Sensory Systems Practice Questions

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

Meissner corpuscles. ***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.

Q: Area of the tongue (arrow) shown in the illustration is the zone for what taste?

Salt. ***Salt*** - **Historically**, saltiness was thought to be predominantly perceived along the **sides and tip** of the tongue according to the traditional "tongue map" theory. - However, **modern physiology shows that all taste qualities can be detected across the entire tongue**, though this question may reference the classical tongue map still found in some textbooks. - Salty taste receptors (ENaC channels) respond to **sodium ions**. *Sweet* - Traditionally mapped to the **tip of the tongue**, but sweet receptors (T1R2/T1R3) are distributed throughout the tongue. - Responds to sugars and certain artificial sweeteners. *Sour* - Classically associated with the **sides of the tongue**, but sour receptors are present across all tongue regions. - Triggered by **hydrogen ions** in acidic substances. *Bitter* - Traditionally mapped to the **back of the tongue**, but bitter receptors (T2R family) are distributed throughout. - This historical placement was theorized to help detect potentially harmful toxins. **Note:** The "tongue map" concept has been largely debunked by modern research showing all taste qualities can be perceived across the entire tongue, though slight regional sensitivity variations may exist.

Q: Primary afferent fibers secrete which nociceptive substance at the dorsal horn?

Substance P. ***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.

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

The ciliary muscles are relaxed. ***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.

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

Thalamus. ***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.

Q: Retinal cells which secrete acetylcholine are:

Amacrine cells. ***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.

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

Cones. ***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.

Q: Which of the following cranial nerves has no role, direct or indirect, in olfaction?

Hypoglossal nerve (CN XII) - controls tongue movements.. ***Hypoglossal nerve (CN XII)*** - This nerve is solely responsible for **motor innervation of the intrinsic and extrinsic muscles of the tongue**, controlling tongue movements essential for speech and swallowing. - It has no known role, either direct or indirect, in the **sense of smell** or any related sensory processing. *Glossopharyngeal nerve (CN IX)* - The glossopharyngeal nerve is responsible for **taste perception from the posterior one-third of the tongue** and general sensation from the pharynx, but not directly involved in olfaction. - It indirectly influences the **perception of complex flavors**, which are a combination of taste and smell (retronasal olfaction), though it does not process odorants itself. *Vagus nerve (CN X)* - The vagus nerve provides **taste sensation from the epiglottis and base of the tongue**, and has extensive autonomic functions throughout the body. - Similar to CN IX, it indirectly contributes to **flavor perception** by integrating taste with olfactory input, creating the complete sensory experience of food, even though it has no direct role in processing **smell information**. *Trigeminal nerve (CN V)* - The trigeminal nerve transmits **general sensory information from the nasal cavity**, including touch, pain, and temperature, which can modulate the perception of smell (e.g., the "burn" of ammonia or cooling of menthol). - Its ophthalmic (V1) and maxillary (V2) divisions innervate the nasal mucosa, providing **chemesthetic somatosensory input** that combines with olfactory signals to create a complete sensory experience, even though it doesn't detect odors itself.

Question 1

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

Accepted Answer

Meissner corpuscles

Answer

Pacinian capsule

Answer

Merkel's disc

Answer

Ruffini's endings

Question 2

Area of the tongue (arrow) shown in the illustration is the zone for what taste?

Accepted Answer

Salt

Answer

Sweet

Answer

Sour

Answer

Bitter

Question 3

Primary afferent fibers secrete which nociceptive substance at the dorsal horn?

Accepted Answer

Substance P

Answer

Acetylcholine

Answer

Norepinephrine

Answer

Epinephrine

Question 4

Which of the following is true during far accommodation of the eyes?

Accepted Answer

The ciliary muscles are relaxed

Answer

The focal length of the lens is decreased to focus on distant objects

Answer

The lens becomes more curved due to ciliary muscle contraction

Answer

The zonula fibers become slack to allow lens flattening

Question 5

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

Accepted Answer

Thalamus

Answer

Dorsal roots of the first cervical spinal nerve

Answer

Hypoglossal nerve

Answer

Lingual nerve

Question 6

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

Accepted Answer

Decreased sodium permeability, unchanged potassium permeability

Answer

Decreased sodium permeability, decreased potassium permeability

Answer

Decreased sodium permeability, increased potassium permeability

Answer

Increased sodium permeability, decreased potassium permeability

Question 7

Retinal cells which secrete acetylcholine are:

Accepted Answer

Amacrine cells

Answer

Bipolar cells

Answer

Ganglion cells

Answer

Horizontal cells

Question 8

Function of the ossicles in the middle ear is to

Accepted Answer

Conduct and amplify sound energy from the tympanic membrane to the oval window

Answer

None of the options is correct

Answer

Only amplify sound without conducting it

Answer

Protect from loud sound

Question 9

Which type of photoreceptor is primarily responsible for color vision?

Accepted Answer

Cones

Answer

Bipolar cells

Answer

Rods

Answer

Occipital cortex

Question 10

Which of the following cranial nerves has no role, direct or indirect, in olfaction?

Accepted Answer

Hypoglossal nerve (CN XII) - controls tongue movements.

Answer

Vagus nerve (CN X) - involved in autonomic and visceral functions.

Answer

Glossopharyngeal nerve (CN IX) - involved in taste and sensory functions.

Answer

Trigeminal nerve (CN V) - transmits sensory information from the face.

Sensory Systems — MCQs

Sensory Systems — MCQs

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