Which of the following is classified as a pain receptor?
Which of the following substances has the same concentration in cerebrospinal fluid (CSF) and plasma?
Which type of muscle fibers has fewer mitochondria?
Which of the following statements is true about red muscle fibers?
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?
Cushing reflex is associated with all except?
NEET-PG 2013 - Physiology NEET-PG Practice Questions and MCQs
Question 31: 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 32: Which of the following substances has the same concentration in cerebrospinal fluid (CSF) and plasma?
- A. Glucose
- B. Ca
- C. HCO3
- D. Cl (Correct Answer)
Explanation: ***Cl*** - **Chloride ions (Cl-)** have the **closest concentration** between CSF and plasma among the listed options, with a CSF-to-plasma ratio of approximately 1.1-1.15. - CSF chloride is **slightly higher** than plasma chloride (CSF: ~120-130 mEq/L; Plasma: ~100-110 mEq/L) because chloride ions freely cross the **blood-brain barrier** and help maintain **electroneutrality** in CSF due to the low protein content. - The elevated chloride compensates for the absence of negatively charged proteins in CSF, making it the **best answer** among the given options. *Glucose* - **Glucose** concentration in CSF is approximately **60-70%** of plasma glucose concentration (CSF: 50-80 mg/dL; Plasma: 70-110 mg/dL). - Transport across the **blood-brain barrier** occurs via **GLUT1 transporters**, which are tightly regulated to meet brain metabolic demands. *Ca* - **Calcium (Ca2+)** concentration in CSF is **significantly lower** than in plasma (CSF: ~2.1-2.5 mg/dL; Plasma: ~8.5-10.5 mg/dL). - Only the **ionized, unbound fraction** can cross the blood-brain barrier, as protein-bound calcium cannot pass through. *HCO3* - **Bicarbonate (HCO3-)** concentration in CSF is typically **slightly lower** than in plasma (CSF: ~20-25 mEq/L; Plasma: ~22-28 mEq/L). - Active regulation maintains **CSF pH** and CO2 buffering capacity independent of plasma bicarbonate levels.
Question 33: Which type of muscle fibers has fewer mitochondria?
- A. Type I fibers (Red fibers)
- B. Type IIb fibers (Fast-twitch fibers) (Correct Answer)
- C. Type IIa fibers
- D. Type IIx fibers (Intermediate fibers)
Explanation: ***Type IIb fibers (Fast-twitch fibers)*** - These fibers rely primarily on **anaerobic glycolysis** for ATP production, which is a less efficient process than aerobic respiration and therefore requires fewer mitochondria. - Their primary function is rapid, powerful contractions over short durations, leading to quick fatigue. *Type IIa fibers* - These fibers are **fast-twitch oxidative-glycolytic** fibers, meaning they have a moderate number of mitochondria to support both aerobic and anaerobic metabolism. - They are capable of generating strong contractions and are more fatigue-resistant than Type IIb fibers but less so than Type I fibers. *Type I fibers (Red fibers)* - Known as **slow-twitch oxidative fibers**, they have a high density of mitochondria to support continuous **aerobic respiration** for sustained, low-intensity contractions. - Their rich blood supply and high myoglobin content give them their characteristic red color and make them highly fatigue-resistant. *Type IIx fibers (Intermediate fibers)* - These fibers are very similar to Type IIb fibers in their metabolic profile, often considered an intermediate or even functionally equivalent type depending on the species. - They also primarily utilize **anaerobic glycolysis** and have a relatively low mitochondrial content, making them prone to fatigue.
Question 34: Which of the following statements is true about red muscle fibers?
- A. Contain fewer mitochondria than white muscle fibers
- B. Have less myoglobin than white muscle fibers
- C. Exhibit more oxidative capacity (Correct Answer)
- D. Utilize glycolytic metabolism
Explanation: ***Exhibit more oxidative capacity*** - **Red muscle fibers**, also known as **slow-twitch fibers**, are rich in **mitochondria** and enzymes for aerobic respiration, allowing for sustained contractions and high oxidative capacity. - Their high oxidative capacity is crucial for activities requiring **endurance**, such as long-distance running or maintaining posture through efficient **ATP production** via the **electron transport chain**. *Contain fewer mitochondria than white muscle fibers* - **Red muscle fibers** contain **more mitochondria** than white muscle fibers to support their greater reliance on **aerobic metabolism** for sustained energy production. - **Mitochondria** are the primary sites of **oxidative phosphorylation**, which is essential for the continuous ATP supply needed by these endurance specialized fibers. *Utilize glycolytic metabolism* - While red fibers can perform some glycolysis, their primary metabolic pathway is **oxidative phosphorylation**, utilizing **fatty acids** and **glucose** aerobically. - **Glycolytic metabolism** is more characteristic of **white muscle fibers (fast-twitch)**, which rely on anaerobic pathways for rapid, high-intensity contractions. *Have less myoglobin than white muscle fibers* - **Red muscle fibers** are characterized by a **high content of myoglobin**, which gives them their characteristic red color and high oxygen storage capacity. - **Myoglobin** is crucial for oxygen delivery to the mitochondria, supporting the sustained aerobic metabolism of these fibers, in contrast to white fibers which have less myoglobin.
Question 35: 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 36: 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 37: 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 38: 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 39: 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 40: Cushing reflex is associated with all except?
- A. Irregular respiration
- B. Hypotension (Correct Answer)
- C. Increased intracranial pressure
- D. Bradycardia
Explanation: ***Hypotension*** - The **Cushing reflex** is a compensatory response to increased intracranial pressure (ICP) aiming to maintain cerebral perfusion, which typically involves **hypertension**, not hypotension. - While prolonged or severe ICP can lead to decompensation and eventual hypotension, it is not a direct component of the reflex itself. *Increased intracranial pressure* - The **Cushing reflex** is triggered by an elevation in **intracranial pressure (ICP)**, as the body attempts to maintain blood flow to the brain. - This increased ICP reduces cerebral perfusion pressure, prompting a systemic response to raise mean arterial pressure. *Bradycardia* - **Bradycardia** is a classic component of the **Cushing reflex**, occurring as a compensatory response to the reflex hypertension. - The increased arterial blood pressure stimulates carotid and aortic baroreceptors, leading to a vagal response that slows the heart rate. *Irregular respiration* - **Irregular respiration** is another key component of the **Cushing reflex**, often manifesting as **Cheyne-Stokes breathing** or **ataxic breathing**. - This respiratory dysregulation is due to direct compression and dysfunction of the brainstem, specifically the medullary respiratory centers, caused by increased ICP.