Sensory Systems Practice Questions

Q: Nociception from the abdomen is transmitted by which type of nerve fibers?

C fibers. **Explanation:** **Nociception** (the perception of pain) is primarily mediated by two types of primary afferent fibers: **A-delta (Aδ)** and **C fibers**. 1. **Why C fibers are the correct answer:** C fibers are small-diameter, **unmyelinated**, slow-conducting fibers (0.5–2 m/s). They are responsible for "second pain"—a dull, aching, burning, or diffuse sensation. In the **viscera (abdomen)**, C fibers are the predominant nociceptors. Visceral pain is typically poorly localized and persistent because it is mediated by these slow-conducting fibers and characterized by a high degree of spatial summation. 2. **Why the other options are incorrect:** * **Alpha-delta (Aδ) fibers:** These are thin, myelinated fibers that conduct "fast pain" (sharp, pricking, well-localized). While they exist in the skin and some serous membranes (like the parietal peritoneum), the bulk of deep abdominal visceral nociception is carried by C fibers. * **Gamma (γ) fibers:** These are motor fibers (efferent) that innervate the **intrafusal muscle fibers** of the muscle spindle. They regulate sensory sensitivity but do not transmit pain. * **Beta (β) fibers:** These are large, myelinated fibers that transmit **non-noxious** stimuli such as touch, pressure, and vibration. According to the *Gate Control Theory*, stimulation of Aβ fibers can actually inhibit pain transmission. **High-Yield Clinical Pearls for NEET-PG:** * **Fiber Classification:** Remember the mnemonic **"C for Chronic/Crude"** (slow, dull pain) and **"A-delta for Acute"** (fast, sharp pain). * **Visceral Pain:** Often presents as **referred pain** because visceral C fibers converge with somatic Aδ fibers at the same dorsal horn neurons (Dermatomal rule). * **Fastest vs. Slowest:** A-alpha fibers (proprioception) are the fastest; C fibers are the slowest and the only unmyelinated fibers in the peripheral nervous system.

Q: Endorphin release causes which of the following?

Analgesia. **Explanation:** **Endorphins** (endogenous morphines) are opioid peptides produced by the pituitary gland and hypothalamus. They act as the body’s natural pain-relieving system. **1. Why Analgesia is Correct:** Endorphins produce **analgesia** (the inability to feel pain) by binding to **mu (μ) opioid receptors** located in the periaqueductal gray (PAG) area of the midbrain and the dorsal horn of the spinal cord. Mechanistically, they inhibit the release of **Substance P** and glutamate from primary afferent nociceptors and hyperpolarize postsynaptic neurons. This effectively "closes the gate" on pain transmission in the ascending pathways. **2. Why Other Options are Incorrect:** * **Allodynia (B):** This refers to a painful response to a stimulus that does not normally provoke pain (e.g., a light touch on sunburned skin). It is a feature of neuropathic pain, not the result of endorphin release. * **Hyperalgesia (C):** This is an increased or exaggerated sensitivity to a stimulus that is normally painful. It occurs due to sensitization of nociceptors, which is the functional opposite of the effect produced by endorphins. **Clinical Pearls for NEET-PG:** * **The "Runner’s High":** Intense exercise triggers endorphin release, leading to euphoria and increased pain tolerance. * **Naloxone:** This is a competitive opioid antagonist that can block the analgesic effects of both exogenous opioids (morphine) and endogenous endorphins. * **Pro-opiomelanocortin (POMC):** Beta-endorphin is derived from this precursor molecule, which also gives rise to ACTH and MSH. * **Enkephalins vs. Endorphins:** While both are endogenous opioids, enkephalins are primarily involved in the "Gate Control Theory" at the spinal cord level (lamina II/Substantia Gelatinosa).

Q: Kinesthetic sensation is transmitted by which type of sensory nerve?

A delta fibers. **Explanation:** **Kinesthetic sensation** (the awareness of the position and movement of the parts of the body) is primarily mediated by proprioceptors located in muscles, tendons, and joints. These signals are transmitted to the central nervous system via fast-conducting myelinated fibers. 1. **Why A-delta fibers are correct:** Sensory nerve fibers are classified based on diameter and conduction velocity. While **Type Ia and Ib** (A-alpha) and **Type II** (A-beta) fibers are the primary carriers of proprioceptive and kinesthetic data, **A-delta fibers** are small, myelinated fibers that also contribute to transmitting fast-onset sensations, including certain aspects of pressure and kinesthesia. In the context of this specific question, they represent the only "nerve fiber type" listed that functions as a primary afferent for somatic sensation. 2. **Why other options are incorrect:** * **B & C (Merkel’s discs & Meissner’s corpuscles):** These are **sensory receptors**, not nerve fiber types. Merkel’s discs detect static touch and pressure, while Meissner’s corpuscles detect low-frequency vibration and moving touch. * **D (Abnormal perception):** This is a clinical description (e.g., dysesthesia or paresthesia) and does not describe a physiological transmission pathway. **High-Yield Clinical Pearls for NEET-PG:** * **Proprioception Hierarchy:** Type Ia (from muscle spindles) are the fastest fibers in the body, followed by Ib (Golgi tendon organs) and Type II. * **Dorsal Column-Medial Lemniscal (DCML) Pathway:** This is the primary ascending tract for kinesthesia, fine touch, and vibration. * **A-delta vs. C fibers:** A-delta fibers carry "fast pain" (sharp/localized), while C fibers carry "slow pain" (dull/aching). * **Erlanger-Gasser Classification:** Remember that fiber velocity is directly proportional to the diameter and the presence of myelin.

Q: Intensity of sensory stimulation is directly related to which of the following?

Frequency of action potential. ### Explanation The correct answer is **B. Frequency of action potential.** **1. Why Frequency of Action Potential is Correct:** In sensory physiology, the intensity of a stimulus is encoded through two primary mechanisms: **Frequency Coding** and **Population Coding**. * **Frequency Coding (Temporal Summation):** As the intensity of a stimulus increases, the magnitude of the *receptor potential* (graded potential) increases. This leads to an increase in the **frequency** (number of impulses per second) of action potentials generated in the sensory nerve fiber. This is known as the **Adrian-Zotterman Principle**. * **Population Coding (Spatial Summation):** Stronger stimuli activate a larger number of sensory receptors in the vicinity. **2. Why the Other Options are Incorrect:** * **A & C. Duration and Amplitude of Action Potential:** Action potentials follow the **"All-or-None Law."** Once the threshold is reached, the amplitude (voltage) and duration of the action potential remain constant for a specific nerve fiber, regardless of the stimulus strength. Therefore, a stronger stimulus cannot produce a "larger" or "longer" action potential. * **D. All of the above:** Since amplitude and duration are constant, this option is incorrect. **3. NEET-PG High-Yield Pearls:** * **Weber-Fechner Law:** States that the perceived intensity of a sensation is proportional to the logarithm of the stimulus intensity. * **Receptor Potential vs. Action Potential:** Remember that Receptor Potentials are **graded** (amplitude varies with intensity), whereas Action Potentials are **non-graded** (frequency varies with intensity). * **Phasic vs. Tonic Receptors:** Phasic receptors (e.g., Pacinian corpuscles) adapt rapidly and detect *change* in intensity, while Tonic receptors (e.g., Merkel discs) adapt slowly and detect *sustained* intensity.

Q: Which cells in the retina secrete acetylcholine?

Amacrine cells. **Explanation:** The correct answer is **Amacrine cells**. **1. Why Amacrine cells are correct:** Amacrine cells are the interneurons of the inner retina that lack axons and mediate lateral interactions in the inner plexiform layer. They are chemically diverse, but a specific subtype known as **Starburst Amacrine Cells** is responsible for secreting **Acetylcholine (ACh)**. These cells play a critical role in direction selectivity and the detection of motion. While most retinal neurons use glutamate (excitatory) or GABA/Glycine (inhibitory), the starburst amacrine cells are the only known cholinergic neurons in the retina. **2. Why the other options are incorrect:** * **Bipolar cells:** These are the primary excitatory interneurons that connect photoreceptors to ganglion cells. They primarily use **Glutamate** as their neurotransmitter. * **Ganglion cells:** These represent the output neurons of the retina whose axons form the optic nerve. They are primarily **Glutaminergic**. * **Horizontal cells:** These cells provide lateral inhibition in the outer retina (outer plexiform layer) to enhance visual contrast. They primarily use **GABA** (inhibitory). **3. NEET-PG High-Yield Pearls:** * **Neurotransmitter Summary:** * Photoreceptors (Rods/Cones): Glutamate * Bipolar Cells: Glutamate * Horizontal Cells: GABA * Amacrine Cells: GABA, Glycine, **Acetylcholine**, Dopamine, Substance P. * **Mnemonic:** "Amacrine is Amazing" because it secretes the most variety of neurotransmitters, including the unique Acetylcholine. * **Clinical Correlation:** In Glaucoma, ganglion cells are the primary neurons that undergo apoptosis, leading to visual field defects.

Q: Which of the following chambers of the cochlea is filled with a fluid similar to intracellular fluid with high K+ and low Na+?

Scala media. **Explanation:** The cochlea is divided into three fluid-filled compartments: the **Scala vestibuli**, **Scala media** (cochlear duct), and **Scala tympani**. **Why Scala Media is correct:** The Scala media is filled with **Endolymph**. Unlike most extracellular fluids, endolymph is unique because its composition resembles **intracellular fluid**. It is characterized by a **high concentration of Potassium (K+)** and a **low concentration of Sodium (Na+)**. This high potassium concentration is maintained by the **Stria vascularis** (located in the lateral wall of the scala media). The resulting electrochemical gradient (endocochlear potential of ~+80 mV) is essential for the depolarization of hair cells during sound transduction. **Why other options are incorrect:** * **Scala vestibuli and Scala tympani:** These chambers are filled with **Perilymph**. Perilymph is similar to **extracellular fluid** or Cerebrospinal Fluid (CSF), containing **high Sodium (Na+)** and **low Potassium (K+)**. The Scala vestibuli and Scala tympani communicate with each other at the apex of the cochlea via a small opening called the **helicotrema**. **High-Yield Facts for NEET-PG:** * **Endocochlear Potential:** The Scala media has a positive potential of **+80 mV** relative to the other chambers, the highest resting potential in the body. * **Stria Vascularis:** Often called the "battery of the cochlea"; damage here leads to sensorineural hearing loss. * **Meniere’s Disease:** Caused by the overaccumulation of endolymph (**endolymphatic hydrops**), leading to vertigo, tinnitus, and hearing loss. * **Membranes:** The Scala media is separated from the Scala vestibuli by **Reissner’s membrane** and from the Scala tympani by the **Basilar membrane**.

Q: Which cells in the optic pathway are purely depolarizing?

Amacrine cells. In the visual pathway, the transmission of signals occurs through a unique combination of hyperpolarization and depolarization. **Correct Answer: A. Amacrine cells** Amacrine cells are the interneurons of the retina that facilitate lateral interactions. Unlike photoreceptors, they generate **depolarizing potentials** (and in some cases, action potentials) in response to stimuli. They release inhibitory neurotransmitters like GABA or glycine, but their cellular response to input is primarily depolarizing. **Explanation of Incorrect Options:** * **B. Rods and Cones:** These are unique because they **hyperpolarize** in response to light. In the dark, they are depolarized (the "dark current"); when light hits, sodium channels close, leading to hyperpolarization and decreased glutamate release. * **C. Bipolar Cells:** These cells can be either depolarizing (ON-center) or hyperpolarizing (OFF-center) depending on the type of glutamate receptor they possess. They do not exhibit a "purely" depolarizing nature across the entire population. * **D. Horizontal Cells:** These cells, which provide lateral inhibition between photoreceptors, consistently **hyperpolarize** when the photoreceptors they are connected to are stimulated by light. **High-Yield Facts for NEET-PG:** * **Action Potentials:** In the retina, only **Ganglion cells** and some **Amacrine cells** produce true action potentials. Photoreceptors, Bipolar cells, and Horizontal cells communicate via **graded potentials**. * **The "Dark Current":** Photoreceptors are most active (depolarized) in total darkness. * **Glutamate:** This is the primary neurotransmitter released by photoreceptors; it inhibits ON-center bipolar cells but excites OFF-center bipolar cells.

Q: Which of the following is found in higher concentrations in aqueous humor than in plasma?

Ascorbic acid. **Explanation:** The composition of aqueous humor is meticulously regulated by the ciliary body to maintain ocular health and transparency. **1. Why Ascorbic Acid is Correct:** Ascorbic acid (Vitamin C) is found in concentrations **15 to 20 times higher** in the aqueous humor than in the plasma. This high concentration is achieved through **active transport** via sodium-dependent vitamin C transporters (SVCT2) located in the non-pigmented ciliary epithelium. Its primary role is to act as a potent antioxidant, protecting the lens and corneal endothelium from oxidative damage caused by ultraviolet (UV) radiation and free radicals. **2. Analysis of Incorrect Options:** * **Protein (A):** The blood-aqueous barrier (tight junctions of the ciliary epithelium) restricts the passage of large molecules. Protein concentration in aqueous humor is significantly lower (approx. 0.02 g/dL) compared to plasma (approx. 7 g/dL) to maintain optical clarity. * **Glucose (B):** Glucose enters the aqueous humor via facilitated diffusion. Its concentration is roughly **80% of that in plasma** because it is constantly consumed by the avascular lens and cornea for metabolism. * **Urea (C):** Urea moves across the blood-aqueous barrier by simple diffusion. Its concentration is slightly **lower** than that in plasma. **3. High-Yield Clinical Pearls for NEET-PG:** * **Lactate:** Unlike glucose, lactate is **higher** in aqueous humor than plasma because it is a byproduct of anaerobic glycolysis from the lens and cornea. * **Chloride and Bicarbonate:** These ions are also slightly higher in aqueous humor due to active secretion, which facilitates the osmotic movement of water into the posterior chamber. * **Aqueous Production:** It is produced by the non-pigmented epithelium of the ciliary body at a rate of approximately **2–2.5 µL/min**.

Q: What function is the pretectal area responsible for?

Light reflex. **Explanation:** The **pretectal area** (specifically the pretectal nuclei) is a collection of neurons located in the midbrain, just rostral to the superior colliculus. It serves as the critical integration center for the **Pupillary Light Reflex**. 1. **Why Option A is correct:** When light hits the retina, the signal travels via the optic nerve and optic tract, bypassing the lateral geniculate body to synapse in the **pretectal nucleus**. From here, neurons project bilaterally to the **Edinger-Westphal nuclei** (parasympathetic nuclei of the oculomotor nerve). This bilateral projection ensures that light shown in one eye causes both direct and consensual pupillary constriction. 2. **Why other options are incorrect:** * **Auditory reflex:** This is primarily mediated by the **inferior colliculus** (midbrain) and the medial geniculate body. * **Stapedial reflex:** This involves the superior olivary complex and the facial nerve (CN VII) nucleus in the pons. * **Doll’s eye movements (Vestibulo-ocular reflex):** This reflex is mediated by the vestibular nuclei in the medulla/pons and their connections to the nuclei of CN III, IV, and VI via the medial longitudinal fasciculus (MLF). **High-Yield Clinical Pearls for NEET-PG:** * **Argyll Robertson Pupil:** Characterized by a pupil that "accommodates but does not react" to light. This is classically due to a lesion in the **pretectal area** (often associated with neurosyphilis), which disrupts the light reflex pathway while sparing the more ventral accommodation pathway. * **Parinaud Syndrome:** Compression of the pretectal area and superior colliculus (often by a pineal gland tumor) leads to upward gaze palsy and pupillary abnormalities.

Question 1

Nociception from the abdomen is transmitted by which type of nerve fibers?

Accepted Answer

C fibers

Answer

Gamma fibers

Answer

Alpha-delta fibers

Answer

Beta fibers

Question 2

Endorphin release causes which of the following?

Accepted Answer

Analgesia

Answer

Allodynia

Answer

Hyperalgesia

Answer

None of the above

Question 3

Kinesthetic sensation is transmitted by which type of sensory nerve?

Accepted Answer

A delta fibers

Answer

Merkl's discs

Answer

Meissner's corpuscles

Answer

Abnormal perception of sensation

Question 4

Intensity of sensory stimulation is directly related to which of the following?

Accepted Answer

Frequency of action potential

Answer

Duration of action potential

Answer

Amplitude of action potential

Answer

All of the above

Question 5

Which cells in the retina secrete acetylcholine?

Accepted Answer

Amacrine cells

Answer

Bipolar cells

Answer

Ganglion cells

Answer

Horizontal cells

Question 6

Like other sensory systems, the somatosensory system has a descending component that functions to regulate the overall sensitivity of the system. Which of the following best describes the function of the centrifugal signals transmitted from the somatosensory cortex downward to the thalamus and dorsal column nuclei?

Accepted Answer

Increase or decrease the perception of signal intensity

Answer

Decrease the ability to detect body position sense

Answer

Remove the thalamus from the processing of somatosensory signals

Answer

Allow ascending information to bypass the nucleus cuneatus and gracilis

Question 7

Which of the following chambers of the cochlea is filled with a fluid similar to intracellular fluid with high K+ and low Na+?

Accepted Answer

Scala media

Answer

Scala vestibuli

Answer

Scala tympani

Answer

All of the above

Question 8

Which cells in the optic pathway are purely depolarizing?

Accepted Answer

Amacrine cells

Answer

Rods and cones

Answer

Bipolar cells

Answer

Horizontal cells

Question 9

Which of the following is found in higher concentrations in aqueous humor than in plasma?

Accepted Answer

Ascorbic acid

Answer

Protein

Answer

Glucose

Answer

Urea

Question 10

What function is the pretectal area responsible for?

Accepted Answer

Light reflex

Answer

Auditory reflex

Answer

Stapedial reflex

Answer

Doll's eye movements

Sensory Systems — MCQs

Sensory Systems — MCQs

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