Sensory Systems — MCQs
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What type of reflex is the righting reflex?
Ruffini end organ is associated with sensation of:
A wave in ERG is due to activity of:
What is the characteristic of the second Purkinje image in relation to eye movement?
Which structure of the eye has the maximum refractive power?
Transducin is a protein found in:
Salty taste is due to?
Meissner's corpuscles are for
Following are the changes during accommodation, except:
What is the primary function of the otolith organs?
Sensory Systems Indian Medical PG Practice Questions and MCQs
Question 441: What type of reflex is the righting reflex?
- A. Cochlear reflex
- B. Spinal reflex
- C. Vestibular reflex (Correct Answer)
- D. None of the options
Explanation: ***Vestibular reflex*** - The **righting reflex** is primarily mediated by the **vestibular system** (labyrinthine apparatus), which detects changes in head position and movement in space. - This reflex helps maintain proper **head and body orientation** relative to gravity, ensuring balance and stability. - Note: Righting reflexes are actually a group of **postural reflexes** that also involve visual, neck proprioceptive, and body proprioceptive inputs, but the **vestibular (labyrinthine) component is the most important** and is often emphasized in medical education. *Cochlear reflex* - The **cochlea** is primarily involved in **hearing**, translating sound vibrations into electrical signals. - The cochlear reflex, such as the **stapedial reflex**, is an auditory protective reflex that dampens loud sounds, not involved in postural control or spatial orientation. *Spinal reflex* - A **spinal reflex** is mediated solely by the **spinal cord** without supraspinal integration (e.g., knee jerk, withdrawal reflex). - The righting reflex requires integration at the **brainstem and higher centers**, involving the vestibular nuclei, and cannot function through spinal cord alone. *None of the options* - This option is incorrect for exam purposes, as the righting reflex is conventionally taught as primarily a **vestibular-mediated postural reflex**. - The vestibular system is the key sensory component for detecting head position changes that trigger righting responses.
Question 442: Ruffini end organ is associated with sensation of:
- A. Heat
- B. Touch
- C. Pressure (Correct Answer)
- D. Cold
Explanation: ***Pressure*** - **Ruffini end organs**, also known as Ruffini corpuscles, are **mechanoreceptors** located in the dermis and subcutaneous tissue. - They are responsible for detecting **sustained pressure**, skin stretch, and contribute to proprioception. *Cold* - The sensation of **cold** is primarily detected by **Krause end bulbs** and specialized unmyelinated free nerve endings. - These receptors are sensitive to temperature drops and are not associated with Ruffini end organs. *Heat* - The sensation of **heat** is primarily detected by specific **thermoreceptors**, often involving unmyelinated free nerve endings. - These receptors respond to increases in temperature and are distinct from the mechanoreceptive function of Ruffini end organs. *Touch* - The sensation of **touch** is a broad category, with different types detected by various receptors. - **Meissner's corpuscles** detect light touch and changes in texture, while **Merkel's discs** detect sustained light touch and pressure, differentiating them from Ruffini's role in sustained pressure and stretch.
Question 443: A wave in ERG is due to activity of:
- A. Pigmented epithelium
- B. Rods and cones (Correct Answer)
- C. Ganglion cell
- D. Bipolar cell
Explanation: ***Rods and cones*** - The **electroretinogram (ERG)** measures the electrical responses of various retinal cells to light stimuli. - The **a-wave** of the ERG primarily reflects the activity of the **photoreceptors (rods and cones)** as they hyperpolarize in response to light. *Pigmented epithelium* - The **retinal pigmented epithelium (RPE)** plays a crucial role in photoreceptor health and function but does not directly generate the primary electrical waves measured by the standard ERG. - Its dysfunction can lead to secondary changes in ERG, but its activity is not the direct source of the a-wave. *Ganglion cell* - **Ganglion cells** are the output neurons of the retina, transmitting visual information to the brain. - Their activity is generally not well-represented in the standard ERG, which primarily assays outer and middle retinal layers. *Bipolar cell* - **Bipolar cells** transmit signals from photoreceptors to ganglion cells and contribute to the **b-wave** component of the ERG. - The b-wave, not the a-wave, is largely generated by the depolarizing activity of bipolar cells and Müller cells.
Question 444: What is the characteristic of the second Purkinje image in relation to eye movement?
- A. Inverted and moves in same direction
- B. Inverted and moves in opposite direction
- C. Erect and moves in same direction (Correct Answer)
- D. Erect and moves in opposite direction
Explanation: ***Erect and moves in same direction*** - The second Purkinje image (P2) is formed by reflection from the **posterior surface of the cornea**. - This surface acts as a convex mirror, producing a **virtual, erect, and diminished image**. - The image moves in the **same direction** as the eye movement, characteristic of reflections from the first three Purkinje images (P1, P2, P3). - P2 is clinically used in keratometry and assessment of corneal curvature. *Erect and moves in opposite direction* - While the image orientation (erect) would apply to P2, the direction of movement is incorrect. - Only the **fourth Purkinje image (P4)**, formed by the **posterior lens surface**, moves in the opposite direction to eye movement. - P4 is the only inverted Purkinje image due to reflection from the concave posterior lens surface. *Inverted and moves in same direction* - The second Purkinje image is **erect, not inverted**. - All Purkinje images are erect except P4, which is inverted due to reflection from the concave posterior lens surface. - This combination (inverted + same direction) does not correspond to any Purkinje image. *Inverted and moves in opposite direction* - This describes the **fourth Purkinje image (P4)**, not the second. - P4 is formed by reflection from the **posterior surface of the lens** (concave surface), which produces an inverted image. - The second Purkinje image (P2) is always erect, being formed by the posterior corneal surface.
Question 445: Which structure of the eye has the maximum refractive power?
- A. Anterior surface of lens
- B. Posterior surface of lens
- C. Anterior surface of cornea (Correct Answer)
- D. Posterior surface of cornea
Explanation: ***Anterior surface of cornea*** - The **cornea** accounts for approximately two-thirds of the eye's total refractive power due to the large difference in refractive index between air and the corneal tissue. - The **anterior surface of the cornea** is the primary site of light refraction as light enters the eye from the air. *Anterior surface of lens* - The **lens** contributes significantly to accommodation, but its overall refractive power is less than that of the cornea in the unaccommodated state. - The change in refractive index between the aqueous humor and the lens is less pronounced compared to the air-cornea interface. *Posterior surface of lens* - The **posterior surface of the lens** also contributes to the focusing power of the lens, but its curvature and refractive index difference are typically less than the anterior surface of the cornea. - Its contribution to total refractive power is secondary to the anterior corneal surface and the anterior lens surface. *Posterior surface of cornea* - The **posterior surface of the cornea** has a much smaller refractive power compared to the anterior surface due to the smaller difference in refractive index between the cornea and the aqueous humor. - This interface does contribute to refraction but is not the primary focusing component.
Question 446: Transducin is a protein found in:
- A. Glomerulus
- B. Retina (Correct Answer)
- C. Skeletal muscle
- D. Adrenal medulla
Explanation: ***Retina*** - **Transducin** is a **G-protein** crucial for **phototransduction** in the retina. - It plays a key role in the cascade that converts light signals into electrical impulses within **rod** and **cone photoreceptor cells**. *Glomerulus* - The **glomerulus** is a capillary network in the **kidney** responsible for filtering blood. - Its primary proteins are involved in filtration barriers, such as **podocin** and **nephrin**, not transducin. *Skeletal muscle* - **Skeletal muscle** contains proteins like **actin**, **myosin**, and **troponins** for contraction. - Transducin is not involved in muscle contraction or skeletal muscle function. *Adrenal medulla* - The **adrenal medulla** produces **catecholamines** like epinephrine and norepinephrine. - Proteins in this gland are involved in hormone synthesis, storage, and release, not light perception.
Question 447: Salty taste is due to?
- A. Sodium ion channels (Correct Answer)
- B. Calcium ion channels
- C. G-protein coupled receptors
- D. Proton channels
Explanation: ***Sodium ion channels*** - The sensation of **salty taste** is primarily mediated by the direct influx of **sodium ions (Na+)** into taste receptor cells. - This influx leads to **depolarization** of the cell membrane, triggering neurotransmitter release and signaling to the brain. *Calcium ion channels* - While calcium ions are crucial for various cellular processes, including **neurotransmitter release**, they are not the primary initiators of the salty taste transduction pathway. - Calcium channels are more directly involved in the sensation of **umami** and **sweet tastes**, often via G-protein coupled receptors. *G-protein coupled receptors* - **G-protein coupled receptors (GPCRs)** are responsible for the transduction of **sweet, bitter, and umami tastes**. - They are not involved in the direct detection of **saline compounds**, which operate through ion channels. *Proton channels* - **Proton channels (H+)** are primarily involved in the sensation of **sour taste**. - The influx of protons causes intracellular acidification, leading to cell depolarization.
Question 448: Meissner's corpuscles are for
- A. Touch (Correct Answer)
- B. Temperature
- C. Pressure
- D. Proprioception
Explanation: ***Touch*** - **Meissner's corpuscles** are specialized mechanoreceptors located in the **dermal papillae** of glabrous (hairless) skin, particularly abundant in fingertips, palms, and soles. - They are responsible for sensing **light touch**, discrimination of textures, and low-frequency vibrations (flutter), playing a crucial role in tactile discrimination. - These are **rapidly adapting** receptors that respond to dynamic skin deformation. *Temperature* - **Thermoreceptors** are primarily **free nerve endings** with specific ion channels (TRPM8 for cold, TRPV1 for heat) that detect temperature changes, not Meissner's corpuscles. - These receptors detect thermal stimuli and are distinct from the mechanoreceptors involved in touch. *Pressure* - **Pacinian corpuscles** detect deep pressure and high-frequency vibrations, while **Merkel cells** sense sustained pressure and fine spatial details. - Meissner's corpuscles respond to light touch and dynamic changes in tactile stimuli, not deep or sustained pressure. *Proprioception* - **Proprioception** is the sense of the relative position of body parts and strength of effort used in movement, mediated by receptors found in muscles (**muscle spindles**), tendons (**Golgi tendon organs**), and joints. - Meissner's corpuscles are cutaneous receptors and do not contribute to proprioception.
Question 449: Following are the changes during accommodation, except:
- A. Constriction of pupil
- B. Dilatation of pupil (Correct Answer)
- C. Convergence of eyeball
- D. Increase in the anterior curvature of lens
Explanation: ***Dilatation of pupil*** - During **accommodation**, the pupils constrict (miosis) to increase the **depth of field** and sharpen the image on the retina. - Dilatation of the pupil (mydriasis) would lead to a larger circle of confusion and a **blurred image** for near vision. *Constriction of pupil* - This is a normal part of the **accommodation reflex**, driven by **parasympathetic activation**, which helps to improve the focus of near objects. - Pupillary constriction **increases the depth of field**, reducing spherical aberration and improving image clarity. *Convergence of eye ball* - As part of the **near reflex triad**, both eyes turn inward (converge) to ensure that the image of the near object falls on the **fovea** of each eye. - This movement helps maintain **binocular single vision** and prevents double vision (diplopia). *Increase in the anterior curvature of lens* - The **ciliary muscles contract**, relaxing the zonular fibers, allowing the **elastic lens** to become more convex, specifically increasing its anterior curvature. - This increased convexity **enhances the refractive power** of the lens, bringing the focal point of near objects onto the retina.
Question 450: What is the primary function of the otolith organs?
- A. Producing the vestibular-ocular reflex
- B. Detecting the position of the head in space (Correct Answer)
- C. Producing rotary nystagmus
- D. Detecting angular acceleration
Explanation: ***Detecting the position of the head in space*** - The **otolith organs**, comprising the **utricle** and **saccule**, are responsible for detecting **linear acceleration** and **gravitational forces**. - This information allows the brain to perceive the **static head position** relative to gravity and linear movements. *Producing the vestibular-ocular reflex* - While the otolith organs contribute to overall vestibular function, the primary role in producing the **vestibular-ocular reflex (VOR)**, especially for rotational movements, is mainly attributed to the **semicircular canals**. - The VOR helps stabilize gaze during head movements, coordinating eye movements in the opposite direction of head motion. *Producing rotary nystagmus* - **Rotary nystagmus** is typically associated with stimulation of the **semicircular canals**, which detect angular acceleration. - The otolith organs detect linear acceleration and static head position, not rotational movements causing nystagmus. *Detecting angular acceleration* - The **semicircular canals** are specialized structures within the inner ear designed to detect **angular acceleration** (rotational movements of the head). - The otolith organs are sensitive to **linear acceleration** and the pull of gravity, not angular motion.
Practice by Chapter
General Sensory Physiology
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Somatosensation
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Retinal Physiology
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Visual Pathways and Processing
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Auditory System
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Vestibular System
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Taste and Smell
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Sensory Integration
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