Sensory Systems — MCQs

Sensory Systems Indian Medical PG Practice Questions and MCQs

Question 451: Parvocellular pathway carries signals for the detection of

A. Color contrast (Correct Answer)
B. Luminous contrast
C. Temporal frequency
D. Saccadic eye movements

Explanation: ***Color contrast*** - The **parvocellular pathway** is specialized for processing **fine spatial details** and **color information**. - It receives input primarily from **red and green cones**, contributing to the perception of hue and saturation. *Luminous contrast* - The detection of **luminosity** or **brightness contrast** is primarily mediated by the **magnocellular pathway**. - The magnocellular pathway is more sensitive to **changes in light intensity** and achromatic contrasts. *Temporal frequency* - **Temporal frequency** (motion detection and flicker) is predominantly handled by the **magnocellular pathway**. - This pathway has a faster response and is better suited for perceiving rapid changes in visual stimuli. *Saccadic eye movements* - While related to vision, **saccadic eye movements** are controlled by motor systems in the brainstem and frontal eye fields, not directly by the parvocellular pathway itself. - The parvocellular pathway processes **visual input** that informs these movements but does not generate them.

Question 452: What is the range of sonic frequencies that can be heard by humans?

A. 1500-6000 Hz
B. 10,000-15,000 Hz
C. 20-20,000 Hz (Correct Answer)
D. 20,000-25,000 Hz

Explanation: **20-20,000 Hz** - This is the standard **audible frequency range** for human hearing, also known as the audible spectrum - Frequencies below 20 Hz are **infrasound** (inaudible to humans) - Frequencies above 20,000 Hz are **ultrasound** (inaudible to humans) - This range represents the full capacity of the human cochlea and auditory system *1500-6000 Hz* - This represents only the **speech frequency range**, critical for understanding human conversation - This is a narrow subset within the full audible spectrum - Excludes perception of both very low-pitched sounds (bass) and very high-pitched sounds (treble) *10,000-15,000 Hz* - This covers only a **small portion of high frequencies** within human hearing - Omits all low and mid-frequency sounds as well as the highest audible frequencies - Does not represent the complete audible range *20,000-25,000 Hz* - This range consists primarily of **ultrasound frequencies** above human hearing threshold - While some young individuals may detect sounds slightly above 20,000 Hz, this is exceptional and not the standard audible range - Most of this range is completely inaudible to humans

Question 453: During the process of accommodation, there is a change in the shape of the lens. This change involves:

A. decrease in the synthesis of rhodopsin
B. contraction of ciliary muscle
C. an increase principally in the anterior curvature of the lens (Correct Answer)
D. an increase principally in the posterior curvature of the lens

Explanation: ***an increase principally in the anterior curvature of the lens*** - During **accommodation** for **near vision**, the **ciliary muscle contracts**, reducing tension on the **suspensory ligaments**. - This allows the **lens** to become more **convex**, with the **anterior surface** showing a **greater increase in curvature** than the posterior surface. - The **anterior surface** moves forward and bulges more significantly, increasing the **refractive power** of the lens to focus on near objects. *an increase principally in the posterior curvature of the lens* - While the **posterior surface** does increase in curvature during accommodation, this change is **less pronounced** than the anterior surface change. - The **anterior surface** is the primary site of curvature change, contributing more to the increased refractive power needed for near vision. *contraction of ciliary muscle* - The **contraction of the ciliary muscle** is the **triggering mechanism** for accommodation, but it is not the actual change in lens shape itself. - Ciliary muscle contraction leads to relaxation of **suspensory ligaments**, which then allows the lens to change its curvature passively due to its elastic properties. *decrease in the synthesis of rhodopsin* - **Rhodopsin** is a **photopigment** found in **rod cells** of the retina, responsible for **scotopic (dim light) vision**. - Its synthesis is related to **light adaptation** and **dark adaptation**, not the process of **accommodation** for focusing at different distances.

Question 454: Which sensory receptor is primarily responsible for mediating slow vibration sensation?

A. Pacinian capsule
B. Merkel's disc
C. Meissner corpuscles (Correct Answer)
D. Ruffini's endings

Explanation: ***Meissner corpuscles*** - These are **rapidly adapting mechanoreceptors** located in the dermal papillae, particularly abundant in glabrous (hairless) skin of fingertips, palms, and soles. - They are highly sensitive to **low-frequency vibration (10-50 Hz)**, which corresponds to **slow vibration sensation**. - They respond to **light touch** and **dynamic skin deformation**, making them ideal for detecting flutter and slow vibratory stimuli. *Ruffini's endings* - These are **slowly adapting mechanoreceptors** (Type II) located deep in the dermis and subcutaneous tissue. - They primarily detect **sustained pressure**, **skin stretch**, and **joint position**, contributing to proprioception. - They are NOT primarily involved in vibration sensation but rather in detecting continuous mechanical deformation. *Pacinian capsule* - These are **rapidly adapting mechanoreceptors** located deep in the dermis, subcutaneous tissue, and periosteum. - They are highly sensitive to **high-frequency vibration (200-300 Hz)**, which corresponds to **fast vibration sensation**. - They detect rapid changes in pressure and are the most sensitive mechanoreceptors to high-frequency stimuli. *Merkel's disc* - These are **slowly adapting mechanoreceptors** (Type I) found at the epidermal-dermal junction. - They are responsible for **sustained touch**, **pressure**, and **fine tactile discrimination** (texture, edges, shapes). - They do not detect vibration but rather respond to continuous indentation of the skin.

Question 455: Which of the following is true during far accommodation of the eyes?

A. The focal length of the lens is decreased to focus on distant objects
B. The lens becomes more curved due to ciliary muscle contraction
C. The ciliary muscles are relaxed (Correct Answer)
D. The zonula fibers become slack to allow lens flattening

Explanation: ***The ciliary muscles are relaxed*** - During **far accommodation**, the eye is set to focus on distant objects, which requires the **lens** to be as thin and flat as possible. - This flattening of the lens is achieved when the **ciliary muscles relax**, increasing tension on the suspensory ligaments. *The lens becomes more curved due to ciliary muscle contraction* - This statement describes **near accommodation**, where the **ciliary muscles contract** to decrease the tension on the suspensory ligaments, allowing the lens to become more spherical and curved. - A more curved lens has greater refractive power, necessary for focusing on close objects. *The focal length of the lens is decreased to focus on distant objects* - A **decreased focal length** means the lens is more powerful and curved, which is needed for **near vision**, not distant vision. - For **distant vision**, the lens flattens, increasing its **focal length** to match the parallel light rays coming from far away. *The zonula fibers become slack to allow lens flattening* - When the **ciliary muscles relax** during far accommodation, they move away from the lens, which **increases the tension** on the zonula fibers (suspensory ligaments). - This increased tension pulls on the lens, causing it to flatten and become thinner.

Question 456: Which of the following best describes the permeability to sodium and potassium in rod cells in response to light?

A. Decreased sodium permeability, decreased potassium permeability
B. Decreased sodium permeability, increased potassium permeability
C. Increased sodium permeability, decreased potassium permeability
D. Decreased sodium permeability, unchanged potassium permeability (Correct Answer)

Explanation: ***Decreased sodium permeability, unchanged potassium permeability*** - In the dark, rod cells are **depolarized** due to an influx of **sodium (Na+)** and **calcium (Ca2+)** ions through cGMP-gated channels. Light causes the breakdown of cGMP, leading to the closure of these channels, thus **decreasing sodium permeability**. - **Potassium (K+)** channels, which contribute to the resting potential and repolarization, are generally unaffected by light directly and their permeability remains relatively **unchanged**. *Decreased sodium permeability, decreased potassium permeability* - While **sodium permeability** does **decrease** in response to light, **potassium permeability** remains largely **unchanged**, as separate channels regulate K+ egress. - A decrease in both would lead to a more complex and potentially less efficient hyperpolarization response. *Increased sodium permeability, decreased potassium permeability* - This option is incorrect because light causes **hyperpolarization** of rod cells, specifically by **decreasing sodium influx**, not increasing it. - A decrease in potassium permeability would also hinder the repolarization process of the cell. *Decreased sodium permeability, increased potassium permeability* - Although **sodium permeability decreases** in response to light, **potassium permeability** does not significantly **increase**. - While increased potassium efflux would contribute to hyperpolarization, the primary mechanism of hyperpolarization in rod cells upon light exposure is the closure of sodium and calcium channels.

Question 457: Impulses generated in the taste buds of the tongue reach the cerebral cortex via the

A. Thalamus (Correct Answer)
B. Dorsal roots of the first cervical spinal nerve
C. Hypoglossal nerve
D. Lingual nerve

Explanation: ***Thalamus*** - The **thalamus** acts as a crucial relay station for almost all sensory information, including taste, before it reaches the **cerebral cortex** for conscious perception. - Taste signals from the cranial nerves (facial, glossopharyngeal, vagus) travel to the **nucleus of the solitary tract** in the brainstem, then to the **ventral posteromedial (VPM) nucleus of the thalamus**, and finally to the **gustatory cortex**. *Dorsal roots of the first cervical spinal nerve* - The dorsal roots of cervical spinal nerves are involved in transmitting **somatosensory information** (touch, pain, temperature, proprioception) from the neck and head region, not taste. - These nerves carry signals from the spinal cord to the brain, whereas taste pathways originate from cranial nerves in the head. *Hypoglossal nerve* - The **hypoglossal nerve (CN XII)** is primarily a **motor nerve** responsible for controlling the muscles of the tongue, essential for speech and swallowing. - It has no direct role in transmitting taste sensations to the cerebral cortex. *Lingual nerve* - The **lingual nerve** is a branch of the **trigeminal nerve (CN V)** and carries **general sensation** (touch, pain, temperature) from the anterior two-thirds of the tongue. - While it runs with the **chorda tympani** (a branch of the facial nerve that carries taste), the lingual nerve itself does not transmit taste signals to the brain.

Question 458: Function of the ossicles in the middle ear is to

A. None of the options is correct
B. Only amplify sound without conducting it
C. Protect from loud sound
D. Conduct and amplify sound energy from the tympanic membrane to the oval window (Correct Answer)

Explanation: ***Conduct and amplify sound energy from the tympanic membrane to the oval window*** - The **ossicles (malleus, incus, stapes)** form a mechanical chain that both **transmits and amplifies** vibrations from the **tympanic membrane (eardrum)** to the **oval window** of the cochlea. - The ossicles provide approximately **22-fold amplification** through two mechanisms: - **Lever action** of the ossicular chain (1.3× amplification) - **Area ratio** between the large tympanic membrane (55 mm²) and small oval window (3.2 mm²) providing ~17× amplification - This amplification is **essential** to overcome the impedance mismatch between air and the fluid in the cochlea, without which 99.9% of sound energy would be lost. *Only amplify sound without conducting it* - The ossicles cannot amplify without conducting - these are **inseparable functions** of the mechanical chain. - Amplification occurs **during** the conduction process due to the physical structure of the ossicular chain. *Protect from loud sound* - The **middle ear reflex** (acoustic reflex) involving the **tensor tympani** and **stapedius muscles** can reduce sound transmission to protect the inner ear from loud sounds. - However, this is a separate, active protective mechanism involving **muscles**, not the inherent function of the **ossicle bones** themselves. *None of the options is correct* - This option is incorrect because the ossicles do indeed conduct and amplify sound energy to the inner ear.

Question 459: Retinal cells which secrete acetylcholine are:

A. Bipolar cells
B. Ganglion cells
C. Amacrine cells (Correct Answer)
D. Horizontal cells

Explanation: ***Amacrine cells*** - A subpopulation of **amacrine cells** in the retina is known to be **cholinergic**, meaning they synthesize and release **acetylcholine**. - These cholinergic amacrine cells play a role in **directional selectivity** and spatial processing within the retina. *Bipolar cells* - **Bipolar cells** primarily act as interneurons that transmit signals from photoreceptors to ganglion cells in the retina. - They typically release **glutamate** as their neurotransmitter, not acetylcholine. *Ganglion cells* - **Ganglion cells** are the output neurons of the retina, whose axons form the **optic nerve**. - While they receive input from cholinergic amacrine cells, ganglion cells themselves do not secrete acetylcholine; they are primarily glutamatergic. *Horizontal cells* - **Horizontal cells** are interneurons that provide lateral inhibition in the outer plexiform layer of the retina. - They primarily release **GABA** (gamma-aminobutyric acid) as their neurotransmitter, not acetylcholine.

Question 460: Which type of photoreceptor is primarily responsible for color vision?

A. Cones (Correct Answer)
B. Bipolar cells
C. Rods
D. Occipital cortex

Explanation: ***Correct Answer: Cones*** - **Cones** are specialized photoreceptor cells in the retina responsible for **color vision** and **high-acuity vision**. - There are **three types of cones**, each sensitive to different wavelengths of light: **L-cones (red)**, **M-cones (green)**, and **S-cones (blue)**. - This trichromatic system allows for the perception of a wide range of colors through photopic (daylight) vision. *Incorrect: Rods* - **Rods** are photoreceptor cells primarily responsible for **scotopic vision** (vision in low light conditions) and **peripheral vision**. - They contain rhodopsin and do not contribute to color perception, instead detecting differences in light intensity. - Rods are more numerous (~120 million) than cones (~6 million) in the human retina. *Incorrect: Bipolar cells* - **Bipolar cells** are second-order interneurons in the retina that transmit signals from photoreceptors (rods and cones) to ganglion cells. - They play a role in the initial processing of visual information but are **not photoreceptors themselves**. - They do not directly detect light or color. *Incorrect: Occipital cortex* - The **occipital cortex** (visual cortex, area V1-V5) is the brain region responsible for processing visual information, including color perception. - It is **not a photoreceptor** but rather the cortical destination for visual signals. - It receives processed input from the retina via the lateral geniculate nucleus of the thalamus.

Practice by Chapter

General Sensory Physiology

Practice Questions

Somatosensation

Practice Questions

Pain Physiology

Practice Questions

Vision and Optics

Practice Questions

Retinal Physiology

Practice Questions

Visual Pathways and Processing

Practice Questions

Auditory System

Practice Questions

Vestibular System

Practice Questions

Taste and Smell

Practice Questions

Sensory Integration

Practice Questions

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