Retinal Physiology — MCQs
Which structure contains the second-order neurons in the optic pathway?
The parvocellular pathway from lateral geniculate nucleus to visual cortex is most sensitive for the stimulus of
Hyperpolarization is caused by which ions?
Colour vision is with the help of:
Which of the following statements about the fovea is true?
Initiation of visual impulse is associated with which of the following?
Which substance is most likely to increase in the rods of the retina when the light is turned on?
Fine touch and rapidly adapting receptor is
Identify the inheritance pattern shown below.
Which of the following cells in the brain are responsible for handling information regarding ability to read the slide below? (Recent NEET Pattern 2016-17)
Retinal Physiology Indian Medical PG Practice Questions and MCQs
Question 1: Which structure contains the second-order neurons in the optic pathway?
- A. Optic nerve
- B. Medial geniculate body
- C. Layer of retina (Correct Answer)
- D. Lateral geniculate body
Explanation: ***Layer of retina*** - The **second-order neurons** in the visual pathway are the **bipolar cells** of the retina [1] - Their **cell bodies are located in the inner nuclear layer** of the retina - These cells synapse with **photoreceptors** (first-order neurons) and transmit signals to **ganglion cells** (third-order neurons) [1], [2] - This makes the retina the correct answer as it contains the second-order neuronal cell bodies *Lateral geniculate body* - The **lateral geniculate body (LGB)** contains cell bodies of neurons that receive input from **retinal ganglion cells** [3] - These are **fourth-order neurons** in the visual pathway, not second-order - The LGB serves as a relay station in the thalamus before visual information reaches the primary visual cortex *Optic nerve* - The **optic nerve** consists of **axons of retinal ganglion cells** (third-order neurons) [3] - It does not contain cell bodies, only nerve fibers - It transmits visual information from the retina to the optic chiasm and then to the lateral geniculate body [3] *Medial geniculate body* - The **medial geniculate body (MGB)** is part of the **auditory pathway**, not the visual pathway - It is a thalamic nucleus that relays auditory information to the auditory cortex - It has no role in visual processing
Question 2: The parvocellular pathway from lateral geniculate nucleus to visual cortex is most sensitive for the stimulus of
- A. Fine spatial detail (Correct Answer)
- B. Saccadic eye movements
- C. Luminance contrast
- D. Temporal frequency
Explanation: ***Fine spatial detail*** - The **parvocellular pathway** is specialized for processing **high-acuity vision**, including color and fine spatial resolution. - Its neurons have **small receptive fields** and respond best to detailed patterns and stationary objects. *Saccadic eye movements* - **Saccadic eye movements** are rapid eye movements controlled by various brain regions, but their generation and control are not directly the primary function of the parvocellular pathway. - These movements are involved in scanning the visual field to bring objects of interest onto the fovea, which is then analyzed by the parvocellular pathway. *Luminance contrast* - While the parvocellular pathway does respond to contrast, the **magnocellular pathway** is more specialized for detecting rapid changes in **luminance contrast** and motion. - The magnocellular pathway has larger receptive fields and processes information about movement and depth. *Temporal frequency* - **Temporal frequency**, or the rate of flicker or motion, is primarily processed by the **magnocellular pathway**. - This pathway is optimized for detecting movement and rapid changes in the visual scene, rather than fine spatial details.
Question 3: Hyperpolarization is caused by which ions?
- A. K+ (Correct Answer)
- B. Na+
- C. HCO3-
- D. Ca2+
Explanation: ***K+*** - **Efflux of K+ ions** out of the cell makes the inside of the cell more negative, leading to **hyperpolarization**. - This efflux is typically mediated by **voltage-gated potassium channels** opening, or by activation of **GABA-A** or **glycine receptors** that increase K+ conductance. *Na+* - **Influx of Na+ ions** into the cell makes the inside of the cell more positive, causing **depolarization**, not hyperpolarization. - This influx is responsible for the **rising phase of an action potential**. *Ca2+* - **Influx of Ca2+ ions** into the cell also contributes to **depolarization** and can trigger various intracellular processes. - Ca2+ influx is crucial for **neurotransmitter release** and muscle contraction, but not for hyperpolarization. *HCO3-* - Bicarbonate ions (**HCO3-**) play a significant role in **maintaining pH balance** in the body and are involved in various physiological processes. - While ion channels can conduct HCO3-, their movement is not typically the primary cause of cell membrane hyperpolarization.
Question 4: Colour vision is with the help of:
- A. Cortex
- B. Optic disc
- C. Rods
- D. Cones (Correct Answer)
Explanation: ***Cones*** - **Cones** are photoreceptor cells in the retina responsible for **color vision** and high spatial acuity in bright light conditions. - There are three types of cones, each sensitive to different wavelengths of light (red, green, and blue). *Cortex* - The **visual cortex** in the brain processes visual information, including color, but it relies on input from the photoreceptors. - The cortex itself does not initially detect color; it interprets signals sent from the retina. *Optic disc* - The **optic disc** is the point where the optic nerve leaves the eye, and it contains no photoreceptor cells. - This area is therefore known as the "blind spot" and cannot detect light or color. *Rods* - **Rods** are photoreceptor cells primarily responsible for **scotopic (low-light) vision** and peripheral vision. - They are highly sensitive to light but do not detect color, only shades of gray.
Question 5: Which of the following statements about the fovea is true?
- A. It contains only cones.
- B. It contains only rods.
- C. It has the lowest threshold for light.
- D. It has maximum visual acuity. (Correct Answer)
Explanation: ***It has maximum visual acuity.*** - The fovea is the central part of the **macula** and is responsible for **sharp, detailed vision** due to a high concentration of cones and a specialized anatomical arrangement. - This region has a 1:1 ratio between **photoreceptors, bipolar cells, and ganglion cells**, and overlying retinal layers are displaced to allow light to strike the cones directly, optimizing visual acuity. *It has the lowest threshold for light.* - The **rods**, not the cones or fovea, are responsible for vision in **low-light conditions** because they are highly sensitive to dim light, contributing to the lowest light threshold. - The fovea, containing only cones, is primarily for **photopic (daylight) vision** and requires more light for stimulation compared to the rod-rich periphery. *It contains only cones.* - While overwhelmingly dominated by cones, the fovea does not exclusively contain only cones; there are a few residual rods at its margins, though the very center, the **foveola**, is rod-free. - Cones are responsible for **color vision** and high spatial resolution, which is why the fovea is central to sharp, color-sensitive vision. *It contains only rods.* - The fovea is entirely devoid of rods in its central part (foveola) and primarily consists of cones, with rods increasing in density in the **retinal periphery**. - Rods are responsible for **scotopic (night) vision** and detecting motion but lack the ability to resolve fine detail or color, which distinguishes them from cones.
Question 6: Initiation of visual impulse is associated with which of the following?
- A. Condensation of opsin with vitamin A aldehyde
- B. Photoisomerization of 11-cis-retinal (Correct Answer)
- C. NADP
- D. NAD
Explanation: ***Photoisomerization of 11-cis-retinal*** - The initiation of a visual impulse begins with the **photoisomerization of 11-cis-retinal** to **all-trans-retinal** upon absorption of light by rhodopsin. - This is the **primary photochemical event** that triggers the entire phototransduction cascade. - The conformational change in retinal subsequently causes a conformational change in the associated **opsin protein**, activating the **rhodopsin molecule** (visual purple) and initiating signal transduction through the G-protein cascade. - This process is also known as **photoactivation** or the first step in **bleaching of rhodopsin**. *Condensation of opsin with vitamin A aldehyde* - **Condensation of opsin with 11-cis-retinal** (vitamin A aldehyde derivative) occurs in the **dark** to form rhodopsin (visual purple). - This process represents the **regeneration of the photopigment**, not the light-triggered initiation of the visual impulse. - This is the reverse process that restores rhodopsin after bleaching. *NADP* - **NADP (nicotinamide adenine dinucleotide phosphate)** is primarily involved in **anabolic reactions** and oxidative stress response, acting as a cofactor in various metabolic pathways. - It is **not directly involved in the phototransduction cascade** that initiates a visual impulse. *NAD* - **NAD (nicotinamide adenine dinucleotide)** is a coenzyme crucial for **catabolic reactions** and energy metabolism, particularly in glycolysis and the citric acid cycle. - Similar to NADP, it plays **no direct role in the primary photochemistry** or signal transduction mechanisms that initiate a visual impulse.
Question 7: Which substance is most likely to increase in the rods of the retina when the light is turned on?
- A. Cyclic guanosine monophosphate (cGMP)
- B. Metarhodopsin II (Correct Answer)
- C. Cyclic adenosine monophosphate (cAMP)
- D. Rhodopsin
Explanation: ***Metarhodopsin II*** - When **light strikes rhodopsin**, it undergoes a conformational change, forming **metarhodopsin II**, which is the active form that initiates the phototransduction cascade. - **Metarhodopsin II** activates a **G-protein (transducin)**, leading to a decrease in cGMP and subsequent rod hyperpolarization. *Cyclic guanosine monophosphate (cGMP)* - **Light activation** of rhodopsin triggers a cascade that **decreases cGMP concentration** in the rods, leading to closing of cGMP-gated sodium channels. - In the **dark**, cGMP levels are high, keeping the sodium channels open and the rod depolarized. *Cyclic adenosine monophosphate (cAMP)* - **cAMP** is a significant second messenger in many cellular processes but is **not directly involved in the primary phototransduction pathway** in rods. - Its levels do not acutely increase in response to light in the same manner as molecules in the phototransduction cascade. *Rhodopsin* - **Rhodopsin** is the **light-sensitive pigment** located in the rod outer segment membranes. - When light is turned on, rhodopsin is **converted** into its active form, metarhodopsin II, meaning the amount of intact rhodopsin itself will decrease, not increase.
Question 8: Fine touch and rapidly adapting receptor is
- A. Ruffini's nerve ending
- B. Pacinian corpuscle
- C. Meissners corpuscle (Correct Answer)
- D. Merkel's disc
Explanation: ***Meissners corpuscles*** - They are responsible for **discriminative touch** and ability to differentiate between two points close together. - These receptors are **rapidly adapting**, meaning they respond strongly to initial stimulation but quickly cease firing if the stimulus is constant. *Ruffini's nerve ending* - These are **slowly adapting receptors** sensitive to **stretch** and sustained pressure. - They provide information about **proprioception** and the shape of objects. *Pacinian corpuscle* - Pacinian corpuscles are **rapidly adapting mechanoreceptors** sensitive to **vibration** and deep pressure. - They have a large receptive field and are less involved in fine touch discrimination. *Merkel's disc* - Merkel's discs are **slowly adapting mechanoreceptors** responsible for sensing sustained touch and **pressure**. - They contribute to the perception of **texture** and edges, having a small receptive field.
Question 9: Identify the inheritance pattern shown below.
- A. Y linked recessive
- B. X linked recessive (Correct Answer)
- C. X linked dominant
- D. Y linked dominant
Explanation: ***X linked recessive*** - The pattern shows that mainly **males are affected**, and the trait skips generations (e.g., individual I-1 is unaffected, but his children are affected). - Affected fathers (like II-3) do not pass the trait to their sons, but their daughters are carriers and can pass it on to their sons (like IV-1). *Y linked recessive* - In Y-linked inheritance, only **males would be affected**, and all sons of an affected father would inherit the trait. - This pedigree shows unaffected fathers having affected sons, and not all sons of affected males are affected directly. *X linked dominant* - In X-linked dominant inheritance, affected fathers pass the trait to **all their daughters**, and at least one parent would be affected in each generation. - This pedigree shows skipping of generations and affected individuals being born to unaffected parents (e.g., II-3 and III-5). *Y linked dominant* - Y-linked inheritance, whether dominant or recessive, would only affect **males** and would be directly passed from father to all sons. - The pedigree shows unaffected parents having affected offspring (e.g., I-1 and I-2 produced II-3), which rules out Y-linked inheritance.
Question 10: Which of the following cells in the brain are responsible for handling information regarding ability to read the slide below? (Recent NEET Pattern 2016-17)
- A. Magnocellular cells
- B. Parvocellular cells (Correct Answer)
- C. Purkinje cells
- D. Pyramidal cells
Explanation: ***Parvocellular cells*** - **Parvocellular cells** (P-cells) are responsible for processing detailed visual information, including **color**, **form**, and fine **texture**. Reading the Ishihara test requires the ability to distinguish specific colors and fine patterns. - They have **small receptive fields** and transmit information about high spatial resolution and chromatic detail, crucial for tasks such as reading and recognizing fine visual cues. *Magnocellular cells* - **Magnocellular cells** (M-cells) are primarily involved in detecting **motion** and processing **low-spatial frequency information**, such as global shape and location. - They have **large receptive fields** and are not primarily responsible for detailed color or pattern discrimination needed for reading. *Purkinje cells* - **Purkinje cells** are a type of large, extensively branched neuron located in the **cerebellar cortex**. - Their primary function is motor coordination, balance, and motor learning, not visual processing or reading. *Pyramidal cells* - **Pyramidal cells** are excitatory neurons found in the cerebral cortex and hippocampus, characterized by their pyramidal-shaped cell bodies. - While they are involved in complex cognitive functions, including parts of visual perception, they are not the specific cells in the primary visual pathway responsible for initial processing of fine details and color as required for reading this type of visual test.
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