Sensory Systems — MCQs

Sensory Systems Indian Medical PG Practice Questions and MCQs

Question 361: Action of ciliary muscle:

A. Change in shape of lens (Correct Answer)
B. Constriction of pupil
C. Dilatation of pupil
D. Facilitates aqueous humor drainage

Explanation: ***Change in shape of lens*** - The ciliary muscle contracts or relaxes to alter the tension on the **suspensory ligaments**, which in turn changes the **curvature and thickness of the lens**. - This process, known as **accommodation**, allows the eye to focus on objects at various distances. *Constriction of pupil* - **Pupillary constriction** is primarily controlled by the **sphincter pupillae muscle**, which is innervated by the parasympathetic nervous system. - This action regulates the amount of light entering the eye, a function distinct from the ciliary muscle's role in focusing. *Dilatation of pupil* - **Pupillary dilatation** is mediated by the **dilator pupillae muscle**, which is innervated by the sympathetic nervous system. - Like pupillary constriction, this action controls light entry and is separate from the functions of the ciliary muscle. *Facilitates aqueous humor drainage* - **Aqueous humor drainage** primarily occurs through the **trabecular meshwork** and **Schlemm's canal**. - While the ciliary body produces aqueous humor, the ciliary muscle's direct action is not to facilitate its drainage, though its position can indirectly influence outflow pathways.

Question 362: Which among the following is determined by the higher auditory centre?

A. Loudness
B. Sound localization (Correct Answer)
C. Speech discrimination
D. Sound frequency

Explanation: ***Sound localization*** - The **higher auditory centers**, particularly in the cerebral cortex (auditory association areas), integrate **binaural cues** (interaural time differences and interaural intensity differences) to determine the precise **spatial location of a sound source**. - This complex cortical processing of information from both ears allows for accurate three-dimensional sound localization. - This is the primary function specifically **determined by** higher auditory cortical centers through binaural integration. *Loudness* - **Loudness** is primarily determined by the **amplitude of sound waves** and is encoded at the **peripheral level** (cochlea) and lower brainstem levels as the firing rate of auditory nerve fibers and the number of activated neurons. - While perceived at the cortical level, its fundamental determination occurs at earlier stages in the auditory pathway. *Speech discrimination* - While speech discrimination does involve higher auditory cortex (Wernicke's area, superior temporal gyrus), it is considered a **specialized language function** rather than a basic auditory property. - It involves **complex linguistic processing** including phoneme recognition, semantic processing, and language comprehension that extends beyond fundamental auditory processing. - In the context of basic auditory physiology, speech discrimination is classified as a language cortical function rather than a primary auditory center function. *Sound frequency* - **Sound frequency** (pitch) is initially encoded at the **peripheral level** by the **basilar membrane's tonotopic organization** and the firing pattern of auditory nerve fibers (place theory and frequency theory). - This fundamental property is determined at the cochlear and lower brainstem levels, with higher centers perceiving the already-encoded pitch information.

Question 363: Which of the following phrases adequately describes Pacinian corpuscles?

A. Slowly adapting touch receptors
B. A type of pain receptors
C. Rapidly adapting touch receptors (Correct Answer)
D. Located in the joints

Explanation: ***Rapidly adapting touch receptors*** - **Pacinian corpuscles** are classic examples of **rapidly adapting (phasic)** mechanoreceptors, meaning they respond strongly to the onset and offset of a stimulus but quickly cease firing during sustained stimulation. - They are responsible for detecting **vibration** and deep pressure due to their concentric lamellar structure which filters out static pressure. *Slowly adapting touch receptors* - **Slowly adapting (tonic)** receptors, such as **Merkel cells** and **Ruffini endings**, continuously fire during sustained stimulation. - These receptors are involved in sensing **sustained pressure** and **texture**. *A type of pain receptors* - **Pain receptors** are known as **nociceptors**, which are free nerve endings that respond to noxious stimuli (e.g., thermal, mechanical, chemical). - Pacinian corpuscles specifically detect mechanical stimuli like **vibration** and pressure, not pain. *Located in the joints* - While present in the deep layers of the skin, such as the **hypodermis**, and in some organs like the pancreas and mesentery, their primary location for touch sensation is not specifically within the joints. - **Receptors in joints** are typically involved in proprioception and kinesthesia, detecting position and movement.

Question 364: Vanilloid receptors are activated by:

A. Pressure
B. Touch
C. Vibration
D. Pain (Correct Answer)

Explanation: ***Pain*** - **Vanilloid receptors**, specifically **TRPV1 (transient receptor potential vanilloid 1)**, are primarily known as **nociceptors** that respond to noxious stimuli. - Activation of these receptors by **painful heat and capsaicin** (the active component in chili peppers) leads to the sensation of pain. *Pressure* - **Mechanoreceptors** such as Merkel cells, Meissner's corpuscles, Ruffini endings, and Pacinian corpuscles are responsible for sensing pressure. - Vanilloid receptors are not the primary transducers of pressure sensation. *Touch* - **Tactile receptors** like Merkel cells, Meissner's corpuscles, and hair follicle receptors mediate the sensation of touch. - Touch is a distinct sensory modality from pain, and vanilloid receptors do not primarily detect light touch. *Vibration* - **Pacinian corpuscles** are highly sensitive mechanoreceptors specifically adapted for detecting vibration. - While some sensory receptors can have overlapping functions, vanilloid receptors are not primarily involved in sensing vibration.

Question 365: Nerve endings sensitive to noxious stimuli are present in all except:

A. Intestine
B. Stomach
C. Liver (Correct Answer)
D. Mesentery

Explanation: ***Liver*** - The **liver parenchyma** itself is notable for its lack of **pain receptors**; therefore, sensations like cutting or burning of the liver tissue do not evoke direct pain. - Pain associated with the liver typically arises from the stretching of its **fibrous capsule (Glisson's capsule)** or involvement of surrounding structures, rather than from within the organ. *Intestine* - The intestine contains abundant **nociceptors** that respond to a variety of noxious stimuli, including **distention**, **ischemia**, and **chemical irritants**. - These nerve endings play a crucial role in mediating **visceral pain** experienced during conditions such as inflammatory bowel disease or irritable bowel syndrome. *Stomach* - The stomach is richly innervated with **nociceptors** that detect painful stimuli such as extreme **distension**, potent **chemical irritants**, and **ischemia**. - These nerve endings contribute to the sensation of **gastric pain** associated with conditions like gastritis, ulcers, and gastroesophageal reflux disease. *Mesentery* - The mesentery contains numerous **nociceptors** that are highly sensitive to **stretching**, **ischemia**, and **inflammation**. - Pain originating from the mesentery can be intense and is often implicated in conditions like **mesenteric ischemia** or **peritonitis**.

Question 366: Caloric test assesses the function of

A. Anterior semicircular canal
B. Superior semicircular canal
C. Posterior semicircular canal
D. Lateral semicircular canal (Correct Answer)

Explanation: ***Lateral semicircular canal*** - The **caloric test** specifically evaluates the function of the **lateral (horizontal) semicircular canal** and its associated neural pathways. - Introducing warm or cold water into the ear canal creates convection currents in the endolymph of the lateral semicircular canal, stimulating or inhibiting the hair cells. *Anterior semicircular canal* - The caloric test primarily affects the horizontal canal due to its anatomical position; it does not directly assess the **anterior semicircular canal**. - The anterior canal is mainly involved in sensing **rotational movements** of the head in the sagittal plane. *Superior semicircular canal* - The **superior semicircular canal** is another name for the anterior semicircular canal and is therefore not directly assessed by the caloric test. - It detects angular accelerations, particularly when the head is tilted forward or backward. *Posterior semicircular canal* - The caloric test has minimal to no direct impact on the **posterior semicircular canal**. - The posterior canal is involved in sensing rotational movements, particularly those in the coronal plane, like tilting the head to the shoulder.

Question 367: Receptors that are stimulated by a change in the chemical composition of the environment are:

A. Nociceptors
B. Chemoreceptors (Correct Answer)
C. Mechanoreceptors
D. None of the options

Explanation: ***Chemoreceptors*** - They are specifically designed to detect and respond to **chemical stimuli**, such as the concentration of various substances in the environment or bodily fluids. - Examples include receptors for taste, smell, blood pH, and oxygen levels. *Nociceptors* - These receptors are responsible for detecting and signaling **painful stimuli**, which can be thermal, mechanical, or chemical, but their primary function is pain detection, not chemical composition change itself. - They are activated by noxious stimuli that threaten tissue damage. *Mechanoreceptors* - These receptors respond to **mechanical forces** such as pressure, stretch, touch, and vibration. - Examples include Pacinian corpuscles, Meissner's corpuscles, and receptors in the skin and muscles responsible for touch and proprioception. *None of the options* - This option is incorrect because **chemoreceptors** accurately describe receptors stimulated by changes in chemical composition.

Question 368: Which of the following will occur in a girl who suddenly stops spinning after several seconds of spinning to the left?

A. Her eyes will move slowly to the right (Correct Answer)
B. The hair cells in the right semicircular canal will depolarize
C. When asked to point to a target, the girl will point to the right of the target
D. The cupula in the right semicircular canal will move away from the utricle

Explanation: ***Her eyes will move slowly to the right*** - After spinning to the left and suddenly stopping, **post-rotatory nystagmus** occurs due to continued endolymph movement. - The endolymph continues to move to the LEFT due to **inertia**, creating a sensation of rotating to the **RIGHT**. - This produces **nystagmus** with the **slow phase to the right** (direction of perceived rotation) and fast corrective phase to the left. - The **vestibulo-ocular reflex** generates this nystagmus as the brain interprets the continued endolymph movement as actual rotation. *The hair cells in the right semicircular canal will depolarize* - This is incorrect. Upon stopping a left spin, the endolymph continues moving LEFT due to inertia. - In the **right horizontal canal**, this creates **ampullary-petal flow** (toward the ampulla), which causes **hyperpolarization**, not depolarization. - During the actual left spin, it was the **left canal** that was depolarized (ampullary-fugal flow in horizontal canals causes excitation). *When asked to point to a target, the girl will point to the right of the target* - After stopping from spinning left, the sensation is of spinning to the RIGHT, causing a **past-pointing phenomenon**. - This perceived rightward rotation causes the person to point to the **LEFT** of the target, not the right. - The brain compensates for the perceived motion in the wrong direction. *The cupula in the right semicircular canal will move away from the utricle* - Upon stopping, the endolymph in the right canal continues moving to the LEFT (original spin direction) due to inertia. - This deflects the cupula **toward the utricle** (ampullary-petal), not away from it. - Ampullary-petal deflection in horizontal canals causes hyperpolarization of hair cells.

Question 369: Ruffini end organ is associated with sensation of?

A. Vibration
B. Position sense (Correct Answer)
C. Cold
D. Pressure

Explanation: ***Position sense*** - **Ruffini end organs** are slow-adapting mechanoreceptors located in the **dermis** and subcutaneous tissue that are primarily specialized for detecting **skin stretch**. - They play a significant role in **proprioception** (position sense) by sensing static skin displacement and joint angles, particularly in the fingers and joints. - Modern physiology emphasizes their contribution to **position sense** and detection of sustained stretch rather than just pressure. *Pressure* - While Ruffini endings can detect sustained pressure, this is not their primary function. - **Merkel discs** are the main receptors for sustained pressure and fine touch discrimination. - **Pacinian corpuscles** detect deep pressure and vibration. *Vibration* - **Pacinian corpuscles** are rapidly adapting mechanoreceptors specialized for detecting **vibration** and deep pressure. - **Meissner's corpuscles** detect light touch and low-frequency vibration. *Cold* - The sensation of **cold** is detected by specialized **cold thermoreceptors** (free nerve endings). - **Krause end bulbs** (whose existence as distinct receptors is now debated) were historically associated with cold sensation.

Question 370: Two point discrimination test exhibits maximum sensitivity in -

A. Toes
B. Shin
C. Soles
D. Finger pads (Correct Answer)

Explanation: ***Finger pads*** - The **finger pads** have a high density of **Meissner's corpuscles** and other sensory receptors, allowing for fine tactile discrimination. - This region is crucial for activities requiring high tactile sensitivity and dexterity, resulting in a very small **two-point discrimination threshold**. *Toes* - While toes have some tactile sensitivity, their receptor density is **significantly lower** than that found in the finger pads. - The primary function of toes involves balance and propulsion rather than fine tactile discrimination. *Shin* - The **shin** (anterior lower leg) has a relatively sparse distribution of tactile receptors compared to distal extremities. - This area is not designed for fine touch perception, resulting in a **large two-point discrimination threshold**. *Soles* - The **soles of the feet** are adapted for sensory input related to pressure, texture, and proprioception for balance and locomotion. - Although the soles have numerous receptors, they are generally less sensitive for **two-point discrimination** than the finger pads, reflecting a different functional specialization.

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

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free