General Sensory Physiology — MCQs
Which of the following is classified as a pain receptor?
Sensory fibers from the taste buds in the back of the tongue and soft palate travel along:
Which sensory receptor is primarily responsible for mediating slow vibration sensation?
The parvocellular pathway from lateral geniculate nucleus to visual cortex is most sensitive for the stimulus of
Which of the following events does NOT occur in rods in response to light
Which one of the following structures is not a part of the auditory pathway?
Primary afferent fibers secrete which nociceptive substance at the dorsal horn?
Which of the following best describes the electrical response of the rods to light?
Impulses generated in the taste buds of the tongue reach the cerebral cortex via the
Taste sensations from the posterior one-third of the tongue are carried by which nerve?
General Sensory Physiology Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following is classified as a pain receptor?
- A. Free nerve endings (Correct Answer)
- B. Meissner's corpuscle
- C. Pacinian corpuscle
- D. Merkel disc
Explanation: ***Free nerve endings*** - **Free nerve endings** are the most common type of sensory receptor in the skin and are responsible for detecting **pain**, temperature, and crude touch. - They lack specialized structures and are found throughout the epidermis and dermis. *Meissner's corpuscle* - **Meissner's corpuscles** are encapsulated nerve endings that detect **light touch** and **vibration**. - They are rapidly adapting and are abundant in sensitive, hairless skin areas like fingertips and lips. *Pacinian corpuscle* - **Pacinian corpuscles** are large, encapsulated receptors that detect **deep pressure** and **vibration**. - They are rapidly adapting and respond to high-frequency stimuli. *Merkel disc* - **Merkel discs** are specialized epithelial cells associated with nerve endings that detect **sustained pressure** and **texture**. - They are slowly adapting receptors crucial for tactile discrimination.
Question 2: Sensory fibers from the taste buds in the back of the tongue and soft palate travel along:
- A. Facial nerve
- B. Trigeminal nerve
- C. Vagus nerve
- D. Glossopharyngeal nerve (Correct Answer)
Explanation: ***Glossopharyngeal nerve*** - The **glossopharyngeal nerve** (cranial nerve IX) innervates the **posterior one-third of the tongue** for general sensation and taste, as well as the **palatoglossal arch** and **soft palate** [1]. - This nerve carries taste sensations from taste buds located in these regions to the brainstem [1]. *Trigeminal nerve* - The **trigeminal nerve** (cranial nerve V) is primarily responsible for **general sensation** from the face, oral cavity, and anterior two-thirds of the tongue, but it does **not** carry taste fibers. - It also provides motor innervation to the muscles of mastication. *Facial nerve* - The **facial nerve** (cranial nerve VII) carries taste sensation from the **anterior two-thirds of the tongue** via the chorda tympani, not the posterior tongue or soft palate. - It also controls the muscles of facial expression. *Vagus nerve* - The **vagus nerve** (cranial nerve X) plays a minor role in taste, primarily innervating taste buds in the **epiglottis** and **pharynx**, which are not specified in this question [1]. - Its main functions include parasympathetic innervation to many visceral organs.
Question 3: 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 4: 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 5: Which of the following events does NOT occur in rods in response to light
- A. Opening of Na+ channels (Correct Answer)
- B. Activation of transducin
- C. Structural changes in rhodopsin
- D. Decreased intracellular cGMP
Explanation: ***Opening of Na+ channels*** - In response to light, **rods hyperpolarize** due to the **closure of Na+ channels**, which reduces the influx of positive ions. - The opening of Na+ channels would lead to depolarization, which is the opposite of what occurs during light detection in rods. *Activation of transducin* - Light causes **conformational changes in rhodopsin**, which in turn activates the G-protein **transducin**. - Activated transducin then goes on to activate **phosphodiesterase (PDE)** as part of the phototransduction cascade. *Structural changes in rhodopsin* - When light strikes the rhodopsin molecule, the **11-cis-retinal chromophore** isomerizes to **all-trans-retinal**. - This **conformational change** in rhodopsin is the initial step that triggers the entire phototransduction pathway. *Decreased intracellular cGMP* - Activated **phosphodiesterase (PDE)**, stimulated by transducin, hydrolyzes **cGMP to GMP**. - The reduction in **cGMP levels** leads to the closure of cGMP-gated Na+ channels, causing hyperpolarization.
Question 6: Which one of the following structures is not a part of the auditory pathway?
- A. Inferior colliculus
- B. Medial geniculate body
- C. Lateral lemniscus
- D. Medial lemniscus (Correct Answer)
Explanation: ***Medial lemniscus*** - The **medial lemniscus** is a major ascending sensory pathway responsible for transmitting **fine touch, vibration, and proprioception** from the body to the cerebral cortex [2]. - It is part of the **somatosensory system** and does not play a role in auditory processing. *Lateral lemniscus* - The **lateral lemniscus** is a key ascending auditory pathway in the brainstem that transmits information from the **cochlear nuclei** to higher auditory centers [1]. - It plays a crucial role in the processing of **auditory information**, including sound localization. *Inferior colliculus* - The **inferior colliculus** is a principal nucleus in the midbrain that serves as a major integrative and relay center for virtually all **auditory information** ascending from lower brainstem nuclei [1]. - It is involved in **sound localization**, frequency discrimination, and the startle reflex. *Medial geniculate body* - The **medial geniculate body (MGB)** is the auditory nucleus of the **thalamus** that serves as a crucial relay station for auditory information between the **inferior colliculus** and the primary auditory cortex [1]. - It is involved in various aspects of auditory processing, including **sound localization** and attention.
Question 7: Primary afferent fibers secrete which nociceptive substance at the dorsal horn?
- A. Substance P (Correct Answer)
- B. Acetylcholine
- C. Norepinephrine
- D. Epinephrine
Explanation: ***Substance P*** - **Substance P** is a neuropeptide released by **C fibers** and **A-delta fibers** (primary afferent nociceptors) in the dorsal horn of the spinal cord. - It acts as a **neurotransmitter** and **neuromodulator**, contributing to the transmission and amplification of pain signals. *Acetylcholine* - **Acetylcholine** is a primary neurotransmitter in the **neuromuscular junction** and the autonomic nervous system. - While it has some roles in the CNS, it is not the primary nociceptive substance secreted by afferent fibers in the dorsal horn. *Norepinephrine* - **Norepinephrine** (noradrenaline) is a neurotransmitter involved in the **fight-or-flight response** and mood regulation. - It can modulate pain, but it is not directly released by primary afferent fibers as a nociceptive substance in the dorsal horn. *Epinephrine* - **Epinephrine** (adrenaline) is a hormone and neurotransmitter primarily associated with the **sympathetic nervous system** and stress response. - It does not serve as a direct nociceptive transmitter released by primary afferent fibers in the spinal cord.
Question 8: Which of the following best describes the electrical response of the rods to light?
- A. Depolarization
- B. Hyperpolarization (Correct Answer)
- C. Action potential
- D. Capacitive discharge
Explanation: ***Hyperpolarization*** - Light causes **rhodopsin** to activate a G-protein cascade, leading to the closure of **cGMP-gated Na+ channels**. - This closure reduces the influx of positive ions (Na+), resulting in the cell becoming **more negative** (hyperpolarized). *Depolarization* - **Depolarization** occurs in the dark due to the continuous influx of Na+ ions through open cGMP-gated channels. - This is the "dark current" which is interrupted by light, leading to hyperpolarization, not depolarization. *Action potential* - **Rods and cones** do not generate action potentials; they produce graded potentials in response to light. - Action potentials are generated by **ganglion cells** further down the visual pathway. *Capacitive discharge* - **Capacitive discharge** is a term related to electrical components and does not describe the physiological electrical response of photoreceptor cells. - This term is irrelevant to the **neurobiological process** of phototransduction.
Question 9: 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 10: Taste sensations from the posterior one-third of the tongue are carried by which nerve?
- A. Glossopharyngeal (Correct Answer)
- B. Lingual
- C. Chorda tympani
- D. Vagus
Explanation: ***Glossopharyngeal*** - The **glossopharyngeal nerve (CN IX)** is responsible for conveying **taste sensation** from the posterior one-third of the tongue [1]. - It also provides general sensation to this region and motor innervation to the stylopharyngeus muscle. *Lingual* - The **lingual nerve** is a branch of the mandibular nerve (CN V3) and carries **general sensation** (touch, pain, temperature) from the anterior two-thirds of the tongue. - It does not carry taste sensation directly; taste fibers from the anterior two-thirds are carried by the chorda tympani, which joins the lingual nerve. *Chorda tympani* - The **chorda tympani** is a branch of the facial nerve (CN VII) and carries **taste sensation** from the anterior two-thirds of the tongue [1]. - It joins the lingual nerve but is distinct in its primary function of conveying taste. *Vagus* - The **vagus nerve (CN X)** innervates a small area of the **epiglottis** and the extreme posterior part of the pharynx for taste sensation [1]. - It does not primarily innervate the posterior one-third of the tongue for taste.
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