Integration center of tonic labyrinthine reflex is?
Which part of the brain is primarily responsible for the righting reflex?
What type of reflex is the righting reflex?
What type of reflex is the righting reflex?
Which type of nerve fibers are responsible for carrying joint position and vibration sense?
Which receptor is primarily stimulated in response to moderate cold temperatures?
Which of the following statements is true regarding post-ganglionic parasympathetic fibers?
Which of the following fiber types is classically categorized as Group B nerve fibers?
Which of the following is classified as a pain receptor?
Spinal pathway mainly regulating fine motor activity?
NEET-PG 2013 - Physiology NEET-PG Practice Questions and MCQs
Question 51: Integration center of tonic labyrinthine reflex is?
- A. Spinal cord
- B. Medulla (Correct Answer)
- C. Midbrain
- D. Cerebral cortex
Explanation: ***Medulla*** - The **tonic labyrinthine reflex** is a primitive reflex originating in the **vestibular system**, specifically the otolith organs, which respond to head position changes. - Its integration center lies in the **medulla oblongata**, a part of the brainstem responsible for essential involuntary functions. *Spinal cord* - The spinal cord integrates simpler reflexes like **stretch reflexes** and **withdrawal reflexes**. - It does not process the complex vestibular input required for the tonic labyrinthine reflex. *Midbrain* - The **midbrain** is involved in integrating reflexes related to visual and auditory stimuli, such as the **startle reflex** and **pupillary light reflex**. - It is superior to the primary integration center for the tonic labyrinthine reflex. *Cerebral cortex* - The **cerebral cortex** is responsible for higher cognitive functions, voluntary movements, and conscious sensation. - Reflexes like the tonic labyrinthine reflex are subcortical and operate without conscious control.
Question 52: Which part of the brain is primarily responsible for the righting reflex?
- A. Pons
- B. Spinal cord
- C. Cortex
- D. Midbrain (Correct Answer)
Explanation: ***Midbrain*** - The **midbrain** plays a crucial role in regulating posture and movement, including the **righting reflex**. - It integrates sensory information from the **vestibular system**, eyes, and proprioceptors to maintain upright posture. *Pons* - The pons is primarily involved in relaying signals between the **cerebrum** and **cerebellum** and regulating respiration and sleep. - While it contributes to motor control, it is not the primary center for the righting reflex. *Spinal cord* - The spinal cord mediates **reflex arcs** and transmits sensory and motor information, but it does not independently control complex postural reflexes like the righting reflex. - It contains the circuits for basic reflexes such as the **stretch reflex** and **withdrawal reflex**. *Cortex* - The cerebral cortex is responsible for **voluntary movements**, higher cognitive functions, and conscious perception. - While it can influence posture, the righting reflex is a subcortical, involuntary process.
Question 53: 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 54: What type of reflex is the righting reflex?
- A. Postural reflex (Correct Answer)
- B. Spinal reflex
- C. Ocular reflex
- D. Stretch reflex
Explanation: ***Postural reflex*** - The **righting reflex** is a mechanism that helps an animal or human maintain or regain their upright body position or head orientation in space, which is a key component of **postural control**. - It involves complex inputs from the **vestibular system**, visual system, and proprioceptors to adjust muscle tone and body position against gravity. - Examples include **neck righting reflex**, **body righting reflex**, and **labyrinthine righting reflex**. *Stretch reflex* - A **stretch reflex** is a monosynaptic reflex that causes a muscle to contract in response to being stretched, primarily to maintain muscle length and tone. - It does not encompass the complex, multi-sensory integration required for maintaining overall body orientation. *Spinal reflex* - A **spinal reflex** is any reflex arc whose neural circuit passes through the spinal cord, and it can be either monosynaptic or polysynaptic. - While the righting reflex involves spinal cord components, it is a broader, more integrated reflex that extends beyond a simple spinal cord circuit. *Ocular reflex* - **Ocular reflexes** are involuntary eye movements or responses, such as pupillary light reflex or vestibulo-ocular reflex, that primarily control eye position or pupil size. - They do not directly relate to the maintenance of the entire body's upright posture.
Question 55: Which type of nerve fibers are responsible for carrying joint position and vibration sense?
- A. A-beta fibers (Correct Answer)
- B. A-alpha fibers
- C. C fibers
- D. A-delta fibers
Explanation: ***A-beta fibers*** - **A-beta fibers** are **large-diameter, myelinated** sensory fibers that conduct impulses rapidly. - They are primarily responsible for transmitting **light touch, pressure, joint position (proprioception), and vibration sense**. - **This is the correct answer** because A-beta fibers carry **BOTH joint position AND vibration sense together**. *A-alpha fibers* - **A-alpha fibers** are the **largest and fastest** conducting nerve fibers. - They include **motor nerves to skeletal muscles** and **sensory fibers from muscle spindles (Ia) and Golgi tendon organs (Ib)**. - While Ia fibers (A-alpha) do carry **proprioception from muscle spindles**, they do **NOT carry vibration sense**. - The question asks for fibers carrying **BOTH** joint position **AND** vibration sense, making A-beta the correct answer. *C fibers* - **C fibers** are **small-diameter, unmyelinated** nerve fibers with **slow conduction velocities**. - They are responsible for transmitting **dull, aching pain, temperature, and crude touch**. *A-delta fibers* - **A-delta fibers** are **small-diameter, thinly myelinated** nerve fibers with an intermediate conduction velocity. - They primarily transmit **sharp, fast pain** and **cold temperature sensations**.
Question 56: Which receptor is primarily stimulated in response to moderate cold temperatures?
- A. Vanilloid Receptor 1 (VR1)
- B. Vanilloid Receptor 2 (VR2)
- C. Vanilloid Receptor-Like 1 (VRL-1)
- D. TRPM8 Receptor (Menthol Receptor) (Correct Answer)
Explanation: ***TRPM8 Receptor (Menthol Receptor)*** - The **TRPM8 receptor** is a **cold-sensitive ion channel** that is primarily activated by moderate cold temperatures (around 8–28°C) and by cooling compounds like **menthol** and **eucalyptol**. - Its activation leads to an influx of cations, primarily **calcium**, causing depolarization and generation of action potentials. *Vanilloid Receptor 1 (VR1)* - Vanilloid Receptor 1, also known as **TRPV1**, is primarily activated by noxious heat (temperatures above 43°C), low pH, and capsaicin. - It plays a significant role in **pain sensation** and inflammation, not moderate cold detection. *Vanilloid Receptor 2 (VR2)* - Vanilloid Receptor 2, or **TRPV2**, is activated by even higher temperatures than TRPV1, typically above 52°C, and is also involved in the detection of **intense heat** and mechanical stimuli. - It does not respond to cold temperatures at all. *Vanilloid Receptor-Like 1 (VRL-1)* - **VRL-1**, or **TRPV3**, is a heat-sensitive channel activated by warm temperatures (above 31°C) and plays a role in the sensation of warmth and heat hyperalgesia. - It is not involved in the detection of cold stimuli.
Question 57: Which of the following statements is true regarding post-ganglionic parasympathetic fibers?
- A. They originate from the spinal cord.
- B. They are part of the sympathetic nervous system.
- C. They are responsible for 'fight or flight' responses.
- D. They release acetylcholine at the target organs. (Correct Answer)
Explanation: ***They release acetylcholine at the target organs.*** - Post-ganglionic parasympathetic fibers are **cholinergic**, meaning they release the neurotransmitter **acetylcholine** at their effector organs. - This action mediates the characteristic "rest and digest" responses of the parasympathetic nervous system. *They originate from the spinal cord.* - **Pre-ganglionic parasympathetic fibers** originate from the **brainstem** (cranial nerves III, VII, IX, X) and the **sacral spinal cord** (S2-S4). - Post-ganglionic fibers originate in ganglia located near or within their target organs, not the spinal cord directly. *They are part of the sympathetic nervous system.* - Post-ganglionic parasympathetic fibers are a component of the **parasympathetic nervous system**, not the sympathetic nervous system. - The sympathetic and parasympathetic systems are distinct divisions of the autonomic nervous system with generally opposing functions. *They are responsible for 'fight or flight' responses.* - The **'fight or flight' response** is characteristic of the **sympathetic nervous system**, which prepares the body for stressful situations. - The parasympathetic nervous system is responsible for **'rest and digest' functions**, promoting energy conservation and maintenance activities.
Question 58: Which of the following fiber types is classically categorized as Group B nerve fibers?
- A. Sympathetic postganglionic
- B. Parasympathetic preganglionic
- C. Parasympathetic post ganglionic
- D. Sympathetic preganglionic (Correct Answer)
Explanation: ***Sympathetic preganglionic*** - **Group B nerve fibers** are **myelinated preganglionic autonomic fibers** with intermediate diameter (3-15 μm) and moderate conduction velocity (3-15 m/s) - Both **sympathetic and parasympathetic preganglionic fibers** are classified as Group B fibers - **Sympathetic preganglionic** neurons are the classical example, originating from T1-L2 spinal segments and synapsing in paravertebral or prevertebral ganglia *Sympathetic postganglionic* - These are **unmyelinated Group C fibers** with slow conduction velocity (0.5-2 m/s) - They extend from ganglia to target organs *Parasympathetic preganglionic* - These are also **Group B fibers** (myelinated preganglionic) - However, **sympathetic preganglionic** is the more commonly cited classical example in standard classifications - They originate from cranial nerves (III, VII, IX, X) and sacral segments (S2-S4) *Parasympathetic postganglionic* - These are **unmyelinated Group C fibers** with the slowest conduction velocities - Short fibers extending from ganglia near or within target organs to effector cells
Question 59: 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 60: Spinal pathway mainly regulating fine motor activity?
- A. Lateral corticospinal tract (Correct Answer)
- B. Vestibulospinal tract
- C. Anterior corticospinal tract
- D. Reticulospinal tract
Explanation: ***Lateral corticospinal tract*** - This pathway contains **85-90% of corticospinal fibers** that cross at the medullary pyramids and descend in the **lateral funiculus** of the spinal cord - It is the **primary pathway for fine, precise, voluntary movements** of **distal extremities**, particularly the hands, fingers, feet, and toes - Enables intricate skilled movements like writing, buttoning, and fine manipulation due to direct monosynaptic connections to motor neurons - Damage results in loss of fine motor control and skilled movements *Anterior corticospinal tract* - Contains only **10-15% of corticospinal fibers** that descend uncrossed in the anterior spinal cord - Controls **bilateral movements of axial and proximal muscles** (neck, trunk, shoulders) - Not specialized for fine motor control of distal limbs *Vestibulospinal tract* - Regulates **posture and balance** by modulating extensor muscle tone - Coordinates head position and maintains upright posture - Does not control fine voluntary movements *Reticulospinal tract* - Modulates **muscle tone, posture, and locomotion** - Provides general motor control and autonomic regulation - Not specialized for precise, intricate fine motor movements