Sensory Systems Practice Questions

Q: What perception results from the motion of the endolymph in the semicircular canals when the head is held still?

Perception of continued rotation. **Explanation:** The correct answer is **C. Perception of continued rotation**. The semicircular canals (SCC) are designed to detect **angular acceleration**. When the head begins to rotate, the bony canal moves, but the endolymph lags behind due to **inertia**. This relative movement displaces the cupula, stimulating hair cells. If rotation continues at a constant velocity, the endolymph eventually catches up with the canal wall, the cupula returns to its neutral position, and the sensation of rotation ceases. However, when the head **suddenly stops**, the endolymph continues to move due to momentum (the "after-effect"). This movement deflects the cupula in the opposite direction, signaling to the brain that the head is still rotating, even though it is stationary. This physiological phenomenon is the basis for **post-rotatory nystagmus** and vertigo. **Why other options are incorrect:** * **Option A & D:** Perception of being upside-down or upright (static equilibrium) is primarily the function of the **otolith organs** (Utricle and Saccule), which detect linear acceleration and head tilt relative to gravity. * **Option B:** Perception of moving in a straight line is also a function of the **otolith organs**, specifically the utricle (horizontal) and saccule (vertical), not the semicircular canals. **High-Yield NEET-PG Pearls:** * **SCC:** Detects angular acceleration (e.g., turning the head). * **Utricle:** Detects horizontal linear acceleration. * **Saccule:** Detects vertical linear acceleration (e.g., riding in an elevator). * **Cupula:** The gelatinous mass in the SCC; it has the same specific gravity as endolymph, making it insensitive to gravity (unlike the otoliths). * **Caloric Reflex Test:** Uses the "COWS" mnemonic (Cold Opposite, Warm Same) to describe the direction of the fast phase of nystagmus.

Q: Which order neuron are ganglionic cells?

Second order. In the visual pathway, the arrangement of neurons differs from the typical sensory pathway (where the dorsal root ganglion is usually the first-order neuron). To understand why retinal ganglion cells are **second-order neurons**, we must look at the layers of the retina: 1. **First-order Neurons (Bipolar Cells):** Although photoreceptors (rods and cones) are the primary receptors that detect light, the **Bipolar cells** are considered the first-order neurons. They receive signals from the photoreceptors and transmit them to the ganglion cells. 2. **Second-order Neurons (Ganglion Cells):** The axons of these cells form the **Optic Nerve**. They receive input from the bipolar cells and carry the visual impulse to the brain. 3. **Third-order Neurons (Lateral Geniculate Body):** The axons of the ganglion cells synapse in the **Lateral Geniculate Nucleus (LGN)** of the thalamus. The neurons originating here project to the primary visual cortex (Area 17) via optic radiations. **Why other options are incorrect:** * **First order:** Incorrect because this role is fulfilled by the Bipolar cells. * **Third order:** Incorrect because this role is fulfilled by the neurons in the Lateral Geniculate Body (LGB). **High-Yield NEET-PG Pearls:** * **Photoreceptors** (Rods/Cones) are modified neuroepithelial cells, not neurons. * The **Optic Nerve** is technically a tract of the CNS (not a peripheral nerve) because it is formed by second-order neurons and myelinated by **oligodendrocytes**, not Schwann cells. * **Action Potentials** in the retina occur first at the level of Ganglion cells; Bipolar cells and photoreceptors communicate via **graded potentials**.

Q: Dynamic response is due to which of the following?

Primary ending. This question pertains to the physiology of the **muscle spindle**, which acts as a stretch receptor. Muscle spindles contain two types of intrafusal fibers: nuclear bag fibers and nuclear chain fibers. ### Why Primary Ending is Correct The **Primary (Type Ia) sensory endings** wrap around the central portions of both nuclear bag and nuclear chain fibers. Because nuclear bag fibers are highly sensitive to the **rate of change** in muscle length, the primary endings are responsible for the **dynamic response**. This means they fire rapidly during the actual movement or change in length, providing the CNS with instantaneous feedback regarding the velocity of stretch. ### Why Other Options are Incorrect * **Secondary (Type II) ending:** These are located primarily on nuclear chain fibers. They are responsible for the **static response**, meaning they fire at a constant rate proportional to the absolute length of the muscle once it has reached a new position. They do not respond to the velocity of change. * **Tertiary ending:** This is a distractor term. In the context of muscle spindle innervation, only primary (Ia) and secondary (II) afferents exist. * **None of the above:** Incorrect, as the primary ending is the established physiological mediator of the dynamic response. ### NEET-PG High-Yield Pearls * **Afferent Summary:** Primary = Ia (Dynamic + Static); Secondary = II (Static only). * **Efferent Summary:** **Gamma ($\gamma$) motor neurons** regulate the sensitivity of the spindle. $\gamma$-dynamic fibers innervate nuclear bag fibers, while $\gamma$-static fibers innervate nuclear chain fibers. * **Clinical Correlation:** The dynamic response of the primary ending is the physiological basis for **tendon jerks** (monosynaptic stretch reflexes). Loss of this response results in areflexia or hypotonia.

Q: Green color blindness is also known as which of the following?

Deuteranopia. ### Explanation Color blindness (Dichromacy) occurs due to the absence or deficiency of one of the three types of cone photopigments (Red, Green, or Blue). These are classified based on the Greek numerical prefixes: **Protos** (First/Red), **Deuteros** (Second/Green), and **Tritos** (Third/Blue). **1. Why Deuteranopia is correct:** **Deuteranopia** refers to the complete absence of green-sensitive cones (M-cones). Since "Deuteros" means second, and green is the second primary color in the visual spectrum, this term specifically denotes green color blindness. Individuals with this condition have difficulty distinguishing between red and green hues. **2. Analysis of Incorrect Options:** * **Protanopia (Option A):** This is red color blindness caused by the absence of L-cones (Red cones). "Protos" means first. * **Tritanopia (Option C):** This is blue color blindness caused by the absence of S-cones (Blue cones). "Tritos" means third. This is the rarest form of dichromacy. * **Dyschromatopsia (Option D):** This is a general medical term for any deficiency or alteration in color vision, rather than a specific type like green color blindness. **3. High-Yield Clinical Pearls for NEET-PG:** * **Inheritance:** Red-green color blindness (Protanopia and Deuteranopia) is **X-linked recessive**, making it significantly more common in males. Tritanopia is **Autosomal Dominant** (Chromosome 7). * **Most Common Type:** Deuteranomaly (a mild *weakness* in green perception) is the most common overall color vision deficiency. * **Screening:** **Ishihara Charts** are the most common screening tool, while the **Nagel Anomaloscope** is the gold standard for definitive diagnosis and differentiation. * **Photopigments:** Red and Green pigments are located on the **X chromosome**, while Blue is on **Chromosome 7**.

Q: The straite cortex is involved in which function?

Vision. **Explanation:** The **striate cortex**, also known as the **Primary Visual Cortex (Brodmann area 17)**, is the principal cortical region responsible for processing visual information. It is located on the medial surface of the occipital lobe, specifically within the walls of the **calcarine fissure**. It receives direct sensory input from the eyes via the lateral geniculate nucleus (LGN) of the thalamus. The term "striate" (meaning striped) is derived from the **Stria of Gennari**, a distinct white matter band visible to the naked eye, representing myelinated fibers from the thalamus. **Analysis of Incorrect Options:** * **B. Auditory processing:** This primarily occurs in the **Primary Auditory Cortex (Brodmann areas 41 and 42)**, located in the Superior Temporal Gyrus (Heschl’s gyri) of the temporal lobe. * **C. Olfaction:** Odor perception is processed in the **Piriform cortex**, amygdala, and entorhinal cortex (Primary Olfactory Cortex), located in the temporal lobe and limbic system. * **D. Speech:** Speech production is governed by **Broca’s area** (Brodmann 44, 45) in the frontal lobe, while speech comprehension is managed by **Wernicke’s area** (Brodmann 22) in the temporal lobe. **High-Yield Facts for NEET-PG:** * **Blood Supply:** The primary visual cortex is supplied by the **Posterior Cerebral Artery (PCA)**. * **Macular Sparing:** In PCA strokes, the "macular" vision is often spared because the occipital pole (representing the macula) has a dual blood supply from both the PCA and the **Middle Cerebral Artery (MCA)**. * **Lesion Effect:** A unilateral lesion of the striate cortex results in **Contralateral Homonymous Hemianopia** with macular sparing.

Q: Ablation of the somatosensory area V of the cerebral cortex leads to what type of sensory deficit?

Loss of tactile localization and two-point discrimination. **Explanation:** The somatosensory cortex (S-I and S-II) is essential for the **spatial orientation** and **discriminative** aspects of sensation. While the thalamus can perceive the presence of crude sensations like pain and temperature, the cerebral cortex is required to process complex sensory information. **1. Why Option D is Correct:** The ability to pinpoint where a stimulus is applied (**tactile localization**) and the ability to distinguish two distinct points applied simultaneously (**two-point discrimination**) are "discriminative" or "fine" sensations. These require high-level cortical processing. Ablation of the somatosensory area destroys the spatial map (homunculus), leading to an inability to localize stimuli or resolve spatial detail. **2. Why Other Options are Incorrect:** * **Options A & B:** Total loss of pain or touch does not occur. This is because the **thalamus** and lower brain centers are capable of perceiving the *quality* and *presence* of crude touch, pressure, and pain. However, the patient will be unable to tell exactly *where* the pain or touch is occurring. * **Option C:** This is incorrect because both localization and two-point discrimination are functionally linked to the dorsal column-medial lemniscal (DCML) pathway and its cortical projection. If one is lost due to cortical ablation, the other is invariably affected as well. **Clinical Pearls for NEET-PG:** * **Astereognosis:** The inability to identify an object by touch (size, shape, texture) in the absence of visual/auditory input is a hallmark of somatosensory cortex lesions. * **Thalamic Sensation:** Remember that the thalamus is the center for "crude" awareness, while the cortex is for "fine" discrimination. * **Brodmann Areas:** Somatosensory Area I (S-I) corresponds to Brodmann areas 3, 1, and 2 in the postcentral gyrus.

Question 1

What perception results from the motion of the endolymph in the semicircular canals when the head is held still?

Accepted Answer

Perception of continued rotation

Answer

Perception of being upside-down

Answer

Perception of moving in a straight line

Answer

Perception of being upright and stationary

Question 2

Which order neuron are ganglionic cells?

Accepted Answer

Second order

Answer

First order

Answer

Third order

Answer

None

Question 3

Sensory receptors that adapt rapidly are well suited to sensing what?

Accepted Answer

The rate at which an extremity is being moved

Answer

The weight of an object held in the hand

Answer

Resting body orientation in space

Answer

Potentially hazardous chemicals in the environment

Question 4

Dynamic response is due to which of the following?

Accepted Answer

Primary ending

Answer

Secondary ending

Answer

Tertiary ending

Answer

None of the above

Question 5

Green color blindness is also known as which of the following?

Accepted Answer

Deuteranopia

Answer

Protanopia

Answer

Tritanopia

Answer

Dyschromatopsia

Question 6

In a transection of the spinal cord, which sensory modality is affected last?

Accepted Answer

Proprioception

Answer

Pinprick

Answer

Temperature

Answer

Pain

Question 7

Which of the following neurons show action potentials?

Accepted Answer

Ganglionic cells

Answer

Amacrine cells

Answer

Cells of the lateral geniculate body

Answer

Rods and cones

Question 8

The straite cortex is involved in which function?

Accepted Answer

Vision

Answer

Auditory processing

Answer

Olfaction

Answer

Speech

Question 9

Ablation of the somatosensory area V of the cerebral cortex leads to what type of sensory deficit?

Accepted Answer

Loss of tactile localization and two-point discrimination

Answer

Total loss of pain sensation

Answer

Total loss of touch sensation

Answer

Loss of tactile localization but not two-point discrimination

Question 10

In angina pectoris, what mediates the pain radiating down the left arm through increased activity in afferent (sensory) fibres?

Accepted Answer

Thoracic splanchnic nerve

Answer

Carotid branch of the glossopharyngeal nerve

Answer

Phrenic nerve

Answer

Vagus nerve and recurrent laryngeal nerve

Sensory Systems — MCQs

Sensory Systems — MCQs

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