achromatopsia**—a condition where the patient sees the world in shades of gray despite having functional retinal cones. **2. Why the other options are incorrect:** * **Area V5 (MT):** This area is specialized for **motion detection**. A lesion here leads to **Akinetopsia** (motion blindness), where patients see moving objects as a series of static "snapshots." * **Area V7:** This area is involved in higher-order visual processing, specifically related to **spatial perception** and visual attention, rather than primary color or motion. * **Area V8:** While some newer research suggests V8 (or V4α) is involved in color, standard medical curriculum and NEET-PG patterns traditionally identify **V4** as the definitive center for color processing. **3. High-Yield Clinical Pearls for NEET-PG:** * **V1 (Primary Visual Cortex/Striate Cortex):** Initial processing of visual input; lesion causes contralateral homonymous hemianopia with macular sparing. * **V2, V3:** Involved in orientation and shape. * **Prosopagnosia:** Inability to recognize faces; usually due to lesions in the **fusiform gyrus** (near V4). * **Ventral Stream:** V1 → V2 → V4 (Object/Color recognition). * **Dorsal Stream:** V1 → V2 → V5 (Motion/Spatial orientation).

Q: ECF K+ levels are seen in which of the following?

Endolymph. **Explanation:** The correct answer is **Endolymph**. In the human body, extracellular fluid (ECF) typically has high sodium ($Na^+$) and low potassium ($K^+$) concentrations. However, the **endolymph** (found in the scala media of the cochlea and the vestibular apparatus) is a unique physiological exception. It is an extracellular fluid that resembles intracellular fluid in its composition, characterized by a **high $K^+$ concentration** (approx. 150 mEq/L) and low $Na^+$ concentration. This high potassium concentration is maintained by the **Stria Vascularis**, which actively pumps $K^+$ into the scala media. This creates an endocochlear potential of $+80$ mV, providing the necessary electrochemical gradient for hair cell depolarization when mechanically gated channels open. **Analysis of Incorrect Options:** * **Aqueous Humour:** This is the clear fluid in the anterior and posterior chambers of the eye. It is a filtrate of plasma with an ionic composition similar to typical ECF (High $Na^+$, Low $K^+$). * **Vitreous Humour:** This is the gelatinous mass behind the lens. Like aqueous humour, its electrolyte profile mirrors standard interstitial fluid. * **Ectolymph:** This is not a standard physiological term. The fluid surrounding the endolymphatic space is called **Perilymph**, which has a composition similar to CSF and typical ECF (High $Na^+$, Low $K^+$). **High-Yield Pearls for NEET-PG:** 1. **Endolymph vs. Perilymph:** Endolymph = High $K^+$ (like ICF); Perilymph = High $Na^+$ (like ECF/CSF). 2. **Stria Vascularis:** Often called the "battery of the ear" because it maintains the high $K^+$ levels. 3. **Meniere’s Disease:** Caused by the distension of the endolymphatic space (endolymphatic hydrops). 4. **Tight Junctions:** The reticular lamina contains tight junctions to prevent the mixing of high-$K^+$ endolymph with low-$K^+$ perilymph, which would otherwise neutralize the potential and cause deafness.

Q: The spinothalamic tract transmits all the following sensations except?

Proprioception. ### Explanation The sensory pathways of the spinal cord are divided into two major systems: the **Anterolateral System (Spinothalamic Tract)** and the **Dorsal Column-Medial Lemniscal (DCML) System**. **1. Why Proprioception is the Correct Answer:** Proprioception (the sense of self-movement and body position), along with fine touch, vibration, and two-point discrimination, is carried by the **Dorsal Column-Medial Lemniscal (DCML) pathway**. These fibers ascend ipsilaterally in the spinal cord and decussate in the medulla. Since proprioception is not a function of the spinothalamic tract, it is the correct "except" choice. **2. Analysis of Incorrect Options:** The Spinothalamic Tract (STT) is responsible for "protopathic" sensations. It is divided into two parts: * **Lateral Spinothalamic Tract:** Specifically transmits **Pain** (Option B) and **Temperature** (Option C). * **Anterior Spinothalamic Tract:** Transmits **Crude Touch** (Option D) and pressure. Because these sensations are primary functions of the STT, these options are incorrect in the context of this "except" question. **3. High-Yield Clinical Pearls for NEET-PG:** * **Decussation:** STT fibers cross the midline at the level of the spinal cord (via the anterior white commissure), whereas DCML fibers cross in the medulla (internal arcuate fibers). * **Brown-Séquard Syndrome:** A hemisection of the spinal cord results in **ipsilateral** loss of proprioception/vibration (DCML) and **contralateral** loss of pain/temperature (STT) 1-2 segments below the lesion. * **Syringomyelia:** Classically affects the anterior white commissure first, leading to a "cape-like" bilateral loss of pain and temperature, while sparing proprioception (dissociated sensory loss).

Question 1

Hot water bottle relieves pain of abdominal spasm by:

Accepted Answer

Stimulation of adrenergic fibers

Answer

Stimulation of cholinergic fibers

Answer

Inhibition of cold receptors

Answer

Inhibition of heat receptors

Question 2

A patient presented with normal eyesight and absence of direct and consensual light reflexes. Which of the following cranial nerves is suspected to be lesioned?

Accepted Answer

Occulomotor

Answer

Trochlear

Answer

Optic

Answer

Abducent

Question 3

Which of the following is not considered a primary color?

Accepted Answer

White

Answer

Green

Answer

Blue

Answer

Red

Question 4

Which of the following is an important functional parameter of pain receptors?

Accepted Answer

Exhibit little or no adaptation

Answer

Not affected by muscle tension

Answer

Signal only flexion at joint capsules

Answer

Can voluntarily be inhibited

Question 5

A lesion in which area of the occipital cortex leads to cerebral achromatopsia?

Accepted Answer

Area V4

Answer

Area V5

Answer

Area V7

Answer

Area V8

Question 6

ECF K+ levels are seen in which of the following?

Accepted Answer

Endolymph

Answer

Ectolymph

Answer

Aqueous humour

Answer

Vitreous humour

Question 7

"Phantom limb phenomenon" is best explained by?

Accepted Answer

Golgi tendon organ

Answer

Weber Freschner law

Answer

Psychodynamic theory

Answer

All of the above

Question 8

The Helmholtz theory of colour vision states that:

Accepted Answer

There are three kinds of cones in the retina responding to the three primary colours.

Answer

There are two kinds of cones called dominators and modulators.

Answer

There is only one kind of cone and the colour is recognised only in area 17.

Answer

There are seven types of cones responding to the seven colours of the spectrum.

Question 9

A man loses his right hand in a farm accident. Four years later, he experiences episodes of severe pain in the missing hand (phantom limb pain). A detailed PET scan study of his cerebral cortex might be expected to show what?

Accepted Answer

Projection of fibers from neighboring sensory areas into the right hand area of his left SI.

Answer

Expansion of the right hand area in his right somatic sensory area I (SI).

Answer

Expansion of the right hand area in his left SI.

Answer

Projection of fibers from neighboring sensory areas into the right hand area of his right SI.

Question 10

The spinothalamic tract transmits all the following sensations except?

Accepted Answer

Proprioception

Answer

Pain

Answer

Temperature

Answer

Touch

Sensory Systems — MCQs

Sensory Systems — MCQs

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